Research activity information

• Involvement of sphingosine 1-phosphate signaling in insulin-like growth factor-II/mannose 6-phosphate receptor trafficking from endosome to the trans-Golgi network.

  Susumu Nishida, Shubi Ambwene Matovelo, Taketoshi Kajimoto, Shun-Ichi Nakamura, Taro Okada

  The insulin-like growth factor II/mannose 6-phosphate (IGF-II/M6P) receptor is a multifunctional glycoprotein not only play roles in IGF-II degradation and pro-TGFβ activation but binding to and transport M6P-bearing lysosomal enzymes from the trans-Golgi network (TGN) or the cell surface to lysosomes. At present, information regarding a retrograde transport of IGF-II/M6P receptor from endosomes to the TGN is still limited. We show here that a continuous ligand-dependent activation of sphingosine 1-phosphate receptor type 3 (S1P3R) on the endosomal membranes is required for subsequent recycling back of cargo-unloaded IGF-II/M6P receptors to the TGN. We have further clarified that Gq coupled with S1P3R plays a critical role in the activation of casein kinase 2, which phosphorylates and keeps PACS1 connector protein active for the association with IGF-II/M6P receptors, which enables transport carrier formation with the aid of other adaptor proteins toward the TGN. These findings shed light on the molecular mechanism underlying how continuous activation of the S1P receptor and subsequent downstream Gq signaling regulates the retrograde transport of the empty IGF-II/M6P receptors back to the TGN.

  Sep. 2024, Communications biology, 7(1) (1), 1182 - 1182, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Extracellular α-synuclein impairs sphingosine 1-phosphate receptor type 3 (S1PR3)-regulated lysosomal delivery of cathepsin D in HeLa cells.

  Susumu Nishida, Shubi Ambwene Matovelo, Taketoshi Kajimoto, Shun-Ichi Nakamura, Taro Okada

  α-Synuclein (α-Syn)-positive intracellular fibrillar protein deposits, known as Lewy bodies, are thought to be involved in the pathogenesis of Parkinson's disease (PD). Although recent lines of evidence suggested that extracellular α-Syn secreted from pathogenic neurons contributes to the propagation of PD pathology, the precise mechanism of action remains unclear. We have reported that extracellular α-Syn caused sphingosine 1-phosphate (S1P) receptor type 1 (S1PR1) uncoupled from Gi and inhibited downstream G-protein signaling in SH-SY5Y cells, although its patho/physiological role remains to be clarified. Here we show that extracellular α-Syn caused S1P receptor type 3 (S1PR3) uncoupled from G protein in HeLa cells. Further studies indicated that α-Syn treatment reduced cathepsin D activity while enhancing the secretion of immature pro-cathepsin D into cell culture medium, suggesting that lysosomal delivery of cathepsin D was disturbed. Actually, extracellular α-Syn attenuated the retrograde trafficking of insulin-like growth factor-II/mannose 6-phosphate (IGF-II/M6P) receptor, which is under the regulation of S1PR3. These findings shed light on the understanding of dissemination of the PD pathology, that is, the mechanism underlying how extracellular α-Syn secreted from pathogenic cells causes lysosomal dysfunction of the neighboring healthy cells, leading to propagation of the disease.

  Mar. 2024, Genes to cells : devoted to molecular & cellular mechanisms, 29(3) (3), 207 - 216, English, International magazine

  [Refereed]

  Scientific journal


• Identification of novel OCRL isoforms associated with phenotypic differences between Dent disease-2 and Lowe syndrome.

  Nana Sakakibara, Takeshi Ijuin, Tomoko Horinouchi, Tomohiko Yamamura, China Nagano, Eri Okada, Shinya Ishiko, Yuya Aoto, Rini Rossanti, Takeshi Ninchoji, Hiroyuki Awano, Hiroaki Nagase, Shogo Minamikawa, Ryojiro Tanaka, Takeshi Matsuyama, Koji Nagatani, Koichi Kamei, Kumiko Jinnouchi, Yasufumi Ohtsuka, Masafumi Oka, Yoshinori Araki, Toju Tanaka, Mari S Harada, Toru Igarashi, Hikaru Kitahara, Naoya Morisada, Shun-Ichi Nakamura, Taro Okada, Kazumoto Iijima, Kandai Nozu

  BACKGROUND: Although Lowe syndrome and Dent disease-2 are both caused by OCRL mutations, their clinical severities differ substantially, and their molecular mechanisms remain unclear. Truncating mutations in OCRL exons 1 through 7 lead to Dent disease-2, whereas those in exons 8 through 24 lead to Lowe syndrome. Herein, we identified the mechanism underlying the action of novel OCRL protein isoforms. METHODS: mRNA samples extracted from cultured urine-derived cells from a healthy control and the Dent disease-2 patient were examined to detect the 5' end of the OCRL isoform. For protein expression and functional analysis, vectors containing (1) the full-length OCRL transcripts, (2) the isoform transcripts, and (3) transcripts with truncating mutations detected in Lowe syndrome and Dent disease-2 patients were transfected into HeLa cells. RESULTS: We successfully cloned the novel isoform transcripts from OCRL exons 6-24, including the translation-initiation codons present in exon 8. In vitro protein-expression analysis detected proteins of two different sizes (105 and 80 kDa) translated from full-length OCRL, whereas only one protein (80 kDa) was found from the isoform and Dent disease-2 variants. No protein expression was observed for the Lowe syndrome variants. The isoform enzyme activity was equivalent to that of full-length OCRL; the Dent disease-2 variants retained > 50% enzyme activity, whereas the Lowe syndrome variants retained < 20% activity. CONCLUSIONS: We elucidated the molecular mechanism underlying the two different phenotypes in OCRL-related diseases; the functional OCRL isoform translated starting at exon 8 was associated with this mechanism.

  Jan. 2022, Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association, 37(2) (2), 262 - 270, English, International magazine

  [Refereed]

  Scientific journal


• Constitutive activation of S1P receptors at the trans-Golgi network is required for surface transport carrier formation

  Taro Okada, Susumu Nishida, Lifang Zhang, Nesma Nabil Ibrahim Mohamed, Tianyou Wang, Takeshi Ijuin, Taketoshi Kajimoto, Shun-Ichi Nakamura

  Lead, Elsevier BV, Nov. 2021, iScience, 24(11) (11), 103351 - 103351, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Involvement of Receptor-Mediated S1P Signaling in EGF-Induced Macropinocytosis in COS7 Cells.

  Shubi Ambwene Matovelo, Lifang Zhang, Nesma Nabil Ibrahim Mohamed, Taketoshi Kajimoto, Takeshi Ijuin, Taro Okada, Shun-Ichi Nakamura

  Macropinocytosis is a highly conserved cellular process of endocytosis by which extracellular fluid and nutrients are taken up into cells through large, heterogeneous vesicles known as macropinosomes. Growth factors such as epidermal growth factor (EGF) can induce macropinocytosis in many types of cells, although precise mechanism underlying EGF-induced macropinocytosis remains unclear. In the present studies we have shown the involvement of S1P signaling in EGF-induced macropinocytosis in COS7 cells. First, EGF-induced macropinocytosis was strongly impaired in sphingosine kinase isozymes, SphK1 or SphK2-depleted cells, which was completely rescued by the expression of the corresponding wild-type isozyme but not the catalytically inactive one, suggesting the involvement of sphingosine 1-phosphate (S1P) in this phenomenon. Next, we observed that EGF-induced macropinocytosis was strongly inhibited in S1P type 1 receptor (S1P1R)-knockdown cells, implying involvement of S1P1R in this event. Furthermore, we could successfully demonstrate EGF-induced trans-activation of S1P1R using one-molecular fluorescence resonance energy transfer (FRET) technique. Moreover, for EGF-induced Rac1 activation, a step essential to F-actin formation and subsequent macropinocytosis, S1P signaling is required for its full activation, as judged by FRET analysis. These findings indicate that growth factors such as EGF utilize receptor-mediated S1P signaling for the regulation of macropinocytosis to fulfil vital cell activity.

  Nov. 2020, The Kobe journal of medical sciences, 66(3) (3), E94-E101, English, Domestic magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Activation of atypical protein kinase C by sphingosine 1-phosphate revealed by an aPKC-specific activity reporter.

  Taketoshi Kajimoto, Alisha D Caliman, Irene S Tobias, Taro Okada, Caila A Pilo, An-Angela N Van, J Andrew McCammon, Shun-Ichi Nakamura, Alexandra C Newton

  Atypical protein kinase C (aPKC) isozymes are unique in the PKC superfamily in that they are not regulated by the lipid second messenger diacylglycerol, which has led to speculation about whether a different second messenger acutely controls their function. Here, using a genetically encoded reporter that we designed, aPKC-specific C kinase activity reporter (aCKAR), we found that the lipid mediator sphingosine 1-phosphate (S1P) promoted the cellular activity of aPKC. Intracellular S1P directly bound to the purified kinase domain of aPKC and relieved autoinhibitory constraints, thereby activating the kinase. In silico studies identified potential binding sites on the kinase domain, one of which was validated biochemically. In HeLa cells, S1P-dependent activation of aPKC suppressed apoptosis. Together, our findings identify a previously undescribed molecular mechanism of aPKC regulation, a molecular target for S1P in cell survival regulation, and a tool to further explore the biochemical and biological functions of aPKC.

  Jan. 2019, Science signaling, 12(562) (562), English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Extracellular α-synuclein drives sphingosine 1-phosphate receptor subtype 1 out of lipid rafts, leading to impaired inhibitory G-protein signaling.

  Shaymaa Mohamed Mohamed Badawy, Taro Okada, Taketoshi Kajimoto, Mitsuhiro Hirase, Shubi Ambwene Matovelo, Shunsuke Nakamura, Daisuke Yoshida, Takeshi Ijuin, Shun-Ichi Nakamura

  α-Synuclein (α-Syn)-positive intracytoplasmic inclusions, known as Lewy bodies, are thought to be involved in the pathogenesis of Lewy body diseases, such as Parkinson's disease (PD). Although growing evidence suggests that cell-to-cell transmission of α-Syn is associated with the progression of PD and that extracellular α-Syn promotes formation of inclusion bodies, its precise mechanism of action in the extracellular space remains unclear. Here, as indicated by both conventional fractionation techniques and FRET-based protein-protein interaction analysis, we demonstrate that extracellular α-Syn causes expulsion of sphingosine 1-phosphate receptor subtype 1 (S1P1R) from the lipid raft fractions. S1P1R regulates vesicular trafficking, and its expulsion involved α-Syn binding to membrane-surface gangliosides. Consequently, the S1P1R became refractory to S1P stimulation required for activating inhibitory G-protein (Gi) in the plasma membranes. Moreover, the extracellular α-Syn also induced uncoupling of the S1P1R on internal vesicles, resulting in the reduced amount of CD63 molecule (CD63) in the lumen of multivesicular endosomes, together with a decrease in CD63 in the released exosomes from α-Syn-treated cells. Furthermore, cholesterol-depleting agent-induced S1P1R expulsion from the rafts also resulted in S1P1R uncoupling. Taken together, these results suggest that extracellular α-Syn-induced expulsion of S1P1R from lipid rafts promotes the uncoupling of S1P1R from Gi, thereby blocking subsequent Gi signals, such as inhibition of cargo sorting into exosomal vesicles in multivesicular endosomes. These findings help shed additional light on PD pathogenesis.

  May 2018, The Journal of biological chemistry, 293(21) (21), 8208 - 8216, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Essential Role of Sphingosine Kinase 2 in the Regulation of Cargo Contents in the Exosomes from K562 Cells.

  Nesma Nabil Ibrahim Mohamed, Taro Okada, Taketoshi Kajimoto, Shun-Ichi Nakamura

  Sphingosine 1-phosphate (S1P) is a bioactive phosphorylated product of sphingosine catalyzed by sphingosine kinase (SphK) and implicated in diverse cellular functions including vesicular trafficking. In the present study we have shown the importance of one of the subtypes of SphK, SphK2, in the regulation of cargo content in exosomes released from human myeloid leukemia K562 cells. First, SphK2 has been shown to localize with N-Rh-PE-positive late endosomes in the cells. Next, siRNA-mediated knockdown of Sphk2 but not SphK1 resulted in a reduction of cargo content in purified exosomes. The involvement of SphK2 in this phenomenon was further investigated by pharmacological approaches. When cells were treated with N,N-dimethylsphingosine (DMS), one of the most frequently used inhibitors for SphK, cargo contents in purified exosomes were enhanced unexpectedly. Finally, it has been shown that DMS has a potency to stimulate SphK2 activity depending on the substrate sphingosine- and the inhibitor-doses as estimated by in vitro assay systems using a purified SphK2. These findings suggest that SphK2/S1P signaling plays an important role in the regulation of cargo content in exosomes in K562 cells.

  May 2018, The Kobe journal of medical sciences, 63(4) (4), E123-E129 - E129, English, Domestic magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Involvement of Gβγ subunits of Gi protein coupled with S1P receptor on multivesicular endosomes in F-actin formation and cargo sorting into exosomes.

  Taketoshi Kajimoto, Nesma Nabil Ibrahim Mohamed, Shaymaa Mohamed Mohamed Badawy, Shubi Ambwene Matovelo, Mitsuhiro Hirase, Shunsuke Nakamura, Daisuke Yoshida, Taro Okada, Takeshi Ijuin, Shun-Ichi Nakamura

  Exosomes play a critical role in cell-to-cell communication by delivering cargo molecules to recipient cells. However, the mechanism underlying the generation of the exosomal multivesicular endosome (MVE) is one of the mysteries in the field of endosome research. Although sphingolipid metabolites such as ceramide and sphingosine 1-phosphate (S1P) are known to play important roles in MVE formation and maturation, the detailed molecular mechanisms are still unclear. Here, we show that Rho family GTPases, including Cdc42 and Rac1, are constitutively activated on exosomal MVEs and are regulated by S1P signaling as measured by fluorescence resonance energy transfer (FRET)-based conformational changes. Moreover, we detected S1P signaling-induced filamentous actin (F-actin) formation. A selective inhibitor of Gβγ subunits, M119, strongly inhibited both F-actin formation on MVEs and cargo sorting into exosomal intralumenal vesicles of MVEs, both of which were fully rescued by the simultaneous expression of constitutively active Cdc42 and Rac1. Our results shed light on the mechanism underlying exosomal MVE maturation and inform the understanding of the physiological relevance of continuous activation of the S1P receptor and subsequent downstream G protein signaling to Gβγ subunits/Rho family GTPases-regulated F-actin formation on MVEs for cargo sorting into exosomal intralumenal vesicles.

  Jan. 2018, The Journal of biological chemistry, 293(1) (1), 245 - 253, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• DHHC5-mediated palmitoylation of S1P receptor subtype 1 determines G-protein coupling.

  Shaymaa Mohamed Mohamed Badawy, Taro Okada, Taketoshi Kajimoto, Takeshi Ijuin, Shun-Ichi Nakamura

  Nov. 2017, Scientific reports, 7(1) (1), 16552 - 16552, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Phospholipase D is Dispensable for Epidermal Growth Factor-Induced Chemotaxis.

  Chihoko Hirai, Shaymaa Mohamed Mohamed Badawy, Lifang Zhang, Taro Okada, Taketoshi Kajimoto, Shunichi Nakamura

  Kobe University School of Medicine, May 2017, The Kobe journal of medical sciences, 62(6) (6), E162-E167 - E167, English, Domestic magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Extracellular α-synuclein induces sphingosine 1-phosphate receptor subtype 1 uncoupled from inhibitory G-protein leaving β-arrestin signal intact.

  Lifang Zhang, Taro Okada, Shaymaa Mohamed Mohadmed Badawy, Chihoko Hirai, Taketoshi Kajimoto, Shun-Ichi Nakamura

  Mar. 2017, Scientific reports, 7, 44248 - 44248, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Impairment of PDGF-induced chemotaxis by extracellular α-synuclein through selective inhibition of Rac1 activation.

  Taro Okada, Chihoko Hirai, Shaymaa Mohamed Mohamed Badawy, Lifang Zhang, Taketoshi Kajimoto, Shun-Ichi Nakamura

  Nov. 2016, Scientific reports, 6, 37810 - 37810, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Identification of mutations in FN1 leading to glomerulopathy with fibronectin deposits.

  Hiromi Ohtsubo, Taro Okada, Kandai Nozu, Yutaka Takaoka, Akemi Shono, Katsuhiko Asanuma, Lifang Zhang, Koichi Nakanishi, Mariko Taniguchi-Ikeda, Hiroshi Kaito, Kazumoto Iijima, Shun-Ichi Nakamura

  Sep. 2016, Pediatric nephrology (Berlin, Germany), 31(9) (9), 1459 - 67, English, International magazine

  [Refereed]

  Scientific journal


• High expression of Mcl-1L via the MEK-ERK-phospho-STAT3 (Ser727) pathway protects melanocytes and melanoma from UVB-induced apoptosis

  Takeshi Fukumoto, Tetsushi Iwasaki, Taro Okada, Takanori Hashimoto, Youbin Moon, Masanobu Sakaguchi, Yasuo Fukami, Chikako Nishigori, Masahiro Oka

  Feb. 2016, GENES TO CELLS, 21(2) (2), 185 - 199, English

  [Refereed]

  Scientific journal


• High expression of Mcl-1 mediated by MEK-ERK1/2-STAT3 signaling pathway protects melanocytes and melanoma cells against ultraviolet B-induced apoptosis

  T. Fukumoto, T. Iwasaki, T. Okada, T. Hashimoto, Y. Moon, M. Sakaguchi, Y. Fukami, C. Nishigori, M. Oka

  May 2015, JOURNAL OF INVESTIGATIVE DERMATOLOGY, 135, S107 - S107, English

  [Refereed]


• Sphingosine kinases modulate the secretion of amyloid β precursor protein from SH-SY5Y neuroblastoma cells: the role of α-synuclein.

  Henryk Jesko, Taro Okada, Robert P Strosznajder, Shun-ichi Nakamura

  2014, Folia neuropathologica, 52(1) (1), 70 - 8, English, International magazine

  [Refereed]

  Scientific journal


• Ongoing activation of sphingosine 1-phosphate receptors mediates maturation of exosomal multivesicular endosomes.

  Taketoshi Kajimoto, Taro Okada, Satoshi Miya, Lifang Zhang, Shun-ichi Nakamura

  Nature Publishing Group, 2013, Nature communications, 4, 2712 - 2712, English, International magazine

  [Refereed]

  Scientific journal


• Regulation of synaptic strength by sphingosine 1-phosphate in the hippocampus.

  T Kanno, T Nishizaki, R L Proia, T Kajimoto, S Jahangeer, T Okada, S Nakamura

  Dec. 2010, Neuroscience, 171(4) (4), 973 - 80, English, International magazine

  [Refereed]

  Scientific journal


• Signal transducer and activator of transcription 3 upregulates interleukin-8 expression at the level of transcription in human melanoma cells

  Masahiro Oka, Masanobu Sakaguchi, Taro Okada, Hiroshi Nagai, Michitaka Ozaki, Toyo Yoshioka, Hiroshi Inoue, Naofumi Mukaida, Ushio Kikkawa, Chikako Nishigori

  Aug. 2010, EXPERIMENTAL DERMATOLOGY, 19(8) (8), E50 - E55, English

  [Refereed]

  Scientific journal


• Sphingosine kinase 1 regulates mucin production via ERK phosphorylation.

  Yuko Kono, Teruaki Nishiuma, Taro Okada, Kazuyuki Kobayashi, Yasuhiro Funada, Yoshikazu Kotani, Saleem Jahangeer, Shun-Ichi Nakamura, Yoshihiro Nishimura

  Feb. 2010, Pulmonary pharmacology & therapeutics, 23(1) (1), 36 - 42, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• CtBP1/BARS is an activator of phospholipase D1 necessary for agonist-induced macropinocytosis.

  Yuki Haga, Noriko Miwa, Saleem Jahangeer, Taro Okada, Shun-ichi Nakamura

  May 2009, The EMBO journal, 28(9) (9), 1197 - 207, English, International magazine

  [Refereed]

  Scientific journal


• Roles of extracellular and intracellular sphingosine 1-phosphate in cell migration.

  Huan Yu, Taro Okada, Masako Kobayashi, Dina M Abo-Elmatty, Saleem Jahangeer, Shun-Ichi Nakamura

  May 2009, Genes to cells : devoted to molecular & cellular mechanisms, 14(5) (5), 597 - 605, English, International magazine

  [Refereed]

  Scientific journal


• Inhalation of sphingosine kinase inhibitor attenuates airway inflammation in asthmatic mouse model.

  Teruaki Nishiuma, Yoshihiro Nishimura, Taro Okada, Emi Kuramoto, Yoshikazu Kotani, Saleem Jahangeer, Shun-ichi Nakamura

  Sphingosine 1-phosphate (S1P) produced by sphingosine kinase (SPHK) is implicated in acute immunoresponses, however, mechanisms of SPHK/S1P signaling in the pathogenesis of bronchial asthma are poorly understood. In this study, we hypothesized that SPHK inhibition could ameliorate lung inflammation in ovalbumin (OVA)-challenged mouse lungs. Six- to eight-week-old C57BL/6J mice were sensitized and exposed to OVA for 3 consecutive days. Twenty-four hours later, mice lungs and bronchoalveolar lavage (BAL) fluid were analyzed. For an inhibitory effect, either of the two different SPHK inhibitors, N,N-dimethylsphingosine (DMS) or SPHK inhibitor [SK-I; 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole], was nebulized for 30 min before OVA inhalation. OVA inhalation caused S1P release into BAL fluid and high expression of SPHK1 around bronchial epithelial walls and inflammatory areas. DMS or SK-I inhalation resulted in a decrease in S1P amounts in BAL fluid to basal levels, accompanied by decreased eosinophil infiltration and peroxidase activity. The extent of inhibition caused by DMS inhalation was higher than that caused by SK-I. Like T helper 2 (Th2) cytokine release, OVA inhalation-induced increase in eotaxin expression was significantly suppressed by DMS pretreatment both at protein level in BAL fluid and at mRNA level in lung homogenates. Moreover, bronchial hyperresponsiveness to inhaled methacholine and goblet cell hyperplasia were improved by SPHK inhibitors. These data suggest that the inhibition of SPHK affected acute eosinophilic inflammation induced in antigen-challenged mouse model and that targeting SPHK may provide a novel therapeutic tool to treat bronchial asthma.

  Jun. 2008, American journal of physiology. Lung cellular and molecular physiology, 294(6) (6), L1085-93, English, International magazine

  Scientific journal


• Requirement of phospholipase D for ilimaquinone-induced Golgi membrane fragmentation.

  Hirofumi Sonoda, Taro Okada, Saleem Jahangeer, Shun-ichi Nakamura

  Nov. 2007, The Journal of biological chemistry, 282(47) (47), 34085 - 92, English, International magazine

  [Refereed]

  Scientific journal


• Sphingosine kinase 1 regulates differentiation of human and mouse lung fibroblasts mediated by TGF-beta1.

  Yuko Kono, Teruaki Nishiuma, Yoshihiro Nishimura, Yoshikazu Kotani, Taro Okada, Shun-Ichi Nakamura, Mitsuhiro Yokoyama

  Oct. 2007, American journal of respiratory cell and molecular biology, 37(4) (4), 395 - 404, English, International magazine

  [Refereed]

  Scientific journal


• Protein kinase D-mediated phosphorylation and nuclear export of sphingosine kinase 2.

  Guo Ding, Hirofumi Sonoda, Huan Yu, Taketoshi Kajimoto, Sravan K Goparaju, Saleem Jahangeer, Taro Okada, Shun-Ichi Nakamura

  Sep. 2007, The Journal of biological chemistry, 282(37) (37), 27493 - 27502, English, International magazine

  [Refereed]

  Scientific journal


• Involvement of sphingosine-1-phosphate in glutamate secretion in hippocampal neurons.

  Taketoshi Kajimoto, Taro Okada, Huan Yu, Sravan K Goparaju, Saleem Jahangeer, Shun-ichi Nakamura

  May 2007, Molecular and cellular biology, 27(9) (9), 3429 - 40, English, International magazine

  Scientific journal


• Involvement of N-terminal-extended form of sphingosine kinase 2 in serum-dependent regulation of cell proliferation and apoptosis.

  Taro Okada, Guo Ding, Hirofumi Sonoda, Taketoshi Kajimoto, Yuki Haga, Ali Khosrowbeygi, Sanyang Gao, Noriko Miwa, Saleem Jahangeer, Shun-Ichi Nakamura

  Oct. 2005, The Journal of biological chemistry, 280(43) (43), 36318 - 25, English, International magazine

  Scientific journal


• Delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) interacts with and activates sphingosine kinase 1.

  Toshitada Fujita, Taro Okada, Shun Hayashi, Saleem Jahangeer, Noriko Miwa, Shun-ichi Nakamura

  Sphingosine kinase (SPHK) is a key enzyme catalysing the formation of sphingosine 1-phosphate (SPP), a lipid messenger that is implicated in the regulation of a wide variety of important cellular events acting through intracellular, as well as extracellular, mechanisms. However, the molecular mechanism of intracellular actions of SPP remains unclear. Here, we have identified delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) as a potential binding partner for SPHK1 by yeast two-hybrid screening. From co-immunoprecipitation analyses, the C-terminal portion of delta-catenin/NPRAP containing the seventh to tenth armadillo repeats was found to be required for interaction with SPHK1. Endogenous delta-catenin/NPRAP was co-localized with endogenous SPHK1 and transfected delta-catenin/NPRAP was co-localized with transfected SPHK1 in dissociated rat hippocampal neurons. MDCK (Madin-Darby canine kidney) cells stably expressing delta-catenin/NPRAP contained elevated levels of intracellular SPP. In a purified system delta-catenin/NPRAP stimulated SPHK1 in a dose-dependent manner. Furthermore, delta-catenin/NPRAP-induced increased cell motility in MDCK cells was completely inhibited by dimethylsphingosine, a specific inhibitor of SPHK1. These results strongly suggest that at least some of delta-catenin/NPRAP functions, including increased cell motility, are mediated by an SPHK-SPP signalling pathway.

  Sep. 2004, The Biochemical journal, 382(Pt 2) (Pt 2), 717 - 23, English, International magazine

  [Refereed]

  Scientific journal


• Down-regulation of melanogenesis by phospholipase D2 through ubiquitin proteasome-mediated degradation of tyrosinase.

  Akiko Kageyama, Masahiro Oka, Taro Okada, Shun-ichi Nakamura, Takehiko Ueyama, Naoaki Saito, Vincent J Hearing, Masamitsu Ichihashi, Chikako Nishigori

  Jun. 2004, The Journal of biological chemistry, 279(26) (26), 27774 - 80, English, International magazine

  [Refereed]

  Scientific journal


• Sphingosine kinase 2 is a nuclear protein and inhibits DNA synthesis.

  Nobuaki Igarashi, Taro Okada, Shun Hayashi, Toshitada Fujita, Saleem Jahangeer, Shun-ichi Nakamura

  Nov. 2003, The Journal of biological chemistry, 278(47) (47), 46832 - 9, English, International magazine

  [Refereed]

  Scientific journal


• PKCdelta inhibits PKCalpha-mediated activation of phospholipase D1 in a manner independent of its protein kinase activity.

  Masahiro Oka, Taro Okada, Shun-ichi Nakamura, Motoi Ohba, Toshio Kuroki, Ushio Kikkawa, Hiroshi Nagai, Masamitsu Ichihashi, Chikako Nishigori

  Nov. 2003, FEBS letters, 554(1-2) (1-2), 179 - 83, English, International magazine

  [Refereed]

  Scientific journal


• Identification and characterization of RPK118, a novel sphingosine kinase-1-binding protein.

  Shun Hayashi, Taro Okada, Nobuaki Igarashi, Toshitada Fujita, Saleem Jahangeer, Shun-Ichi Nakamura

  Sep. 2002, The Journal of biological chemistry, 277(36) (36), 33319 - 24, English, International magazine

  [Refereed]

  Scientific journal


• Dual regulation of phospholipase D1 by protein kinase C alpha in vivo.

  Masahiro Oka, Tomohiro Hitomi, Taro Okada, Shun-ichi Nakamura Si, Hiroshi Nagai, Motoi Ohba, Toshio Kuroki, Ushio Kikkawa, Masamitsu Ichihashi

  Jun. 2002, Biochemical and biophysical research communications, 294(5) (5), 1109 - 13, English, International magazine

  [Refereed]

  Scientific journal


• Regulation of mammalian phospholipase D2: interaction with and stimulation by G(M2) activator

  S Sarkar, N Miwa, H Kominami, N Igarashi, S Hayashi, T Okada, S Jahangeer, S Nakamura

  Nov. 2001, BIOCHEMICAL JOURNAL, 359, 599 - 604, English

  [Refereed]

  Scientific journal


• Synergistic activation of a family of phosphoinositide 3-kinase via G-protein coupled and tyrosine kinase-related receptors.

  T Katada, H Kurosu, T Okada, T Suzuki, N Tsujimoto, S Takasuga, K Kontani, O Hazeki, M Ui

  Phosphoinositide 3-kinase (PI 3-kinase) is a key signaling enzyme implicated in a variety of receptor-stimulated cell responses. Stimulation of receptors possessing (or coupling to) protein-tyrosine kinase activates heterodimeric PI 3-kinases, which consist of an 85-kDa regulatory subunit (p85) containing Src-homology 2 (SH2) domains and a 110-kDa catalytic subunit (p110 alpha or p110 beta). Thus, this form of PI 3-kinases could be activated in vitro by a phosphotyrosyl peptide containing a YMXM motif that binds to the SH2 domains of p85. Receptors coupling to alpha beta gamma-trimeric G proteins also stimulate the lipid kinase activity of a novel p110 gamma isoform, which is not associated with p85, and thereby is not activated by tyrosine kinase receptors. The activation of p110 gamma PI 3-kinase appears to be mediated through the beta gamma subunits of the G protein (G beta gamma). In addition, rat liver heterodimeric PI 3-kinases containing the p110 beta catalytic subunit are synergistically activated by the phosphotyrosyl peptide plus G beta gamma. Such enzymatic properties were also observed with a recombinant p110 beta/p85 alpha expressed in COS-7 cells. In contrast, another heterodimeric PI 3-kinase consisting of p110 alpha and p85 in the same rat liver, together with a recombinant p110 alpha/p85 alpha, was not activated by G beta gamma, though their activities were stimulated by the phosphotyrosyl peptide. Synergistic activation of PI 3-kinase by the stimulation of the two major receptor types was indeed observed in intact cells, such as chemotactic peptide (N-formyl-Met-Leu-Phe) plus insulin (or Fc gamma II) receptors in differentiated THP-1 and CHO cells and adenosine (A1) plus insulin receptors in rat adipocytes. Thus, PI 3-kinase isoforms consisting of p110 beta catalytic and SH2-containing (p85 or its related) regulatory subunits appeared to function as a 'cross-talk' enzyme between the two signal transduction pathways mediated through tyrosine kinase and G protein-coupled receptors.

  Apr. 1999, Chemistry and physics of lipids, 98(1-2) (1-2), 79 - 86, English, International magazine

  Scientific journal


• Enhancement of chemotactic peptide-induced activation of phosphoinositide 3-kinase by granulocyte-macrophage colony-stimulating factor and its relation to the cytokine-mediated priming of neutrophil superoxide-anion production.

  T Kodama, K Hazeki, O Hazeki, T Okada, M Ui

  Incubation of human neutrophils with a chemotactic peptide [N-formylmethionyl-leucylphenylalanine (fMLP)] gave rise to an increase in the phosphoinositide 3-kinase (PI3K) activity, phosphorylation of p47phox and superoxide-anion (O2(-)) generation in the same fMLP-concentration-dependent manner. These responses to fMLP were markedly enhanced when the cells had been incubated for 10 min before the addition of fMLP with increasing concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF) that were only slightly effective themselves. Wortmannin, an inhibitor of PI3K, suppressed all of these fMLP actions in the same concentration-dependent manner in either GM-CSF-primed or non-primed cells. Sustained activation of protein kinase C by the addition of PMA caused marked phosphorylation of p47phox and respiratory burst itself without activation of PI3K. This strong action of PMA was not primed by GM-CSF. The chemotactic peptide was without effect in pertussis-toxin-treated cells, indicating that its actions are mediated by betagamma-subunits liberated from toxin-susceptible heterotrimeric Gi proteins (Gbetagamma). Thus one of the mechanisms of GM-CSF-mediated priming of fMLP-induced respiratory burst is synergistic activation of wortmannin-sensitive PI3K by Gbetagamma in the presence of tyrosine-phosphorylated proteins in GM-CSF-treated cells, as recently indicated in a cell-free system [Kurosu, Maehama, Okada, Yamamoto, Hoshino, Fukui, Ui, Hazeki and Katada (1997) J. Biol. Chem. 272, 24252-24256]. GM-CSF primed fMLP-induced MAP (mitogen-activated protein) kinase activation enormously as well. The MAP kinase activation was primed even in the presence of wortmannin, indicating that PI3K was not the sole site where tyrosine kinase-related and Gbetagamma-mediated intracellular signals converge to elicit the priming. The GM-CSF priming of fMLP-induced PI3K activation and O2(-) generation was much smaller in magnitude in neutrophils in which cAMP accumulated upon incubation with prostaglandin E1 than in the cells without the nucleotide accumulation. Thus the GM-CSF priming site, in addition to PI3K, might be just the target of cAMP-dependent protein kinase A in fMLP-initiated signalling cascades or could be localized immediately downstream thereof.

  Jan. 1999, The Biochemical journal, 337 ( Pt 2), 201 - 9, English, International magazine

  Scientific journal


• Requirement of G(M2) ganglioside activator for phospholipase D activation

  S Nakamura, T Akisue, H Jinnai, T Hitomi, S Sarkar, N Miwa, T Okada, K Yoshida, S Kuroda, U Kikkawa, Y Nishizuka

  Oct. 1998, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 95(21) (21), 12249 - 12253, English

  [Refereed]

  Scientific journal


• Activation of PI 3-kinase by G protein betagamma subunits.

  O Hazeki, T Okada, H Kurosu, S Takasuga, T Suzuki, T Katada

  We have reported that fMLP-induced activation of pertussis toxin-sensitive GTP-binding proteins in THP-1 cells potentiates the insulin-induced accumulation of PtdIns(3,4,5)P3, a product of phosphoinositide 3-kinase (T. Okada et al., Biochem. J. 317, 475-480, 1996). The synergism in PtdIns(3,4,5)P3 accumulation was observed in Chinese hamster ovary cells expressing both insulin and fMLP receptors. In rat adipocytes, which represent the physiological target cells of insulin, receptor-mediated activation of GTP-binding protein by adenosine and prostaglandin E2 potentiated the insulin-induced PtdIns(3,4,5)P3 accumulation. In cell-free systems, the activity of the p85/p110beta subtype of phosphoinositide 3-kinase was, while that of p85/p110alpha was not, stimulated by the betagamma subunits of the GTP-binding proteins. We propose here a hypothesis that the p85/p110beta subtype is under the control of both the insulin receptors and the GTP-binding protein-coupled receptors in intact cell systems.

  1998, Life sciences, 62(17-18) (17-18), 1555 - 9, English, International magazine

  Scientific journal


• Heterodimeric phosphoinositide 3-kinase consisting of p85 and p110beta is synergistically activated by the betagamma subunits of G proteins and phosphotyrosyl peptide.

  H Kurosu, T Maehama, T Okada, T Yamamoto, S Hoshino, Y Fukui, M Ui, O Hazeki, T Katada

  Phosphoinositide 3-kinase (PI 3-kinase) is a key signaling enzyme implicated in variety of receptor-stimulated cell responses. Receptors with intrinsic or associated tyrosine kinase activity recruit heterodimeric PI 3-kinases consisting of a 110-kDa catalytic subunit (p110) and an 85-kDa regulatory subunit (p85). We separated a PI 3-kinase that could be stimulated by the betagamma subunits of G protein (Gbetagamma) from rat liver. The Gbetagamma-sensitive PI 3-kinase appeared to be a heterodimer consisting of p110beta and p85 (or their related subunits). The stimulation by Gbetagamma was inhibited by the GDP-bound alpha subunit of the inhibitory GTP-binding protein. Moreover, the stimulatory action of Gbetagamma was markedly enhanced by the simultaneous addition of a phosphotyrosyl peptide synthesized according to the amino acid sequence of the insulin receptor substrate-1. Such enzymic properties could be observed with a recombinant p110beta/p85alpha expressed in COS-7 cells with their cDNAs. In contrast, another heterodimeric PI 3-kinase consisting of p110alpha and p85 in the same rat liver, together with a recombinant p110alpha/p85alpha, was not activated by Gbetagamma, although their activities were stimulated by the phosphotyrosyl peptide. These results indicate that p110beta/p85 PI 3-kinase may be regulated in a cooperative manner by two different types of membrane receptors, one possessing tyrosine kinase activity and the other activating GTP-binding proteins.

  Sep. 1997, The Journal of biological chemistry, 272(39) (39), 24252 - 6, English, International magazine

  Scientific journal


• Synergistic activation of PtdIns 3-kinase by tyrosine-phosphorylated peptide and beta gamma-subunits of GTP-binding proteins.

  T Okada, O Hazeki, M Ui, T Katada

  Stimulation of differentiated THP-1 cells by insulin led to rapid accumulation of PtdIns(3,4,5)P3, a product of PtdIns 3-kinase. Stimulation of the GTP-binding-protein-linked receptor by N-formylmethionyl-leucyl-phenylalanine (fMLP) also induced the accumulation of PtdIns(3,4,5)P3 in the cells. The effect of insulin was, while that of fMLP was not, accompanied by increased PtdIns 3-kinase activity in the anti-phosphotyrosine immuno-precipitate. The combination of insulin and fMLP induced more PtdIns(3,4,5)P3 production than the sum of the individual effects. The insulin-induced recruitment of PtdIns 3-kinase activity in the anti-phosphotyrosine immunoprecipitate was unaffected by the combined treatment with fMLP. To investigate the mechanism underlying the synergistic accumulation of PtdIns(3,4,5)P3, we separated the cytosolic proteins of THP-1 cells on a Mono Q column. PtdIns 3-kinase activities were eluted in two peaks, and one of the peaks markedly increased on the addition of beta gamma-subunits of GTP-binding proteins (G beta gamma). The other peak was affected only slightly by G beta gamma, but was synergistically increased by G beta gamma and a tyrosine-phosphorylated peptide which was synthesized accordingly to the amino acid sequence of insulin receptor substrate-1. The activity in the latter fraction was completely immunoprecipitated by an antibody against the regulatory subunit of PtdIns 3-kinase (p85). These results suggest that the conventional PtdIns 3-kinase (p85/p110), which has been implicated in insulin-induced cellular events, or a closely related isoenzyme is controlled by a combination of a tyrosine-phosphorylated protein and a GTP-binding protein in intact cells.

  Jul. 1996, The Biochemical journal, 317 ( Pt 2), 475 - 80, English, International magazine

  Scientific journal


• Wortmannin as a unique probe for an intracellular signalling protein, phosphoinositide 3-kinase.

  M Ui, T Okada, K Hazeki, O Hazeki

  Wortmannin is a fungal metabolite that so far has been shown to act as a selective inhibitor of phosphoinositide 3-kinase. It can therefore be used to investigate the convergence between two major cellular signalling systems: those involving G-protein-coupled receptors and those involving receptor tyrosine kinases. Importantly, wortmannin can enter intact cells, making whole-cell studies of the above signalling pathways possible.

  Aug. 1995, Trends in biochemical sciences, 20(8) (8), 303 - 7, English, International magazine

  Scientific journal


• Involvement of phosphatidylinositol 3-kinase in Fc gamma receptor signaling.

  N Ninomiya, K Hazeki, Y Fukui, T Seya, T Okada, O Hazeki, M Ui

  Wortmannin, a potent and selective inhibitor of phosphatidylinositol (PI) 3-kinase (Okada, T., Sakuma, L., Fukui, Y., Hazeki, O., and Ui, M. (1994) J. Biol. Chem. 269, 3563-3567), prevented Fc receptor for IgG (Fc gamma R)-dependent phagocytosis of the human monocytic cell line U937 or guinea pig neutrophils. Cross-linking of Fc gamma R on the surface of U937 cells increased PI 3-kinase activity that was immunoprecipitated with antibody against phosphotyrosine or antibody against the 85-kDa regulatory subunit of PI 3-kinase. Specific cross-linking of Fc gamma R subclass Fc gamma RI or Fc gamma RII, using monoclonal antibodies against each receptor subclass and the F(ab')2 fragment of goat antibody against mouse IgG, increased anti-phosphotyrosine-precipitable PI 3-kinase activity. Treatment of cells with anti-Fc gamma RIII antibody plus the same F(ab')2 did not affect the activity, reflecting the lack of Fc gamma RIII in U937 cells. Fcy gamma R stimulation triggered prominent tyrosine phosphorylation of several proteins, among which the 115-kDa peptide showed strong association with PI 3-kinase. Thus, Fc gamma R appears to be coupled functionally, via a tyrosine kinase, to PI 3-kinase, which may regulate the phagocytotic activity of the cells.

  Sep. 1994, The Journal of biological chemistry, 269(36) (36), 22732 - 7, English, International magazine

  Scientific journal


• Blockage of chemotactic peptide-induced stimulation of neutrophils by wortmannin as a result of selective inhibition of phosphatidylinositol 3-kinase.

  T Okada, L Sakuma, Y Fukui, O Hazeki, M Ui

  Wortmannin, a fungal metabolite, inhibited 32P labeling of phosphatidylinositol trisphosphate, a product of phosphatidylinositol 3-kinase (PI 3-kinase), selectively in formyl peptide-stimulated 32P-loaded guinea pig neutrophils. The inhibition was of the same concentration dependence (with the half-maximal inhibition around 50 nM) as was observed for the simultaneous inhibition of formyl peptide-induced superoxide anion production. Wortmannin inhibited all three of the PI 3-kinase activities found in the cytosol fraction of guinea pig neutrophils, with a similar dose dependence (the half-maximal effects at 5 nM). Wortmannin was also effective on an immunologically purified preparation of the enzyme. The inhibition was of a noncompetitive type with regard to ATP and was observed consistently when PI, PI monophosphate, or PI bisphosphate was used as substrate. PI 4-kinase activity was not affected. It is concluded, therefore, that wortmannin abolished the formyl peptide-induced stimulation of neutrophils as a result of the inhibition of PI 3-kinase. An essential role of PI 3-kinase in receptor-mediated signaling in neutrophils thus evidenced with the use of wortmannin will be expanded to other cellular signaling systems.

  Feb. 1994, The Journal of biological chemistry, 269(5) (5), 3563 - 7, English, International magazine

  Scientific journal


• Essential role of phosphatidylinositol 3-kinase in insulin-induced glucose transport and antilipolysis in rat adipocytes. Studies with a selective inhibitor wortmannin.

  T Okada, Y Kawano, T Sakakibara, O Hazeki, M Ui

  Significant activity of phosphatidylinositol 3-kinase (PI 3-kinase) was detected in the membrane fractions, or in the immunoprecipitates prepared with anti-phosphotyrosine antibodies, from rat adipocytes that had been incubated with insulin for 20 min. The PI 3-kinase activity in these preparations as well as in the whole cell lysates of adipocytes not treated with insulin was inhibited by the addition of wortmannin, a fungal metabolite, to the enzyme assay mixture. The inhibition was dependent on the inhibitor concentration with IC50 being less than 10 nM and perfect inhibition at 100 nM. The effect of insulin to induce membrane PI 3-kinase activity was mostly abolished, but its effects to tyrosine-phosphorylate the beta-subunit of the insulin receptor or other cellular substrate proteins including insulin-receptor-substrate-1 were not at all antagonized, by wortmannin added to the cell incubation medium. Insulin stimulation of cellular 2-deoxyglucose uptake and inhibition of isoproterenol-induced lipolysis observable in adipocytes under the same conditions were also antagonized by wortmannin added in the same concentration range as used for the inhibition of insulin-susceptible PI 3-kinase. It is concluded, therefore, that activation of wortmannin-sensitive PI 3-kinase plays a pivotal role in the intracellular signaling pathways arising from the insulin receptor autophosphorylation and leading to certain metabolic responses.

  Feb. 1994, The Journal of biological chemistry, 269(5) (5), 3568 - 73, English, International magazine

  Scientific journal


• Insulin-stimulated GLUT4 translocation is relevant to the phosphorylation of IRS-1 and the activity of PI3-kinase.

  F Kanai, K Ito, M Todaka, H Hayashi, S Kamohara, K Ishii, T Okada, O Hazeki, M Ui, Y Ebina

  We examined the role of 185-kDa insulin receptor substrate-1 (IRS-1) and phosphatidylinositol 3-kinase (PI3-kinase) in the signaling pathway of insulin-stimulated GLUT4 translocation. We had already developed a novel cell line to detect GLUT4 on the cell surface, directly and sensitively (Kanai, F., Nishioka, Y., Hayashi, H., Kamohara, S., Todaka, M., and Ebina, Y. (1993) J. Biol. Chem. 268, 14523-14526). We stably expressed a mutant insulin receptor in which Tyr972 was replaced with phenylalanine. Insulin-stimulated tyrosyl phosphorylation of IRS-1 and GLUT4 translocation were decreased in cells expressing the mutant receptor, as compared to findings in cells expressing the normal receptor. Wortmannin, an inhibitor of PI3-kinase, inhibits the insulin-stimulated PI3-kinase activity and GLUT4 translocation at 50 nM, but not the NaF-stimulated GLUT4 translocation. These results suggest that the tyrosine phosphorylation of IRS-1 and activation of PI3-kinase may be involved in the signaling pathway of the insulin-stimulated GLUT4 translocation.

  Sep. 1993, Biochemical and biophysical research communications, 195(2) (2), 762 - 8, English, International magazine

  Scientific journal

• 【エンドソームの多彩な機能:細胞内分子輸送の新ルートマップ公開】 エキソソームの形成機構

  Kajimoto Taketoshi, Okada Taro, Nakamura Shun-ichi

  学研メディカル秀潤社 ; 1982-, Jan. 2015, 細胞工学, 34(2号) (2号), 168 - 173, Japanese

  Introduction commerce magazine


• Sphingosine 1-phosphate signaling regulates exosomal cargo sorting

  Taketoshi Kajimoto, Taro Okada, Satoshi Miya, Lifang Zhang, Shun-ichi Nakamura

  Apr. 2014, FASEB JOURNAL, 28(1) (1), English

  Summary international conference


• [Role of S1P acting both inside and outside the cells].

  Taro Okada, Shun-ichi Nakamura

  Feb. 2012, Seikagaku. The Journal of Japanese Biochemical Society, 84(2) (2), 92 - 101, Japanese, Domestic magazine


• Sphingolipid signaling and neuronal function

  Shun-ichi Nakamura, Eri Fukai, Satoshi Miya, Henryk Jesko, Taro Okada

  Sep. 2011, PHARMACOLOGICAL REPORTS, 63(5) (5), 1279 - 1280, English

  Summary international conference


• Sphingolipid signaling and neuronal function

  Shun-ichi Nakamura, Eri Fukai, Satoshi Miya, Henryk Jesko, Taro Okada

  Aug. 2011, CHEMISTRY AND PHYSICS OF LIPIDS, 164, S9 - S9, English

  Summary international conference


• Sphingosine kinase/sphingosine 1-phosphate signalling in central nervous system.

  Taro Okada, Taketoshi Kajimoto, Saleem Jahangeer, Shun-ichi Nakamura

  Jan. 2009, Cellular signalling, 21(1) (1), 7 - 13, English, International magazine

  [Refereed]


• Involvement of sphingosine-1-phosphate in glutamate secretion in hippocampal neurons

  GOPARAJU Sravan, JAHANGEER Saleem

  05 Jun. 2007, 脂質生化学研究, 49, 222 - 224, Japanese

• S1P 受容体タイプ３−Ｇｑ−カゼインキナーゼ系による レトログレード輸送およびリソソーム機能の制御

  岡田 太郎

  第１８回スフィンゴテラピィ研究会, Mar. 2025

  Oral presentation


• 脂肪族アルデヒドの代謝異常がゲノム安定性に及ぼす影響

  酒井 恒, 䑺谷智也, 梶本武利, 岡田太郎, 篠原正和, 横井雅幸, 菅澤 薫

  日本環境変異原ゲノム学会第53回大会, Dec. 2024

  Oral presentation


• アルデヒド脱水素酵素ALDH3A2の欠損がゲノム安定性維持に及ぼす影響の解析

  䑺谷智也, 岡田太郎, 梶本武利, 篠原正和, 横井 雅幸, 菅澤 薫, 酒井 恒

  第４７回日本分子生物学会年会, Nov. 2024

  Poster presentation


• 脂質代謝過程で生じるアルデヒドのゲノム安定性維持における影響

  酒井 恒, 䑺谷 智, 槻侑, 藤元成, 笹野真唯, 白石 萌, 松田 俊, 松田知成, 梶本武利, 岡田太郎, 横井雅幸, 菅澤 薫

  日本環境変異原ゲノム学会, Nov. 2023


• SphK1/S1P受容体系はエンドソームからTGNへのCI-M6PRの逆行輸送に寄与することでライソゾーム酵素Cathepsin Dの活性を制御する

  西田晋, 中村俊一, 岡田太郎

  第９６回日本生化学会大会, Nov. 2023

  Poster presentation


• Effect of extracellular alpha-synuclein on S1P receptor

  Taro Okada

  第15回セラミド研究会・第１６回スフィンゴテラピィ研究会合同学術大会, Oct. 2022

  [Invited]

  Invited oral presentation


• 細胞外α−シヌクレインによるスフィンゴシン−１−リン酸受容体の阻害とその影響

  岡田 太郎

  共創の場形成支援プログラム・JSTムーンショット型研究開発事業共催・第一回先端医科学研究セミナー, Sep. 2022

  [Invited]

  Public discourse


• トランスゴルジネットワークから形質膜へのタンパク質 輸送におけるスフィンゴシン 1-リン酸受容体の役割

  岡田太郎, 中村俊一

  第１５回スフィンゴテラピィ研究会, Nov. 2021

  Oral presentation


• トランスゴルジネットワークから形質膜へのタンパク質輸送における スフィンゴシン 1-リン酸（S1P）受容体の役割

  岡田太郎, 中村俊一

  スフィンゴテラピィ研究会, Nov. 2021

  Oral presentation


• 新規プロテインキナーゼC活性化レポーターにより明らかとなるアポトーシス回避の分子メカニズム

  梶本 武利, キャリマン アリシャ, トバイアス アイリーン, 岡田 太郎, パイロ ケイラ, ヴァン アンジェラ, マキャモン アンドリュー, 中村 俊一, ニュートン アレキサンドラ

  第60回日本組織細胞化学会総会・学術集会, Sep. 2019

  Oral presentation


• 非典型プロテインキナーゼCのスフィンゴシン-１リン酸による新規活性化メカニズム

  Kajimoto, T, Caliman, A.D, Tobias, I.S, Okada, T, Pilo, C.A, Van, A.A, McCammon J.A, Nakamura, S, Newton, A.C

  第71回日本細胞生物学会大会, Jun. 2019


• 非典型プロテインキナーゼC特異的活性化レポーターにより明らかとなる非典型プロテインキナーゼCの新規活性化メカニズム

  Taketoshi Kajimoto, Alisha D. Caliman, Irene S. Tobias, Taro Okada, J. Andrew McCammon, Shun-ichi Nakamura, Alexandra C. Newton

  第41回 日本分子生物学会年会, Nov. 2018, Japanese, 日本分子生物学会, 横浜, Domestic conference

  Poster presentation


• エクソソームへの積荷ソーティングにおける三量体Gタンパク質βγサブユニットシグナリングの役割

  KAJIMOTO TAKETOSHI, モハメド ネスマ, バダウィー シャイマー, マトベロ シュビー, 平瀬 光寛, 中村 俊介, 吉田 大亮, OKADA TARO, IJUIN TAKESHI, NAKAMURA SHUN-ICHI

  第91回 日本生化学会大会, Sep. 2018, Japanese, 日本生化学会, 京都, Domestic conference

  Oral presentation


• エクソソームへの積荷ソーティングにおけるRhoファミリー低分子量Gタンパク質の役割

  KAJIMOTO TAKETOSHI, モハメド ネスマ, バダウィー シャイマー, マトベロ シュビー, 平瀬 光寛, 中村 俊介, 吉田 大亮, OKADA TARO, IJUIN TAKESHI, NAKAMURA SHUN-ICHI

  第133回 日本薬理学会近畿部会, Jun. 2018, Japanese, 日本薬理学会, 広島, Domestic conference

  Oral presentation


• Atypical Protein Kinase C-specific Activity Reporter Reveals Novel Activation Mechanism of Atypical Protein Kinase C by Sphingosine 1-phosphate

  Taketoshi Kajimoto, Alisha D. Caliman, Irene S. Tobias, Taro Okada, J. Andrew McCammon, Shun-ichi Nakamura, Alexandra C. Newton

  Experimental Biology 2018, Apr. 2018, English, American Society for Biochemistry and Molecular Biology, San Diego, International conference

  Poster presentation


• Sphingosine 1-phosphate signaling on multivesicular endosome triggers sorting of protein cargo into exosomes

  Kajimoto Taketoshi, Okada Taro, Satoshi Miya, Lifang Zhang, Nakamura Shun-ichi

  2015 ASCB Annual Meeting, Dec. 2015, English, American Society for Cell Biology (ASCB), San Diego, USA, International conference

  Poster presentation


• MEK-ERK-STAT3経路で制御されるMcl-1Lによる色素細胞のアポトーシス抑制とメラノーマ発症

  福本 毅, Sakaguchi Masanobu, Nishigori Chikako, Oka Masahiro, 岩崎 哲史, 橋本 孝則, 文 有彬, 深見 泰夫, Okada Taro

  第2回関西若手皮膚科医の集い, Oct. 2015, Japanese, 鳥居薬品・京都大学, 京都, Domestic conference

  Oral presentation


• High expression of Mcl-1L via the MEK-ERK-STAT3 signaling pathway protects melanocytes from UVB-induced apoptosis: a mechanism essential for melanomagenesis

  Takeshi Fukumoto, Nishigori Chikako, Oka Masahiro, Sakaguchi Masanobu, Yasuo Fukami, Tetsushi Iwasaki, Takanori Hashimoto, Youbin Moon, Okada Taro

  45th Annual ESDR Meeting, Sep. 2015, English, European Society for Dermatological Research, Rotterdam, Netherlands, International conference

  Oral presentation


• High expression of Mcl-1 mediated by MEK–ERK1/2–STAT3 signaling pathway protects melanocytes and melanoma cells against ultraviolet B-induced apoptosis.

  Takeshi Fukumoto, Tetsushi Iwasaki, Okada Taro, Takanori Hashimoto, Youbin Moon, Sakaguchi Masanobu, Yasuo Fukami, Nishigori Chikako, Oka Masahiro

  2015 SID Annual Meeting, May 2015, English, Society for Investigative Dermatology, Atlanta, USA, International conference

  Oral presentation


• Sphingosine 1-phosphate signaling triggers exosomal protein sorting

  Kajimoto Taketoshi, Okada Taro, 宮 聡志, 張 麗芳, Nakamura Shun-ichi

  University of Washington and Kobe UniversityInternational Joint Symposium, Dec. 2014, English, Kobe University, 神戸, Domestic conference

  Poster presentation


• Ongoing activation of sphingosine 1-phosphate receptors mediates maturation of exosomal multivesicular endosomes

  Kajimoto Taketoshi, Okada Taro, 宮聡志, 張麗芳, Nakamura Shun-ichi

  Japan Biochemical Society、８７th, Oct. 2014, Japanese, Japan Biochemical Society, 京都, Domestic conference

  Oral presentation


• Ultraviolet B-induced up-regulation of Mcl-1 mediated by MEK-ERK1/2-STAT3 signaling pathway has a protective role in apoptosis in melanocytes

  Takeshi Fukumoto, Oka Masahiro, Sakaguchi Masanobu, Nishigori Chikako, Tetsushi Iwasaki, Takanori Hashimoto, Youbin Moon, Yasuo Fukami, Okada Taro

  XXII International Pigment Cell Conference, Sep. 2014, English, International Pigment Cell Conference, Singapore, シンガポール, International conference

  Oral presentation


• フィブロネクチン腎症（FN）におけるFN1遺伝子変異の同定およびその機能解析に関する研究

  大坪 裕美, Okada Taro, Kajimoto Taketoshi, Nozu Kandai, Kamiyoshi Naohiro, Matsunoshita Natsuki, Ninchoji Takeshi, Kaito Hiroshi, Nakamura Shun-ichi, Iijima Kazumoto

  第49回日本小児腎臓病学会学術集会, Jun. 2014, Japanese, 日本小児腎臓病学会, 秋田, Domestic conference

  Oral presentation


• Sphingosine 1-phosphate signaling triggers exosomal cargo sorting

  Kajimoto Taketoshi, Okada Taro, 宮 聡志, 張 麗芳, Nakamura Shun-ichi

  The 66th Annual Meeting of the Japan Society for Cell Biology, Jun. 2014, Japanese, Japan Society for Cell Biology, 奈良, Domestic conference

  Poster presentation


• エクソソームへの積み荷ソーティングにおける生理活性物質スフィンゴシン1-リン酸の役割

  Kajimoto Taketoshi, Okada Taro, 宮 聡志, 張 麗芳, Nakamura Shun-ichi

  The 66th Annual Meeting of the Japanese Pharmacological Society, Jun. 2014, Japanese, The Japanese Pharmacological Society, 岡山, Domestic conference

  Oral presentation


• Sphingosine 1-phosphate signaling regulates exosomal cargo sorting

  Kajimoto Taketoshi, Okada Taro, 宮 聡志, 張 麗芳, Nakamura Shun-ichi

  2014 ASBMB Annual Meeting, Apr. 2014, English, American Society for Biochemistry and Molecular Biology, San Diego, USA, International conference

  Poster presentation


• Critical role of sphingosine 1-phosphate in exosome biogenesis

  Kajimoto Taketoshi, Okada Taro, 宮 聡志, 張 麗芳, Nakamura Shun-ichi

  The 36th Annual Meeting of the Molecular Biology Society of Japan, Dec. 2013, Japanese, The Molecular Biology Society of Japan, 神戸, Domestic conference

  Poster presentation


• Regulation of multivesicular body-maturation by S1P signaling

  Nakamura Shun-ichi, Kajimoto Taketoshi, 宮 聡志, 張 麗芳, Okada Taro

  The 8th Sphingotherapy Conference, Jul. 2013, Japanese, Sphingotherapy Conference, 加賀, Domestic conference

  Oral presentation


• Regulation of hippocampal function by sphingolipid signaling

  Nakamura Shun-ichi, 深井 絵里, 宮 聡, H Jesko, Okada Taro

  The Days of Neurochemistry "Genetic and molecular mechanisms of neurological diseases. Progress in diagnosis and therapy.", Oct. 2011, English, ポーランド科学アカデミー, ワルシャワ, ポーランド, International conference

  Invited oral presentation


• Sphingolipid signaling and neuronal function

  Nakamura Shun-ichi, 深井 絵里, 宮 聡, H Jesko, Okada Taro

  52nd International Conference on the Bioscience of Lipids, Aug. 2011, English, ワルシャワ, ポーランド, International conference

  [Invited]

  Invited oral presentation


• Sphingolipid signaling in the nucleus:Mechanism underlying nucleo/cytoplasmic shuttlingof sphingosine kinase 2

  Nakamura Shun-ichi, Eri Fukai, Henryk Jesko, Okada Taro

  第33回日本分子生物学会年会・第83回日本生化学会大会 合同大会, Dec. 2010, English, 日本分子生物学会、日本生化学会, 神戸, Domestic conference

  Oral presentation


• Regulation of neurotransmitter release by S1P signaling

  Nakamura Shun-ichi, Okada Taro

  The 27th Naito Conference, Jun. 2010, Japanese, 内藤記念財団, 札幌, Domestic conference

  Poster presentation


• Expression pattern of sphingosin kinase in the mouse central nervous system

  Katsuyama Yu, Okada Taro, Nakamura Shun-ichi, Terashima Toshio

  第115回日本解剖学会総会・全国学術集会, Mar. 2010, Japanese, 日本解剖学会, 盛岡, Domestic conference

  Poster presentation


• Signal transducer and activator of transcription 3 (STAT3) upregulates interleukin-8 (IL-8) expression at the level of transcription in human melanoma cells

  Oka Masahiro, Sakaguchi Masanobu, Okada Taro, Michitaka Ozaki, Toyo Yoshioka, Hiroshi Inoue, Naofumi Mukaida, Ushio Kikkawa, Nishigori Chikako

  Joint Meeting 7th World Congress on Melanoma & 5th Congress of the European Association of Dermato-Oncology, May 2009, English, Congress on Melanoma, Congress of the European Association of Dermato-Oncology, Vienna, オーストリア, International conference

  Poster presentation


• Regulation of exosomal release by sphingosine kinase 2

  Nakamura Shun-ichi, Okada Taro

  第3回スフィンゴテラピィ（STC）研究会, Jul. 2008, Japanese, スフィンゴテラピィ研究会, 鳥取, Domestic conference

  Oral presentation


• Involvement of sphingosine-1-phosphate in glutamate secretion in hippocampal neurons

  Nakamura Shun-ichi, Kajimoto Taketoshi, Okada Taro, JAHANGEER SALEEM

  第４９回日本脂質生化学会, Jun. 2007, Japanese, 日本脂質生化学会, 札幌, Domestic conference

  Oral presentation


• Involvement of N-Terminally Extended Form of Sphingosine kinase 2 in Serum-Dependent Regulation of Cell Proliferation and Apoptosis

  OKADA, Taro, 丁 国, 園田 洋史, 梶本 武利, 羽賀 雄紀, Ali Khosrowbeygi, 高山 陽, MIWA, Noriko, JAHANGEER, SALEEM, NAKAMURA, Syunichi

  第２８回日本分子生物学会年会, Dec. 2005, Japanese, 日本分子生物学会, 福岡, Domestic conference

  Oral presentation


• Sphingosine Kinase 2 is a Nuclear Protein and Inhibits DNA Synthesis

  NAKAMURA, Syunichi, OKADA, Taro

  Gordon Research Conference, Feb. 2005, English, Gordon Research Conference, Santa Barbara,CA, International conference

  [Invited]

  Invited oral presentation


• スフィンゴシンキナーゼ／S1P系を介する細胞内情報伝達の分子機構解析

  OKADA, Taro, 林 俊, 五十嵐 宣明, 藤田 敏忠, NAKAMURA, Syunichi

  第38回神戸バイオサイエンス研究会, Jan. 2005, Japanese, 神戸大学, 神戸, Domestic conference

  Invited oral presentation


• Sphingosine kinase 2 is a nuclear protein and inhibits DNA sythesis.

  五十嵐 宣明, OKADA, Taro, 林 俊, NAKAMURA, Syunichi

  第76回日本生化学会大会, Oct. 2003, Japanese, 日本生化学, 横浜, Domestic conference

  Oral presentation


• スフィンゴシンキナーゼの細胞内局在とその生理的意義

  OKADA, Taro, 林 俊, 五十嵐 宣明, NAKAMURA, Syunichi

  第3回生命科学研究会, Jul. 2003, Japanese, 宇井理生, 東京, Domestic conference

  Invited oral presentation

• スフィンゴテラピィ研究会

  Apr. 2019 - Present


• 日本生化学会

• シヌクレイノパチーにおける細胞外αシヌクレインによる新規病変伝播機構の解明

  岡田 太郎

  日本学術振興会, 科学研究費助成事業 基盤研究(C), 基盤研究(C), 神戸大学, 01 Apr. 2022 - 31 Mar. 2025


• パーキンソン病の病態におけるＳ１Ｐ受容体シグナルおよびエキソソーム放出の関与

  岡田 太郎

  学術研究助成基金助成金／基盤研究(C), Apr. 2018 - Mar. 2021, Principal investigator

  Competitive research funding


• S1Pシグナルを介したエキソソーム放出の分子機構の解析

  中村 俊一

  科学研究費補助金／基盤研究(B), Apr. 2018 - Mar. 2021

  Competitive research funding


• S1Pシグナルを介したパーキンソン病の病態解析

  中村 俊一

  学術研究助成基金助成金／挑戦的研究（萌芽）, Jun. 2018 - Mar. 2020

  Competitive research funding


• 細胞外α－シヌクレインによるＳ１Ｐ受容体シグナル伝達抑制機構の解析

  岡田 太郎

  学術研究助成基金助成金／基盤研究(C), Apr. 2015 - Mar. 2018, Principal investigator

  Competitive research funding


• リゾビスフォスファチジン酸（LBPA）とS1Pシグナルのカップリング機構の解析

  中村 俊一

  学術研究助成基金助成金／挑戦的萌芽研究, Apr. 2015 - Mar. 2016

  Competitive research funding


• エキソソームへの積荷ソーティング調節を介した癌の悪性化制御

  中村 俊一

  学術研究助成基金助成金／挑戦的萌芽研究, Apr. 2014 - Mar. 2015

  Competitive research funding


• 気道アレルギー免疫応答に対するスフィンゴリン脂質系の役割の解明

  西村 善博

  科学研究費補助金／基盤研究(C), Apr. 2012 - Mar. 2015

  Competitive research funding


• 海馬神経細胞のＳ１Ｐ受容体をターゲットとした新規てんかん治療法の開発

  岡田 太郎

  科学研究費補助金／基盤研究(C), Apr. 2012 - Mar. 2015, Principal investigator

  Competitive research funding


• スフィンゴシンキナーゼ・Ｓ１Ｐシグナル伝達系による脳機能の調節機構

  中村 俊一

  科学研究費補助金／基盤研究(B), 2010

  Competitive research funding


• 海馬歯状回顆粒細胞の神経回路形成におけるスフィンゴシンキナーゼの機能

  岡田 太郎

  科学研究費補助金／基盤研究(C), 2009, Principal investigator

  Competitive research funding


• スフィンゴシンを介した気道粘液産生の制御

  西村 善博

  科学研究費補助金／基盤研究(C), 2009

  Competitive research funding


• スフィンゴ脂質による神経伝達物質放出機構の解析

  中村 俊一

  科学研究費補助金／特定領域研究, 2008

  Competitive research funding


• Research of sphingosine kinase modification in acute lung injury

  NISHIMURA Yoshihiro, KOTANI Yoshikazu, OKADA Taro, NISHIUMA Teruaki, HIRATA Kenichi

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Kobe University, 2006 - 2007

  The metabolism of sphingosine kinase (SPHK)/sphingosine 1-phosphate (SIP) system in lung diseases has been reported recently. In this project, we focused on the role of SPHK in lung epithelial cells and fibroblasts in injured lungs. 1. We investigated the mechanism of myofibroblast differentiation in lung fibroblasts of acute lung injury. Bleomycin treatment increased SPHK expression and fibrotic changes in injured lungs. Our study reported that TGF-beta treatment increased SPHK1 activation in lung fibroblasts. S1P produced by SPHK1 induced the transactivation of S1P receptors and recruitment of activated RhoA. This data was accepted in Am J Respir Cell Mol Biol in 2007. 2. Using mouse asthmatic model, we examined whether the effect of SPHK inhibitors attenuates airway inflammation. The inhalation of SPHK inhibitors by nebulizing maneuver showed significant decrease of airway hyperresponsiveness and eosinophilic inflammation induced by ovalbumin treatment, whereas intravenous delivery showed limited effects. Our data indicated that intratracheal treatment of SPHK inhibitor may be one of therapeutic approach for lung inflammation. This data was accepted in Am J Physiol Lung Cell Mol Physiol in 2008. 3. In this animal model, we found that SPHK activity was increased in bronchial epithelial areas in asthmatic lungs. Then we examined the function of SPHK in goblet cell formation around epithelial walls. In vitro studies using airway liquid interface demonstrated that SPHK was activated and played a pivotal role in cell changes by IL-13 treatment. This data will be exhibited in American Thoracic Society in 2008. Thus, our studies clarified that SPHK works for morphological cell changes in lung inflammation.


• スフィンゴシンキナーゼの細胞質・核間シャトル機構の解析

  中村 俊一

  科学研究費補助金／基盤研究(C), 2007

  Competitive research funding


• 糖尿病をモデルとしたシグナル伝達病拠点

  春日 雅人

  2006

  Competitive research funding


• 急性肺傷害に対するスフィンゴリン脂質代謝酵素を用いた遺伝子治療の試み

  西村 善博

  科学研究費補助金／基盤研究(C), 2006

  Competitive research funding


• 糖尿病をモデルとしたシグナル伝達病拠点

  春日 雅人

  2005

  Competitive research funding


• スフィンゴシン１リン酸に結合する核内受容体の同定

  岡田 太郎

  科学研究費補助金／若手研究(B), 2005, Principal investigator

  Competitive research funding


• エンドソーム形成の分子メカニズムの解析

  中村 俊一, 岡田 太郎, 三輪 教子, JAHANGEER Saleem

  日本学術振興会, 科学研究費助成事業, 萌芽研究, 神戸大学, 2002 - 2003

  スフィンゴシン1燐酸(SPP)は酵母からヒトに至る真核生物に広く存在し、強力な細胞増殖促進能やアポトーシス抑制能を有する脂質情報伝達物質である。SPPの作用点として細胞外からの作用と細胞内での作用が以前から想定されてきた。しかしながら、SPPの細胞内での作用点は依然不明のままであった。我々は最近、酵母・ツーハイブリッド法を用いてSPPの産生酵素であるスフィンゴシシ・キナーゼ1(SPHK1)に対する新規なソーティング分子RPK118を発見した。 RPK118は分子量118Kの可溶性タンパク質で、分子内にPX領域、ESP領域、偽キナーゼ領域1,2等の他のタンパク質との構造上の類似領域を含むことを構造解析の結果明らかにした。このPX領域は細胞の小胞輸送に必要な初期エンドソーム膜に結合する際のセンサー部位として働くことを証明した。また、ESP領域は他のタンパク質との結合に関与するらしい。偽キナーゼ領域1及び2に関しては今回の構造解析の結果初めて明らかにされたドメイン構造であり、タンパク質合成の際に必要なリボゾームS6キナーゼに構造上頼似しているが、キナーゼ活性に必須なアミノ酸が欠如しているためにこのように命名された。RPK118はこの偽キナーゼ領域2に於いてSPHK1と結合し、SPHK1を初期エンドソームにソーティングすることが分かった。細胞に偽キナーゼ領域2のみからなるフラグメントを発現させるとSPHK1が初期エンドソームに集積しなくなり、初期エンドソームの形態異常が観察された。 これらの知見は現在まで不明であったSPPの細胞内での作用点の理解に重要な知見を提供するものであり、また、SPPの作用が細胞内小胞輸送の調節に関与する可能性を強く示唆しており、今後の医学への応用、新薬の開発に期待が持てる。


• 低分子G蛋白質ARF依存性ホスホリパーゼDの活性化機構の解析

  中村 俊一, JAHANGEER Saleem, 岡田 太郎, 三輪 教子

  日本学術振興会, 科学研究費助成事業, 特定領域研究(B), 神戸大学, 2000 - 2001

  我々はこれまでG_アクチベーターによるホスホリパーゼD1(PLD1)の活性調節機構について報告してきた。本年度はこの研究計画の最終年度にあたることを鑑み、総括的な観点からPLDの活性化機構を調べる目的で、比較的研究の遅れているPLD2に焦点を絞り競究をおこなった.PLD2はPLD1と異なりARFやPKCαにより活性化されず、その活性化機構に関しては不明であった。そこで我々はG_アクチベーターによるPLD2の活性調節の有無を調べるため、リコンビナントPLD2を作成しこの精製タンパク質を用いてin vitroに於けるPLDの活性測定を行った。その結果、我々が開発した硫酸アンモニウムを用いたPLD活性測定法においてもBrownらの開発した活性測定法を用いても、PLD2はG_アクチベーターにより強力に(約5倍)活性化された。興味深いことに、PLD2の活性化には影響を与えないとされていたARFは単独ではPLD2を活性化しないが、G_アクチベーター存在下に於いてはPLD1と同様に相乗的にPLD2を活性化した。更に免疫沈降実験に於いて、G_アクチベーターとPLD2が結合すること。またG_アクチベーター存在下ではPLD2とARFの結合が亢進することが明らかにされた。今までPLD2はPIP_2存在下で高い活性を示すことから、細胞内では抑制的にその活性が調節され、細胞刺激の結果その抑制が解除され活性を発現すると考えられてきた。今回の我々の結果は、PLD2はPLD1と同様に、複数の活性化因子が組み合わさって活性化を引き起こすことが強く示唆された。以上の結果から、刺激に連動したPLD2の活性化機構解明には至らなかったものの、分子レベルに於けるPLD2の活性化機備の瑛解に大きな進展が見られたと言えよう。


• Studies on the mechanism of activation of phospholipase D

  NAKAMURA Shun-ichi, OKADA Taro, MIWA Noriko

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B)., Kobe University, 1999 - 2000

  We have recently reported that an important factor for ganglioside metabolism known as GM2 activator is involved in the regulation of phospholipase D (PLD) activation. In an in vitro study recombinant GM2 activator activated PLD1 and PLD2 in a dose-dependent manner. GM2 activator stimulated PLD1 synergistically with ARF.In contrast to the concerted activation of activators, PLD2 was stimulated by GM2 activator acting almost solely. In GM2 activator-deficient fibroblasts PLD activation by PMA was almost normal compared with the stimulation pattern in wild-type cells. In the cells stably expressing dominant-negative GM2 activator, PLD activation by PMA was remarkably suppressed. Taken together, these data strongly suggest that similar factors to GM2 activator redundantly regulate PLD activity in the cells. Identification of these factors is essential for the understanding of the mechanism of receptor-mediated PLD activation.


• G_アクチベーターによるホスホリパーゼDの活性化機構に関する研究

  中村 俊一, 岡田 太郎, 三輪 教子

  日本学術振興会, 科学研究費助成事業, 萌芽的研究, 神戸大学, 1998 - 1998

  ホスホリパーゼD(PLD)は、様々な細胞刺激に連動して活性化され、ホスファチジルコリンを加水分解し、脂質メディエーターを産生する情報変換酵素である。PLDの活性化にはARFなとの低分子量型G蛋白質が関与することが報告されていたが、精製された系ではその活性化が弱いことから、別の因子の関与が示唆されてきた。我々は、ラットの腎臓の可溶性画分にPLDに対する熱に安定な活性化因子を見い出し、これを単離精製した。この因子は、電気泳動上分子量約23kの蛋白質で、in vitroに於いてARFと相乗的にPLDを活性化した。次に、この蛋白質をプロテアーゼ処理を行い、得られたペプチドのアミノ酸配列を決定したところ、ガングリオシド代謝に関与するG_アクチベーターと一致した。更に、精製されたPLDの活性化因子を用いて、G_アクチベーター活性として知られる、βヘキソミニダーゼAの活性化を測定した結果、この酵素の活性化能を有することが分かった。以上の結果は、G_アクチベーターが多機能を有する調節蛋白質であるとともに、G_アクチベーター欠損の結果引き起こされる、G_ガングリオシドーシスの病態にPLDが関与することを示唆するものである。