Involvement of Rabphilin3 in Endocytosis through Interaction with Rabaptin5*
- From the Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita 565, Japan
Abstract
Rabphilin3 and rabaptin5 are downstream target molecules of the Rab3 and -5 subfamily small G proteins that are implicated in exocytosis and endocytosis, respectively. We examined here the physical and functional relationship between the Rab3-rabphilin3 and Rab5-rabaptin5 systems. Rabphilin3 interacted with rabaptin5 at the N-terminal region (amino acids 1–280), which GTP-Rab3A interacted with. The interaction of rabphilin3 with rabaptin5 was inhibited by guanosine 5′-(3-O-thio)triphosphate-Rab3A. Overexpression of the N-terminal fragment of rabphilin3 (amino acids 1–280) inhibited the receptor-mediated endocytosis of transferrin, and this inhibition was overcome by co-transfection with a dominant active mutant of Rab3A or rabaptin5 in PC12 and HeLa cells. These results suggest that rabphilin3, free of GTP-Rab3A, regulates endocytosis through interaction with rabaptin5 after rabphilin3 complexed with GTP-Rab3A regulates exocytosis.
Footnotes
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↵* This work was supported by grants-in-aid for Scientific Research and for Cancer Research from the Ministry of Education, Science, Sports, and Culture, Japan (1996, 1997), by grants-in-aid for Abnormalities in Hormone Receptor Mechanisms and for Aging and Health from the Ministry of Health and Welfare, Japan (1996, 1997), and by grants from the Human Frontier Science Program (1996, 1997) and the Uehara Memorial Foundation (1996).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Present address: The Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka 812-82, Japan.
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↵§ To whom correspondence should be addressed. Tel.: 81-6-879-3410; Fax: 81-6-879-3419; E-mail: ytakai{at}molbio.med.osaka-u.ac.jp.
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↵1 The abbreviations used are: GDI, GDP dissociation inhibitor; GEP, GDP/GTP exchange protein; GAP, GTPase activating protein; GTPγS, guanosine 5′-(3-O-thio)triphosphate; HA, hemagglutinin; aa, amino acid; SD, synthetic dextrose; PAGE, polyacrylamide gel electrophoresis; FITC, fluorescein isothiocyanate.
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- Received August 19, 1997.
- Revision received October 20, 1997.
- The American Society for Biochemistry and Molecular Biology, Inc.
