INVOLVEMENT OF RABPHILIN3 IN ENDOCYTOSIS THROUGH INTERACTION WITH RABAPTIN5

Rabphilin3 and rabaptin5 are downstream target molecules of the Rab3 a nd -5 subfamily small G proteins that are implicated in exocytosis and endocytosis, respectively. We examined here the physical and function al 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 rab philin3 with rabaptin5 was inhibited by guanosine 5'-(3-0-thio)triphos phate-Rab3A. Overexpression of the N-terminal fragment of rabphilin3 ( amino acids 1-280) inhibited the receptor-mediated endocytosis of tran sferrin, and this inhibition was overcome by co-transfection with a do minant active mutant of Rab3A or rabaptin5 in PC12 and HeLa cells. The se results suggest that rabphilin3, free of GTP-Rab3A, regulates endoc ytosis through interaction with rabaptin5 after rabphilin3 complexed w ith GTP-Rab3A regulates exocytosis.