Abstract
Rabphilin is generally thought to be involved in the regulation of secretory vesicle exocytosis in neurons and neuroendocrine cells. The N-terminal part of rabphilin has recently been shown to function as an effector domain for Rab3A/Rab27A in PC12 cells, but the function of the C2 domains of rabphilin during secretory vesicle exocytosis is largely unknown. In this study we investigated the interaction between rabphilin and exocytotic proteins and found that the C2B domain of rabphilin directly interacts with a plasma membrane protein, SNAP-25. Furthermore, vesicle dynamics were imaged by total internal reflection fluorescent microscopy in a single PC12 cell expressing a lumen-targeted pH-insensitive yellow fluorescent protein (Venus), neuropeptide Y-Venus. Expression of the wild-type rabphilin in PC12 cells significantly increased the number of docked vesicles to the plasma membrane without altering the kinetics of individual secretory events, whereas expression of the mutant rabphilin lacking the C2B domain, rabphilin-deltaC2B, decreased the number of docked vesicle or fusing at the plasma membrane. These findings suggest that rabphilin is involved in the docking step of regulated exocytosis in PC12 cells, possibly through interaction between the C2B domain and SNAP-25. [J Physiol Sci. 2008;58 Suppl:S61]
