TBC1D16 is a Rab4A GTPase activating protein that regulates receptor recycling and EGF receptor signaling

Abstract

Rab4A is a master regulator of receptor recycling from endocytic compartments to the plasmamembrane. The protein TBC1D16 is upregulated in melanoma, and TBC1D16-overexpressing melanoma cells are dependent on TBC1D16. We show here that TBC1D16 enhances the intrinsic rate of GTP hydrolysis by Rab4A. TBC1D16 is both cytosolic and membrane associated; the membrane-associated pool colocalizes with transferrin and EGF receptors (EGFRs) and early endosome antigen 1, but not with LAMP1 protein. Expression of two TBC1D16 isoforms, but not the inactive R494A mutant, reduces transferrin receptor recycling but has no effect on transferrin receptor internalization. Expression of TBC1D16 alters GFPRab4A membrane localization. In HeLa cells, overexpression of TBC1D16 enhances EGF-stimulated EGFR degradation, concomitant with decreasedEGFRlevels andsignaling. Thus,TBC1D16is a GTPase activating protein for Rab4A that regulates transferrin receptor recycling and EGFR trafficking and signaling.