Interactions between Rab and Arf GTPases regulate endosomal phosphatidylinositol-4,5-bisphosphate during endocytic recycling

Abstract

A fter endocytosis, a selective endocytic recycling process returns many endocytosed molecules back to the plasma membrane. The RAB-10/Rab10 GTPase is known to be a key recycling regulator for specific cargo molecules. New evidence, focused on C. elegans RAB-10 in polarized epithelia, points to a key role of RAB-10 in the regulation of endosomal phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) levels. In turn, PI(4,5)P2 levels strongly influence the recruitment of many peripheral membrane proteins, including those important for vesicle budding through their membrane bending activities. Part of the effect of RAB-10 on endosomal PI(4,5)P2 is through its newly identified effector CNT-1, a predicted GTPase activating protein (GAP) of the small GTPase ARF-6/ Arf6. In mammals PI(4,5)P2 generating enzymes are known Arf6 effectors. In C. elegans we found that RAB-10, CNT-1 and ARF-6 are present on the same endosomes, that RAB-10 recruits CNT-1 to endosomes, and that loss of CNT-1 or RAB-10 leads to overaccumulation of endosomal PI(4,5)P2, presumably via hyperactivation of endosomal ARF-6. In turn this leads to over-recruitment of PI(4,5)P2-dependent membrane-bending proteins RME-1/Ehd and SDPN-1/ Syndapin/PACSIN. Conversely, in arf-6 mutants, endosomal PI(4,5)P2 levels were reduced and endosomal recruitment of RME-1 and SDPN-1 failed. This work makes an unexpected link between distinct classes of small GTPases that control endocytic recycling, and provides insight into how this interaction affects

The Rab7 effector PLEKHM1 binds Arl8b to promote cargo traffic to lysosomes

“…activities. Previous studies suggest that dual or shared effectors represent a point of convergence of Rab, Arf, and Arl signals in membrane traffic (Burguete et al, 2008;Shi and Grant, 2013). In line with this, we noted that recently characterized Rab7 effector, PLE KHM1, shares ∼40% similarity over the length of its RUN domain with the known Arl8b effector SKIP.…”

LET-413/Erbin acts as a RAB-5 effector to promote RAB-10 activation during endocytic recycling

“…S1, L and M). CNT-1 acts as an ARF-6 GAP, modulating ARF-6 activity and maintaining levels of the lipid PI(4,5)P2 on these endosomes ( Shi et al, 2012 ; Shi and Grant, 2013 ). Consistent with a loss of RAB-10 activation, we found that CNT-1-GFP labeling became diffusive in let-413(ycx23) or let-413(RNAi) animals, with a distinct loss of CNT-1 from punctate endosomes ( Fig.…”

mTOR Regulates Endocytosis and Nutrient Transport in Proximal Tubular Cells

“…32 RAB10 has been localized to many organelles, such as endoplasmic reticulum (ER), Golgi, early endosomes, and recycling endosomes, and mediates membrane trafficking within the cell partly by regulating endosomal phosphatidylinositol-4,5-bisphosphate levels. 33,34 Together, these data reveal a novel theme of mTOR function by regulating a series of proteins being specifically involved in endocytosis and vesicle transport.…”