Rab35 GTPase: A Central Regulator of Phosphoinositides and F‐actin in Endocytic Recycling and Beyond

Abstract

Rab35 is one of the first discovered members of the large Rab GTPase family, yet it received little attention for 10 years being considered merely as a Rab1-like GTPase. In 2006, Rab35 was recognized as a unique Rab GTPase localized both at the plasma membrane and on endosomes, playing essential roles in endocytic recycling and cytokinesis. Since then, Rab35 has become one of the most studied Rabs involved in a growing number of cellular functions, including endosomal trafficking, exosome release, phagocytosis, cell migration, immunological synapse formation and neurite outgrowth. Recently, Rab35 has been acknowledged as an oncogenic GTPase with activating mutations being found in cancer patients. In this review, we provide a comprehensive summary of known Rab35-dependent cellular functions and detail the few Rab35 effectors characterized so far. We also review how the Rab35 GTP/GDP cycle is regulated, and emphasize a newly discovered mechanism that controls its tight activation on newborn endosomes. We propose that the involvement of Rab35 in such diverse and apparently unrelated cellular functions can be explained by the central role of this GTPase in regulating phosphoinositides and F-actin, both on endosomes and at the plasma membrane.

Rab35 protein regulates evoked exocytosis of endothelial Weibel–Palade bodies

“…35). Although mainly considered an endocytic Rab, some reports have also linked the protein and its GAPs TBC1D10A to -C to exocytotic processes, such as the secretion of exosomes and the tethering of intracellular vesicles containing apical determinants to the newly forming apical membrane domain in the early steps of epithelial cyst formation (19, 36).…”

“…In endocytosis, Rab35 is thought to function at two stages (for a review, see Ref. 35). First, through recruiting its effector OCRL, a phosphoinositide phosphatase, Rab35 reduces the level of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) at newly formed clathrin-coated vesicles and thereby facilitates the uncoating of these early endosomal vesicles (37).…”

“…Because Arf6 is a positive regulator of PI(4)P 5-kinase, its inactivation is important to maintain elevated PI(4)P levels at these endosomes, which in turn are required for recruitment and/or stabilization of downstream factors, such as the dynamin-like protein EHD1 (40, 41). Thus, Rab35 and Arf6 act antagonistically in endocytosis and endosomal recycling: Arf6–GTP at the plasma membrane elevates PI(4,5)P 2 levels via PI(4)P 5-kinase activation and inhibition of Rab35 through binding to its GAPs TBC1D10A to -C (42, 43); Rab35–GTP on endosomes, on the other hand, recruits ACAP2, and the resulting inactivation of Arf6 ensures low PI(4,5)P 2 levels at endosomes (35). This scenario appears to differ in the control of evoked WPB exocytosis.…”

“…A block of such uptake could possibly feed back onto the secretion machinery, resulting in the reduction of exocytotic fusion events. In such cases, Rab35 most likely operates independently of Arf6 because their antagonistic actions in endocytosis have been shown in several system (35). Future work will be required to reveal the exact mechanism underlying the function of Rab35 in WPB exocytosis, for example by visualizing a possible enrichment of Rab35 at WPB fusion sites by high-resolution live cell microscopy.…”

Emerging biological roles of Cl− intracellular channel proteins

“…In HeLa and MDA-MB-231carcinoma cells, cytosolic CLIC4 is homogeneously distributed and colocalizes with a subset of early endosome antigen 1 (EEA1)-and Rab35-positive endosomes (Argenzio et al, 2014). Rab35 is a central regulator of endocytic recycling and shuttles between the plasma membrane and endosomes (Allaire et al, 2013;Klinkert and Echard, 2016;Kouranti et al, 2006). Consistently, knockdown of CLIC4 in HeLa and MDA-MB-231 cells results in impaired endocytosis of α5β1 integrin and a reduction of integrin recycling upon stimulation with serum or LPA (Argenzio et al, 2014).…”