VARP Is Recruited on to Endosomes by Direct Interaction with Retromer, Where Together They Function in Export to the Cell Surface

Abstract

SummaryVARP is a Rab32/38 effector that also binds to the endosomal/lysosomal R-SNARE VAMP7. VARP binding regulates VAMP7 participation in SNARE complex formation and can therefore influence VAMP7-mediated membrane fusion events. Mutant versions of VARP that cannot bind Rab32:GTP, designed on the basis of the VARP ankyrin repeat/Rab32:GTP complex structure described here, unexpectedly retain endosomal localization, showing that VARP recruitment is not dependent on Rab32 binding. We show that recruitment of VARP to the endosomal membrane is mediated by its direct interaction with VPS29, a subunit of the retromer complex, which is involved in trafficking from endosomes to the TGN and the cell surface. Transport of GLUT1 from endosomes to the cell surface requires VARP, VPS29, and VAMP7 and depends on the direct interaction between VPS29 and VARP. Finally, we propose that endocytic cycling of VAMP7 depends on its interaction with VARP and, consequently, also on retromer.

Role of tetanus neurotoxin insensitive vesicle-associated membrane protein in membrane domains transport and homeostasis

“…In addition, Varp interacts with Vps29, a subunit of the retromer, and both are involved in the transport of the glucose transporter GLUT1 to the PM whereas VAMP7 is involved in exocytosis of both GLUT1 and GLUT4. 19,40 GLUT1 and GLUT4 are known to function in membrane domains. 41,42 In addition, phospholipase D1 (PLD1) is transported in VAMP7 vesicles, controls its fusion capacity 43 and is an effector of Arf1 44,45 so that the absence of VAMP7 could alter Golgi lipidic content and confer BFA-resistance via an accumulation or altered activity of PLD1 at the TGN.…”

“…18 In addition, VAMP7 is involved in the transport of GLUT1 and Lat, two other membrane domain associated proteins. 19,20 Altogether, these findings led us to hypothesize a more direct contribution of VAMP7 in membrane organization and membrane domains homeostasis.…”

Structure-Function Analyses of the Small GTPase Rab35 and Its Effector Protein Centaurin-β2/ACAP2 during Neurite Outgrowth of PC12 Cells

“…Rab7-binding site) (40) and the ANKR domain of VPS9-ankyrin repeat protein (Varp) (i.e. Rab32/38-binding site) (32,41) with the centaurin-␤2 ANKR domain. Because of their low sequence conservation, however, we were unable to identify shared key residues that are responsible for Rab binding by these three ANKR domains.…”

Multiple Types of Guanine Nucleotide Exchange Factors (GEFs) for Rab Small GTPases

“…Varp is also involved in melanogenic enzyme transport to melanosomes, which are known as lysosome-related organelles, through interaction with Rab32 and Rab38 via the ANKR1 domain (Tamura et al, 2009(Tamura et al, , 2011 and with Rab40C via the ANKR2 domain (Yatsu et al, 2015). Moreover, Varp interacts with two subunits of the retromer complex (VPS29 and VPS35) and is involved in the endosome-to-plasma-membrane recycling of certain transmembrane proteins (Hesketh et al, 2014;McGough et al, 2014). Thus, rather than simply being a Rab21-GEF, Varp plays multiple roles in endosomal trafficking through interaction with other membrane trafficking regulators (Fukuda, 2016).…”

“…Rab22B/31 (Kajiho et al, 2011) 4 ALS2 ANKRD27 (84079) Varp Rab21 (Zhang et al, 2006) 2,3 (Tamura et al, 2011) 3 Rab32 (Tamura et al, 2009) Rab38 (Wang et al, 2008) VAMP7 (Burgo et al, 2009) VPS29 (Hesketh et al, 2014) VPS35 (McGough et al, 2014) Rab40 (Yatsu et al, 2015) RACK1 (Marubashi et al, 2016b) VPS9D1 ( Rab8 (Hattula et al, 2002) 1,2,3…”