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and J.A.B. membrane lipid composition coordinately regulate SNARE-mediated fusion in intact cells remains elusive (Bethani et al., 2007). Trafficking of SNARE molecules to the correct membranes, as well as shielding of their SNARE motifs from non-physiological SNARE interactions during their transport, are key determinants in sustaining the high level of pairing specificity that R-SNAREs exert towards their cognate Q-SNARE partners (Fasshauer et al., 1998). Maintaining the subcellular localization of SNAREs against a circulation of fusion events requires retrieval of R-SNAREs from target membranes and their recycling to correct vesicular donor membranes for successive rounds of fusion. Sorting of SNAREs has been demonstrated to occur independently of cargo sorting, through non-competitive binding to clathrin adaptors (Miller et al., 2011). In addition, proper SNARE pairing might be facilitated by lateral segregation of R-SNAREs to unique membrane subdomains within an individual donor compartment. This is especially important at the sorting endosome, where cargoes directed towards recycling, retrograde or degradative pathways segregate to unique subdomains of the common compartment (Hsu et al., 2012; Maxfield and McGraw, 2004). VAMP7 and VAMP3 are among important R-SNAREs that co-reside at this compartment, and whereas VAMP7 directly binds adaptor protein complex 3 (AP-3) and regulates fusion with late endosomes, VAMP3 preferentially segregates into tubular membranes, where it facilitates fusion with the ERD-308 endocytic recycling compartment (ERC) and Golgi (McMahon et al., 1993). VAMP3 is usually a tetanus neurotoxin (TeNT)-sensitive SNARE (Galli et al., 1994; McMahon et al., 1993) that regulates recycling of integrins, transferrin and the transferrin receptor (TfR) to the plasma membrane (Galli et Rabbit polyclonal to IL11RA al., 1994; McMahon et al., 1993), as well as -granule transport in platelets (Feng et al., 2002; Polgr et al., 2002) and retrograde transport of mannose-6 phosphate receptor (M6PR) to the Golgi (Ganley et al., 2008). PI4K2A is one of the phosphoinositide kinases present at the sorting endosome. As a ERD-308 member of the phosphatidylinositol (PtdIns) 4-kinase family, PI4K2A catalyzes synthesis of PtdIns4in the cell, along with its sister enzyme, PI4K2B, and two type III PI4K enzymes, PI4KA and PI4KB (Balla and Balla, 2006). Among these enzymes, PI4K2A exhibits the most diverse distribution, being present at the Golgi, the trans-Golgi network (TGN) and various endosomal compartments, including sorting, late and recycling endosomes (Craige et al., 2008; Wang et al., 2003). Even though tight membrane association of PI4K2A, mediated through its palmitoyl moieties, implies that this enzyme cycles between endosomes and Golgi (Barylko et al., 2001), it is not known whether and how PI4K2A cycles between these compartments. The importance of PI4K2A endosomal localization is usually underscored by its role in epidermal growth factor (EGF) receptor degradation (Minogue et al., 2006) and Wnt signaling (Pan et al., 2008). In addition, deletion of the enzyme causes ERD-308 late-onset neurodegeneration (Simons et al., 2009). As a component of the AP-3CBLOC-1 tripartite complex, PI4K2A colocalizes with VAMP7 on sorting endosomes and regulates sorting of lysosome-bound cargoes to late endosomes (Craige et al., 2008; Ryder et al., 2013; Salazar et al., 2009). PI4K2A depletion also results in aberrant localization of the late-endosomal Q-SNAREs Vti1b and syntaxin 8 (Craige et al., 2008). In addition, PI4K2A has been implicated in endocytic recycling, being present on endosomes traversed by endocytosed TfR and angiotensin AT1a receptor en route to the plasma membrane (Balla et al., 2002). Consequently, PI4K2A knockdown results in mislocalization of TfR (Balla et al., 2002; Craige et al., 2008). In this study, we describe a new conversation between PI4K2A and VAMP3 that is important in sorting and localization of both PI4K2A and VAMP3. We show that targeting of VAMP3 into correct vesicular membranes, where it can mediate fusion with target compartments, requires association with PI4K2A, as well as production of PtdIns4on endosomal membranes traversed by VAMP3. RESULTS An endosomal pool of PI4K2A interacts with VAMP3 PI4K2A localizes to the Golgi and to a diverse pool of endocytic structures, ranging from the early endosome antigen 1 (EEA1)-positive early endosomes to TfR-containing perinuclear recycling endosomes and late endosomes (Balla et al., 2002; Craige et al., 2008; Jovi? et al., 2012; Salazar et al., 2009; Wang et al., 2003). So far, the best-characterized function of the endosomal pool of PI4K2A is usually along the lysosomal trafficking route, where it coordinates sorting of lysosomal-associated membrane protein 1.