SNARE-associated proteins and receptor trafficking

A wide variety of receptors that function on the cell surface are regulated, at least in part, through intracellular membrane trafficking including endocytosis, recycling and subsequent degradation. Soluble N-ethylmaleimide sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) are essential molecules for the final step of intracellular membrane trafficking, i.e. fusion of transport vesicles with the target membrane. SNAREs on two opposing membranes form a trans -SNARE complex consisting of a four-helical bundle and drive a membrane fusion. The resultant cis -SNARE complex is disassembled through a process mediated by NSF and SNAPs. Cells contain families of SNAREs, and the interaction of cognate SNAREs at least contributes to the specificity of membrane fusion. The SNARE complex formation and dissociation are modulated by many SNARE-associated proteins at multiple steps including tethering, assembly and disassembly. Diverse molecular mechanisms, such as scaffolding, phosphorylation and ubiquitylation of SNARE proteins, and phosphoinositide production, are utilized for the modulation. In this review, we summarize recent progress in understanding the role of SNARE-associated proteins required for the endocytic recycling and degradation of epidermal growth factor receptor, transferrin receptor and integrins. We also discuss the physiological and pathological relevance of SNAREs and SNARE-associated proteins in the receptor trafficking.