VPS26A retromer complex and SNX27 mediate stress-induced Golgi bypass of membrane proteins

Abstract

Many proteins can reach the cell surface through a Golgi-independent unconventional protein secretion (UPS) pathway, particularly under cellular stress conditions. However, the molecular mechanisms that mediate UPS remain largely elusive. In this study, VPS26A-containing retromer complex, along with the sorting nexin SNX27, is identified as a regulator of UPS of transmembrane proteins, including the trafficking-deficient triangle F508 mutant CFTR, which causes cystic fibrosis, and the SARS-CoV-2 spike protein, associated with COVID-19. A targeted CRISPR knockout screen identified VPS26A as a key contributor in the UPS of triangle F508-CFTR. Subsequent molecular analyses revealed that SNX27 recruits triangle F508-CFTR to the VPS26A-VPS35-VPS29 retromer complex, facilitating its transport to the cell surface under UPS-inducing conditions. Additionally, VPS26A and SNX27 are necessary for UPS of the spike protein, enabling the formation of intact SARS-CoV-2 virions. These findings suggest that the retromer complex and SNX27, known for their roles in recycling endosomes, mediate previously unrecognized functions in the UPS of transmembrane proteins.