SURO-2/TMEM39 Facilitates Collagen Secretion through the Formation of Large COPII Vesicles

Fibrosis of various tissues is a typical disease caused by excessive production and secretion of extracellular matrix. We used Caenorhabditis elegans to investigate the formation of large transport vesicles to understand collagen secretion, a critical factor in fibrosis formation. The suro-2 mutant displays obvious defects in collagen secretion and cuticle structure including a rupture phenotype in early adults. Transmission electron microscopy exhibited that the cuticle thickness of the suro-2 mutant was severely reduced. SURO-2/TMEM39 has 8 transmembrane domains and localizes in the endoplasmic reticulum (ER) membrane. SURO-2 interacts directly with NPP-20/Sec13, a component of the coat protein II (COPII) complex responsible for ER-to-Golgi transport. SURO-2 and NPP-20 localized at the same large puncta, a large COPII vesicle enough to accommodate collagens. We report here that SURO-2/TMEM39 is highly conserved among animal species and is a specialized regulator of bulky collagen secretion rather than general transport in C. elegans.