The conserved ER-transmembrane protein TMEM39 coordinates with COPII to promote collagen secretion and prevent ER stress

Dysregulation of collagen production and secretion contributes to aging and tissue fibrosis of major organs. How premature collagen proteins in the endoplasmic reticulum (ER) route as specialized cargos for secretion remains to be fully elucidated. Here, we report that TMEM39, an ER-localized transmembrane protein, regulates production and secretory cargo trafficking of procollagen. We identify the C. elegans ortholog TMEM-39 from an unbiased RNAi screen and show that deficiency of tmem-39 leads to striking defects in cuticle collagen production and constitutively high ER stress response. RNAi knockdown of the tmem-39 ortholog in Drosophila causes similar defects in collagen secretion from fat body cells. The cytosolic domain of human TMEM39A binds to Sec23A, a vesicle coat protein that drives collagen secretion and vesicular trafficking. TMEM-39 regulation of collagen secretion is independent of ER stress response and autophagy. We propose that roles of TMEM-39 in collagen secretion and preventing ER stress are likely evolutionarily conserved. ### Competing Interest Statement The authors have declared no competing interest.