MIA3/TANGO1 enables efficient secretion by constraining COPII vesicle budding

Complex machinery is required to drive secretory cargo export from the endoplasmic reticulum, an essential process in eukaryotic cells. In vertebrates, the Mia3 gene encodes two major forms of Transport ANd Golgi Organization Protein 1 (TANGO1S and TANGO1L). Here, using genome engineering of human cells, light microscopy, secretion assays, genomics, and proteomics we show that disruption of the longer form, TANGO1L, results in relatively minor defects in secretory pathway organization and function including limited impacts on procollagen secretion. In contrast, loss of both long and short forms results in major defects in cell organization and secretion. These include a failure to maintain the localization of ERGIC53 and SURF4 to the ER-Golgi Intermediate Compartment and dramatic changes to the ultrastructure of the ER-Golgi interface. Disruption of TANGO1 expression also causes significant changes in early secretory pathway gene and protein expression. Disruption of both TANGO1L and TANGO1S expression impairs secretion not only of large proteins, including procollagens, but of all types of secretory cargo including small soluble proteins. Our data support a general role for Mia3/TANGO1 in maintaining both secretory pathway structure and function in vertebrate cells.