A general role for TANGO1, encoded by MIA3, in secretory pathway organization and function

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), previously implicated in selective trafficking of procollagen. Using genome engineering of human cells, light microscopy, secretion assays, genomics, and proteomics we show that disruption of the longer form, 35 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 causes significant 40 changes in early secretory pathway gene and protein expression, and impairs secretion not only of large proteins, but of all types of secretory cargo including small soluble proteins. Our data support a general role for Mia3/TANGO1 in maintaining secretory pathway structure and function in vertebrate cells.