Mitotic ER exit site dissociation and reassembly is regulated by TANGO1 phosphorylation status

Golgi fragmentation and ER exit site dissociation are considered as the leading causes of mitotic block of secretion from the ER. Although the mechanisms of Golgi fragmentation have been extensively characterized, ER exit block early in mitosis is not well-understood. We previously found that TANGO1 organizes ER exit sites by directly interacting with Sec16. Here, we showed that TANGO1 is phosphorylated by casein kinase 1 (CK1) during mitosis. Interestingly, the interaction with Sec16 was abrogated by phosphorylation of TANGO1, leading to dissociation of the ER exit sites. Moreover, a TANGO1 mutant deficient in phosphorylation inhibited the mitotic dissociation of ER exit sites. In contrast, a TANGO1 mutant mimicking CK1-mediated phosphorylation dissociated ER exit sites in interphase cells. Although CK1 activity remains constant throughout the cell cycle, PP1, a phosphatase for which activity decreases during mitosis, participates in the regulation of TANGO1 phosphorylation. This is the first report demonstrating the mechanisms of ER exit site dissociation during mitosis.