The role of ubiquitin-conjugating enzyme Ube2j1 phosphorylation and its degradation by proteasome during endoplasmic stress recovery

The human Ube2j1 and Ube2j2 are the only ubiquitin-conjugating enzymes (E2s) that are localized to endoplasmic reticulum (ER) through its C-terminal transmembrane domains. Ube2j1 is a known substrate of MAPK signalling pathway and it is phosphorylated at serine-184 during ER stress. Here, we demonstrate that Ube2j1, not Ube2j2 is essential for the recovery of cells from transient ER stress. The ectopic expression of wild-type Ube2j1 and phospho-mimic mutant, Ube2j1^S184D but not phospho-mutant Ube2j1^S184A can recover cells from ER stress. We also found that ubiquitin-ligase (E3), c-IAP1 preferentially interacts with phosphorylated Ube2j1. Moreover, we noticed that phosphorylated Ube2j1 is rapidly degraded by the proteasome during ER stress cell recovery. Taken together, these data suggest that Ube2j1 and its phosphorylation is important for transient ER stress cell recovery and the phosphorylated Ube2j1 is degraded by the proteasome.