Phosphorylation of Ube2J1 at serine S184 is regulated by protein phosphatase 2A.

The Ube2J1 enzyme that mediates the ubiquitination and proteasomal degradation of misfolded proteins at the ER is phosphorylated at serine S184. Following anisomycin treatment of HEK293T cells, we observed an inverse relationship between phosphorylation and dephosphorylation at this site. This suggested a dynamic interchange between the two forms, and we show that S184 is a target for protein phosphatase 2A. The S184-phosphorylated protein is known to exhibit increased sensitivity to proteasomal degradation, and we found that mutation at K186R increased the ratio of S184-phosphorylated to S184-dephosphorylated protein. Although the K186R mutant retained some sensitivity to proteasomal inhibition, our results show that Ube2J1 steady state expression can be exercised at multiple levels, and can involve dynamic phosphorylation and dephosphorylation at S184.