hMutSα is Protected from Ubiquitin-proteasome-dependent Degradation by Atypical Protein Kinase Cζ Phosphorylation Original Research Article

The hMutSα (hMSH2-hMSH6) protein heterodimer plays a critical role in the detection of DNA mispairs in the mismatch repair (MMR) process. We recently reported that hMutSα proteins were degraded by the ubiquitin-proteasome pathway in a cell-type-dependent manner, indicating that one or several regulator(s) may interfere with hMutSα protein ubiquitination and degradation. On the other hand, we and others have shown that protein kinase C (PKC) is involved as a positive regulator of MMR activity. Here, we provide evidence that the atypical PKCζ regulates ubiquitination, degradation, and levels of hMutSα proteins. Using both PKCζ -transfected U937 and PKCζ siRNA-transfected MRC-5 cell lines, we found that PKCζ protein expression was correlated with that of hMutSα as well as with MMR activity, but was inversely correlated with hMutSα protein ubiquitination and degradation. Interestingly, PKCζ interacts with hMSH2 and hMSH6 proteins and phosphorylates both. Moreover, in an in vitro assay PKCζ mediates phosphorylation events decreasing hMutSα protein degradation via the ubiquitin-proteasome pathway. Altogether, our results indicate that PKCζ modulates hMutSα stability and protein levels, and suggest a role for PKCζ in genome stability by regulating MMR activity.