Protein phosphatase 4 is involved in the cellular responses to DNA damage and is overexpressed in human tumors Free

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Reversible protein phosphorylation by kinases and phosphatases is the most common mechanism in controlling most, if not all, the cellular processes. Dephosphorylation on Serine/Threonine residues is regulated by two distinct groups of functionally diverse phosphatases, the phosphoprotein M (PPM) and phosphoprotein phosphatases (PPP). Protein phosphatase 4 (PP4)-containing complexes are involved in Cisplatin sensitivity. In this report, we showed that endogenous PP4C forms at least three mutually exclusive complexes. Down-regulation of PPP4C expression by siRNA leads to a defective DNA damage-induced G2/M checkpoint. Furthermore, overexpression of a PP4C subcomplex has been detected in human breast, lung, and ovary tumors. Our results indicate that PP4C-containing complexes are potential targets for cancer treatment.