Phosphorylation of protein phosphatase 2Cζ by c-Jun NH2-terminal kinase at Ser92 attenuates its phosphatase activity

The protein phosphatase 2C (PP2C) family represents one of the four major protein Ser/Thr phosphatase activities in mammalian cells and contains at least 13 distinct gene products. Although PP2C family members regulate a variety of cellular functions, mechanisms of regulation of their activities are largely unknown. Here, we show that PP2C zeta, a PP2C family member that is enriched in testicular germ cells, is phosphorylated by c-Jun NH2-terminal kinase (JNK) but not by p38 in vitro. Mass spectrometry and mutational analyses demonstrated that phosphorylation occurs at Ser(92), Thr(202), and Thr(205) of PP2C zeta. Phosphorylation of these Ser and Thr residues of PP2C zeta ectopically expressed in 293 cells was enhanced by osmotic stress and was attenuated by a JNK inhibitor but not by p38 or MEK inhibitors. Phosphorylation of PP2C zeta by TAK1-activated JNK repressed its phosphatase activity in cells, and alanine mutation at Ser(92) but not at Thr(202) or Thr(205) suppressed this inhibition. Taken together, these results suggest that specific phosphorylation of PP2C zeta at Ser(92) by stress-activated JNK attenuates its phosphatase activity in cells.