Molecular mechanism of response of living body to environmental stress

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Protein phosphatase 2C (PP2C) is implicated in the negative regulation of tress-activated protein kinase (SAPK) cascades in yeast and mammalian cells. In this study, we determined the role of PP2Cβ-1, a major isoform of mammalian PP2C, in the TAK1 signaling pathway, a SAPK cascade that is activated by interleukin-1 (IL-1), transforming growth factor-β or stress. Ectopic expression of PP2Cβ-1 inhibited the TAK1-mediated mitogen-activated protein kinase kinase 4 (MKK4)-c-Jun N-terminal kinase (JNK) and MKK6-p38 signaling pathways. In vitro, PP2Cβ-1 dephosphorylated and inactivated TAK1. Co-immunoprecipitation experiments indicated that PP2Cβ-1 associates with the central region of TAK1. A phosphatase-negative mutant of PP2Cβ-1, PP2Cβ-1(R/G), acted as a dominant negative mutant, inhibiting dephosphorylation of TAK1 by wild-type PP2Cβ-1 in vitro. In addition, ectopic expression of PP2Cβ-1(R/G) enhanced IL-1-induced activation of an AP-1 reporter gene. Collectively, these results indicate that PP2Cβ negatively regulates the TAK1 signaling pathway by direct dephosphorylation of TAK1.