Regulation of stress-activated protein kinase signaling pathway by protein phosphatase 2C (PP2C)

(1)PP2C ε在哺乳动物细胞中的异位表达抑制了两种丝裂原活化蛋白激酶TAK1和ASK1的活性。PP2C ε通过与这些激酶结合并使其去磷酸化，使这些激酶在静止细胞中保持非活性状态。PP2C ε在静止细胞中与TAK1和ASK1相关，但分别用IL-1和H_2_O_2处理细胞时，这种相关性被短暂抑制，IL-1和H_2_O_2分别激活这些相应的激酶。在此基础上，我们推测PP2C ε通过一种共同的调控机制调控TAK1和ASK1通路。(2)PP2C δ（ILKAP）参与ASK1的正向调节与PP2C ε不同，PP2C δ（ILKAP）是TNF诱导的SAPK信号的正向调节者。PP2C δ（ILKAP）在293细胞中的瞬时表达增强了TNF诱导的JNK和p38的活化。PP2C δ（ILKAP）与ASK1相关，这种相关性在TNF治疗后增强。这些结果表明，PP2C δ（ILKAP）可以使ASK1的抑制性磷酸化位点去磷酸化。(3)JNK负性调节PP2C β PP2C β是PP2C家族成员，在睾丸生殖细胞中富集，在体内和体外均通过JNK而不是p38或ERK在Ser92和Thr202/205处磷酸化。我们发现，磷酸化的PP2C丝氨酸92，但不是在Thr202/205抑制其磷酸酶活性。

(1) PP2Cε precipitates in negative regulation of TAK1 and ASK1Ectopic expression of PP2Cε in mammalian cells represses the activity of TAK1 and ASK1, two mitogen-activated protein kinase kinase kinases. PP2Cε keeps these kinases in an inactive state in quiescent cells by associating with and dephosphorylating them. PP2Cε associated with TAK1 and ASK1 in quiescent cells, but the association was transiently suppressed in response to treatment of the cells with IL-1 and H_2_O_2, respectively, which activate these respective kinases. On the basis of these results we proposed that PP2Cε regulates TAK1 and ASK1 pathways by a common regulatory mechanism.(2) PP2Cδ (ILKAP) participates in positive regulation of ASK1In contrast to PP2Cε, PP2Cδ (ILKAP) acts as a positive regulator of TNF induced SAPK signaling. Transient expression of PP2Cδ (ILKAP) in 293 cells enhanced TNF induced activation of JNK and p38. PP2Cδ (ILKAP) associated with ASK1 and this association was enhanced in response to TNF treatment. These results suggested that PP2Cδ (ILKAP) may dephosphorylate inhibitory phosphorylation site(s) of ASK1.(3) JNK negatively regulates PP2CζPP2Cζ, a PP2C family member that is enriched in testicular germ cells, is phosphorylated at Ser92 and Thr202/205 by JNK but not by p38 or ERK both in vivo and in vitro. We show that phosphorylation of PP2Cζ at Ser92 but not at Thr202/205 repressed its phosphatase activity.