Hanada M, Kobayashi T, Ohnishi M, Ikeda S, Wang H, Katsura K, Yanagawa Y, Hiraga A, Kanamaru R, Tamura S
Department of Biochemistry, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
FEBS Lett. 1998 Oct 23;437(3):172-6. doi: 10.1016/s0014-5793(98)01229-0.
Protein phosphatase 2Calpha (PP2Calpha) or PP2Cbeta-1 expressed in COS7 cells suppressed anisomycin- and NaCl-enhanced phosphorylations of p38 co-expressed in the cells. PP2Calpha or PP2Cbeta-1 expression also suppressed both basal and stress-enhanced phosphorylations of MKK3b and MKK6b, which are upstream protein kinases of p38, and of MKK4, which is one of the major upstream protein kinases of JNK. Basal activity of MKK7, another upstream protein kinase of JNK, was also suppressed by PP2Calpha or PP2Cbeta-1 expression. However, basal as well as serum-activated phosphorylation of MKK1alpha, an upstream protein kinase of ERKs, was not affected by PP2Cbeta or PP2Cbeta-1. A catalytically inactive mutant of PP2Cbeta-1 further enhanced the NaCl-stimulated phosphorylations of MMK3b, MKK4 and MKK6b, suggesting that this mutant PP2Cbeta-1 works as a dominant negative form. These results suggest that PP2C selectively inhibits the SAPK pathways through suppression of MKK3b, MKK4, MKK6b and MKK7 activities in mammalian cells.
在COS7细胞中表达的蛋白磷酸酶2Cα（PP2Cα）或PP2Cβ-1可抑制细胞中共同表达的p38因茴香霉素和NaCl增强的磷酸化。PP2Cα或PP2Cβ-1的表达还可抑制MKK3b和MKK6b（p38的上游蛋白激酶）以及MKK4（JNK的主要上游蛋白激酶之一）的基础磷酸化和应激增强的磷酸化。JNK的另一个上游蛋白激酶MKK7的基础活性也受到PP2Cα或PP2Cβ-1表达的抑制。然而，细胞外调节蛋白激酶（ERK）的上游蛋白激酶MKK1α的基础磷酸化以及血清激活的磷酸化不受PP2Cβ或PP2Cβ-1的影响。PP2Cβ-1的催化失活突变体进一步增强了NaCl刺激的MKK3b、MKK4和MKK6b的磷酸化，表明该突变体PP2Cβ-1作为一种显性负性形式起作用。这些结果表明，PP2C通过抑制哺乳动物细胞中MKK3b、MKK4、MKK6b和MKK7的活性来选择性抑制应激激活蛋白激酶（SAPK）途径。
