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Sun, L., Yu, M.C., Kong, L., Zhuang, Z.H., Hu, J.H., Ge, B.X. (2008). Molecular identification and functional characterization of a Drosophila dual-specificity phosphatase DMKP-4 which is involved in PGN-induced activation of the JNK pathway.  Cell. Signal. 20(7): 1329--1337.
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MAP (Mitogen-activated protein) kinases play an important role in regulating many critical cellular processes. The inactivation of MAP kinases is always accomplished by a family of dual-specificity phosphatases, termed MAPK phosphatases (MKPs). Here, we have identified a novel MKP-like protein, designated DMKP-4, from the Drosophila genome. DMKP-4 is a protein of 387 amino acids, with a dual-specificity phosphatase (DSP) catalytic domain. Recombinant protein DMKP-4 retains intrinsic phosphatase activity against chromogenic substrate pNPP. Overexpression of DMKP-4 inhibited the activation of ERK, JNK and p38 by H(2)O(2), sorbitol and heat shock in HEK293-T cells, and JNK activation in Drosophila S2 cells under PGN stimuli. "Knockdown" of DMKP-4 expression by RNAi significantly enhanced the PGN-stimulated activation of JNK, but not ERK nor p38. Further study revealed that DMKP-4 interacted specifically with JNK via its DSP domain. Mutation of Cys-126 to serine in the DSP domain of DMKP-4 not only eliminated its interaction with JNK, but also markedly reduced its phosphatase activity. Thus, DMKP-4 is a Drosophila homologue of mammalian MKPs, and may play important roles in the regulation of various developmental processes.

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    Cell. Signal.
    Cellular Signalling
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