title: Activation of p42 mitogen-activated protein kinase (MAPK), but not c-Jun NH(2)-terminal kinase, induces phosphorylation and stabilization of MAPK phosphatase XCL100 in Xenopus oocytes.
abstract: Dual-specificity protein phosphatases are implicated in the direct down-regulation of mitogen-activated protein kinase (MAPK) activity in vivo. Accumulating evidence suggests that these phosphatases are components of negative feedback loops that restore MAPK activity to low levels after diverse physiological responses. Limited information exists, however, regarding their posttranscriptional regulation. We cloned two Xenopus homologs of the mammalian dual-specificity MAPK phosphatases MKP-1/CL100 and found that overexpression of XCL100 in G2-arrested oocytes delayed or prevented progesterone-induced meiotic maturation. Epitope-tagged XCL100 was phosphorylated on serine during G2 phase, and on serine and threonine in a p42 MAPK-dependent manner during M phase. Threonine phosphorylation mapped to a single residue, threonine 168. Phosphorylation of XCL100 had no measurable effect on its ability to dephosphorylate p42 MAPK. Similarly, mutation of threonine 168 to either valine or glutamate did not significantly alter the binding affinity of a catalytically inactive XCL100 protein for active p42 MAPK in vivo. XCL100 was a labile protein in G2-arrested and progesterone-stimulated oocytes; surprisingly, its degradation rate was increased more than twofold after exposure to hyperosmolar sorbitol. In sorbitol-treated oocytes expressing a conditionally active DeltaRaf-DD:ER chimera, activation of the p42 MAPK cascade led to phosphorylation of XCL100 and a pronounced decrease in the rate of its degradation. Our results provide mechanistic insight into the regulation of a dual-specificity MAPK phosphatase during meiotic maturation and the adaptation to cellular stress.
authors.affiliation: Department of Molecular Pharmacology and Program in Cancer Biology, Stanford University School of Medicine, Stanford, California 94305-5174, USA. sohaskey@socrates.berkeley.edu
authors.forename: Michael L
authors.initials: ML
authors.lastname: Sohaskey
authors.forename: James E
authors.initials: JE
authors.lastname: Ferrell
mesh_terms: D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D004789:Enzyme Activation; D004795:Enzyme Stability; D005260:Female; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D007202:Indicators and Reagents / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D054639:Mitogen-Activated Protein Kinase Phosphatases; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation; D011374:Progesterone / Q000502:physiology; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000378:metabolism* / Q000502:physiology
chemical_list: D018076:DNA, Complementary; D017874:Immediate-Early Proteins; D007202:Indicators and Reagents; D029867:Xenopus Proteins; D011374:Progesterone; D013012:Sorbitol; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases; C096688:DUSP1 protein, Xenopus; D054639:Mitogen-Activated Protein Kinase Phosphatases; D017027:Protein Tyrosine Phosphatases