Activation of p42 Mitogen-activated Protein Kinase (MAPK), but not c-Jun NH₂-Terminal Kinase, Induces Phosphorylation and Stabilization of MAPK PhosphataseXCL100 inXenopusOocytes

Abstract

Dual-specificity protein phosphatases are implicated in the direct down-regulation of mitogenactivated 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 MAPKdependent 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 ⌬Raf-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. INTRODUCTIONMembers of the mitogen-activated protein kinase (MAPK) family play fundamental roles in the cellular response to diverse extracellular stimuli, including mitogens, cytokines, and environmental stresses (reviewed by Waskiewicz and Cooper, 1995;Ferrell, 1996;Lewis et al., 1998;Davis, 2000;Pearson et al., 2001). Activation of p42 MAPK and p44 MAPK in quiescent fibroblasts, for example, contributes to the induction of cyclin D expression and entry into the cell cycle (Pagès et al., 1993;Sun et al., 1994;Brondello et al., 1995;Cheng et al., 1998). Constitutive activation of MAPK cascades can cause cell transformation in fibroblasts (Cowley et al., 1994;Mansour et al., 1994) and, in a context-dependent and MAPK-specific manner, either promote or prevent apoptosis (Xia et al., 1995;Meier and Evan, 1998;Bonni et al., 1999). Thus, from a cellular perspective, precise regulation of MAPK activity can literally signify the difference between life and death.The meiotic maturation of Xenopus oocytes provides an elegant system for studying the biochemistry of p42 MAPK regulation. Activation of the p42 MAPK cascade is important at multiple points during maturation: for the initial activation of Cdc2 triggering the G2-M transition (Sagata et al., 1988;Kosako et al., 1994bKosako et al., , 1996Gotoh et al., 1995;Palmer et al., 1998); for Cdc2 reactivation and the suppressi...

Restraint of Proinflammatory Cytokine Biosynthesis by Mitogen-Activated Protein Kinase Phosphatase-1 in Lipopolysaccharide-Stimulated Macrophages

“…7), possibly via phosphorylation by ERK or other protein kinases. Recently, threonine 168 has been identified as a third phosphorylation site targeted by ERK (37). Whether threonine 168 plays a role in LPS-stimulated MKP-1 stabilization remains to be examined.…”

Activation of ERK Induces Phosphorylation of MAPK Phosphatase-7, a JNK Specific Phosphatase, at Ser-446

“…Xenopus CL100 (XCL100), a homologue of human MKP-1, is phosphorylated by ERK in a cell cycle-dependent manner. In the case of XCL100, serine residue(s) were phosphorylated during the G 2 phase, and serine and threonine residues were phosphorylated during M-phase (53). Although the biological consequence of MKP-7 phosphorylation is currently unknown, it is important that Ser-446 in the CTS is a phosphorylation site.…”

Heat Shock Protein 25 or Inducible Heat Shock Protein 70 Activates Heat Shock Factor 1

“…6A, serine-phosphorylated MKP1 expression was increased in HSP25 or HSP70i overexpressed cells, and interaction between HSP25 or HSP70i and MKP1 was also increased. Transient transfection of site-directed mutants of Mkp1 on cysteine 258 to serine (Mkp1-C258S), which abolished phosphatase activity of MKP1 (23), revealed that expressions of HSP25, HSP70i, and HSF1 were reduced by Mkp1-C258S transfection, and phosphorylations of both HSF1 and ERK1/2 by HSP25 or HSP70i were restored by this mutant (Fig. 6B), even though mutation of Mkp1 on cysteine 258 did not affect the binding activity with HSP25 or HSP70i (data not shown).…”