Hsp90 is required for c-Mos activation and biphasic MAP kinase activation in Xenopus oocytes

doi:10.1093/emboj/19.7.1516

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Hsp90 is required for c-Mos activation and biphasic MAP kinase activation in Xenopus oocytes

D.L. Fisher, E. Mandart and M. Dorée

CNRS-CRBM, 1919 Route de Mende, 34293 Montpellier, Cedex 05, France
¹   Present address: IGH, CNRS-UPR 1142, 141 rue de la Candonille, 34396 Montpellier, Cedex 05, France
²   Corresponding author
   e-mail doree{at}crbm.cnrs-mop.fr

During Xenopus oocyte maturation, the Mos protein kinase is synthesized and activates the MAP kinase cascade. In this report,we demonstrate that the synthesis and activation of Mos are twoseparable processes. We find that Hsp90 function is required foractivation and phosphorylation of Mos and full activation of theMAP kinase cascade. Once Mos is activated, Hsp90 function is nolonger required. We show that Mos interacts with both Hsp90 andHsp70, and that there is an inverse relationship between associationof Mos with these two chaperones. We propose that Mos proteinkinase is activated by a novel mechanism involving sequentialassociation with Hsp70 and Hsp90 as well as phosphorylation. Wealso present evidence for a two-phase activation of MAP kinasein Xenopus oocytes.