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Hsp90 is required for c-Mos activation and biphasic MAP kinase activation in Xenopus oocytes
D L Fisher1, E Mandart, M Dorée
1CNRS-CRBM, 1919 Route de Mende, 34293 Montpellier, Cedex 05, France.
Abstract:
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 two separable processes. We find that Hsp90 function is required for activation and phosphorylation of Mos and full activation of the MAP kinase cascade. Once Mos is activated, Hsp90 function is no longer required. We show that Mos interacts with both Hsp90 and Hsp70, and that there is an inverse relationship between association of Mos with these two chaperones. We propose that Mos protein kinase is activated by a novel mechanism involving sequential association with Hsp70 and Hsp90 as well as phosphorylation. We also present evidence for a two-phase activation of MAP kinase in Xenopus oocytes.
Insights
Heat shock protein 90 (Hsp90) is crucial for activating Mos protein kinase during Xenopus oocyte maturation. This activation is a distinct step from Mos synthesis, involving sequential chaperone interactions and phosphorylation.
Area of Science:
- Cellular biology
- Molecular biology
- Developmental biology
Background:
- Mos protein kinase is essential for initiating Xenopus oocyte maturation.
- Mos activates the mitogen-activated protein kinase (MAPK) cascade, a key signaling pathway.
Purpose of the Study:
- To investigate the distinct processes of Mos synthesis and activation.
- To elucidate the role of heat shock proteins (HSPs) in Mos activation and MAPK signaling.
Main Methods:
- Studying Mos protein synthesis and activation in Xenopus oocytes.
- Investigating the requirement of Hsp90 function for Mos activation and phosphorylation.
- Analyzing the interaction of Mos with Hsp90 and Hsp70 chaperones.
Main Results:
- Mos synthesis and activation are separable events.
- Hsp90 is required for Mos activation and phosphorylation, and subsequent MAPK cascade activation.
- Mos interacts with both Hsp70 and Hsp90, with an inverse relationship in their association.
- Evidence suggests a two-phase activation of MAPK in Xenopus oocytes.
Conclusions:
- Mos activation involves a novel mechanism requiring sequential association with Hsp70 and Hsp90, followed by phosphorylation.
- Hsp90's role in Mos activation is transient, no longer required once Mos is activated.