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

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.

Requirement of Hsp90 activity for IκB kinase (IKK) biosynthesis and for constitutive and inducible IKK and NF-κB activation

“…This was further supported by a pulse-chase analysis, which revealed that strongly reduced amounts of IKKa and IKKb were synthesized in the presence of GA during the labeling reaction. Under the conditions chosen, GA does not generally inhibit protein synthesis, as shown here for p65 and for other substrates in previous studies (Bijlmakers and Marsh, 2000;Fisher et al, 2000). In contrast to the pronounced effect during synthesis, GA did not grossly affect the half-life of preformed IKKa and IKKb, which was in the range of several hours (Figure 7 and data not shown).…”

Kicked by Mos and tuned by MPF—the initiation of the MAPK cascade inXenopusoocytes

“…Nevertheless, the cells exhibit individual concentration variation (as we will also see below). These data are consistent with previous works reporting Mos detection in MAPK inhibiting conditions such as HSP-90-inhibitor geldanamycin incubation (Fisher et al, 2000) or U0126 treatment of oocytes stimulated by insulin through a Rasdependent pathway (Baert et al, 2003). Considering that no significant differences in Mos levels appear in presence or in absence of MAPK activity, MAPK obviously does not contribute as a major component in the initiation of the cascade.…”

Cloning of cytoplasmic heat shock protein 90 (FcHSP90) from Fenneropenaeus chinensis and its expression response to heat shock and hypoxia

“…The highest expression was detected in ovary of shrimp. Previous reports demonstrated that HSP90 was essential to phosphorylation of Mos, a proto-oncogene protein, and to activation of the mitogen-activated protein kinase pathway that is responsible for oocyte maturation in Xenopus (Ali et al 1998;Fisher et al 2000). Therefore, we speculate that the extraordinary expression detected in ovary suggests that FcHSP90 might mediate a similar cascade regulating ovary maturation in F. chinensis.…”