Ribosomal S6 kinase p90rsk and mRNA cap‐binding protein eIF4E phosphorylations correlate with MAP kinase activation during meiotic reinitiation of mouse oocytes

Abstract

During meiotic reinitiation of the mouse oocyte, entry into M-phase is regulated by changes of protein phosphorylation and by the stimulation of selective mRNA translation following the nuclear membrane dissolution. Our results reveal that M-phase kinases (MAP kinase and histone H1 kinase) are being activated together with S6 kinase and with the phosphorylation of eIF4E, the cap-binding subunit of the initiation factor eIF-4F. In order to test which signaling pathway(s) is(are) involved, okadaic acid and cycloheximide have been used as tools for differentially modulating MAP and histone H1 kinase activities. A role for MAP kinases in the phosphorylation of eIF4E and the activation of S6 kinase is suggested. The possible implication of p90rsk and/or of p70s6k in the overall increase in S6 kinase activity has been examined. p70s6k does not appear to be involved since phosphorylated forms are found in prophase and maturing oocytes. In contrast, p90rsk is phosphorylated and activated in maturing oocytes. p90rSk phosphorylation correlates with the activation of S6 kinase. These results suggest that the overall increase of S6 kinase activity is mostly due to p90rsk activation. The roles of eIF4E phosphorylation and S6 kinase activation in the physiological induction of M-phase and in the okadaic acid-induced premature mitotic events are discussed.

Activation of ribosomal S6 kinase (RSK) during porcine oocyte maturation

“…This indicates that activation of RSK occurred before GVBD in porcine oocytes, as has been reported in Xenopus oocytes (Erikson & Maller, 1989). In mouse oocytes, however, activation and phosphorylation of RSK were observed after GVBD (Gavin & Schorderet-Slatkine, 1997). The reason why the timing of RSK activation differs between mouse and porcine oocytes is not clear.…”

“…Biochemical and molecular cloning studies have indicated that RSK is the protein kinase responsible for S6 phosphorylation during meiotic maturation of Xenopus oocytes (Erikson & Maller, 1985, 1986. Furthermore, p70 S6K was inactive throughout the maturation period of Xenopus and mouse oocytes (Gavin & Schorderet-Slatkine, 1997;Schwab et al, 1999). These indicate that the present S6 protein kinase activity should be the activity of RSK.…”

“…The reason why the timing of RSK activation differs between mouse and porcine oocytes is not clear. RSK is one of the substrates of MAP kinase, and the increase in RSK phosphorylation in parallel with MAP kinase activation has been reported during Xenopus and mouse oocyte maturation (Gross et al, 2000;Gavin & Schorderet-Slatkine, 1997). The present results with the specific MAP kinase kinase inhibitor, U0126, suggested that this is the case also in porcine oocyte maturation.…”

Phosphorylation pattern of the p90rskand mitogen-activated protein kinase (MAPK) molecule: comparison ofin vitroandin vivomatured porcine oocytes

“…Sugiura et al . (2002) discuss that biochemical and molecular studies indicated that RSK is the protein kinase responsible for S6 phosphorylation during meiotic maturation of Xenopus oocytes (Erikson & Maller, 1985, 1986, 1989) and, furthermore, that p70S6K was inactive throughout the maturation period of Xenopus and mouse oocytes (Gavin & Schorderet-Slatkine, 1997; Schwab et al ., 1999). Therefore the present and measured S6 kinase activity should be the activity of RSK.…”

Phosphorylation of p90rsk during meiotic maturation and parthenogenetic activation of rat oocytes: correlation with MAP kinases

“…Our experiment showed that the full phosphorylation of p90 rsk and activation of MAP kinase were inhibited by CHX, a protein synthesis inhibitor, after 6 h of culture. CHX may inhibit protein synthesis that is required for the activation of ERK1+2, while it has no influence on GVBD and less influence on the activation of MPF in mouse oocytes (Gavin & Schorderet-Slatkine, 1997). OA, an inhibitor of phosphatase 1 and 2A, was able to induce the activation of both ERK1+2 and p90 rsk in the presence of IBMX or accelerate the activation of the two kinases in IBMXfree medium, while p34cdc2/cyclin B kinase was not significantly influenced by the treatment (Gavin et al, 1994;Oh et al, 1998).…”