Mos stimulates MAP kinase in Xenopus oocytes and activates a MAP kinase kinase in vitro

Mol Cell Biol. 1993 Apr;13(4):2546-53. doi: 10.1128/mcb.13.4.2546-2553.1993.

Abstract

Several protein kinases, including Mos, maturation-promoting factor (MPF), mitogen-activated protein (MAP) kinase, and MAP kinase kinase (MAPKK), are activated when Xenopus oocytes enter meiosis. De novo synthesis of the Mos protein is required for progesterone-induced meiotic maturation. Recently, bacterially synthesized maltose-binding protein (MBP)-Mos fusion protein was shown to be sufficient to initiate meiosis I and MPF activation in fully grown oocytes in the absence of protein synthesis. Here we show that MAP kinase is rapidly phosphorylated and activated following injection of wild-type, but not kinase-inactive mutant, MBP-Mos into fully grown oocytes. MAP kinase activation by MBP-Mos occurs within 20 min, much more rapidly than in progesterone-treated oocytes. The MBP-Mos fusion protein also activates MPF, but MPF activation does not occur until approximately 2 h after injection. Extracts from oocytes injected with wild-type but not kinase-inactive MBP-Mos contain an activity that can phosphorylate MAP kinase, suggesting that Mos directly or indirectly activates a MAPKK. Furthermore, activated MBP-Mos fusion protein is able to phosphorylate and activate a purified, phosphatase-treated, rabbit muscle MAPKK in vitro. Thus, in oocytes, Mos is an upstream activator of MAP kinase which may function through direct phosphorylation of MAPKK.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Enzyme Activation
  • Microinjections
  • Mitosis
  • Oocytes / enzymology
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Kinases / metabolism*
  • Proto-Oncogene Proteins c-mos / metabolism*
  • Xenopus laevis / embryology*

Substances

  • Phosphoproteins
  • Protein Kinases
  • Proto-Oncogene Proteins c-mos
  • Calcium-Calmodulin-Dependent Protein Kinases