Progesterone and cAMP-dependent protein kinase regulate in vivo the level of phosphorylation of two proteins (Mr 20,000 and Mr 32,000) in Xenopus oocytes.
The [32P]phosphoproteins and [35S]thiophosphoproteins were analyzed by electrophoresis and autoradiography after microinjection of [gamma-32P]ATP or of [35S]ATP-gamma-S into living Xenopus oocytes. The level of 32P incorporation into a 20-kDA protein was decreased following progesterone treatment (between 1 and 2 hr). This 20-kDa protein was partially thiophosphorylated in vivo by [35S]ATP-gamma-S. Furthermore it was found that this phosphoprotein was partially purified by TCA (1%) extraction and heat treatment. Microinjection of the C-subunit of cAMP-dependent protein kinase (0.6 to 1.2 pmole) inhibited maturation and provoked an increase in the level of phosphorylation of the 20-kDa protein and of a 32-kDa protein, indicating that both proteins were in vivo substrates (directly or indirectly) for cAMP-dependent protein kinase. When inhibitor-1 of protein phosphatase-1 was microinjected (5 to 10 pmole per oocyte) meiotic maturation was inhibited and the level of phosphorylation of the 32-kDa protein was increased; the same result was obtained following ATP-gamma-S (1 mM) microinjection. Altogether these results suggest that a 20-kDa phosphoprotein, whose level of phosphorylation is decreased by progesterone, could be involved in the regulation of maturation by lowering the level phosphorylation of a 32-kDa phosphoprotein. An attractive hypothesis would be that the 20-kDa phosphoprotein is an inhibitor of protein phosphatase-1.
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D008540:Meiosis; D008845:Microinjections; D008970:Molecular Weight; D009865:Oocytes / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011374:Progesterone / Q000502:physiology*; D011494:Protein Kinases / Q000502:physiology*; D054645:Protein Phosphatase 1; D013873:Thionucleotides / Q000494:pharmacology; D014982:Xenopus laevis / Q000196:embryology
D010750:Phosphoproteins; D013873:Thionucleotides; C022571:adenosine 5'-O-(3-thiotriphosphate); D011374:Progesterone; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1