Document Detail

Progesterone-inhibited phosphorylation of an unique Mr 48,000 protein in the plasma membrane of Xenopus laevis oocytes.
MedLine Citation:
PMID:  2982868     Owner:  NLM     Status:  MEDLINE    
The meiotic maturation of Xenopus laevis oocytes is induced in vitro by progesterone which interacts at the cell surface level. A cell-free membrane preparation (P-10,000) incorporated 32P from [gamma-32P]ATP, mostly into two proteins, Mr approximately 56,000 and approximately 48,000 (as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Progesterone, added in vitro, specifically inhibited the phosphorylation of the Mr approximately 48,000 protein (named p48). Half-maximal inhibition of p48 phosphorylation occurred with progesterone approximately 8 microM, in good correlation with hormone concentration inducing oocyte maturation. The effect was not due to stimulation of protein phosphatase activity. The potent maturation inducers testosterone and deoxycorticosterone also inhibited p48 phosphorylation, whereas biologically inactive steroids or cholesterol did not. p48 phosphorylation was not affected by cAMP, cGMP, polyamines, calmodulin, and phospholipids + diolein. EGTA had a stimulatory effect which was reversed by added Ca2+. The inhibitory effects of progesterone and Ca2+ were additive, suggesting two distinct sites of action. Phospho-p48 was not detected in yolk platelets, microsomes, and cytosol of oocytes. Contrary to p48 itself, the p48 kinase activity was loosely associated with P-10,000. Progesterone inhibited p48 phosphorylation produced by either cytosol or exogenous pure catalytic subunit of cAMP-dependent protein kinase. Conversely, phosphorylation of casein and histones by protein kinase activity present in P-10,000 was not modified by progesterone. It is then suggested that progesterone regulates p48 phosphorylation by affecting the protein substrate in the membrane, rather than by inhibiting the protein kinase enzyme itself. The data demonstrate a direct effect (not mediated by change of protein synthesis) of steroids on p48 phosphorylation in the plasma membrane, and they suggest that this protein could be implicated in the initial action of progesterone on oocyte maturation.
J P Blondeau; E E Baulieu
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  260     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  1985 Mar 
Date Detail:
Created Date:  1985-04-24     Completed Date:  1985-04-24     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  3617-25     Citation Subset:  IM    
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MeSH Terms
Cell Membrane / metabolism
Egtazic Acid / pharmacology
Membrane Proteins / metabolism*
Molecular Weight
Oocytes / drug effects,  metabolism*
Phosphoprotein Phosphatases / metabolism
Progesterone / pharmacology*
Protein Kinases / metabolism
Xenopus laevis
Reg. No./Substance:
0/Membrane Proteins; 57-83-0/Progesterone; 67-42-5/Egtazic Acid; EC 2.7.-/Protein Kinases; EC Phosphatases

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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