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Endocrinology, Vol 133, 1266-1273, Copyright © 1993 by Endocrine Society

ARTICLES

The endogenous inhibitor of protein kinase-C in the rat ovary is a protein phosphatase

KM Eyster, MS Waller, TL Miller, CJ Miller, MJ Johnson and JS Persing
Department of Physiology and Pharmacology, University of South Dakota, Vermillion 57069-2390.

Calcium- and lipid-dependent protein kinase (PKC) activity in the ovary of the pseudopregnant rat is masked by an endogenous inhibitor of PKC. These studies were undertaken to examine the mechanism of action of the endogenous inhibitor of PKC in the rat ovary. The addition of the phosphatase inhibitors calyculin-A (0.09 nM), microcystin-LR (6.4 nM), and okadaic acid (10 nM) resulted in the loss of PKC inhibitory activity and an increase in basal PKC activity in rat ovarian cytosol. In phosphatase assays, significant dephosphorylation of histone-III-S or myelin basic protein that had been phosphorylated by PKC occurred within 4 min after the addition of ovarian cytosol from the pseudopregnant rat. This dephosphorylation was prevented from the pseudopregnant rat. This dephosphorylation was prevented by the addition of calyculin-A (0.73 nM) and was removed by fractionation of ovarian cytosol on diethylaminoethyl cellulose. No inhibition of PKC activity was observed when the PKC-specific peptides AcMBP-(4-14) and [Ser25]PKC-(19-31) were used as the substrate for phosphorylation. In addition, rat ovarian cytosol did not exhibit phosphatase activity when the peptide AcMBP-(4-14) was used as the substrate. Addition of ovarian cytosol resulted in dephosphorylation of phosphorylase-alpha phosphorylated by phosphorylase kinase, but not dephosphorylation of histone-II-A or histone-VIII-S phosphorylated by PKA. The data suggest that the endogenous inhibitor of PKC in the rat ovary is a protein phosphatase.


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M. V Sheth, C. J Mark, and K. M Eyster
Expression of type 1 and 2A protein phosphatase subunits in the rat corpus luteum across pregnancy
J. Endocrinol., November 1, 2007; 195(2): 293 - 299.
[Abstract] [Full Text] [PDF]


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