Presence of an Endogenous Inhibitor of Protein Kinase C Throughout Pseudopregnancy in the Rat Ovary

Eyster, Kathleen M.

doi:10.1007/978-1-4612-3200-1_22

Cited by 2 publications

(6 citation statements)

References 13 publications

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“…The modified assay also uses protamine as substrate. Many of our previously published studies utilized histone III-S as substrate [10,11,13,22], although we have also demonstrated the utility of protamine as an excellent substrate for phosphorylation by PKC and dephosphorylation by the ovarian phosphatase [13]. Protamine was used as the substrate in this assay because it precipitated with ammonium sulfate, whereas adequate precipitation of histone III-S with ammonium sulfate was not achieved.…”

Section: Phosphatase Assay Of Pkc-phosphorylated Substratesmentioning

confidence: 98%

“…Ovaries were collected from pregnant rats on Days 7,10,12,14,17, and 20 of pregnancy. Corpora lutea were dissected free, and luteal cytosols were prepared in the presence or absence of sodium fluoride (NaF) and inorganic phosphate (PPi) to prevent autodephosphorylation of the phosphatase during tissue processing.…”

Section: Experimental Designmentioning

confidence: 99%

“…In addition, Cutler and coworkers [9] have shown an estradiol-stimulated increase in synthesis of the delta isoform of PKC in the pregnant rat corpus luteum. The endogenous inhibitor of PKC is present in the rat corpus luteum throughout pregnancy [8] as well as pseudopregnancy [10]. Therefore, we reasoned that if the in vitro inhibition of PKC accurately reflects the in vivo state, then in order for the rat luteal cells to experience PKC activity they must have some means of regulating the inhibitor of PKC.…”

Section: Introductionmentioning

confidence: 98%

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Protein Phosphatase Activity in the Rat Ovary Throughout Pregnancy and Pseudopregnancy1

Eyster

Berger

Rodrigo

et al. 1998

Biology of Reproduction

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Specific protein phosphatase activity against protein kinase C-phosphorylated substrate was measured in the rat ovary during pseudopregnancy and pregnancy. Tissues were processed in the presence of sodium fluoride and inorganic phosphate to inhibit the phosphatase and thereby prevent autodephosphorylation of the type 2A protein phosphatase (PP2A) during homogenization. Manganese was added at the time of enzyme assay to reactivate the phosphatase. The specific activity of the protein phosphatase did not vary significantly across pseudopregnancy (p > 0.05). In contrast, the specific activity of protein phosphatase decreased significantly between Day 7 and Day 10 of pregnancy (28.8 +/- 5 pmol/min x microg protein and 20.7 +/- 2 pmol/min x microg protein, respectively; p < 0.05) and remained at the decreased value for the remainder of pregnancy. To determine whether hormones of pregnancy could regulate PP2A activity in the ovaries, pseudopregnant rats were treated with prolactin (3 IU twice a day), bromocriptine (100 microg twice a day), or estradiol benzoate (50 microg). Bromocriptine and estradiol treatments caused a decrease in PP2A-specific activity, but prolactin had no effect. Bromocriptine treatment caused a decrease in the protein content of the PP2A catalytic subunit, but prolactin and estradiol treatments had no effect. The data suggest that the specific activity and protein content of PP2A in the rat ovary are hormonally regulated.

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Section: Phosphatase Assay Of Pkc-phosphorylated Substratesmentioning

confidence: 98%

Section: Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Protein Phosphatase Activity in the Rat Ovary Throughout Pregnancy and Pseudopregnancy1

Eyster

Berger

Rodrigo

et al. 1998

Biology of Reproduction

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“…The current studies were undertaken to measure Ca 2 +-dependent and Ca2+-independent PKC activity in the CL of the normally cycling, nonpregnant rhesus monkey ovary at midluteal phase and to determine whether the rhesus monkey CL contained an endogenous inhibitor or an endogenous heat-stable PKC-stimulatory factor similar to those reported for the rat ovary [6][7][8]17].…”

Section: Introductionmentioning

confidence: 98%

“…Some of the difficulty in defining the role of PKC in the ovary may be due to an incomplete characterization of the cellular regulation of PKC in the ovary. We have shown that PKC activity in cytosolic preparations of the ovary of the pseudopregnant and pregnant rat is masked by an endogenous inhibitor of PKC [6][7][8], and we have recently demonstrated that this PKC-inhibitory factor in the rat ovary is a protein phosphatase [9]. Endogenous inhibitors have been identified in other tissues [10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Endogenous Modulation of Protein Kinase C in the Rhesus Monkey Corpus Luteum1

Eyster

1994

Biology of Reproduction

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The activity of protein kinase C (PKC) and the presence of endogenous PKC-modulatory factors in monkey CL have not been previously reported. The specific activity of Ca(2+)- and lipid-dependent PKC activity in cytosols prepared from CL obtained from rhesus monkeys at midluteal phase was 515.1 +/- 79 pmol/min x mg; Ca(2+)-independent PKC activity was 233.2 +/- 31 pmol/min x mg. No PKC-inhibitory activity was seen when luteal cytosol was mixed with a control preparation of PKC (control PKC 10.2 +/- 2.0 pmol/min; luteal cytosol plus control PKC 26.0 +/- 2.1 pmol/min). However, the monkey CL contained PKC-phosphatase activity (the endogenous inhibitor of PKC in the rat ovary is a protein phosphatase). Specific activity of luteal PKC phosphatase activity was 609.0 +/- 94 pmol/min x mg. Kinetic studies suggested that the monkey CL contained a competitive inhibitor of the phosphatase. Heat-treated cytosol mixed with control PKC (9.0 +/- 0.7 pmol/min) resulted in enzyme activity that was significantly greater than that of the control (13.7 +/- 1.2 pmol/min). Luteal cytosol that had been heat-treated and extracted with petroleum ether substituted for lipids in the activation of PKC. In summary, the activity of PKC in the monkey CL was readily measurable; it was not masked by an endogenous PKC-inhibitory factor. The monkey CL did contain a heat-stable PKC-stimulatory activity.

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Presence of an Endogenous Inhibitor of Protein Kinase C Throughout Pseudopregnancy in the Rat Ovary

Cited by 2 publications

References 13 publications

Protein Phosphatase Activity in the Rat Ovary Throughout Pregnancy and Pseudopregnancy1

Protein Phosphatase Activity in the Rat Ovary Throughout Pregnancy and Pseudopregnancy1

Endogenous Modulation of Protein Kinase C in the Rhesus Monkey Corpus Luteum1

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