Modulation of luteinizing hormone-stimulated inositol phosphate accumulation by phorbol esters in bovine luteal cells.
The present studies were conducted to evaluate the effects of protein kinase C activators on the inositol phospholipid-phospholipase C second messenger system in isolated bovine luteal cells. This report describes the effects of phorbol esters on inositol phosphate accumulation in LH- and prostaglandin F2 alpha (PGF2 alpha)-stimulated bovine luteal cells. Corpora lutea of early pregnancy were dispersed with collagenase and luteal cells were prelabelled for 3 h with [3H]inositol. Inositol phosphates produced in response to LH or PGF2 alpha were analyzed by ion exchange column chromatography. The tumor promoter and protein kinase C activator 12-O-tetradecanolyphorbol 13-acetate (TPA) had no effect on basal levels of inositol phosphates but inhibited LH-stimulated accumulation of inositol mono-, bis-, and trisphosphates by 72%, 68%, and 65%, respectively. TPA reduced the response to maximally effective concentrations of LH and tripled the concentrations of LH required to evoke half-maximal accumulation of inositol mono-, bis-, trisphosphates. The inhibitory effects of TPA were rapid (5 min) whether added before or after treatment with LH. Treatment with TPA also reduced (58%) the initial phase of intracellular calcium mobilization in LH-treated cells. The inhibitory effects of TPA were not associated with acute reductions in [3H]inositol incorporation, [3H]inositol phospholipid levels, cAMP levels, or progesterone accumulation in control or LH-stimulated luteal cells. The effects of phorbol esters were concentration dependent and specific for active tumor promoters with 10-50 nM TPA producing maximal inhibitory effects. A synthetic diacylglycerol, 1-oleyl-2-acetylglycerol, mimicked the inhibitory effects of TPA. In contrast, pretreatment with a physiological activator of protein kinase C, PGF2 alpha, had no effect on LH-stimulated inositol phosphate accumulation. The inhibitory effects of TPA could not be explained by a generalized inhibition of phospholipase C or G-proteins since the accumulation of inositol phosphates in PGF2 alpha- and NaF-treated cells was not inhibited by TPA. These results demonstrate that tumor promoting phorbol esters modulate the inositol phospholipid-phospholipase C transmembrane signaling system in LH-stimulated bovine luteal cells. The results suggest that phorbol esters may alter the coupling of the LH-receptor complex to phospholipase C. These findings implicate protein kinase C in the regulation of transmembrane signaling in the bovine corpus luteum.
Davis
J S
JS
Department of Veterans Affairs Medical Center, Women's Research Institute, Wichita, Kansas.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D000242:Cyclic AMP / Q000378:metabolism; D015237:Dinoprost / Q000494:pharmacology; D005260:Female; D007294:Inositol / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D008184:Luteal Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011247:Pregnancy; D011374:Progesterone / Q000096:biosynthesis; D012969:Sodium Fluoride / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D015240:Phorbol 12,13-Dibutyrate; D011374:Progesterone; D007294:Inositol; D012969:Sodium Fluoride; D007986:Luteinizing Hormone; D015237:Dinoprost; D000242:Cyclic AMP; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium