Endocrinology, Vol 131, 749-757, Copyright © 1992 by Endocrine Society

ARTICLES

Modulation of luteinizing hormone-stimulated inositol phosphate accumulation by phorbol esters in bovine luteal cells

JS Davis
Department of Veterans Affairs Medical Center, Women's Research Institute, Wichita, Kansas.

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.

This article has been cited by other articles:

				J. K. Pru, I. R. Hendry, J. S. Davis, and B. R. Rueda Soluble Fas Ligand Activates the Sphingomyelin Pathway and Induces Apoptosis in Luteal Steroidogenic Cells Independently of Stress-Activated p38MAPK Endocrinology, November 1, 2002; 143(11): 4350 - 4357. [Abstract] [Full Text] [PDF]

				J. Suter, I. R. Hendry, L. Ndjountche, K. Obholz, J. K. Pru, J. S. Davis, and B. R. Rueda Mediators of Interferon {{gamma}}-Initiated Signaling in Bovine Luteal Cells Biol Reprod, May 1, 2001; 64(5): 1481 - 1486. [Abstract] [Full Text]

				B. R. Rueda, I. R. Hendry, W. J. Hendry III, F. Stormshak, O.D. Slayden, and J. S. Davis Decreased Progesterone Levels and Progesterone Receptor Antagonists Promote Apoptotic Cell Death in Bovine Luteal Cells Biol Reprod, February 1, 2000; 62(2): 269 - 276. [Abstract] [Full Text]

				A. Chamson-Reig, O. P. Pignataro, C. Libertun, and V. A. R. Lux-Lantos Alterations in Intracellular Messengers Mobilized by Gonadotropin-Releasing Hormone in an Experimental Ovarian Tumor Endocrinology, August 1, 1999; 140(8): 3573 - 3580. [Abstract] [Full Text]

				D.-b. Chen, S. D. Westfall, H. W. Fong, M. S. Roberson, and J. S. Davis Prostaglandin F2{alpha} Stimulates the Raf/MEK1/Mitogen-Activated Protein Kinase Signaling Cascade in Bovine Luteal Cells Endocrinology, September 1, 1998; 139(9): 3876 - 3885. [Abstract] [Full Text] [PDF]

				R. M. Rajagopalan-Gupta, M. M. Rasenick, and M. Hunzicker-Dunn Luteinizing Hormone/Choriogonadotropin-Dependent, Cholera Toxin-Catalyzed Adenosine 5'-Diphosphate (ADP)-Ribosylation of the Long and Short Forms of Gs{alpha} and Pertussis Toxin-Catalyzed ADP-Ribosylation of Gi{alpha} Mol. Endocrinol., May 1, 1997; 11(5): 538 - 549. [Abstract] [Full Text]