Involvement of protein phosphatases in gonadotropin releasing hormone regulated gonadotropin secretion.
The role of persistent protein phosphorylation upon gonadotropin releasing hormone (GnRH) stimulated luteinizing hormone (LH) release was investigated by the use of the selective inhibitors of protein phosphatase type 1 (PP1) and 2A (PP2A), okadaic acid (OA) and calyculin A. Pre-incubation of cultured rat pituitary cells with OA (24 h) or calyculin A (30 min) resulted in inhibition of GnRH-stimulated LH release with significant inhibition being detected at 10 nM and 30 nM for OA and calyculin A, respectively. The inactive OA analog norokadone and the protein tyrosine phosphatase inhibitor vanadyl hydroperoxide had no significant effect on GnRH-induced LH release. The stimulatory effects of the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 50 ng/ml) or the Ca2+ ionophore, ionomycin (1 micron), upon LH release were also abolished by pretreatment with OA (10-20 nM) or calyculin A (30 nM). Stimulation of LH release by high K+ (28 mM) or residual LH release stimulated by GnRH in Ca(2+)-free medium were also blocked by OA. These observations indicate that protein dephosphorylation is involved positively in GnRH-stimulated LH release. The site of action of the protein phosphatases PP1 and PP2A is most likely downstream to Ca2+ elevation and PKC activation by GnRH.
Marantz
Y
Y
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
Reiss
N
N
Przedecki
F
F
Naor
Z
Z
D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D015759:Ionomycin / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D008387:Marine Toxins; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D010902:Pituitary Gland / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004988:Ethers, Cyclic; D008387:Marine Toxins; D010080:Oxazoles; D019319:Okadaic Acid; D007987:Gonadotropin-Releasing Hormone; D015759:Ionomycin; C059041:calyculin A; D007986:Luteinizing Hormone; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate