Cholera toxin and dibutyryl cyclic adenosine 3',5'-monophosphate sensitize gonadotropin-releasing hormone-stimulated inositol phosphate production to inhibition in protein kinase-C (PKC)-depleted cells: evidence for cross-talk between a cholera toxin-sensitive G-protein and PKC.
The present study assesses the relationship between G-proteins and protein kinase-C (PKC) in the gonadotrope. Cells were depleted of PKC with 1 microM phorbol 12-myristate 13-acetate for 12 h, followed by medium 199-BSA for 6 h before treatment with vehicle, pertussis toxin (PTX), cholera toxin (CTX), or (Bu)2cAMP (dBcAMP) for 18 h. PTX (10 ng/ml) significantly decreased GnRH-stimulated inositol phosphate (IP) production over a range of 10(-8)-10(-6) M GnRH. The degree of this inhibition was the same in control cells and PKC-depleted cells. Pretreatment with CTX (0.5 microgram/ml) significantly decreased GnRH-stimulated IP production over a range of 10(-9)-10(-6) M GnRH in PKC-depleted cells. This effect was mimicked by pretreatment with 3 mM dBcAMP. Although CTX and dBcAMP both decreased GnRH-stimulated IP production in control cells, this effect was enhanced in PKC-depleted cells. CTX (0.1 microgram/ml) and dBcAMP (3 mM) both enhanced GnRH-stimulated LH release, whereas PTX (100 ng/ml) had no effect. This was observed in control as well as PKC-depleted cells. Both PKA and PKC are capable of regulating IP turnover by phosphorylating phospholipase-C at distinct sites. CTX activates a G-protein that increases cAMP. cAMP can then activate PKA. In PKC-depleted cells, CTX inhibits GnRH-stimulated IP production. This effect is mimicked by dBcAMP, which suggests a role for PKA in the gonadotrope. The results of this study provide evidence for cross-talk between a CTX-sensitive G-protein and PKC.
Barnes
S J
SJ
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109.
Conn
P M
PM
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D007986:Luteinizing Hormone / Q000378:metabolism; D037342:Pertussis Toxin; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000172:deficiency*; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010566:Virulence Factors, Bordetella; D007987:Gonadotropin-Releasing Hormone; D003994:Bucladesine; D007986:Luteinizing Hormone; D002772:Cholera Toxin; D037342:Pertussis Toxin; D011493:Protein Kinase C