Endocrinology, Vol 133, 2756-2760, Copyright © 1993 by Endocrine Society

ARTICLES

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

SJ Barnes and PM Conn
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109.

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.

This article has been cited by other articles:

				R. Grosse, A. Schmid, T. Schoneberg, A. Herrlich, P. Muhn, G. Schultz, and T. Gudermann Gonadotropin-releasing Hormone Receptor Initiates Multiple Signaling Pathways by Exclusively Coupling to Gq/11 Proteins J. Biol. Chem., March 24, 2000; 275(13): 9193 - 9200. [Abstract] [Full Text] [PDF]

				J. Weck, P. C. Fallest, L. K. Pitt, and M. A. Shupnik Differential Gonadotropin-Releasing Hormone Stimulation of Rat Luteinizing Hormone Subunit Gene Transcription by Calcium Influx and Mitogen-Activated Protein Kinase-Signaling Pathways Mol. Endocrinol., March 1, 1998; 12(3): 451 - 457. [Abstract] [Full Text]

				D. Stanislaus, J. A. Janovick, S. Brothers, and P. M. Conn Regulation of Gq/11{{alpha}} by the Gonadotropin-Releasing Hormone Receptor Mol. Endocrinol., June 1, 1997; 11(6): 738 - 746. [Abstract] [Full Text]