Biphasic action of cyclic adenosine 3',5'- monophosphate in gonadotropin-releasing hormone (GnRH) analog-stimulated hormone release from GH3 cells stably transfected with GnRH receptor complementary deoxyribonucleic acid.
GH3 cells are a PRL-secreting adenoma cell line derived from pituitary lactotropes. These cells have been stably transfected with rat GnRH receptor complementary DNA to produce four cell lines: GGH(3)1', GGH(3)2', GGH(3)6', and GGH(3)12'. In response to either GnRH or Buserelin (a metabolically stable GnRH agonist), these cell lines synthesize PRL in a cAMP-dependent manner. Only GGH(3)6' cells desensitize in response to persistent treatment with 10(-7) g/ml Buserelin. GGH(3)1', GGH(3)2', and GGH(3)12' cells, however, can be made refractory to Buserelin stimulation by raising cAMP levels either by the addition of (Bu)2cAMP to the medium or by treatment with cholera toxin. In GGH(3) cells, low levels of cAMP fulfill the requirements for a second messenger, whereas higher levels appear to mediate the development of desensitization. The observation that in GGH(3)6' cells, cAMP production persists after the onset of desensitization is consistent with the view that the mechanism responsible for desensitization is distal to the production of cAMP. Moreover, the absence of any significant difference in the amount of cAMP produced per cell in GGH(3)2', GGH(3)6', or GGH(3)12' cells suggests that elevated cAMP production per cell does not explain the development of desensitization in GGH(3)6' cells. We suggest that Buserelin-stimulated PRL synthesis in GGH(3)6' cells is mediated by a different cAMP-dependent protein kinase pool(s) than that in nondesensitizing GGH(3) cells. Such a protein kinase A pool(s) may be more susceptible to degradation via cAMP-mediated mechanisms than the protein kinase pools mediating the Buserelin response in nondesensitizing GGH(3) cells. A similar mechanism has been reported in other systems.
Stanislaus
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D
Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97201, USA.
Arora
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Awara
W M
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Conn
P M
PM
D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D002064:Buserelin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D018076:DNA, Complementary / Q000235:genetics*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D051381:Rats; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured
D018931:Antineoplastic Agents, Hormonal; D018076:DNA, Complementary; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D002064:Buserelin