Vasoactive intestinal peptide increases intracellular cAMP and gonadotropin-alpha gene activity in JEG-3 syncytial trophoblasts. Constraints posed by desensitization.
Expression of the human chorionic gonadotropin (hCG)-alpha gene in placental trophoblasts is markedly stimulated by cAMP, a property preserved in a reporter plasmid containing its cAMP response elements (CREs) linked to the chloramphenicol acetyltransferase coding sequence (CRE alpha CAT). In search of a potential physiologic regulator of hCG gene expression via cAMP, we found that JEG-3 syncytial trophoblast cells have specific binding sites for vasoactive intestinal peptide (VIP) with dissociation constant of 1 nM. VIP maximally increased the transient expression of CRE alpha CAT and the expression of endogenous hCG-alpha mRNA in JEG-3 cells by 4- and 9-fold, respectively. Exposure of JEG-3 cells to 30 nM VIP increased cAMP levels 60-fold after 10-30 min, but cAMP rapidly declined thereafter. As a consequence of this desensitization, the effect of VIP on stimulation of both CRE alpha CAT and endogenous hCG-alpha and hCG-beta mRNA levels more closely resembled that of forskolin or 8-br-cAMP at time points much less than 24 h. Moreover, transient exposure to 8-br-cAMP was much less effective than 24 h of continuous incubation on CRE alpha CAT activity. We conclude that VIP rapidly increases cAMP content and activates hCG-alpha gene expression in JEG-3 cells, but sustained elevations in cAMP are necessary for maximal accumulation of this CRE-regulated gene product.
Department of Medicine, Cornell University Medical College, New York, New York 10021.
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D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D001667:Binding, Competitive; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D002822:Choriocarcinoma; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics*; D006728:Hormones / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D011247:Pregnancy; D012333:RNA, Messenger / Q000235:genetics; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism*; D018005:Receptors, Vasoactive Intestinal Peptide; D014162:Transfection; D014594:Uterine Neoplasms; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism / Q000494:pharmacology*
D015292:Glycoprotein Hormones, alpha Subunit; D006728:Hormones; D012333:RNA, Messenger; D011964:Receptors, Gastrointestinal Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP; D015500:Chloramphenicol O-Acetyltransferase