Interrelationships among estrogen, insulin-like growth factor-I and cyclic adenosine monophosphate in the regulation of uterine progesterone and estrogen receptors

Studies were undertaken to examine regulation of progesterone receptor gene expression and estrogen receptor bioactivity in uterine cells, and to determine the cellular mechanisms through which various factors mediate regulation of these receptor proteins. Exposure of uterine cells maintained in primary culture to estradiol, IGF-I, or to agents which raised intracellular cAMP levels stimulated significant increases in progesterone receptor (PR) content. Stimulation of PR levels by these agents was suppressed equally by co-treatment with antiestrogen (ICI 164,384) or protein kinase inhibitors, or by pre-treatment of cells with actinomycin D or cycloheximide. These results suggest that regulation of PR occurs at the level of the PR gene, and that induction of PR stimulated by these agents requires activation of estrogen receptor (ER) and the action of protein kinases. Treatment with cGMP and activators of protein kinase C failed to alter the basal level of PR, or the induction of PR stimulated by other agents.The level of estrogen receptor (ER) increased significantly in uterine cells treated with cAMP and IGF-I. However, co-treatment of cells with cAMP and estradiol suppressed the increase in ER, suggesting that cAMP may stimulate ER expression as a means for the target cell to re-establish basal ER levels and remain estrogen-responsive. The ligand binding affinity of ER was not altered by treatment with any test agent. Exposure of cells to cAMP, IGF-I or estradiol increased the phosphorylation state of uterine ER, and activated ER-mediated gene transcription in transfected cells. Activation of ER-mediated transcription stimulated by cAMP or IGF-I was also shown to occur in the presumed absence of estrogen, suggesting that ER stimulation can occur in a ligand-independent manner.Exposure of uterine cells and MCF-7 human breast cancer cells to estrogens and antiestrogens rapidly stimulated increases in cellular cAMP levels. Increases in cAMP were also shown for intact uteri treated with estrogen and antiestrogens in vivo. These increases in cAMP were not blocked by pre-treatment of cells with actinomycin D or cylcoheximide, suggesting a non-genomic mechanism of activation by estrogen and antiestrogens. Estrogen and antiestrogen treatment was shown to increase adenylate cyclase activity in membranes isolated from treated cells, but did not alter cellular phosphodiesterase activity. The increases in cAMP stimulated by estrogen and antiestrogens were sufficient to activate cAMP-mediated target gene transcription in transfected cells. These observations suggest that estrogens and antiestrogens can effect gene activation through the alteration of cellular cAMP levels, and provides additional evidence for interaction between various cellular pathways in the regulation of steroid hormone receptor gene expression and biological activity.U of I OnlyETDs are only available to UIUC Users without author permissio