Cyclic AMP regulates transcription of the genes encoding human chorionic gonadotropin with different kinetics.
Choriocarcinoma cell lines characteristically synthesize and secrete the alpha- and beta-subunits of human chorionic gonadotropin (hCG), as well as the intact heterodimer. Treatment of one such cell line, BeWo, with 8-bromo-adenosine 3':5'-cyclic monophosphate (8-Br-cAMP) causes at least a 10-fold increase in the concentration of the mRNA encoding each subunit. Changes in mRNA concentrations are associated with similar changes in transcription rates of both the CG alpha and CG beta genes, although the kinetics of their transcriptional responses are different. Transcription of the alpha-subunit gene increases rapidly and becomes maximal within 1 hr after addition of 8-Br-cAMP. By contrast, transcription of the CG beta gene increases slowly and progressively for at least 8 hr after treatment with 8-Br-cAMP. The slow transcriptional response of the CG beta gene(s) appears to be unique compared to that of other cAMP-responsive genes, and suggests that the cyclic nucleotide may regulate transcription of the CG genes by different mechanisms.