Cyclic AMP (cAMP) effects on chorionic gonadotropin gene transcription and mRNA stability: labile proteins mediate basal expression whereas stable proteins mediate cAMP stimulation.

Cyclic AMP stimulates a marked accumulation of CG alpha and CG beta mRNAs that reflects, in part, increased rates of gene transcription. We find that a major component of cAMP stimulation of alpha and CG beta mRNAs is independent of new protein synthesis. After treatment of JEG-3 choriocarcinoma cells with cycloheximide, basal levels of alpha and CG beta mRNAs decreased over 12 h to 27% and 13% of control values, respectively. However, cycloheximide treatment did not affect the degree of cAMP-stimulation of alpha and CG beta mRNA levels which increased 20- and 26-fold, respectively. Similarly, cycloheximide did not block cAMP-stimulated transcription of the alpha and CG beta genes. The effect of cAMP treatment on alpha and CG beta mRNA stability was assessed by decay after removal of cAMP, pulse-chase analyses, and decay after inhibition of RNA synthesis by actinomycin D. The half-lives of alpha and CG beta mRNAs determined by decay rates after removal of cAMP were 6.0 h and 7.2 h, respectively. Consistent with these measurements of mRNA stability, alpha and CG beta mRNA half-lives determined by pulse-chase analyses were 8.8 h and 8.6 h, respectively. Cyclic AMP treatment increased the half-lives of alpha and CG beta mRNAs 1.8- and 3.4-fold, respectively. Thus, the effects of cAMP on alpha and CG beta gene expression are predominantly transcriptional, but cAMP also increases mRNA levels via a posttranscriptional mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)