Human renin mRNA stability is increased in response to cAMP in Calu-6 cells

The human carcinoma-derived cell line Calu-6 has previously been demonstrated to endogenously express human renin (hREN) mRNA and to markedly increase steady-state hREN mRNA levels (100-fold after 24 hours) in response to analogues of cAMP and postreceptor activators of adenylyl cyclase such as forskolin. However, both transfection analysis using hREN promoter-reporter constructs and nuclear run-on experiments suggest that transcriptional activity alone cannot account for this level of induction. We performed primer extension, reverse transcription-polymerase chain reaction, and 3' rapid amplification of cDNA ends to compare hREN mRNA between unstimulated and forskolin-stimulated cells. We demonstrate that hREN mRNA is identical under both conditions with respect to (1) utilization of the appropriate transcription start site, (2) processing of renin mRNA, and (3) utilization of the proper polyadenylation site and length of the poly-A tail. To address the mechanism of induction caused by cAMP, we used transcriptional inhibition and measured decay of hREN mRNA before and after forskolin or phorbol ester treatment. Experiments with both actinomycin D and 5, 6-dichlororibofuranosylbenzimidazole (DRB) showed that forskolin treatment markedly stabilized hREN mRNA in Calu-6 cells. A 2.3-fold increase in hREN mRNA half-life was also observed after treatment of Calu-6 cells with phorbol ester. Experiments with DRB demonstrated a similar robust stabilization of hREN mRNA after forskolin and phorbol ester treatment. These data demonstrate that the induction in hREN mRNA in response to both cAMP and phorbol ester occurs by a mechanism involving a posttranscriptional component.