Cyclic AMP selectively increases renin mRNA stability in cultured juxtaglomerular granular cells

Abstract

This study was undertaken to examine the regulation of renin release and gene expression in primary cultures of juxtaglomerular granular (JGG) cells. JGG cells, isolated from mouse kidney, demonstrated high purity and showed regulated renin release in vitro. Changes in steady-state renin mRNA levels were assessed by quantitative polymerase chain reaction techniques, with polymerase chain reaction amplification efficiency monitored by co-amplification of experimental samples with a dilution series of cDNA for a mutant template. When the cells were incubated in the presence or absence of forskolin, isoproterenol, or 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine for 24 h or cholera toxin for 12 h, renin mRNA levels were increased 3.9-, 4.4-, 5.1-, and 3.3-fold, respectively (all, p < 0.05). A significant increase in renin mRNA levels was observed 8 h after treatment with forskolin, but no change was detectable at 4 h. Cycloheximide did not prevent the increase in renin mRNA by isoproterenol. When RNA synthesis was inhibited by incubation with actinomycin D (5 micrograms/ml), renin mRNA levels declined with a half-life of 3.0 +/- 0.8 h. Treatment with forskolin increased renin mRNA half-life to 10.8 +/- 2.7 h (p < 0.025). The half-life of beta-actin, endothelin-1, or the facilitative glucose transporter-1 (GLUT-1) mRNA expressed in the same cells was not altered, although the steady-state levels of GLUT-1 mRNA increased 2.2-fold after treatment with forskolin. These data demonstrate that cAMP increases renin release and mRNA levels in JGG cells in vitro, that the stimulatory effect of cAMP on renin mRNA is delayed but does not require new protein synthesis, and that the increased renin mRNA levels induced by cAMP are due in part to a selective increase in renin mRNA stability.