Although the cyclic AMP signalling cascade is considered to be the main activator of renin gene expression in renal juxtaglomerular (JG) cells, the molecular pathways along which cAMP exerts this effect remain a matter of controversy. Here in this study we used the mouse JG cell line As4.1, which shares a number of functional similarities with native JG cells. We found that forskolin, an activator of adenylate cyclase, in the presents of IBMX time-dependently increased renin mRNA levels and prorenin secretion up to threefold. The stimulation of renin gene expression by forskolin/IBMX was markedly attenuated by an inhibitor of protein kinase A (H-89, 10 microM). Forskolin/IBMX had no effect on the decline of renin mRNA after general inhibition of transcription by actinomycin D (2 microM). Conversely, forskolin/IBMX increased the activity of a 2.8-kb fragment of the renin promoter threefold. The promoter region responsible for the stimulatory effect of forskolin/IBMX was narrowed down to three 4 bp of the mouse Ren1(C) gene, which are known as putative CRE-sites. The CRE-binding protein was found to be phosphorylated under forskolin/IBMX stimulation. It appears likely therefore that cAMP stimulates renin gene expression in JG cells by activating protein kinase A and subsequent phosphorylation of the CRE-binding protein.