Background: Angiotensin II (Ang II) down-regulates renin expression in juxtaglomerular cells, however, recent experimental evidence obtained in transgenic mice suggested that Ang II may "paradoxically" increase transcriptional activity of the proximal renin promoter.
Methods: To dissect signalling mechanisms contributing to the up-regulation of the proximal renin promoter by Ang II, porcine proximal tubular cells stably expressing the rabbit AT(1) receptor (LLC-PK/AT(1)) were transiently transfected with a luciferase reporter construct containing the 582 bp long piece of the human renin promoter. Activation of mitogen-activated protein kinases (MAPK) was detected by western blotting using phospho-MAPK-specific antibodies.
Results: Ang II dose-dependently stimulated the transcriptional activity of the human renin promoter (10(-7) M Ang II: 3.50+/-1.25-fold stimulation). In these cells Ang II activated both extracellular signal-regulated kinase (ERK) and the c-Jun-N-terminal kinase (JNK). Inhibition of the ERK cascade did not reduce the stimulation of the renin promoter by Ang II, however, two expression vectors designed to inhibit the JNK pathway, the dominant negative JNK and the Jun-kinase interacting peptide inhibited the fold stimulation induced by Ang II (2.75+/-0.69 vs 1.6+/-0.23 and 1.8+/-0.34, respectively; P<0.01). Furthermore, genistein, a tyrosine kinase inhibitor, blocked the effect of Ang II both on the JNK and the promoter activation.
Conclusion: Ang II may have a stimulatory effect on the proximal renin promoter in proximal tubular cells and this effect is mediated by tyrosine kinases and the JNK cascade.