DOWN-REGULATION OF ANGIOTENSIN-II TYPE-1 RECEPTOR GENE-TRANSCRIPTION BY NITRIC-OXIDE

Nitric oxide (NO) plays an important role not only in the regulation o f blood vessel tone, but also in the growth of vascular smooth muscle cells (VSMC). The precise mechanism involved in the inhibition of VSMC growth by NO is not known. To further explore the effect of NO on VSM C growth, we examined the effect of NO on the expression of angiotensi n II type 1 receptor (AT(1)-R) that is important for hypertrophy and h yperplasia of VSMC. S-nitroso acetyl DL-penicillamine (SNAP; 200 mu mo l/L), a potent NO donor, suppressed expression level of AT(1)-R mRNA b y 90% and AT(1)-R number by 60% after 24 hours of stimulation. The sup pressive effect was dose-dependent. Actinomycin D, which is an inhibit or of gene transcription, did not affect the decrease of AT(1)-R mRNA by NO. Cyclic guanosine monophosphate (cGMP) analogue, 8 bromo-cGMP, d id not affect AT(1)-R mRNA level. Deletion mutants of the promoter reg ion of rat AT(1)a-R gene were fused to luciferase reporter gene and in troduced to VSMC. Transfected cells were stimulated with SNAP, and luc iferase activity was measured. Inhibitory effect of NO was still obser ved in the shortest deletion mutant that contained 61 bp upstream from transcription start site. In this DNA segment, two DNA binding protei n were observed by gel mobility shift assay, and one of these binding proteins was decreased on stimulation by NO. NO downregulates AT(1)-R gene expression independently of cGMP. A DNA binding protein that bind s to the proximal promoter region of AT(1)-R gene may be responsible f or this inhibitory effect. The inhibition of AT(1)-R gene expression m ay be implicated in the anti-atherogenic property of NO.