Insulin induces upregulation of vascular AT(1) receptor gene expression byposttranscriptional mechanisms

Background-An interaction of insulin with angiotensin II effects could be p athophysiologically important for the pathogenesis of atherosclerosis and h ypertension. Methods and Results-We examined the effect of insulin on AT(1) receptor gen e expression in cultured vascular smooth muscle cells (VSMCs). A 24-hour in cubation with insulin (100 nmol/L) produced a 2-fold increase in AT(1) rece ptor density on VSMCs, as assessed by radioligand binding assays. This enha nced AT(1) receptor expression was caused by a time- and concentration-depe ndent upregulation of the AT(1) receptor mRNA levels, as assessed by Northe rn analysis. The maximal effect was detected after a 24-hour incubation of cells with 100 nmol/L insulin (270+/-20%). AT(1) receptor upregulation was caused by a stabilization of the AT(1) receptor mRNA, because the AT(1) rec eptor mRNA half-life was prolonged from 5 hours under basal conditions to 1 0 hours after insulin stimulation. In contrast, insulin had no influence on AT(1) receptor gene transcription, as assessed by nuclear run-on assays. T he insulin-induced AT(1) receptor upregulation was followed by an increased functional response, because angiotensin II evoked a significantly elevate d intracellular release of calcium in cells that were preincubated with 100 nmol/L insulin for 24 hours. The insulin-induced AT(1) receptor upregulati on was dependent on tyrosine kinases, as assessed by experiments with the t yrosine kinase inhibitor genistein. Furthermore, experiments using the intr acellular calcium chelator bis(2-amino-5-methylphenoxy)ethane-N,N,N',N'-tet raacetic acid tetraacetoxymethyl ester suggest that intracellular calcium r elease may be involved in AT(1) receptor regulation. Conclusions-Insulin-induced upregulation of the AT(1) receptor by posttrans criptional mechanisms may explain the association of hyperinsulinemia with hypertension and arteriosclerosis, because activation of the AT(1) receptor plays a key role in the regulation of blood pressure and fluid homeostasis .