Modulation of the AT2 subtype receptor gene activation and expression by the AT1 receptor in endothelial cells

Objective To investigate whether angiotensin II type 2 (AT(2)) receptor (AT(2)-r) promoter activity and expression are modulated by angiotensin II (Ang II), and whether the AT(1) receptor (AT(1)-r) is involved in this effect. Design and methods Primary endothelial cells obtained from neonatal rat aorta, expressing both receptors, were transfected with the rat AT(2)-r promoter region cloned into a pCAT-reporter vector. The reporter-expression study was performed in a transient transfection assay system. Transfected cells were studied following angiotensin-converting enzyme inhibition to prevent endogenous formation of Ang II, Cells were subsequently stimulated for 6 h with Ang II, either alone or in combination with the AT(1)-r antagonist DuP753. AT(2)-r mRNA was assessed by RNase protection assay during the same pharmacological stimuli. Results Stimulation with Ang II caused an increase in promoter activity (+50%, P < 0.05 versus baseline), whereas mRNA expression was reduced by 50% (P < 0.05 versus baseline). Concomitant treatment with DuP753 and Ang II was associated with a 98% increase in promoter activity (P < 0.05 versus baseline). DuP753 also prevented the reduction in mRNA; it actually produced a 100% increase in AT(2)-r mRNA accumulation (P < 0.01 versus baseline), Studies with the AT(2)-r antagonist PD123319 indicate that the AT(2)-r is also involved in the regulation of AT(2)-r gene promoter activity. Conclusions These data indicate that Ang II increases AT(2)-r promoter activity and decreases AT(2)-r mRNA accumulation in endothelial cells, The AT(1) subtype receptor is involved in the modulation of both effects of Ang II. These findings suggest that changes in the expression of AT(2) receptors may occur during treatment with AT(1)-r antagonists, and they indicate the existence of a cross-talk between AT(1) and AT(2) receptors. J Hypertens 1999, 17:1873-1877 (C) Lippincott Williams & Wilkins.