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

To investigate whether angiotensin II type 2 (AT2) receptor (AT2-r) promoter activity and expression are modulated by angiotensin II (Ang II), and whether the AT1 receptor (AT1-r) is involved in this effect.

Primary endothelial cells obtained from NEONATAL rat aorta, expressing both receptors, were transfected with the rat AT2-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 AT1-r antagonist DuP753. AT2-r mRNA was assessed by RNase protection assay during the same pharmacological stimuli.

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 AT2-r mRNA accumulation (P < 0.01 versus baseline). Studies with the AT2-r antagonist PD123319 indicate that the AT2-r is also involved in the regulation of AT2-r gene promoter activity.

These data indicate that Ang II increases AT2-r promoter activity and decreases AT2-r mRNA accumulation in endothelial cells. The AT1 subtype receptor is involved in the modulation of both effects of Ang II. These findings suggest that changes in the expression of AT2 receptors may occur during treatment with AT1-r antagonists, and they indicate the existence of a cross-talk between AT1 and AT2 receptors.