Multiple growth factors modulate mRNA expression of angiotensin II type-2 receptor in R3T3 cells.

Previous studies showed that angiotensin II type-2 receptor (AT2) sites were increased when R3T3 cells were growth arrested and decreased when they were stimulated with fibroblast growth factor or serum. We examined the effects of several other growth factors on the expression of AT2 mRNA to clarify the relation between the AT2 receptor and growth factors. R3T3 cells were cultured in the medium containing 10% FCS until they were confluent and then serum was removed. AT2 mRNA was increased after serum was depleted, and the expression level reached a plateau after 2 days of serum depletion. The presence of serum (10%), fibroblast growth factor (10 ng/mL), or lysophosphatidic acid (1 mumol/L) reduced the AT2 mRNA expression. Phorbol ester (1 to 100 nmol/L) also suppressed the AT2 mRNA expression in a dose-dependent manner. Interleukin-1 beta (1 ng/mL) enhanced the AT2 mRNA expression 1.6-fold and the AT2 receptor number 1.4-fold. Insulin (100 nmol/L) enhanced AT2 mRNA expression 1.4-fold and the AT2 receptor number 1.6-fold. These results suggest that AT2 mRNA expression is modulated by multiple growth factors in both positive and negative directions. The presence of potential cis DNA elements that respond to interleukin-1 beta (CCAAT enhancer binding protein site), insulin [insulin response sequence of phospho(enol)pyruvate carboxykinase gene], and phorbol ester (AP-1 site) in the promoter region of the mouse AT2 gene suggests that the effects of these growth factors and phorbol ester may be mediated via these cis DNA elements.