Angiotensin AT(1) and AT(2) receptors differentially regulate angiopoietin-2 and vascular endothelial growth factor expression and angiogenesis by modulating heparin binding-epidermal growth factor (EGF)-mediated EGF receptor transactivation

Angiotensin II (Ang II)-mediated signals are transmitted via heparin bindin g epidermal growth factor (EGF)-like growth factor (HB-EGF) release followe d by transactivation of EGF receptor (EGFR), Although Ang II and HB-EGF ind uce angiogenesis, their Link to the angiopoietin (Ang)-Tie2 system remains undefined, We tested the effects of Ang II on Ang1, Ang2, or Tie2 expressio n in cardiac microvascular endothelial cells expressing the Ang II receptor s AT(1) and AT(2). Ang II significantly induced Ang2 mRNA accumulations wit hout affecting Ang1 or Tie2 expression, which was inhibited by protein kina se C inhibitors and by intracellular Ca2+ chelating agents. Ang II transact ivated EGFR via AT(1), and inhibition of EGFR abolished the induction of An g2. Ang II caused processing of pro-HB-EGF in a metalloproteinase-dependent manner to stimulate maturation and release of HB-EGF, Neutralizing anti-HB -EGF antibody blocked EGFR phosphorylation by Ang II. Ang II also upregulat ed vascular endothelial growth factor (VEGF) expression in an HB-EGF/EGFR-d ependent manner. AT(2) inhibited AT(1)-mediated Ang2, expression and phosph orylation of EGFR, In an in vivo corneal assay, AT(1) induced angiogenesis in an HB-EGF-dependent manner and enhanced the angiogenic activity of VEGF. Although neither Ang2 nor An,al alone induced angiogenesis, soluble Tie2-F c that binds to angiopoietins attenuated AT(1)-mediated angiogenesis, These findings suggested that (1) Ang II induces Ang2 and VEGF expression withou t affecting Ang1 or Tie2 and (2) AT(1) stimulates processing of pro-HB-EGF by metalloproteinases, and the released HB-EGF transactivates EGFR to induc e angiogenesis via the combined effect of Ang2 and VEGF, whereas AT(2) atte nuates them by blocking EGFR phosphorylation, Thus, Ang II is involved in t he VEGF-Ang-Tie2 system via HB-EGF-mediated EGFR transactivation, and this link should be considerable in pathological conditions in which collateral blood flow is required.