Angiotensin II Potentiates Vascular Endothelial Growth Factor–Induced Angiogenic Activity in Retinal Microcapillary Endothelial Cells

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Abstract
—Angiotensin II (Ang II) plays a role in the development of many vascular diseases. In the present study, we have investigated the effect of Ang II on vascular endothelial growth factor (VEGF) receptor expression and VEGF-induced angiogenic activity in bovine retinal microcapillary endothelial cells (BRECs). Ang II induced a significant increase of kinase domain–containing receptor/total liver kinase (KDR/Flk-1) mRNA in a time- and dose-dependent manner, with a maximal 4.3±0.8-fold increase after a 4-hour stimulation. Ang II increased the rate of KDR gene transcription by 5.4-fold, whereas the half-life of KDR mRNA was not increased significantly. The increase depended partially on new protein synthesis. The Ang II–induced KDR mRNA increase was inhibited by either [Sar 1 ,Ile 8 ]angiotensin or angiotensin type 1 receptor antagonists but was not significantly altered by angiotensin type 2 receptor antagonists. The PKC inhibitor reduced Ang II–induced KDR mRNA expression by 70±15%. The tyrosine kinase inhibitor reduced the Ang II– and phorbol 12-myristate 13-acetate–induced KDR mRNA increases by 35±8% and 44±26%, respectively. Ang II increased by 3.1-fold the 35 S-labeled KDR/Flk-1 immunoprecipitated by a specific antibody to KDR/Flk-1. Scatchard analysis demonstrated that Ang II induced a significant increase of binding sites without changing binding affinity. Ang II enhanced VEGF-induced cell growth and tube formation. Ang II itself had no effect on cell growth, tube formation, or mRNA levels of VEGF and tms -like tyrosine kinase (Flt-1) in BRECs. These findings suggest that Ang II might potentiate VEGF-induced angiogenic activity through an increase of the VEGF receptor KDR/Flk-1.