Angiotensin type 1 receptor is linked to inhibition of nitric oxide production in pulmonary endothelial cells

We previously demonstrated that angiotensin II (Ang II) stimulates an increase in nitric oxide synthase (NOS) mRNA levels, eNOS protein expression and NO production via the type 2 (AT2) receptor, whereas signaling via the type 1 (AT1) receptor negatively regulates NO production in bovine pulmonary artery endothelial cells (BPAECs). In the present study, we investigated the components of the AT1 receptor-linked signaling pathway(s) that are involved in the downregulation of eNOS protein expression in BPAECs. Treatment of BPAECs with either AT1 receptor antagonists or an anti-AT1 receptor antibody induced eNOS protein expression. Furthermore, intracellular delivery of GP-Antagonist-2A, an inhibitor of Gαq proteins, and treatment of BPAECs with U73122, a phosphatidylinositol-phospholipase C (PLC)-specific inhibitor, enhanced eNOS protein expression. Treatment of BPAECs with the cell-permeable calcium chelator, BAPTA/AM, increased eNOS protein expression at 8 h, while increasing intracellular calcium with either thapsigargin or A23187 prevented Ang II-induced eNOS protein expression. Phorbol myristate acetate (PMA), a protein kinase C (PKC) activator, completely prevented Ang II-stimulated eNOS protein expression at 8 h, whereas depletion of PKC by long-term treatment with PMA, induced eNOS protein expression. Treatment of BPAECs with a PKCα-specific inhibitor or transfection of BPAECs with an anti-PKCα neutralizing antibody stimulated eNOS protein expression. Conversely, rottlerin, a PKCδ specific isoform inhibitor had no effect on basal or Ang II-stimulated eNOS protein expression. Moreover, treatment of BPAECs with U73122, BAPTA/AM and PKCα-specific inhibitors increased NO production at 8 h. In conclusion, Ang II downregulates eNOS protein expression via an AT1 receptor-linked pathway involving Gαq/PLC/calcium/PKCα signaling pathway in BPAECs.