Regulation of type II nitric oxide synthase (NOS) expression by hypoxia

The regulation of Type II NOS expression in response to hypoxia was examined in bovine pulmonary endothelial cells. Transfection analysis, using a plasmid containing the 5' flanking region of the Type II NOS gene linked to the reporter gene chloramphenicol acetyl transferase, demonstrated a three fold increase in expression in response to hypoxia compared to the normoxic controls. These results are consistent with data from our laboratory showing an increased expression of Type II NOS in the lung in a rat model of pulmonary hypertension induced by chronic hypoxia. The 5' flanking region of the Type II NOS gene contains a region with 100% homology to the hypoxia-inducible factor 1 (HIF-1) binding site in the enhancer that is required for hypoxic regulation of the human erythropoietin gene. Northern analysis of RNA isolated from the lungs of rats exposed to hypoxia for 3 weeks and from bovine pulmonary endothelial cells exposed to hypoxia for 48 hours revealed increased expression of both HIF-la and HIF-lp. These results, taken together, suggest a possible role for HIF-1 in the hypoxic regulation of Type II NOS gene transcription. This work is supported by NIH Grants RO1-HL-39706 and RO1-GM-49111.