Modulation of cGMP by human HO-1 retrovirus gene transfer in pulmonary microvessel endothelial cells

Carbon monoxide (CO) stimulates guanylate cyclase (GC) and increases guanosine 3', 5'-cyclic monophosphate (cGMP) levels. We transfected rat-lung pulmonary endothelial cells with a retrovirus-mediated human heme oxygenase (hHO)-i gene. Pulmonary cells that expressed hHO-1 exhibited a fourfold increase in HO activity associated with decreases in the steady-state levels of heme and cGMP without changes in soluble GC (sGC) and endothelial nitric oxide synthase (NOS) proteins or basal nitrite production. Heme elicited significant increases in CO production and intracellular cGMP levels in both pulmonary endothelial and pulmonary hHO-1-expressing cells. [[N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOS, significantly decreased cGMP levels in heine-treated pulmonary endothelial cells but not heme-treated hHO-1-expressing cells. In the presence of exogenous heine, CO and cGMP levels in hHO-1-expressing cells exceeded the corresponding levels in pulmonary endothelial cells. Acute exposure of endothelial cells to Sn[Cl.sub.2], which is an inducer of HO-1, increased cGMP levels, whereas chronic exposure decreased heine and cGMP levels. These results indicate that prolonged overexpression of HO-1 ultimately decreases sGC activity by limiting the availability of cellular heine. Heme activates sGC and enhances cGMP levels via a mechanism that is largely insensitive to NOS inhibition. guanosine 3',5'-cyclic monophosphate; retroviral vector; soluble guanylate cyclase; heine oxygenase