Molecular cloning and expression of cDNAs coding for soluble guanylate cyclase from rat lung

Complementary DNA clones corresponding to the 70- and 82-kDa subunits of soluble guanylate cyclase of rat lung have been isolated. Blot hybridization of total poly(A)+ RNA from rat tissues detected mRNA of about 3.4 kilobases for the 70-kDa subunit and about 5.5 kilobases for the 82-kDa subunit. Messenger RNA levels of both subunits were abundant in lung and cerebrum, moderate in cerebellum, heart, and kidney, and low in liver and muscle, consistent with previously described enzyme activities in these tissues. Southern blot analysis of high molecular weight genomic DNA from rat liver indicated that the genes for the 70- and 82-kDa subunits are different. The carboxyl-terminal region of the 70- and 82-kDa subunits showed a high degree of homology and also had a partial homology with the putative catalytic domain of particulate guanylate cyclase and adenylate cyclase, indicating that both the 70- and 82-kDa subunits have catalytic domains. The cDNAs were subcloned to an expression vector and transfected to L cells. The cells transfected with cDNA of the 70-kDa subunit or the 82-kDa subunit showed no guanylate cyclase activity, whereas the cells transfected with both the 70- and 82-kDa subunit cDNAs showed significant guanylate cyclase activity that was activated markedly by sodium nitroprusside. These data suggest that both subunits are required for both the basal catalytic and regulatory activity of soluble guanylate cyclase. Presumably both catalytic subunits must be present and interactive to permit synthesis of cyclic GMP and nitrovasodilator activation.