ARTIFICIAL MUTATIONS IN P450C11AS (ALDOSTERONE SYNTHASE) CAN INCREASEENZYMATIC-ACTIVITY - A MODEL FOR LOW-RENIN HYPERTENSION

The conversion of 11-deoxycorticosterone (DOC) to aldosterone is catal yzed by a single enzyme, termed P450c11AS, which has 11 beta-hydroxyla se, 18-hydroxylase and 18-oxidase activities. The normotensive Dahl sa lt-resistant (R) rat has two mutation in P450c11AS that increase its a ldosterone synthase activity. If such a mutation were to occur in huma n patients the predicted phenotype would be low-renin hypertension wit h elevated ratios of plasma aldosterone to plasma renin activity. Befo re searching for P450c11AS mutations in such patients we sought to det ermine if mutations in human P450c11AS could increase enzymatic activi ty in a fashion analogous to the Dahl R rat. We used site-directed mut agenesis of the human P450c11AS cDNA to create the mutants Glu 136 --> Asp, Lys 251 --> Arg and the combination of the two; these mutations correspond to those seen in the Dahl R rat. Cells transfected with the se mutant human P450c11AS sequences could convert [C-14]DOC to cortico sterone, 18OH-corticosterone and aldosterone. In particular the Lys 25 1 --> Arg mutant produced 4 times as much 18OH-corticosterone and 50-8 0% more aldosterone than the wild type. These data show that mutations of human P450c11AS can increase enzymatic activity, suggesting that s uch mutations could, in theory, be the basis of some forms of human lo w-renin hypertension.