Isolation and characterization of rat CYP11B genes involved in late steps of mineralo- and glucocorticoid syntheses.

We isolated and characterized four forms of rat CYP11B genes, which were tentatively named CYP11B1, -B2, -B3, and -B4. Genomic Southern analyses indicated that the members of the rat CYP11B gene subfamily were confined to these four genes; among them, CYP11B1 and -B2 encoded steroid 11 beta-hydroxylase and aldosterone synthase, respectively, while CYP11B3 was a gene highly homologous to CYP11B1 without a known expression product. By being devoid of a region spanning two exons conserved in the other three, CYP11B4 was presumably a pseudogene. In the nucleotide sequences, CYP11B1, -B3, and -B4 showed 95-96 and 93-100% identities in the coding and 0.5-kilobase 5'-flanking regions, respectively. However, the homology between the nucleotide sequences of one of the three and CYP11B2 was rather low, about 90 and 50% in the coding and 0.5-kilobase 5'-flanking regions, respectively. As a whole, CYP11B2 rather than CYP11B1, -B3, or -B4 was more homologous to CYP11B genes of other animals such as cow and human. In transient transfection experiments using mouse adrenocortical Y1 cells and chloramphenicol acetyltransferase gene constructs, the 0.5-kilobase 5'-flanking region of CYP11B1 had a 4- and 10-fold higher promoter activity than the corresponding regions of CYP11B2 and -B3, respectively. The possible presence of a suppressive element(s) was noted in the upstream of the 0.5-kilobase region of CYP11B1. Although a variant of cAMP-responsive element, which was present in rat CYP11B2 and all known CYP11B genes of other animals, was modified in rat CYP11B1 and -B3 genes, dibutyryl cAMP stimulated all the promoter activities of the 5'-flanking regions of the rat genes by 3-fold.