Cytochrome P-45017alpha (P-45017alpha) is an enzyme that catalyzes a critical reaction in the biosynthesis of androgen, estrogen and glucocorticoid steroid hormones. The expression of the P-45017alpha gene is both tissue specific and hormonally regulated. In adrenal cortical tissue of some species, such as human and cattle, it is constitutively expressed and expression is stimulated by ACTH; constitutively expressed but minimally stimulated by ACTH in the guinea pig; not constitutively expressed but expression stimulated by ACTH in the rabbit; and expressed neither before nor after ACTH stimulation in the rat. It is of interest to determine the structural features that are responsible for the regulation of this gene, and a comparison of the nucleotide sequences of the P- 45017alpha gene from the different species may provide some insight to the reason for these differences. Abnormalities in the activity and/or expression of the P-450xvii gene cause a type of congenital adrenal hyperplasia, which can result in hypertension, hyperkalemia, sexual infantilism and hypospadias. Therefore, the elucidation of the structural elements responsible for control of this P-450xvii gene is of interest from a clinical as well as an academic point of view. the rat is a species in which the P-450xvii gene is apparently not expressed in adrenal tissue, and transcription of the gene is not affected by adrenocorticotropic (ACTH) stimulation, as judged by the lack of 17alpha-hydroxylase activity both before and after ACTH stimulation. A previously isolated and sequenced full-length rat P-45017alpha cDNA clone will be used as a probe in the following experiments. The first experiments will measure p-45017alpha mRNA in rat, rabbit and guinea pig adrenal tissue before and after ACTH stimulation to determine the effect of ACTH on mRNA levels and, presumably, gene expression. Assuming that ACTH will be found to increase P-45017alpha mRNA in rabbits, but not in rats or guinea pigs, P-450xvii clones will be isolated from rat, rabbit and guinea pig genomic libraries. Restriction fragments will be subcloned and screened for those bearing sequences complementary to the 5'-end of the cDNA. DNA sequencing will be performed by the dideoxy chain termination technique of Sanger, as modified to use the bacteriophage T7 DNA polymerase. Sequences of the 5'-non-translated region will be compared with those of bovine and human, which are both normally expressed and stimulated by ACTH.
| Mach, K E; Fevold, H R (1994) Post-transcriptional action of ACTH in the control of P450c17 expression in rabbit adrenal glands. J Steroid Biochem Mol Biol 51:149-56 |
| Fevold, H R; Ivanovitch, J D; Zanger, U M et al. (1993) The sequence of the 5'-end of the rat CYP17 gene, the transcription initiation site and a comparison with the homologous genes of other species. Mol Cell Endocrinol 95:95-100 |
