Receptor-mediated gene delivery approach demonstrates the role of 5'-proximal DNA region in conferring phenobarbitone responsiveness to CYP2B2 gene in rat liver in vivo

The phenobarbitone (PB) responsiveness of the 5'-proximal region of the CYP2B1/B2 gene was examined in detail with plasmid DNA constructs containing G-free cassette as reporter, using in vivo targeting of the same DNA constructs into rat liver as galactosylated-polylysine complexes. The contribution of the proximal region (-1 to -179 bp) and the positive element (-69 to -98 bp) identified earlier in this laboratory to PB responsiveness was assessed. The results obtained on PB treatment of rats subjected to receptor-mediated gene delivery to liver were conclusive and dramatic, with the control (saline-treated) rats manifesting very little expression of the reporter, reflecting the in vivo picture of CYP2B1/B2 gene expression. The positive element conferred PB responsiveness to homologous and heterologous promoters. Deletion of the positive element led to elimination of PB response. The entire -179 bp region was significantly more effective in responding to PB treatment than the region up to -98 bp, both containing one copy of the positive element. Thus, the positive element and its flanking sequences in the 5'-proximal region are involved in conferring PB responsiveness to the CYP2B1/B2 gene.     

Two distinct areas of unequal crossingover within the steroid 21-hydroxylase genes produce absence of CYP21B

We mapped crossover sites in chimeric, recombinant CYP21 genes from six patients with salt-losing congenital adrenal hyperplasia (CAH). Nucleotide sequences unique to the CYP21A pseudogene or to the active CYP21B gene were mapped using gene-specific restriction sites and oligonucleotide hybridizations. Each chimeric CYP21 gene in the CYP21-deletion linked haplotypes contained sequences near the 5' end that were characteristic of CYP21A and only a single transition from sequences of CYP21A to those of CYP21B at the 3' end. The transitions all occurred within either of two discrete regions (+470 to +999 and +1375 to +1993). All eight chimeric CYP21 genes coupled with HLA-Bw47 in five unrelated patients had the CYP21A-CYP21B sequence transition within the same gene region (+1375 to +1993). One of the three other "CYP21B deletion" haplotypes (HLA-B7) had a sequence transition within this same region, while in the other two haplotypes (HLA-B61 and HLA-B18) the transition occurred between base pairs +470 and +999. By contrast, both CYP21 genes in a haplotype containing a gene conversion of CYP21B to CYP21A contained apparent transitions between sequences of CYP21A and CYP21B. We conclude that a single, unequal crossingover between the CYP21A and the CYP21B genes yields deletion of the active CYP21 gene and salt-losing CAH and that these crossingovers do not occur randomly within the CYP21 genes of our patients.