Elia, Andrew Panayioti; (1996) Tissue specific regulation of CYP2B gene expression. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Phenobarbital (PB) and picrotoxin increased the expression of both CYP2B1 and CYP2B2 genes in the rat liver. Using western blotting and RNase protection assays it was shown that both compounds increased only CYP2B1 in the small intestine. Gel retardation assays using nuclear extracts from the liver and small intestine and the region -183 to -199 of the CYP2B2 gene promoter revealed that this DNA sequence binds a protein only from liver extracts and hence is probably involved in the tissue-specific expression of the CYP2B2 gene. The abundance or activity of this transcription factor was increased in liver nuclear extracts by both PB and picrotoxin. The CYP2B1 gene promoter was cloned. Gel retardation assays using fragments of the CYP2B1 gene promoter were used to compare: 1) the effect of PB and picrotoxin treatments on the abundance of DNA-protein complexes. 2) to compare the DNA-protein complexes formed with liver and small intestinal samples from both treated and untreated animals. A C/EBP binding site was located within the region -2 to -178. Supershift assays indicate that both C/EBPα and C/EBPδ bind to this region of the CYP2B1 promoter. In the region -179 to -347 a DNA-protein complex that was of greater abundance with liver extracts from PB-treated animals was identified. Two DNA-protein complexes were identified in the region -348 to -451 that were of greater abundance with extracts from the livers of untreated animals. Distinct tissue-specific patterns of DNA-protein complexes were observed. GST subunit 7 and the transcription factor HNF-4 were found also to be induced by PB and picrotoxin in the small intestine, whereas cytochrome P450 reductase, cytochrome b5 and cytochrome b5 reductase are expressed but not induced by these chemicals in the small intestine.

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