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|Title:||Transcriptional regulatory elements for basal expression and effects of phenobarbital and dexamethasone onmRNA levels of rabbit CYP2C genes|
|Author(s):||Venepally, Pratap Rao|
|Doctoral Committee Chair(s):||Kemper, Byron W.|
|Department / Program:||Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
Biology, Animal Physiology
|Abstract:||Cytochrome P450 (CYP) genes, expressed in many species, are involved in the oxidative metabolism of many xenobiotis as well as endogenous compounds. Expression of the rabbit CYP2C1 gene is observed only after induction with phenobarbital and is confined to the liver. The CYP2C2 gene is inducible in both liver and kidney. In order to identify the DNA domains involved in the regulation of general as well as hepatic-specific transcription, 5$\sp\prime$-flanking fragments from CYP2C1 (C1) and CYP2C2 (C2) genes were inserted in front of the firefly luciferase reporter gene and analyzed for promoter activity in HepG2 (hepatic) and COS-1 (non-hepatic) cells. Maximum basal expression in HepG2 and COS-1 cells was observed when the constructions contained C1 and C2 gene fragments that extended to $-$2000 and $-$410 bp (base pairs), respectively.
In other studies, effects of dexamethasone and phenobarbital, either separately or in conjunction with each other, on the rabbit CYP2C mRNA levels have been analyzed by dot blot hybridizations. Phenobarbital increased CYP2C1, CYP2C2, and CYP2C4 mRNAs markedly, but had only a slight positive effect on CYP2C3 mRNA levels. Dexamethasone treatment resulted in a 2.5 to 4-fold induction in the mRNA levels of all four. Dexamethasone also induced CYP2C3 mRNA to a greater extent than phenobarbital. The levels of CYPC2 and CYPC3 mRNA obtained from the rabbits treated with both phenobarbital and dexamethasone were not significantly different from those observed in the rabbits treated with either phenobarbital or dexamethasone alone. However, compared to the phenobarbital induction, the simultaneous exposure to both phenobarbital and dexamethasone resulted in an increase in CYP2C4 mRNA and a decrease in CYP2C1 mRNA levels.
In HepG2 cells phenobarbital and phenobarbital-like compounds such as 2-allyl-2-isopropylacetamide (AIA) and 2-propyl-2-isopropylacetamide (PIA) inhibited activity from CYP2C1 promoter by about 60% compared to that observed in untreated control. Treatment with compounds that either activate protein kinase C or elevate intracellular cyclic AMP levels had no effect on the induction of CYP2C1 promoter activity by phenobarbital. (Abstract shortened with permission of author.)
|Rights Information:||Copyright 1992 Venepally, Pratap Rao|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9236615|