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Transcriptional derepression of the murine Cyp1a‐1 gene by mevinolin
Author(s) -
Puga Alvaro,
Raychaudhurl Baisakhi,
Nebert Daniel W.
Publication year - 1992
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.6.2.1311272
Subject(s) - derepression , gene , microbiology and biotechnology , biology , genetics , gene expression , psychological repression
In mouse hepatoma Hepa‐1c1c7 cultures, polycyclic aromatic compounds such as benzol[a]pyrene and 2,3,7,8‐tetrachlorodibenzo‐ p ‐dioxin (TCDD; dioxin) activate the Cyp1a‐1 (cytochrome P 1 450) and Nmo‐1 [NAD(P)H:menadione oxidoreductase] genes, two members of the aromatic hydrocarbon (Ah)‐responsive gene battery. Mevinolin is known to inhibit 3‐hydroxy‐3‐methylglutaryl CoA (HMG‐CoA) reductase (EC 1.1.1.34), the rate‐limiting step in cholesterol biosynthesis. We show here that in the absence of TCDD, mevinolin markedly increases Cyp1a‐1 transcription, CYP1A1 mRNA and protein levels and enzyme activity, and NMO1 mRNA concentrations. Addition of mevalonate, the product of HMG‐CoA reductase activity, fails to reverse the effects of mevinolin. In fact, when used at high concentrations, mevalonate activates Cyp1a‐1 transcription. Mevinolin‐induced Cyp1a‐1 gene activation: ( 1 ) occurs independently of the lipid content of the growth medium, ( 2 ) is not suppressed by adding 25‐hydroxycholesterol, which blocks MHG‐CoA reductase activity, and ( 3 ) requires a functional Ah receptor and unimpaired nuclear translocation of the receptor. It is possible that an unknown metabolite (or metabolites) of mevinolin activates Cyp1a‐1 expression and that high concentrations of mevalonate act via the same mechanism. Using chimaeric plasmids that contain different lengths of Cyp1a‐1 5′ flanking regions fused to the bacterial neomycin (neo) gene, we find that the mevinolin effect on Cyp1a‐1 induction requires the 5′ flanking sequences between ‐1647 and ‐824, which are also needed for TCDD induction. Mevinolin, however, is not a ligand for the Ah receptor. Gel mobility shift assays revealed that Cyp1a‐1 activation caused by mevinolin does not involve the ligand‐dependent formation of a functional Ah receptor‐dependent DNA‐binding complex, but instead appears to be correlated with release of a putative repressor from its cognate DNA site. Our results suggest that the basel level of Cyp1a‐1 transcription is maintained by an unknown negative regulatory factor. We propose that Cyp1a‐1 transcriptional activation can result not only from induction by polycyclic aromatic compounds but also from derepression by mevinolin, independent of HMG‐CoA reductase inhibition.—Puga, A.; Ray‐Chaudhuri, B.; Nebert, D. W. Transcriptional derepression of the murine Cyp1a‐1 gene by mevinolin. FASEB J. 6: 777‐785; 1992.