Abstract
Previously, we demonstrated that protein–DNA interactions at the drug response element (DRE) in the human apoA-I promoter were important for the induction of apoA-I gene expression by gemfibrozil. We now report the cloning and characterization of a DRE transactivating factor. The cloned protein is identical to the putative helicase and potential transcription factor human S mu binding protein-2 (HSμBP2). It is also related to glial factor-1 (GF1), an incomplete version of HSμBP2 lacking the first 494 and the last 128 amino acids. Gel mobility shift assays demonstrated that HSμBP2 binds apoA-I DRE oligomers and forms a specific protein–DNA complex. Northern blot analysis showed that HSμBP2 mRNA is expressed at various levels in a wide range of human tissues. Transient cotransfection experiments performed in HepG2 cells demonstrated that overexpression of HSμBP2 or GF1 induced apoA-I proximal promoter activity by 3-fold and that the apoA-I DRE was necessary for transactivation. Additionally, we demonstrated that transactivation was increased a further 2- to 3-fold by exposing the cells to gemfibrozil. Together these observations indicate that HSμBP2 acts as a transcription factor that regulates apoA-I gene expression in hepatoma cells and whose activity may be stimulated by gemfibrozil treatment.—Mohan, W. S., Z-Q. Chen, X. Zhang, K. Khalili, T. Honjo, R. G. Deeley, and S-P. Tam. Human S mu binding protein-2 binds to the drug response element and transactivates the human apoA-I promoter: role of gemfibrozil.
Highlights
We demonstrated that protein–DNA interactions at the drug response element (DRE) in the human Apolipoprotein A-I (apoA-I) promoter were important for the induction of apoA-I gene expression by gemfibrozil
We have shown that modulation of apoA-I gene expression by gemfibrozil in hepatoma cells is mediated through interaction of drug-induced nuclear factors with a cis-acting element, termed the drug response element or DRE [22]
Oligonucleotide apoA-I DRE, 5Ј-GGTGGCCGGGG CTGGGCTTATCAGCCTCCCAGCCCAGACC-3Ј corresponding to the nucleotides between nucleotides Ϫ77 and Ϫ45 of the human apoA-I gene [11, 12]; oligonucleotide xenobiotic response element (XRE), 5Ј-AGT GCTGTCACGCTAG-3Ј corresponding to nucleotides between Ϫ1092 and Ϫ1078 of the rat cytochrome P450 1A1 (CYP1A1) gene [27]; oligonucleotide CYP1A1 DRE, 5Ј-CACAGGG GCTGGGGAG-3Ј corresponding to nucleotides between Ϫ3422 to Ϫ3406 of the rat CYP1A1 gene [23]; oligonucleotide AP1, 5Ј-CCAGTCACAGTGACTCAGCA GAATCT-3Ј corresponding to nucleotides between Ϫ471 and Ϫ446 of the human NAD(P)H:quinone oxidoreductase gene [28]; oligonucleotide mutant apoA-I DRE (m-apoA-I DRE), 5Ј-GGAATTTTAGTTATTACTAGC CTAAATAAAGACCC-3Ј; in which the consensus DRE sequence was replaced (G → T, C → A, T → G, and A → C)
Summary
We demonstrated that protein–DNA interactions at the drug response element (DRE) in the human apoA-I promoter were important for the induction of apoA-I gene expression by gemfibrozil. Transient cotransfection experiments performed in HepG2 cells demonstrated that overexpression of HSBP2 or GF1 induced apoA-I proximal promoter activity by 3-fold and that the apoA-I DRE was necessary for transactivation. We demonstrated that transactivation was increased a further 2- to 3-fold by exposing the cells to gemfibrozil. Together these observations indicate that HSBP2 acts as a transcription factor that regulates apoA-I gene expression in hepatoma cells and whose activity may be stimulated by gemfibrozil treatment.—Mohan, W.
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