Transcriptional Modulators Affect in Vivo Protein Binding to the Low Density Lipoprotein Receptor and 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase Promoters

Abstract

Treatment of HepG2 cells with known effectors of low density lipoprotein receptor (LDLR) gene expression altered the in vivo pattern of protein-DNA interactions in the promoter. The observed changes are consistent with proteins binding in vivo to the sterol regulatory element (SRE), to Sp1-like sites, as well as to other regions. Protein bound to the SRE in all conditions, but the nature of the dimethyl sulfate reactivity changed depending on the physiological state of the cell. Hypermethylation within the SRE of the low density lipoprotein receptor promoter was observed when cells were treated with cholesterol synthesis inhibitors, insulin, or phorbol 12-myristate 13-acetate, suggesting that the SRE regulates this promoter through sterol-independent as well as sterol-dependent mechanisms. No significant changes were observed in binding to the Sp1-like sites, suggesting that differential binding to these sites does not play a role in altered transcription levels. Analysis of the 3-hydroxy-3-methylglutaryl coenzyme A reductase promoter also revealed protections that varied in a cell type-specific manner. Binding to the 3-hydroxy-3-methylglutaryl coenzyme A reductase SRE and putative nuclear factor 1 sites could be observed but varied little in different physiological conditions.