Nutrient regulation of gene expression by the sterol regulatory element binding proteins: Increased recruitment of gene-specific coregulatory factorsand selective hyperacetylation of histone H3 in vivo

We have evaluated the mechanism for sterol-regulated gene expression by the sterol regulatory element binding proteins (SREBPs) in intact cells. We sh ow that activation of SREBPs by sterol depletion results in the increased b inding of Sp1 to a site adjacent to SREBP in the promoter for the low densi ty lipoprotein (LDL) receptor gene in vivo. Similarly, sterol depletion res ulted in the increased recruitment of two distinct SREBP coregulatory facto rs, NF-Y and CREB, to the promoter for hydroxymethyl glutaryl CoA reductase , another key gene of intracellular cholesterol homeostasis. Furthermore, i ncreased acetylation of histone H3 but not H4 was also detected in chromati n from both promoters on SREBP activation, Thus, SREBP activation results i n the similar selective recruitment of different coregulatory generic trans cription factors to two separate cholesterol-regulated promoters. These stu dies demonstrate the utility of the chromatin immunoprecipitation technique for analyzing the differential action of low-abundance transcription facto rs in fundamental regulatory events in intact cells. Our results also provi de key in vivo support for the mechanism proposed from cell-free experiment s, where SREBP increased the binding of Spl to the LDL receptor promoter. F inally, our findings also indicate that subtle differences in the pattern o f core histone acetylation play a role in selective gene activation.