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

Abstract

We have evaluated the mechanism for sterol-regulated gene expression by the sterol regulatory element binding proteins (SREBPs) in intact cells. We show that activation of SREBPs by sterol depletion results in the increased binding of Sp1 to a site adjacent to SREBP in the promoter for the low density lipoprotein (LDL) receptor gene in vivo. Similarly, sterol depletion resulted in the increased recruitment of two distinct SREBP coregulatory factors, NF-Y and CREB, to the promoter for hydroxymethyl glutaryl CoA reductase, another key gene of intracellular cholesterol homeostasis. Furthermore, increased acetylation of histone H3 but not H4 was also detected in chromatin from both promoters on SREBP activation. Thus, SREBP activation results in the similar selective recruitment of different coregulatory generic transcription factors to two separate cholesterol-regulated promoters. These studies demonstrate the utility of the chromatin immunoprecipitation technique for analyzing the differential action of low-abundance transcription factors in fundamental regulatory events in intact cells. Our results also provide key in vivo support for the mechanism proposed from cell-free experiments, where SREBP increased the binding of Sp1 to the LDL receptor promoter. Finally, our findings also indicate that subtle differences in the pattern of core histone acetylation play a role in selective gene activation. F eedback regulation of mammalian cholesterol homeostasis is mediated by a positive regulatory mechanism through the sterol regulatory element binding proteins (SREBPs) (1). The SREBPs also regulate key genes of fatty acid metabolism so they control flux into the two major lipid classes in mammalian cells (1, 2). When sterol levels fall in cultured cells, the SREBPs are released from membranes of the endoplasmic reticulum and nuclear envelope through the action of two sequential proteolytic activities (3). The resulting soluble mature transcription factor enters the nucleus, where it activates a set of target genes that are involved in lipid accumulation.In all promoters for SREBP target genes that have been carefully studied thus far, SREBP-dependent regulation requires an additional generic coregulatory DNA binding factor(s) for efficient expression (4). The identity of the coregulatory factor and the position of its binding site relative to the binding site(s) for the SREBPs differs from promoter to promoter. The common use of SREBP provides a mechanism for coordinate regulation. However, the unique coregulatory factors and subtle differences in promoter architecture provide the opportunity for more subtle promoter-specific regulatory effects that integrate other cellular signaling pathways with simple nutrient sensing to provide optimal control of cellular lipid levels.To understand the mechanism for coordinate and genespecific activation by the SREBPs, we have been investigating how they function to activate transcription synergistically with distinct coregulatory factors in different promoters. The gene that encode...

Cholesterol supply and SREBPs modulate transcription of the Niemann-Pick C-1 gene in steroidogenic tissues

“…A study of HMG-CoA reductase and LDL receptor transcription in the cholesterol depletion paradigm demonstrated that SREBP activation was accompanied by an increased association of both promoters with acetylated histone H3 (23). In the present investigation, the association of the NPC-1 promoter with acetylated H3 was augmented in cells depleted of cholesterol, further supporting the concept of nutrient regulation of the NPC-1 gene.…”

“…PCR amplification of a sequence of similar size from the coding region of the NPC-1 gene indicated that the response was specific to the promoter region. It was shown previously that SREBP activation of two sterol-sensitive genes, those encoding the LDL receptor and HMG-CoA reductase, engenders a promoterassociated increase in histone H3 acetylation (23). To establish the presence of a similar regulation of NPC-1 expression, extracts of primary porcine granulosa cells cultured in cholesterol-replete or -depleted medium were immunoprecipitated with antiserum specific to H3 acetylated on lysine residues 9 and 14.…”

Phorbol ester promotes histone H3-Ser10 phosphorylation at the LDL receptor promoter in a protein kinase C-dependent manner

“…Similar to our results, inducible histone H3-Ser10 phosphorylation, without any changes in histone H3 acetylation, has recently been linked to the induction of retinoic acid receptor expression by retinoids (16). Although increased histone H3 acetylation has been shown earlier at the LDL receptor chromatin in response to depletion of sterols (32), the role of this modification in the induction process was not studied. Another point that should be noted is that Tjian and colleagues (33) earlier demonstrated that CREB-binding protein-associated histone acetyltransferase activity is not critical for the synergistic activation of the LDL receptor promoter by sterol-regulatory element binding protein-1a/Sp1 on chromatin templates, which argues against the involvement of histone acetylation in the induction process.…”

Targeting the Y/CCAAT box in cancer: YB-1 (YBX1) or NF-Y?

“…80 Co-transfections of the NF-Y trimer with TFs binding the loci neighboring CCAAT boxes in mammalian and Drosophila cells synergistically activate transcription of CCAAT promoters. 52,81,82 Finally, transfections of recombinant proteins in which NF-YA was linked to a cell-penetrating TAT peptide activate endogenous CCAAT genes but not CCAAT-less units. 83,84 All these features are quite standard for TFs: sequence specificity, modularity of DBD and TA, and synergistic activation with neighboring TFs.…”