PROMOTER SELECTIVE TRANSCRIPTIONAL SYNERGY MEDIATED BY STEROL REGULATORY ELEMENT-BINDING PROTEIN AND SP1 - A CRITICAL ROLE FOR THE BTD DOMAIN OF SP1

Cellular cholesterol and fatty acid levels : are coordinately regulate d by a family of transcriptional regulatory proteins designated sterol regulatory element binding proteins (SREBPs). SREBP-dependent transcr iptional activation from all promoters examined thus far is dependent on the presence of an additional binding site for a ubiquitous coactiv ator, In the low-density lipoprotein (LDL) receptor, acetyl coenzyme A carboxylase (ACC), and fatty acid synthase (FAS) promoters, which are all regulated by SREBP, the coactivator is the transcription factor S pl, In this report, we demonstrate that Sp3, another member of the Spl family, is capable of substituting for Spl in coactivating transcript ion from all three of these promoters, Results of an earlier study sho wed that efficient activation of transcription from the LDL receptor p romoter required domain C of Spl; however, this domain is not crucial for activation of the simian virus 40 promoter, where synergistic acti vation occurs through multiple Spl binding sites and does not require SREBP, Also in the present report, we further localize the critical de terminant of the C domain required for activation of the LDL receptor to a small region that is highly conserved between Spl and Sp3. This c rucial domain encompasses the buttonhead box, which is a 10-amino-acid stretch that is present in several Spl family members, including the Drosophila buttonhead gene product, Interestingly, neither the buttonh ead box nor the entire C domain is required for the activation of the FAS and ACC promoters even though both SREBP and Spl are critical play ers. ACC and FAS each contain two critical SREBP sites, whereas there is only one in the LDL receptor promoter, This finding suggested that buttonhead-dependent activation by SREBP and Spl may be limited to pro moters that naturally contain a single SREBP recognition site, Consist ent with this model, a synthetic construct containing three tandem cop ies of the native LDL receptor SREBP site linked to a single Spl site was also significantly activated in a buttonhead-independent fashion. Taken together, these studies indicate that transcriptional activation through the concerted action of SREBP and Spl can occur by at least t wo different mechanisms, and promoters that are activated by each one can potentially be identified by the number of critical SREBP binding sites that they contain.