A critical role for cAMP response element-binding protein (CREB) as a co-activator in sterol-regulated transcription of 3-hydroxy-3-methylglutaryl coenzyme A synthase promoter

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase, a key regulatory enzyme in the pathway for endogenous cholesterol synthesis, is a target for negative feedback regulation by cholesterol, When cellular sterol levels a re low, the sterol regulatory element-binding proteins (SREBPs) are release d from the endoplasmic reticulum membrane, allowing them to translocate to the nucleus and activate SREBP target genes. However, in all SREBP-regulate d promoters studied to date, additional co-regulatory transcription factors are required for sterol-regulated activation of transcription. We have pre viously shown that, in addition to SREBPs, NF-Y/CBF is required for sterol- regulated transcription of HMG-CoA synthase, This heterotrimeric transcript ion factor has recently been shown to function as a co-regulator in several other SREBP-regulated promoters, as well. In addition to cis-acting sites for both SREBP and NF-Y/CBF, the sterol regulatory region of the synthase p romoter also contains a consensus cAMP response element (CRE), an element t hat binds members of the CREB/ATF family of transcription factors. Here, we show that this consensus CRE is essential for sterol-regulated transcripti on of the synthase promoter. Using in vitro binding assays, we also demonst rate that CREB binds to this CRE, and mutations within the CRE that result in a loss of CREB binding also result in a loss of sterol-regulated transcr iption. We further show that efficient activation of the synthase promoter in Drosophila SL2 cells requires the simultaneous expression of all three f actors: SREBPs, NF-Y/CBF, and CREB. To date this is the first promoter show n to require CREB for efficient sterol-regulated transcription, and to requ ire two different co-regulatory factors in addition to SREBPs for maximal a ctivation.