Regulation of new genes and pathways that are regulated in response to changing levels of cellular sterols

To identify new genes that are transcriptionally regulated in response to changing levels of sterol regulatory element binding protein (SREBP), we used mRNA differential display and mutanl cells that express either high or low nuclear levels of SREBP. We identified a number of genes including stearoyl CoA desaturase 2 (SCD2), an enzyme involved in the synthesis of unsaturated fatty acids. Detailed studies show that i) transcription of the SCD2 gene is repressed by oxysterols ii) the SCD2 promoter contains a novel binding site for SREBP and iii) coexpression of SREBP results in increased transcription of SCD2 promoter-reporter genes by a process that also requires a second DNA binding protein, NF-Y. We demonstrate that a number of SREBP-regulated genes require the coactivator ('BP for maximal transcription. A 451 amino acid domain of CBP (2441 aa) both interacts with SREBP in vitro and functions as a dominant negative regulator of transcription of SREBP-dependent genes in vivo. We have also identified a protein whose mRNA levels increase > 100-fold when specific oxysterols are added to cells. This induction is likely independent of SREBP. Thus, oxysterols function as signaling molecules that can either inhibit or activate transcription of specific target genes and effect the regulation of diverse metabolic pathways. Grant support:NIH HL 30568.