TRANSCRIPTIONAL ACTIVATION OF THE STEAROYL-COA DESATURASE-2 GENE BY STEROL REGULATORY ELEMENT-BINDING PROTEIN ADIPOCYTE DETERMINATION AND DIFFERENTIATION FACTOR-1/

To identify genes that are transcriptionally activated by sterol regul atory element-binding proteins (SREBPs), we utilized mRNA differential display and mutant cells that express either high car low levels of t ranscriptionally active SREBP. This approach identified stearoyl-CoA d esaturase 2 (SCD2) as a new SREBP-regulated gene. Cells were transient ly transfected with reporter genes blinder the control of different fr agments of the mouse SCD2 promoter. Constructs containing >199 base pa irs of the SCD2 proximal promoter were activated following incubation of cells in sterol-depleted medium or as a result of co-expression of SREBP-1a, SREBP-2, or rat adipocyte determination and differentiation factor 1 (ADD1). Electromobility shift assays and DNase I footprint an alysis demonstrated that recombinant SREBP-1a hound to a novel cis ele ment (5'-AGCAGATTGTG-3') in the proximal promoter of the SCD2 gene. Th e finding that the endogenous SCD2 mRNA Bevels were induced when wild- type Chinese hamster ovary fibroblasts were incubated in sterol-defici ent medium is consistent with a role for SREBP in regulating transcrip tion of the gene. These studies identify SCD2 as a new member of the f amily of genes that are transcriptionally regulated in response to cha nging levels of nuclear SREBP/ADD1. In addition, the sterol regulatory element in the SCD2 promoter is distinct from all previously characte rized motifs that confer SREBP- and ADD1-dependent transcriptional act ivation.