NF-Y HAS A NOVEL ROLE IN STEROL-DEPENDENT TRANSCRIPTION OF 2 CHOLESTEROGENIC GENES

The transcription of farnesyl diphosphate (FPP) synthase is regulated up to 30-fold by the sterol status of the cell. Point mutations in a 6-base pair ATTGGC sequence in the promoter disrupt both sterol-dependent transcription in vivo as well as binding of the transcription factor NF-Y in vitro. Co-transfection of cells with NF YA29, a dominant negative form of NF-Y, and various promoter-reporter genes specifically inhibits the sterol-dependent regulation of FPP synthase and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase. In contrast, NP-YA29 does not affect the regulation of reporter genes under the control of promoters derived from either the HMG-CoA reductase or the low density lipoprotein receptor gene. Transient expression of the 68 kDa transcriptionally active fragment of sterol regulatory element-binding protein in cells stimulates an HMG-CoA synthase-reporter gene over 90-fold. This induction is blocked in cells eo expressing NF-YA29. We hypothesize that NF-Y plays a novel role in sterol-de pendent regulation of two key genes in the cholesterol biosynthetic pathway and that this role requires a specific interaction with the sterol regulatory element-binding protein or related transcription factors.