SYNERGISTIC ACTIVATION OF TRANSCRIPTION BY NUCLEAR FACTOR-Y AND STEROL REGULATORY ELEMENT-BINDING PROTEIN

The cur-rent studies define the role of three distinct cis-elements in the proximal promoter of the rat farnesyl diphosphate (FPP) synthase gene. The three cis-elements, a sterol regulatory element 3 (SRE-3) fl anked by an ATTGG motif (inverted CCAAT box), and a CCAAT box, form a sterol regulatory unit that is necessary and sufficient for sterol-reg ula;ed expression of FPP synthase promoter-reporter genes. FPP synthas e promoter-reporter genes, that contain promoters with either wild-typ e nucleotide sequences or mutations in one or more of the three cis-el ements, were transiently transfected into CV-1 cells. The activity of the wild-type promoter-reporter gene increased when the cells were inc ubated in sterol-depleted media or when the cells were co-transfected with a plasmid encoding the mature form of SRE binding protein (SREBP- 1a). The results with the mutant promoter-reporter genes demonstrated that all three cis-elements were necessary for normal expression/regul ation of the reporter gene by either sterols or by co-expressed SREBP- 1a. Gel mobility shift assays demonstrated that the synergistic bindin g of SREBP-1a to SRE-3 was dependent on the binding of recombinant nuc lear factor Y (NF-Y) to the DNA, consistent with the in vivo regulatio n studies.