The FIRE3-Mediated Sterol Response of the FAS Promoter Requires NF-Y/CBF as a Coactivator

The transcription of the fatty acid synthase (FAS) gene is regulated by the sterol status of the cell via cleavage of the sterol regulatory elementbinding protein (SREBP). When human HepG2 hepatoma cells were cotransfected with an expression plasmid for mature SREBP-1a together with FAS promoter/reporter constructs significant increases in reporter activity were observed. Deletion analysis of the FAS promoter between 151 and 52 relative to the transcription start site pinpoint two ciselements important in sterol regulation of the FAS gene. One element, FIRE3, between 71 and 52 can bind in vitro translated and transcribed SREBP-1a whereas the other element, the inverted CCAAT element ICE( 97/ 92), binds the trimeric transcription factor NFY/CBF as shown with rat liver extract and reconstituted, recombinant NFY. The results clearly show that the coactivator for SREBP-1a in this cell line is NFY. This finding was confirmed by using a dominant negative form of NFYA, NFYAm29, which interferes with the effect of ectopically expressed SREBP-1a on FAS reporter activity.