Nuclear protein that binds sterol regulatory element of low density lipoprotein receptor promoter. I. Identification of the protein and delineation of its target nucleotide sequence

The current paper reports the identification of a protein in rat liver nuclei that binds to the sterol regulatory element (SRE-1) in the promoter of the gene for the low density lipoprotein receptor. The 10-base pair SRE-1 is embedded within a 16-base pair sequence designated Repeat 2 located immediately upstream of a related sequence designated Repeat 3. To confirm that DNA recognition by the SRE-1 binding protein (SREBP) correlates with sterol-regulated transcription, we synthesized an artificial promoter that contains two copies of wild-type or mutant Repeat 2 + 3 sequences immediately upstream of a TATA box from adenovirus. The synthetic promoters were inserted upstream of a reporter gene and tested for transcriptional activity in the absence and presence of sterols after transient transfection into monkey CV-1 cells. The reporter gene with two copies of the wild-type Repeat 2 + 3 sequence was transcribed actively in sterol-deprived cells and was repressed by more than 80% when sterols were present. Binding of SREBP to the SRE-1 sequence, assessed by gel mobility shift assays, correlated precisely on a nucleotide-by-nucleotide basis with the transcriptional activity of each of 16 synthetic promoters with point mutations in Repeat 2. The SREBP bound to the nine mutant promoters that were positive for sterol-regulated transcription, and it did not bind to any of the nine point mutants that abolished transcription. We conclude that SREBP is a DNA binding protein that mediates sterol-regulated transcription of the low density lipoprotein receptor gene.