Transcriptional regulation of the ATP citrate-lyase gene by sterol regulatory element-binding proteins

In an attempt to identify unknown target genes for SREBP-1, total RNA from a stable Chinese hamster ovary cell line (CHO-487) expressing a mature form of human SREBP-1a (amino acids 1-487) with a LacSwitch Inducible Mammalian Expression System was subjected to a polymerase chain reaction subtraction method. One of the fragments was found to have 90 and 86% homology with ra t and human ATP citrate-lyase (ACL) cDNA, respectively. When Hep G2 cells a re cultured under either sterol-loaded or -depleted conditions, expression of the gene is induced approximately 2-3-fold by sterol depletion. To inves tigate the direct effect of SREBP-1a on transcription, luciferase assays us ing the promoter of the human ACL gene were performed. These deletion studi es indicated that a minimum 160-base pair segment contains the information required for the transcriptional regulation brought about by enforced expre ssion of SREBP-1a. Luciferase assays using mutant reporter genes revealed t hat SREBP-dependent transcriptional regulation is mediated by two nearby mo tifs, the SREBP-binding site (a TCAGGCTAG sequence) and the NF-Y-binding si te (a CCAAT box). It was confirmed by gel mobility shift assays that recomb int SREBP-1a binds to the sequence. Data from studies with transgenic mice and reporter assays show that the ACL gene promoter is activated by SREBP-1 a more strongly than SREBP-2 in contrast to the HMG CoA synthase and LDL re ceptor gene promoters, which exhibit the same preference for the two factor s. Therefore, SREBPs transcriptionally regulates ACL enzyme activity, which generates the cytosolic acetyl CoA required for both cholesterol and fatty acid synthesis.