THE HUMAN MEDIUM-CHAIN ACYL-COA DEHYDROGENASE GENE PROMOTER CONSISTS OF A COMPLEX ARRANGEMENT OF NUCLEAR RECEPTOR RESPONSE ELEMENTS AND SP1BINDING-SITES

Expression of the gene encoding the mitochondrial fatty acid beta-oxid ation enzyme, medium-chain acyl-CoA dehydrogenase (MCAD), is regulated among tissues during development and in response to alterations in su bstrate availability. To identify and characterize cis-acting MCAD gen e promoter regulatory elements and corresponding transcription factors , DNA-protein binding studies and mammalian cell transfection analyses were performed with human MCAD gene promoter fragments, DNA:protein b inding studies with nuclear protein extracts prepared from hepatoma G2 cells, 3T3 fibroblasts, or Y-1 adrenal tumor cells identified three s equences (nuclear receptor response element 1 or NRRE-1, NRRE-2, and N RRE-3) that bind orphan mem members of the steroid/thyroid nuclear rec eptor superfamily including chicken ovalbumin upstream promoter transc ription factor and steroidogenic factor 1, Sp1 binding sites (A-C) wer e identified in close proximity to each of the NRREs. NRRE-3 conferred cell line-specific transcriptional repression by interacting with chi cken ovalbumin upstream promoter transcription factor or activation vi a steroidogenic factor 1. In contrast, the Sp1 binding site A behaved as a transcriptional activator in all cell lines examined, Ne propose that multiple nuclear receptor transcription factors interact with MCA D gene promoter elements to differentially regulate transcription amon g a variety of cell types.