IDENTIFICATION OF GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE AS AN ADIPOCYTE DETERMINATION AND DIFFERENTIATION FACTOR-1- AND STEROL REGULATORY ELEMENT-BINDING PROTEIN-RESPONSIVE GENE

We demonstrate that the mRNA levels of glycerol-3-phosphate acyltransf erase (GPAT), a mitochondrial enzyme catalyzing the initial step in gl ycerolipid synthesis, are induced during the differentiation of 3T3-L1 preadipocytes to adipocytes and following ectopic expression of rat a dipocyte determination and differentiation factor 1 (ADD1), a protein with high homology to the human sterol regulatory element-binding prot ein-1 (SREBP-1), The increase in GPAT mRNA levels that occurs during d ifferentiation is partially prevented by ectopic expression of a domin ant negative form of ADD1. Nucleotide sequences corresponding to the p roximal promoter of the murine mitochondrial GPAT gene (Jerkins, A. A. , Liu, W. R., Lee, S., and Sul, H. S. (1995) J. Biol. Chem, 270, 1416- 1421) bound SREBP-1a and NF-Y in electromobility shift assays, In addi tion, GPAT promoter-luciferase reporter genes were stimulated by co ex pression of SREBP-1a, This increase was attenuated when either a domin ant negative form of NF-Y was cotransfected into the cells or when the GPAT promoter contained mutations in the putative binding sites for S REBP-1a or NF-Y, These studies demonstrate that the regulated expressi on of the mitochondrial GPAT gene requires both NF-Y and ADD1/SREBPs. Thus, SREBPs/ADD1 regulate not only genes involved in cholesterol home ostasis and fatty acid synthesis but also a key enzyme in glycerolipid synthesis.