ISOLATION AND EXPRESSION OF AN ISOFORM OF HUMAN CDP-DIACYLGLYCEROL SYNTHASE CDNA

Phosphatidic acid (PA) is a phospholipid involved in signal transducti on and in glycerolipid biosynthesis. CDP-diacylglycerol synthase (CDS) or CTP:phosphatidate cytidylyltransferase (EC 2.7.7.41) catalyzes the conversion of PA to CDP-diacylglycerol (CDP-DAG), an important precur sor for the synthesis of phosphatidylinositol, phosphatidylglycerol, a nd cardiolipin. We describe in this study the isolation and characteri zation of a human cDNA clone that encodes amino acid sequences homolog ous to Escherichia coil, yeast, and Drosophila CDS sequences. Expressi on of this human cDNA under the control of a GAL1 promoter in a null c ds1 mutant yeast strain complements its growth defect and produces CDS activity when induced with galactose. Transfection of this cDNA into mammalian cells leads to increased CDS activity in cell-free extracts using an in vitro assay that measures the conversion of [alpha-P-32]CT P to [P-32]CDP-DAG. This increase in CDS activity also leads to increa sed secretion of tumor necrosis factor-alpha and interleukin-6 from en dothelial ECV304 cells upon stimulation with interleukin-1 beta, sugge sting that CDS overexpression may amplify cellular signaling responses from cytokines.