Molecular cloning of a novel human diacylglycerol kinase highly selective for arachidonate-containing substrates

Abstract

Diacylglycerol (DAG) is a second messenger that activates protein kinase C and also occupies a central role in phospholipid biosynthesis. Conversion of DAG to phosphatidic acid by DAG kinase regulates the amount of DAG and the route it takes. We used degenerate primers to amplify polymerase chain reaction products from cDNA derived from human endothelial cells. A product with a novel sequence was identified and used to clone a 2.6-kilobase cDNA from an endothelial cell library. When transfected with a truncated version of this cDNA, COS-7 cells had a marked increase in DAG kinase activity, which demonstrated clear selectivity for arachidonoyl-containing species of diacylglycerol. The open reading frame of this clone has 567 residues with a predicted protein of 64 kDa. This enzyme, which we designated DGKε, has two distinctive zinc finger-like structures in its N-terminal region, but does not contain the E-F hand motifs found in several other mammalian DGKs. The catalytic domain of DGKε, which is related to other DGKs, contains two ATP- binding motifs. Northern blotting demonstrated that DGKε is expressed predominantly in testis. This unique diacylglycerol kinase may terminate signals transmitted through arachidonoyl-DAG or may contribute to the synthesis of phospholipids with defined fatty acid composition.