CD39L2, a gene encoding a human nucleoside diphosphatase, predominantly expressed in the heart

E-NTPDases are extracellular enzymes that hydrolyze nucleotides. The human E-NTPDase gene family currently consists of five reported members (CD39, CD 39L1, CD39L2, CD39L3, and CD39L4). Both membrane-bound and secreted family members have been predicted by encoded transmembrane and leader peptide mot ifs. In this report, we demonstrate that the human CD39L2 gene is expressed predominantly in the heart. In situ hybridization results from heart indic ate that the CD39L2 message is expressed in muscle and capillary endothelia l cells. We also show that the CD39L2 gene encodes an extracellular E-NTPDa se. Flow cytometric experiments show that transiently expressed CD39L2 is p resent on the surface of COS-7 cells. Transfected cells also produce recomb inant glycosylated protein in the medium, and this process can be blocked b y brefeldin A, an inhibitor of the mammalian secretory pathway. The enzymol ogy of CD39L2 shows characteristic features of a typical E-NTPDase, but wit h a much higher degree of specificity for NDPs over NTPs as enzymatic subst rates. The kinetics of the ADPase activity exhibit positive cooperativity. The predominance of CD39L2 expression in the heart supports a functional ro le in regulating platelet activation and recruitment in this organ.