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Gene Expression and Activity Profiling Reveal a Significant Contribution of Exo‐Phosphotransferases to the Extracellular Nucleotides Metabolism in HUVEC Endothelial Cells

Purinergic signaling maintains local tissue homeostasis in blood vessels via the regulation of vascular tone, blood platelet aggregation, cell proliferation, and differentiation as well as inflammatory responses. Extracellular purines are important signaling molecules in the vasculature, and both purine‐hydrolysing as well as ‐phosphorylating enzymes are considered to selectively govern extracellular nucleotide/nucleoside metabolism. Recent studies have provided some evidence for the existence of these enzymes in a soluble form in human blood and their secretion into the extracellular space under physiological and pathological conditions. However, the comprehensive analysis of endothelium‐derived enzymes involved in purine metabolic pathways has received no attention so far. In the presented study, in vitro cultured human umbilical vein endothelial cells (HUVEC) are shown to be an abundant source of exo‐nucleotidases comprising 5′‐nucleotidase (exo‐5′‐NT), and nucleoside triphosphate diphosphohydrolases (exo‐NTPDase) as well as phosphotransferases, represented by nucleoside diphosphate kinase (exo‐NDPK) and adenylate kinase (exo‐AK). An attempt is also made to demonstrate that, in contrast to the metabolic pattern determined on the endothelial cell surface, exo‐phosphorylating activities markedly predominate over exo‐hydrolytic ones. We present for the first time the expression profiles of genes encoding isoenzymes belonging to distinct nucleotide kinase and nucleotidase families. The genes encoding NDPK1, NDPK2, AK1, and AK2 phosphotransferases have been shown to be expressed at the highest level in HUVEC cells. The data indicate the coexistence of secreted and cell‐associated factors of endothelial origin mediating ATP‐consuming and ATP‐generating pathways with the predominance of exo‐phosphotransferases activity. The described enzymes contribute to the regulation of purinergic signal duration and extent in the venous vasculature. J. Cell. Biochem. 118: 1341–1348, 2017. © 2016 Wiley Periodicals, Inc.