title: Activation of deoxycytidine kinase by gamma-irradiation and inactivation by hyperosmotic shock in human lymphocytes.
abstract: Deoxycytidine kinase (dCK) is a key enzyme in the intracellular metabolism of deoxynucleosides and their analogues, phosphorylating a wide range of drugs used in the chemotherapy of leukaemia and solid tumours. Previously, we found that activity of dCK can be enhanced by incubating primary cultures of lymphocytes with substrate analogues of the enzyme, as well as with various genotoxic agents. Here we present evidence that exposure of human lymphocytes to 0.5-2 Gy dosage of gamma-radiation as well as incubation of cells with calyculin A, a potent inhibitor of protein phosphatase 1 and 2A, both elevate dCK activity without changing the level of dCK protein. When cells were gamma-irradiated in the presence of calyculin A, a more pronounced activation of dCK was observed. In contrast, both basal and stimulated dCK activities were reduced by hyperosmotic treatment of the cells. DNA repair determined by the Comet assay and by thymidine incorporation was induced by irradiation. Complete repair of gamma-irradiated DNA was detected within 1 hr following the irradiation along with dCK activation, but the rate of repair was not accelerated by calyculin A. These data provide evidence for the activation of dCK upon DNA damage and repair that seems to be mediated by phosphorylation of the enzyme, suggesting the role of dCK in DNA repair processes.
authors.affiliation: Institute of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, P.O. Box 260, H-1444 Budapest, Hungary.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Csapo
authors.forename: Gergely
authors.initials: G
authors.lastname: Keszler
authors.forename: Geza
authors.initials: G
authors.lastname: Safrany
authors.forename: Tatjana
authors.initials: T
authors.lastname: Spasokoukotskaja
authors.forename: Iannis
authors.initials: I
authors.lastname: Talianidis
authors.forename: Maria
authors.initials: M
authors.lastname: Staub
authors.forename: Maria
authors.initials: M
authors.lastname: Sasvari-Szekely
mesh_terms: D020552:Comet Assay; D004260:DNA Repair; D003842:Deoxycytidine Kinase / Q000378:metabolism*; D003853:Deoxyribonucleosides / Q000378:metabolism; D004789:Enzyme Activation / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000187:drug effects / Q000201:enzymology / Q000528:radiation effects*; D008387:Marine Toxins; D009994:Osmolar Concentration; D010080:Oxazoles / Q000494:pharmacology; D011827:Radiation
chemical_list: D003853:Deoxyribonucleosides; D008387:Marine Toxins; D010080:Oxazoles; C059041:calyculin A; D003842:Deoxycytidine Kinase