title: Factors influencing the inhibition of repair of irradiation-induced DNA damage by 2'-deoxycoformycin and deoxyadenosine.
abstract: Permeabilized L5178Y cells were used to investigate the mechanism underlying inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine. Permeabilized cells repaired DNA strand breaks as effectively as did intact cells, and at deoxyadenosine concentrations that produced similar levels of deoxyadenosine triphosphate (dATP), repair of DNA strand breaks was inhibited by 2'-deoxycoformycin plus deoxyadenosine to a comparable extent in both types of cells. Accompanying the increase in intracellular dATP produced by 2'-deoxycoformycin combined with deoxyadenosine was a fall in levels of deoxythymidine triphosphate (dTTP), deoxyguanosine triphosphate (dGTP), and deoxycytidine triphosphate (dCTP). The addition of dTTP, dGTP, and dCTP reversed the inhibition of DNA repair by 2'-deoxycoformycin plus deoxyadenosine, although the level of dATP was not affected. Reducing the phosphorylation of deoxy-adenosine to dATP by the addition of adenosine prevented the decrease in levels of dTTP, dGTP, and dCTP and the inhibition of DNA repair by 2'-deoxycoformycin and deoxyadenosine. In contrast, increasing the intracellular levels of dATP by the addition of 2'-deoxycoformycin together with dATP, deoxyadenosine diphosphate (dADP), or deoxyadenosine monophosphate (dAMP) had no effect on the levels of the other deoxynucleotide triphosphates and did not inhibit DNA repair. Moreover, DNA repair was not inhibited by the breakdown products of deoxyadenosine, adenine, or deoxyribose. These results suggest that inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine requires the phosphorylation of deoxyadenosine and involves alterations in the levels of deoxynucleotide triphosphates.
authors.affiliation: Department of Internal Medicine, University of Manitoba, Winnipeg, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Begleiter
authors.forename: L
authors.initials: L
authors.lastname: Verburg
authors.forename: L G
authors.initials: LG
authors.lastname: Israels
authors.forename: J B
authors.initials: JB
authors.lastname: Johnston
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000502:physiology / Q000528:radiation effects*; D003839:Deoxyadenosines / Q000378:metabolism / Q000494:pharmacology*; D008223:Lymphoma / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008811:Mice, Inbred DBA; D009711:Nucleotides / Q000378:metabolism; D015649:Pentostatin / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation; D014407:Tumor Cells, Cultured
chemical_list: D004273:DNA, Neoplasm; D003839:Deoxyadenosines; D009711:Nucleotides; D015649:Pentostatin; D000241:Adenosine