title: Poly(ADP-ribose) synthesis and inhibition of DNA synthesis in Chinese hamster cells treated with methylating agents and thymidine.
abstract: A possible role of poly(ADP-ribose) synthesis in modulating the response of V79 cells to DNA damage induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and methyl methanesulfonate (MMS) was investigated. Inhibition of [3H]thymidine (dThd) incorporation into DNA and lowering of NAD+ levels in intact cells were employed as parameters of DNA-synthesis inhibition and poly(ADP-ribose) synthesis, respectively. Dose responses of these parameters were studied in cells 2 and 24 h after treatment with the methylating agents in medium with or without dThd. The initial inhibition of DNA synthesis was uniformly associated with stimulation of poly(ADP-ribose) synthesis whether the cells were treated with MNNG or MMS, incubated with or without 20 microM dThd which did not inhibit poly(ADP-ribose) synthesis, or incubated with 3 mM dThd which did inhibit the latter synthesis. By contrast, the DNA-synthesis inhibition detected 24 h after treatment with MNNG was not associated with poly(ADP-ribose) synthesis. These data suggest that (i) the mechanism of this later inhibition of DNA synthesis is different from that of the initial inhibition, (ii) DNA-synthesis inhibition does not stimulate poly(ADP-ribose) synthesis, and (iii) single-strand breaks, resulting from N-methylation of the DNA, stimulate poly(ADP-ribose) synthesis, which may produce the initial inhibition of DNA synthesis. The initial inhibition of DNA synthesis was not uniformly associated with mutagenesis and dThd facilitation of MNNG-induced cytotoxicity and mutagenesis. This indicates that O-methylation of DNA does not stimulate poly(ADP-ribose) synthesis. Our data suggest that, in V79 cells treated with methylating agents, poly(ADP-ribose) synthesis is stimulated by single-strand breaks, inhibits DNA synthesis, and thereby serves to allow time for repair of the DNA prior to replication.
mesh_terms: D000818:Animals; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair; D004261:DNA Replication / Q000187:drug effects*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000187:drug effects; D008168:Lung; D008297:Male; D008741:Methyl Methanesulfonate / Q000494:pharmacology*; D008745:Methylation; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D009243:NAD / Q000032:analysis; D009702:Nucleoside Diphosphate Sugars / Q000096:biosynthesis*; D011064:Poly Adenosine Diphosphate Ribose / Q000096:biosynthesis*; D013936:Thymidine / Q000494:pharmacology
chemical_list: D009702:Nucleoside Diphosphate Sugars; D009243:NAD; D008769:Methylnitronitrosoguanidine; D011064:Poly Adenosine Diphosphate Ribose; D008741:Methyl Methanesulfonate; D013936:Thymidine