Association between transcriptional activity, local chromatin structure, and the efficiencies of both subpathways of nucleotide excision repair of melphalan adducts.
The repair of melphalan-induced N-alkylpurine monoadducts and interstrand cross-links was examined in different repair backgrounds, focusing on four genes (beta-actin, p53, N-ras, and delta-globin) with dissimilar transcription activities. Adducts were found to be substrates for both global genome repair (GGR) and transcription-coupled repair (TCR), with TCR being less efficient than GGR. In nucleotide excision repair-deficient cells, adducts accumulated to similar levels in all four genes. The repair efficiency in different gene loci varied in a qualitatively and quantitatively similar way in both GGR-deficient and TCR-deficient backgrounds and correlated with transcriptional activity and local chromatin condensation. No strand-specific repair was found in GGR(+)/TCR(+) cells, implying that GGR dominated. Adducts were lost over two sharply demarcated phases: a rapid phase resulting in the removal within 1 hour of up to approximately 80% of the adducts, and a subsequent phase with t(1/2) approximately 36 to 48 hours. Following pretreatment of cells with alpha-amanitin, the rate of transcription, the state of chromatin condensation, and the repair efficiencies (both TCR and GGR) of the transcribed beta-actin, p53, and N-ras genes became similar to those of the nontranscribed delta-globin gene. In conclusion, a continuous, parallel variation of the state of transcription and local chromatin condensation, on one hand, and the rates of both GGR and TCR, on the other hand, have been shown.
Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece.
Hara
H
Episkopou
Soterios A
SA
Kyrtopoulos
Petros P
PP
Sfikakis
Maria
M
Fousteri
Meletios A
MA
Dimopoulos
Leon H F
LH
Mullenders
Vassilis L
VL
Souliotis
D000199:Actins / Q000187:drug effects / Q000235:genetics; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002843:Chromatin / Q000187:drug effects / Q000235:genetics*; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D016158:Genes, p53 / Q000187:drug effects; D011905:Genes, ras / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D008558:Melphalan / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*; D055546:delta-Globins / Q000187:drug effects / Q000235:genetics
D000199:Actins; D018906:Antineoplastic Agents, Alkylating; D002843:Chromatin; D055546:delta-Globins; D008558:Melphalan