Association between Transcriptional Activity, Local Chromatin Structure, and the Efficiencies of Both Subpathways of Nucleotide Excision Repair of Melphalan Adducts

Abstract

The repair of melphalan-induced N-alkylpurine monoadducts and interstrand cross-links was examined in different repair backgrounds, focusing on four genes (b-actin, p53, N-ras, and d-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 GGRdeficient 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 f80% of the adducts, and a subsequent phase with t 1/2 f36 to 48 hours. Following pretreatment of cells with A-amanitin, the rate of transcription, the state of chromatin condensation, and the repair efficiencies (both TCR and GGR) of the transcribed b-actin, p53, and N-ras genes became similar to those of the nontranscribed d-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.

Chemotherapy induced DNA damage response

“…Gene ontology analyses of Bendamustine treated cells indicated DDR as the top regulated pathway with some evidence that the BER pathway is in part responsible for processing bendamustine induced DNA adducts 58 . While there is also evidence that melphalan mono and di-adducts melphalan are repaired via the NER pathway as demonstrated by the hypersensitivity of NER deficient cells to treatment, 61 this has not been addressed for bendamustine. Bendamustine activation of the DDR has been studied in a few models.…”

Initiation of DNA interstrand cross‐link repair in mammalian cells

“…The first mechanism results from the formation of open chromatin structures surrounding a transcribed region, which permits access to repair factors. The second mechanism is initiated by the presence of a stalled elongating RNA polymerase (Laine and Egly 2006; Episkopou et al 2009). The first mechanism would not discriminate between the two DNA strands and would also involve XPC as a recognition factor, whereas the second mechanism would be XPC-independent, CSA- and CSB-dependent, and would repair lesions preferentially on the transcribed strand.…”

DNA repair of myeloma plasma cells correlates with clinical outcome: the effect of the nonhomologous end-joining inhibitor SCR7

“…10 Failure to repair ICLs' lesions before the DNA replication process may induce DNA breaks or chromosomal rearrangements, or lead to cell death. 11 N-alkylpurine-monoadducts are exclusively repaired by nucleotide excision repair (NER), 12 whereas molecular components of NER, Fanconi anemia repair pathway, homologous recombination (HR), nonhomologous end-joining (NHEJ), and translesion synthesis are all required for adequate ICL repair. [13][14][15] DNA double-strand breaks (DSBs) are indirectly formed as a consequence of melphalan-induced oxidative stress, 16 and as intermediates of DNA repair pathways such as base-excision repair and ICL repair.…”