Chemical biology of mutagenesis and DNA repair: cellular responses to DNA alkylation

Abstract

The reaction of DNA-damaging agents with the genome results in a plethora of lesions, commonly referred to as adducts. Adducts may cause DNA to mutate, they may represent the chemical precursors of lethal events and they can disrupt expression of genes. Determination of which adduct is responsible for each of these biological endpoints is difficult, but this task has been accomplished for some carcinogenic DNA-damaging agents. Here, we describe the respective contributions of specific DNA lesions to the biological effects of low molecular weight alkylating agents.

Multiplexed DNA repair assays for multiple lesions and multiple doses via transcription inhibition and transcriptional mutagenesis

“…Base misincorporation opposite DNA lesions that are bypassed by DNA polymerase during replication has been studied extensively for many lesions (53). Misincorporation during transcription by RNA polymerase has been documented for a growing number of lesions and often mirrors that of DNA polymerase during replication (54).…”

Leukemia cells are sensitized to temozolomide, carmustine and melphalan by the inhibition of O6-methylguanine-DNA methyltransferase

“…BCNU-mediated interstrand crosslinks are repaired by NER and recombination, while O 6 -alkylguanine is repaired by NER (20). The ERCC1-XPF heterodimer is an endonuclease that is involved in the NER pathway (15).…”

Inducible tumor difference between rapid and slow rat Nat2 congenic Fischer 344 rats administered methyl-nitrosourea.

“…The mutagenic and toxic effects of abasic sites have been well described previously [48]. N 3 -alkyladenine is not particularly mutagenic, but it is a cytotoxic DNA lesion because it is able to block replication and able to generate abasic sites [47]. N 3 -alkyladenine has been shown to cause sister chromatid exchange, chromosome gaps and breaks, S phase arrest, accumulation of p53, and apoptosis in mammalian cells [49].…”

“…N 7 -alkylguanine, N 3 -alkyladenine, and O 6 -alkylguanine account for 68%, 8%, and 7.5% of total methylation after MNU treatment, respectively [46]. The N 7 atom of guanine is the most vulnerable site for attack by alkylating agents; however N 7 -alkylguanine alone has no pronounced mutagenic and cytotoxic effect [47]. Alkylation of the N 7 atom does cause chemical instability at the N-glycosidic bond, causing spontaneous abasic/apurinic sites to form.…”

“…N 3 -alkyladenine has been shown to cause sister chromatid exchange, chromosome gaps and breaks, S phase arrest, accumulation of p53, and apoptosis in mammalian cells [49]. O 6 -alkylguanine is the primary mutagenic lesion under most conditions of alkylation damage to the genome causing G →A transitions after two replications [47,50] (Figure 2). In addition to the point mutations following DNA replication, O 6 -alkylguanine can also result in mismatch repair-mediated DNA recombination and cell death [51].…”