Novel Role of Base Excision Repair in Mediating Cisplatin Cytotoxicity

Abstract

Using isogenic mouse embryonic fibroblasts and human cancer cell lines, we show that cells defective in base excision repair (BER) display a cisplatin-specific resistant phenotype. This was accompanied by enhanced repair of cisplatin interstrand crosslinks (ICLs) and ICL-induced DNA double strand breaks, but not intrastrand adducts. Cisplatin induces abasic sites with a reduced accumulation in uracil DNA glycosylase (UNG) null cells. We show that cytosines that flank the cisplatin ICLs undergo preferential oxidative deamination in vitro, and AP endonuclease 1 (APE1) can cleave the resulting ICL DNA substrate following removal of the flanking uracil. We also show that DNA polymerase ␤ has low fidelity at the cisplatin ICL site after APE1 incision. Down-regulating ERCC1-XPF in BER-deficient cells restored cisplatin sensitivity. Based on our results, we propose a novel model in which BER plays a positive role in maintaining cisplatin cytotoxicity by competing with the productive cisplatin ICL DNA repair pathways.

NEIL1 Responds and Binds to Psoralen-induced DNA Interstrand Crosslinks

“…NER and recombinational repair, including XPC recruitment), leading to slower crosslink removal and increased sensitivity to trioxsalen ϩ UVA. This model is broadly consistent with the model of Patrick and colleagues, who based on a series of biochemical and cell biology experiments proposed that, upon cytosine deamination near a cisplatin interstrand crosslink, a uracil-directed BER response will hamper the normal cellular repair processes for the crosslink damage (13). Our studies indicate an interfering role for the NEIL1 glycosylase in the repair of psoralen-induced DNA interstrand crosslinks that involves binding at the crosslink site, seemingly without the formation of a cognate substrate.…”

“…Unlike the above work, which suggested a role for BER components in the repair of crosslink adducts, Patrick and co-workers found that cells deficient in BER display a cisplatin-resistant phenotype, which is accompanied by enhanced excision of cisplatin-induced interstrand crosslinks (13). In particular, they demonstrated that the region around a cisplatin interstrand crosslink is susceptible to increased spontaneous decay, namely cytosine deamination, due to a local structural distortion in the duplex.…”

The role of DNA repair pathways in cisplatin resistant lung cancer

“…In one study, patients with low human apurinic/apyrimidinic endonuclease (APE1) expression levels had a greater response to cisplatin and a significantly improved survival rate compared to those with high levels of expression [38,39]. In contrast, a recent study by Kothandapani et al observed an increase in resistance to cisplatin in DNA polymerase b (Pol-b)-deficient mouse embryonic fibroblasts following inhibition of APE-1using the small molecule inhibitor, methoxyamine, indicating that a functional BER pathway promotes cell death in response to this platinum drug [40]. This increased resistance was associated with an increased repair rate of inter-strand cross-links and double strand breaks, but not with intra-strand cross-links.…”

Intrinsic mutagenic properties of 5-chlorocytosine: A mechanistic connection between chronic inflammation and cancer

“…To this end, we determined binary (pol/DNA) and ternary (pol/DNA/dNTP) X-ray crystal structures of human DNA polymerase β (pol β) with 5ClC in the templating position of a 1-nt-gapped DNA duplex (Table 2). Pol β is a model mammalian DNA polymerase involved in base excision repair and may encounter DNA lesions in the templating strand during repair of the genome (32)(33)(34). The binary DNA complex structure with 5ClC in the templating position diffracted to 2.0 Å.…”