Epistatic role of base excision repair and mismatch repair pathways in mediating cisplatin cytotoxicity

Anbarasi Kothandapani,Akshada Sawant,Robert W Sobol,Steve M Patrick,Venkata Srinivas Mohan Nimai Dangeti

doi:10.1093/nar/gkt479

Abstract

Base excision repair (BER) and mismatch repair (MMR) pathways play an important role in modulating cis-Diamminedichloroplatinum (II) (cisplatin) cytotoxicity. In this article, we identified a novel mechanistic role of both BER and MMR pathways in mediating cellular responses to cisplatin treatment. Cells defective in BER or MMR display a cisplatin-resistant phenotype. Targeting both BER and MMR pathways resulted in no additional resistance to cisplatin, suggesting that BER and MMR play epistatic roles in mediating cisplatin cytotoxicity. Using a DNA Polymerase β (Polβ) variant deficient in polymerase activity (D256A), we demonstrate that MMR acts downstream of BER and is dependent on the polymerase activity of Polβ in mediating cisplatin cytotoxicity. MSH2 preferentially binds a cisplatin interstrand cross-link (ICL) DNA substrate containing a mismatch compared with a cisplatin ICL substrate without a mismatch, suggesting a novel mutagenic role of Polβ in activating MMR in response to cisplatin. Collectively, these results provide the first mechanistic model for BER and MMR functioning within the same pathway to mediate cisplatin sensitivity via non-productive ICL processing. In this model, MMR participation in non-productive cisplatin ICL processing is downstream of BER processing and dependent on Polβ misincorporation at cisplatin ICL sites, which results in persistent cisplatin ICLs and sensitivity to cisplatin.

Highlights

Base excision repair (BER) and mismatch repair (MMR) pathways play an important role in modulating cis-Diamminedichloroplatinum (II) cytotoxicity
Using synthetic DNA oligonucleotides, we have recently shown that cisplatin interstrand cross-link (ICL) can be substrates for the BER machinery and that Polymerase b (Polb) has low fidelity at the DNA flanking a cisplatin ICL [30]
We show that MMR acts downstream of BER, and that activation of MMR is dependent on Polb misincorporation at cisplatin ICL sites

Summary

Introduction

Base excision repair (BER) and mismatch repair (MMR) pathways play an important role in modulating cis-Diamminedichloroplatinum (II) (cisplatin) cytotoxicity. MSH2 preferentially binds a cisplatin interstrand cross-link (ICL) DNA substrate containing a mismatch compared with a cisplatin ICL substrate without a mismatch, suggesting a novel mutagenic role of Polb in activating MMR in response to cisplatin These results provide the first mechanistic model for BER and MMR functioning within the same pathway to mediate cisplatin sensitivity via non-productive ICL processing. We show that MMR acts downstream of BER, and that activation of MMR is dependent on Polb misincorporation at cisplatin ICL sites Based on these results, we propose a model in which BER and MMR processing of cisplatin ICL DNA leads to non-productive repair of the cisplatin ICLs and the resulting persistent ICLs mediate cisplatin sensitivity. This is the first evidence that BER and MMR pathways play an epistatic role in mediating cisplatin sensitivity

Methods

Results

Conclusion