Abstract
Cisplatin exert its anticancer effect by creating intrastrand and interstrand DNA cross-links which block DNA replication and is a major drug used to treat lung cancer. However, the main obstacle of the efficacy of treatment is drug resistance. Here, we show that expression of translesion synthesis (TLS) polymerase Q (POLQ) was significantly elevated by exposure of lung cancer cells A549/DR (a cisplatin-resistant A549 cell line) to cisplatin. POLQ expression correlated inversely with homologous recombination (HR) activity. Co-depletion of BRCA2 and POLQ by siRNA markedly increased sensitivity of A549/DR cells to cisplatin, which was accompanied with impairment of double strand breaks (DSBs) repair reflected by prominent cell cycle checkpoint response, increased chromosomal aberrations and persistent colocalization of p-ATM and 53BP1 foci induced by cisplatin. Thus, co-knockdown of POLQ and HR can efficiently synergize with cisplatin to inhibit A549/DR cell survival by inhibiting DNA DSBs repair. Similar results were observed in A549/DR cells co-depleted of BRCA2 and POLQ following BMN673 (a PARP inhibitor) treatment. Importantly, the sensitization effects to cisplatin and BMN673 in A549/DR cells by co-depleting BRCA2 and POLQ was stronger than those by co-depleting BRCA2 and other TLS factors including POLH, REV3, or REV1. Our results indicate that there is a synthetic lethal relationship between pol θ-mediated DNA repair and HR pathways. Pol θ may be considered as a novel target for lung cancer therapy.
Highlights
Platinum-based chemotherapy agents, such as cisplatin, are first-line treatment drugs of advanced nonsmall cell lung cancer (NSCLC)
To investigate molecular mechanism underlying the protective effect of Pol θ on A549/DR cells upon treatment with cisplatin, the timedependent expressions of polymerase Q (POLQ) mRNA was examined by real-time quantitative (RTQ)-PCR
The results showed that the percentage of BRCA2 and POLQ codepleted cells exhibiting P-ATM and 53BP1-colocalized foci persisted at higher levels 48 hours after cisplatin treatment, suggesting that double strand breaks (DSBs) repair in these cells was affected to a larger degree, compared to the cells depleting BRCA2 or POLQ alone, and the cells co-depleted of BRCA2 and POLH, or REV3, or REV1 (Figure 6E)
Summary
Platinum-based chemotherapy agents, such as cisplatin, are first-line treatment drugs of advanced nonsmall cell lung cancer (NSCLC). ICLs comprised only a small fraction of the induced DNA damage, these are the most cytotoxic and genotoxic lesions produced by cisplatin [2,3,4]. The effectiveness of the therapy is often compromised largely because cancer cells develop resistance to the drug [3, 4]. Multiple mechanisms that mediate intrinsic or acquired resistance to cisplatin have been identified, including decreased drug uptake, increase of drug metabolism and inactivation, defects in apoptosis programs, and enhanced DNA repair capacity [5, 6]. Enhanced DNA repair pathways are found in a subset of drug-resistant cancer cells [7,8,9,10]. DNA damage repair is one of main cisplatin resistant mechanisms
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