Expression of xeroderma pigmentosum complementation group C protein predicts cisplatin resistance in lung adenocarcinoma patients

DNA repair has been suggested to be a major cause of spontaneous drug resistance in patients with lung adenocarcinomas (LADC). Among the DNA repair-related proteins, excision repair cross-complementation group 1 (ERCC1) has been shown to be essential for repairing cisplatin-induced interstrand cross-linkage. However, the role of other DNA repair-related proteins in drug resistance has not been clearly elucidated. In this study, we used suppression subtractive hybridization and microarray analysis to identify the DNA repair-related genes associated with cisplatin resistance. We focused on the association of XPC protein expression, which plays a pivotal role in the earliest response to global genomic repair, with the survival of LADC patients. Using suppression subtractive hybridization and a microarray analysis to identify drug resistance-associated DNA repair-related genes, we found that the mRNA levels of ERCC1, MSH-3, MSH-6 and XPC were significantly increased in LADC patients. Since the results of ERCC1 mRNA expression corresponded well with those in previous reports, in this study we focused on the clinical correlation between XPC expression and patient survival. The level of XPC protein was determined by immunohistochemical and immunoblotting analyses. We detected the XPC protein in 46 (43%) of 107 pathological LADC samples. XPC protein expression correlated with tumor stage, cigarette smoking and poor survival. In the in vitro experiments with LADC cell lines, increased XPC expression was associated with elevated drug resistance, and silencing of XPC expression reduced cisplatin resistance. Our results suggest that XPC expression predicts drug resistance in LADC.