Expression Of Ku80in Lung Adenocarcinoma And Its Effect On Cispiatin Response Of Lung Adenocarcinoma

Lung cancer is one of the most common malignancies, the leading cause ofcancer death in males and the second-leading cause of cancer deaths in femalesworldwide. Lung adenocarcinoma, one histological subtype of non-small cell lungcancer (NSCLC), is the most common histologic type among all lung cancersdiagnosed. Platinum based combination chemotherapy is the standard chemotherapyfor NSCLC. However, individuals response to chemotherapy differently and theefficacy of cisplatin treatment is often impaired by the emergence of resistance tothis drug. Therefore, elucidating the mechanism underlying the development ofchemoresistance would provide a major advance for our understanding of lungcancer progression and treatment failure.The heterodimeric Ku antigen, which acts as a molecular detector of DNAdouble strands, consists of two subunits of70kDa (Ku70) and80kDa (Ku80orKu86) and has been reported to activate DNA protein kinase(DNA-PK) by bindingdirectly to free DNA termini in a non-sequence-specific manner. Either Ku70orKu80itself has a unique function that is dependent of the other Ku subunit. Despitemany studies established with Ku80and other cancers, little is known about theexpression of Ku80and cisplatin resistance in human lung adenocarcinoma.In this study, we therefore assessed the expression of Ku80in lungadenocarcinoma specimens, and investigated whether it relates with tumorprogression and response to cisplatin chemotherapy in patients with lungadenocarcinoma receiving curative surgical resection.Methods: Tumor specimens and medical records of106patients with operablelung adenocarcinoma were obtained. the expression of Ku80between tumor andadjacent normal tissues and the clinical characteristics was analysed. Overallsurvival and progression-free survival were calculated using the Kaplan–Meiermethod and log-rank tests. Ku80mRNA and protein expression of the tumor samples, cultured human lung adenocarcinoma cells A549cells and their cisplatinresistant variant A549/DDP cells was examined by semi-quantitative reversetranscription PCR and western blot analyses, respectively. Next, the Ku80-specificsiRNA was transfected into A549/DDP cells, prior to treatment with cisplatin. MTTassay was performed to evaluate the chemosensitivity to cisplatin. Apoptosis wasassesed by flow cytometric analysis with Annexin-V-FITC apoptosis Kit, andcleaved caspase-3and cleaved PARP were detected by western blot analyses.Results: Ku80expression is increased in lung adenocarcinoma tissues. Ku80overexpression showed significant correlations with lymph node metastasis statusand TNM stage (P <0.001), but no correlation was noticed between age, gender,smoking status and tumor grade and Ku80expression level. Analysis using theKaplan–Meier method indicated that lung adenocarcinoma patients with high levelKu80had a significantly shorter median overall survival compared to those with lowlevel Ku80. Moreover, the progress-free interval was significantly (P <0.0001)higher in the low level Ku80group than in the high level Ku80group. All52.17%（12/23） and78.26%(18/23) cisplatin-resistant tumors showed high Ku80mRNAand protein expression levels, while16.67%（7/42） and18.60%（8/43）cisplatin-sensitive tumors showed high Ku80mRNA and protein expression levels(p <0.01). Univariate analysis indicated that overall survival and progression-freesurvival were significantly better in NSCLC patients with low vs those with highKu80expression levels (p <0.01). The Ku80mRNA and protein expression weresignificantly increased in A549/DDP cells compared with in parental A549cells.Downregulation Ku80with siRNA resensitized the response of A549/DDP tocisplatin, resulting in a significant increase in apoptosis induced by cisplatin.Conclusions: Ku80was markedly overexpressed in primary human lungadenocarcinoma and was associated with poor clinical outcomes and resistance tocisplatin-based chemotherapy. Targeted down-regulation of Ku80using siRNAenhanced the proapoptotic effects of chemotherapy on cisplatin-resistant lungadenocarcinoma cells A549/DDP. Combination therapy using siRNA to Ku80and cisplatin induced a marked increase in apoptosis compared with either agent alone.Combined, these data suggest an important role for Ku80in lung cancer progressionand a promising role for Ku80as a molecular target for resensitizing nonrespondersto cisplatin.Our results demonstrate that Ku80may serve as a biomarker for the predictionof cisplatin-based chemotherapy response and a prognositic indicator in lung cancerpatients. Our findings also suggest that a possible therapeutic strategy ofKu80-siRNA for enhancing and resensitizing nonresponders to cisplatin.