The Expression And Clinical Significance Of Rad51C In Non-Small Cell Lung Cancer And The Effect Of Rad51c On Chemotherapy And Radiotherapy

Objective: Rad51 C is indispensable for homologous recombination(HR) and genomic stability, and it may be important in DNA damage response(DDR). Rad51 C may get involved in tumorgenesis and cancer therapy, too. However, the expression profile and clinical value of Rad51 C protein in malignant tumor has not been clearly clarified. We investigated the expression level and clinical significance of Rad51 c in non-small-cell lung cancer(NSCLC), and determined the effect of Rad51 c on NSCLC cell chemosensitivity and radiosensitivity.Methods: First of all, Rad51 c expression was detected using immunohistochemistry(IHC) in NSCLC patient samples and adjacent normal tissues. Our purpose is to explore the roles of Rad51 C in the occurrence and development of lung cancer and its clinical prognostic significance. Furthermore, A549 human lung adenocarcinoma cell line was stably transferred with retroviruses coexpressing Rad51C-sh RNA and green fluorescent protein(GFP), and then Rad51C-defective A549 cell line(sh Rad51 C group) was constructed. The Control group is this A549 cell line with a lentivirus carrying the corresponding control scrambled sh RNA sequence. Blank group is the normal A549 cell line without any sh RNA. By Western blotting assay, MTT proliferation assay and Clonogenic survival assay, we insure the stably Rad51C-defective A549 cell line. Lastly, after Rad51 C knockdown, a series of cell experiments were used to see the effect of ionizing radiation(IR) and cisplatin treat.Results: Kaplan–Meier analysis revealed that high Rad51 c expression was an independent predictor of short overall survival(OS) and disease-free survival(DFS) in NSCLC patients receiving chemotherapy and/or radiotherapy(P < 0.01). Kaplan–Meier analysis revealed that high Rad51 c expression was an independent predictor of short overall survival(OS) and disease-free survival(DFS) in NSCLC patients receiving chemotherapy and/or radiotherapy(P<0.05). MTT assay showed that inhibition of Rad51 C did not affect cell growth compared with control or untreated cells. However, knockdown of Rad51 c increased the sensitivity of A549 cells to cisplatin-mediated growth inhibition. Flow cytometry(FCW) assay showed that inhibition of Rad51 c significantly increased apoptosis in cells exposed to cisplatin for 48 h(**P<0.01), contrasting with negative controls. Finishly, Increased numbers of ?H2AX foci—which are a hallmark of DNA damage—were present in Rad51 c knockdown A549 cells compared with controls(*P<0.05). We then investigated whether down-regulation of Rad51 C influenced the repair of cisplatin-induced DNA damage in A549 cells. Inhibition of Rad51 c had no effect on the capacity of untreated cells to form colonies. However, clonogenic survival was obviously reduced in Rad51C-knockdown A549 cells exposed to ionizing radiation(IR). Additionally, we examined the effect of Rad51 C knockdown on the repair of IR-induced DNA damage. Unrepaired IR-induced DNA damage was significantly increased in Rad51C-depleted A549 cells by contrast the negative controls(**P<0.01).Conclusions: These findings suggest that increased expression of Rad51 c may be a novel predictor of aggressive NSCLC that is resistant to chemotherapy and/or radiotherapy, and also an independent prognostic factor for patient outcome. Therefore, targeting Rad51 C may represent an improved therapeutic strategy for NSCLC patients with locally advanced disease.