ABSTRACT
Objective: To investigate the expression of X-ray repair cross complementing 1 (XRCC1) in human breast cancer and its relationship with the clinical characteristics, and to analyze the effects of XRCC1 over-expression on the proliferation and migration of breast cancer MB-231 cells and the molecular mechanism. Methods: The expression level of XRCC1 mRNA in breast cancer cell lines and human breast cancer tissues was detected by real-time fluorescent quantitative PCR. The expression of XRCC1 protein in human breast cancer tissues was detected by immunohistochemistry. The relationship between the expression of XRCC1 protein and the clinicopathological characteristics of breast cancer patients was analyzed. The pcDNA3.1(+)-Flag-XRCC1 plasmids were transfected into breast cancer MB-231 cells for the overexpression of XRCC 1 gene. Then the proliferation activity was detected by CCK-8 and soft agar plate clone formation assay. The cell cycle and apoptosis were detected by FCM method. The cell migration and invasion were detected by Transwell chamber assay. The expressions of cell cycle-, apoptosis- and migration-related proteins were detected by Western blotting. Results: The expression level of XRCC1 mRNA was significantly decreased in most breast cancer cell lines (all P < 0.001). As compared with the normal mammary epithelium and the paired adjacent breast tissues, the expression levels of XRCC1 mRNA and protein were downregulated in human breast cancer tissues (all P < 0.001). The expression level of XRCC1 mRNA was positively correlated with the prognosis of breast cancer patients (γ 2=0.052, P =0.046), and XRCC1 protein expression was correlated with tumor diameter, lymph node metastasis, histological grade and TNM stage (all P < 0.05). After the overexpression of XRCC 1 gene, the proliferation, colony formation, invasion and migration of breast cancer MB-231 cells were significantly inhibited (all P < 0.01), the cell cycle was significantly blocked in G1 phase (P < 0.001), and the apoptosis rate was significantly increased (P < 0.001). Furthermore, the expressions of p21, p27, Bax, cleaved caspase-3 and E-cadherin were significantly upregulated (all P < 0.001), while the expressions of cyclin-dependent kinase 4/6 (CDK4/6), cyclin D1, Bcl-2, N-cadherin and vimentin were down-regulated (all P < 0.001) in MB-231 cells with XRCC1 overexpression. Conclusion: XRCC1 expression is down-regulated in breast cancer cell lines and tissues, and its expression level is positively correlated with the prognosis of breast cancer patients. Restoring XRCC 1 gene expression can inhibit cell growth, migration and invasion, and can induce apoptosis. So XRCC1 may be a potential tumor suppressor regulating the occurrence and development of human breast cancer.