The Methylation Status And Biological Functions Of Tumor Suppressor Gene PAX5 In Non-Small Cell Lung Cancer

Objective:To detect the expression and methylation status of PAX5 in non-small cell lung cancer (NSCLC). The correlation between PAX5 methylation and clinicopathologic features were analyzed. Forthermore, the biological functions of PAX5 in NSCLC were also studied.Methods:We used RT-PCR and real-time PCR to detect the expression of PAX5 in normal adults tissues、NSCLC tissues and cell lines. The methylation status of PAX5 in primary NSCLC tumor tissues, normal lung tissues, malignant pleural fluid and benign pleural fluid were studied by MSP. We then investigated the reationship between PAX5 methylation and clinical parameters by χ2 test. The PAX5 plasmid was transfected into NSCLC cell lines A549 and H1975 (which did not express PAX5) in order to analysis the influence of PAX5 in NSCLC. The biological functions of PAX5 were detected by colony formation assay, CCK8 viability assay, flow cytometry cell cycle and apoptosis analyses, transwell migration and invasion assays, along with in vivo tumorigenicity assay.Results:PAX5 was frequently expressed in normal adult tissues, but it was silenced or down-expressed in 86%(12/14) of primary NSCLC tissues (P<0.0001) and in 87.5%(7/8) of NSCLC cell lines. The methylation frequency of PAX5 in primary tumor tissues and normal lung tissues were 70%(33/47) and 14%(2/16) respectively (P<0.001). The methylation frequency of PAX5 in malignant and benign pleural fluid were 65% (20/31) and 11%(1/9), P=0.004.χ2 test showed that PAX5 methylation was correlated with histological types (P=0.006), PAX5 methylation rate was higher in adenocarcinoma, but was not correlated with age, gender, smoking history, TNM grade, differentiated degree, lymph node metastasis and distant metastasis (P>0.05). Re-expression of PAX5 can significantly reduce cancer cell proliferation, migration and invasion ability, induce cell cycle G2 arrest and increase cell apoptosis in vitro and inhibit tumor growth in vivo.Conclusion:PAX5 was silenced or down-regulated in NSCLC because of its promoter hypermethlation and can inhibit biological functions of NSCLC. As a novel candidate functional tumor suppressor in NSCLC, PAX5 provided a promising biomarker for the diagnosis and individualized treatment of NSCLC.