Expression and promoter methylation of microRNA-34a gene in human breast cancer

Objective: To investigate the expression and clinical significance of microRNA-34a (miR-34a) in human breast cancer tissues, and to analyze the correlation of methylation status of miR-34a gene promoter with the expression of mature miR-34a and the survival of patients with breast cancer. Methods: The expression level of mature miR-34a in breast cancer tissues (n = 93) and benign breast lesions (n = 5, as the control) was detected by TaqMan probe-based real-time fluorescent quantitative PCR (TaqMan® MicroRNA Assay Kit). The bisulfite conversion and purification of genomic DNA from each formalin-fixed and paraffin-embedded breast cancer samples were performed by EpiTect Fast FFPE Bisulfite Kit. The methylation status of miR-34a gene promoter in breast cancer samples was assessed by methylation-specific PCR. The relationship between miR-34a expression and miR-34a gene methylation was statistically analyzed. The prognostic value of miR-34a gene methylation was analyzed by Kaplan-Meier curve. Results: The expression level of miR-34a in breast cancer was significantly lower than that in benign breast lesions (P = 0.006). The expression of miR-34a was negative correlated with tumor size (r = -0.312, P = 0.021), lymph node metastasis (r = -0.378, P = 0.004) and tumor grade (r = －0.341, P = 0.011). However, the expression of miR-34a was not associated with estrogen receptor (ER), progesterone receptor (PR) or human epidermal growth factor receptor-2 (HER-2) (all P > 0.05). The level of mature miR-34a in unmethylated group was significantly higher than that in methylated/unmethylated group or methylated group (both P < 0.001). Compared with unmethylated group and methylated/unmethylated group, the recurrence-free survival (P < 0.001, P = 0.019) and overall survival (P = 0.002, P < 0.001) of patients with breast cancer were significantly reduced in miR-34a gene methylated group. Conclusion: In some patients with breast cancer, the methylation of miR-34a gene may lead to the down-regulation of mature miR-34a expression. Furthermore, the methylation status of miR-34a gene is associated with the risk of tumor recurrence and poor prognosis in patients with breast cancer. DOI:10.3781/j.issn.1000-7431.2016.33.687