The association between miR-34 dysregulation and distant metastases formation in lung adenocarcinoma

Lung cancer has the highest mortality rate amongst human cancers and the majority of deaths can be attributed to metastatic spread. The miR-34 family includes three tumor suppressive miRs: miR-34a, miR-34b and miR-34c. miR-34 downregulation is a frequent observation in human malignancies and is often attributed to hypermethylation of the miR-34a and miR-34b/c promoters. Here, the potential association between aberrant miR-34 expression and promoter methylation and distant metastases formation in lung adenocarcinoma (LAC) is investigated. The expression levels of miR-34a, miR-34b and miR-34c, as well as the methylation status of the miR-34a and miR-34b/c promoters were determined in a LAC patient cohort comprising 26 non-metastasizing and 26 metastasizing primary LACs, as well as 24 paired distant metastases and 25 tumor-adjacent normal lung samples using RT-qPCR and Methylation-Sensitive High Resolution Melting (MS-HRM) analysis. No difference in expression was observed for miR-34a when comparing metastasizing and non-metastasizing LACs (p=0.793). For both miR-34b and miR-34c, a significantly lower expression level was determined in metastasizing LACs compared to non-metastasizing LACs (p=0.0005 and p=0.002) with similarly decreased expression levels observed in the paired distant metastases. Hypermethylation was detected in 35/51 LACs compared to 0/25 tumor-adjacent normal lungs for the miR-34a promoter (p<0.0001). Similarly, 18/51 LACs compared to 1/25 tumor-adjacent normal lungs showed hypermethylation of the miR-34b/c promoter (p=0.003). No difference in methylation was observed between metastasizing and non-metastasizing LACs for neither the miR-34a (p=0.832) nor the miR-34b/c (p=0.900) promoter. In conclusion, miR-34a and miR-34b/c promoter hypermethylation is a frequent event in LAC occurring in 68.7% and 35.3% of tested cases (n=51), respectively. Low miR-34b and miR-34c expression was associated with distant metastases formation in LAC. These changes can be targeted as novel biomarkers in LAC.