miR-200b restoration and DNA methyltransferase inhibitor block lung metastasis of mesenchymal-phenotype hepatocellular carcinoma

Epithelial-to-mesenchymal transition (EMT) is associated with poor prognosis and metastasis in hepatocellular carcinoma. We have previously demonstrated an in vivo model of liver cancer in which mesenchymal cells post-EMT demonstrate a high rate of invasive growth and metastasis. Here, we investigate the role of microRNA 200 (miR-200) family members and epigenetic modifications on the maintenance of mesenchymal/metastatic phenotype after EMT. Mesenchymal cells post-EMT demonstrates high levels of E-box repressors Zeb1 and Zeb2 and downregulation of four miR-200 family members (miR-200a, miR-200b, miR-200c and miR-429). In addition, DNA sequencing after bisulfite modification demonstrates that several CpG sites within the E-cadherin promoter are methylated in mesenchymal cells. In mesenchymal cells, forced expression of miR-200b results in a significant increase in E-cadherin and a reduction in cell migration/invasion. Despite these mesenchymal-to-epithelial transition (MET) changes in vitro, there is no significant change in metastatic potential after miR-200b upregulation in vivo. After the mesenchymal cells were treated with combination of DNA methyltransferase (DNMT) inhibitor and upregulation of miR-200b, invasive phenotype was significantly reduced and metastatic potential was eliminated. Direct targeting of E-cadherin with short hairpin RNA does not restore metastatic potential after DNMT inhibition and miR-200b re-expression. In addition, restoration of E-cadherin alone was unable to block metastatic potential in primary mesenchymal cells. In conclusion, targeting mesenchymal liver cancer cells with miR-200b and DNMT inhibitor reduces metastatic potential irrespective of E-cadherin expression. Thus, the broader differentiation and MET effects of DNMT inhibition and miR-200b must be considered in terms of rescuing metastatic potential.