miR-122 enhances sensitivity of hepatocellular carcinoma to oxaliplatin via inhibiting MDR1 by targeting Wnt/β-catenin pathway

Background: Hepatocellular carcinoma (HCC) is one of the primary causes of cancer-related death and resistance to cytotoxic chemotherapy is the major cause of mortality in HCC patients. miR-122 is a liver specific miRNA and is found to be reduced in HCC, however, the function of miR-122 in HCC chemosensitivity remains elusive. Methods: We used qRT-PCR to measure expressions of miR-122, beta-catenin and MDR1 in four HCC cell lines. And we assessed the effects of miR-122 or beta-catenin on cell viability and apoptosis upon oxaliplatin (OXA) treatment by MTT assay and flow cytometry. In addition, we validated the interactions of miR-122/beta-catenin and beta-catenin/MDR1 by dual luciferase reporter assay and chromatin immunoprecipitation (ChIP). Western blotting was used to determine the protein levels of beta-catenin, Wnt1 and MDR1. In the end, we verified the anti-tumor effect of miR-122 in vivo by using mouse tumor xenograft model. Results: We found that miR 122 was down regulated in HCC cells. Up-regulation of miR-122 or inhibition of Wnt/beta-catenin signaling promoted HCC cells apoptosis and increased the sensitivity of HCC cells to OXA. On the molecular level, we showed that miR-122 directly targeted and suppressed Wnt/beta-catenin pathway while beta-catenin bound with MDR1 promoter and activated its transcription. Overexpression of miR-122 inhibited MDR1 expression via directly suppressing Wnt/beta-catenin pathway. Conclusion: Our study fully demonstrated that miR-122 inhibits MDR1 expression via suppression of Wnt/beta-catenin pathway, thereby enhancing HCC sensitivity to OXA. Therefore, miR-122 could serve as a novel potential therapeutic target for HCC.