Therefore, miRNAs are implicated in many important cellular processes, such as cell-cycle progression, cell differentiation, apoptosis, and cytoskeletal reorganization. Increasing evidences demonstrated the interplay between miRNAs BAY 73-4506 and epigenetic alterations in human cancers. For example, the oncogenic, enhancer of zeste homolog 2 (EZH2), has been found to be overexpressed in various cancer tissues, and EZH2 is targeted by miR-101, miR-124, and miR-214.29-31 Frequent down-regulation of these miRNAs in human cancers thereby accounted for the up-regulation of EZH2. Similar examples have also been reported
between the niR-29 family and DNMT3A/B,32 miR-449 and histone deacetylase 1,33 and miR-200c and Bmi-1.34 All these evidences suggested that miRNAs may play a crucial role in modulating epigenetic events. In this study, we explored the possibility of miRNA deregulation as a contributing factor in SUV39H1 expression in human HCC. Interestingly, in silico analysis of SUV39H1 3′ UTR suggested the potential regulation of SUV39H1 mRNA by miR-125b. We have previously identified miR-125b as the tumor-suppressor miRNA that is frequently down-regulated in HCC.22 In this study, we experimentally validated the complementary binding between miR-125b and SUV39H1 3′ UTR by luciferase reporter assay. Ectopic expression of
miR-125b apparently reduced endogenous see more Endonuclease SUV39H1 mRNA and protein levels in HCC cell lines. In concordance with our findings, a recent study indicated that miR-125b up-regulation may contribute to the increased expression of inflammatory genes in vascular smooth muscle cell (VSMC) of type 2 diabetic db/db mice by targeting SUV39H1.22 Opposite to the VSMCs of db/db mice, miR-125b is frequently down-regulated in human HCC. Interestingly, an inverse correlation was observed between SUV39H1 and
miR-125b expression in clinical human HCC samples. Therefore, we speculated that targeting of SUV39H1 by miR-125b may be a conserved event throughout the mammalian cell system, and up-regulation of SUV39H1 in HCC was contributed by the loss of miR-125b. In conclusion, we provide the first evidence that SUV39H1 is an important oncogene that contributes to HCC tumor growth and metastasis. Besides this, up-regulation of SUV39H1 was, in part, the consequence of tumor-suppressive miRNA-125b underexpression in HCC. This observation further suggested the possible interplay between miRNA and histone methylation during the course of liver carcinogenesis. Our findings have enriched the knowledge of the molecular mechanisms underlying hepatocarcinogenesis and provide potential targets for future therapeutic invention. The authors thank Ms. Tracy CM Lau from the Faculty Core Facility and Mr.