Long non-coding RNA HOTTIP is frequently up-regulated in hepatocellular carcinoma and is targeted by tumour suppressive miR-125b

Background & aims: Hepatocellular carcinoma (HCC) is one of the most common human cancers. Recently, emerging evidence has suggested the role of long non-coding RNAs (lncRNAs) in human carcinogenesis. In this study, we aimed to investigate the expression and functional implications of lncRNAs in human HCC.

Methods: Eighty-eight well-annotated lncRNAs were profiled in primary HCC by quantitative RT-PCR. Functional relevance of lncRNAs was elucidated in HCC cell lines and nude mice models. The regulatory relationship between miRNA and lncRNA was predicted in silico and further validated by luciferase reporter assay and expression analysis.

Results: In our profiling study, HOTTIP was identified as the most significantly up-regulated lncRNA in human HCCs, even in early stage of HCC formation. Functionally, knock-down of HOTTIP attenuated HCC cell proliferation in vitro and markedly abrogated tumourigenicity in vivo. In addition, knock-down of HOTTIP also inhibited migratory ability of HCC cells and significantly abrogated lung metastasis in orthotopic implantation model in nude mice. HOTTIP is an antisense lncRNA mapped to the distal end of the HOXA gene cluster. Knock-down of HOTTIP significantly suppressed the expression of a number of HOXA genes. Furthermore, we identified miR-125b as a post-transcriptional regulator of HOTTIP. Ectopic expression of miR-125b reduced HOTTIP-coupled luciferase activity and suppressed the endogenous level of HOTTIP. Moreover, in human HCCs, HOTTIP expression negatively correlated with that of miR-125b.

Conclusions: HOTTIP is a novel oncogenic lncRNA, which negatively regulated by miR-125b. Overexpression of HOTTIP contributes to hepatocarcinogenesis by regulating the expression of its neighbouring protein-coding genes.