Hepatocellular carcinoma (HCC) is the fifth most prevalent human malignancy and the third leading cause of cancer deaths in the world. MicroRNAs (miRNA) are conserved, small noncoding RNA molecules that regulate gene expression of protein-coding gene posttranscriptionally. Dysregulation of miRNA is implicated in many human malignancies including HCC, yet little is known regarding the regulatory mechanisms of these small noncoding RNAs. Hypoxia is a prevalent! tumor microenvironment in HCC because of its rapid growth often to large size and plays a key role in modulating tumor aggressiveness. In the present study, we investigated the effects of hypoxia on microRNA expression in human HCCs, identified and characterized hypoxia-inducible microRNAs that are important for the development of aggressive phenotypes.
To initialize the study, we examined the miRNA expression profiles with TaqMan human microRNA Low-Density Array and identified a panel of microRNAs differentially expressed in HCC cells under hypoxic conditions. We observed that miR-210 was consistently upregulated by hypoxia in a total of 7 different HCC cell lines, via a HIF1α-dependent mechanism. In human HCCs, miRL210 overexpression significantly correlated with poorer overall and disease-free survival of patients, as well as aggressive pathologic features, including advanced tumor stages of HCC and the presence of venous invasion. These findings established miRL210 as a surrogate marker of aggressive HCC with high metastatic potential.
In most human malignancies, cancer metastasis contributes to about 90% of cancer-related mortality. Given the correlation of miR-210 levels with poorer patient survival and aggressive clinical features of HCC, we then characterized the metastatic role of miRL210 by functional assays in the second part of the study. The findings from in vitro and in vivo experiments using both gain- and loss-of-function approaches led us to conclude that the hypoxic induction of miRL210 enhanced metastatic potential of HCC cells. The pro-metastatic effect of miRL210 was attributed, at least partly, to the downregulation of TIMP2 by hypoxia, through a feedback loop circuit consisting of HIF1α, miRL210, and HIF3α.
The impact of miR-210 on HCC metastasis was not the only scope of this study since hypoxia has long been recognized as a major obstacle in chemotherapy. Given that activation of the HIF1α-miR-210 axis was frequently observed in hypoxic HCC cells, in the last part of the study we also investigated whether hypoxic induction of miRL210 promoted cell survival against cytotoxic treatments, including cisplatin and 5-flurouracil. Here, we demonstrated that induction of HIF1α-miR-210 axis conferred chemoresistance to HCC cells under hypoxic conditions, and inhibition of miR-210 re-sensitized HCC cells to these cytotoxic drugs. Mechanistically, we also revealed that RAD52 was a direct functional target of miRL210 that linked hypoxia to chemoresistance in HCC cells.
The overall findings of this study have enriched our understanding of miR-210 as a mediator of hypoxic responses in HCC, in particular metastasis and chemoresistance. We have highlighted the clinical significance of this microRNA by showing that miR-210 can serve not only as a prognostic marker for HCC progression, but also as a mediator for the hypoxic tumor microenvironment to modulate tumor aggressiveness. / published_or_final_version / Pathology / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/200359 |
| Date | January 2013 |
| Creators | Kai, Ka-lun, Alan, 奚家麟 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | Creative Commons: Attribution 3.0 Hong Kong License, The author retains all proprietary rights, (such as patent rights) and the right to use in future works. |
| Relation | HKU Theses Online (HKUTO) |
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