Characterization of molecular targets contributing to metastasis and stemness in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the commonest type of primary liver cancer and a major cause for cancer death worldwide. The aggressive clinical behavior is depicted by the frequent tumor recurrence, high propensity for metastasis and chemoresistance. Apart from the surgical and local ablative treatment modalities currently being adopted, recent advances in targeted therapies offer promising results in prolonging the survival of HCC patients. The genetic content of HCC is highly complex; therefore, identification of functional molecular targets responsible for the treatment hurdles is a strategic approach. In this regard, cancer stemness has been highlighted in the research field during the past decade due to its clinical relevance to tumor relapse, chemoresistance and metastasis. Among the different theories accounting for the origin of cancer stem cells, the cell plasticity hypothesis emphasizes the potential of cancer cells to switch between differentiated state and stemness state as driven by molecular alteration in cancer cells. This renders molecular targets driving reprogramming of cancer cells appealing subjects of study. In addition, the well-characterized hypoxic microenvironment in HCC was shown to foster cancer metastasis and stemness properties. In the current thesis, molecular targets contributing to metastasis and cancer stemness in HCC were identified and characterized. PIM1, a hypoxia-induced target, was overexpressed in HCC primary tumor tissues and its expression was further enhanced in metastatic HCC tissues. Functional characterization revealed the role of PIM1 in promoting metastasis, enhancing glycolysis, and increasing chemoresistance. In addition, the acquisition of stemness properties through dysregulation of three other molecular targets was demonstrated including Sox9, Cripto-1 and GATA6. Sox9 and Cripto-1 were overexpressed in HCC and the overexpression was associated with prognostic significance. By means of in vitro and in vivo functional assays, Sox9 and Cripto-1 increased stemness properties of HCC. On delineation of downstream molecular mechanisms, both Sox9 and Cripto-1 were found to regulate the canonical Wnt pathway. Sox9 was demonstrated to be a transcriptional regulator of Frizzled-7; while Cripto-1 formed a functional complex with Frizzled-7, LRP7 and DVL3 to modulate DVL3 expression and β-catenin activity. On the other hand, GATA6 was downregulated in HCC and the underexpression was associated with worse disease-free survival. Functionally, suppression of GATA6 in HCC cells led to enhanced stemness properties and diverted HCC cells to glycolytic metabolism via transcriptional regulation of PKM2, a key glycolytic enzyme. The findings in the thesis collectively enrich our understanding on the roles of key molecular targets and mechanisms conferring metastatic and stemness phenotypes of HCC. Further exploration of the efficacy of targeted therapies in the forms of specific inhibitors, monoclonal antibodies, oligonucleotides, or through epigenetic approaches could potentially expand the treatment options and improve the disease outcome for HCC.