Functional characterization of GATA6 in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC), ranked as the second highest cancer-related mortalities globally, is often diagnosed at a late stage and associated with aggressive clinical features, poor prognosis, resistance to chemotherapeutic drugs, high metastatic and recurrence rate. It was believed that the presence of cancer stem cells in the tumor niche which possess tumor-initiating and self-renewal ability were responsible for the high recurrence rate and poor survival outcome of HCC patients. Recently, accumulating evidence have highlighted the remarkable plasticity of liver cells and demonstrated that the mature hepatocytes have the capacity to dedifferentiate and revert back to the hepatic progenitors with enhanced stemness features. In other words, it has been postulated that those cancer stem cells present in the tumor bulk could possibly be derived from the differentiated tumor cells.

GATA6, a member of the GATA transcription factors, is essential in normal endoderm formation and liver differentiation. Aberrant expression of GATA6 had been reported in many malignancies, particularly in the endoderm-derived organs. Although the liver originates from the endoderm layer, there is no direct study investigating the clinical relevance and functional roles of GATA6 in HCC. In this regard, given GATA6’s indispensable role in liver development, we hypothesized that the dysregulation of GATA6 expression may contribute to hepatocarcinogenesis.

In this study, the clinical significance of GATA6 and its association with the various clinicopathological parameters in the human HCC cases were first examined. Subsequently, using both knockdown and overexpression approach, various functional assays were employed to characterize GATA6’s contribution to HCC progression.

Clinically, GATA6 expression levels was significantly downregulated in HCC tumor tissues and this was associated with poor cellular differentiation and poor disease-free survival. Loss of GATA6 could stimulate HCC cell proliferation rate, augment self-renewal ability, promote metastatic capacity, enhance tumorigenicity and the stemness features of HCC cells. Furthermore, silencing of GATA6 could foster the aerobic glycolysis pathway in HCC cells through the upregulation of glycolytic genes expression and the acceleration of the glucose uptake rate and lactate production. Mechanistically, pyruvate kinase muscle 2 (PKM2) was identified as a direct transcriptional regulatory target of GATA6 using ChIP-qPCR and luciferase reporter assays, further demonstrating GATA6’s involvement in the regulation of metabolic genes and pathways.

In conclusion, this study has once again recapitulated the plastic nature of hepatocytes and illustrated how the alterations of GATA6 expression could have deep implications in the stemness properties and metabolic phenotype of HCC cells. More specifically, loss of GATA6 in the HCC tumor could promote the oncogenic reprogramming of the cells to undergo dedifferentiation and regain the progenitor cell-like features, as well as metabolic rewiring to adopt a more glycolytic phenotype. This is the first piece of evidence to highlight the tumor suppressive role of GATA6 in HCC, whose expression could be of prognostic significance in HCC patients.