Expression and Function of Four-and-a-Half LIM-domain protein 2 (FHL2) in Hepatocellular Carcinoma

The four-and-a-half LIM-domain protein 2 (FHL2) is an adaptor protein that can bind to different proteins, directing the functions of the protein complexes formed. FHL2 has been described to have multiple, often opposing functions in different cells and tissues. Also in different types of cancer, FHL2 has been associated with both pro- and anti-tumorigenic functions.

The aim of this study was to investigate the expression and role of FHL2 in hepatocellular carcinoma (HCC).

Methods and results:

FHL2 mRNA and protein expression were found to be significantly reduced in 4 human HCC cell lines compared to primary human hepatocytes. Also in human HCC tissues, FHL2 expression was significantly lower than in corresponding adjacent non-tumorous liver tissue. FHL2 expression was not increased in precancerous liver tissue of Mdr2 knockout mice, suggesting that the downregulation of FHL2 does not occur during HCC development but rather in advanced HCC. Analysis of HCC patient data showed that FHL2 expression was lower in high risk patient group (based on prognostic index) and correlated inversely with patients' survival. To get further insight into the role of FHL2 in HCC, we assessed HCC cells with siRNA-induced FHL2 suppression or adenoviral-mediated overexpression of FHL2 in functional in vitro assays. Neither knockdown nor overexpression of FHL2 had a significant effect on the proliferation of HCC cells. Furthermore, FHL2 suppression did not affect colony formation and colony growth in clonogenic assays. However, colony formation was significantly inhibited in FHL2 overexpressing cells. Furthermore, FHL2 suppression resulted in reduced expression of pro-inflammatory genes (IL-8 and ICAM-1) and an accumulation of p62 in HCC cells, indicative for impaired autophagy. Autophagy is known to affect the response to the multikinase inhibitor sorafenib, and interestingly, we observed that sorafenib treatment induced the expression of FHL2 in HCC cells. FHL2 depletion enhanced the sensitivity of HCC cells for sorafenib.

Summary and conclusion:

Expression analyses suggest an anti-tumorigenic role of FHL2 in HCC. However, functional analysis indicate both pro- and anti-tumorigenic effects of FHL2 in HCC cells and a complex role of FHL2 in combination with sorafenib treatment, which requires further investigation.