Nuclear EpICD expression and its role in hepatocellular carcinoma

Regulated intramembrane proteolysis of epithelial cell adhesion molecule (EpCAM) results in shedding of the extracellular domain (EpEX) and release of the intra-cellular domain (EpICD) into the cytoplasm. Released EpICD associates with FHL2, β-catenin and Lef-1 to form a nuclear complex and triggers oncogenic signaling. This study was conducted to examine the nuclear expression of EpICD in hepatocellular carcinoma (HCC) and to assess the role of EpICD in HCC. EpICD immunoexpression was examined in 100 cases of HCC using tissue microarrays and correlated with clinicopathological parameters. We also examined the role of EpICD in HCC using EpICD cDNA transfected HCC cell line and EpCAM silenced HCC cell line by small interfering RNA (siRNA). Nuclear expression of EpICD was observed in 19 of 100 (19%) cases. Nuclear expression of EpICD significantly correlated with nuclear expression of β-catenin, and Ki-67 labeling index. In addition, nuclear expression of EpICD was associated with higher histologic grade and advanced T category. Forced overexpression of EpICD in the HCC cell significantly increased the cell proliferation, migration and invasion. The overexpression of EpICD also increased the expression levels of the active form of β-catenin and c-myc and cyclin D1. In contrast, downregulation of EpCAM by siRNA decreased the cell proliferation, migration, invasion and the expression of active form of β-catenin, c-myc and cyclin D1. Our present data suggest that EpICD plays important roles in HCC progression by modulating expression of target genes of EpCAM.