Cloning and characterization of hepaCAM, a novel Ig-like cell adhesion molecule suppressed in human hepatocellular carcinoma

Background/Aims Previously, we reported on gene HEPN1 that was silenced in hepatocellular carcinoma (HCC) and its capability of arresting cell growth. In this study, we identified another novel gene hepaCAM from the liver, which contains the full-length HEPN1 on its antisense strand in the 3′-noncoding region, and assessed its expression, characteristics and functions in HCC. Methods Full-length hepaCAM cDNA was isolated by rapid amplification of cDNA ends. The gene expression was examined by semi-quantitative RT-PCR in 23 paired HCC liver specimens and 5 HCC cell lines. Transfection studies, coupled with immunocytochemistry, cellular interaction analyses, colony formation and microtetrazolium assay, were employed to elucidate the localization and functions of hepaCAM. Results The expression of hepaCAM decreased in 20/23 of HCC samples and was undetectable in 5 HCC cell lines tested. The gene product consisting of 416 amino acids displayed the typical structure of Ig-like cell adhesion molecules. The protein was glycosylated and predominantly localized on the cytoplasmic membrane. When re-expressed in HepG2, hepaCAM accelerated cell spreading (P<0.001), increased cell motility (P=0.0011), reduced colony formation (P=0.0022), and inhibited cell growth (P<0.001). Conclusions Gene hepaCAM, frequently silenced in HCC, encodes an Ig-like transmembrane glycoprotein and is involved in cell adhesion and growth control.