Decreased expression of biliary glycoprotein in hepatocellular carcinomas

Biliary glycoprotein (BGP) is an adhesion and anti-cell-growth molecule of the carcinoembryonic antigen family. We have earlier demonstrated that BGP mRNA is expressed in hepatocellular carcinomas (HCCs) and the adjacent non-cancerous regions, neither of which express CEA and NCA mRNA. To define an expression level and pattern of BGP at the protein level in HCCs, TS135, a monoclonal antibody (MAb) against BGP, was prepared. This MAb clearly reacted with BGP with a molecular weight of 110 kDa and 85 kDa (BGP-110/85). It cross-reacted weakly with NCA-90 from NCA transfectants, but not at all with CEA-200 from the serum of a colon-cancer patient. The BGP transfectants of cultured hepatocellular carcinoma cHc-4 cells showed Ca2+-dependent cell aggregation, which was partially inhibited by modulating BGP on the cell surface with MAb TS135. Immunostaining of non-cancerous liver tissues with MAb TS135 indicated that BGP could be expressed in the bile canalicular domain of hepatocytes. In HCCs, the expression of BGP was predominantly found in the well-differentiated type, where the bile canaliculi and the apical portion of pseudoglands were positively stained, although their staining intensity and stained area were lower and more limited, respectively, than those of non-cancerous regions. The percentage of faintly positive and negative cases (n = 22) from the total (n = 30) was 73%. This suggests that the expression level of BGP decreased in HCCs as compared with adjacent non-cancerous regions.