Identification of an Mr 64,000 plasma membrane glycoprotein mediating adhesion of tumor H-59 cells to hepatocytes.

Tumor H-59 is a variant of the Lewis lung carcinoma which is metastatic to the liver. In previous studies we have shown that liver metastasis in this tumor model correlates with adhesion in vitro to hepatocyte monolayers (Brodt, P., Clin. Exp. Metastasis, 7: 525-539, 1989). In an attempt to identify the adhesion molecule(s) involved, monoclonal antibodies were produced. One monoclonal antibody (MAb C-11) was highly specific to hepatocyte-adherent tumor cells. The antibody (an IgG1) and F(ab)2 fragments blocked tumor cell attachment to hepatocytes while having no effect on tumor cell adhesion to basement membrane proteins coated onto culture dishes. Western blot analysis of solubilized 11-59 plasma membranes or cell lysates showed that the antibody recognizes an Mr 64,000 protein. Treatment with N-glycosidase F prior to Western blot analysis revealed that N-linked carbohydrate residues constitute approximately 43% of the total weight of this molecule. This glycoprotein is only weakly expressed on tumor M-27, a lung-specific subline of the Lewis lung carcinoma (Brodt, P., Cancer Res., 46: 2442-2448, 1986), is undetectable in plasma membrane preparations obtained from spleen cells and thymocytes, but can be detected on cultured hepatocytes and in hepatocyte cell lysates. Pretreatment of the hepatocytes with MAb C-11 also resulted in inhibition of tumor cell adhesion. These results suggest that this glycoprotein mediates the attachment of H-59 cells to hepatocytes.