The CD24/P-selectin binding pathway initiates lung arrest of human A125 adenocarcinoma cells

Carbohydrates on tumor cells have been shown to play an important role in tumor metastasis. We demonstrated before that CD24, a M(r) 35,000-60,000 mucine-type glycosylphosphatidylinosito-linked cell surface molecule, can function as ligand for P-selectin and that the sialylLe(x) carbohydrate is essential for CD24-mediated rolling of tumor cells on P-selectin. To investigate the role of both antigens more closely, we transfected human A125 adenocarcinoma cells with CD24 and/or fucosyltransferase VII (Fuc TVII) cDNAs. Stable transfectants expressed CD24 and/or sialylLe(x). Biochemical analysis confirmed that in A125-CD24/FucTVII double transfectants, CD24 was modified with sialylLe(x). Only double transfectants showed rolling on P-selectin in vivo. When injected into mice, double transfectants arrested in the lungs, and this step was P-selectin dependent because it was strongly enhanced in lipopolysaccharide (LPS) pretreated wild-type mice but not in P-selectin knockout mice. CD24 modified by sialylLe(x) was required on the tumor cells because the LPS-induced lung arrest was abolished by removal of CD24 from the cell surface by phosphatidylinositol-specific phospholipase C. A125-FucTVII single transfectants expressing sialylLe(x) but not CD24 did not show P-selectin-mediated lung arrest. The sialylLe(x) epitope is abundantly expressed on human carcinomas, and significant correlations between sialylLe(x) expression and clinical prognosis exist. Our data suggest an important role for sialylLe(x)-modified CD24 in the lung colonization of human tumors.