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 t umor metastasis, We demonstrated before that CD24, a M-r 35,000-60,000 muci ne-type glycosylphosphatidylinositol-linked cell surface molecule, can func tion as ligand for P-selectin and that the sialylLe(x) carbohydrate is esse ntial for CD24-mediated rolling of tumor cells on P-selectin, To investigat e the role of both antigens more closely, we transfected human A125 adenoca rcinoma cells with CD24 and/or fucosyltransferase VII (Fuc TVII) cDNAs, Sta ble transfectants expressed CD24 and/or sialylLe(x). Biochemical analysis c onfirmed that in A125-CD24/ FucTVII double transfectants, CD24 was modified with sialylLe(x), Only double transfectants showed rolling on P-selectin i n vivo, When injected into mice, double transfectants arrested in the lungs , and this step was P-selectin dependent because it was strongly enhanced i n 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-Fuc TVII single transfectants expressing sialylLe(x) but not CD24 did not show P-selectin-mediated lung arrest, The sialylLe(x) epitope is abundantly expr essed on human carcinomas, and significant correlations between sialylLe(x) expression and clinical prognosis exist. Our data suggest an important rol e for sialylLe(x)-modified CD24 in the lung colonization of human tumors.