Le(y) glycolipid acts as a co-factor for tumor procoagulant activity

We have generated a monoclonal antibody (MAb), FS01, which inhibits the procoagulant activity (CCA-1) produced by a human squamous cell carcinoma cell line, LK52. Expression of the antigen recognized by FS01 MAb in various cancer cell lines correlated well with the procoagulant activities of the expressing cell lines. Our objective was to characterize the molecule reacting with FS01 MAb and to analyze its involvement in the CCA-1 procoagulant activity. The molecule was identified as a glycolipid and found to be involved in the procoagulant activity because both procoagulant activity and reactivity to FS01 MAb were lost after endoglycoceramidase treatment of CCA-1. Furthermore, FS01 MAb recognized the Lewis Y (Le[y]) antigen. To confirm the involvement of a glycolipid incorporating the Le(y) antigen in the procoagulant activity, we attempted to purify CCA-1 from LK52 culture supernatant. In one of the purification steps, a fraction containing low procoagulant activity (CCA-1p) separated from the Le(y)-positive fraction (CCA-1c). Although CCA-1c alone did not show procoagulant activity, the procoagulant activity of CCA-1p was augmented by CCA-1c and this augmentation was inhibited by FS01 MAb. Furthermore, CCA-1c enhanced the procoagulant activity of 33 cell lines tested as well as CCA-1p. In addition, purified Le(y) glycolipid from canine intestine augmented the procoagulant activity of CCA-1p, and this augmentation also could be inhibited by FS01 MAb. We conclude that Le(y) glycolipid is a co-factor for the procoagulant activity derived from cancer cells.