A secreted mucin carrying sialyl-Lewis a from colon carcinoma cells binds to E-selectin and inhibits HL-60 cell adhesion.

Sialyl-Lewis x and a are known as ligands for E-selectin (ELAM-I) involved in leukocyte-endothelial adhesion. L-CanAg (light cancer antigen), secreted by a colon carcinoma cell line COLO 205, is a soluble mucin-type glycoprotein expressing sialyl-Lewis a antigens. L-CanAg was purified from spent culture medium by trichloracetic acid precipitation and Superose 6 gel filtration. With a monoclonal antibody against E-selectin (BBAI) as a positive control, the purified L-CanAg was shown to bind to E-selectin-Fc coated into plastic microtiter wells and to the surface of transiently E-selectin-transfected COS-I cells in a Ca(2+)-dependent way. Immunofluorescent double labelling showed that both BBAI and L-CanAg stained the same cells and morphological co-localization on E-selectin-transfected COS-I cells. Like BBAI, L-CanAg can inhibit leukocyte HL-60 cell adhesion to E-selectin-transfected COS-I cells, and this inhibition can be blocked by a F(ab')2 fragment directed against the sialyl-Lewis a epitope.