Expression of Mucin‐associated Sulfo‐Le(a) Carbohydrate Epitopes on Human Colon Carcinoma Cells

The level of sulfo‐Le(a) (SO(3)‐3Galβ1‐3(Fucα1‐4)GlcNAc) epitope recognized by monoclonal antibody (mAb) 91.9H in hepatic metastasis of colon carcinoma is known to be lower than at the primary sites. We examined 19 human colon carcinoma cell lines for their production of this epitope. Sixteen cell lines were found to produce high M(r) components that metabolically incorporated [(35)S]sulfate and were resistant to heparitinase I and chondroitinase ABC, and 8 of them were reactive with mAb 91.9H as shown by western blotting analysis. These were all of the 4 cell lines derived from well differentiated primary tumors (HCCP‐2998, LS174T, GEO, and CBS), 2 of 10 cell lines (DLD‐1 and HCT116) from moderately to poorly differentiated primary tumors, and 2 of 5 cell lines (SW480 and HCC‐M1544) from metastases. Incubation of LS174T cells with benzyl‐N‐acetyl‐α‐d‐galactosaminide abrogated the incorporation of [(35)S]sulfate and the reactivity of mAb 91.9H with high M(r) components in the cell lysates. Sodium chlorate, which inhibits the formation of 3′‐phosphoadenosine 5′‐phosphosulfate, also inhibited the [(35)S]sulfate incorporation and reactivity with mAb 91.9H. These treatments did not change the incorporation of [(14)C]threonine into high M(r) components. These results indicated that sulfo‐Le(a) epitopes were expressed on O‐linked carbohydrate chains in sulfomucins. Immunohistochemical studies of tumor tissues in nude mice indicated that sulfo‐Le(a) was expressed at the site of orthotopic transplantation in the cecum. The expression appeared to be suppressed in liver metastatic foci in nude mice.