INVASION POTENTIAL AND N-ACETYLGALACTOSAMINE EXPRESSION IN A HUMAN-MELANOMA MODEL

Reactivity of the N-acetylgalactosamine-binding Helix pomatia agglutin in (HPA) in tumours has been associated with poor prognosis and metast asis development. In our LOX/FEMX-I human melanoma model, the binding of HPA correlates with experimental lung metastasis formation in athym ic nude mice. In the present study, the metastatic potential of 2 huma n melanoma cell lines (LOX and FEMX-I) was assessed in relation to car bohydrate and invasive phenotype. Immunocytological and invasion assay s highlighted significant differences between these 2 cell lines. Immu no-cytochemical analysis confirmed the widespread expression of HPA-bi nding glycoconjugates on LOX but not FEMX-I cells. One of these HPA-bi nding glycoconjugates, the Tn antigen, was expressed highly on the sur face of LOX cells but only weakly in the cytoplasm of FEMX-I cells. Th e sialyl Tn antigen was expressed in FEMX-I but not in LOX cells. Ther e was no difference between the cell lines in adhesion/rate of trappin g in athymic nude mouse lung tissues. In Matrigel invasion assays, LOX cells demonstrated an invasion potential more than 6 times greater th an that observed with FEMX-I cells. Matrigel invasion of LOX cells was inhibited after incubation with HPA (89%) compared to controls with H PA and GalNAc blocking sugar or without HPA (p < 0.0005 at 5 df). In c ontrast, there was no inhibitory effect with the anti-Tn antibody IE3. Invasion of FEMX-I cells was not affected by the lectin and the IE3 a ntibody. Immuno-cytochemical analysis revealed expression of the termi nal galactose-and polylactosamine-binding lectin galectin 3 (Mac-2) in these melanoma cell lines. Expression of both the lectin and its rece ptor may be a contributory feature in the pulmonary invasion of LOX me lanoma cells. Overall, our findings suggest that HPA-binding glycoconj ugates other than the alpha GalNAc-O-Ser/Thr of the Tn antigen may be important in the extracellular matrix invasion of LOX melanoma cells. (C) 1998 Wiley-Liss, Inc.