EXPRESSION OF LAMP-1 AND LAMP-2 AND THEIR INTERACTIONS WITH GALECTIN-3 IN HUMAN TUMOR-CELLS

Lysosomal-membrane-associated glycoproteins (Lamps) 1 and 2 are rarely found on the plasma membranes of normal cells. There is evidence sugg esting an increase in their cellsurface expression in tumor cells, wit h some data indicating that the adhesion of some cancer cells to the e xtracellular matrix is partly mediated by interactions between Lamps a nd E-selectin and between Lamps and galectins (endogenous-galactoside- binding lectins). The present study examined the expression of Lamp-1 and Lamp-2 and their interactions with galectin-3 in different human t umor cell lines. Indirect immunofluorescence staining revealed accumul ation of Lamp molecules at the edges of A2058 human metastasizing mela noma cells suggesting that these glycoproteins could participate in ce ll adhesion. Flow cytometry showed the presence of cellsurface Lamps i n A2058, HT1080 (human fibrosarcoma) and CaCo-2 (human colon-adenocarc inoma) cells. Treatment with 2 mM sodium butyrate for 24 and 48 hr res ulted in a significant increase in Lamps surface expression. A strong binding of A2058 to recombinant galectin-3 was detected by FACS. The a pplication of 2 and 5 mM butyrate for the same incubation period enhan ced galectin-3 binding to Lamps-expressing cells. Our results support the idea that Lamps may be considered a new family of adhesive glycopr oteins participating in the complex process of tumor invasion and meta stasis. (C) 1998 Wiley-Liss, Inc.