The level of cell surface β1,4-galactosyltransferase I influences the invasive potential of murine melanoma cells

β1,4-Galactosyltransferase I (GalT I) is localized on the leading lamellipodia of migrating cells, where it associates with the cytoskeleton and facilitates cell spreading and migration on basal lamina matrices. It has previously been reported that a variety of highly metastatic murine and human cell lines are characterized by elevated levels of cell surface GalT I although the intracellular biosynthetic pool is similar between cells of high and low metastatic potential. In this study we examined whether the elevated expression of surface GalT I characteristic of metastatic cells is instructive or incidental to their metastatic behavior by altering the expression of surface GalT I and by the use of GalT I-specific perturbants. Surface GalT I levels were positively and negatively altered on murine melanoma cells by either overexpressing full-length GalT I or by homologous recombination, respectively. The consequences of altered surface GalT I expression on cell invasion in vitro and lung colonization in vivo were determined. Increasing surface GalT I expression on cells of low metastatic potential to levels characteristic of highly metastatic cells recapitulated the highly invasive phenotype in vitro. Alternatively, decreasing surface GalT I expression on highly metastatic cells to levels characteristic of low metastatic cells reduced their invasive behavior in vitro and metastatic activity in vivo. Within the physiological range of surface GalT I expression, the invasive potential of each clonal cell line correlated strongly with the level of surface GalT I expressed. As an independent means to assess the involvement of surface GalT I in metastatic behavior, cells were pretreated with two different classes of surface GalT I perturbants, a competitive oligosaccharide substrate and a substrate modifier protein. Both perturbants inhibited metastatic colonization of the lung, whereas control reagents did not. Finally, as reported by others, surface GalT I on metastatic cells selectively interacted with one glycoprotein substrate, or ligand, of approximately 100 kDa, the identity of which remains obscure. These results show that the elevated expression of surface GalT I characteristic of highly metastatic cells contributes to their invasive phenotype in vitro and to their metastatic phenotype in vivo.