Murine
melanoma cells readily bind and spread on murine
laminin. Uncoupling of spreading from adhesion occurs when unglycosylated
laminin is used as the cellular substratum; spreading is restored by soluble glycosylated
laminin or soluble
glycopeptides of
laminin. In this study, using
kifunensine, we produced and characterized an
oligomannoside-rich glycoform of
laminin. When used as a substratum for cell attachment and spreading, this
laminin was as effective as mature glycosylated
laminin. When added in
solution to unglycosylated
laminin-adherent cells,
kifunensine-
laminin was more effective in promoting cell spreading than mature glycosylated
laminin. Reconstitution with soluble
polysaccharides showed that cell spreading was initiated rapidly by microgram amounts of
mannan but not other
polysaccharides and approached a maximum within 1 h; titration with
mannan yielded an adsorption isotherm profile.
Mannose was an antagonist, preventing
mannan from restoring cell spreading, but it was not an agonist. A
Pronase digest of mature glycosylated
laminin, depleted of its
oligomannoside-
peptides, was unable to restore cell spreading, whereas a control digest was fully active.
Melanoma cells were unable to bind to three different neoglycoprotein surfaces, but when soluble unglycosylated
laminin was present in the medium the cells adhered to and spread only upon
mannosylated bovine serum albumin. Of the various cell lines known to interact with glycosylated
laminin only murine
melanoma cells showed
oligomannoside-dependent spreading on an unglycosylated
laminin substratum. The composite results indicate that
oligomannosides are necessary to initiate murine
melanoma cell spreading on
laminin but are not sufficient for cell adhesion.