Oligomannosides initiate cell spreading of laminin-adherent murine melanoma cells.

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.