Human melanoma cells (M21) actively attach and spread on a fibronectin substrate. Indirect immunofluorescence assays with specific monoclonal antibodies directed to the disialoganglioside GD2, the major ganglioside expressed on M21 melanoma cells, indicate that during the cell attachment process this molecule redistributes into microprocesses that make direct contact with the fibronectin substrate. Scanning and transmission immunoelectron microscopic studies with anti-GD2 monoclonal antibodies and immuno-gold staining demonstrate that GD2 preferentially localizes into substrate-associated microprocesses that emanate from the plasma membrane of the M21 cells. Staining with monoclonal antibodies directed to other melanoma surface antigens fails to demonstrate a similar distribution pattern on these cells. Direct evidence is provided that GD2 is involved in M21 cell attachment to fibronectin, since treatment of these cells with anti-GD2 monoclonal antibodies causes cell rounding and detachment from a fibronectin substrate. Moreover, scanning electron microscopy demonstrates that this loss of attachment of fibronectin is characterized by a perturbation of the cell attachment-promoting microprocesses that in the presence of these antibodies lose contact with the fibronectin substrate.

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