Incubation of the human monoblastoid tumor cell line U937 with 5 × 10-9m 12-O-tetradecanoylphorbol-13-acetate (TPA) for 3 days was associated with marked morphological and functional changes including adherence of the cells and cessation of proliferation. While growth arrest and the viability of the cells were not influenced, the TPA-induced adherence of U937 cells could be totally blocked by incubation with tunicamycin, suggesting an involvement of N-linked carbohydrates in these cell attachment processes. The isolation and characterization of endogenous lectins with specificities for lactose, l-fucose, and d-mannose from U937 controls and TPA-differentiated U937 cells demonstrated marked differences in either the pattern and the distribution of these sugar-specific carbohydrate-binding proteins. Our results indicate that alterations in cell-surface carbohydrates are of central importance for the attachment of the differentiating U937 tumor cells.

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Supported by the Deutsche Forschungsgemeinschaft SFB244/B5.

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