Concanavalin A Receptors on the Surfaces of Human Breast Cancer Cells in Organ Culture

The binding of concanavalin A (Con A) at the free apical membranes of surface tumor cells in human breast cancer explants grown in organ culture was studied cytochemically with horseradish peroxidase (HRP) as a marker. On the cell membranes in aldehyde-fixed explants or explants exposed to Con A at 4° C, a continuous label covered the entire free surface of the cell, which indicated the dispersed distribution of Con A binding sites. The binding of Con A at 20° C resulted in discontinuous label of the cell surface, with gaps of unlabeled membrane and partial endocytosis of the label. Incubation at 37° C, following the binding of Con A and HRP at both temperatures, induced more extensive, incubation time-dependent discontinuities of the surface label that led to complete disappearance of the label from the surface and its eventual endocytosis. Con A was topically stabilized on the surface only in those regions where two membranes or a different part of a folded membrane were in close contact. No differences were found in the binding, redistribution, and internalization of bound Con A among the various tumors studied.