Interaction of urokinase with specific receptors abolishes the time of commitment to terminal differentiation of murine erythroleukaemia (Friend) cells.

We have shown the presence of specific receptors for human urokinase on the surface of mouse erythroleukaemic cells. The receptor number increases when undifferentiated cells undergo hexamethylene-bisacetamide induced differentiation, while affinity between receptor and ligand does not change. A monoclonal antibody against the 17,500 mol wt fragment of the non-catalytic chain of urokinase (A chain) inhibits the specific binding, as we have previously shown in A431 cells. We have found that, upon the simultaneous addition of both urokinase or the A chain and hexamethylenebisacetamide, commitment is initiated immediately without the lag shown by control cultures of undifferentiated cells treated with the low molecular weight inducer alone. A series of mechanisms possibly involved in the action of urokinase on mouse erythroleukaemic differentiation are also discussed.