Mobility of Carbohydrate-Containing Structures on the Surfaces Membrane and the Normal Differentiation of Myeloid Leukemic Cells to Macrophages and Granulocytes

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RESUMO

Clones (D+) of a cultured line of myeloid leukemic cells can be induced to undergo normal differentiation to mature macrophages and granulocytes. There are also clones derived from the same cell line (D-) that could not be induced to differentiate. The carbohydrate-binding protein concanavalin A was used as a probe to study the mobility of carbohydrate-containing sites on the surface membrane of these cells. Changes in the distribution of concanavalin A binding sites on the surface membrane can be induced by concanavalin A. With the appropriate site mobility, this induction of a new distribution resulted in a concentration of concanavalin A-membrane site complexes on one pole of the cell to form a cap. D+ and D- clones showed 50 and 5% of cells with caps, respectively, although both types of cells bound a similar number of concanavalin A molecules. Treatment of cells with trypsin increased cap formation from 5 to 40% in D- cells, but did not change the percentage of cells with caps in D+ cells. The results show a difference in the mobility of concanavalin A binding sites in these two types of cells and suggest a difference in the fluid state of these carbohydrate-containing structures on the surface membrane. It is suggested that a gain of the ability of myeloid leukemic cells to undergo normal differentiation is associated with an increase in the fluidity of structures on the surface membrane where the concanavalin A sites are located. Differences in fluidity of specific membrane sites may also explain differences in the response of cells to other differentiation-inducing stimuli.

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