Differentiation of myeloid leukemia cells and changes in their contractile proteins.

In this report we tried to draw a sketch of our recent work on the changes in actomyosin system during the differentiation of a myeloid leukemia cell line (M1). Before the differentiation, the M1 cells do not have a locomotive and phagocytic activity but do after the differentiation. The rather peculiar properties of actin shown by the leukemic M1 cells, low polymerizability and low affinity to myosin ATPase as well as the presence of polymerization inhibitor may explain their inability of motility and phagocytosis. Enhanced binding of actin and myosin on the plasma membrane looks necessary to carry out those differentiated functions which must need vigorous movement of the membrane. The cell movement also anticipates cell deformability which accompanies gelation in a part of cytoplasm and solation in another part. We have already isolated several gelation-factors as well as inhibitors. Not only chemical modifications of actin and myosin molecules but also quantitative variations in those regulatory proteins must be taken into consideration. Thus, studies on the cellular contractile proteins are casting a new light on the process of differentiation of the M1 cell line.