[Changes of cellular contractile proteins associated with differentiation of leukemic cells].

A myeloid leukemia cell line, M1, can be induced to differentiate to macrophages and gains motile and phagocytic functions which are not present before differentiation. The appearance of these differentiated functions were always accompanied with a loss of mitotic activity. It is well known that the intracellular contractile proteins play an important role in both cell motility and cytokinesis. Our question is, why the actomyosin system in the M1 cell line is utilized only for cell division and not for cell motility before differentiation, and why the opposite situation takes place after differentiation. Changes in contractile proteins hitherto revealed during the differentiation of this cell line are as follows: Actin; contents, synthetic rate, ability to polymerize, ratio of gamma-actin, activity to activate the myosin Mg2+ ATPase, and binding to plasma membrane all showed an increase after differentiation. Changes in the chemical structure of actin molecule were suggested by peptide mapping. In the undifferentiated M1 cytoplasms, an inhibitor protein for actin polymerization was identified. Myosin; contents, ratio of light chain L2, and binding to plasma membrane showed an increase after differentiation. Which one plays the most essential role in the transition from cell division to cell motility, and what interrelation is there among those changes are remained to be disclosed.