Changes in contractile proteins during differentiation of myeloid leukemia cells. I. Polymerization of actin.

Abstract

Quantitative and qualitative changes in cellular actin were followed during differentiation of a myeloid leukemia cell line, M1, which was inducible with conditioned medium (CM). During 3 days of incubation with CM, when the M1 cells differentiated to macrophages and lost their mitotic activity, the actin content, F-actin ratio in total actin and the actin synthesis showed an increase. A greater difference before and after differentiation was found in the ability of G-actin to polymerize. Actin harvested from CM-treated cells showed a greater ability to polymerize, depending on the increased concentration of MgCl2 and/or KCl and proteins, as compared with the actin from untreated M1 cells. Actin harvested from the Mm1 cell line, a macrophage line, had a particularly high polymerizability with or without CM treatment. In contrst, the actin from the D- subline, which is insensitive to CM, showed almost no polymerization.