Characterization of a differentiation-inhibitory activity from nondifferentiating mouse myeloid leukemia cells.

Mouse myeloid leukemic M1 cells are induced to differentiate by various differentiation inducers. Activity for inhibition of induction of differentiation of M1 cells (I-activity) has been found in conditioned medium of variant M1 cell clones resistant to differentiation inducers, and this I-activity has been shown to be closely associated with resistance of the cells to differentiation inducers. In this work, the I-activity in the conditioned medium of the resistant M1 cells was shown to bind to Carboxymethyl-Sepharose CL-6B and to be eluted with 0.27-0.4 M NaCl. The profile of gel filtration of I-activity from Sephadex G-200 indicated considerable heterogeneity in molecules with I-activity; the apparent molecular range of the main I-activity was 60,000-80,000. On chromatofocusing, the I-activity was eluted with Polybuffer 96-acetic acid at pH 8.8-9.0. The I-activity was inactivated by treatment with trypsin or by heating at 75 degrees C for 30 min. Therefore, the main I-activity seemed to be due to a basic protein(s).