Identity of a differentiation inhibiting factor for mouse myeloid leukemia cells with NM23/nucleoside diphosphate kinase.

Mouse myeloid leukemic line M1 cells can be induced to differentiate into the monocyte/macrophage pathway by various inducers. The induction of differentiation of M1 cells can be inhibited by protein inhibitors termed differentiation inhibiting factors (I-factors) in a cell lysate and conditioned medium of differentiation resistant M1 cells. Production of the I-factor activity in resistant M1 cells is well associated with development of resistance of M1 cells to differentiation inducers. We have now purified one of the I-factors from conditioned medium of differentiation resistant M1 cells. The purified I-factor has a relative molecular mass of approximately 16000-17000 Da (16K I-factor). The amino acid sequence of all fragments of the 16K I-factor we have found are identical with Nm23/nucleoside diphosphate kinase (EC2.7.4.6) protein involved in tumor metastasis. The findings indicate that the I-factor, a candidate suppressor protein for differentiation of leukemic cells, is Nm23/nucleoside diphosphate kinase protein.