Protein factors that regulate the growth and differentiation of mouse myeloid leukaemia cells.

We have purified and characterized several protein factors that regulate the growth and differentiation of mouse myeloid leukaemia M1 cells. The differentiation factor (D-factor) from conditioned medium (CM) of Ehrlich ascites tumour cells is a glycoprotein of Mr 40,000-50,000. Its amino acid sequence was found to be almost identical to that of leukaemia inhibitory factor (LIF) from Krebs II ascites cells. The differentiation inhibitory factor (I-factor) from the CM of variant M1 cell clones which were resistant to several differentiation inducers is a basic protein of apparent Mr 68,000. The growth inhibitory factor (GI-factor) that specifically inhibits the partially differentiated and still growing monocytic leukaemia M1 cells was isolated from the CM of a clone of M1 cells resistant to the differentiation inducers. This GI-factor is a basic protein with an Mr of 25,000. Regulation by these protein factors together with other known cytokines of growth and differentiation of M1 cells is reported.