Mouse myeloid leukemic M1 cells can be induced to differentiate into macrophages and granulocytes in vitro by a factor(s) stimulating differentiation of the cells (D-factor), which is suggested to be a glycoprotein. On the other hand, growth and differentiation of normal precursor cells of macrophages and granulocytes can be stimulated by a glycoprotein termed colony-stimulating factor (CSF). Mouse fibroblast L929 cells were found to produce both the D-factor and CSF. The properties of the D-factor and CSF and the roles of carbohydrates in the molecules of these factors were examined using tunicamycin, a specific inhibitor of asparagine-linked glycosylation.
Although both the D-factor and CSF were produced by L-cells in usual medium containing fetal calf serum, production of D-factor, but not CSF, was reduced by omission of serum from the medium. The activity of the D-factor was slightly decreased by treating the L-cells with tunicamycin (0.5 µg/ml) in the presence of 2% fetal calf serum, without any decrease in CSF activity. Conditioned medium of L-cells incubated with or without tunicamycin was fractionated by gel filtration on a Sephadex G-200 column. Normal D-factor appeared as a single peak with an apparent molecular weight of 67,000. D-factor produced in the presence of tunicamycin had an apparent molecular weight of 25,000. On the other hand, most of the CSF was eluted in the void volume, even when it was produced in the presence of tunicamycin. The D-factor produced in the presence of tunicamycin was more sensitive than normal D-factor was to trypsin or heat treatment at 70°. The CSF produced in the presence of tunicamycin was resistant to these treatments. These results indicate that the D-factor is distinct from CSF. Furthermore, the results suggest that the D-factor produced by L-cells is also a glycoprotein and that, although carbohydrate is not essential for production or activity of the D-factor, it contributes to stabilizing the protein portion of D-factor.
Supported in part by Grants-in-Aid for Cancer Research from the Ministry of Education, Science and Culture of Japan.