A colony-stimulating factor produced by mouse L . P3 cells in the presence of tunicamycin or 2-deoxy-D-glucose

L . P3 cells grown in serum-free synthetic medium produced a colony-stimulating factor (CSF: a sialoglycoprotein stimulating proliferation of granulocyte-macrophage progenitor cells). Addition of tunicamycin (2 microgram/ml) or 2-deoxy-D-glucose (10 mM) to the culture neither decreased the yield of CSF relative to the cell number grown nor induced heterogeneity of the produced CSF. However, CSF produced in the presence of tunicamycin (CSF-tm) was about 23 percent smaller in its molecular weight than normally produced CSF (CSF-normal). Similarly, the addition of 2-deoxy-D-glucose resulted in the formation of a CSF (CSF-dGlc) which was about 16 percent smaller than CSF-normal. However, both CSF-tm and CSF-dGlc seemed to have retained sialic acid residues, because they were focused respectively at pH 4.2 and pH 3.7 upon isoelectric focusing, and both were converted to a pH 5.2 species by treatment with neuraminidase. In addition, CSF-tm was significantly less heat-stable than CSF-normal, whereas CSF-dGlc was only slightly less stable. These results suggest that complete glycosylation of the factor is not necessary for its production nor for its stimulatory action on the proliferation of myeloid stem cells, but is necessary for its maximal stabilization.