CHARACTERIZATION OF MACROPHAGE-INDUCING AND GRANULOCYTE-INDUCING PROTEINS FOR NORMAL AND LEUKEMIC MYELOID CELLS PRODUCED BY THE KREBS ASCITES TUMOR

Medium from serum-free cultures of Krebs [mouse] ascites tumor cells contains 2 macrophage and granulocyte inducing (MGI) activities that can act on the myeloid precursors of these hematopoietic cells. One activity, MGI-1, induced the formation of macrophage and granulocyte colonies from normal myeloid precursors. The 2nd activity, MGI-2, induced macrophage and granulocyte differentiation in myeloid leukemic cells that no longer required MGI-1 for colony formation. The medium contained 1 species of MGI-1 and 2 species of MGI-2. One species of MGI-2, MGI-2A, copurified through 5 stages of purification with MGI-1 but separated from the other MGI-2 species, MGI-2B, at an early stage in purification. MGI-1, MGI-2A and MGI-2B were purified 1490, 1140 and 678-fold, respectively. When bands with biological activity cut from non-denaturing polyacrylamide gels were run on SDS(sodium dodecyl sulfate)-polyacrylamide gel electrophoresis, MGI-1 and MGI-2A activities were associated with similar MW and each activity showed 2 band,s one of 23,000 and the other 25,000. MGI-2B activity showed 1 band with a MW of 45,000. Secretion did not appear to involve glycosylation, none of the species bound to concanavalin A, soybean agglutinin or wheat germ agglutinin agarose columns and they did not appear to contain carbohydrates. The assays for MGI-1 and MGI-2 activities were not affected by adding protease inhibitors. But MGI-2 was more readily destroyed by treatment with proteases and was more labile at high temperature and low pH than MGI-1. The level of cellular proteases may play a role in regulating the relative amounts of MGI-1 and MGI-2 that are present in vivo.