Control of lysozyme induction in the differentiation of myeloid leukemic cells

A system has been developed with clones of mouse myeloid leukemic cells in culture to study the induction of synthesis and secretion of lysozyme in relation to other steps in myeloid cell differentiation. Lysozyme was initially absent in all the clones studied. The different clones can be divided into three types according to their ability to be induced to undergo normal cell differentiation by the protein inducer MGI (macrophage and granulocyte inducer). One type of clone that can be induced by MGI to form Fc and C3 receptors and differentiate to mature macrophages and granulocytes (MGI+D+) was also induced by MGI to synthesize and secrete lysozyme. Lysozyme was induced after Fc and C3 receptors, and labeling with 35S-methionine has shown that the induced lysozyme was newly synthesized. MGI+D+ clones were also induced to synthesize and secrete lysozyme by dexamethasone, prednisolone, cytosine arabinoside, or thymidine and in one of four clones by dimethylsulfoxide but not by sodium butyrate. Inhibition of cell multiplication by itself was not sufficient to induce lysozyme synthesis. A second type of clone which can be induced by MGI to form Fc and C3 receptors but not mature cells (MGI+D-) was more weakly inducible by MGI for lysozyme and was not inducible by any of the other compounds. A third type of clone (MGI-D) MGI for receptors or mature cells. One of four MGI-D- clones was induced to synthesize but not secrete lysozyme by dexamethasone together with sodium butyrate, but there was no lysozyme induction by MGI or any of the other compounds separately. The different clones maintained their different properties for at least 6 months in culture. The results indicate that clones with different hereditary blocks in the ability to be induced to differentiate by specific compounds can be used to dissect the process of myeloid cell differentiation, that the sequence of differentiation is induction of Fc and C3 receptors leads to lysozyme leads to mature cells, and that there are separate controls for these developmental steps.