[The expression and effects of isoforms of macrophage colony stimulating factor in human leukemic cell lines]

To explore the expression and effects of isoforms of macrophage colony-stimulating factor (M-CSF) in human leukemic cell lines.

Three normal human peripheral blood mononuclear cells (PBMCs) and 4 human myelomonocytic leukemic cell lines including J6-1, J6-2, K562 and HL-60 were studied using ABC immunoperoxidase assay, indirect immunofluorescence staining, flow cytometry, Western blot and reverse enzyme-linked DNA-protein interaction assay (reverse ELDIA).

M-CSF was noticed to be localized in the cytoplasm, nucleus and at the cell membrane in 4 human leukemic cell lines; expression of M-CSF was not detected in normal human PBMCs without PHA stimulation. Human PBMCs stimulated by PHA expressed a low level of M-CSF. Frequencies of membrane bound M-CSF expression in J6-1, J6-2, K562 and HL-60 were 71.6%, 69.7%, 42.7% and 57.4% respectively. Frequencies of cytoplasm and nucleus associated M-CSF were 65.7%, 45.4%, 36.5% and 72.5% respectively. The cytosolic bound M-CSF was expressed in J6-1 cell as four isoforms with a molecular weight of 14,000, 16,000, 20,000 and 44,000. While nucleus associated M-CSF expressed as two isoforms with a molecular weight of 16,000 and 20,000. Anti-M-CSF monoclonal antibody could dramatically inhibit proliferation of leukemic cells and its inhibitory effect was related to the levels of membrane bound M-CSF expression in leukemic cells. Reverse ELDIA showed that M-CSF could bind with DNA in vitro.

Expression of M-CSF isoforms is heterogeneous and polymorphous in leukemic cells. Membrane bound M-CSF is crucial for the proliferation of leukemic cells, which might be a DNA-bound protein and could be involved in the transformation and tumorigenesis of hematopoietic cells.