Dexamethasone increases the expression of membrane macrophage colony stimulating factor from retrovirally transduced tumor cells expressing macrophage colony stimulating factor

Abstract Many different tumor cell types (breast, ovarian, glioma, liver and colon) were retrovirally transduced with the human macrophage colony stimulating factor (M-CSF) gene (either the membrane associated form [mM-CSF] or the secreted form [sM-CSF]). These cells were tested for their ability to display increased amounts of mM-CSF in response to dexamethasone. M-CSF-transfected tumor cells expressed additional mM-CSF in response to 18–72 h incubations with 3–15 μg/ml dexamethasone, while non-transfected parental cells were unaffected by this treatment. Increased mM-CSF protein expression on the M-CSF transduced cells was observed by flow cytometry and Western blotting using M-CSF specific antibodies. Northern blot analysis revealed an increase in the mM-CSF specific transcripts within the dexamethasone-treated mM-CSF transduced cells, but this was not seen within the non-transfected tumor cells that were treated with dexamethasone. ICAM-1 expression was unaffected by dexamethasone treatment, indicating that this response is mM-CSF specific. All trans-retinal and 1,25-dihydroxy vitamin D3 compounds that have been reported to induce M-CSF expression failed to increase mM-CSF. When dexamethasone-treated mM-CSF transfected clones were used as target cells for macrophage-mediated cytotoxicity assays, an increased killing with the dexamethasone-treated cells was seen. The macrophage-mediated cytotoxicity of these mM-CSF expressing tumor cells was blocked with excess recombinant M-CSF by saturating M-CSF receptors on the macrophage that is required for this form of tumor cell killing. This work suggests the possibility that dexamethasone may prove useful for vaccination purposes using mM-CSF retrovirally transfected tumor cells.