Glucocorticoids downregulate gene expression of GM-CSF, NAP-1/IL-8, and IL-6, but not of M-CSF in human fibroblasts

Abstract

Cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage-CSF (M-CSF), neutrophil-activating peptide-1/interleukin-8 (NAP-1/IL-8), and interleukin-6 (IL-6) are pivotal in the regulation of hematopoiesis and immune responses. In mesenchymal cells, their expression is induced by tumor necrosis factor α (TNF) and other agents. We now show that, while induction of cytokine expression by TNF in human lung fibroblasts was parallel, glucocorticoid hormones differentially affected their production. Dexamethasone (1 μmol/L) concordantly repressed expression of GM-CSF, NAP-1/IL-8 and IL-6. RNA and protein levels were reduced to approximately 5%, 20%, and 30% of control cells, respectively, as determined by Northern blot analyses and immunoassays. A 50% reduction of RNA levels for all three cytokines occurred in the range of 1 hour. In contrast, dexamethasone (1 μmol/L) did not decrease M-CSF RNA levels and protein release. M-CSF RNA and protein levels were maintained even when dexamethasone (1 μmol/L) was present for the whole duration of a 48-hour TNF stimulation. Further experiments showed that dexamethasone downregulates expression of GM-CSF, NAP-1 /IL-8, and IL-6 mainly by decreasing the mRNA stability of these cytokines, and that the dexamethasone-mediated repression of cytokine expression depends on ongoing protein and RNA syntheses. Our study suggests that glucocorticoid hormones repress expression of a set of cytokine genes important in conditions of stress. However, they seem not to affect M-CSF expression, which is likely to be more crucial in maintaining long-term functions of myeloid cells. © 1992 by The American Society of Hematology.