Pro-inflammatory cytokines induce c-fos expression followed by IL-6 release in human airway smooth muscle cells

Abstract

Background: Airway smooth muscle (ASM) is considered to be a target for mediators released during airway inflammation. Aims: To investigate the expression of c-fos, a constituent of the transcription factor activator protein-1, in human ASM cells. In addition, to measure the release of interleukin (IL)-6 into the conditioned medium of stimulated ASM cells, as well as DNA biosynthesis and changes in cell number. Methods: Serum-deprived human ASM cells in the G0/G1 phase were stimulated with the pro-inflammatory cytokines; tumour necrosis factor-α, IL-1β, IL-5 and IL-6. The expression of mRNA encoding the proto-oncogene c-fos was measured by Northern blot analysis. Cell proliferation was assessed by [3H]-thymidine incorporation assays and cell counting, and IL-6 levels in cell-conditioned medium were measured by enzyme-linked immunosorbent assay. Results: All of the cytokines investigated induced a rapid (within l h) and transient increase in the expression of mRNA encoding c-fos, followed by the expression and enhanced release of IL-6. Cell proliferation remained unchanged in cytokine-stimulated cells. Conclusions: Cytokine-induced c-fos expression in human ASM cells could be described as a marker of cell 'activation'. The possible association of these results with airway inflammation, through secondary intracellular mechanisms such as cytokine production, is discussed.