Tumor necrosis factor-alpha enhances mRNA expression and secretion of interleukin-6 in cultured human airway smooth muscle cells

Airway smooth muscle (ASM) is considered to be an end-target cell for the e ffects of mediators released during airway wall inflammation. Several repor ts suggest that activated ASM may be capable of generating various proinfla mmatory cytokines. We investigated the effects of tumor necrosis factor (TN F)-alpha, a potent proinflammatory cytokine, on cultured human ASM cells by examining the expression and release of the cytokine interleukin (IL)-6, c ell proliferation, and the expression pattern of c-fos and c-jun, two nucle ar proto-oncogenes constituting the activator protein-1 transcription facto r. Growth-arrested cell monolayers were stimulated with human recombinant T NF-alpha in a concentration- and time-dependent manner. TNF-alpha stimulate d the expression of IL-6 messenger RNA (mRNA), which was detected after 15 min, reaching a maximum at 1 h, IL-6 protein was readily detected in ASM ce ll-conditioned medium after Z h of TNF-alpha stimulation. Protein levels in creased in a time- and concentration-dependent manner. Release of IL-6 elic ited by TNF-alpha was significantly inhibited by dexamethasone, cycloheximi de, and nordihydroguaiaretic acid (NDGA). TNF-alpha did not alter DNA biosy nthesis up to 48 h or cell numbers up to 120 h. Northern blot analysis of p roto-oncogene expression revealed that c-fos and c-jun mRNA levels were ele vated after 30 min of TNF-alpha incubation with maximum levels at 1 h and 4 5 min, respectively. Expression of c-fos mRNA was downregulated by NDGA. Fo ur hours of TNF-alpha treatment resulted in translocation of c-jun immunofl uorescence from the cytoplasm to the nucleus in human ASM cells. Our result s suggest that despite the lack of a mitogenic response to TNF-alpha, upreg ulation of primary response genes in human ASM cells may account for the in duction of proinflammatory cytokines, such as IL-6, in human airways.