TGFβ1 induces IL‐6 and inhibits IL‐8 release in human bronchial epithelial cells: The role of Smad2/3

Human bronchial epithelial (HBE) cells contribute to asthmatic airway inflammation by secreting cytokines, chemokines, and growth factors, including interleukin (IL)‐6, IL‐8 and transforming growth factor (TGF) β1, all of which are elevated in asthmatic airways. This study examines the signaling pathways leading to TGFβ1 induced IL‐6 and IL‐8 in primary HBE cells from asthmatic and non‐asthmatic volunteers. HBE cells were stimulated with TGFβ1 in the presence or absence of signaling inhibitors. IL‐6 and IL‐8 protein and mRNA were measured by ELISA and real‐time PCR respectively, and cell signaling kinases by Western blot. TGFβ1 increased IL‐6, but inhibited IL‐8 production in both asthmatic and non‐asthmatic cells; however, TGF induced significantly more IL‐6 in asthmatic cells. Inhibition of JNK MAP kinase partially reduced TGFβ1 induced IL‐6 in both cell groups. TGFβ1 induced Smad2 phosphorylation, and blockade of Smad2/3 prevented both the TGFβ1 modulated IL‐6 increase and the decrease in IL‐8 production in asthmatic and non‐asthmatic cells. Inhibition of Smad2/3 also increased basal IL‐8 release in asthmatic cells but not in non‐asthmatic cells. Using CHIP assays we demonstrated that activated Smad2 bound to the IL‐6, but not the IL‐8 promoter region. We conclude that the Smad2/3 pathway is the predominant TGFβ1 signaling pathway in HBE cells, and this is altered in asthmatic bronchial epithelial cells. Understanding the mechanism of aberrant pro‐inflammatory cytokine production in asthmatic airways will allow the development of alternative ways to control airway inflammation. J. Cell. Physiol. 225: 846–854, 2010. © 2010 Wiley‐Liss, Inc.