Background: Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction and persistent inflammation in the airways and lung parenchyma. Oxidative stress contributes to the pathogenesis of COPD. Interleukin (IL)-32 expression has been reported to increase in the lung tissue of patients with COPD. Here, we show that IFN gamma upregulated IL-32 expression and that oxidative stress augmented IFN gamma-induced-IL-32 expression in airway epithelial cells. We further investigated transcriptional regulation responsible for IFN gamma induced IL-32 expression in human airway epithelial cells.
Methods: Human bronchial epithelial (HBE) cells were stimulated with H2O2 and IFN gamma, and IL-32 expression was evaluated. The cell viability was confirmed by MTT assay. The intracellular signaling pathways regulating IL-32 expression were investigated by examining the regulatory effects of MAPK inhibitors and JAK inhibitor after treatment with H2O2 and IFN gamma, and by using a ChIP assay to identify transcription factors (i.e. c-Jun, CREB) binding to the IL-32 promoter. Promoter activity assays were conducted after mutations were introduced into binding sites of c-Jun and CREB in the IL-32 promoter. IL-32 expression was also examined in HBE cells in which the expression of either c-Jun or CREB was knocked out by siRNA of indicated transcription factors.
Results: There were no significant differences of cell viability among groups. After stimulation with H2O2 or IFN gamma for 48 hours, IL-32 expression in HBE cells was increased by IFN gamma and synergistically upregulated by the addition of H2O2. The H2O2 augmented IFN gamma induced IL-32 mRNA expression was suppressed by a JNK inhibitor, but not by MEK inhibitor, p38 inhibitor, and JAK inhibitor I. Significant binding of c-Jun and CREB to the IL-32 promoter was observed in the IFN gamma + H2O2 stimulated HBE cells. Introducing mutations into the c-Jun/CREB binding sites in the IL-32 promoter prominently suppressed its transcriptional activity. Further, knocking down CREB expression by siRNA resulted in significant suppression of IL-32 induction by IFN gamma and H2O2 in HBE cells.
Conclusion: IL-32 expression in airway epithelium may be augmented by inflammation and oxidative stress, which may occur in COPD acute exacerbation. c-Jun and CREB are key transcriptional factors in IFN gamma and H2O2 induced IL-32 expression.