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Modulation of Human β-Defensin-2 Transcription in Pulmonary Epithelial Cells by Lipopolysaccharide-Stimulated Mononuclear Phagocytes Via Proinflammatory Cytokine Production1

Human β-defensin (hBD)-2, a cationic antimicrobial peptide primarily induced in epithelial cells in response to inflammatory stimuli, plays an important role in host defense. To elucidate the expression mechanism of hBD-2 in the lung, we investigated the modulation of hBD-2 transcription in pulmonary epithelial cells by mononuclear phagocytes stimulated with LPS. Coculture of A549 pulmonary epithelial cells with Mono-Mac-6 monocytic cells in the presence of Escherichia coli LPS markedly up-regulated hBD-2 promoter activity, whereas A549 alone did not respond to LPS to activate the hBD-2 promoter. Furthermore, IL-1β and TNF-α in the culture supernatants from LPS-stimulated monocytic cells activated the hBD-2 promoter in A549 cells. Of note, IL-1β was more potent than TNF-α in this effect. In addition, a mutation of the NF-κB site at −200 (pκB1 site) completely abolished this IL-1β- and TNF-α-induced hBD-2 promoter activation, whereas NF-κB inhibitors (MG-132 and helenalin) strongly suppressed it. Moreover, electrophoretic mobility shift assay suggested that NF-κB, consisting of p65-p50 heterodimer, could bind to the pκB1 site in cytokine-stimulated A549 cells. Interestingly, flow cytometric analysis revealed that A549 cells expressed CD14 but lacked Toll-like receptor 4, which may account for the hyporesponsiveness of A549 cells to LPS. Taken together, these results suggest that hBD-2 expression in pulmonary epithelial cells is modulated by NF-κB via the actions of IL-1β and TNF-α produced by LPS-stimulated mononuclear phagocytes.