Early Secreted Antigenic Target of 6 kDa (ESAT-6) Protein of Mycobacterium tuberculosis Induces Interleukin-8 (IL-8) Expression in Lung Epithelial Cells via Protein Kinase Signaling and Reactive Oxygen Species

Abstract

Early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis is critical for the virulence and pathogenicity of M. tuberculosis . IL-8, a major chemotactic cytokine for neutrophils and T lymphocytes, plays important roles in the development of lung injury. To further understand the role of ESAT-6 in lung pathology associated with tuberculosis development, we studied the effects of ESAT-6 on the regulation of IL-8 expression in lung epithelial cells. ESAT-6 induced IL-8 expression by increasing IL-8 gene transcription and mRNA stability. ESAT-6 induction of IL-8 promoter activity was dependent on nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) binding and sensitive to pharmacological inhibition of PKC and ERK and p38 MAPK pathways. ESAT-6 activated ERK and p38 MAPK phosphorylation and rapidly induced reactive oxygen species (ROS) production. Dimethylthiourea but not mannitol inhibited IL-8 induction by ESAT-6, further supporting the involvement of ROS in the induction of IL-8 expression. Exposure of mice to ESAT-6 induced localized inflammatory cell aggregate formation with characteristics of early granuloma concomitant with increased keratinocyte chemoattractant CXCL 1 staining in bronchiolar and alveolar type II epithelial cells and alveolar macrophages. Our studies have identified a signal transduction pathway involving ROS, PKC, ERK, and p38 MAPKs and NF-κB and AP-1 in the ESAT-6 induction of IL-8 expression in lung epithelial cells. This has important implications for the understanding of lung innate immune responses to tuberculosis and the pathogenesis of lung injury in tuberculosis. Background: The role of early secreted antigenic target of 6-kDa in tuberculosis is unclear. Results: Early secreted antigenic target of 6 kDa induces interleukin-8 in lung epithelial cells via reactive oxygen species and protein kinases and promotes granuloma formation. Conclusion: Early secreted antigenic target of 6 kDa induces interleukin-8 to promote granuloma formation. Significance: Induction of interleukin-8 expression by early secreted antigenic target of 6 kDa is a potential mechanism for tuberculosis pathogenesis.