Multiple TLRs activate EGFR via a signaling cascade to produce innate immune responses in airway epithelium.
Toll-like receptors (TLRs) are critical for the recognition of inhaled pathogens that deposit on the airway epithelial surface. The epithelial response to pathogens includes signaling cascades that activate the EGF receptor (EGFR). We hypothesized that TLRs communicate with EGFR via epithelial signaling to produce certain innate immune responses. Airway epithelium expresses the highest levels of TLR2, TLR3, TLR5, and TLR6, and here we found that ligands for these TLRs increased IL-8 and VEGF production in normal human bronchial epithelial cells. These effects were prevented by treatment with a selective inhibitor of EGFR phosphorylation (AG-1478), a metalloprotease (MP) inhibitor, a reactive oxygen species (ROS) scavenger, and an NADPH oxidase inhibitor. In an airway epithelial cell line (NCI-H292), TNF-alpha-converting enzyme (TACE) small interfering RNA (siRNA) was used to confirm that TACE is the MP involved in TLR ligand-induced IL-8 and VEGF production. We show that transforming growth factor (TGF)-alpha is the EGFR ligand in this signaling cascade by using TGF-alpha neutralizing antibody and by showing that epithelial production of TGF-alpha occurs in response to TLR ligands. Dual oxidase 1 (Duox1) siRNA was used to confirm that Duox1 is the NADPH oxidase involved in TLR ligand-induced IL-8 and VEGF production. We conclude that multiple TLR ligands induce airway epithelial cell production of IL-8 and VEGF via a Duox1--> ROS--> TACE--> TGF-alpha--> EGFR phosphorylation pathway. These results show for the first time that multiple TLRs in airway epithelial cells produce innate immune responses by activating EGFR via an epithelial cell signaling cascade.
Koff
Jonathan L
JL
Cardiovascular Research Institute, University of California-San Francisco, San Francisco, California 94143-0130, USA.
Shao
Matt X G
MX
Ueki
Iris F
IF
Nadel
Jay A
JA
D051722:ADAM Proteins / Q000502:physiology; D000072198:ADAM17 Protein; D001980:Bronchi / Q000502:physiology; D002478:Cells, Cultured; D000074623:Dual Oxidases; D066246:ErbB Receptors / Q000502:physiology*; D006801:Humans; D007113:Immunity, Innate / Q000502:physiology*; D016209:Interleukin-8 / Q000096:biosynthesis; D019255:NADPH Oxidases / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D020545:Respiratory Mucosa / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D051193:Toll-Like Receptors / Q000502:physiology*; D016211:Transforming Growth Factor alpha / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis
D016209:Interleukin-8; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D051193:Toll-Like Receptors; D016211:Transforming Growth Factor alpha; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D000074623:Dual Oxidases; D019255:NADPH Oxidases; C431513:DUOX1 protein, human; D066246:ErbB Receptors; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human