Inflammation is a hallmark of many important human diseases. Appropriate inflammation is critical for host defense. However, overactive response is detrimental to the host. Thus inflammation must be tightly regulated. The molecular mechanisms underlying the tight regulation of inflammation remain largely unknown. Ecotropic viral integration site 1 (EVI1), a proto-oncogene and zinc finger transcription factor, plays important roles in the normal development and leukemogenesis. However, its role in regulating NF-κB-dependent inflammation remains unknown. Here, we show that EVI1 negatively regulates nontypeable Haemophilus influenzae (NTHi)- and TNF-α-induced NF-κB-dependent inflammation in vitro and in vivo. EVI1 directly binds to the NF-κB p65 subunit and inhibits its acetylation at lysine 310, thereby inhibiting its DNA binding activity. Moreover, expression of EVI1 itself is induced by NTHi and TNF-α in a NF-κB-dependent manner, thereby unveiling a novel inducible negative feedback loop to tightly control NF-κB-dependent inflammation. Thus our study may not only provide important insights into the novel role of EVI1 in negatively regulating NF-κB-dependent inflammation, but may also shed light on the future development of novel anti-inflammatory strategies.

BackgroundInflammation is a hallmark of many serious human diseases. Nontypeable Haemophilus influenzae (NTHi) is an important human pathogen causing respiratory tract infections in both adults and children. NTHi infections are characterized by inflammation, which is mainly mediated by nuclear transcription factor-kappa B (NF-κB)-dependent production of proinflammatory mediators. Epidermal growth factor receptor (EGFR) has been shown to play important roles in regulating diverse biological processes, including cell growth, differentiation, apoptosis, adhesion, and migration. Its role in regulating NF-κB activation and inflammation, however, remains largely unknown.Methodology/Principal FindingsIn the present study, we demonstrate that EGFR plays a vital role in NTHi-induced NF-κB activation and the subsequent induction of proinflammatory mediators in human middle ear epithelial cells and other cell types. Importantly, we found that AG1478, a specific tyrosine kinase inhibitor of EGFR potently inhibited NTHi-induced inflammatory responses in the middle ears and lungs of mice in vivo. Moreover, we found that MKK3/6-p38 and PI3K/Akt signaling pathways are required for mediating EGFR-dependent NF-κB activation and inflammatory responses by NTHi.Conclusions/SignificanceHere, we provide direct evidence that EGFR plays a critical role in mediating NTHi-induced NF-κB activation and inflammation in vitro and in vivo. Given that EGFR inhibitors have been approved in clinical use for the treatment of cancers, current studies will not only provide novel insights into the molecular mechanisms underlying the regulation of inflammation, but may also lead to the development of novel therapeutic strategies for the treatment of respiratory inflammatory diseases and other inflammatory diseases.