Sharlene Velichko

Regulation of Airway MUC5AC Expression by IL-1β and IL-17A; the NF-κB Paradigm

Mucin over-production is one of the hallmarks of chronic airway diseases such as chronic obstructive pulmonary disease, asthma, and cystic fibrosis. NF-κB activation in airway epithelial cells has been shown to play a positive inflammatory role in chronic airway diseases; however, the role of NF-κB in mucin gene expression is unresolved. In this study, we have shown that the proinflammatory cytokines, IL-1β and IL-17A, both of which utilize the NF-κB pathway, are potent inducers of mucin (MUC)5AC mRNA and protein synthesis by both well-differentiated primary normal human bronchial epithelial cells and the human bronchial epithelial cell line, HBE1. MUC5AC induction by these cytokines was both time- and dose-dependent and occurred at the level of promoter activation, as measured by a reporter gene assay. These effects were attenuated by the small molecule inhibitor NF-κB inhibitor III, as well as p65 small-interfering RNA, suggesting that the regulation of MUC5AC expression by these cytokines is via an NF-κB-based transcriptional mechanism. Further investigation of the promoter region identified a putative NF-κB binding site at position-3594/-3582 in the promoter of MUC5AC as critical for the regulation of MUC5AC expression by both IL-1β and IL-17A. Chromatin immunoprecipitation analysis confirmed enhanced binding of the NF-κB subunit p50 to this region following cytokine stimulation. We conclude that an NF-κB-based transcriptional mechanism is involved in MUC5AC regulation by IL-1β and IL-17A in the airway epithelium. This is the first demonstration of the participation of NF-κB and its specific binding site in cytokine-mediated airway MUC5AC expression.

IL-17A and Th17 cells in lung inflammation: an update on the role of Th17 cell differentiation and IL-17R signaling in host defense against infection.

The significance of Th17 cells and interleukin- (IL-)17A signaling in host defense and disease development has been demonstrated in various infection and autoimmune models. Numerous studies have indicated that Th17 cells and its signature cytokine IL-17A are critical to the airways immune response against various bacteria and fungal infection. Cytokines such as IL-23, which are involved in Th17 differentiation, play a critical role in controlling Klebsiella pneumonia (K. pneumonia) infection. IL-17A acts on nonimmune cells in infected tissues to strengthen innate immunity by inducing the expression of antimicrobial proteins, cytokines, and chemokines. Mice deficient in IL-17 receptor (IL-17R) expression are susceptible to infection by various pathogens. In this review, we summarize the recent advances in unraveling the mechanism behind Th17 cell differentiation, IL-17A/IL-17R signaling, and also the importance of IL-17A in pulmonary infection.

NF-κB Mediates IL-1β– and IL-17A–Induced MUC5B Expression in Airway Epithelial Cells

A major pathological feature of chronic airway diseases is the elevated expression of gel-forming mucins. NF-κB activation in airway epithelial cells has been shown to play a proinflammatory role in chronic airway diseases; however, the specific role of NF-κB in mucin gene expression has not been characterized. In this study, we show that the proinflammatory cytokines, IL-1β and IL-17A, both of which use the NF-κB pathway, are potent inducers of MUC5B mRNA expression in both well differentiated primary normal human bronchial epithelial cells and the human bronchial epithelial cell line, HBE1. MUC5B induction by these cytokines was both time- and dose-dependent, and was attenuated by the small molecule inhibitor, NF-κB inhibitor III, as well as p65 small interfering RNA, suggesting that the regulation of MUC5B expression by these cytokines is via an NF-κB-based transcriptional mechanism. Deletion analysis of the MUC5B promoter demonstrated that IL-1β- and IL-17A-induced promoter activity resides within the -4.17-kb to -2.56-kb region relative to the transcriptional start site. This region contains three putative κB-binding sites (NF-κB-1, -3,786/-3,774; NF-κB-2, -3,173/-3,161; and NF-κB-3, -2,921/-2,909). Chromatin immunoprecipitation analysis confirmed enhanced binding of the p50 NF-κB subunit to the NF-κB-3 site after cytokine stimulation. We conclude that an NF-κB-based transcriptional mechanism is involved in MUC5B regulation by IL-1β and IL-17A in airway epithelium. This is the first demonstration of the participation of NF-κB and its specific binding site in cytokine-mediated airway MUC5B expression.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced MUC5AC expression: aryl hydrocarbon receptor-independent/EGFR/ERK/p38-dependent SP1-based transcription.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxicant. Epidemiological studies have associated TCDD exposure with the development of chronic obstructive pulmonary disease, which is manifested by mucous/goblet cell hyperplasia. The purpose of this research was to elucidate the pathway/mechanisms that lead to TCDD-induced gene expression in both primary normal human bronchial epithelial cells and an immortalized cell line, HBE1, under air-liquid interface conditions. TCDD exposure induced a time-dependent elevation of MUC5AC mRNA and protein synthesis, and cytochrome p450 1A1 (CYP1A1) expression in these cells. Treatment with an aryl hydrocarbon receptor antagonist had no effect on TCDD-induced MUC5AC expression, but significantly suppressed CYP1A1 induction. However, treatments with inhibitors of signaling pathways and the expression of dominant negative mutants of epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase (ERK) and p38, but not the inhibition of c-Jun N-terminal kinase pathway, abrogated MUC5AC induction, but not that of CYP1A1. These effects also occurred at the MUC5AC promoter-reporter level using the chimeric construct for a transient transfection study. Western blot analysis confirmed the phosphorylation of activated EGFR, ERK, and p38 signaling molecules, but not the c-Jun N-terminal kinase, in cells after TCDD exposure. Specificity protein 1 (Sp1) phosphorylation also occurred in cells after TCDD exposure. Both MUC5AC expression and the promoter activity were inhibited by mithramycin A, an inhibitor specific to Sp1-based transcription. These results lead to the conclusion that TCDD induced MUC5AC expression through a noncanonical aryl hydrocarbon receptor-independent, EGFR/ERK/p38-mediated signaling pathway-mediated/Sp1-based transcriptional mechanism.

A novel nuclear function for the interleukin-17 signaling adaptor protein Act1

In the context of the human airway, interleukin-17A (IL-17A) signaling is associated with severe inflammation, as well as protection against pathogenic infection, particularly at mucosal surfaces such as the airway. The intracellular molecule Act1 has been demonstrated to be an essential mediator of IL-17A signaling. In the cytoplasm, it serves as an adaptor protein, binding to both the intracellular domain of the IL-17 receptor as well as members of the canonical nuclear factor kappa B (NF-κB) pathway. It also has enzymatic activity, and serves as an E3 ubiquitin ligase. In the context of airway epithelial cells, we demonstrate for the first time that Act1 is also present in the nucleus, especially after IL-17A stimulation. Ectopic Act1 expression can also increase the nuclear localization of Act1. Act1 can up-regulate the expression and promoter activity of a subset of IL-17A target genes in the absence of IL-17A signaling in a manner that is dependent on its N- and C-terminal domains, but is NF-κB independent. Finally, we show that nuclear Act1 can bind to both distal and proximal promoter regions of DEFB4, one of the IL-17A responsive genes. This transcriptional regulatory activity represents a novel function for Act1. Taken together, this is the first report to describe a non-adaptor function of Act1 by directly binding to the promoter region of IL-17A responsive genes and directly regulate their transcription.

Cholera toxin enhances interleukin-17A production in both CD4+ and CD8+ cells via a cAMP/protein kinase A-mediated interleukin-17A promoter activation

Cholera toxin (CT) is a bacterial component that increases intracellular cAMP levels in host cells and suppresses T‐cell activation. Recently, CT was reported to induce T helper type 17‐skewing dendritic cells and activate interleukin‐17A (IL‐17A) production in CD4+ T cells through a cAMP‐dependent pathway. However, the underlying mechanism by which cAMP regulates IL‐17A production in T cells is not completely defined. In this study, we took advantage of a small molecule protein kinase A (PKA) inhibitor (H89) and different cAMP analogues: a PKA‐specific activator (N6‐benzoyl‐adenosine‐cAMP), an exchange protein activated by cAMP‐specific activator (Rp‐8‐chlorophenylthio‐2′‐O‐methyl cAMP), and a PKA inhibitor (Rp‐8‐bromo‐cAMP), to elucidate the signalling cascade of cAMP in IL‐17A regulation in T cells. We found that CT induced IL‐17A production and IL‐17A promoter activity in activated CD4+ T cells through a cAMP/PKA pathway. Moreover, this regulation was via cAMP‐response element binding protein (CREB) ‐mediated transcriptional activation by using the transfection of an IL‐17A promoter–luciferase reporter construct and CREB small interfering RNA in Jurkat cells. Also, we showed that CREB bound to the CRE motif located at −183 of the IL‐17A promoter in vitro. Most interestingly, not only in CD4+ T cells, CT also enhanced cAMP/PKA‐dependent IL‐17A production and CREB phosphorylation in CD8+ T cells. In conclusion, our data suggest that CT induces an IL‐17A‐dominated immune microenvironment through the cAMP/PKA/CREB signalling pathway. Our study also highlights the potentials of CT and cAMP in modulating T helper type 17 responses in vivo.