AhR and Arnt differentially regulate NF-κB signaling and chemokine responses in human bronchial epithelial cells

Abstract

BackgroundThe aryl hydrocarbon receptor (AhR) has gradually emerged as a regulator of inflammation in the lung and other tissues. AhR may interact with the p65-subunit of the nuclear factor (NF)-κB transcription factors, but reported outcomes of AhR/NF-κB-interactions are conflicting. Some studies suggest that AhR possess pro-inflammatory activities while others suggest that AhR may be anti-inflammatory. The present study explored the impact of AhR and its binding partner AhR nuclear translocator (Arnt) on p65-activation and two differentially regulated chemokines, CXCL8 (IL-8) and CCL5 (RANTES), in human bronchial epithelial cells (BEAS-2B).ResultsCells were exposed to CXCL8- and CCL5-inducing chemicals, 1-nitropyrene (1-NP) and 1-aminopyrene (1-AP) respectively, or the synthetic double-stranded RNA analogue, polyinosinic-polycytidylic acid (Poly I:C) which induced both chemokines. Only CXCL8, and not CCL5, appeared to be p65-dependent. Yet, constitutively active unligated AhR suppressed both CXCL8 and CCL5, as shown by siRNA knock-down and the AhR antagonist α-naphthoflavone. Moreover, AhR suppressed activation of p65 by TNF-α and Poly I:C as assessed by luciferase-assay and p65-phosphorylation at serine 536, without affecting basal p65-activity. In contrast, Arnt suppressed only CXCL8, but did not prevent the p65-activation directly. However, Arnt suppressed expression of the NF-κB-subunit RelB which is under transcriptional regulation by p65. Furthermore, AhR-ligands alone at high concentrations induced a moderate CXCL8-response, without affecting CCL5, but suppressed both CXCL8 and CCL5-responses by Poly I:C.ConclusionAhR and Arnt may differentially and independently regulate chemokine-responses induced by both inhaled pollutants and pulmonary infections. Constitutively active, unligated AhR suppressed the activation of p65, while Arnt may possibly interfere with the action of activated p65. Moreover, ligand-activated AhR suppressed CXCL8 and CCL5 responses by other agents, but AhR ligands alone induced CXCL8 responses when given at sufficiently high concentrations, thus underscoring the duality of AhR in regulation of inflammation. We propose that AhR-signaling may be a weak activator of p65-signaling that suppresses p65-activity induced by strong activators of NF-κB, but that its anti-inflammatory properties also are due to interference with additional pathways.

EWS‐FLI1 impairs aryl hydrocarbon receptor activation by blocking tryptophan breakdown via the kynurenine pathway

“…IL‐8, a pro‐inflammatory cytokine, is another AHR‐activated target gene and mRNA strikingly increases in EFL cells, but can be down‐regulated by silencing TDO2 (Fig. D).…”

“…Microarray data for several human tumors, among them ES, revealed a correlation of TDO2 expression with the expression of CYP1B1 [14], suggesting that some ES tumors express TDO2, which might have therapeutic potential. IL-8, a pro-inflammatory cytokine, is another AHRactivated target gene [54] and mRNA strikingly increases in EFL cells, but can be down-regulated by silencing TDO2 (Fig. 4D).…”

Cytokine responses induced by diesel exhaust particles are suppressed by PAR-2 silencing and antioxidant treatment, and driven by polar and non-polar soluble constituents

“…Thus, AhR-activation by classical PAHs or other AhR-ligands does not appear to be the driving force in DEP-induced inflammation in this cell line. Indeed recent findings suggest that AhR ligands may rather suppress pro-inflammatory responses by other agents (Beamer et al, 2012;Furumatsu et al, 2011;Øvrevik et al, 2014). However, PAHs with lower affinity for the AhR may possibly contribute to DEP-induced cytokine/chemokine responses through other mechanisms (Mayati et al, 2014;Øvrevik et al, 2013).…”

Norisoboldine, an Anti-Arthritis Alkaloid Isolated from Radix Linderae, Attenuates Osteoclast Differentiation and Inflammatory Bone Erosion in an Aryl Hydrocarbon Receptor-Dependent Manner

“…After being activation, AhR associates with NF-κB-p65 and interferes with the translocation of NF-κB-p65 from the cytoplasm to nucleus 25 . In RAW264.7 cells, RANKL (100 ng/mL) stimulation for 15 min markedly decreased the formation of the AhR-NF-κB-p65 complex, whereas NOR (30 μM) treatment markedly augmented the accumulation of this complex (Fig.…”