6E) . Activation of the NF-κB subunit p65/RelA controls the intensity of IL-12 p40 transcription . Because of this, we analyzed p65/RelA activation directly by assessing its binding to the promoter of Il12b, which encodes IL-12 p40, by chromatin immunoprecipitation (ChIP) assay. Interestingly, p65/RelA occupancy of the Il12b promoter was elevated in Itgb2−/− macrophages after 8 h of TLR4 stimulation (Fig. 6C), demonstrating a direct effect of β2 integrins on NF-κB subunit binding to the Il12b locus. Taken together with our gene expression data and signaling analyses,
these observations clearly show that one way by which β2 integrins suppress macrophage activation and inflammatory cytokine Transmembrane Transproters modulator production is by fine-tuning NF-κB pathway activation. While β2 integrin signals
direct modest, but consistent, changes in IκBα expression after TLR stimulation, these changes are sufficient to dramatically reduce inflammatory cytokine production in myeloid cells and demonstrate a critical role for β2 integrins in dampening TLR responses. A variety of cell surface receptors use ITAM-containing adapters to relay external https://www.selleckchem.com/products/smoothened-agonist-sag-hcl.html signals and enable appropriate cellular changes, including the β2 integrins, which signal via DAP12 and FcRγ [4, 14]. Yet while signals through DAP12 and FcR-γ have been clearly shown to block inflammation [10, 11, 36], defining the connection between the β2 integrins themselves and inflammatory processes has proven difficult due to conflicting data showing both positive and negative regulatory roles for this family of adhesion molecules [16-20, 37]. We have (-)-p-Bromotetramisole Oxalate clarified how β2 integrin activation influences TLR responses by using macrophages and DCs derived from the Itgb2−/− mouse, which lack all β2 integrin surface expression. Itgb2−/− macrophages and DCs produced more IL-12 p40 and IL-6 in response to stimulation with a variety of TLR agonists and Itgb2−/− mice generated more inflammatory cytokines after LPS injection than did WT control animals, demonstrating that β2 integrins are essential for inhibiting TLR activity in vitro and in vivo.
While these phenotypic findings are consistent with other studies reporting a suppressive role for β2 integrins, our use of Itgb2−/− myeloid cells provided a useful system with which to test various aspects of TLR regulation and to define the molecular requirements for β2 integrin-mediated TLR inhibition. To this end, we have identified a novel role for β2 integrins in calibrating NF-κB pathway activation downstream of TLR ligation. Without β2 integrin inhibitory signals, macrophage total IκBα levels remained consistently lower throughout the course of TLR stimulation. Curiously, we did not find consistently enhanced phosphorylated IκBα levels in Itgb2−/− cells after TLR stimulation, though this may be due to complications arising from using the proteasome inhibitor MG-132 in these experiments to inhibit the rapid degradation of IκBα.