title: Late-phase synthesis of IκBα insulates the TLR4-activated canonical NF-κB pathway from noncanonical NF-κB signaling in macrophages.
abstract: The nuclear factor κB (NF-κB) transcription factors coordinate the inflammatory immune response during microbial infection. Pathogenic substances engage canonical NF-κB signaling through the heterodimer RelA:p50, which is subjected to rapid negative feedback by inhibitor of κBα (IκBα). The noncanonical NF-κB pathway is required for the differentiation of immune cells; however, cross-talk between both pathways can occur. Concomitantly activated noncanonical signaling generates p52 from the p100 precursor. The synthesis of p100 is induced by canonical signaling, leading to the formation of the late-acting RelA:p52 heterodimer. This cross-talk prolongs inflammatory RelA activity in epithelial cells to ensure pathogen clearance. We found that the Toll-like receptor 4 (TLR4)-activated canonical NF-κB signaling pathway is insulated from lymphotoxin β receptor (LTβR)-induced noncanonical signaling in mouse macrophage cell lines. Combined computational and biochemical studies indicated that the extent of NF-κB-responsive expression of Nfkbia, which encodes IκBα, inversely correlated with cross-talk. The Nfkbia promoter showed enhanced responsiveness to NF-κB activation in macrophages compared to that in fibroblasts. We found that this hyperresponsive promoter engaged the RelA:p52 dimer generated during costimulation of macrophages through TLR4 and LTβR to trigger synthesis of IκBα at late time points, which prevented the late-acting RelA cross-talk response. Together, these data suggest that, despite the presence of identical signaling networks in cells of diverse lineages, emergent cross-talk between signaling pathways is subject to cell type-specific regulation. We propose that the insulation of canonical and noncanonical NF-κB pathways limits the deleterious effects of macrophage-mediated inflammation.
authors.affiliation: Systems Immunology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.|Kusuma School of Biological Sciences, IIT-Delhi, Hauz Khas, New Delhi, India.
authors.forename: Budhaditya
authors.initials: B
authors.lastname: Chatterjee
authors.affiliation: Systems Immunology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.
authors.forename: Balaji
authors.initials: B
authors.lastname: Banoth
authors.affiliation: Systems Immunology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.
authors.forename: Tapas
authors.initials: T
authors.lastname: Mukherjee
authors.affiliation: National Centre for Cell Science, Pune, India.
authors.forename: Nandaraj
authors.initials: N
authors.lastname: Taye
authors.affiliation: Systems Immunology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.
authors.forename: Bharath
authors.initials: B
authors.lastname: Vijayaragavan
authors.affiliation: National Centre for Cell Science, Pune, India.
authors.forename: Samit
authors.initials: S
authors.lastname: Chattopadhyay
authors.affiliation: Kusuma School of Biological Sciences, IIT-Delhi, Hauz Khas, New Delhi, India.
authors.forename: James
authors.initials: J
authors.lastname: Gomes
authors.affiliation: Systems Immunology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.
authors.forename: Soumen
authors.initials: S
authors.lastname: Basak
mesh_terms: D000818:Animals; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D000072000:NF-KappaB Inhibitor alpha / Q000096:biosynthesis* / Q000235:genetics; D052003:NF-kappa B p52 Subunit / Q000235:genetics / Q000378:metabolism*; D000067996:RAW 264.7 Cells; D020218:Response Elements; D015398:Signal Transduction / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000096:biosynthesis* / Q000235:genetics; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*
chemical_list: D052003:NF-kappa B p52 Subunit; C498207:Nfkb2 protein, mouse; C000606205:Nfkbia protein, mouse; C498144:Rela protein, mouse; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha