NF-κB Signaling in Inflammation: Mechanisms and Regulation

By Dr. Zubair Khalid, DVM, MS, PhD ·

NF-κB Signaling in Inflammation: Mechanisms and Regulation

Introduction to NF-κB Signaling in Inflammation

Nuclear factor kappa B (NF-κB) is a family of inducible transcription factors that serves as a master regulator of the inflammatory response. First identified in 1986 as a nuclear factor binding to the kappa light chain enhancer in B cells, NF-κB is now recognized as a ubiquitous signaling hub that controls the expression of hundreds of genes involved in inflammation, immunity, cell survival, and proliferation. In resting cells, NF-κB dimers are sequestered in the cytoplasm by inhibitor proteins. Upon stimulation, a cascade of phosphorylation, ubiquitination, and proteasomal degradation liberates NF-κB, allowing its nuclear translocation and target gene activation. This pathway is remarkably conserved across metazoans and is central to both acute host defense and chronic inflammatory pathology.

The NF-κB Family

The mammalian NF-κB family comprises five proteins that share a conserved N-terminal Rel homology domain (RHD) responsible for DNA binding, dimerization, and interaction with inhibitor IκB proteins: NF-κB1 (p50, derived from p105), NF-κB2 (p52, derived from p100), RelA (p65), RelB, and c-Rel. These proteins form homo- and heterodimers, with the p50/RelA heterodimer being the predominant canonical form. The RHD also contains a nuclear localization sequence (NLS) that is masked by IκB binding in the cytoplasm. Transcriptional activation requires the C-terminal transactivation domain (TAD) present in RelA, RelB, and c-Rel; p50 and p52 lack TADs and must partner with TAD-containing subunits or coactivators to activate transcription.

Inflammation and NF-κB

Inflammation is a protective response to infection, tissue injury, or cellular stress. NF-κB lies at the apex of this response, rapidly inducing pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), chemokines (IL-8, MCP-1), adhesion molecules (ICAM-1, VCAM-1, E-selectin), and inducible enzymes (iNOS, COX-2). This transcriptional program recruits immune cells, promotes vasodilation and vascular permeability, and coordinates pathogen clearance. However, dysregulated NF-κB activation underlies chronic inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease, asthma, and atherosclerosis. Understanding the precise molecular mechanisms of NF-κB regulation is therefore essential for both basic immunology and therapeutic development.

The Canonical NF-κB Pathway

The canonical pathway is the principal route of NF-κB activation in response to pro-inflammatory stimuli. It is rapid, transient, and depends on the inducible degradation of IκB proteins. This pathway shares upstream receptor-proximal components with other inflammatory signaling cascades, and its activation is tightly controlled at multiple levels.

Stimuli and Receptors

Canonical NF-κB is triggered by a diverse array of stimuli, including:

  • TNF-α binding to TNF receptor 1 (TNFR1)
  • IL-1β binding to IL-1 receptor (IL-1R)
  • Toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS) binding to TLR4
  • Antigen receptor engagement on B and T cells
  • CD40 ligation on antigen-presenting cells

These receptors converge on the IKK complex through distinct adaptor proteins. TNFR1 recruits TRADD and RIPK1, which then activate the IKK complex. IL-1R and TLRs recruit MyD88, IRAK kinases, and TRAF6, which catalyze K63-linked polyubiquitin chains that serve as scaffolds for IKK activation. TRAF6, an E3 ubiquitin ligase, generates ubiquitin chains that recruit the TAK1 kinase complex via TAB2/TAB3 adaptors. TAK1 then phosphorylates and activates IKKβ.

IKK Complex Activation

The IKK complex is a high-molecular-weight assembly (700–900 kDa) containing two catalytic subunits, IKKα (IKK1) and IKKβ (IKK2), and a regulatory subunit, NEMO (NF-κB essential modulator, also called IKKγ). IKKβ is the primary kinase for canonical activation, while IKKα plays a minor role in this pathway but is essential for the non-canonical pathway. NEMO serves as a scaffold that links the complex to upstream activators and is required for IKK activation by most stimuli.

Activation of IKKβ occurs through phosphorylation at the activation loop serines (Ser177 and Ser181 in human IKKβ) by TAK1. This phosphorylation induces a conformational change that opens the kinase active site. Activated IKKβ then phosphorylates IκB proteins at two conserved serine residues within their N-terminal degradation motif (Ser32 and Ser36 in IκBα). This phosphorylation is the committed step in canonical NF-κB activation.

IκB Ubiquitination and Degradation

IκB proteins (IκBα, IκBβ, IκBε) bind NF-κB dimers and mask their nuclear localization sequences, retaining them in the cytoplasm. IκBα is the most abundant and rapidly regulated isoform, with a half-life of approximately 1–2 hours in resting cells. Upon IKKβ-mediated phosphorylation at Ser32/Ser36, IκBα becomes a substrate for the SCFβ-TrCP E3 ubiquitin ligase complex. β-TrCP recognizes the phosphorylated degron and catalyzes K48-linked polyubiquitination at Lys21 and Lys22 of IκBα.

The polyubiquitinated IκBα is then rapidly degraded by the 26S proteasome, with a half-life of less than 2 minutes after phosphorylation. This degradation exposes the NLS on RelA, allowing the p50/RelA heterodimer to translocate to the nucleus. Once in the nucleus, NF-κB binds to κB consensus sequences (5′-GGGRNNYYCC-3′) in the promoters and enhancers of target genes. Nuclear import is mediated by importin-α/β, and nuclear export of inactive NF-κB is regulated by CRM1-dependent pathways.

The entire canonical pathway from receptor engagement to nuclear NF-κB occurs within 5–15 minutes for most stimuli, making it one of the fastest transcriptional responses in biology.

The Non-Canonical NF-κB Pathway

The non-canonical pathway is a slower, more selective route of NF-κB activation that operates independently of IKKβ and IκB degradation. It is critical for adaptive immunity, particularly B-cell survival, lymphoid organogenesis, and humoral immune responses.

NIK and IKKα

The non-canonical pathway is triggered by a limited set of receptors, including CD40, BAFF-R (B-cell activating factor receptor), LTβR (lymphotoxin β receptor), and RANK (receptor activator of NF-κB). These receptors signal through TRAF2/TRAF3, which in resting cells maintain the kinase NIK (NF-κB-inducing kinase) in a constant state of degradation. TRAF3 recruits the E3 ligase cIAP1/cIAP2 to ubiquitinate NIK, targeting it for proteasomal degradation.

Receptor engagement causes TRAF2/TRAF3 to be recruited to the receptor complex and degraded, relieving NIK from constitutive degradation. Stabilized NIK accumulates and phosphorylates IKKα, which exists as a homodimer in this pathway. Activated IKKα then phosphorylates the C-terminal region of p100, the NF-κB2 precursor protein.

p100 Processing

p100 is unique among NF-κB family members because it contains both an N-terminal RHD and a C-terminal IκB-like domain with multiple ankyrin repeats. In resting cells, p100 is sequestered in the cytoplasm, often bound to RelB. IKKα-mediated phosphorylation of p100 at Ser866 and Ser870 creates a binding site for β-TrCP, which ubiquitinates p100 and targets it for partial proteasomal processing.

The proteasome degrades the C-terminal IκB-like domain of p100 but spares the N-terminal RHD, generating the mature p52 subunit. This processing is incomplete—the proteasome stalls at a glycine-rich region—resulting in the production of p52 rather than complete degradation. The p52/RelB heterodimer then translocates to the nucleus and activates a distinct set of target genes involved in B-cell survival, lymphoid organ development, and humoral immunity.

Unlike the canonical pathway, non-canonical activation requires hours rather than minutes, reflecting the need for NIK stabilization and de novo protein synthesis in some contexts. The two pathways are not entirely independent; certain stimuli can activate both, and cross-talk occurs at the level of shared downstream targets and regulatory proteins.

Regulation of NF-κB Activity

NF-κB signaling is subject to multiple layers of negative regulation that ensure the response is transient and appropriately scaled. Dysregulation of these feedback mechanisms contributes to chronic inflammation and cancer.

Negative Feedback Loops

The most important negative feedback loop involves IκBα itself. NF-κB target genes include NFKBIA, which encodes IκBα. Newly synthesized IκBα enters the nucleus, removes NF-κB from DNA, and exports it back to the cytoplasm, restoring the resting state. This creates an oscillatory pattern of NF-κB nuclear localization, with cycles of approximately 100 minutes in response to continuous TNF-α stimulation.

A20 (TNFAIP3) is another critical NF-κB-induced negative regulator. A20 is a dual-function enzyme with deubiquitinase (DUB) and E3 ligase activities. It removes K63-linked ubiquitin chains from RIPK1 and TRAF6, terminating upstream signaling, and also adds K48-linked chains to promote their degradation. A20 deficiency in mice causes severe multi-organ inflammation and premature death, underscoring its essential role.

Other negative regulators include:

  • CYLD, a deubiquitinase that removes K63 chains from IKK components
  • IκBε, which provides a slower, sustained inhibition
  • BCL-3, which can act as a transcriptional coactivator or repressor depending on context
  • SHP-1 and SOCS proteins, which attenuate upstream receptor signaling

Post-Translational Modifications

NF-κB activity is finely tuned by post-translational modifications beyond phosphorylation. RelA is subject to acetylation at multiple lysine residues (K218, K221, K310) by p300/CBP acetyltransferases. Acetylation at K310 is required for full transcriptional activity, while acetylation at K221 regulates DNA binding affinity. Deacetylation by HDAC3 terminates RelA activity.

Methylation of RelA at K314 and K315 by SETD6 promotes its degradation, while methylation at K37 by SET9 enhances transcriptional activity. Phosphorylation of RelA at Ser276 by protein kinase A (PKA) or MSK1/2 promotes interaction with coactivators, while phosphorylation at Ser536 by IKKβ or other kinases modulates nuclear localization and transcriptional activity. These modifications create a "phosphorylation code" that determines which target genes are expressed and how strongly.

NF-κB Target Genes in Inflammation

NF-κB regulates over 400 target genes, many of which are central to the inflammatory response. These can be grouped into functional categories that together orchestrate the full inflammatory cascade.

Cytokines and Chemokines

NF-κB directly induces the expression of key pro-inflammatory cytokines:

  • TNF-α: A master pro-inflammatory cytokine that activates NF-κB itself, creating a positive feedback loop
  • IL-1β: A pyrogenic cytokine that also activates NF-κB through IL-1R
  • IL-6: A pleiotropic cytokine driving acute-phase responses and T-cell differentiation
  • IL-12p40: A subunit of IL-12 and IL-23, promoting Th1 and Th17 responses

Chemokines induced by NF-κB include IL-8 (CXCL8), which recruits neutrophils, and MCP-1 (CCL2), which recruits monocytes and macrophages. These chemokines establish chemotactic gradients that direct leukocyte infiltration to sites of inflammation.

Adhesion Molecules

NF-κB upregulates adhesion molecules on endothelial cells that enable leukocyte extravasation:

  • ICAM-1 (CD54): Binds LFA-1 on leukocytes, mediating firm adhesion
  • VCAM-1 (CD106): Binds VLA-4, important for monocyte and lymphocyte adhesion
  • E-selectin (CD62E): Mediates initial rolling of leukocytes on endothelium

These molecules are induced within 1–4 hours of NF-κB activation and are essential for recruiting immune cells from the bloodstream into inflamed tissues.

Enzymes like iNOS and COX-2

NF-κB also induces enzymes that amplify the inflammatory response:

  • iNOS (NOS2): Produces nitric oxide (NO), a potent vasodilator and cytotoxic molecule. iNOS is induced by NF-κB in macrophages and produces micromolar concentrations of NO, compared to nanomolar levels from constitutive eNOS.
  • COX-2 (PTGS2): Catalyzes the production of prostaglandins, particularly PGE2, which mediate pain, fever, and vasodilation. COX-2 is undetectable in most resting tissues but is rapidly induced by NF-κB.

Other NF-κB target genes include matrix metalloproteinases (MMP-1, MMP-3, MMP-9), which degrade extracellular matrix and facilitate tissue remodeling, and acute-phase proteins such as serum amyloid A and C-reactive protein.

Methods to Study NF-κB Signaling

Studying NF-κB requires techniques that assess different aspects of the pathway: activation status, DNA binding, transcriptional activity, and subcellular localization.

Reporter Assays

The most common reporter assay uses a luciferase gene under the control of a minimal promoter containing tandem κB binding sites (typically 3–5 copies of the consensus sequence). Cells are transfected with the reporter plasmid, stimulated, and luciferase activity is measured using a luminometer. This assay quantifies net transcriptional output but does not distinguish between different NF-κB dimers.

A more sophisticated approach uses NF-κB-GFP fusion proteins to track nuclear translocation in live cells by time-lapse microscopy. This reveals the oscillatory dynamics of NF-κB localization and can be combined with microfluidic devices for precise stimulus control.

Protein Analysis

Western blotting is the standard method to assess IκBα degradation and RelA phosphorylation. Cells are lysed in RIPA buffer containing protease and phosphatase inhibitors (e.g., 1 mM PMSF, 1 mM Na3VO4, 1 mM NaF). Lysates are separated by SDS-PAGE, transferred to PVDF membranes, and probed with antibodies against phospho-IκBα (Ser32/36), total IκBα, phospho-RelA (Ser536), or total RelA. IκBα degradation is typically observed within 10–15 minutes of TNF-α stimulation, with resynthesis by 60 minutes.

Electrophoretic mobility shift assay (EMSA) detects NF-κB DNA binding. Nuclear extracts are incubated with a 32P-labeled double-stranded oligonucleotide containing a κB consensus sequence, then resolved on a non-denaturing 4–6% polyacrylamide gel. Bound NF-κB retards the probe's migration. Supershift assays using antibodies against specific subunits identify the dimer composition. EMSA is semi-quantitative and requires radioactive labeling, so many laboratories now use ELISA-based DNA binding assays (e.g., TransAM) that are faster and non-radioactive.

Immunofluorescence visualizes NF-κB subcellular localization. Cells are fixed with 4% paraformaldehyde, permeabilized with 0.1% Triton X-100, and stained with anti-RelA antibodies followed by fluorescent secondary antibodies. Confocal microscopy reveals cytoplasmic staining in resting cells and nuclear accumulation after stimulation. This method is particularly useful for assessing cell-to-cell heterogeneity.

Genetic Approaches

Knockout mice for each NF-κB family member and IKK subunit have been generated. RelA knockout mice die embryonically at day 15 due to TNF-induced liver apoptosis, demonstrating RelA's role in cell survival. IKKβ and NEMO knockouts are also embryonic lethal. Conditional knockouts using Cre-loxP technology allow tissue-specific deletion, such as myeloid-specific IKKβ deletion to study macrophage function.

RNA interference (siRNA/shRNA) and CRISPR-Cas9 gene editing enable acute or stable knockdown in cell lines. CRISPR is particularly powerful for generating complete knockouts of NF-κB pathway components in human cells, allowing mechanistic studies without the complications of embryonic lethality.

NF-κB in Inflammatory Diseases

Chronic activation of NF-κB is a hallmark of many inflammatory diseases. Understanding the specific contributions of NF-κB in each disease context has informed therapeutic strategies.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation, pannus formation, and joint destruction. NF-κB is constitutively active in RA synovial tissue, particularly in macrophages and fibroblast-like synoviocytes. This activation drives the expression of TNF-α, IL-6, IL-1β, and MMPs that degrade cartilage and bone.

TNF-α, a key NF-κB target, is itself a potent NF-κB activator, creating a self-sustaining inflammatory loop. The success of TNF inhibitors (infliximab, etanercept) in RA validates this pathway as a therapeutic target. However, NF-κB inhibition also blocks the anti-inflammatory effects of glucocorticoids, which work partly by inducing IκBα synthesis and transrepressing NF-κB target genes.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), encompassing Crohn's disease and ulcerative colitis, involves chronic intestinal inflammation driven by dysregulated immune responses to gut microbiota. NF-κB is strongly activated in intestinal macrophages and epithelial cells of IBD patients. NEMO knockout in intestinal epithelial cells causes severe colitis in mice, indicating that NF-κB in the epithelium is protective, while NF-κB in myeloid cells is pathogenic.

This cell-type-specific duality is a critical consideration for therapeutic targeting. Pan-NF-κB inhibition might exacerbate epithelial damage while suppressing myeloid inflammation. The complexity of NF-κB's role in IBD illustrates why cell-type-specific approaches are needed.

Asthma

Asthma is a chronic inflammatory airway disease characterized by eosinophilic inflammation, mucus hypersecretion, and airway hyperresponsiveness. NF-κB is activated in airway epithelial cells and macrophages of asthmatic patients. It drives the expression of Th2-promoting cytokines (TSLP, IL-25, IL-33), chemokines (eotaxin), and adhesion molecules that recruit eosinophils. Corticosteroids, the mainstay of asthma therapy, work partly by inhibiting NF-κB through induction of IκBα and direct transrepression of NF-κB target genes.

Therapeutic Targeting of NF-κB

Given its central role in inflammation, NF-κB is an attractive therapeutic target. However, its ubiquitous expression and essential functions in normal immunity pose significant challenges.

Inhibitors and Challenges

Several classes of NF-κB inhibitors have been explored:

  • IKKβ inhibitors (e.g., BMS-345541, MLN120B): Block the kinase activity of IKKβ, preventing IκBα phosphorylation. These show efficacy in animal models of RA and IBD but have not advanced to clinical use due to toxicity and lack of selectivity.
  • Proteasome inhibitors (e.g., bortezomib): Block IκBα degradation by inhibiting the 26S proteasome. Bortezomib is approved for multiple myeloma but causes significant immunosuppression and peripheral neuropathy.
  • Glucocorticoids: Potent anti-inflammatory drugs that induce IκBα transcription and transrepress NF-κB target genes. Their use is limited by metabolic side effects with chronic use.
  • Natural compounds: Curcumin, resveratrol, and parthenolide inhibit NF-κB at various levels. These are generally weak and non-specific but have been used as dietary supplements.
  • Oligonucleotide decoys: Double-stranded DNA containing κB consensus sequences that competitively bind NF-κB and prevent its interaction with genomic targets. These have been tested in clinical trials for atopic dermatitis.

The major challenge is that NF-κB is essential for host defense. Global inhibition causes immunosuppression, increasing susceptibility to infections. The embryonic lethality of NF-κB knockout mice underscores its non-redundant roles. Current efforts focus on:

  • Selective inhibition of specific NF-κB dimers (e.g., p50/c-Rel inhibitors)
  • Cell-type-specific delivery using nanoparticles or antibody-drug conjugates
  • Targeting upstream regulators that are more disease-specific, such as individual TLRs or cytokine receptors
  • Inhibiting NF-κB transcriptional activity rather than activation, using drugs that block the interaction of RelA with coactivators

Common Pitfalls and Practical Summary

Students and researchers studying NF-κB often encounter several conceptual and technical pitfalls.

Oversimplifying the pathway: NF-κB is not a single linear pathway but a network with extensive cross-talk, feedback, and cell-type specificity. The canonical and non-canonical pathways are not mutually exclusive, and many stimuli activate both to different degrees.

Ignoring cell-type specificity: NF-κB responses differ dramatically between cell types. What is true in HeLa cells may not hold in primary macrophages or epithelial cells. Always verify findings in the relevant cell type.

Confusing activation with transcription: NF-κB nuclear translocation does not guarantee transcriptional activity. Post-translational modifications and chromatin context determine target gene expression. A reporter assay measures net output, not activation per se.

Using too much stimulus: Supraphysiological doses of TNF-α (e.g., 100 ng/mL) can trigger apoptosis or non-physiological responses. Use dose-response curves to find the minimal effective concentration.

Technical artifacts in EMSA: Non-specific DNA binding proteins can complicate EMSA interpretation. Always include competition controls with unlabeled probe and supershift controls with specific antibodies.

Misinterpreting IκBα degradation: IκBα degradation is transient; by 60 minutes, resynthesized IκBα may restore cytoplasmic retention. Sampling only at late time points can miss the activation peak.

Key Takeaways

  • NF-κB is a family of five transcription factors that form homo- and heterodimers, with p50/RelA being the predominant canonical form.
  • The canonical pathway involves IKKβ-mediated IκBα phosphorylation, ubiquitination, and proteasomal degradation, leading to rapid nuclear translocation.
  • The non-canonical pathway processes p100 to p52 via NIK and IKKα, activating RelB-containing dimers over hours.
  • NF-κB is negatively regulated by IκBα resynthesis, A20, CYLD, and other feedback inhibitors that ensure transient responses.
  • NF-κB induces pro-inflammatory cytokines, chemokines, adhesion molecules, and enzymes like iNOS and COX-2 that orchestrate inflammation.
  • Chronic NF-κB activation drives rheumatoid arthritis, IBD, asthma, and many cancers, making it a therapeutic target despite challenges of specificity.
  • Studying NF-κB requires multiple complementary methods including Western blotting, EMSA, reporter assays, and genetic approaches.

Common Misconceptions

  • "NF-κB is a single protein": It is a family of five related proteins with distinct functions.
  • "NF-κB is always pro-inflammatory": In some contexts, NF-κB promotes cell survival and tissue repair, and in intestinal epithelium it is protective.
  • "The canonical pathway is the only important one": The non-canonical pathway is essential for adaptive immunity and B-cell function.
  • "IKKβ inhibition is a safe therapeutic strategy": Global IKKβ inhibition causes immunosuppression and has failed in clinical trials due to toxicity.

Frequently Asked Questions

What is the role of NF-κB in inflammation?

NF-κB is a master transcription factor that coordinates the inflammatory response by inducing the expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), chemokines (IL-8, MCP-1), adhesion molecules (ICAM-1, VCAM-1), and inducible enzymes (iNOS, COX-2). It is activated within minutes of inflammatory stimuli and orchestrates both the initiation and resolution of inflammation through its target gene program.

How is NF-κB activated?

The canonical pathway is activated by pro-inflammatory cytokines, TLR ligands, and antigen receptor engagement. These stimuli activate the IKK complex, which phosphorylates IκBα at Ser32/Ser36. Phosphorylated IκBα is ubiquitinated by SCFβ-TrCP and degraded by the proteasome, freeing NF-κB to translocate to the nucleus. The non-canonical pathway is activated by a smaller set of receptors (CD40, BAFF-R, LTβR) and involves NIK-mediated IKKα activation, leading to p100 processing to p52.

What is the difference between canonical and non-canonical NF-κB pathways?

The canonical pathway is rapid (minutes), requires IKKβ and NEMO, degrades IκBα, and activates p50/RelA dimers. The non-canonical pathway is slow (hours), requires NIK and IKKα but not NEMO, processes p100 to p52, and activates p52/RelB dimers. The canonical pathway responds to diverse inflammatory stimuli, while the non-canonical pathway responds to a limited set of developmental and immune stimuli.

What are the main target genes of NF-κB?

NF-κB targets include TNF-α, IL-1β, IL-6, IL-8, MCP-1, ICAM-1, VCAM-1, E-selectin, iNOS, COX-2, MMPs, and anti-apoptotic genes like Bcl-xL and cIAP2. It also induces its own negative regulators, IκBα and A20, creating feedback control.

How is NF-κB activity negatively regulated?

The primary negative feedback is IκBα resynthesis, which removes NF-κB from the nucleus and restores cytoplasmic sequestration. A20 and CYLD deubiquitinases terminate upstream signaling. Post-translational modifications such as acetylation and methylation also modulate NF-κB transcriptional activity and stability.

What methods are used to detect NF-κB activation?

Common methods include Western blotting for IκBα degradation and RelA phosphorylation, EMSA for DNA binding, luciferase reporter assays for transcriptional activity, immunofluorescence for nuclear localization, and knockout or knockdown approaches for functional studies.

Why is NF-κB a target for anti-inflammatory drugs?

NF-κB drives the expression of many pro-inflammatory mediators, and its constitutive activation is found in chronic inflammatory diseases. Inhibiting NF-κB can reduce inflammation, but global inhibition causes immunosuppression. Current therapeutic strategies aim for selective or cell-type-specific inhibition to balance efficacy and safety.

Key Takeaways

  • NF-κB is a family of five transcription factors (p50, p52, RelA, RelB, c-Rel) that dimerize to regulate hundreds of inflammatory genes.
  • The canonical pathway is the primary route of inflammatory NF-κB activation, operating through IKKβ, IκBα degradation, and p50/RelA nuclear entry within minutes.
  • The non-canonical pathway processes p100 to p52 via NIK and IKKα, activating p52/RelB over hours and serving adaptive immunity functions.
  • Negative feedback through IκBα, A20, and CYLD ensures that NF-κB activation is transient and self-limiting.
  • NF-κB target genes include cytokines, chemokines, adhesion molecules, and enzymes that collectively orchestrate the inflammatory response.
  • Chronic NF-κB activation is pathogenic in rheumatoid arthritis, IBD, asthma, and cancer, but global inhibition is limited by immunosuppression.
  • Studying NF-κB requires complementary methods: Western blotting for protein changes, EMSA for DNA binding, reporter assays for transcription, and genetic models for function.
  • Cell-type specificity and context determine whether NF-κB is protective or pathogenic, as exemplified by its opposing roles in intestinal epithelium versus myeloid cells in IBD.

Further Reading

  • Saha S et al. An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation. Molecules (Basel, Switzerland). 2020. PubMed 33238435
  • Hoesel B, Schmid JA. The complexity of NF-κB signaling in inflammation and cancer. Molecular cancer. 2013. PubMed 23915189
  • Park MY et al. Scutellarein Inhibits LPS-Induced Inflammation through NF-κB/MAPKs Signaling Pathway in RAW264.7 Cells. Molecules (Basel, Switzerland). 2022. PubMed 35744907
  • Wang H, Cho CH. Effect of NF-κB signaling on apoptosis in chronic inflammation-associated carcinogenesis. Current cancer drug targets. 2010. PubMed 20482486
  • You Z et al. The Novel KLF4/BIG1 Regulates LPS-mediated Neuro-inflammation and Migration in BV2 Cells via PI3K/Akt/NF-kB Signaling Pathway. Neuroscience. 2022. PubMed 35090882
  • El-Shitany NA, Eid BG. Icariin modulates carrageenan-induced acute inflammation through HO-1/Nrf2 and NF-kB signaling pathways. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 2019. PubMed 31670031

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