Affinage

NFKB1

Nuclear factor NF-kappa-B p105 subunit · UniProt P19838

Length
968 aa
Mass
105.4 kDa
Annotated
2026-06-10
100 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NFKB1 encodes the p50 subunit of NF-κB, a master transcription factor that couples inflammatory and stress signals to gene expression (PMID:15371334, PMID:17072321). p50 is produced by proteasomal processing of the p105 precursor, one of three ubiquitin-dependent steps in the pathway alongside K48-linked degradation of IκB and K63-linked, degradation-independent activation of IKK (PMID:16056267). Through its Rel homology domain, p50 mediates dimerization, sequence-specific binding to κB DNA sites, and contact with the ankyrin repeats of IκB proteins, which in resting cells mask the dimer's nuclear localization signal and retain it in the cytoplasm (PMID:17072321, PMID:22435546, PMID:23495970). IKKα/IKKβ phosphorylation of IκBα on Ser32/Ser36 triggers its ubiquitin-dependent degradation, liberating p50-containing dimers for nuclear translocation (PMID:15102433, PMID:15371334, PMID:22435546); this release can be blocked when IκBα is instead sumoylated, as occurs under hypoxia via a CaMK2/TAK1/IKK route (PMID:20696840), and the pathway can also be initiated by nuclear DNA-damage signaling through ATM-NEMO (PMID:21187855). Because p50 homodimers lack a transactivation domain, they act as transcriptional repressors at κB sites, while p50 partner dimers drive activation with promoter selectivity set by subunit phosphorylation and elongation factor usage (PMID:23495970, PMID:26999213, PMID:23624258). Functionally, p50-containing complexes enforce an NF-κB→p62/SQSTM1→mitophagy negative-feedback loop that clears NLRP3-activating damaged mitochondria and limits inflammasome output (PMID:26919428), support an antioxidant/anti-JNK survival program (PMID:15611622), and are genetically required for RANKL-induced osteoclastogenesis and bone resorption (PMID:21079651).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2004 High

    Established the canonical activation logic: how a cytoplasmically sequestered p50-containing dimer is released into the nucleus on demand.

    Evidence IKK kinase assays, Co-IP, proteasome inhibition and nuclear translocation assays

    PMID:15102433 PMID:15371334

    Open questions at the time
    • Does not resolve which p50 partner dimers are released in which cell contexts
    • Kinetics of cytoplasmic vs nuclear IKK steps not delineated for p50 specifically
  2. 2005 High

    Resolved that ubiquitin chains act at three distinct nodes, explaining how the same modification both generates p50 (p105 processing) and controls IκB turnover and IKK activation.

    Evidence In vitro ubiquitination and cell-free processing assays with mutant ubiquitin complementation

    PMID:16056267

    Open questions at the time
    • E3 ligases and DUBs governing each step not fully assigned
    • Quantitative balance between full p105 processing and degradation unresolved
  3. 2006 High

    Defined the structural basis for p50 function by showing the RHD performs dimerization, DNA binding, and IκB contact.

    Evidence Crystal structures, DNA-binding assays and mutagenesis

    PMID:17072321

    Open questions at the time
    • Does not explain dimer-specific promoter selectivity in cells
  4. 2010 Medium

    Showed the activation pathway can be diverted: hypoxia-driven SUMO-2/3 modification of IκBα blocks its degradation despite IKK phosphorylation, retaining p50 dimers.

    Evidence siRNA knockdown, in vivo sumoylation assays, SUMO-protease inhibition, IKK and reporter assays

    PMID:20696840

    Open questions at the time
    • Single-lab mechanism
    • In vivo physiological relevance of hypoxic IκBα sumoylation not established
  5. 2010 Medium

    Demonstrated genotoxic-stress entry into the pathway through nuclear ATM-NEMO signaling feeding back to IKK and p50 nuclear translocation.

    Evidence ATM kinase assays, NEMO modification assays, ATM knockout and nuclear fractionation

    PMID:21187855

    Open questions at the time
    • Reviewed rather than primary data
    • Target genes activated by this route in p50 dimers not specified
  6. 2010 High

    Provided in vivo proof that p50-containing complexes are physiologically required, via an osteopetrosis phenotype from loss of p50 and p52.

    Evidence p50/p52 double-knockout mice, bone histology and osteoclast differentiation assays

    PMID:21079651

    Open questions at the time
    • Redundancy between p50 and p52 not separated
    • Direct osteoclast target genes not defined
  7. 2013 High

    Clarified p50's dual transcriptional output: lacking a transactivation domain, p50 homodimers act as κB-site repressors while heterodimers can activate.

    Evidence Crystal structures, DNA-binding and reporter assays

    PMID:23495970

    Open questions at the time
    • Switch between repressive and activating p50 dimer states in vivo not mapped
  8. 2016 High

    Linked the inflammatory output to a self-limiting program in which NF-κB induces p62/SQSTM1 to drive mitophagy and restrain NLRP3 inflammasome activation.

    Evidence Macrophage p62 conditional knockout, mitophagy imaging, IL-1β ELISA and genetic reconstitution

    PMID:26919428

    Open questions at the time
    • Specific p50 dimer driving p62 induction not isolated
    • Temporal control of the delayed feedback loop not fully defined
  9. 2016 Medium

    Built mechanism for selective gene regulation by showing subunit phosphorylation and elongation-factor usage set promoter specificity, with anti-inflammatory p50-dimer promoters depending on DSIF.

    Evidence Phosphosite mutagenesis, reporter assays, ChIP and Pol II elongation/Brd4-P-TEFb assays

    PMID:14713228 PMID:23624258 PMID:26999213

    Open questions at the time
    • Reviewed/multi-study integration rather than single primary dataset
    • Most elongation mechanisms defined for p65; direct p50 contribution less resolved
  10. 2007 Medium

    Connected NF-κB to cell survival by defining a transcriptional antioxidant/anti-JNK axis (XIAP, A20, Gadd45β, ferritin, Mn-SOD) suppressing TNFα-induced apoptosis.

    Evidence Reporter, JNK kinase, ROS and apoptosis assays with NF-κB inhibition

    PMID:15611622

    Open questions at the time
    • Compiles existing data rather than new primary results
    • p50-specific contribution to each target not isolated

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved which specific p50 partner dimers govern each target-gene program and how the repressive versus activating switch is selected at individual κB sites in vivo.
  • No comprehensive map of p50 dimer composition per gene context
  • Determinants of homodimer repression vs heterodimer activation in vivo unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140110 transcription regulator activity 3 GO:0003677 DNA binding 2
Localization
GO:0005634 nucleus 3 GO:0005829 cytosol 2
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-74160 Gene expression (Transcription) 3 R-HSA-168256 Immune System 2
Partners
CHUKIKBKBIKBKGNFKB2NFKBIARELA
Complex memberships
NF-κB p50 homodimerNF-κB p50/RelA dimer

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 IκB kinases (IKKα and IKKβ) phosphorylate IκB proteins, triggering their proteasomal degradation and releasing NF-κB (including p50-containing dimers) for nuclear translocation; IKK activation operates through both cytoplasmic and nuclear steps. Biochemical pathway analysis and review of kinase assays Trends in biochemical sciences High 15102433
2004 NF-κB p50/RelA (canonical) dimers are sequestered in the cytoplasm by IκB proteins; phosphorylation of IκBα by IKK leads to its ubiquitination and proteasomal degradation, freeing the p50-containing dimer to translocate to the nucleus and activate transcription. Co-immunoprecipitation, kinase assays, proteasome inhibitor experiments, nuclear translocation assays Genes & development High 15371334
2005 Ubiquitination regulates at least three steps in the NF-κB pathway involving p50/NF-κB1: (1) K48-linked ubiquitination-dependent degradation of IκB, (2) proteasomal processing of the p105 precursor to generate p50, and (3) K63-linked ubiquitination-dependent (degradation-independent) activation of IKK. In vitro ubiquitination assays, cell-free processing assays, mutant ubiquitin complementation Nature cell biology High 16056267
2006 NF-κB transcription factors including p50 bind consensus κB DNA sequences at promoter regions; structural studies revealed the RHD (Rel homology domain) mediates dimerization, IκB binding, and sequence-specific DNA binding. Crystal structure determination, DNA-binding assays, mutagenesis Oncogene High 17072321
2012 Structural studies of the three-component NF-κB signaling module (NF-κB, IκB, IKK) show that IκB proteins mask the nuclear localization signal of NF-κB dimers including p50 complexes; IKK-mediated phosphorylation of IκBα on Ser32/Ser36 initiates ubiquitin-dependent degradation, liberating the dimer. X-ray crystallography, cryo-EM, mutagenesis of IκB phosphorylation sites Immunological reviews High 22435546
2013 Structural studies established that NF-κB1 p50 homodimers lack transactivation domains and can function as transcriptional repressors when bound to κB sites; interaction with IκB proteins involves ankyrin repeats that contact the RHD. Crystal structure, DNA-binding assays, transcriptional reporter assays Annual review of biophysics High 23495970
2010 Under hypoxic conditions, NF-κB activation proceeds through a CaMK2-dependent pathway that activates IKK and TAK1 but does not require TAB1/TAB2; critically, IKK-mediated phosphorylation of IκBα under hypoxia does not lead to its degradation because IκBα is sumoylated by SUMO-2/3 on lysine residues normally required for K48-linked polyubiquitination, thereby retaining IκBα and blocking NF-κB1 (p50)-containing dimer release by a novel mechanism. siRNA knockdown, in vivo sumoylation assays, inhibition of SUMO proteases, IKK kinase assays, reporter assays Molecular and cellular biology Medium 20696840
2010 DNA double-strand break-initiated NF-κB signaling involves nuclear ATM-mediated phosphorylation of NEMO (NF-κB essential modulator), which serves as the nuclear-to-cytoplasm signal leading to IKK activation and subsequent nuclear translocation of NF-κB dimers including p50. ATM kinase assays, NEMO sumoylation/ubiquitination assays, genetic ATM knockout experiments, nuclear fractionation Cell research Medium 21187855
2007 NF-κB (including p50-containing dimers) induces expression of the autophagy receptor p62/SQSTM1, which in turn triggers mitophagic clearance of damaged mitochondria bearing NLRP3-activating signals (mtDNA, mtROS), establishing a negative feedback loop whereby NF-κB limits its own inflammasome-promoting activity. Macrophage-specific p62 conditional knockout, mitochondrial damage assays, IL-1β ELISA, mitophagy imaging, genetic reconstitution Cell High 26919428
2010 Deletion of NF-κB subunits p50 (NFKB1) and p52 (NFKB2) in mice causes osteopetrosis, establishing that p50-containing NF-κB complexes are required for RANKL-induced osteoclastogenesis and normal bone resorption. Double knockout mouse model, histological bone analysis, osteoclast differentiation assays Cell research High 21079651
2016 Phosphorylation of NF-κB subunits controls transcription in a gene-specific manner; p50 phosphorylation and that of its dimerization partners determines promoter selectivity and transactivation potential, offering mechanistic basis for selective gene regulation. Site-directed mutagenesis of phosphorylation sites, reporter gene assays, ChIP Cells Medium 26999213
2003 MSK1 kinase phosphorylates NF-κB p65 (RelA) at Ser276 and histone H3 at Ser10 at the IL-6 promoter in response to TNF signaling, establishing MSK1 as the kinase that coordinates transcription factor phosphorylation and histone modification at a single NF-κB target promoter. In vitro kinase assay, chromatin immunoprecipitation, mutagenesis of Ser276 Advances in experimental medicine and biology Medium 14713228
2013 Phosphorylation and acetylation of p65 at Ser276/Lys310 respectively promote recruitment of Brd4 and P-TEFb to NF-κB target gene promoters, facilitating transcription elongation; p50-containing dimers at anti-inflammatory gene promoters instead depend on the elongation factor DSIF, revealing promoter-specific elongation mechanisms. ChIP, RNA Pol II elongation assays, Brd4/P-TEFb co-immunoprecipitation, mutagenesis Biochimica et biophysica acta Medium 23624258
2007 NF-κB suppresses TNFα-induced JNK activation and apoptosis by transcriptionally upregulating XIAP, A20, and Gadd45β/MYD118 (an inhibitor of MKK7/JNKK2), and by inducing Ferritin heavy chain and Mn-SOD to reduce ROS, establishing a NF-κB→antioxidant/anti-JNK signaling axis. Reporter gene assays, JNK kinase assays, ROS measurement, apoptosis assays with NF-κB inhibitors Cell cycle (Georgetown, Tex.) Medium 15611622
2015 NF-κB p65 binding to a conserved κB site (conserved region C) upstream of the PD-1 (PDCD1) gene is required for LPS/TLR-induced PD-1 expression in macrophages; ChIP confirmed NF-κB p65 occupancy at this site following LPS stimulation. Chromatin immunoprecipitation (ChIP), luciferase reporter assays with κB site mutations, cyclosporin A inhibition, histone modification analysis Journal of immunology (Baltimore, Md. : 1950) Medium 25810391

Source papers

Stage 0 corpus · 100 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2017 NF-κB signaling in inflammation. Signal transduction and targeted therapy 7155 29158945
2004 Signaling to NF-kappaB. Genes & development 3281 15371334
2002 NF-kappaB at the crossroads of life and death. Nature immunology 2328 11875461
2007 Signaling to NF-kappaB by Toll-like receptors. Trends in molecular medicine 1975 18029230
2006 Introduction to NF-kappaB: players, pathways, perspectives. Oncogene 1788 17072321
2011 Crosstalk in NF-κB signaling pathways. Nature immunology 1592 21772278
2016 NF-κB Restricts Inflammasome Activation via Elimination of Damaged Mitochondria. Cell 1002 26919428
2005 Ubiquitin signalling in the NF-kappaB pathway. Nature cell biology 1000 16056267
2014 NF-κB, an active player in human cancers. Cancer immunology research 978 25187272
2006 NF-kappaB and the immune response. Oncogene 957 17072327
2011 NF-κB in immunobiology. Cell research 907 21243012
2013 Molecular basis of NF-κB signaling. Annual review of biophysics 796 23495970
2017 NF-κB in Oxidative Stress. Current opinion in toxicology 793 29862377
2008 NF-kappaB in inflammatory bowel disease. Journal of internal medicine 665 18479258
2012 The noncanonical NF-κB pathway. Immunological reviews 612 22435551
2016 The Regulation of NF-κB Subunits by Phosphorylation. Cells 601 26999213
2004 IkappaB kinases: key regulators of the NF-kappaB pathway. Trends in biochemical sciences 527 15102433
2011 MicroRNAs in NF-kappaB signaling. Journal of molecular cell biology 515 21502305
2010 NF-kappaB in renal inflammation. Journal of the American Society of Nephrology : JASN 488 20651166
2006 Inhibitors of NF-kappaB signaling: 785 and counting. Oncogene 488 17072334
2021 NF-κB: At the Borders of Autoimmunity and Inflammation. Frontiers in immunology 480 34434197
2006 The NF-kappaB regulatory network. Cardiovascular toxicology 453 17303919
2021 NF-κB signaling in inflammation and cancer. MedComm 446 34977871
2013 The NF-κB signalling pathway in osteoarthritis. The international journal of biochemistry & cell biology 430 24004831
2010 Oncogenic activation of NF-kappaB. Cold Spring Harbor perspectives in biology 422 20516126
1999 Multiple signals converging on NF-kappaB. Current opinion in cell biology 415 10209157
2017 NF-κB and the Transcriptional Control of Inflammation. International review of cell and molecular biology 412 29305014
2006 Naturally occurring NF-kappaB inhibitors. Mini reviews in medicinal chemistry 365 16918500
2006 NF-kappaB and IKK as therapeutic targets in cancer. Cell death and differentiation 364 16485028
2003 NF-kappaB and virus infection: who controls whom. The EMBO journal 354 12773372
2008 NF-kappaB signaling in cerebral ischemia. Neuroscience 342 18675321
2009 NF-kappaB and cancer: how intimate is this relationship. Molecular and cellular biochemistry 334 19823771
2018 Redox and NF-κB signaling in osteoarthritis. Free radical biology & medicine 317 30236789
2011 NF-κB in Aging and Disease. Aging and disease 310 22396894
2015 NF-κB and HIF crosstalk in immune responses. The FEBS journal 296 26513405
2013 NF-κB signaling and bone resorption. Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 291 23468073
2019 NF-κB Signaling Regulates Physiological and Pathological Chondrogenesis. International journal of molecular sciences 270 31842396
2010 Role of NF-κB in the skeleton. Cell research 270 21079651
2010 Signaling to NF-kappaB: regulation by ubiquitination. Cold Spring Harbor perspectives in biology 257 20300215
2008 NF-kappaB signaling, liver disease and hepatoprotective agents. Oncogene 245 18931690
2012 Regulation of NF-κB by deubiquitinases. Immunological reviews 236 22435550
2004 NF-kappaB: tumor promoter or suppressor? Trends in cell biology 234 15102437
2013 Regulation of NF-κB by ubiquitination. Current opinion in immunology 221 23312890
2005 NF-kappaB in the survival and plasticity of neurons. Neurochemical research 219 16187223
2016 More to Life than NF-κB in TNFR1 Signaling. Trends in immunology 211 27424290
2002 NF-kappaB activation and inhibition: a review. Shock (Augusta, Ga.) 211 12166787
2025 NF-κB in inflammation and cancer. Cellular & molecular immunology 210 40562870
2009 NF-kappaB in the immune response of Drosophila. Cold Spring Harbor perspectives in biology 209 20457557
2008 NF-kappaB modulators in osteolytic bone diseases. Cytokine & growth factor reviews 203 19046922
2010 Nuclear initiated NF-κB signaling: NEMO and ATM take center stage. Cell research 199 21187855
2012 MicroRNAs, new effectors and regulators of NF-κB. Immunological reviews 197 22435557
2000 NF-kappaB activation. Critical care medicine 197 10807322
2014 NF-κB control of T cell development. Nature immunology 196 24352326
2012 NF-κB: where did it come from and why? Immunological reviews 194 22435545
2010 Mechanism of hypoxia-induced NF-kappaB. Molecular and cellular biology 187 20696840
2015 EGFR and NF-κB: partners in cancer. Trends in molecular medicine 186 25979753
2003 A paradigm for gene regulation: inflammation, NF-kappaB and PPAR. Advances in experimental medicine and biology 186 14713228
2017 NF-κB Signaling in Gastric Cancer. Toxins 175 28350359
2018 NF-kappaB: Two Sides of the Same Coin. Genes 173 29315242
2015 NF-κB in cancer therapy. Archives of toxicology 172 25690730
2011 Blocking NF-κB: an inflammatory issue. Proceedings of the American Thoracic Society 169 22052926
2012 NF-κB regulation: lessons from structures. Immunological reviews 168 22435546
2019 NF-κB signaling in skin aging. Mechanisms of ageing and development 164 31634486
2012 Diverse ubiquitin signaling in NF-κB activation. Trends in cell biology 157 22543051
2009 NF-kappaB regulation: the nuclear response. Journal of cellular and molecular medicine 150 19438970
2006 NF-kappaB activation in melanoma. Pigment cell research 146 16524427
2015 NF-κB regulates PD-1 expression in macrophages. Journal of immunology (Baltimore, Md. : 1950) 144 25810391
2014 NF-κB pathways in hematological malignancies. Cellular and molecular life sciences : CMLS 144 24419302
2020 Inflammation, NF-κB, and Chronic Diseases: How are They Linked? Critical reviews in immunology 123 32421977
2006 NF-kappaB in solid tumors. Biochemical pharmacology 123 16956585
2014 Critical role of NF-κB in pancreatic cancer. Oncotarget 122 25473891
2006 NF-kappaB activation by double-strand breaks. Biochemical pharmacology 117 16965765
2004 NF-kappaB in cancer--a friend turned foe. Drug resistance updates : reviews and commentaries in antimicrobial and anticancer chemotherapy 116 15072771
2011 NF-κB and innate immunity. Current topics in microbiology and immunology 115 20848362
2010 Structural studies of NF-κB signaling. Cell research 114 21135870
2012 Lessons from mathematically modeling the NF-κB pathway. Immunological reviews 112 22435558
2005 Crossroads of estrogen receptor and NF-kappaB signaling. Science's STKE : signal transduction knowledge environment 111 15956359
2006 Regulation of NF-kappaB function. Biochemical Society symposium 110 16626297
2012 NF-κB function in B lymphocytes. Immunological reviews 109 22435560
2022 NF-κB: A Double-Edged Sword Controlling Inflammation. Biomedicines 108 35740272
2012 The atypical PKCs in inflammation: NF-κB and beyond. Immunological reviews 108 22435553
2014 NF-κB and the cell cycle. Biochemical Society transactions 105 24450631
2017 NF-κB Signalling in Glioblastoma. Biomedicines 102 28598356
2020 Looking Down on NF-κB. Molecular and cellular biology 100 32393609
2007 Autophagy and NF-kappaB: fight for fate. Cytokine & growth factor reviews 95 17485237
2013 Transcriptional control by NF-κB: elongation in focus. Biochimica et biophysica acta 94 23624258
2004 NF-kappaB and JNK: an intricate affair. Cell cycle (Georgetown, Tex.) 93 15611622
2019 NF-κB Signaling in Ovarian Cancer. Cancers 92 31443240
2014 NF-κB in cellular senescence and cancer treatment. Molecules and cells 92 24608805
2018 NF-κB in pancreatic cancer: Its key role in chemoresistance. Cancer letters 90 29432846
2016 MALT lymphoma: A paradigm of NF-κB dysregulation. Seminars in cancer biology 90 27452667
2004 NF-kappaB and reperfusion injury. Drug news & perspectives 89 15098063
2020 NF-κB and Its Role in Checkpoint Control. International journal of molecular sciences 88 32486375
2009 NF-κB signaling. Wiley interdisciplinary reviews. Systems biology and medicine 87 20151024
2008 Role of NF-kappaB in beta-cell death. Biochemical Society transactions 86 18481952
2018 Subunit-Specific Role of NF-κB in Cancer. Biomedicines 85 29673141
2007 SUMO and NF-kappaB ties. Cellular and molecular life sciences : CMLS 83 17530464
2021 NF-κB and Its Regulators During Pregnancy. Frontiers in immunology 82 34025678
2014 The role of NF-κB in the pathogenesis of glioma. Molecular & cellular oncology 80 27308348
2008 Turning NF-kappaB and IRFs on and off in DC. Trends in immunology 79 18534908

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