TIFAB

TIFAB is an FHA-domain protein that functions as a negative regulator of innate immune signaling by sequestering monomeric TIFA into a pseudo-dimer that lacks the TRAF6-binding motif, thereby blocking TIFA oligomerization and downstream NF-κB activation (PMID:38442163, PMID:15047173). TIFAB also forms a complex with TRAF6 and promotes its lysosome-dependent degradation, constraining TLR4 signaling amplitude in hematopoietic cells (PMID:26458771). Beyond NF-κB, TIFAB regulates USP15 deubiquitinase activity toward substrates MDM2 and KEAP1, thereby attenuating p53 levels in hematopoietic stem/progenitor cells and modulating leukemic cell fitness (PMID:32101751). In KMT2A-rearranged AML, TIFAB suppresses the non-canonical NF-κB component RelB, leading to transcriptional upregulation of HOXA9 and HNF4A, which enhance leukemia stem cell self-renewal and metabolic reprogramming (PMID:34877491, PMID:39626355).

1. 2004 Medium

   The initial discovery that TIFAB binds TIFA and inhibits TIFA-mediated NF-κB activation established TIFAB as a negative regulator of innate immune signaling, though the mechanism of inhibition was unclear.

   Evidence Co-immunoprecipitation and NF-κB reporter assay in HEK293 cells

   PMID:15047173

   Open questions at the time

   • Single Co-IP system without reciprocal endogenous validation
   • Structural basis for TIFAB–TIFA interaction unknown
   • In vivo relevance not demonstrated
2. 2009 Medium

   Identification of TIFAB's predominant expression in immune cells (B cells, dendritic cells, macrophages) and its downregulation upon TRAF6-mediated stimulation placed TIFAB in a negative feedback loop within the innate immune system.

   Evidence Flow cytometry-based cell sorting, microinjection into NIH3T3 cells with cell cycle analysis

   PMID:19470519

   Open questions at the time

   • Mechanism of TIFAB downregulation upon TRAF6 stimulation not defined
   • No genetic loss-of-function in vivo model yet
3. 2015 High

   Demonstration that TIFAB complexes with TRAF6 and promotes its lysosome-dependent degradation revealed a second arm of NF-κB suppression beyond the TIFA interaction, with TIFAB knockout mice showing hematopoietic dysfunction and TLR4 hypersensitivity.

   Evidence Tifab knockout mice, competitive transplantation, lysosome inhibitor rescue, reciprocal Co-IP

   PMID:26458771

   Open questions at the time

   • How TIFAB directs TRAF6 to lysosomal degradation rather than proteasomal is unclear
   • Whether TIFAB directly contacts TRAF6 or acts through an intermediary not resolved
4. 2020 High

   Discovery that TIFAB regulates USP15 deubiquitinase activity toward MDM2 and KEAP1 expanded TIFAB's function beyond NF-κB, linking it to p53 homeostasis and hematopoietic stress responses.

   Evidence Mass spectrometry interactome, in vitro ubiquitin hydrolase assay, genetic epistasis with USP15 rescue in MLL-AF9 leukemia transplantation model

   PMID:32101751

   Open questions at the time

   • Structural basis for TIFAB regulation of USP15 catalytic activity unknown
   • Whether TIFAB–USP15 interaction is direct or scaffolded not resolved
   • Relationship between TIFAB's NF-κB and USP15 functions not dissected
5. 2021 Medium

   Establishing that TIFAB is transcriptionally repressed by RelB and that TIFAB in turn suppresses RelB to upregulate HOXA9 revealed a reciprocal regulatory circuit driving leukemia stem cell programs in MLL-AF9 AML.

   Evidence RelB KO, retroviral forced expression, gene set enrichment analysis, AML transplantation model

   PMID:34877491

   Open questions at the time

   • Single-lab finding; independent replication needed
   • Mechanism by which TIFAB suppresses RelB protein or activity not defined
6. 2024 High

   Crystal structure of the TIFAB–TIFA heterodimer resolved the 20-year-old question of how TIFAB inhibits NF-κB: TIFAB sequesters monomeric TIFA into a pseudo-dimer that lacks key phosphorylation and TRAF6-binding sites, preventing TIFA homodimerization.

   Evidence X-ray crystallography, biochemical binding assays, mutagenesis, cell-based NF-κB reporter validation

   PMID:38442163

   Open questions at the time

   • Whether the pseudo-dimer forms in vivo under physiological stoichiometries not shown
   • Dynamics of monomer–dimer equilibrium in stimulated immune cells not measured
7. 2025 Medium

   Linking TIFAB to metabolic reprogramming in AML through RelB-dependent upregulation of HNF4A showed that TIFAB's NF-κB inhibitory function directly controls glucose uptake and mitochondrial activity in leukemia stem cells.

   Evidence Tifab KO and forced expression, metabolic assays, HNF4A rescue and shRNA epistasis in leukemia transplantation model

   PMID:39626355

   Open questions at the time

   • Single-lab study; independent validation needed
   • Whether HNF4A regulation is direct or entirely mediated through RelB not fully delineated
   • Relevance to non-KMT2A-rearranged leukemias unknown

• It remains unknown how TIFAB coordinates its dual functions — TIFA sequestration, TRAF6 lysosomal degradation, and USP15 regulation — within the same cell, and whether these activities are context-dependent or operate concurrently.
• No integrated model linking all three TIFAB effector arms
• Post-translational regulation of TIFAB itself largely uncharacterized
• Role in normal steady-state hematopoiesis versus stress hematopoiesis not dissected