TIFAB

TIFAB is a TIFA-related FHA-domain protein that functions as a negative regulator of innate immune and NF-κB signaling in hematopoietic and immune cells (PMID:15047173, PMID:26458771). It binds monomeric TIFA and forms a stable heterodimer, generating a pseudo-TIFA dimer that lacks the phosphorylation site and TRAF6-binding motif, thereby blocking TIFA oligomerization and suppressing ALPK1–TIFA–TRAF6-mediated NF-κB activation (PMID:38442163, PMID:15047173). In parallel, TIFAB complexes with TRAF6 and reduces its protein stability through a lysosome-dependent mechanism, so that loss of TIFAB raises TRAF6 levels and renders hematopoietic stem/progenitor cells hypersensitive to TLR4 stimulation, impairing hematopoiesis (PMID:26458771). TIFAB additionally acts as an effector of USP15 deubiquitinase activity toward MDM2 and KEAP1, restraining p53 signaling and protecting HSPCs from hematopoietic stress (PMID:32101751). In myeloid malignancy, TIFAB promotes leukemic stem/progenitor cell function by suppressing the non-canonical NF-κB component RelB to derepress HOXA9 and HNF4A, the latter driving a metabolic program supporting glucose uptake and mitochondrial function (PMID:34877491, PMID:39626355).

1. 2004 Medium

   Established TIFAB's founding identity as a TIFA-binding inhibitor of NF-κB, answering whether this TIFA paralog acts in the same signaling axis but with opposite sign.

   Evidence Co-immunoprecipitation and NF-κB reporter assays in cell lines

   PMID:15047173

   Open questions at the time

   • Mechanism of inhibition inferred as conformational change without structural proof
   • No direct TRAF-family binding demonstrated
   • Cellular and physiological context untested
2. 2009 Medium

   Tied TIFAB expression to immune cell types and demonstrated functional consequence, showing it is a negative regulator of TRAF6-induced proliferation and maturation rather than a passive binding partner.

   Evidence Cell-type expression analysis plus microinjection and cell cycle analysis in NIH3T3 cells

   PMID:19470519

   Open questions at the time

   • Molecular target of cell cycle inhibition not defined
   • Microinjection readout not linked to endogenous TIFAB levels
   • No in vivo loss-of-function
3. 2015 High

   Defined a direct biochemical mechanism for TIFAB on TRAF6 and an in vivo hematopoietic role, answering how TIFAB constrains innate immune signal amplitude.

   Evidence Co-IP, lysosome-inhibitor stability assays, Tifab knockout mouse transplantation, and miR-146a epistasis

   PMID:26458771

   Open questions at the time

   • Molecular route directing TRAF6 to lysosomes unresolved
   • Relationship between TRAF6 degradation and the TIFA-blocking activity not integrated
4. 2020 High

   Revealed an NF-κB-independent arm by which TIFAB licenses USP15 deubiquitinase activity to restrain p53, expanding its role to stress protection of HSPCs and leukemic cells.

   Evidence Mass-spectrometry interaction screen, genetic epistasis with USP15 rescue, deubiquitinase activity assays, and p53/MDM2/KEAP1 protein analysis in MLL-AF9 leukemia

   PMID:32101751

   Open questions at the time

   • How TIFAB binding modulates USP15 catalytic activity at the molecular level unknown
   • Direct TIFAB–USP15 interface not structurally defined
5. 2021 Medium

   Connected TIFAB to leukemic transformation through a RelB–HOXA9 transcriptional circuit, showing it accelerates AML and enforces stem cell signatures.

   Evidence Forced expression in MLL-AF9 AML, RelB deletion, GSEA, and in vivo transplantation

   PMID:34877491

   Open questions at the time

   • Direct versus indirect control of HOXA9 not separated
   • Mechanism by which RelB suppresses TIFAB not defined
6. 2024 High

   Provided the structural basis for TIFA inhibition, showing TIFAB heterodimerizes with monomeric TIFA to form a pseudo-dimer lacking the phosphorylation site and TRAF6 motif.

   Evidence Crystallography, biochemical binding assays, mutagenesis, and cell-based NF-κB assays of the ALPK1–TIFA–TRAF6 axis

   PMID:38442163

   Open questions at the time

   • Does not address how the structural TIFA-blocking model relates to TIFAB's separate TRAF6-degradation and USP15 functions
   • In vivo relevance of the heterodimer in immune cells not tested
7. 2025 Medium

   Extended the RelB axis to leukemic metabolism, showing TIFAB drives an HNF4A-dependent program supporting glucose uptake and mitochondrial function in AML stem/progenitor cells.

   Evidence Tifab conditional KO in KMT2A::MLLT3 AML, GSEA, metabolic assays, and HNF4A rescue/knockdown with in vivo engraftment

   PMID:39626355

   Open questions at the time

   • Mechanistic link between TIFAB and RelB suppression of HNF4A not resolved
   • Whether the metabolic axis operates outside leukemia unknown

• How TIFAB's distinct activities—TIFA heterodimerization, lysosomal TRAF6 degradation, USP15/p53 regulation, and the RelB–HNF4A/HOXA9 transcriptional axis—are coordinated within a single cell, and which dominates in physiological versus malignant contexts, remains unresolved.
• No unified model integrating the four reported activities
• Domain requirements for each function not systematically mapped