TNKS

TNKS (tankyrase/PARP5A) is a poly-ADP-ribose polymerase that regulates the Wnt/β-catenin pathway through both its catalytic PARylation of AXIN — which targets AXIN for RNF146-dependent ubiquitination and degradation — and a scaffolding function within the β-catenin destruction complex [PMID:38967608, PMID:bio_10.1101_2025.09.22.677768]. These two activities are functionally distinct: catalytic inhibition prevents TNKS turnover and drives its accumulation in the destruction complex, where its scaffold rigidifies the complex into AXIN puncta and paradoxically impedes β-catenin turnover, whereas targeted degradation of TNKS stabilizes AXIN without puncta and more deeply suppresses Wnt signaling [PMID:bio_10.1101_2025.09.22.677768]. TNKS directly binds β-catenin and acts as a positive regulator of the pathway, with knockdown suppressing tumor cell growth and invasion (PMID:31849489); its protein stability is controlled by the deubiquitinase USP25, which protects it from proteasomal degradation, and disruption of the TNKS–USP25 interaction depletes TNKS and triggers apoptosis (PMID:35450028, PMID:38261825). Beyond Wnt, TNKS scaffolds an AXIN–KIF3A complex on the trans-Golgi network and, with AXIN, acts upstream of Tiam1–Rac1 to drive insulin-stimulated GLUT4 translocation, with insulin/Akt signaling controlling TNKS activity and abundance (PMID:22473005, PMID:41207648). In a separate role, TNKS is recruited by TAX1BP1 with RNF146 into liquid-like condensates upon necroptosis induction, where it PARylates activated RIPK1 to promote its PARylation-dependent ubiquitination and proteasomal degradation, restraining cell death (PMID:38272024). TNKS and TNKS2 also bind the peroxisomal membrane protein PEX14 and regulate peroxisome protein import (PMID:38967608). TNKS1 and TNKS2 are functionally redundant, such that chromosome 8p loss depleting TNKS1 creates a selective dependency on TNKS2 [PMID:bio_10.1101_2025.03.04.641305].

1. 2003 Medium

   Establishing the first direct binding partners of tankyrase began to define how it is recruited to substrates and complexes.

   Evidence Yeast two-hybrid and endogenous co-immunoprecipitation identifying FBP17 binding via a TNKS-binding motif

   PMID:14596906

   Open questions at the time

   • Functional consequence of the FBP17–TNKS interaction not established
   • No PARylation substrate role for FBP17 demonstrated
2. 2012 High

   Resolved how tankyrase couples insulin signaling to glucose uptake by scaffolding a Golgi-localized AXIN–KIF3A complex whose stability is gated by its own enzymatic activity.

   Evidence Co-IP, component knockdown, TNKS2 knockout mice with metabolic phenotyping, and co-localization imaging on the trans-Golgi network

   PMID:22473005

   Open questions at the time

   • Mechanism linking Akt to suppression of TNKS ADP-ribosylase activity not fully resolved
   • Relative contribution of catalysis vs. scaffolding to complex stability unclear
3. 2019 Medium

   Confirmed a direct TNKS1–β-catenin interaction and a pro-tumorigenic role for TNKS1 as a positive Wnt regulator in glioblastoma.

   Evidence Co-IP with β-catenin and TNKS1 knockdown/overexpression with viability and invasion readouts

   PMID:31849489

   Open questions at the time

   • Whether the β-catenin interaction is direct or AXIN-bridged not distinguished
   • Catalytic requirement for the growth phenotype not tested
4. 2020 Low

   Proposed that secretory-pathway TNKS2 participates in sequential ADP-ribosylation of VEGF downstream of a PARP-16 priming event.

   Evidence Co-IP and ADP-ribosylation assays with sequential enzymatic dependency tests in secretory compartments

   PMID:32472322

   Open questions at the time

   • Single Co-IP and enzymatic assay with limited mechanistic follow-up
   • Functional consequence of VEGF PARylation not established
5. 2022 Medium

   Identified USP25 as a deubiquitinase that stabilizes TNKS1 and thereby sustains Wnt/β-catenin activity, defining a post-translational control point over TNKS abundance.

   Evidence Co-IP ubiquitination assays plus USP25 knockdown/overexpression with Wnt marker Western blots

   PMID:35450028

   Open questions at the time

   • Site of TNKS1 ubiquitin removal by USP25 not mapped
   • E3 ligase opposing USP25 on TNKS1 not identified
6. 2023 Medium

   Validated the TNKS–USP25 interaction as a druggable node by showing that chemical PPI disruption depletes TNKS and triggers apoptosis in colorectal cancer models.

   Evidence Small-molecule PPI inhibitor UAT-B with Western blot, in vitro and xenograft models

   PMID:38261825

   Open questions at the time

   • Structural basis of the TNKS–USP25 interface not defined
   • Selectivity of UAT-B not fully characterized
7. 2024 High

   Revealed a cell-death restraint function in which TNKS is condensate-recruited to PARylate activated RIPK1 and target it for degradation, distinct from its Wnt and metabolic roles.

   Evidence Phase-separation reconstitution, Co-IP, RIPK1 K376 mutagenesis, proteasome inhibition, and MEF loss-of-function

   PMID:38272024

   Open questions at the time

   • TAX1BP1–TNKS recruitment determinants not fully mapped
   • In vivo necroptosis relevance not established
8. 2024 Medium

   Connected TNKS/TNKS2 to peroxisome biology by showing PEX14 binding and regulation of peroxisome import, with peroxisome loss feeding back onto AXIN1 degradation and β-catenin transcription.

   Evidence Genome-wide CRISPRi screen, RNF146 genetic epistasis, peroxisome import assays, and β-catenin reporter

   PMID:38967608

   Open questions at the time

   • Direct PARylation substrate at the peroxisome membrane not identified
   • Physiological setting of peroxisome–Wnt crosstalk unclear
9. 2025 Medium

   Distinguished TNKS catalytic from scaffolding functions, explaining why catalytic inhibitors fail — enzyme-dead accumulated TNKS rigidifies the destruction complex — while degraders suppress Wnt more effectively.

   Evidence PROTAC degradation vs. catalytic inhibition with AXIN puncta imaging in APC-mutant colorectal cancer cells (preprint)

   PMID:bio_10.1101_2025.09.22.677768

   Open questions at the time

   • Preprint, single lab
   • Structural basis of scaffold-induced AXIN puncta not resolved
10. 2025 Medium

    Extended the insulin/GLUT4 mechanism by placing the Axin1/TNKS axis upstream of Tiam1–Rac1 and parallel to Akt–AS160 in skeletal muscle.

    Evidence Co-IP, siRNA, XAV939 inhibition, GLUT4myc translocation, and PAK phosphorylation readout in C2C12 myotubes

    PMID:41207648

    Open questions at the time

    • Direct Rac1-pathway substrate of TNKS PARylation not identified
    • In vivo muscle relevance not tested
11. 2025 Medium

    Demonstrated TNKS1/TNKS2 functional redundancy as a therapeutic vulnerability, enabling a TNKS2-selective inhibitor effective in TNKS1-deficient (8p-loss) tumors.

    Evidence Structure-guided drug design with TNKS1-depleted cell line and organoid WNT reporter models (preprint)

    PMID:bio_10.1101_2025.03.04.641305

    Open questions at the time

    • Preprint, single lab
    • Breadth of 8p-loss tumor responsiveness not validated clinically
12. 2025 Low

    Linked TNKS1 to vascular ferroptosis via SLC7A11 binding, associating TNKS1 with smooth muscle phenotypic switching.

    Evidence Co-IP, TNKS1 overexpression, ferroptosis marker assays, and aortic dissection model

    PMID:40359887

    Open questions at the time

    • Single Co-IP with limited mechanistic follow-up
    • Whether SLC7A11 is a PARylation substrate not tested

• How TNKS partitions its catalytic and scaffolding activities across its many contexts — Wnt, GLUT4 trafficking, necroptosis, peroxisome import, ferroptosis — and what determines substrate selection in each remains unresolved.
• No unified model for context-specific substrate recruitment
• Structural determinants distinguishing scaffold vs. catalytic output not defined
• Telomere maintenance role not represented by direct evidence in this corpus