TNKS2

TNKS2 (tankyrase-2, PARP-5b) is a poly(ADP-ribose) polymerase of the tankyrase subfamily that recognizes substrates through ankyrin-repeat clusters (ARCs) and modifies them by PARsylation to control WNT/β-catenin signaling, telomere protein interactions, peroxisome biology, and DNA repair (PMID:11294570, PMID:38967608). It was first defined as a perinuclear PARP that binds the telomere protein TRF1, with enzymatic activity required for its overexpression-induced necrotic cell death (PMID:11454873). A dominant cellular output is regulation of β-catenin: TNKS2 (with the PARsylation-dependent E3 ligase RNF146) drives degradation of the destruction-complex scaffold AXIN1, and this axis couples peroxisome status to WNT activity via the peroxisomal membrane partner PEX14 (PMID:38967608). TNKS2 also engages substrate-recruitment partners through tankyrase-binding motifs, including SASH1 (via a motif containing S519), an interaction that supports stem-like properties in melanocytes (PMID:37808724), and it cooperates with PARP-16 to PARsylate VEGF in the secretory pathway, dampening VEGF activity (PMID:32472322). In a carcinogen-induced squamous carcinoma model, loss of TNKS2 abolishes 53BP1+ double-strand-break foci and shifts repair toward homologous recombination, establishing a required role in nonhomologous end joining during tumorigenesis (PMID:34710250). TNKS2 is functionally redundant with TNKS1 in sustaining WNT signaling, so selective TNKS2 inhibition suppresses WNT/β-catenin activity in tumors that have lost TNKS1, and structural studies of both the catalytic domain and the ARC4 peptide-binding site have enabled selective inhibitors that block this pathway [PMID:40093088, PMID:32435397, PMID:bio_10.1101_2025.03.31.646301].

1. 2001 Medium

   Established TNKS2 as a distinct PARP-family enzyme: it was cloned as a paralog of tankyrase with ankyrin-repeat, SAM, and PARP catalytic domains, and was shown to physically bind the telomere protein TRF1, defining a two-member tankyrase family with telomeric associations.

   Evidence Serological cDNA cloning, sequence/domain analysis, and chromosomal mapping; yeast two-hybrid and in vitro TRF1 binding with localization and PARP-inhibitor rescue of overexpression toxicity

   PMID:11294570 PMID:11454873

   Open questions at the time

   • Endogenous telomeric function not demonstrated
   • Physiological substrates beyond TRF1 binding not identified
   • Necrotic phenotype derives from overexpression, not loss of function
2. 2016 Medium

   Placed TNKS2 in a regulatory hierarchy controlling β-catenin signaling in cancer, showing it acts downstream of miR-490-3p to promote proliferation and invasion.

   Evidence siRNA knockdown with miR-resistant TNKS2 rescue, 3′UTR luciferase reporter, β-catenin assays, and xenografts in triple-negative breast cancer cells

   PMID:27506313

   Open questions at the time

   • Direct enzymatic substrate in this context not defined
   • Redundancy with TNKS1 not addressed
   • Single tumor-type model
3. 2020 Medium

   Defined a sequential ADP-ribosylation mechanism in the secretory pathway and the structural basis for selective catalytic inhibition.

   Evidence Biochemical ADP-ribosylation assays showing PARP-16 priming of VEGF for TNKS2 poly-ADP-ribosylation; X-ray crystallography of the TNKS2 catalytic domain with bis-quinazolinone inhibitors plus WNT reporter assays

   PMID:32435397 PMID:32472322

   Open questions at the time

   • In vivo relevance of VEGF PARsylation not shown
   • PARP-16/TNKS2 cooperation tested in single lab/method set
   • Inhibitor selectivity not validated against full PARP panel in vivo
4. 2021 Medium

   Demonstrated a required role for TNKS2 in nonhomologous end joining during tumorigenesis, with its loss driving a switch toward homologous recombination repair.

   Evidence PARP5B-null carcinogen-induced squamous carcinoma mouse model, 53BP1/ATM immunofluorescence, co-IP of an HR repair complex, and XAV939+etoposide treatment

   PMID:34710250

   Open questions at the time

   • Direct DSB substrate of TNKS2 PARsylation not identified
   • Mechanism linking TNKS2 to 53BP1 foci formation unresolved
   • Single model system
5. 2024 Medium

   Connected TNKS2 PARsylation to peroxisome biology and AXIN1-mediated WNT control, and identified SASH1 as a tankyrase-motif partner relevant to stem-like phenotypes.

   Evidence Genome-wide CRISPRi screen with epistasis, PEX14 binding and AXIN1 degradation assays, β-catenin reporters; Co-IP and NMR binding kinetics of SASH1 S519 motif with functional melanocyte assays (preprint)

   PMID:37808724 PMID:38967608

   Open questions at the time

   • Direct peroxisomal PARsylation substrates not enumerated
   • SASH1 interaction from single lab and preprint
   • Relative TNKS1 vs TNKS2 contribution at peroxisomes not partitioned
6. 2025 Medium

   Validated TNKS2 as a tumor-selective WNT target and expanded druggable sites beyond the catalytic pocket to the ARC4 substrate-binding domain.

   Evidence Structure-guided TNKS2-selective catalytic inhibitor tested in TNKS1-deficient (chr8p-loss) cell/organoid models; ARC4-targeting compound ARCher-142/S8 confirmed by FRET screen, NMR, and X-ray, with WNT reporter readouts (preprints)

   PMID:40093088 PMID:bio_10.1101_2025.03.31.646301

   Open questions at the time

   • In vivo efficacy and on-target selectivity not established in the corpus
   • Preprint status
   • Whether ARC4 inhibition phenocopies catalytic inhibition broadly unresolved

• The full set of physiological TNKS2 PARsylation substrates and the determinants of TNKS1/TNKS2 functional division of labor across telomeres, peroxisomes, DNA repair, and WNT signaling remain undefined.
• No comprehensive substrate map
• Endogenous telomeric role not resolved in the corpus
• Tissue-specific non-redundant TNKS2 functions unclear