TNKS2

TNKS2 is a poly(ADP-ribose) polymerase (PARP) family member that uses ankyrin repeat cluster (ARC) domains to scaffold substrates and a catalytic PARP domain to poly-ADP-ribosylate them, thereby regulating telomere homeostasis, Wnt/β-catenin signaling, peroxisome protein import, and DNA double-strand break repair pathway choice. TNKS2 directly binds TRF1 at telomeres and PEX14 at peroxisomes, and PARsylates substrates such as AXIN1 to promote their RNF146-dependent degradation, activating β-catenin transcription (PMID:11454873, PMID:38967608). In the Golgi, TNKS2 extends mono-ADP-ribose primers deposited by PARP-16 on VEGF, reducing VEGF biological activity (PMID:32472322). Loss of TNKS2 abolishes 53BP1 foci and ATM activation at double-strand breaks, shifting repair from NHEJ toward homologous recombination, and TNKS2 becomes uniquely essential for Wnt signaling in tumors that have lost its paralog TNKS1 through chromosome 8p deletion (PMID:34710250, PMID:40093088).

1. 2001 High

   Identification of TNKS2 as a second tankyrase with PARP activity and TRF1-binding capacity established that tankyrase function is encoded by a two-gene family with overlapping domain architecture but distinct N-termini.

   Evidence Yeast two-hybrid, in vitro binding, domain analysis, and sequence cloning from two independent groups

   PMID:11294570 PMID:11454873

   Open questions at the time

   • Endogenous TNKS2–TRF1 interaction at telomeres not demonstrated
   • Functional redundancy versus specialization with TNKS1 not addressed
   • No in vivo loss-of-function data
2. 2001 High

   Demonstrating that TNKS2 overexpression causes PARP-dependent necrosis established that its catalytic activity has potent cellular consequences and that TNKS2 localizes to a perinuclear compartment.

   Evidence Overexpression imaging, mitochondrial membrane potential assay, rescue by PARP inhibitor 3-aminobenzamide

   PMID:11454873

   Open questions at the time

   • Perinuclear compartment not identified as a specific organelle
   • Relevance of overexpression-induced necrosis to endogenous TNKS2 function unclear
3. 2016 Medium

   Showing that miR-490-3p directly targets TNKS2 3′-UTR to suppress β-catenin signaling provided the first evidence linking endogenous TNKS2 expression levels to Wnt pathway output in cancer cells.

   Evidence Dual-luciferase 3′-UTR reporter, Western blot, knockdown and rescue in TNBC cells

   PMID:27506313

   Open questions at the time

   • TNKS2 PARsylation of AXIN1 not directly measured in this study
   • Contribution of TNKS1 not controlled for
4. 2020 Medium

   Revealing that TNKS2 poly-ADP-ribosylates VEGF in the Golgi, extending mono-ADP-ribose primers placed by ER-localized PARP-16, defined a sequential inter-PARP modification cascade on a secreted growth factor.

   Evidence In vitro PARP assay, subcellular fractionation, co-immunoprecipitation, sequential modification assay

   PMID:32472322

   Open questions at the time

   • In vivo relevance of VEGF PARsylation to angiogenesis not tested
   • No structural data on TNKS2–VEGF interface
   • Single-lab observation
5. 2021 Medium

   Loss of TNKS2 in vivo eliminated 53BP1 foci and ATM signaling while activating ATR, establishing TNKS2 as a determinant of NHEJ versus HR pathway choice at DNA double-strand breaks.

   Evidence PARP5B-null mouse HNSCC model, immunofluorescence for repair factors, PARP inhibitor combination

   PMID:34710250

   Open questions at the time

   • Direct PARsylation substrate at DSBs not identified
   • Whether TNKS1 compensates in wild-type context not resolved
   • Single carcinogen-induced tumor model
6. 2024 High

   A genome-wide CRISPRi screen uncovered TNKS2 binding to the peroxisomal membrane protein PEX14, showing that tankyrase PARsylation of peroxisomal substrates regulates protein import and linking the RNF146–tankyrase axis to both peroxisome biology and AXIN1 degradation–driven Wnt activation.

   Evidence CRISPRi screen, Co-IP/pulldown for PEX14, peroxisome import assay, Wnt reporter assay

   PMID:38967608

   Open questions at the time

   • Identity of PARsylated peroxisomal membrane proteins beyond PEX14 not determined
   • Relative contributions of TNKS1 vs TNKS2 to peroxisome import not dissected
7. 2025 Medium

   Genetic and pharmacological studies demonstrated that TNKS2 becomes uniquely essential for Wnt signaling when TNKS1 is lost through chromosome 8p deletion, defining a paralog-based collateral vulnerability in cancer; structural targeting of both the PARP catalytic site and the ARC4 substrate-binding domain independently attenuates Wnt output.

   Evidence Structure-guided TNKS2-selective inhibitor in organoids and cell lines (preprint); NMR/X-ray of ARC4 with pyrrolone compound plus Wnt reporter (preprint); TNKS1 genetic depletion

   PMID:40093088 PMID:bio_10.1101_2025.03.31.646301

   Open questions at the time

   • Preprint data; not yet peer-reviewed
   • In vivo therapeutic efficacy of TNKS2-selective inhibitors not demonstrated
   • Selectivity over other ARC-domain-containing proteins not fully profiled

• The full substrate repertoire of TNKS2 PARsylation, the structural basis of TNKS2-specific versus TNKS1-redundant functions, and the endogenous contexts in which TNKS2 scaffolding (ARC domains) versus catalytic activity are rate-limiting remain unresolved.
• No proteome-wide PARsylation substrate catalog specific to TNKS2
• No full-length TNKS2 structure or cryo-EM model
• Relative contribution of TNKS2 versus TNKS1 in normal physiology unclear beyond double-KO studies