HINT3

HINT3 is a eukaryote-specific member of the HIT superfamily that acts as an adenylate and phosphoramidate hydrolase, using an active-site histidine (His145, aligned with HINT1 His112) as the catalytic nucleophile and proceeding through an adenylated protein intermediate; it preferentially hydrolyzes aminoacyl-adenylate substrates and can cleave the lysyl-adenylate intermediate generated by lysyl-tRNA synthetase (PMID:17870088). Biochemically and structurally it diverges from HINT1/HINT2 — adopting a range of oligomeric states rather than an obligate homodimer and possessing an Aprataxin-like helix α3 — placing it in a distinct branch of the HIT family, and it distributes to both cytosol and nucleus (PMID:17870088, PMID:41172780). Beyond its catalytic identity, HINT3 has been linked to several cellular regulatory roles: it physically interacts with the succinate dehydrogenase subunit SDHA and suppresses HDAC1-mediated SDHA deacetylation at K335 to limit SDH activity and mitochondrial ROS, conferring protection in myocardial ischemia-reperfusion injury (PMID:40755357); it is stabilized by the deubiquitinase USP11 and interacts with BCL2 to support endothelial apoptosis resistance (PMID:40376595); and it suppresses breast cancer cell proliferation and migration by transcriptionally upregulating PTEN to inactivate AKT/mTOR signaling (PMID:37203409). How its hydrolase activity mechanistically connects to these protein-interaction and signaling functions has not been established in the available corpus.

1. 2007 High

   Established HINT3's molecular identity as a HIT-superfamily hydrolase and pinpointed its catalytic mechanism, answering whether this uncharacterized HINT paralog retained enzymatic activity.

   Evidence Steady-state kinetics with fluorogenic substrates, H145A active-site mutagenesis, and in vitro reconstitution with hLysRS

   PMID:17870088

   Open questions at the time

   • No physiological substrate identified in cells
   • Significance of cleaving lysyl-adenylate for tRNA charging or translation untested in vivo
2. 2007 Medium

   Showed HINT3 is biochemically and structurally distinct from HINT1 in substrate preference, oligomeric behavior, and localization, defining it as a separate functional branch rather than a HINT1 redundant copy.

   Evidence Kinetic profiling across substrates, SEC/AUC oligomeric analysis, and tetracysteine-tag live imaging in HeLa cells

   PMID:17870088

   Open questions at the time

   • Functional consequence of the multimeric range vs HINT1 dimer unknown
   • Tag-induced aggregation may confound native localization
   • No endogenous localization data
3. 2023 Medium

   Linked HINT3 to tumor suppression, addressing whether the enzyme has a cellular signaling role beyond in vitro catalysis.

   Evidence siRNA knockdown and overexpression in breast cancer lines plus mouse xenograft, with PTEN/AKT/mTOR pathway readouts

   PMID:37203409

   Open questions at the time

   • Mechanism by which HINT3 transcriptionally upregulates PTEN unknown
   • Whether His145 hydrolase activity is required for tumor suppression untested
4. 2025 Medium

   Connected HINT3 to mitochondrial redox control via SDHA, establishing a protective role in ischemia-reperfusion injury through an acetylation-regulatory mechanism.

   Evidence Reciprocal Co-IP, cardiomyocyte-specific knockout and overexpression in mouse I/R and OGD/R models, K335 acetylation mapping, SDH activity and ROS assays

   PMID:40755357

   Open questions at the time

   • How HINT3 suppresses HDAC1 expression mechanistically unclear
   • Whether the SDHA interaction depends on HINT3 catalytic activity untested
5. 2025 Medium

   Identified HINT3 stabilization by USP11 and a BCL2 interaction governing endothelial apoptosis resistance, adding a ubiquitin-regulated survival axis.

   Evidence Reciprocal Co-IP for USP11–HINT3 and HINT3–BCL2, siRNA knockdown and USP11 overexpression with BCL2 protein readouts in HPAECs

   PMID:40376595

   Open questions at the time

   • Ubiquitin ligase that opposes USP11 not identified
   • Direct vs indirect nature of HINT3–BCL2 effect on BCL2 levels unresolved
6. 2025 Medium

   Refined HINT3's substrate range and structural placement, showing nucleotide-derivative hydrolysis with adenosine preference and an Aprataxin-like architecture.

   Evidence In vitro hydrolase assays across substrate panels, Kd measurements, and 3D structural modeling/docking of the Gly36 monomeric variant

   PMID:41172780

   Open questions at the time

   • Structural predictions (helix α3, disulfide sites) not validated by mutagenesis or experimental structure
   • No physiological substrate confirmed

• Whether HINT3's hydrolase activity mechanistically underlies its protein-interaction and signaling roles (SDHA, BCL2, PTEN axes) remains unresolved.
• No study tests whether His145 catalysis is required for any cellular phenotype
• Endogenous physiological substrate unidentified
• No unifying mechanism linking enzyme activity to the diverse interactomes