THADA

THADA is a large ARM-repeat scaffold protein that operates in two largely independent contexts: as an auxiliary subunit of a tRNA-modifying methyltransferase complex and as a regulator of ER calcium handling and apoptosis (PMID:28399403, PMID:40483304). In tRNA modification, THADA partners with the methyltransferase FTSJ1 (yeast Trm7), binding it via the FTSJ1 C-terminus, and anchors the tRNA substrate within itself through defined residues to enable 2'-O-methylation at position 32 of the anticodon loop (Nm32); a conserved RRSAGLP motif in its DUF2428 domain is required for this catalytic activity (PMID:40483304, PMID:35559166). Independently, THADA binds the SERCA Ca2+ ATPase and acts as an uncoupler, dissociating ATP hydrolysis from Ca2+ transport, a function conserved from Drosophila — where its loss causes obesity, hyperphagia, reduced energy production, and cold sensitivity rescued by lowering SERCA activity — to mammals (PMID:28399403). In pancreatic β-cells, THADA depletes ER Ca2+ stores via SERCA2 inhibition and RyR2-mediated leak, and under sustained ER stress assembles and activates a DR5/FADD/caspase-8 pro-apoptotic complex, such that Thada loss in mice improves glycemic control and β-cell survival (PMID:36823211). In cancer cells, THADA mediates COPII-dependent Golgi trafficking of PD-L1 by bridging PD-L1 cargo to the SEC24A vesicle module, with its loss redirecting PD-L1 to ER-associated degradation (PMID:34341130), and chromosomal THADA gene fusions drive overexpression of full-length IGF2BP3 to activate IGF2/IGF1R/PI3K/MAPK signaling in thyroid neoplasia (PMID:28193878).

1. 2007 Low

   Established the first structural inference about THADA — that it is an ARM-repeat protein likely engaged in protein-protein interactions — and linked disruption of its most conserved domain to follicular thyroid neoplasia.

   Evidence Comparative sequence analysis across vertebrate orthologs and mapping of thyroid adenoma translocation breakpoints to the conserved domain

   PMID:17889454

   Open questions at the time

   • Computational domain prediction only, no biochemical or cell-biological validation
   • No molecular function assigned to the ARM repeats
   • Mechanism by which domain loss promotes neoplasia not tested
2. 2009 Low

   Connected a THADA variant to β-cell physiology, indicating a role in β-cell mass or function rather than acute glucose-stimulated secretion, but without a molecular mechanism.

   Evidence Hyperglycemic clamp with GLP-1 and arginine stimuli in a human cohort (n=336) with genotyping

   PMID:19833888

   Open questions at the time

   • Genetic association only, no causal molecular pathway established
   • Single cohort
   • Does not distinguish effects on β-cell mass versus signaling
3. 2017 High

   Defined the first direct molecular function of THADA — uncoupling SERCA Ca2+ transport from ATP hydrolysis — and placed SERCA genetically downstream to explain its role in energy balance.

   Evidence Drosophila knockout phenotyping, THADA-SERCA binding assay, and genetic epistasis rescuing obesity by reducing SERCA activity

   PMID:28399403

   Open questions at the time

   • Structural basis of SERCA uncoupling not resolved
   • Conservation of the mammalian SERCA interaction not directly demonstrated here
   • Does not address tRNA modification role
4. 2017 High

   Showed that cancer-associated THADA fusions act not by producing chimeric protein but by driving full-length IGF2BP3 overexpression and downstream growth signaling, explaining a recurrent oncogenic rearrangement.

   Evidence Whole-transcriptome/genome sequencing, western blotting, proliferation/invasion/transformation assays, xenografts, and IGF1R inhibitor treatment

   PMID:28193878

   Open questions at the time

   • Does not address normal THADA protein function
   • Mechanism by which the fusion elevates IGF2BP3 transcription not fully defined
   • Generalizability across fusion partners limited
5. 2021 Medium

   Identified a trafficking function for THADA, bridging PD-L1 cargo to the COPII module SEC24A to maintain PD-L1 secretion, revealing an immune-evasion-relevant role.

   Evidence siRNA knockdown in colorectal cancer cells, co-IP of PD-L1 with SEC24A via THADA, fractionation/IF, T cell killing assay, and MC38 tumor model

   PMID:34341130

   Open questions at the time

   • Single lab without reciprocal structural validation
   • Selectivity for PD-L1 over other COPII cargoes not fully mapped
   • Relationship to THADA's ER calcium and tRNA functions unknown
6. 2022 Medium

   Defined THADA as the auxiliary subunit of the Trm7/FTSJ1 tRNA methyltransferase, pinpointing a conserved DUF2428 motif required for 2'-O-methylation at position 32.

   Evidence Yeast cell-based tRNA modification assays, mutagenesis of Trm732 variants, and complementation with human THADA

   PMID:35559166

   Open questions at the time

   • Single lab
   • Structural mechanism of substrate engagement not resolved at this stage
   • Catalytic contribution of THADA versus FTSJ1 not separated biochemically
7. 2023 High

   Established that THADA controls β-cell ER Ca2+ homeostasis and, under ER stress, activates a DR5/FADD/caspase-8 apoptotic complex, providing a mechanistic basis for its diabetes association.

   Evidence Global and β-cell-specific Thada knockout mice, Ca2+ imaging, co-IP of the apoptotic complex, and pharmacological inhibition with alnustone

   PMID:36823211

   Open questions at the time

   • How ER stress triggers THADA-dependent apoptotic complex assembly is undefined
   • Relationship between SERCA2 inhibition and RyR2 leak not fully integrated
   • Direct binding interfaces within the DR5/FADD/caspase-8 complex not mapped
8. 2025 High

   Provided the structural mechanism by which THADA enables FTSJ1 catalysis, showing FTSJ1 binds via its C-terminus and the tRNA substrate is anchored inside THADA through identified residues.

   Evidence Cryo-EM of human FTSJ1-THADA with and without tRNA, biochemical methylation assays, and mutagenesis of THADA residues

   PMID:40483304

   Open questions at the time

   • Does not reconcile the tRNA-modification role with the cytoplasmic ER/SERCA functions
   • Substrate specificity determinants beyond Nm32 not detailed
   • Regulation of complex assembly in cells unknown

• How a single protein reconciles its roles as a nuclear/cytoplasmic tRNA-modification subunit, an ER membrane Ca2+ regulator and apoptotic scaffold, and a Golgi-trafficking adaptor remains unresolved.
• No study integrates the tRNA, SERCA/ER calcium, apoptosis, and PD-L1 trafficking functions
• Whether these reflect distinct pools, isoforms, or context-specific partners is unknown
• No unified model of how ARM/DUF2428 architecture supports such diverse activities