EFHD1

EFHD1 is a Ca2+- and Zn2+-binding EF-hand protein of the inner mitochondrial membrane that couples cytoskeletal and ion-handling activities to control mitochondrial function and cellular energy metabolism (PMID:28524857, PMID:33537316). Structurally, its core comprises two EF-hands and a ligand-mimic helix, and it binds β-actin constitutively while bundling/crosslinking actin in a Ca2+- and Zn2+-dependent manner (PMID:33537316, PMID:36862489). At the inner mitochondrial membrane EFHD1 participates in Ca2+-induced mitoflashes and governs reactive oxygen species production; loss of EFHD1 lowers basal mitochondrial ROS and mitoflash events and confers resistance to hypoxic injury (PMID:28524857, PMID:35304170). It restrains mitochondrial Ca2+ uptake by physically binding the mitochondrial calcium uniporter MCU through its N-terminal domain (PMID:36747492), and limits mitochondrial permeability transition pore opening by binding adenine nucleotide translocase ANT3 and blocking its conformational change, thereby preserving mitochondrial integrity (PMID:38795203). As a Ca2+-dependent actin crosslinker EFHD1 also stabilizes ER–mitochondria contact sites by sensing coincident inter-organellar proximity and ER Ca2+ release (PMID:41756893). Through these mitochondrial functions EFHD1 regulates axonal morphogenesis downstream of Lkb1, where its loss produces mitochondrial dysfunction, reduced axonal ATP, AMPK-Ulk1 activation and increased autophagy (PMID:32414840), and it shapes B-cell development by tuning the balance between oxidative phosphorylation and glycolysis (PMID:28524857). In multiple carcinomas EFHD1 modulates Hippo/YAP signaling, acting via the MCU interaction and STARD13 to promote YAP phosphorylation (PMID:36747492) and via a SIK3-Hippo axis to suppress EMT and metastasis (PMID:39895792).

1. 2011 Low

   Before direct characterization, EFHD1 was placed by sequence/structure prediction as a mitochondria-associated EF-hand protein potentially modulating apoptosis and oxidative-stress responses, framing the hypotheses later tested experimentally.

   Evidence Secondary-structure prediction and comparative analysis with literature review

   PMID:21244694

   Open questions at the time

   • No direct experimental validation in this work
   • Predicted coiled-coil and disordered regions not functionally tested
   • Mitochondrial association inferred, not demonstrated
2. 2017 High

   Established EFHD1 as a bona fide inner-mitochondrial-membrane Ca2+-binding protein controlling mitoflashes and the OXPHOS/glycolysis balance, and connected it to a developmental switch in B cells.

   Evidence Knockdown/knockout in B-cell lines plus transgenic mouse, with metabolic flux (OCR/ECAR), membrane potential and ROS measurements

   PMID:28524857

   Open questions at the time

   • Molecular partners mediating mitoflash regulation not identified here
   • Mechanism linking EFHD1 to PGC-1α not defined
   • Direct ion-binding stoichiometry not resolved in this study
3. 2020 High

   Placed EFHD1 in an Lkb1-driven energy-homeostasis pathway that supports axonal growth, showing its loss causes mitochondrial dysfunction and AMPK-Ulk1-driven autophagy in neurons.

   Evidence Efhd1 knockout mice with axonal morphometry, ATP measurement, mitochondrial imaging, and pathway/autophagic-flux analysis

   PMID:32414840

   Open questions at the time

   • Direct biochemical link between Lkb1 and EFHD1 not established
   • Molecular target of EFHD1 at the mitochondrion in neurons unidentified
   • Whether actin-binding contributes to the axonal phenotype untested
4. 2021 High

   Solved the EFHD1 core structure and demonstrated Ca2+-independent actin binding with Ca2+-dependent actin bundling, defining its cytoskeletal biochemistry and a possible Zn2+-driven multimerization.

   Evidence X-ray crystallography plus in vitro actin-binding and bundling assays

   PMID:33537316

   Open questions at the time

   • Zn2+-mediated multimerization inferred from crystal contacts, not confirmed in solution
   • Cellular relevance of actin bundling not addressed
   • Link between actin activity and mitochondrial roles not made
5. 2023 High

   Added Zn2+ as a second regulatory ion, showing Zn2+ coordination within the EF-hands and Zn2+-dependent actin bundling, broadening the metal-sensing repertoire beyond Ca2+.

   Evidence X-ray crystallography with anomalous diffraction at the Zn K-edge plus actin assays

   PMID:36862489

   Open questions at the time

   • Physiological Zn2+ concentrations driving this in cells not defined
   • Interplay of Ca2+ vs Zn2+ regulation unresolved
   • In vivo consequence of Zn2+ binding untested
6. 2023 Medium

   Identified MCU as a direct N-terminal-domain partner through which EFHD1 suppresses mitochondrial Ca2+ uptake and, via STARD13, modulates Hippo/YAP signaling and cell migration.

   Evidence Co-IP plus overexpression/knockdown, rescue, mitochondrial Ca2+ measurement and migration assays in ccRCC

   PMID:36747492

   Open questions at the time

   • Mechanism connecting MCU binding to STARD13 upregulation not defined
   • Single-lab interaction without reciprocal structural validation
   • Direct vs indirect nature of YAP regulation unclear
7. 2024 Medium

   Defined a second mitochondrial effector mechanism: EFHD1 binds ANT3 and prevents its conformational change to inhibit mPTP opening, preserving mitochondrial function and promoting tumor-cell survival.

   Evidence Co-IP, knockdown/overexpression, viability assays, and pharmacological ANT3 modulation with CATR/BKA in osteosarcoma

   PMID:38795203

   Open questions at the time

   • Structural basis of ANT3 conformational locking not resolved
   • Whether MCU and ANT3 binding are mutually exclusive unknown
   • Single-lab interaction evidence
8. 2022 Medium

   Showed that EFHD1 loss lowers basal mitochondrial ROS and mitoflashes and protects cardiomyocytes from hypoxic injury, while leaving Ca2+-overload susceptibility unchanged, dissociating its ROS/mitoflash role from Ca2+-overload handling.

   Evidence Efhd1 knockout mouse with ROS, mitoflash imaging, cardiac phenotyping and hypoxia/Ca2+-overload assays

   PMID:35304170

   Open questions at the time

   • Molecular source of the ROS phenotype not pinpointed
   • No basal cardiac phenotype limits interpretation
   • Relationship to MCU/ANT3 interactions not tested here
9. 2025 Medium

   Extended EFHD1's cancer signaling roles, implicating a SIK3-Hippo axis in metastasis suppression and, separately, estrogen-receptor signaling in breast cancer proliferation.

   Evidence Overexpression/knockdown with genetic rescue (SIK3, ESR1) and in vivo metastasis models

   PMID:39895792 PMID:40441345

   Open questions at the time

   • Biochemical mechanism linking EFHD1 to SIK3/ESR1 not established
   • ESR1 study is single-lab, Low-confidence
   • Reconciliation of pro- versus anti-tumor roles across cancers unresolved
10. 2026 Medium

    Reframed EFHD1 as a coincidence detector that stabilizes ER-mitochondria contact sites, where pathological upregulation drives mitochondrial fragmentation, dsRNA escape and a PKR antiviral response in steatohepatitis.

    Evidence ERMCS and mitochondrial imaging, dsRNA/PKR analysis, EFHD1 inhibition in human and mouse MASH models, and Mendelian randomization (preprint)

    PMID:41756893

    Open questions at the time

    • Preprint, not yet peer-reviewed
    • Direct molecular tethers at ERMCS bound by EFHD1 not identified
    • Causality of EFHD1 in human disease beyond genetic association unconfirmed

• How EFHD1's Ca2+/Zn2+-regulated actin-crosslinking activity is mechanistically coupled to its distinct mitochondrial partner interactions (MCU, ANT3) and to its divergent context-dependent signaling outputs remains unresolved.
• No unified model integrating actin, MCU, and ANT3 functions
• Structural basis of inner-membrane localization undefined
• Determinants of pro- vs anti-tumor behavior across tissues unknown