SLC25A39

SLC25A39 is a mitochondrial inner-membrane carrier that imports glutathione (GSH) from the cytosol into the mitochondrial matrix, coupling cellular redox homeostasis to mitochondrial iron-sulfur cluster integrity and OXPHOS (PMID:34707288, PMID:35513392). Loss of SLC25A39 selectively depletes the mitochondrial GSH pool without affecting whole-cell GSH, and combined loss with its paralogue SLC25A40 destabilizes iron-sulfur cluster proteins, impairs cell proliferation, and blocks red blood cell development in mice (PMID:34707288); its GSH import function operates jointly with SLC25A37-mediated mitochondrial iron uptake to sustain OXPHOS (PMID:35513392). SLC25A39 is a short-lived protein controlled by a dual post-translational mechanism: the matrix m-AAA protease AFG3L2 degrades it through its matrix loop 1, while binding of iron-sulfur clusters at four matrix cysteines inhibits this degradation, so that protein abundance reports on both GSH availability and iron status (PMID:34707288, PMID:38157846). This stability switch is the node at which physiological and pathological signals converge — FGF21 stabilizes SLC25A39 by blocking AFG3L2-mediated degradation to confer neuroprotection (PMID:41039428), and the interactors DLAT, CRABP2 (via AFG3L2), and PRDX1 modulate SLC25A39 abundance or downstream redox state to tune ferroptosis, necroptosis, and proliferation in multiple cancers (PMID:42009144, PMID:41558298, PMID:40305785). SLC25A39 was originally identified as the mitochondrially localized protein CGI-69 (PMID:11139402).

1. 2001 Medium

   Established the basic cell biology of the then-uncharacterized CGI-69 protein, showing it is a mitochondrial protein but arguing against an uncoupling function — the first step toward defining its true transport role.

   Evidence FLAG-tag localization in MCF7 cells and membrane potential measurement in HEK-293 cells

   PMID:11139402

   Open questions at the time

   • No transported substrate identified
   • Function beyond mitochondrial residence undefined
2. 2021 High

   Resolved the long-standing question of how mitochondria acquire GSH by identifying SLC25A39 as the carrier required for mitochondrial GSH import and linking that import to iron-sulfur protein function and erythropoiesis.

   Evidence Organellar proteomics, metabolomics, single/double KO of SLC25A39/SLC25A40, mitochondrial GshF rescue, and mouse RBC development assays

   PMID:34707288

   Open questions at the time

   • Direct demonstration of GSH translocation by reconstituted protein not shown
   • Redundancy with SLC25A40 leaves single-gene contribution partly masked
   • Structural basis of transport unknown
3. 2022 High

   Independently corroborated the GSH transport function and revealed that SLC25A39-mediated GSH homeostasis is genetically buffered by SLC25A37-mediated iron uptake, defining a joint requirement for OXPHOS.

   Evidence Pooled dual CRISPR screening across metabolic states, organelle transport assays, structure-guided mutagenesis, mitochondrial metabolite profiling

   PMID:35513392

   Open questions at the time

   • Molecular basis of the SLC25A37/SLC25A39 genetic interaction not defined
   • No structure of the transporter
4. 2023 High

   Explained how SLC25A39 abundance is dynamically set, identifying AFG3L2 as its protease and four matrix cysteines as an iron-sulfur cluster sensor that gates degradation, thereby coupling mitochondrial GSH levels to iron status.

   Evidence Co-IP/MS, CRISPR KO, cysteine site-directed mutagenesis, protein stability assays in cells and neurons

   PMID:38157846

   Open questions at the time

   • Identity and assembly route of the bound Fe-S species not fully defined
   • How GSH availability feeds into the degradation switch mechanistically unresolved
5. 2024 Medium

   Placed SLC25A39 within a stress-response pathway, showing the NFE2L2-GSH-SLC25A39 axis imports GSH to chelate copper and restrain cuproptosis, with pathway inhibition enhancing tumor suppression.

   Evidence Genetic loss-of-function of NFE2L2, GCLM, GCLC, SLC25A39 in PDAC cells and mouse tumors, copper chelation and GSH assays

   PMID:39609608

   Open questions at the time

   • Direct copper handling by mitochondrial GSH not biochemically isolated
   • Single lab, one tumor type
6. 2025 Medium

   Identified physiological and protein-level regulators acting through the AFG3L2 stability switch — FGF21 stabilizes SLC25A39 for neuroprotection, and DLAT and CRABP2 enhance its stability to support redox balance and proliferation.

   Evidence Neuron-specific Slc25a39 KO mice with FGF21 administration; Co-IP and protein stability assays for DLAT (CRC) and CRABP2-AFG3L2 (CRC, conditional KO mouse)

   PMID:40305785 PMID:41039428 PMID:42009144

   Open questions at the time

   • Whether DLAT and CRABP2 act directly on the AFG3L2 reaction or indirectly unresolved
   • Single-lab findings per regulator
   • Reciprocal validation limited for some interactions
7. 2025 Medium

   Mapped downstream death pathways controlled by SLC25A39-dependent GSH import, linking its loss to ferroptosis, necroptosis, and apoptosis across cancers and identifying PRDX1 as a partner whose overexpression rescues redox phenotypes.

   Evidence MS/Co-IP/IF for PRDX1 binding with rescue (HCC); knockdown with lipid peroxidation and ferroptosis readouts (CRC); AFG3L2-dependent stabilization driving OXPHOS impairment and apoptosis (lung adenocarcinoma)

   PMID:40993178 PMID:41558298 PMID:42009144

   Open questions at the time

   • Mechanistic link between matrix GSH and cytosolic death pathways incompletely defined
   • Context-dependent oncogenic vs tumor-suppressive roles not reconciled
   • Single lab per study

• The structural mechanism of GSH translocation and the physical chemistry of the Fe-S/cysteine degradation switch remain unresolved.
• No experimental transporter structure
• Stoichiometry and energetics of GSH transport undefined
• Identity of the Fe-S cluster and its assembly pathway onto SLC25A39 not established