SEPHS1

SEPHS1 is a paralog of the selenophosphate synthetase SEPHS2 that has lost the catalytic Sec/Cys residue required for selenophosphate synthesis but retains ATPase activity yielding ADP and inorganic phosphate, and it physically associates with SEPHS2, SEPSECS, and SECp43 within the selenocysteine biosynthesis complex (PMID:28414460, PMID:36202216). Functionally, its dominant role across cell types is the maintenance of redox homeostasis: loss of SEPHS1 drives superoxide and lipid peroxide accumulation through induction of xanthine oxidase and NADPH oxidase and downregulation of SOD1/SOD3, producing DNA damage, G2/M arrest, and impaired angiogenesis (PMID:34769076). This redox control underlies pleiotropic developmental requirements — Sephs1-null mice die by E11.5 with progressive ROS-driven apoptosis and disrupted retinoic acid, Wnt, prolactin, and IGF signaling (PMID:34769078), and SEPHS1 is dispensable for ESC pluripotency yet indispensable for germ-layer and cardiac differentiation (PMID:34974300) and for survival during human pluripotent cell reprogramming (PMID:31607477). Through ROS modulation SEPHS1 also intersects multiple signaling axes: it positively regulates SMAD2/3/4 levels to promote TGF-β-driven migration and invasion in hepatocellular carcinoma (PMID:33622411), suppresses Hippo-YAP/TAZ activation to delay nucleus pulposus senescence and disc degeneration (PMID:38105759), and limits CXCL9/10 chemokine expression to restrain CD8+ T cell infiltration and promote tumor immune evasion (PMID:41441975). De novo missense variants at Trp352 (destabilizing) and Arg371 (interaction-modulating) enhance neuronal cell proliferation via altered ROS homeostasis, linking SEPHS1 to a human neurodevelopmental disorder (PMID:38531365).

1. 2017 Medium

   Established that SEPHS1 is a physical member of the selenocysteine biosynthesis machinery rather than an isolated enzyme, situating it among SEPHS2, SEPSECS, and SECp43.

   Evidence BRET assay and reciprocal co-immunoprecipitation in mammalian cells

   PMID:28414460

   Open questions at the time

   • Stoichiometry and architecture of the complex not resolved
   • Functional consequence of each interaction not tested
   • Single-lab interaction data
2. 2021 Medium

   Defined a concrete molecular mechanism for SEPHS1 deficiency, showing redox imbalance via specific oxidase induction and SOD loss drives DNA damage and cell cycle arrest.

   Evidence CRISPR/Cas9 knockout in mouse 2H11 endothelial cells with ROS, enzyme activity, cell cycle, γH2AX, and tube formation assays

   PMID:34769076

   Open questions at the time

   • Mechanism linking SEPHS1 loss to oxidase induction unknown
   • Endothelial-specific vs general phenotype not separated
   • No direct enzymatic substrate identified
3. 2021 Medium

   Demonstrated that the redox role of SEPHS1 is essential in vivo, with loss causing embryonic lethality preceded by staged disruption of multiple developmental signaling pathways.

   Evidence Systemic Sephs1 knockout mice with morphology, apoptosis/DNA damage markers, and bioinformatic pathway analysis

   PMID:34769078

   Open questions at the time

   • Causal ordering of pathway changes is partly bioinformatic
   • Tissue of primary failure not pinpointed
   • Direct molecular targets not identified
4. 2021 Medium

   Placed SEPHS1 upstream of TGF-β/SMAD signaling, connecting it to EMT and cancer cell invasion.

   Evidence siRNA knockdown, overexpression, and SEPHS1-OE/SMAD3-KD epistasis with migration/invasion assays in HCC cell lines

   PMID:33622411

   Open questions at the time

   • How SEPHS1 regulates SMAD protein levels mechanistically unknown
   • Whether effect is ROS-dependent not tested
   • Single cancer type
5. 2019 Medium

   Showed SEPHS1 supports stem cell survival during reprogramming through redox signaling rather than by controlling core pluripotency genes.

   Evidence siRNA knockdown in hESCs with reprogramming/clonogenicity assays, transcriptome and ROS pathway analysis

   PMID:31607477

   Open questions at the time

   • Knockdown not knockout
   • Direct redox effector not identified
   • Single method set
6. 2021 Medium

   Distinguished SEPHS1 requirement in differentiation from pluripotency, identifying a specific block in germ-layer and cardiac lineage specification.

   Evidence CRISPR/Cas9 KO mouse ESCs with gastruloid aggregation, RNA-seq, embryoid body beating, and marker assays

   PMID:34974300

   Open questions at the time

   • Molecular basis of differentiation block not defined
   • Link to ROS in this context not established
   • Other lineages less characterized
7. 2023 Medium

   Linked SEPHS1 redox control to suppression of Hippo-YAP/TAZ signaling and to a senescence/degeneration disease phenotype.

   Evidence IL-1β NPC senescence model and rat needle-puncture IVDD model with overexpression, Hippo inhibitor rescue, and ROS assays

   PMID:38105759

   Open questions at the time

   • Mechanism connecting SEPHS1/ROS to Hippo activation unknown
   • Direct vs indirect YAP/TAZ regulation unresolved
   • Single tissue model
8. 2024 Medium

   Connected SEPHS1 to a human neurodevelopmental disorder via de novo missense variants and showed two distinct biophysical mechanisms (destabilization vs interaction modulation) converge on ROS-driven proliferation.

   Evidence Structural modeling, thermal stability assays, and ROS/proliferation assays in SH-SY5Y cells

   PMID:38531365

   Open questions at the time

   • Specific protein interactions altered by Arg371 not identified
   • Patient phenotype-to-cellular mechanism link incomplete
   • Single study
9. 2025 Medium

   Identified SEPHS1 as a tumor-intrinsic driver of immune evasion that suppresses CD8+ T cell-recruiting chemokines, with knockdown enhancing anti-PD-1 efficacy.

   Evidence Knockdown in melanoma cells with T cell co-culture, flow cytometry, transcriptomics, and in vivo anti-PD-1 tumor models

   PMID:41441975

   Open questions at the time

   • Pathway linking SEPHS1 to CXCL9/10 suppression undefined
   • Whether ROS mediates chemokine suppression untested
   • Single tumor type

• How SEPHS1 ATPase activity and complex membership mechanistically connect to its broad redox-regulatory and signaling functions remains unresolved.
• No in vitro reconstitution of SEPHS1 ATPase function and its biological role
• No direct substrate or effector linking ATPase activity to ROS control
• Unifying mechanism across TGF-β, Hippo, and immune phenotypes not established