Affinage

SMOX

Spermine oxidase · UniProt Q9NWM0

Length
555 aa
Mass
61.8 kDa
Annotated
2026-06-10
16 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SMOX (PAOh1/SMO) is a flavin-dependent spermine oxidase that catabolizes polyamines and generates hydrogen peroxide as a byproduct, positioning it as a central enzymatic source of oxidative stress in both cytotoxic and pathological contexts (PMID:12727196, PMID:16207710). The purified recombinant enzyme preferentially oxidizes spermine (Km ~1.6 µM) over N1-acetylspermine and does not oxidize spermidine, and its activity is selectively blocked by oligamine analogues and dedicated small-molecule inhibitors (PMID:12727196, PMID:36135832). SMOX is a highly inducible enzyme: antitumor polyamine analogues bearing multiple three-carbon linkers upregulate it through increased transcription, mRNA stabilization, and new protein synthesis rather than protein stabilization (PMID:12827295, PMID:15496143). Functionally, SMOX-derived H2O2 is the exclusive source of cytotoxic peroxide produced through polyamine catabolism in analogue-treated cancer cells, and its knockdown confers resistance to analogue-induced growth inhibition (PMID:16207710). Across disease models, SMOX-generated ROS act upstream of multiple signaling cascades: it suppresses Nrf2 to compromise blood-brain barrier integrity in stroke (PMID:37984250), drives AKT-mTOR signaling and epithelial-mesenchymal transition in hepatocellular carcinoma (PMID:41444797), and elevates ROS that transcriptionally induces TRIB3 to suppress GSK-3β and activate Wnt/β-catenin in colorectal cancer (PMID:42262434). SMOX expression is itself controlled post-transcriptionally and transcriptionally by factors including miR-139-5p, PUS1-mediated mRNA pseudouridylation, and the transcription factor ZNF263 (PMID:41444797, PMID:42262434, PMID:39993614). Genetic or pharmacological SMOX inhibition is protective in models of cerebral ischemia, acute kidney injury, and rheumatoid arthritis, consistent with its role as a driver of oxidative and inflammatory tissue injury (PMID:30576531, PMID:40683494, PMID:41485416).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2003 High

    Establishing that SMOX is a bona fide flavin-dependent oxidase with defined substrate preference answered what reaction this protein catalyzes and how it differs from related polyamine oxidases.

    Evidence In vitro enzymatic assays on purified recombinant protein with substrate Km determinations and inhibitor screening

    PMID:12727196

    Open questions at the time
    • No structural model of the active site provided
    • Physiological versus pharmacological substrate balance in cells not addressed
  2. 2003 Medium

    Demonstrating that polyamine analogues induce SMOX mRNA and activity, with potency tied to specific linker chemistry, connected enzyme regulation to a structure-activity relationship for inducers.

    Evidence mRNA expression and enzyme activity assays with analogue structure-activity comparison across lung carcinoma cell lines

    PMID:12827295

    Open questions at the time
    • Transcriptional machinery mediating induction not identified
    • Did not distinguish transcription from mRNA stability
  3. 2005 High

    Dissecting the levels of analogue-induced SMOX regulation answered whether induction is transcriptional or post-transcriptional, showing it combines new transcription with mRNA stabilization but not protein stabilization.

    Evidence Actinomycin D mRNA half-life assays, cycloheximide treatment, and promoter reporter constructs

    PMID:15496143

    Open questions at the time
    • The cis-elements and trans-factors stabilizing the mRNA not defined
    • Promoter elements driving transcription not mapped
  4. 2005 High

    Identifying SMOX as the exclusive source of cytotoxic H2O2 in analogue-treated cells, with knockdown conferring resistance, established the enzyme as the causal node linking polyamine catabolism to oxidative cell death.

    Evidence Stable siRNA knockdown with H2O2, growth, and polyamine pool measurements in breast cancer cells

    PMID:16207710

    Open questions at the time
    • Downstream targets of the H2O2 not identified in this context
    • Did not address non-cancer cell types
  5. 2019 Medium

    Showing that SMOX knockdown reduces infarct volume and inflammation in stroke, and that SMOX-deficient neurons produce less microglia-activating medium, extended SMOX function from cytotoxicity to neuroinflammatory signaling in vivo.

    Evidence AAV-RNAi knockdown in a rat MCAO model plus OGD/R neuron-microglia conditioned medium transfer

    PMID:30576531

    Open questions at the time
    • The specific oxidative product mediating microglial activation not identified
    • Signaling pathway downstream of SMOX not resolved here
  6. 2022 Medium

    Identification of selective small-molecule SMOX inhibitors with sub-micromolar potency established that the enzyme is pharmacologically druggable.

    Evidence Virtual and physical screening with in vitro IC50/Ki determination and selectivity profiling

    PMID:36135832

    Open questions at the time
    • In vivo efficacy of these compounds not tested
    • Binding mode not structurally confirmed
  7. 2023 Medium

    Placing SMOX-derived H2O2 upstream of Nrf2 suppression in BBB endothelium, via brusatol rescue, defined a specific signaling axis through which SMOX oxidative stress damages the blood-brain barrier.

    Evidence siRNA lentivirus knockdown in tMCAO mouse and bEnd.3 cells with Nrf2 inhibitor epistasis and BBB permeability assays

    PMID:37984250

    Open questions at the time
    • Mechanism by which H2O2 suppresses Nrf2 not detailed
    • Single lab, single disease context
  8. 2025 Medium

    Linking SMOX to AKT-mTOR signaling and EMT in hepatocellular carcinoma, with miR-139-5p as a direct repressor, connected SMOX to a pro-metastatic signaling program and a post-transcriptional control point.

    Evidence Dual-luciferase reporter assay, phospho-Western blots, and overexpression/knockdown rescue experiments

    PMID:41444797

    Open questions at the time
    • Whether AKT-mTOR activation is ROS-dependent not directly demonstrated
    • Single tumor type
  9. 2025 Medium

    Identifying PUS1-mediated pseudouridylation as a stabilizer of SMOX mRNA, under USF1 control, added a novel RNA-modification layer to SMOX regulation in renal cancer.

    Evidence PUS1 knockdown/overexpression in ccRCC lines with migration assays and pseudouridylation analysis

    PMID:39993614

    Open questions at the time
    • Direct mapping of pseudouridine sites on SMOX mRNA limited
    • Causal chain inferred from functional assays
  10. 2025 Low

    Modeling SMOX manipulation in a Drosophila α-synuclein Parkinson's model linked SMOX-mediated polyamine catabolism to α-synuclein levels and organismal lifespan/motility.

    Evidence RNAi knockdown and transgenic overexpression in a Drosophila PD model with lifespan, motility, and α-synuclein measurements (preprint)

    PMID:bio_10.1101_2025.03.06.641237

    Open questions at the time
    • Preprint; no direct biochemical mechanism linking SMOX to α-synuclein
    • Human relevance not established
  11. 2026 Medium

    Defining a SMOX-ROS-TRIB3-GSK-3β-β-catenin axis with ZNF263 as a transcriptional activator established both an upstream regulator and a complete downstream signaling cascade for SMOX in colorectal cancer.

    Evidence Co-IP, ChIP-qPCR, ROS measurement, and in vivo xenograft/peritoneal metastasis models with SMOX perturbation

    PMID:42262434

    Open questions at the time
    • Generality of the ZNF263-SMOX-TRIB3 axis beyond colorectal cancer untested
    • Direct ROS-to-TRIB3 transcriptional mechanism not fully resolved
  12. 2026 Medium

    Demonstrating that SMOX silencing and inhibition reduce inflammatory phenotypes in rheumatoid arthritis synoviocytes and arthritis severity in vivo broadened SMOX as a therapeutic target in inflammatory disease.

    Evidence siRNA knockdown in RA-FLS and JNJ-9350 pharmacological inhibition in vitro and in a CAIA mouse model

    PMID:41485416

    Open questions at the time
    • Signaling pathway downstream of SMOX in synoviocytes not defined
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved how SMOX-generated H2O2 is mechanistically channeled to specific downstream effectors (Nrf2, AKT-mTOR, TRIB3) in a context-dependent manner, and whether a unifying redox-sensing step governs this selectivity.
  • No structural model of human SMOX in the corpus
  • Endogenous physiological role distinct from pathological ROS signaling not established
  • Direct molecular targets of SMOX-derived peroxide not identified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016491 oxidoreductase activity 2 GO:0140098 catalytic activity, acting on RNA 1
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-8953897 Cellular responses to stimuli 2

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 Purified recombinant human PAOh1/SMO (SMOX) is a flavin-dependent polyamine oxidase that oxidizes spermine (Km=1.6 µM) and N1-acetylspermine (Km=51 µM) but does not oxidize spermidine; specific oligamine analogues are potent inhibitors of spermine oxidation by PAOh1/SMO. In vitro enzymatic assay with purified recombinant protein; substrate kinetics determination; inhibitor screening Biochemical and biophysical research communications High 12727196
2005 In polyamine analogue (BENSpm)-treated human breast cancer cells, SMO(PAOh1)/SMOX—not the peroxisomal acetylpolyamine oxidase PAO—is the exclusive source of cytotoxic H2O2 produced through polyamine catabolism; stable siRNA knockdown of SMOX rendered MDA-MB-231 cells significantly resistant to BENSpm-induced growth inhibition. Stable siRNA knockdown; H2O2 measurement; cell growth and polyamine pool assays; enzyme activity assays The Journal of biological chemistry High 16207710
2003 PAOh1/SMO (SMOX) is induced at the mRNA and activity level by multiple antitumor polyamine analogues in human lung carcinoma cell lines, with the most potent inducers possessing multiple three-carbon linkers between nitrogens (e.g., N1,N11-bis(ethyl)norspermine). mRNA expression analysis; enzyme activity assays; analogue structure-activity comparison across cell lines Cancer chemotherapy and pharmacology Medium 12827295
2005 Analogue (CPENSpm)-induced expression of SMOX is regulated at the levels of new mRNA synthesis, mRNA stabilization (half-life increased from ~8.8 h to ~17.1 h upon treatment), and newly synthesized protein, with a 30–90% increase in transcription demonstrated by promoter reporter constructs; protein stabilization does not play a significant role. Actinomycin D mRNA half-life assays; cycloheximide protein synthesis inhibition; promoter reporter constructs; enzyme activity assays The Biochemical journal High 15496143
2019 SMOX downregulation by AAV-mediated RNAi in a rat MCAO model significantly reduced brain infarct volume, neuronal apoptosis, and inflammatory reactions (IL-6, TNF-α); neurons with reduced SMOX after OGD/R produced conditioned medium that caused less microglial activation, implicating SMOX-derived H2O2/oxidative products as mediators of neuroinflammatory signaling. AAV-RNAi knockdown in vivo (MCAO rat model); OGD/R primary neuron culture; conditioned medium transfer to microglia; cytokine measurement; infarct volume quantification Toxicological sciences Medium 30576531
2022 Novel small-molecule SMOX inhibitors (compounds 6 and 7) with IC50 values of 0.54 µM and 0.23 µM, and Ki values of 1.60 µM and 0.46 µM respectively, were identified via virtual and physical screening, demonstrating that SMOX enzymatic activity is pharmacologically targetable with high selectivity. Virtual screening; in vitro enzyme inhibition assays (IC50, Ki determination); selectivity profiling Medical sciences (Basel, Switzerland) Medium 36135832
2023 Knockdown of SMOX with siRNA lentivirus in the tMCAO stroke model protected blood-brain barrier integrity by reducing oxidative stress and activating the Nrf2 pathway; blocking Nrf2 with brusatol abolished the protective effects, placing SMOX-mediated H2O2 production upstream of Nrf2 suppression in BBB endothelial cells. siRNA lentivirus knockdown in vivo (tMCAO mouse model) and in vitro (bEnd.3 cells); Nrf2 pathway inhibition with brusatol; BBB permeability assays; oxidative stress markers; apoptosis markers International immunopharmacology Medium 37984250
2025 SMOX promotes hepatocellular carcinoma cell proliferation, migration, and invasion by activating the AKT-mTOR signaling pathway and epithelial-mesenchymal transition (EMT); SMOX overexpression increased phosphorylation of AKT, mTOR, and downstream effectors, and upregulated EMT markers (N-cadherin, vimentin, Snail) while downregulating E-cadherin. miR-139-5p directly targets SMOX (confirmed by dual-luciferase assay) and suppresses this pathway. Dual-luciferase reporter assay (miR-139-5p targeting SMOX 3'UTR); Western blotting for pathway phosphorylation; overexpression and knockdown functional assays; rescue experiments Scientific reports Medium 41444797
2026 SMOX elevates intracellular ROS, which transcriptionally upregulates the pseudokinase TRIB3; TRIB3 interacts with and suppresses GSK-3β activity, thereby stabilizing β-catenin and activating the Wnt/β-catenin pathway in colorectal cancer. ZNF263 was identified as a transcriptional activator of SMOX by directly binding the SMOX promoter (ChIP-qPCR). SMOX knockdown suppressed proliferation, migration, invasion, and peritoneal metastasis in vivo. Co-IP (TRIB3-GSK-3β interaction); ChIP-qPCR (ZNF263 binding to SMOX promoter); Western blotting; ROS measurement; in vivo xenograft and peritoneal metastasis models; SMOX knockdown/overexpression functional assays Apoptosis Medium 42262434
2025 PUS1 stabilizes SMOX mRNA via pseudouridylation, promoting ccRCC cell migration; PUS1 silencing reduced cell migration, while overexpression increased it. The upstream transcription factor USF1 regulates PUS1 expression by binding to its promoter. PUS1 knockdown/overexpression in ccRCC cell lines; migration assays; mRNA pseudouridylation analysis; promoter binding assay for USF1 Cellular signalling Medium 39993614
2025 In a Drosophila model of Parkinson's disease overexpressing human α-synuclein, RNAi knockdown of SMOX significantly affected fly lifespan and motility; overexpression of SMOX had positive enduring effects on lifespan and altered α-synuclein protein levels, implicating SMOX-mediated polyamine catabolism in modulation of α-synuclein levels. RNAi knockdown and transgenic overexpression in Drosophila PD model; lifespan and motility assays; α-synuclein protein level measurement bioRxivpreprint Low bio_10.1101_2025.03.06.641237
2025 Pharmacological inhibition of SMOX (in vivo) significantly alleviated tubular injury, preserved renal function, and reduced oxidative stress in acute kidney injury; in vitro SMOX inhibition maintained epithelial cell integrity and viability while suppressing oxidative damage in renal tubular cells. Pharmacological SMOX inhibition in vivo (AKI model) and in vitro (renal tubular cells); functional readouts (tubular injury markers, renal function, oxidative stress markers, cell viability) International journal of biological macromolecules Low 40683494
2026 SMOX silencing in rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) inhibited migration, invasion, and cytokine production while inducing apoptosis; pharmacological SMOX inhibition with JNJ-9350 produced comparable anti-inflammatory effects in vitro and reduced arthritis severity in collagen antibody-induced arthritis (CAIA) mice in vivo. SMOX siRNA knockdown in RA-FLS; pharmacological inhibition with JNJ-9350 in vitro and in vivo (CAIA mouse model); migration/invasion assays; cytokine measurement; histopathological analysis Molecular immunology Medium 41485416

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Spermine oxidase SMO(PAOh1), Not N1-acetylpolyamine oxidase PAO, is the primary source of cytotoxic H2O2 in polyamine analogue-treated human breast cancer cell lines. The Journal of biological chemistry 105 16207710
2003 Properties of purified recombinant human polyamine oxidase, PAOh1/SMO. Biochemical and biophysical research communications 105 12727196
2003 Induction of the PAOh1/SMO polyamine oxidase by polyamine analogues in human lung carcinoma cells. Cancer chemotherapy and pharmacology 54 12827295
2007 TGFbeta receptor saxophone non-autonomously regulates germline proliferation in a Smox/dSmad2-dependent manner in Drosophila testis. Developmental biology 33 17651718
2005 Induction of human spermine oxidase SMO(PAOh1) is regulated at the levels of new mRNA synthesis, mRNA stabilization and newly synthesized protein. The Biochemical journal 30 15496143
2019 Targeting Smox Is Neuroprotective and Ameliorates Brain Inflammation in Cerebral Ischemia/Reperfusion Rats. Toxicological sciences : an official journal of the Society of Toxicology 21 30576531
2018 The activin signaling transcription factor Smox is an essential regulator of appendage size during regeneration after autotomy in the crayfish. Evolution & development 12 30588766
2022 Identification and Characterization of Novel Small-Molecule SMOX Inhibitors. Medical sciences (Basel, Switzerland) 11 36135832
2023 Knockdown of Smox protects the integrity of the blood-brain barrier through antioxidant effect and Nrf2 pathway activation in stroke. International immunopharmacology 5 37984250
2020 Safety and Efficacy of s-MOX Regimen in Patients with Colorectal Cancer Who Developed Cardiotoxicity Following Fluoropyrimidine Administration: A Case Series. Archives of medical case reports 4 32964213
2025 Molecular characterization and functional prioritization of CD46, IL6R, KLRC1, LEAP2 and SMOX as candidate targets in acute kidney injury. International journal of biological macromolecules 3 40683494
2025 PUS1 facilitates cell migration in clear cell renal cell carcinoma through the promotion of mRNA pseudouridylation and the stabilization of the SMOX gene. Cellular signalling 1 39993614
2025 Targeting SMOX Preserves Optic Nerve Myelin, Axonal Integrity, and Visual Function in Multiple Sclerosis. Biomolecules 1 40001462
2026 Investigating the role of SMOX in rheumatoid arthritis. Molecular immunology 0 41485416
2026 A novel ZNF263-SMOX-ROS-TRIB3 signaling axis drives Wnt/β-catenin activation and metastatic progression in colorectal cancer. Apoptosis : an international journal on programmed cell death 0 42262434
2025 miR-139-5p suppresses hepatocellular carcinoma progression by targeting SMOX to inhibit AKT-mTOR pathway and epithelial-mesenchymal transition. Scientific reports 0 41444797

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