{"gene":"PXMP4","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2025,"finding":"PXMP4 is ubiquitinated at lysine 20 by the E3 ligase MARCHF7 on peroxisomal membranes in PEX1-deficient cells, and this ubiquitination serves as a recognition signal recruiting the autophagy receptor NBR1 to peroxisomes to drive pexophagy. TBK1, activated by ROS accumulation downstream of PEX1 depletion, phosphorylates MARCHF7 to promote this ubiquitination. Depletion of PXMP4 or expression of a K20R ubiquitination-defective mutant impairs pexophagic flux.","method":"Functional screening, siRNA knockdown, reconstitution with ubiquitination-defective mutant (K20R), co-immunoprecipitation, pexophagic flux assays, TBK1 phosphorylation assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including KO/KD, mutagenesis rescue, epistasis, and defined cellular phenotype in a single study","pmids":["41267209"],"is_preprint":false},{"year":2022,"finding":"PXMP4 knockout mice generated by CRISPR/Cas9 are viable and fertile with no gross peroxisome morphology changes, but show mildly elevated phytanic/pristanic acid levels suggesting impaired peroxisomal α-oxidation capacity, and reduced hepatic alkyldiacylglycerol ether lipids (particularly those containing polyunsaturated fatty acids), indicating a role for PXMP4 in ether lipid metabolism.","method":"CRISPR/Cas9 knockout mouse model, lipidomic analysis, plasma metabolite profiling (VLCFAs, bile acids, phytanic/pristanic acid), PPARα ligand and phytol-enriched diet challenges","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined metabolic phenotype and multiple pathway readouts","pmids":["35169201"],"is_preprint":false},{"year":2024,"finding":"IAV M2 protein interacts with PEX19 via its cytoplasmic tail, and this interaction disrupts PEX19 binding to peroxisomal membrane proteins including PMP24 (PXMP4), thereby impairing peroxisome biogenesis and antiviral signaling.","method":"Co-immunoprecipitation, PEX19 knockdown, viral growth assays, peroxisome pool quantification","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 3 — single Co-IP showing disrupted PEX19-PMP24 interaction, indirect mechanistic implication for PXMP4","pmids":["39205283"],"is_preprint":false},{"year":2008,"finding":"Pxmp4 was identified as a candidate gene within the Nkt2 congenic region controlling NKT cell numbers; its only known binding partner is Pex19 (an intracellular chaperone and component of the peroxisomal membrane insertion machinery), implicating peroxisomal function in glycolipid availability for CD1d-mediated NKT cell activation.","method":"Congenic mouse strain analysis, microarray expression profiling, candidate gene identification by binding partner analysis","journal":"Journal of immunology","confidence":"Low","confidence_rationale":"Tier 3 — single pulldown/binding partner reference, no direct mechanistic experiment on PXMP4 function","pmids":["18714012"],"is_preprint":false},{"year":2004,"finding":"PMP24 (PXMP4) expression is silenced by hypermethylation of its 5' CpG island in prostate cancer cells; reactivation by 5-aza-2'-deoxycytidine or transient transfection of PMP24 into silenced cells reduces cell growth and soft-agar colony formation, indicating a functional role in suppressing cancer cell proliferation.","method":"Bisulfite genomic sequencing, semiquantitative RT-PCR, 5-aza-dC treatment, transient transfection with growth/colony assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — methylation-reactivation and loss-of-function/gain-of-function with defined proliferation phenotype","pmids":["14712230"],"is_preprint":false},{"year":2010,"finding":"A single intronic CpG dinucleotide (first CpG in intron 1) is a critical methylation-sensitive regulatory element of PMP24 (PXMP4); methylation at this site disrupts DNA-protein interactions and suppresses gene expression, as demonstrated by limited demethylation, gel shift assays, and transfection of a methylated oligonucleotide.","method":"Limited demethylation with 5-aza-dC, gel shift (EMSA) assays, methylated oligonucleotide transfection, bisulfite sequencing of microdissected specimens, in situ hybridization","journal":"The Prostate","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro EMSA plus functional methylation rescue experiments with multiple orthogonal methods","pmids":["20054818"],"is_preprint":false},{"year":2024,"finding":"Knockdown or overexpression of PXMP4 in gastric cancer cells modulates proliferation, invasion, and migration, and influences EMT through activation or suppression of the PI3K/AKT signaling pathway; PI3K inhibitor LY294002 blocks PI3K/AKT-related proteins without affecting PXMP4, placing PXMP4 upstream of PI3K/AKT in this pathway.","method":"siRNA knockdown, overexpression, cell proliferation/invasion/migration assays, Western blot for EMT markers and PI3K/AKT pathway proteins, PI3K inhibitor (LY294002) treatment","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 — single lab, indirect pathway placement by inhibitor experiment without direct binding evidence","pmids":["38401002"],"is_preprint":false},{"year":2016,"finding":"Pmp24 (PXMP4) is identified as a Tim17 protein family member based on sequence analysis, placing it in the same structural superfamily as mitochondrial inner membrane translocases (Tim17, Tim22, Tim23), suggesting it may function as a membrane channel/transporter in the peroxisomal membrane.","method":"Comprehensive sequence analysis of 5631 proteomes, phylogenetic analysis","journal":"Biology direct","confidence":"Low","confidence_rationale":"Tier 4 — computational/sequence analysis only, no direct functional validation of PXMP4 channel activity","pmids":["27760563"],"is_preprint":false}],"current_model":"PXMP4 is a peroxisomal membrane protein whose best-characterized molecular role is as a substrate for MARCHF7-mediated ubiquitination at K20 (driven by TBK1 activation via ROS) that recruits NBR1 to flag damaged peroxisomes for pexophagy; additionally, PXMP4 interacts with the peroxisomal biogenesis chaperone PEX19, its expression is epigenetically regulated by CpG methylation, and its loss in mice impairs ether lipid metabolism and mildly reduces peroxisomal α-oxidation capacity."},"narrative":{"teleology":[{"year":2004,"claim":"The discovery that PXMP4 is epigenetically silenced in prostate cancer by CpG island hypermethylation, and that its re-expression suppresses proliferation, established it as a functionally relevant peroxisomal membrane protein with growth-regulatory consequences — moving it from a poorly characterized peroxisomal protein to one with a defined cellular phenotype upon loss.","evidence":"Bisulfite sequencing, 5-aza-dC demethylation reactivation, and transient transfection with colony formation assays in prostate cancer cell lines","pmids":["14712230"],"confidence":"Medium","gaps":["Mechanism by which PXMP4 suppresses proliferation was not identified","Whether PXMP4 silencing is a driver or passenger event in prostate tumorigenesis was not resolved","No direct link to a specific peroxisomal metabolic pathway was established"]},{"year":2008,"claim":"Identification of PEX19 as a binding partner of PXMP4 placed PXMP4 within the peroxisomal membrane protein import pathway, providing the first molecular interaction context for its biogenesis.","evidence":"Congenic mouse strain analysis with candidate gene binding partner identification","pmids":["18714012"],"confidence":"Low","gaps":["PEX19 interaction was referenced from prior data without independent validation in this study","No direct functional test of PXMP4 in NKT cell biology was performed","The mechanism by which PEX19 chaperones PXMP4 to the peroxisomal membrane was not characterized"]},{"year":2010,"claim":"Fine-mapping of PXMP4 epigenetic regulation to a single intronic CpG dinucleotide that controls DNA-protein binding revealed the precise mechanism of its transcriptional silencing, explaining how methylation at one site can shut down expression.","evidence":"Limited 5-aza-dC demethylation, EMSA gel shift assays, methylated oligonucleotide transfection, bisulfite sequencing of microdissected specimens","pmids":["20054818"],"confidence":"Medium","gaps":["The transcription factor binding at the critical intronic CpG was not identified","Whether this epigenetic mechanism operates in tissues beyond prostate was not tested"]},{"year":2016,"claim":"Computational classification of PXMP4 as a Tim17 protein family member suggested it may function as a channel or transporter in the peroxisomal membrane, providing a structural hypothesis for its molecular activity.","evidence":"Phylogenetic and sequence analysis across 5631 proteomes","pmids":["27760563"],"confidence":"Low","gaps":["No experimental validation of channel or transporter activity was performed","No substrate or solute specificity was tested","Structural prediction has not been confirmed by biochemical reconstitution or structural biology"]},{"year":2022,"claim":"Generation of PXMP4 knockout mice resolved the longstanding question of whether the protein is essential for peroxisome biogenesis (it is not) and instead revealed a specific metabolic role in ether lipid synthesis and α-oxidation capacity.","evidence":"CRISPR/Cas9 knockout mouse model with lipidomic analysis, plasma metabolite profiling, and dietary challenge studies","pmids":["35169201"],"confidence":"High","gaps":["The direct molecular mechanism by which PXMP4 supports ether lipid metabolism is unknown","Whether PXMP4 functions as a metabolite transporter in the peroxisomal membrane was not tested","Tissue-specific contributions beyond liver were not deeply characterized"]},{"year":2024,"claim":"Demonstration that influenza A virus M2 protein disrupts PEX19–PXMP4 binding provided independent confirmation of the PEX19 interaction and showed it is biologically targetable by pathogens to impair peroxisome biogenesis.","evidence":"Co-immunoprecipitation, PEX19 knockdown, viral growth assays, peroxisome quantification in IAV-infected cells","pmids":["39205283"],"confidence":"Medium","gaps":["The stoichiometry and affinity of the PEX19–PXMP4 interaction were not measured","Whether PXMP4 loss specifically mediates the antiviral signaling defect was not isolated from other PEX19 clients"]},{"year":2025,"claim":"The discovery that MARCHF7 ubiquitinates PXMP4 at K20 downstream of TBK1-ROS signaling to recruit NBR1 for pexophagy established the first complete signaling pathway for selective peroxisome turnover through PXMP4, defining its primary molecular function as a pexophagy signal.","evidence":"Functional screening, siRNA knockdown, K20R mutant reconstitution, co-immunoprecipitation, pexophagic flux assays, and TBK1 phosphorylation assays in PEX1-deficient cells","pmids":["41267209"],"confidence":"High","gaps":["Whether PXMP4-dependent pexophagy operates in physiological contexts beyond PEX1 deficiency is not established","Whether other peroxisomal membrane proteins serve redundant pexophagy signals is unknown","The structural basis for MARCHF7 recognition of PXMP4 K20 has not been determined"]},{"year":null,"claim":"It remains unknown whether PXMP4 functions as a membrane channel or transporter as predicted by its Tim17 family membership, and whether its metabolic role in ether lipid synthesis is mechanistically linked to or independent of its pexophagy signaling function.","evidence":"","pmids":[],"confidence":"Low","gaps":["No reconstituted transport or channel activity has been demonstrated","The relationship between PXMP4's metabolic and pexophagy functions has not been dissected","No structural data for PXMP4 exists"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005777","term_label":"peroxisome","supporting_discovery_ids":[0,1,2]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1]}],"complexes":[],"partners":["MARCHF7","NBR1","TBK1","PEX19"],"other_free_text":[]},"mechanistic_narrative":"PXMP4 (PMP24) is a peroxisomal integral membrane protein that functions as a key signal for selective autophagy of damaged peroxisomes (pexophagy) and contributes to peroxisomal metabolic homeostasis. Upon peroxisomal damage, TBK1 is activated by ROS accumulation and phosphorylates the E3 ubiquitin ligase MARCHF7, which ubiquitinates PXMP4 at lysine 20 on the peroxisomal membrane; this ubiquitin tag recruits the autophagy receptor NBR1 to initiate pexophagy, and a K20R ubiquitination-defective mutant impairs pexophagic flux [PMID:41267209]. PXMP4 knockout mice are viable but exhibit mildly elevated phytanic/pristanic acid levels and reduced hepatic ether lipids enriched in polyunsaturated fatty acids, establishing a role in peroxisomal α-oxidation and ether lipid metabolism [PMID:35169201]. PXMP4 interacts with the peroxisomal biogenesis chaperone PEX19, and its expression is regulated by CpG methylation at a critical intronic site whose hypermethylation silences the gene in prostate cancer cells, where re-expression suppresses proliferation [PMID:39205283, PMID:14712230, PMID:20054818]."},"prefetch_data":{"uniprot":{"accession":"Q9Y6I8","full_name":"Peroxisomal membrane protein 4","aliases":["24 kDa peroxisomal intrinsic membrane protein"],"length_aa":212,"mass_kda":24.3,"function":"","subcellular_location":"Peroxisome membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y6I8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PXMP4","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PXMP4","total_profiled":1310},"omim":[{"mim_id":"616397","title":"PEROXISOMAL MEMBRANE PROTEIN 4; PXMP4","url":"https://www.omim.org/entry/616397"},{"mim_id":"602750","title":"D-DOPACHROME TAUTOMERASE; DDT","url":"https://www.omim.org/entry/602750"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Peroxisomes","reliability":"Approved"},{"location":"Nucleoli fibrillar center","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PXMP4"},"hgnc":{"alias_symbol":["PMP24"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y6I8","domains":[{"cath_id":"-","chopping":"18-117","consensus_level":"medium","plddt":94.1928,"start":18,"end":117},{"cath_id":"-","chopping":"153-206","consensus_level":"medium","plddt":91.7693,"start":153,"end":206},{"cath_id":"1.20.5","chopping":"118-150","consensus_level":"medium","plddt":94.1788,"start":118,"end":150}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6I8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6I8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6I8-F1-predicted_aligned_error_v6.png","plddt_mean":91.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PXMP4","jax_strain_url":"https://www.jax.org/strain/search?query=PXMP4"},"sequence":{"accession":"Q9Y6I8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y6I8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y6I8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6I8"}},"corpus_meta":[{"pmid":"19710929","id":"PMC_19710929","title":"Comparative analysis of gene regulation by the transcription factor PPARalpha between mouse and human.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19710929","citation_count":259,"is_preprint":false},{"pmid":"7721939","id":"PMC_7721939","title":"Pmp27 promotes peroxisomal proliferation.","date":"1995","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/7721939","citation_count":178,"is_preprint":false},{"pmid":"27760563","id":"PMC_27760563","title":"Evolution of the Tim17 protein family.","date":"2016","source":"Biology direct","url":"https://pubmed.ncbi.nlm.nih.gov/27760563","citation_count":56,"is_preprint":false},{"pmid":"20054818","id":"PMC_20054818","title":"Methylation of a single intronic CpG mediates expression silencing of the PMP24 gene in prostate cancer.","date":"2010","source":"The Prostate","url":"https://pubmed.ncbi.nlm.nih.gov/20054818","citation_count":53,"is_preprint":false},{"pmid":"24358884","id":"PMC_24358884","title":"Proteins and lipids of glycosomal membranes from Leishmania tarentolae and Trypanosoma brucei.","date":"2013","source":"F1000Research","url":"https://pubmed.ncbi.nlm.nih.gov/24358884","citation_count":36,"is_preprint":false},{"pmid":"17041235","id":"PMC_17041235","title":"MMASS: an optimized array-based method for assessing CpG island methylation.","date":"2006","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/17041235","citation_count":34,"is_preprint":false},{"pmid":"14712230","id":"PMC_14712230","title":"PMP24, a gene identified by MSRF, undergoes DNA hypermethylation-associated gene silencing during cancer progression in an LNCaP model.","date":"2004","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/14712230","citation_count":29,"is_preprint":false},{"pmid":"18714012","id":"PMC_18714012","title":"Congenic analysis of the NKT cell control gene Nkt2 implicates the peroxisomal protein Pxmp4.","date":"2008","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/18714012","citation_count":27,"is_preprint":false},{"pmid":"25271210","id":"PMC_25271210","title":"Identification of genes whose expression is altered by obesity throughout the arterial tree.","date":"2014","source":"Physiological genomics","url":"https://pubmed.ncbi.nlm.nih.gov/25271210","citation_count":23,"is_preprint":false},{"pmid":"32265992","id":"PMC_32265992","title":"HSD17B4, ACAA1, and PXMP4 in Peroxisome Pathway Are Down-Regulated and Have Clinical Significance in Non-small Cell Lung Cancer.","date":"2020","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32265992","citation_count":19,"is_preprint":false},{"pmid":"33387576","id":"PMC_33387576","title":"Identification of four methylation-driven genes as candidate biomarkers for monitoring single-walled carbon nanotube-induced malignant transformation of the lung.","date":"2020","source":"Toxicology and applied pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/33387576","citation_count":14,"is_preprint":false},{"pmid":"35169201","id":"PMC_35169201","title":"Mice with a deficiency in Peroxisomal Membrane Protein 4 (PXMP4) display mild changes in hepatic lipid metabolism.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/35169201","citation_count":13,"is_preprint":false},{"pmid":"33791307","id":"PMC_33791307","title":"Study on the Reparative Effect of PEGylated Growth Hormone on Ovarian Parameters and Mitochondrial Function of Oocytes From Rats With Premature Ovarian Insufficiency.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/33791307","citation_count":12,"is_preprint":false},{"pmid":"34867906","id":"PMC_34867906","title":"Copper Tolerance Mechanism of the Novel Marine Multi-Stress Tolerant Yeast Meyerozyma guilliermondii GXDK6 as Revealed by Integrated Omics Analysis.","date":"2021","source":"Frontiers in microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/34867906","citation_count":11,"is_preprint":false},{"pmid":"39205283","id":"PMC_39205283","title":"The M2 Protein of the Influenza A Virus Interacts with PEX19 to Facilitate Virus Replication by Disrupting the Function of Peroxisome.","date":"2024","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/39205283","citation_count":3,"is_preprint":false},{"pmid":"41267209","id":"PMC_41267209","title":"Regulation of pexophagy by a novel TBK1-MARCHF7-PXMP4-NBR1 axis in PEX1-depleted HeLa cells.","date":"2025","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/41267209","citation_count":2,"is_preprint":false},{"pmid":"35694189","id":"PMC_35694189","title":"Characterizing the KRAS G12C mutation in metastatic colorectal cancer: a population-based cohort and assessment of expression differences in The Cancer Genome Atlas.","date":"2022","source":"Therapeutic advances in medical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35694189","citation_count":2,"is_preprint":false},{"pmid":"35464075","id":"PMC_35464075","title":"Alteration of Ileal lncRNAs After Duodenal-Jejunal Bypass Is Associated With Regulation of Lipid and Amino Acid Metabolism.","date":"2022","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/35464075","citation_count":2,"is_preprint":false},{"pmid":"38401002","id":"PMC_38401002","title":"PXMP4 promotes gastric cancer cell epithelial-mesenchymal transition via the PI3K/AKT signaling pathway.","date":"2024","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/38401002","citation_count":1,"is_preprint":false},{"pmid":"37560637","id":"PMC_37560637","title":"Lnc-PXMP4-2-4 alleviates myocardial cell damage by activating the JAK2/STAT3 signaling pathway.","date":"2023","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/37560637","citation_count":1,"is_preprint":false},{"pmid":"38415547","id":"PMC_38415547","title":"High Expression of PXMP4 in Hepatocellular Carcinoma Tissues.","date":"2024","source":"Asian Pacific journal of cancer prevention : APJCP","url":"https://pubmed.ncbi.nlm.nih.gov/38415547","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12640,"output_tokens":2103,"usd":0.034732},"stage2":{"model":"claude-opus-4-6","input_tokens":5391,"output_tokens":2248,"usd":0.124732},"total_usd":0.159464,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2025,\n      \"finding\": \"PXMP4 is ubiquitinated at lysine 20 by the E3 ligase MARCHF7 on peroxisomal membranes in PEX1-deficient cells, and this ubiquitination serves as a recognition signal recruiting the autophagy receptor NBR1 to peroxisomes to drive pexophagy. TBK1, activated by ROS accumulation downstream of PEX1 depletion, phosphorylates MARCHF7 to promote this ubiquitination. Depletion of PXMP4 or expression of a K20R ubiquitination-defective mutant impairs pexophagic flux.\",\n      \"method\": \"Functional screening, siRNA knockdown, reconstitution with ubiquitination-defective mutant (K20R), co-immunoprecipitation, pexophagic flux assays, TBK1 phosphorylation assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including KO/KD, mutagenesis rescue, epistasis, and defined cellular phenotype in a single study\",\n      \"pmids\": [\"41267209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PXMP4 knockout mice generated by CRISPR/Cas9 are viable and fertile with no gross peroxisome morphology changes, but show mildly elevated phytanic/pristanic acid levels suggesting impaired peroxisomal α-oxidation capacity, and reduced hepatic alkyldiacylglycerol ether lipids (particularly those containing polyunsaturated fatty acids), indicating a role for PXMP4 in ether lipid metabolism.\",\n      \"method\": \"CRISPR/Cas9 knockout mouse model, lipidomic analysis, plasma metabolite profiling (VLCFAs, bile acids, phytanic/pristanic acid), PPARα ligand and phytol-enriched diet challenges\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined metabolic phenotype and multiple pathway readouts\",\n      \"pmids\": [\"35169201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IAV M2 protein interacts with PEX19 via its cytoplasmic tail, and this interaction disrupts PEX19 binding to peroxisomal membrane proteins including PMP24 (PXMP4), thereby impairing peroxisome biogenesis and antiviral signaling.\",\n      \"method\": \"Co-immunoprecipitation, PEX19 knockdown, viral growth assays, peroxisome pool quantification\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP showing disrupted PEX19-PMP24 interaction, indirect mechanistic implication for PXMP4\",\n      \"pmids\": [\"39205283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Pxmp4 was identified as a candidate gene within the Nkt2 congenic region controlling NKT cell numbers; its only known binding partner is Pex19 (an intracellular chaperone and component of the peroxisomal membrane insertion machinery), implicating peroxisomal function in glycolipid availability for CD1d-mediated NKT cell activation.\",\n      \"method\": \"Congenic mouse strain analysis, microarray expression profiling, candidate gene identification by binding partner analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single pulldown/binding partner reference, no direct mechanistic experiment on PXMP4 function\",\n      \"pmids\": [\"18714012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PMP24 (PXMP4) expression is silenced by hypermethylation of its 5' CpG island in prostate cancer cells; reactivation by 5-aza-2'-deoxycytidine or transient transfection of PMP24 into silenced cells reduces cell growth and soft-agar colony formation, indicating a functional role in suppressing cancer cell proliferation.\",\n      \"method\": \"Bisulfite genomic sequencing, semiquantitative RT-PCR, 5-aza-dC treatment, transient transfection with growth/colony assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — methylation-reactivation and loss-of-function/gain-of-function with defined proliferation phenotype\",\n      \"pmids\": [\"14712230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A single intronic CpG dinucleotide (first CpG in intron 1) is a critical methylation-sensitive regulatory element of PMP24 (PXMP4); methylation at this site disrupts DNA-protein interactions and suppresses gene expression, as demonstrated by limited demethylation, gel shift assays, and transfection of a methylated oligonucleotide.\",\n      \"method\": \"Limited demethylation with 5-aza-dC, gel shift (EMSA) assays, methylated oligonucleotide transfection, bisulfite sequencing of microdissected specimens, in situ hybridization\",\n      \"journal\": \"The Prostate\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro EMSA plus functional methylation rescue experiments with multiple orthogonal methods\",\n      \"pmids\": [\"20054818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Knockdown or overexpression of PXMP4 in gastric cancer cells modulates proliferation, invasion, and migration, and influences EMT through activation or suppression of the PI3K/AKT signaling pathway; PI3K inhibitor LY294002 blocks PI3K/AKT-related proteins without affecting PXMP4, placing PXMP4 upstream of PI3K/AKT in this pathway.\",\n      \"method\": \"siRNA knockdown, overexpression, cell proliferation/invasion/migration assays, Western blot for EMT markers and PI3K/AKT pathway proteins, PI3K inhibitor (LY294002) treatment\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, indirect pathway placement by inhibitor experiment without direct binding evidence\",\n      \"pmids\": [\"38401002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Pmp24 (PXMP4) is identified as a Tim17 protein family member based on sequence analysis, placing it in the same structural superfamily as mitochondrial inner membrane translocases (Tim17, Tim22, Tim23), suggesting it may function as a membrane channel/transporter in the peroxisomal membrane.\",\n      \"method\": \"Comprehensive sequence analysis of 5631 proteomes, phylogenetic analysis\",\n      \"journal\": \"Biology direct\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational/sequence analysis only, no direct functional validation of PXMP4 channel activity\",\n      \"pmids\": [\"27760563\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PXMP4 is a peroxisomal membrane protein whose best-characterized molecular role is as a substrate for MARCHF7-mediated ubiquitination at K20 (driven by TBK1 activation via ROS) that recruits NBR1 to flag damaged peroxisomes for pexophagy; additionally, PXMP4 interacts with the peroxisomal biogenesis chaperone PEX19, its expression is epigenetically regulated by CpG methylation, and its loss in mice impairs ether lipid metabolism and mildly reduces peroxisomal α-oxidation capacity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PXMP4 (PMP24) is a peroxisomal integral membrane protein that functions as a key signal for selective autophagy of damaged peroxisomes (pexophagy) and contributes to peroxisomal metabolic homeostasis. Upon peroxisomal damage, TBK1 is activated by ROS accumulation and phosphorylates the E3 ubiquitin ligase MARCHF7, which ubiquitinates PXMP4 at lysine 20 on the peroxisomal membrane; this ubiquitin tag recruits the autophagy receptor NBR1 to initiate pexophagy, and a K20R ubiquitination-defective mutant impairs pexophagic flux [PMID:41267209]. PXMP4 knockout mice are viable but exhibit mildly elevated phytanic/pristanic acid levels and reduced hepatic ether lipids enriched in polyunsaturated fatty acids, establishing a role in peroxisomal α-oxidation and ether lipid metabolism [PMID:35169201]. PXMP4 interacts with the peroxisomal biogenesis chaperone PEX19, and its expression is regulated by CpG methylation at a critical intronic site whose hypermethylation silences the gene in prostate cancer cells, where re-expression suppresses proliferation [PMID:39205283, PMID:14712230, PMID:20054818].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"The discovery that PXMP4 is epigenetically silenced in prostate cancer by CpG island hypermethylation, and that its re-expression suppresses proliferation, established it as a functionally relevant peroxisomal membrane protein with growth-regulatory consequences — moving it from a poorly characterized peroxisomal protein to one with a defined cellular phenotype upon loss.\",\n      \"evidence\": \"Bisulfite sequencing, 5-aza-dC demethylation reactivation, and transient transfection with colony formation assays in prostate cancer cell lines\",\n      \"pmids\": [\"14712230\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which PXMP4 suppresses proliferation was not identified\",\n        \"Whether PXMP4 silencing is a driver or passenger event in prostate tumorigenesis was not resolved\",\n        \"No direct link to a specific peroxisomal metabolic pathway was established\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of PEX19 as a binding partner of PXMP4 placed PXMP4 within the peroxisomal membrane protein import pathway, providing the first molecular interaction context for its biogenesis.\",\n      \"evidence\": \"Congenic mouse strain analysis with candidate gene binding partner identification\",\n      \"pmids\": [\"18714012\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"PEX19 interaction was referenced from prior data without independent validation in this study\",\n        \"No direct functional test of PXMP4 in NKT cell biology was performed\",\n        \"The mechanism by which PEX19 chaperones PXMP4 to the peroxisomal membrane was not characterized\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Fine-mapping of PXMP4 epigenetic regulation to a single intronic CpG dinucleotide that controls DNA-protein binding revealed the precise mechanism of its transcriptional silencing, explaining how methylation at one site can shut down expression.\",\n      \"evidence\": \"Limited 5-aza-dC demethylation, EMSA gel shift assays, methylated oligonucleotide transfection, bisulfite sequencing of microdissected specimens\",\n      \"pmids\": [\"20054818\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The transcription factor binding at the critical intronic CpG was not identified\",\n        \"Whether this epigenetic mechanism operates in tissues beyond prostate was not tested\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Computational classification of PXMP4 as a Tim17 protein family member suggested it may function as a channel or transporter in the peroxisomal membrane, providing a structural hypothesis for its molecular activity.\",\n      \"evidence\": \"Phylogenetic and sequence analysis across 5631 proteomes\",\n      \"pmids\": [\"27760563\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No experimental validation of channel or transporter activity was performed\",\n        \"No substrate or solute specificity was tested\",\n        \"Structural prediction has not been confirmed by biochemical reconstitution or structural biology\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Generation of PXMP4 knockout mice resolved the longstanding question of whether the protein is essential for peroxisome biogenesis (it is not) and instead revealed a specific metabolic role in ether lipid synthesis and α-oxidation capacity.\",\n      \"evidence\": \"CRISPR/Cas9 knockout mouse model with lipidomic analysis, plasma metabolite profiling, and dietary challenge studies\",\n      \"pmids\": [\"35169201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The direct molecular mechanism by which PXMP4 supports ether lipid metabolism is unknown\",\n        \"Whether PXMP4 functions as a metabolite transporter in the peroxisomal membrane was not tested\",\n        \"Tissue-specific contributions beyond liver were not deeply characterized\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstration that influenza A virus M2 protein disrupts PEX19–PXMP4 binding provided independent confirmation of the PEX19 interaction and showed it is biologically targetable by pathogens to impair peroxisome biogenesis.\",\n      \"evidence\": \"Co-immunoprecipitation, PEX19 knockdown, viral growth assays, peroxisome quantification in IAV-infected cells\",\n      \"pmids\": [\"39205283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The stoichiometry and affinity of the PEX19–PXMP4 interaction were not measured\",\n        \"Whether PXMP4 loss specifically mediates the antiviral signaling defect was not isolated from other PEX19 clients\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The discovery that MARCHF7 ubiquitinates PXMP4 at K20 downstream of TBK1-ROS signaling to recruit NBR1 for pexophagy established the first complete signaling pathway for selective peroxisome turnover through PXMP4, defining its primary molecular function as a pexophagy signal.\",\n      \"evidence\": \"Functional screening, siRNA knockdown, K20R mutant reconstitution, co-immunoprecipitation, pexophagic flux assays, and TBK1 phosphorylation assays in PEX1-deficient cells\",\n      \"pmids\": [\"41267209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether PXMP4-dependent pexophagy operates in physiological contexts beyond PEX1 deficiency is not established\",\n        \"Whether other peroxisomal membrane proteins serve redundant pexophagy signals is unknown\",\n        \"The structural basis for MARCHF7 recognition of PXMP4 K20 has not been determined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown whether PXMP4 functions as a membrane channel or transporter as predicted by its Tim17 family membership, and whether its metabolic role in ether lipid synthesis is mechanistically linked to or independent of its pexophagy signaling function.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No reconstituted transport or channel activity has been demonstrated\",\n        \"The relationship between PXMP4's metabolic and pexophagy functions has not been dissected\",\n        \"No structural data for PXMP4 exists\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005777\",\n        \"supporting_discovery_ids\": [0, 1, 2]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-9612973\",\n        \"supporting_discovery_ids\": [0]\n      },\n      {\n        \"term_id\": \"R-HSA-1430728\",\n        \"supporting_discovery_ids\": [1]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"MARCHF7\",\n      \"NBR1\",\n      \"TBK1\",\n      \"PEX19\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}