{"gene":"HSD17B4","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1999,"finding":"HSD17B4 encodes a multifunctional 80 kDa peroxisomal enzyme with three distinct functional domains: (1) N-terminal domain (amino acids 1-323) with 3-hydroxyacyl-CoA dehydrogenase and 17β-hydroxysteroid dehydrogenase activity (oxidizing D- but not L-stereoisomers), (2) central domain (amino acids 324-596) with 2-enoyl-acyl-CoA hydratase activity, and (3) C-terminal domain (amino acids 597-737) with sterol carrier protein activity facilitating lipid transfer between membranes in vitro. The 80 kDa protein is N-terminally cleaved to a 32 kDa enzymatically active fragment.","method":"In vitro enzymatic assays with truncated recombinant protein domains, membrane lipid transfer assays","journal":"Journal of molecular endocrinology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple distinct in vitro enzymatic assays with defined domain constructs, replicated across two papers (PMID:10343282 and PMID:10419023)","pmids":["10343282"],"is_preprint":false},{"year":1999,"finding":"The G16S mutation in HSD17B4 inactivates the enzyme by abolishing interaction with NAD+, establishing that the dehydrogenase active site requires Gly16 for cofactor binding.","method":"Mutation analysis with functional enzymatic assay","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro mutagenesis with enzymatic readout, single lab, single paper","pmids":["10419023"],"is_preprint":false},{"year":2002,"finding":"Molecular dynamics simulations of the SCP-2L domain of HSD17B4 revealed that upon ligand removal, the binding pocket closes (occupied by Phe93 making hydrophobic contact with Trp36) and the C-terminal peroxisomal targeting signal (PTS1) becomes buried. An anti-correlation exists between burial of PTS1 and binding pocket size, supporting a ligand-assisted peroxisomal targeting mechanism.","method":"Molecular dynamics simulation of crystal structure of SCP-2L domain","journal":"Journal of molecular biology","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational simulation only, no experimental validation of the proposed mechanism","pmids":["12368102"],"is_preprint":false},{"year":2010,"finding":"Compound heterozygous mutations in HSD17B4 (p.Y217C in the dehydrogenase domain and p.Y568X nonsense mutation) cause severely reduced HSD17B4 protein expression, establishing that loss of HSD17B4 function underlies Perrault syndrome. Structural analysis predicted that the Y217C missense mutation destabilizes the dehydrogenase domain.","method":"Whole-exome sequencing, Sanger confirmation, Western blot of patient-derived cells","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient genetics combined with protein expression measurement by Western blot and structural prediction, single lab","pmids":["20673864"],"is_preprint":false},{"year":2013,"finding":"Small-angle X-ray scattering (SAXS) of human MFE-2 (HSD17B4) in solution determined that the SCP-2L domain is positioned as part of the full-length protein quaternary structure, providing direct structural support for the biological role of the SCP-2L domain in the holoenzyme.","method":"Synchrotron SAXS with ab initio and rigid body modeling","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — structural method applied to full-length protein in solution, single lab, single paper","pmids":["23313254"],"is_preprint":false},{"year":2017,"finding":"Estrone (E1) upregulates HSD17B4 acetylation at lysine 669 (K669), promoting its degradation via chaperone-mediated autophagy (CMA). CREBBP acts as the acetyltransferase (writer) and SIRT3 as the deacetylase (eraser) dynamically controlling K669 acetylation. A K669 mutation that prevents acetylation stabilizes HSD17B4 and confers migratory/invasive properties to MCF7 cells upon E1 treatment.","method":"Site-directed mutagenesis, co-immunoprecipitation, acetylation assays, CMA degradation assays, cell migration/invasion assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP identifying writer/eraser, mutagenesis of modification site with functional phenotypic readout, independently supported by PMID:32678070","pmids":["28296597"],"is_preprint":false},{"year":2017,"finding":"Cytisine-linked isoflavonoids (CLIFs) specifically bind the C-terminus (SCP-2L domain) of HSD17B4, identified by pull-down assay with biotin-modified CLIF. CLIFs selectively inhibit the enoyl-CoA hydratase activity of HSD17B4 but not the D-3-hydroxyacyl-CoA dehydrogenase activity, establishing domain-specific inhibition.","method":"Biotin-affinity pull-down assay, truncated domain constructs, enzymatic activity assays","journal":"Organic & biomolecular chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — affinity pull-down with biotin-modified ligand plus domain mapping and selective enzymatic inhibition, single lab","pmids":["28868548"],"is_preprint":false},{"year":2018,"finding":"Using CRISPR knockout cell lines and pharmacological inhibition, HSD17B4 was established as essential for peroxisomal oxidation of medium- and long-chain fatty acids (lauric and palmitic acid) when mitochondrial fatty acid oxidation is impaired. HSD17B4 KO mice showed altered plasma acylcarnitine profiles after acute CPT2 inhibition, confirming in vivo relevance. Peroxisomes can oxidize both acyl-CoAs and acylcarnitines via this pathway.","method":"CRISPR-Cas9 knockout cell lines, pharmacological inhibition, isotope tracing, Hsd17b4 KO mouse model, plasma acylcarnitine profiling","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple CRISPR KO lines with biochemical flux measurements, validated in vivo with mouse KO model","pmids":["30540494"],"is_preprint":false},{"year":2018,"finding":"Of five alternative splice forms of HSD17B4, only isoform 2 encodes an enzyme capable of inactivating testosterone and dihydrotestosterone (converting them to their respective 17-keto steroids). Functional expression of isoform 2 is specifically suppressed in castration-resistant prostate cancer. Genetic silencing of isoform 2 shifts metabolic balance toward active 17β-OH androgens, stimulating androgen receptor signaling and CRPC development.","method":"Splice isoform expression analysis in patient samples, isoform-specific enzymatic assays, genetic silencing with androgen measurement and androgen receptor signaling readouts","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific enzymatic activity established in vitro combined with genetic loss-of-function in cells and patient tissue validation","pmids":["29346776"],"is_preprint":false},{"year":2019,"finding":"Ceramide interacts with HSD17B4 via its sterol carrier protein 2-like (SCP-2L) domain, adjacent to the C-terminal peroxisomal targeting signal PTS1. Ceramide binding prevents interaction of HSD17B4 with the peroxin Pex5 (the import receptor) and retains HSD17B4 at ceramide-enriched mitochondria-associated membranes (CEMAMs). Inhibition of ceramide biosynthesis induces HSD17B4 translocation to peroxisomes, its interaction with Pex5, and upregulation of DHA production, establishing ceramide as a molecular switch for HSD17B4 peroxisomal import.","method":"Affinity chromatography, co-immunoprecipitation, proximity ligation assay, immunocytochemistry, molecular docking, in vitro mutagenesis","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (affinity chromatography, Co-IP, proximity ligation, mutagenesis) in a single study establishing mechanism of subcellular targeting regulation","pmids":["31176039"],"is_preprint":false},{"year":2020,"finding":"HSD17B4 protein stability is regulated by K669 acetylation in prostate cancer cells: SIRT3 directly interacts with HSD17B4 to inhibit acetylation (enhancing stability), while CREBBP promotes K669 acetylation leading to CMA-mediated degradation. Dihydrotestosterone (DHT) increases HSD17B4 acetylation and promotes its degradation. HSD17B4 knockdown suppresses PCa cell proliferation, migration, and invasion.","method":"Co-immunoprecipitation, acetylation assays, CMA degradation assays, siRNA knockdown, cell proliferation/migration/invasion assays","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional knockdown, corroborates PMID:28296597 with additional androgen-related stimulus, single lab","pmids":["32678070"],"is_preprint":false},{"year":2020,"finding":"HSD17B4 deficiency in fibroblasts reduces dimerization of DBP protein. Protein levels of HSD17B4 mutants (p.Ala175Thr) are diminished by Western blot without change in mRNA levels, indicating a post-translational stability effect of this mutation. Residual functional DBP correlates with milder clinical phenotype.","method":"Immunoblot for protein levels and dimerization, quantitative RT-PCR for mRNA","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct protein analysis (Western blot) in patient fibroblasts showing dimerization dependence, single lab","pmids":["32042923"],"is_preprint":false},{"year":2021,"finding":"Phosphatidylserine (PS) interacts with HSD17B4 via its SCP-2L domain. PS association was specific (not phosphatidylcholine or sphingomyelin), disrupted by PS in liposomes but not free PS. Translocation of PS to the outer leaflet of the plasma membrane enriched HSD17B4 in peroxisomes, establishing PS as a regulator of HSD17B4 subcellular localization.","method":"Pulldown assay with biotin-PS-coated magnetic beads, domain-mapping with truncation constructs, immunofluorescence localization assay upon PS translocation","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — affinity pulldown with domain mapping plus functional localization assay, single lab, two orthogonal methods","pmids":["33935042"],"is_preprint":false},{"year":2025,"finding":"DTX2 (an E3 ubiquitin ligase) ubiquitinates HSD17B4 at lysine K645 via its RING domain targeting the SCP structural domain of HSD17B4, leading to K48-linked ubiquitination-mediated proteasomal degradation of HSD17B4. This reduces HSD17B4-dependent peroxisomal β-oxidation, lowers DHA-phospholipid levels, and suppresses ferroptosis in hepatocellular carcinoma cells. STAT3 activation drives DTX2 transcription upstream of this pathway.","method":"CRISPR screening, Co-IP, ubiquitination assays, site-specific mutagenesis (K645), lipidomics, in vivo xenograft models, DHA supplementation rescue experiments","journal":"Drug resistance updates","confidence":"High","confidence_rationale":"Tier 2 / Strong — identified specific ubiquitination site (K645) by mutagenesis with Co-IP and functional rescue, in vivo validation, multiple orthogonal methods","pmids":["40058099"],"is_preprint":false},{"year":2025,"finding":"HSD17B4 deficiency impairs primary ciliogenesis and alters cilia-mediated signaling. HSD17B4 is required for peroxisomal β-oxidation and acetyl-CoA synthesis; its loss reduces acetyl-CoA levels. Elevation of acetyl-CoA (via acetate administration) rescues ciliary defects through HDAC6-mediated ciliogenesis in HSD17B4-deficient cells, and restores motor function and Purkinje cell layer preservation in Hsd17b4-KO mice.","method":"HSD17B4-KO cell lines and mouse model, primary cilia imaging, acetate supplementation rescue, HDAC6 pathway analysis, metabolite measurement","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO cell lines and KO mouse model with mechanistic rescue via acetyl-CoA/HDAC6 axis, multiple orthogonal methods","pmids":["40102401"],"is_preprint":false},{"year":2025,"finding":"Loss of MFE-2 (HSD17B4) in microglia leads to lipid accumulation with excessive arachidonic acid, increased mitochondrial reactive oxygen species, and proinflammatory cytokine production. Microglia-specific ablation of MFE-2 drove neuroinflammation and Aβ deposition in Alzheimer's disease models. The compound CKBA binds to MFE-2 and restores its levels, ameliorating AD pathology.","method":"Microglia-specific conditional KO mouse model, lipidomics, ROS measurement, cytokine assays, CKBA binding assay, AD model behavioral and pathological readouts","journal":"Nature aging","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional cell-type-specific KO in vivo with mechanistic lipid metabolic readouts and pharmacological rescue with identified binding compound","pmids":["41162676"],"is_preprint":false},{"year":2023,"finding":"HSD17B4 knockout in BT-474 HER2-positive breast cancer cells caused accumulation of very long-chain fatty acids (VLCFA), decreased polyunsaturated fatty acids (DHA and arachidonic acid), increased Akt phosphorylation (attributed to decreased DHA), upregulation of oxidative phosphorylation and electron transport chain genes, increased mitochondrial ATP production, and enhanced glucose dependence, resulting in approximately tenfold increased sensitivity to the HER2/Akt inhibitor lapatinib.","method":"CRISPR KO cell lines, Seahorse metabolic flux analysis, lipidomics, Western blot for signaling pathway activation","journal":"Breast cancer research and treatment","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with metabolic flux and lipidomics measurements, single lab, multiple orthogonal methods","pmids":["37378696"],"is_preprint":false},{"year":2025,"finding":"Gamma-tocotrienol (γ-T3) directly interacts with HSD17B4 protein (identified by anti-FLAG immunoprecipitation with quantification of γ-T3 in precipitate), and inhibits HSD17B4 catalytic activity in converting estradiol (E2) to estrone, reducing cyclin D1 expression and suppressing ERK, MEK, AKT, and STAT3 signaling, inhibiting proliferation of HSD17B4-overexpressing HepG2 cells.","method":"Co-immunoprecipitation/pulldown with FLAG-tagged HSD17B4 and γ-T3 quantification, enzymatic activity assay, Western blot for signaling pathways, xenograft mouse model","journal":"Current cancer drug targets","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding assay plus enzymatic inhibition assay and in vivo validation, single lab","pmids":["38934283"],"is_preprint":false},{"year":2017,"finding":"A homozygous HSD17B4 missense variant (p.A100S) leads to markedly reduced HSD17B4 protein expression compared to wild-type when expressed in SH-SY5Y cells, establishing pathogenicity through protein instability.","method":"Transfection of wild-type vs. mutant HSD17B4 plasmids in SH-SY5Y cells with Western blot comparison","journal":"BMC medical genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Western blot experiment in transfected cells, single lab, single method","pmids":["28830375"],"is_preprint":false}],"current_model":"HSD17B4 encodes a multifunctional peroxisomal enzyme (D-bifunctional protein, DBP) with three catalytic domains: an N-terminal NAD+-dependent D-3-hydroxyacyl-CoA dehydrogenase/17β-hydroxysteroid dehydrogenase domain, a central 2-enoyl-acyl-CoA hydratase domain, and a C-terminal SCP-2L (sterol carrier protein 2-like) domain that facilitates lipid transfer and mediates peroxisomal targeting via PTS1; it is essential for peroxisomal β-oxidation of very long-chain, branched-chain, and medium-chain fatty acids (including acylcarnitines when mitochondrial FAO is impaired), generates acetyl-CoA and DHA, and its peroxisomal import is regulated by ceramide and phosphatidylserine binding to the SCP-2L domain modulating interaction with the import receptor Pex5; protein stability is controlled by CREBBP-mediated acetylation at K669 (promoting CMA degradation) opposed by SIRT3 deacetylation, and by DTX2-mediated K48-ubiquitination at K645 (promoting proteasomal degradation); loss of HSD17B4 impairs primary ciliogenesis via reduced acetyl-CoA/HDAC6 signaling, drives microglial lipid accumulation and neuroinflammation, and only isoform 2 retains androgen-inactivating enzymatic activity relevant to prostate cancer."},"narrative":{"mechanistic_narrative":"HSD17B4 encodes a multifunctional 80 kDa peroxisomal enzyme (D-bifunctional protein) organized into three catalytic/functional modules: an N-terminal D-specific 3-hydroxyacyl-CoA dehydrogenase/17β-hydroxysteroid dehydrogenase domain, a central 2-enoyl-acyl-CoA hydratase domain, and a C-terminal sterol carrier protein-2-like (SCP-2L) domain that mediates lipid transfer between membranes [PMID:10343282]. Through these activities it executes peroxisomal β-oxidation of medium- and long-chain fatty acids—and of acylcarnitines when mitochondrial fatty acid oxidation is impaired—generating acetyl-CoA and polyunsaturated fatty acids such as DHA [PMID:30540494, PMID:40102401]. The SCP-2L domain doubles as a regulated targeting module: it carries the C-terminal PTS1 import signal, and binding of lipids such as ceramide or phosphatidylserine to this domain controls the protein's interaction with the import receptor Pex5 and thereby partitions HSD17B4 between mitochondria-associated membranes and peroxisomes [PMID:31176039, PMID:33935042]. Enzyme abundance is further set post-translationally by competing modifications—CREBBP-mediated K669 acetylation drives chaperone-mediated autophagy and is opposed by SIRT3 deacetylation, while DTX2-mediated K48-linked ubiquitination at K645 targets the SCP domain for proteasomal degradation [PMID:28296597, PMID:32678070, PMID:40058099]. Downstream of its metabolic output, HSD17B4-derived acetyl-CoA supports HDAC6-dependent primary ciliogenesis, and loss of the enzyme produces lipid accumulation, oxidative stress, and neuroinflammation in microglia [PMID:40102401, PMID:41162676]. Compound heterozygous and homozygous loss-of-function mutations that destabilize the protein cause Perrault syndrome [PMID:20673864, PMID:32042923]. A splice isoform-specific androgen-inactivating activity (isoform 2) links HSD17B4 to castration-resistant prostate cancer [PMID:29346776].","teleology":[{"year":1999,"claim":"Established the fundamental architecture and chemistry of HSD17B4, defining it as a single polypeptide carrying three distinct activities relevant to both fatty acid and steroid metabolism.","evidence":"In vitro enzymatic assays on truncated recombinant domains plus membrane lipid transfer assays, with mutational mapping of the NAD+-binding dehydrogenase site","pmids":["10343282","10419023"],"confidence":"High","gaps":["Physiological substrate hierarchy not established in vitro","Did not address how the three domains coordinate flux in the holoenzyme"]},{"year":2002,"claim":"Proposed a ligand-assisted peroxisomal targeting mechanism in which SCP-2L ligand occupancy gates exposure of the C-terminal PTS1 signal.","evidence":"Molecular dynamics simulation of the SCP-2L crystal structure","pmids":["12368102"],"confidence":"Low","gaps":["Computational only with no experimental validation at the time","Identity of physiological gating ligand unknown"]},{"year":2010,"claim":"Connected HSD17B4 loss of function to human disease, showing that destabilizing mutations cause Perrault syndrome.","evidence":"Whole-exome sequencing with Sanger confirmation, Western blot of patient cells, structural prediction","pmids":["20673864"],"confidence":"Medium","gaps":["Tissue-specific basis of the ovarian and auditory phenotype not resolved","Single family / single lab"]},{"year":2013,"claim":"Confirmed that the SCP-2L domain is an integral structural element of the full-length holoenzyme rather than an isolated module, supporting its biological role in the intact protein.","evidence":"Synchrotron SAXS with ab initio and rigid-body modeling of human full-length protein in solution","pmids":["23313254"],"confidence":"Medium","gaps":["Low-resolution solution model only","Did not capture ligand-dependent conformational changes"]},{"year":2017,"claim":"Revealed that HSD17B4 abundance is dynamically controlled by reversible K669 acetylation coupling its degradation to estrogen signaling.","evidence":"Site-directed mutagenesis, reciprocal Co-IP identifying CREBBP/SIRT3, CMA degradation and migration/invasion assays in MCF7 cells","pmids":["28296597"],"confidence":"High","gaps":["How acetylation routes the protein specifically into CMA not detailed","Link between enzyme abundance and metastatic phenotype mechanistically indirect"]},{"year":2018,"claim":"Demonstrated that HSD17B4 is required for peroxisomal oxidation of medium- and long-chain fatty acids and acylcarnitines, a pathway that becomes important when mitochondrial FAO is blocked.","evidence":"CRISPR-Cas9 KO cell lines, isotope tracing, Hsd17b4 KO mice with plasma acylcarnitine profiling after CPT2 inhibition","pmids":["30540494"],"confidence":"High","gaps":["Quantitative contribution of peroxisomal FAO under normal physiology unclear","Mechanism of acylcarnitine entry into peroxisomes not defined"]},{"year":2018,"claim":"Identified an isoform-specific androgen-inactivating function, linking suppression of HSD17B4 isoform 2 to castration-resistant prostate cancer.","evidence":"Isoform-specific enzymatic assays, genetic silencing with androgen and AR signaling readouts, patient tissue expression analysis","pmids":["29346776"],"confidence":"High","gaps":["Mechanism suppressing isoform 2 expression in CRPC not defined","Subcellular site of androgen inactivation not localized"]},{"year":2019,"claim":"Established ceramide as a molecular switch for HSD17B4 peroxisomal import by binding SCP-2L and blocking Pex5 interaction, experimentally validating the ligand-assisted targeting concept.","evidence":"Affinity chromatography, Co-IP, proximity ligation, immunocytochemistry, docking and mutagenesis","pmids":["31176039"],"confidence":"High","gaps":["In vivo relevance of CEMAM retention not tested","How ceramide levels are sensed to time import not resolved"]},{"year":2020,"claim":"Extended the acetylation-controlled stability model to prostate cancer, showing androgen stimulus drives K669 acetylation and degradation with functional consequences for proliferation.","evidence":"Co-IP, acetylation and CMA degradation assays, siRNA knockdown with proliferation/migration/invasion readouts","pmids":["32678070"],"confidence":"Medium","gaps":["Single lab corroboration of the CREBBP/SIRT3 axis","Direct enzymatic-output basis of the proliferative phenotype not isolated"]},{"year":2020,"claim":"Showed that disease-associated mutations act by impairing protein dimerization and stability rather than by altering transcription.","evidence":"Immunoblot for protein level and dimerization, qRT-PCR for mRNA in patient fibroblasts","pmids":["32042923"],"confidence":"Medium","gaps":["Structural basis of dimerization defect not resolved","Genotype-phenotype correlation based on small patient set"]},{"year":2021,"claim":"Identified phosphatidylserine as a second SCP-2L-binding lipid that regulates HSD17B4 peroxisomal localization, broadening the lipid-sensing control of targeting.","evidence":"Biotin-PS bead pulldown with truncation mapping and immunofluorescence localization upon PS translocation","pmids":["33935042"],"confidence":"Medium","gaps":["Physiological trigger linking PS exposure to import not defined","Relationship to the ceramide switch not reconciled"]},{"year":2025,"claim":"Defined a second degradation route via DTX2-mediated K48 ubiquitination of the SCP domain at K645, linking HSD17B4 turnover to peroxisomal DHA output and ferroptosis suppression in hepatocellular carcinoma.","evidence":"CRISPR screen, Co-IP, ubiquitination assays, K645 mutagenesis, lipidomics, xenografts and DHA rescue","pmids":["40058099"],"confidence":"High","gaps":["Interplay between K645 ubiquitination and K669 acetylation not tested","Generality beyond STAT3-driven HCC unknown"]},{"year":2025,"claim":"Connected HSD17B4 metabolic output to organelle biogenesis, showing that acetyl-CoA generated by peroxisomal β-oxidation drives HDAC6-dependent primary ciliogenesis.","evidence":"KO cell lines and KO mice, primary cilia imaging, acetate supplementation rescue, HDAC6 pathway analysis, motor and Purkinje cell readouts","pmids":["40102401"],"confidence":"High","gaps":["Direct molecular link between acetyl-CoA pool and HDAC6 activity not fully traced","Neuronal cell-type specificity of the rescue not delineated"]},{"year":2025,"claim":"Demonstrated a cell-type-specific role in microglia where HSD17B4 loss causes lipid accumulation, ROS, and neuroinflammation driving Alzheimer's-like pathology.","evidence":"Microglia-specific conditional KO mice, lipidomics, ROS and cytokine assays, AD model readouts with CKBA pharmacological rescue","pmids":["41162676"],"confidence":"High","gaps":["Mechanism linking arachidonic acid accumulation to cytokine production not fully defined","Whether findings extend to human microglia untested"]},{"year":2023,"claim":"Showed that HSD17B4 loss rewires fatty acid pools toward VLCFA accumulation and DHA depletion, activating Akt and mitochondrial respiration and sensitizing HER2+ breast cancer to lapatinib.","evidence":"CRISPR KO cells, Seahorse metabolic flux, lipidomics, Western blot for signaling","pmids":["37378696"],"confidence":"Medium","gaps":["Causal chain from DHA loss to Akt activation only correlative","Single cell-line context"]},{"year":null,"claim":"How the lipid-sensing (ceramide/PS), acetylation (K669), and ubiquitination (K645) control layers are integrated to set HSD17B4 localization and abundance in a given tissue remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No study tests acetylation, ubiquitination, and lipid-gated import together","Tissue-specific dominance of each regulatory layer unknown","Structural model of the regulated SCP-2L/PTS1 switch in the holoenzyme not solved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,8,17]},{"term_id":"GO:0016829","term_label":"lyase activity","supporting_discovery_ids":[0,6]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,9,12]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005777","term_label":"peroxisome","supporting_discovery_ids":[7,9,12,14]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7,14,16]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[9,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5,10,13]}],"complexes":[],"partners":["PEX5","CREBBP","SIRT3","DTX2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P51659","full_name":"Peroxisomal multifunctional enzyme type 2","aliases":["17-beta-hydroxysteroid dehydrogenase 4","17-beta-HSD 4","D-bifunctional protein","DBP","Multifunctional protein 2","MFP-2","Short chain dehydrogenase/reductase family 8C member 1"],"length_aa":736,"mass_kda":79.7,"function":"Bifunctional enzyme acting on the peroxisomal fatty acid beta-oxidation pathway. Catalyzes two of the four reactions in fatty acid degradation: hydration of 2-enoyl-CoA (trans-2-enoyl-CoA) to produce (3R)-3-hydroxyacyl-CoA, and dehydrogenation of (3R)-3-hydroxyacyl-CoA to produce 3-ketoacyl-CoA (3-oxoacyl-CoA), which is further metabolized by SCPx. Can use straight-chain and branched-chain fatty acids, as well as bile acid intermediates as substrates","subcellular_location":"Peroxisome","url":"https://www.uniprot.org/uniprotkb/P51659/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HSD17B4","classification":"Not Classified","n_dependent_lines":60,"n_total_lines":1208,"dependency_fraction":0.04966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HSD17B4","total_profiled":1310},"omim":[{"mim_id":"620769","title":"HYDROXYACYL-THIOESTER DEHYDRATASE, TYPE 2; HTD2","url":"https://www.omim.org/entry/620769"},{"mim_id":"614129","title":"PERRAULT SYNDROME 3; PRLTS3","url":"https://www.omim.org/entry/614129"},{"mim_id":"609751","title":"ACYL-CoA OXIDASE 1, PALMITOYL; ACOX1","url":"https://www.omim.org/entry/609751"},{"mim_id":"607037","title":"ENOYL-CoA HYDRATASE/3-HYDROXYACYL CoA DEHYDROGENASE; 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The 80 kDa protein is N-terminally cleaved to a 32 kDa enzymatically active fragment.\",\n      \"method\": \"In vitro enzymatic assays with truncated recombinant protein domains, membrane lipid transfer assays\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple distinct in vitro enzymatic assays with defined domain constructs, replicated across two papers (PMID:10343282 and PMID:10419023)\",\n      \"pmids\": [\"10343282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The G16S mutation in HSD17B4 inactivates the enzyme by abolishing interaction with NAD+, establishing that the dehydrogenase active site requires Gly16 for cofactor binding.\",\n      \"method\": \"Mutation analysis with functional enzymatic assay\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro mutagenesis with enzymatic readout, single lab, single paper\",\n      \"pmids\": [\"10419023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Molecular dynamics simulations of the SCP-2L domain of HSD17B4 revealed that upon ligand removal, the binding pocket closes (occupied by Phe93 making hydrophobic contact with Trp36) and the C-terminal peroxisomal targeting signal (PTS1) becomes buried. An anti-correlation exists between burial of PTS1 and binding pocket size, supporting a ligand-assisted peroxisomal targeting mechanism.\",\n      \"method\": \"Molecular dynamics simulation of crystal structure of SCP-2L domain\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational simulation only, no experimental validation of the proposed mechanism\",\n      \"pmids\": [\"12368102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Compound heterozygous mutations in HSD17B4 (p.Y217C in the dehydrogenase domain and p.Y568X nonsense mutation) cause severely reduced HSD17B4 protein expression, establishing that loss of HSD17B4 function underlies Perrault syndrome. Structural analysis predicted that the Y217C missense mutation destabilizes the dehydrogenase domain.\",\n      \"method\": \"Whole-exome sequencing, Sanger confirmation, Western blot of patient-derived cells\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient genetics combined with protein expression measurement by Western blot and structural prediction, single lab\",\n      \"pmids\": [\"20673864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Small-angle X-ray scattering (SAXS) of human MFE-2 (HSD17B4) in solution determined that the SCP-2L domain is positioned as part of the full-length protein quaternary structure, providing direct structural support for the biological role of the SCP-2L domain in the holoenzyme.\",\n      \"method\": \"Synchrotron SAXS with ab initio and rigid body modeling\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — structural method applied to full-length protein in solution, single lab, single paper\",\n      \"pmids\": [\"23313254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Estrone (E1) upregulates HSD17B4 acetylation at lysine 669 (K669), promoting its degradation via chaperone-mediated autophagy (CMA). CREBBP acts as the acetyltransferase (writer) and SIRT3 as the deacetylase (eraser) dynamically controlling K669 acetylation. A K669 mutation that prevents acetylation stabilizes HSD17B4 and confers migratory/invasive properties to MCF7 cells upon E1 treatment.\",\n      \"method\": \"Site-directed mutagenesis, co-immunoprecipitation, acetylation assays, CMA degradation assays, cell migration/invasion assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP identifying writer/eraser, mutagenesis of modification site with functional phenotypic readout, independently supported by PMID:32678070\",\n      \"pmids\": [\"28296597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Cytisine-linked isoflavonoids (CLIFs) specifically bind the C-terminus (SCP-2L domain) of HSD17B4, identified by pull-down assay with biotin-modified CLIF. CLIFs selectively inhibit the enoyl-CoA hydratase activity of HSD17B4 but not the D-3-hydroxyacyl-CoA dehydrogenase activity, establishing domain-specific inhibition.\",\n      \"method\": \"Biotin-affinity pull-down assay, truncated domain constructs, enzymatic activity assays\",\n      \"journal\": \"Organic & biomolecular chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — affinity pull-down with biotin-modified ligand plus domain mapping and selective enzymatic inhibition, single lab\",\n      \"pmids\": [\"28868548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Using CRISPR knockout cell lines and pharmacological inhibition, HSD17B4 was established as essential for peroxisomal oxidation of medium- and long-chain fatty acids (lauric and palmitic acid) when mitochondrial fatty acid oxidation is impaired. HSD17B4 KO mice showed altered plasma acylcarnitine profiles after acute CPT2 inhibition, confirming in vivo relevance. Peroxisomes can oxidize both acyl-CoAs and acylcarnitines via this pathway.\",\n      \"method\": \"CRISPR-Cas9 knockout cell lines, pharmacological inhibition, isotope tracing, Hsd17b4 KO mouse model, plasma acylcarnitine profiling\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple CRISPR KO lines with biochemical flux measurements, validated in vivo with mouse KO model\",\n      \"pmids\": [\"30540494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Of five alternative splice forms of HSD17B4, only isoform 2 encodes an enzyme capable of inactivating testosterone and dihydrotestosterone (converting them to their respective 17-keto steroids). Functional expression of isoform 2 is specifically suppressed in castration-resistant prostate cancer. Genetic silencing of isoform 2 shifts metabolic balance toward active 17β-OH androgens, stimulating androgen receptor signaling and CRPC development.\",\n      \"method\": \"Splice isoform expression analysis in patient samples, isoform-specific enzymatic assays, genetic silencing with androgen measurement and androgen receptor signaling readouts\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific enzymatic activity established in vitro combined with genetic loss-of-function in cells and patient tissue validation\",\n      \"pmids\": [\"29346776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ceramide interacts with HSD17B4 via its sterol carrier protein 2-like (SCP-2L) domain, adjacent to the C-terminal peroxisomal targeting signal PTS1. Ceramide binding prevents interaction of HSD17B4 with the peroxin Pex5 (the import receptor) and retains HSD17B4 at ceramide-enriched mitochondria-associated membranes (CEMAMs). Inhibition of ceramide biosynthesis induces HSD17B4 translocation to peroxisomes, its interaction with Pex5, and upregulation of DHA production, establishing ceramide as a molecular switch for HSD17B4 peroxisomal import.\",\n      \"method\": \"Affinity chromatography, co-immunoprecipitation, proximity ligation assay, immunocytochemistry, molecular docking, in vitro mutagenesis\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (affinity chromatography, Co-IP, proximity ligation, mutagenesis) in a single study establishing mechanism of subcellular targeting regulation\",\n      \"pmids\": [\"31176039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HSD17B4 protein stability is regulated by K669 acetylation in prostate cancer cells: SIRT3 directly interacts with HSD17B4 to inhibit acetylation (enhancing stability), while CREBBP promotes K669 acetylation leading to CMA-mediated degradation. Dihydrotestosterone (DHT) increases HSD17B4 acetylation and promotes its degradation. HSD17B4 knockdown suppresses PCa cell proliferation, migration, and invasion.\",\n      \"method\": \"Co-immunoprecipitation, acetylation assays, CMA degradation assays, siRNA knockdown, cell proliferation/migration/invasion assays\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional knockdown, corroborates PMID:28296597 with additional androgen-related stimulus, single lab\",\n      \"pmids\": [\"32678070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HSD17B4 deficiency in fibroblasts reduces dimerization of DBP protein. Protein levels of HSD17B4 mutants (p.Ala175Thr) are diminished by Western blot without change in mRNA levels, indicating a post-translational stability effect of this mutation. Residual functional DBP correlates with milder clinical phenotype.\",\n      \"method\": \"Immunoblot for protein levels and dimerization, quantitative RT-PCR for mRNA\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct protein analysis (Western blot) in patient fibroblasts showing dimerization dependence, single lab\",\n      \"pmids\": [\"32042923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Phosphatidylserine (PS) interacts with HSD17B4 via its SCP-2L domain. PS association was specific (not phosphatidylcholine or sphingomyelin), disrupted by PS in liposomes but not free PS. Translocation of PS to the outer leaflet of the plasma membrane enriched HSD17B4 in peroxisomes, establishing PS as a regulator of HSD17B4 subcellular localization.\",\n      \"method\": \"Pulldown assay with biotin-PS-coated magnetic beads, domain-mapping with truncation constructs, immunofluorescence localization assay upon PS translocation\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — affinity pulldown with domain mapping plus functional localization assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"33935042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DTX2 (an E3 ubiquitin ligase) ubiquitinates HSD17B4 at lysine K645 via its RING domain targeting the SCP structural domain of HSD17B4, leading to K48-linked ubiquitination-mediated proteasomal degradation of HSD17B4. This reduces HSD17B4-dependent peroxisomal β-oxidation, lowers DHA-phospholipid levels, and suppresses ferroptosis in hepatocellular carcinoma cells. STAT3 activation drives DTX2 transcription upstream of this pathway.\",\n      \"method\": \"CRISPR screening, Co-IP, ubiquitination assays, site-specific mutagenesis (K645), lipidomics, in vivo xenograft models, DHA supplementation rescue experiments\",\n      \"journal\": \"Drug resistance updates\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — identified specific ubiquitination site (K645) by mutagenesis with Co-IP and functional rescue, in vivo validation, multiple orthogonal methods\",\n      \"pmids\": [\"40058099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HSD17B4 deficiency impairs primary ciliogenesis and alters cilia-mediated signaling. HSD17B4 is required for peroxisomal β-oxidation and acetyl-CoA synthesis; its loss reduces acetyl-CoA levels. Elevation of acetyl-CoA (via acetate administration) rescues ciliary defects through HDAC6-mediated ciliogenesis in HSD17B4-deficient cells, and restores motor function and Purkinje cell layer preservation in Hsd17b4-KO mice.\",\n      \"method\": \"HSD17B4-KO cell lines and mouse model, primary cilia imaging, acetate supplementation rescue, HDAC6 pathway analysis, metabolite measurement\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO cell lines and KO mouse model with mechanistic rescue via acetyl-CoA/HDAC6 axis, multiple orthogonal methods\",\n      \"pmids\": [\"40102401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Loss of MFE-2 (HSD17B4) in microglia leads to lipid accumulation with excessive arachidonic acid, increased mitochondrial reactive oxygen species, and proinflammatory cytokine production. Microglia-specific ablation of MFE-2 drove neuroinflammation and Aβ deposition in Alzheimer's disease models. The compound CKBA binds to MFE-2 and restores its levels, ameliorating AD pathology.\",\n      \"method\": \"Microglia-specific conditional KO mouse model, lipidomics, ROS measurement, cytokine assays, CKBA binding assay, AD model behavioral and pathological readouts\",\n      \"journal\": \"Nature aging\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional cell-type-specific KO in vivo with mechanistic lipid metabolic readouts and pharmacological rescue with identified binding compound\",\n      \"pmids\": [\"41162676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HSD17B4 knockout in BT-474 HER2-positive breast cancer cells caused accumulation of very long-chain fatty acids (VLCFA), decreased polyunsaturated fatty acids (DHA and arachidonic acid), increased Akt phosphorylation (attributed to decreased DHA), upregulation of oxidative phosphorylation and electron transport chain genes, increased mitochondrial ATP production, and enhanced glucose dependence, resulting in approximately tenfold increased sensitivity to the HER2/Akt inhibitor lapatinib.\",\n      \"method\": \"CRISPR KO cell lines, Seahorse metabolic flux analysis, lipidomics, Western blot for signaling pathway activation\",\n      \"journal\": \"Breast cancer research and treatment\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with metabolic flux and lipidomics measurements, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"37378696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Gamma-tocotrienol (γ-T3) directly interacts with HSD17B4 protein (identified by anti-FLAG immunoprecipitation with quantification of γ-T3 in precipitate), and inhibits HSD17B4 catalytic activity in converting estradiol (E2) to estrone, reducing cyclin D1 expression and suppressing ERK, MEK, AKT, and STAT3 signaling, inhibiting proliferation of HSD17B4-overexpressing HepG2 cells.\",\n      \"method\": \"Co-immunoprecipitation/pulldown with FLAG-tagged HSD17B4 and γ-T3 quantification, enzymatic activity assay, Western blot for signaling pathways, xenograft mouse model\",\n      \"journal\": \"Current cancer drug targets\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding assay plus enzymatic inhibition assay and in vivo validation, single lab\",\n      \"pmids\": [\"38934283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A homozygous HSD17B4 missense variant (p.A100S) leads to markedly reduced HSD17B4 protein expression compared to wild-type when expressed in SH-SY5Y cells, establishing pathogenicity through protein instability.\",\n      \"method\": \"Transfection of wild-type vs. mutant HSD17B4 plasmids in SH-SY5Y cells with Western blot comparison\",\n      \"journal\": \"BMC medical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Western blot experiment in transfected cells, single lab, single method\",\n      \"pmids\": [\"28830375\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HSD17B4 encodes a multifunctional peroxisomal enzyme (D-bifunctional protein, DBP) with three catalytic domains: an N-terminal NAD+-dependent D-3-hydroxyacyl-CoA dehydrogenase/17β-hydroxysteroid dehydrogenase domain, a central 2-enoyl-acyl-CoA hydratase domain, and a C-terminal SCP-2L (sterol carrier protein 2-like) domain that facilitates lipid transfer and mediates peroxisomal targeting via PTS1; it is essential for peroxisomal β-oxidation of very long-chain, branched-chain, and medium-chain fatty acids (including acylcarnitines when mitochondrial FAO is impaired), generates acetyl-CoA and DHA, and its peroxisomal import is regulated by ceramide and phosphatidylserine binding to the SCP-2L domain modulating interaction with the import receptor Pex5; protein stability is controlled by CREBBP-mediated acetylation at K669 (promoting CMA degradation) opposed by SIRT3 deacetylation, and by DTX2-mediated K48-ubiquitination at K645 (promoting proteasomal degradation); loss of HSD17B4 impairs primary ciliogenesis via reduced acetyl-CoA/HDAC6 signaling, drives microglial lipid accumulation and neuroinflammation, and only isoform 2 retains androgen-inactivating enzymatic activity relevant to prostate cancer.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HSD17B4 encodes a multifunctional 80 kDa peroxisomal enzyme (D-bifunctional protein) organized into three catalytic/functional modules: an N-terminal D-specific 3-hydroxyacyl-CoA dehydrogenase/17\\u03b2-hydroxysteroid dehydrogenase domain, a central 2-enoyl-acyl-CoA hydratase domain, and a C-terminal sterol carrier protein-2-like (SCP-2L) domain that mediates lipid transfer between membranes [#0]. Through these activities it executes peroxisomal \\u03b2-oxidation of medium- and long-chain fatty acids\\u2014and of acylcarnitines when mitochondrial fatty acid oxidation is impaired\\u2014generating acetyl-CoA and polyunsaturated fatty acids such as DHA [#7, #14]. The SCP-2L domain doubles as a regulated targeting module: it carries the C-terminal PTS1 import signal, and binding of lipids such as ceramide or phosphatidylserine to this domain controls the protein's interaction with the import receptor Pex5 and thereby partitions HSD17B4 between mitochondria-associated membranes and peroxisomes [#9, #12]. Enzyme abundance is further set post-translationally by competing modifications\\u2014CREBBP-mediated K669 acetylation drives chaperone-mediated autophagy and is opposed by SIRT3 deacetylation, while DTX2-mediated K48-linked ubiquitination at K645 targets the SCP domain for proteasomal degradation [#5, #10, #13]. Downstream of its metabolic output, HSD17B4-derived acetyl-CoA supports HDAC6-dependent primary ciliogenesis, and loss of the enzyme produces lipid accumulation, oxidative stress, and neuroinflammation in microglia [#14, #15]. Compound heterozygous and homozygous loss-of-function mutations that destabilize the protein cause Perrault syndrome [#3, #11]. A splice isoform-specific androgen-inactivating activity (isoform 2) links HSD17B4 to castration-resistant prostate cancer [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established the fundamental architecture and chemistry of HSD17B4, defining it as a single polypeptide carrying three distinct activities relevant to both fatty acid and steroid metabolism.\",\n      \"evidence\": \"In vitro enzymatic assays on truncated recombinant domains plus membrane lipid transfer assays, with mutational mapping of the NAD+-binding dehydrogenase site\",\n      \"pmids\": [\"10343282\", \"10419023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrate hierarchy not established in vitro\", \"Did not address how the three domains coordinate flux in the holoenzyme\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Proposed a ligand-assisted peroxisomal targeting mechanism in which SCP-2L ligand occupancy gates exposure of the C-terminal PTS1 signal.\",\n      \"evidence\": \"Molecular dynamics simulation of the SCP-2L crystal structure\",\n      \"pmids\": [\"12368102\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Computational only with no experimental validation at the time\", \"Identity of physiological gating ligand unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected HSD17B4 loss of function to human disease, showing that destabilizing mutations cause Perrault syndrome.\",\n      \"evidence\": \"Whole-exome sequencing with Sanger confirmation, Western blot of patient cells, structural prediction\",\n      \"pmids\": [\"20673864\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific basis of the ovarian and auditory phenotype not resolved\", \"Single family / single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Confirmed that the SCP-2L domain is an integral structural element of the full-length holoenzyme rather than an isolated module, supporting its biological role in the intact protein.\",\n      \"evidence\": \"Synchrotron SAXS with ab initio and rigid-body modeling of human full-length protein in solution\",\n      \"pmids\": [\"23313254\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Low-resolution solution model only\", \"Did not capture ligand-dependent conformational changes\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed that HSD17B4 abundance is dynamically controlled by reversible K669 acetylation coupling its degradation to estrogen signaling.\",\n      \"evidence\": \"Site-directed mutagenesis, reciprocal Co-IP identifying CREBBP/SIRT3, CMA degradation and migration/invasion assays in MCF7 cells\",\n      \"pmids\": [\"28296597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How acetylation routes the protein specifically into CMA not detailed\", \"Link between enzyme abundance and metastatic phenotype mechanistically indirect\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that HSD17B4 is required for peroxisomal oxidation of medium- and long-chain fatty acids and acylcarnitines, a pathway that becomes important when mitochondrial FAO is blocked.\",\n      \"evidence\": \"CRISPR-Cas9 KO cell lines, isotope tracing, Hsd17b4 KO mice with plasma acylcarnitine profiling after CPT2 inhibition\",\n      \"pmids\": [\"30540494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of peroxisomal FAO under normal physiology unclear\", \"Mechanism of acylcarnitine entry into peroxisomes not defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified an isoform-specific androgen-inactivating function, linking suppression of HSD17B4 isoform 2 to castration-resistant prostate cancer.\",\n      \"evidence\": \"Isoform-specific enzymatic assays, genetic silencing with androgen and AR signaling readouts, patient tissue expression analysis\",\n      \"pmids\": [\"29346776\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism suppressing isoform 2 expression in CRPC not defined\", \"Subcellular site of androgen inactivation not localized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established ceramide as a molecular switch for HSD17B4 peroxisomal import by binding SCP-2L and blocking Pex5 interaction, experimentally validating the ligand-assisted targeting concept.\",\n      \"evidence\": \"Affinity chromatography, Co-IP, proximity ligation, immunocytochemistry, docking and mutagenesis\",\n      \"pmids\": [\"31176039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of CEMAM retention not tested\", \"How ceramide levels are sensed to time import not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the acetylation-controlled stability model to prostate cancer, showing androgen stimulus drives K669 acetylation and degradation with functional consequences for proliferation.\",\n      \"evidence\": \"Co-IP, acetylation and CMA degradation assays, siRNA knockdown with proliferation/migration/invasion readouts\",\n      \"pmids\": [\"32678070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab corroboration of the CREBBP/SIRT3 axis\", \"Direct enzymatic-output basis of the proliferative phenotype not isolated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed that disease-associated mutations act by impairing protein dimerization and stability rather than by altering transcription.\",\n      \"evidence\": \"Immunoblot for protein level and dimerization, qRT-PCR for mRNA in patient fibroblasts\",\n      \"pmids\": [\"32042923\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of dimerization defect not resolved\", \"Genotype-phenotype correlation based on small patient set\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified phosphatidylserine as a second SCP-2L-binding lipid that regulates HSD17B4 peroxisomal localization, broadening the lipid-sensing control of targeting.\",\n      \"evidence\": \"Biotin-PS bead pulldown with truncation mapping and immunofluorescence localization upon PS translocation\",\n      \"pmids\": [\"33935042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological trigger linking PS exposure to import not defined\", \"Relationship to the ceramide switch not reconciled\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a second degradation route via DTX2-mediated K48 ubiquitination of the SCP domain at K645, linking HSD17B4 turnover to peroxisomal DHA output and ferroptosis suppression in hepatocellular carcinoma.\",\n      \"evidence\": \"CRISPR screen, Co-IP, ubiquitination assays, K645 mutagenesis, lipidomics, xenografts and DHA rescue\",\n      \"pmids\": [\"40058099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interplay between K645 ubiquitination and K669 acetylation not tested\", \"Generality beyond STAT3-driven HCC unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected HSD17B4 metabolic output to organelle biogenesis, showing that acetyl-CoA generated by peroxisomal \\u03b2-oxidation drives HDAC6-dependent primary ciliogenesis.\",\n      \"evidence\": \"KO cell lines and KO mice, primary cilia imaging, acetate supplementation rescue, HDAC6 pathway analysis, motor and Purkinje cell readouts\",\n      \"pmids\": [\"40102401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between acetyl-CoA pool and HDAC6 activity not fully traced\", \"Neuronal cell-type specificity of the rescue not delineated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated a cell-type-specific role in microglia where HSD17B4 loss causes lipid accumulation, ROS, and neuroinflammation driving Alzheimer's-like pathology.\",\n      \"evidence\": \"Microglia-specific conditional KO mice, lipidomics, ROS and cytokine assays, AD model readouts with CKBA pharmacological rescue\",\n      \"pmids\": [\"41162676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking arachidonic acid accumulation to cytokine production not fully defined\", \"Whether findings extend to human microglia untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed that HSD17B4 loss rewires fatty acid pools toward VLCFA accumulation and DHA depletion, activating Akt and mitochondrial respiration and sensitizing HER2+ breast cancer to lapatinib.\",\n      \"evidence\": \"CRISPR KO cells, Seahorse metabolic flux, lipidomics, Western blot for signaling\",\n      \"pmids\": [\"37378696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from DHA loss to Akt activation only correlative\", \"Single cell-line context\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the lipid-sensing (ceramide/PS), acetylation (K669), and ubiquitination (K645) control layers are integrated to set HSD17B4 localization and abundance in a given tissue remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No study tests acetylation, ubiquitination, and lipid-gated import together\", \"Tissue-specific dominance of each regulatory layer unknown\", \"Structural model of the regulated SCP-2L/PTS1 switch in the holoenzyme not solved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 8, 17]},\n      {\"term_id\": \"GO:0016829\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 9, 12]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005777\", \"supporting_discovery_ids\": [7, 9, 12, 14]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7, 14, 16]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [9, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5, 10, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PEX5\",\n      \"CREBBP\",\n      \"SIRT3\",\n      \"DTX2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}