{"gene":"SLC27A4","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2001,"finding":"FATP4 encodes a very long chain acyl-CoA synthetase with substrate specificity biased towards very long chain fatty acids; transfection of FATP4 cDNA into COS1 cells produced a 2-fold increase in palmitoyl-CoA synthetase (C16:0) activity and a 5-fold increase in lignoceroyl-CoA synthetase (C24:0) activity from membrane extracts.","method":"Transfection of FATP4 cDNA into COS1 cells with enzymatic activity assays on membrane extracts","journal":"Gene","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic activity assay with quantitative readout, replicated across multiple subsequent studies","pmids":["11404000"],"is_preprint":false},{"year":2003,"finding":"Fatp4 knockout mice display neonatally lethal restrictive dermopathy with hyperproliferative hyperkeratosis, disturbed epidermal barrier, and a disturbed fatty acid composition of epidermal ceramides (specifically decreased C26:0 and C26:0-OH fatty acid substitutes), establishing an essential function of Fatp4 in epidermal barrier formation.","method":"Targeted gene disruption (knockout mouse), histology, lipid analysis of epidermal ceramides","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular and lipid phenotype, replicated in multiple subsequent studies","pmids":["12821645"],"is_preprint":false},{"year":2005,"finding":"Purified FATP4 is an acyl-CoA synthetase with kinetic activity for both long chain (C16:0) and very long chain (C24:0) fatty acids; it is insensitive to triacsin C inhibition but sensitive to feedback inhibition by acyl-CoA. Extracts from skin and intestine of FATP4 null mice showed reduced esterification specifically for C24:0 but not C16:0 or C18:1, suggesting FATP4 preferentially activates very long chain fatty acids in vivo.","method":"Affinity purification of FLAG-tagged FATP4, kinetic enzymatic assays, acyl-CoA synthetase activity in tissue extracts from knockout mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — purified protein with kinetic analysis plus corroborating knockout tissue data, multiple orthogonal methods","pmids":["15653672"],"is_preprint":false},{"year":2005,"finding":"Epidermal keratinocyte-specific inactivation of Fatp4 reproduces the hyperproliferative hyperkeratosis and disturbed epidermal barrier seen in global Fatp4 knockouts, establishing that intrinsic Fatp4 deficiency in keratinocytes (not secondary loss in other organs) is responsible for the epidermal structural abnormalities.","method":"Conditional keratinocyte-specific Fatp4 knockout (Cre-lox), histology, epidermal barrier assays","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined tissue-specific phenotype, corroborated by rescue experiments in other studies","pmids":["16354193"],"is_preprint":false},{"year":2006,"finding":"FATP4 localizes to the endoplasmic reticulum (not the plasma membrane), and its enhancement of cellular fatty acid uptake is dependent on its acyl-CoA synthetase enzymatic activity; ER-localized FATP4 drives fatty acid uptake indirectly by esterification (metabolic trapping) rather than by direct translocation at the plasma membrane.","method":"Immunofluorescence localization, quantitative fatty acid uptake assays at single-cell level, enzymatic activity mutant analysis, expression of mitochondrial acyl-CoA synthetase as control","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — subcellular localization with functional consequence, activity-dependent uptake assay, replicated across multiple labs","pmids":["17062637"],"is_preprint":false},{"year":2007,"finding":"Keratinocyte-specific expression of FATP4 rescues the neonatally lethal skin phenotype of Fatp4-/- mice, while expression of an FATP4 variant with mutations in the acyl-CoA synthetase domain fails to rescue, establishing that the acyl-CoA synthetase activity of FATP4 in suprabasal keratinocytes is necessary for normal skin development and cornified envelope formation.","method":"Transgenic rescue experiments (wild-type and ACS-domain mutant FATP4), tetraploid aggregation, phenotypic analysis of skin barrier","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — structure-function rescue with active site mutant, multiple transgenic lines tested","pmids":["17401141"],"is_preprint":false},{"year":2009,"finding":"Independent overexpression of FATP4 in rat skeletal muscle increases fatty acid transport; FATP4 is 1.7-fold more effective than FABPpm and FATP1 at enhancing fatty acid transport. All transporters increased long chain fatty acid oxidation, but FABPpm and FAT/CD36 had 3-fold greater effects on oxidation than FATP1 and FATP4. FATP4 overexpression did not alter rates of fatty acid esterification into triacylglycerols.","method":"In vivo electroporation-mediated overexpression in rat skeletal muscle, fatty acid transport assays, oxidation and esterification measurements","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo overexpression with defined metabolic readouts, single lab","pmids":["19380575"],"is_preprint":false},{"year":2010,"finding":"FATP4-deficient epidermis exhibits increased expression of EGF family members (Ereg, Areg, Epgn) associated with elevated EGFR activation and downstream STAT3 signaling in suprabasal cells; pharmacological inhibition of EGFR or STAT3 attenuated STAT3 activation and partially suppressed skin thickening and barrier abnormalities, placing FATP4 activity upstream of EGFR-STAT3 signaling in skin development.","method":"Gene expression profiling in Fatp4 mutant skin, EGFR/STAT3 activation assays, pharmacological inhibition (Tyrphostin AG1478, curcumin) with phenotypic readout","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via pharmacological inhibition with cellular phenotype, single lab","pmids":["20513444"],"is_preprint":false},{"year":2011,"finding":"FATP4 localizes to the endoplasmic reticulum (not plasma membrane) in C2C12 muscle cells; stable FATP4 overexpression doubles acyl-CoA synthetase activity and cellular oleate uptake. Insulin treatment increases acyl-CoA synthetase activity within minutes in a wortmannin-sensitive manner, and affinity-purified FATP4 from insulin-treated cells shows enhanced enzyme activity, suggesting insulin regulation of FATP4 enzymatic activity as a mechanism for insulin-stimulated fatty acid uptake.","method":"Stable overexpression, acyl-CoA synthetase activity assays, subcellular fractionation and immunofluorescence, insulin treatment with wortmannin inhibition, affinity purification of FATP4 from insulin-treated cells","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzyme activity assay with purified protein from treated cells, localization confirmed by two methods, single lab","pmids":["21750264"],"is_preprint":false},{"year":2011,"finding":"FATP2 and FATP4 localize to the ER in HuH7 and HepG2 hepatoma cells; overexpression of FATP4 increases acyl-CoA synthetase activity and enhances uptake of [3H]-oleic acid and fluorescent Bodipy-C12 fatty acid, consistent with ER-based metabolic trapping as the mechanism for FA uptake enhancement.","method":"Immunofluorescence localization, overexpression, acyl-CoA synthetase activity assays, radiolabeled and fluorescent fatty acid uptake assays, quantitative FACS","journal":"International journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal uptake assays plus localization, single lab","pmids":["22022213"],"is_preprint":false},{"year":2011,"finding":"Adipocyte-specific Fatp4 knockout mice show no change in fatty acid uptake into adipose tissue under standard conditions, establishing that FATP4 is not required for fatty acid uptake in adipocytes. Under high-fat diet, Fatp4-deficient adipocytes show altered metabolism of complex lipids (decreased phospholipids, sphingomyelin, and cholesteryl esters) with adipose hypertrophy.","method":"Adipocyte-specific Cre-lox knockout, radiolabeled fatty acid uptake assays, lipidomics, histology, metabolic phenotyping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — negative result for FA uptake with direct assay in tissue-specific KO, positive lipidomic result, multiple methods","pmids":["21808061"],"is_preprint":false},{"year":2012,"finding":"FATP1 and ACSVL4/FATP4 both localize to the ER (not plasma membrane) in 3T3-L1 adipocytes as confirmed by confocal microscopy and subcellular fractionation; stable overexpression increases acyl-CoA synthetase activity and fatty acid uptake. Insulin increases fatty acid uptake without changing the ER localization of FATP1 or FATP4.","method":"Retroviral stable overexpression, confocal microscopy, subcellular fractionation, acyl-CoA synthetase activity assays, fatty acid uptake assays, insulin treatment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — localization confirmed by two orthogonal methods, functional assays, single lab","pmids":["23024797"],"is_preprint":false},{"year":2013,"finding":"FATP4 was identified as a negative regulator of RPE65 isomerase activity; FATP4 inhibits synthesis of 11-cis-retinol (11cROL) in the visual cycle through two mechanisms: (1) competition with RPE65 for substrate, and (2) production of lignoceroyl (C24:0)-CoA which inhibits 11cROL synthesis. FATP4-deficient RPE shows significantly higher RPE65 isomerase activity, faster 11-cis-retinaldehyde regeneration, and faster rod light sensitivity recovery, but increased accumulation of cytotoxic all-trans retinaldehyde and hypersusceptibility to light-induced photoreceptor degeneration.","method":"Expression screening of bovine RPE cDNA library, FATP4-deficient mice, isomerase activity assays, retinoid analysis, electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including enzymatic activity, substrate competition assay, and in vivo functional validation in knockout mice","pmids":["23407971"],"is_preprint":false},{"year":2012,"finding":"FATP4 and ichthyin (NIPAL4 product) show close proximity interaction in the upper stratum granulosum of normal epidermis by proximity ligation assay. In IPS skin lacking FATP4, ichthyin expression is reduced; conversely, NIPAL4-mutant skin shows increased FATP4 staining, suggesting mutual interdependence in epidermal lipid processing.","method":"Immunofluorescence, proximity ligation assay (PLA) in human skin biopsies and organotypic epidermis with siRNA silencing","journal":"Journal of dermatological science","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proximity ligation assay confirms interaction, with siRNA corroboration in two models, single lab","pmids":["23290633"],"is_preprint":false},{"year":2015,"finding":"SLC27A4 directly interacts with ATG4B (a cysteine protease required for autophagy) in lung cancer cell lines, as shown by co-immunoprecipitation and GST-pull down assays; SLC27A4 stabilizes ATG4B protein and maintains its intracellular concentration, promoting rapid ATG4B-mediated autophagy in response to chemotherapy stress.","method":"Tandem affinity purification/mass spectrometry (TAP/MS), co-immunoprecipitation, GST-pulldown, siRNA knockdown with autophagy and drug sensitivity readouts","journal":"Tumour biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reciprocal pulldown confirms interaction, functional siRNA data, but cancer cell line context and single lab","pmids":["26662804"],"is_preprint":false},{"year":2019,"finding":"ETEC K88 challenge reduces FATP4 protein expression in intestinal epithelial cells via phosphorylation of ERK1/2 and PPARγ (ERK1/2-PPARγ pathway), impairing FATP4-dependent long-chain fatty acid (LCFA) uptake; gene knockdown and overexpression confirmed FATP4 as the responsible transporter for LCFA (C16:0) but not medium-chain fatty acid (C12:0) uptake in IPEC-J2 cells.","method":"In vivo piglet model, polarized IPEC-J2 cell model, FATP4 knockdown and overexpression, ERK1/2 inhibitor (U0126) and PPARγ antagonist (T0070907), BODIPY-labeled fatty acid uptake assays","journal":"Frontiers in physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway placement via pharmacological inhibitors and gene KD/OE with defined uptake readout, single lab","pmids":["31281267"],"is_preprint":false},{"year":2020,"finding":"FATP4 exhibits acyl-CoA synthetase activity toward ω-hydroxy fatty acids, intermediates in the acylceramide synthetic pathway; Fatp4 knockout mice show severely reduced total acylceramide levels (~10% of wild type), decreased and shortened saturated non-acylated ceramides, and reduced ELOVL1 elongase expression, establishing FATP4 as the acyl-CoA synthetase responsible for acylceramide synthesis required for epidermal permeability barrier formation.","method":"In vitro ACS activity assay with ω-hydroxy fatty acid substrate, Fatp4 KO mice lipidomics, siRNA knockdown in human keratinocytes, ELOVL1 expression analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic activity with specific substrate plus KO mouse lipidomics plus human cell knockdown, multiple orthogonal methods","pmids":["31974308"],"is_preprint":false},{"year":2021,"finding":"FATP4 inactivation in macrophages (THP-1 knockdown and bone marrow-derived macrophages from Fatp4M-/- mice) causes a metabolic shift towards triacylglycerides, decreases ceramide levels, and attenuates M1 activation- or ER stress-induced pro-inflammatory cytokine release (IL-8, TNF-α, IL-12). FATP4 deficiency specifically attenuates tunicamycin-induced activation of IRE1α but not other unfolded protein response pathways.","method":"siRNA knockdown in THP-1-derived macrophages, macrophage-specific Fatp4-KO mice (BMDMs), lipidomics, cytokine measurements, UPR pathway analysis","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two complementary KD/KO models with lipidomic and functional readouts, single lab","pmids":["33900381"],"is_preprint":false},{"year":2023,"finding":"PLIN5 interacts with FATP4 at lipid droplet-mitochondria contact sites; the C-terminal domains of PLIN5 and FATP4 constitute a minimal protein interaction sufficient to induce organelle contacts. Phosphorylation of PLIN5 upon starvation promotes LD-to-mitochondria fatty acid trafficking and β-oxidation, requiring an intact PLIN5 mitochondrial tethering domain and functional FATP4 on mitochondria for conversion of fatty acids to acyl-CoAs.","method":"Co-immunoprecipitation, domain mapping (C-terminal interaction), organelle contact site imaging, starvation/phosphorylation experiments in human and murine myoblasts, β-oxidation assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP with domain mapping, functional contact site induction, multiple cell models, β-oxidation readout","pmids":["37290445"],"is_preprint":false},{"year":2023,"finding":"SLC27A4 overexpression promotes selective uptake of mono-unsaturated fatty acids (MUFAs) in HCC cells, leading to elevated MUFA-containing phosphatidylcholine and phosphatidylethanolamine, which confers resistance to lipid peroxidation and ferroptosis; SLC27A4 silencing sensitizes HCC cells to sorafenib both in vitro and in vivo.","method":"Lipidomic analysis, SLC27A4 overexpression and siRNA knockdown, ferroptosis assays, xenograft mouse model","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lipidomics plus in vitro/in vivo KD with defined ferroptosis readout, single lab","pmids":["36924851"],"is_preprint":false},{"year":2024,"finding":"Hepatocyte-specific SLC27A4 deletion ameliorates NAFLD in mice; SLC27A4 overexpression increases hepatic phosphatidylcholine (PC) accumulation, which activates pregnane X receptor (PXR) signaling and further induces SLC27A4 expression forming a feedforward loop. PXR overexpression reverses the protective effect of Slc27a4 deletion, while PXR deficiency reduces the effect of Slc27a4 overexpression on NAFLD.","method":"AAV-mediated liver overexpression, hepatocyte-specific Cre-lox KO, lipidomics, RNA-seq, PXR genetic epistasis (overexpression and KO crosses), biochemical and histological analysis","journal":"Metabolism: clinical and experimental","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with gain- and loss-of-function for both SLC27A4 and PXR, lipidomic mechanism, multiple dietary models","pmids":["39489412"],"is_preprint":false},{"year":2024,"finding":"Enterocyte-specific Fatp4 knockout mice show a metabolic shift from very long-chain to long-chain fatty acids and from polar lipids (ceramides, sphingomyelin, phosphatidylcholine) to neutral lipids predominantly in the ileum, resulting in elevated plasma triglycerides, chylomicrons, and lipoproteins after fat loading or high-fat feeding, establishing FATP4's role in controlling intestinal lipid processing and blood lipid levels.","method":"Villin-Cre enterocyte-specific Fatp4 KO mice, lipidomics of intestinal segments, plasma lipid and lipoprotein measurements after oral fat loading and chronic HFHC feeding","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tissue-specific KO with detailed lipidomics and multiple dietary challenges, single lab","pmids":["38915276"],"is_preprint":false},{"year":2025,"finding":"sEV-NAMPT activates NF-κB through TLR4, leading to elevated SLC27A4 expression; SLC27A4 then increases intracellular triacylglycerol (TG) and dihydroxyacetone phosphate (DHAP) levels, linking lipid metabolism to glycolysis by facilitating conversion of glycerol-3-phosphate to DHAP via lipolysis of TG.","method":"Mass spectrometry protein analysis of HCC-derived sEV, NF-κB signaling assays, lipidomic and metabolomic analysis, SLC27A4 knockdown/overexpression, hepatic lipase activity assays","journal":"Journal of extracellular vesicles","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lipidomics plus metabolomics with KD/OE and upstream signaling pathway, single lab","pmids":["40237223"],"is_preprint":false}],"current_model":"SLC27A4/FATP4 is an integral membrane very long-chain acyl-CoA synthetase localized primarily to the endoplasmic reticulum (and mitochondria in some contexts) that drives cellular fatty acid uptake indirectly through metabolic trapping via esterification rather than direct plasma membrane translocation; in skin, its ACS activity toward ω-hydroxy fatty acids is essential for acylceramide synthesis and epidermal permeability barrier formation (loss causes ichthyosis prematurity syndrome); in the RPE it inhibits RPE65 isomerase activity by substrate competition and via C24:0-CoA production; it interacts with PLIN5 at lipid droplet-mitochondria contact sites to channel fatty acids to β-oxidation; in macrophages its ACS activity channels fatty acids into ceramides/phospholipids, and loss shifts metabolism toward triacylglycerides and suppresses pro-inflammatory cytokine release; in liver it drives phosphatidylcholine accumulation that activates PXR in a feedforward loop promoting steatosis; and in the intestine it controls the balance between polar and neutral lipids in the ileum to regulate plasma lipid levels."},"narrative":{"mechanistic_narrative":"SLC27A4 (FATP4) is an endoplasmic reticulum-localized very long-chain acyl-CoA synthetase that governs cellular fatty acid handling by esterifying fatty acids to acyl-CoAs, thereby driving fatty acid uptake indirectly through metabolic trapping rather than direct plasma-membrane translocation [PMID:11404000, PMID:17062637]. Its enzyme is biased toward very long-chain substrates (e.g. C24:0) over long-chain fatty acids, is insensitive to triacsin C, and is feedback-inhibited by acyl-CoA [PMID:11404000, PMID:15653672]. ER residence with activity-dependent uptake enhancement has been confirmed across muscle, hepatoma, and adipocyte cell models [PMID:17062637, PMID:21750264, PMID:22022213, PMID:23024797]. In skin, FATP4 acyl-CoA synthetase activity in suprabasal keratinocytes is essential for epidermal permeability barrier formation: it activates ω-hydroxy fatty acids for acylceramide synthesis, and its loss abolishes acylceramides and causes hyperproliferative hyperkeratosis with a defective barrier, downstream of which EGFR-STAT3 signaling is aberrantly activated [PMID:12821645, PMID:16354193, PMID:17401141, PMID:31974308, PMID:20513444]. Beyond skin, FATP4 channels fatty acids into distinct lipid pools in a tissue-specific manner—partitioning toward complex/polar lipids in adipocytes, macrophages, and enterocytes—so that its loss shifts metabolism toward neutral lipids (triacylglycerides) and alters inflammatory output and plasma lipid levels [PMID:21808061, PMID:33900381, PMID:38915276]. It interacts with PLIN5 at lipid droplet-mitochondria contact sites to supply acyl-CoAs for β-oxidation [PMID:37290445], negatively regulates RPE65 isomerase activity in the visual cycle by substrate competition and C24:0-CoA production [PMID:23407971], and in liver drives phosphatidylcholine accumulation that activates PXR in a feedforward loop promoting steatosis [PMID:39489412]. In cancer contexts it has been linked to MUFA-dependent ferroptosis resistance and to ATG4B-mediated autophagy [PMID:36924851, PMID:26662804].","teleology":[{"year":2001,"claim":"Established that FATP4 is an enzyme—a very long-chain acyl-CoA synthetase—rather than a passive transporter, defining its core biochemical activity.","evidence":"Transfection of FATP4 cDNA into COS1 cells with acyl-CoA synthetase activity assays on membrane extracts","pmids":["11404000"],"confidence":"High","gaps":["Did not define subcellular site of activity","Did not establish physiological substrate preference in vivo"]},{"year":2003,"claim":"Demonstrated an essential in vivo function in epidermal barrier formation, linking FATP4 loss to defective ceramide fatty acid composition.","evidence":"Targeted Fatp4 knockout mice with histology and epidermal ceramide lipid analysis","pmids":["12821645"],"confidence":"High","gaps":["Could not distinguish keratinocyte-intrinsic from systemic effects","Molecular target lipid in ceramide synthesis not yet defined"]},{"year":2005,"claim":"Resolved substrate specificity and confirmed enzymatic identity using purified protein plus knockout tissue, showing preferential activation of very long-chain fatty acids in vivo.","evidence":"Affinity-purified FLAG-FATP4 kinetics and acyl-CoA synthetase assays in knockout skin/intestine extracts","pmids":["15653672"],"confidence":"High","gaps":["Did not address localization","Mechanism of feedback inhibition not structurally defined"]},{"year":2006,"claim":"Established that FATP4 enhances fatty acid uptake indirectly via ER-based metabolic trapping (esterification), settling the transporter-versus-enzyme question of how uptake is driven.","evidence":"Immunofluorescence localization, single-cell uptake assays, and ACS-activity mutant analysis","pmids":["17062637"],"confidence":"High","gaps":["Did not rule out tissue-specific plasma-membrane pools","Quantitative contribution to whole-body FA flux unaddressed"]},{"year":2005,"claim":"Showed keratinocyte-intrinsic FATP4 deficiency suffices for the skin phenotype and that its ACS catalytic activity is required, linking enzyme function directly to barrier development.","evidence":"Keratinocyte-specific conditional knockout and transgenic rescue with wild-type versus ACS-domain mutant FATP4","pmids":["16354193","17401141"],"confidence":"High","gaps":["Specific lipid substrate in keratinocytes not yet identified","Downstream signaling consequences not defined"]},{"year":2010,"claim":"Placed FATP4 activity upstream of EGFR-STAT3 signaling, connecting a metabolic lipid defect to a proliferative signaling cascade in skin.","evidence":"Expression profiling in mutant skin plus pharmacological EGFR/STAT3 inhibition with phenotypic rescue","pmids":["20513444"],"confidence":"Medium","gaps":["Causal lipid linking FATP4 loss to EGF ligand induction unidentified","Pharmacological inhibitors lack genetic confirmation"]},{"year":2011,"claim":"Generalized ER localization and metabolic-trapping uptake mechanism across muscle, hepatoma, and adipocyte cells, and linked insulin to acute regulation of FATP4 enzymatic activity.","evidence":"Stable overexpression, fractionation/confocal localization, ACS and FA-uptake assays with insulin/wortmannin treatment","pmids":["21750264","22022213","23024797"],"confidence":"Medium","gaps":["Molecular mechanism of insulin-induced activity increase not defined","Phosphorylation or modification of FATP4 not directly demonstrated"]},{"year":2011,"claim":"Demonstrated FATP4 is dispensable for adipocyte fatty acid uptake but shapes complex lipid metabolism, refining the view that its role is biosynthetic partitioning rather than bulk uptake.","evidence":"Adipocyte-specific knockout with radiolabeled uptake assays and lipidomics under high-fat diet","pmids":["21808061"],"confidence":"High","gaps":["Redundant transporters compensating for uptake unidentified","Mechanism linking loss to adipose hypertrophy unclear"]},{"year":2013,"claim":"Identified FATP4 as a negative regulator of the RPE65 visual cycle isomerase, expanding its role beyond bulk lipid metabolism to enzyme-level regulation via substrate competition and product (C24:0-CoA) inhibition.","evidence":"Expression cloning, FATP4-deficient RPE isomerase and retinoid analyses, and electrophysiology","pmids":["23407971"],"confidence":"High","gaps":["Physical interaction with RPE65 not established","Relative weight of competition versus C24:0-CoA inhibition unquantified"]},{"year":2012,"claim":"Provided in situ evidence that FATP4 functions in proximity to NIPAL4/ichthyin in epidermis, implicating a coordinated lipid-processing module in barrier formation.","evidence":"Proximity ligation assay in human skin and organotypic epidermis with siRNA silencing","pmids":["23290633"],"confidence":"Medium","gaps":["PLA proximity does not prove direct binding","Functional consequence of the interaction not biochemically defined"]},{"year":2020,"claim":"Pinpointed the biochemical substrate explaining the skin phenotype: FATP4 activates ω-hydroxy fatty acids for acylceramide synthesis essential for the permeability barrier.","evidence":"In vitro ACS assay with ω-hydroxy fatty acid substrate, knockout mouse lipidomics, and human keratinocyte knockdown","pmids":["31974308"],"confidence":"High","gaps":["Mechanism coupling FATP4 to ELOVL1 expression unclear","Structural basis of ω-hydroxy substrate recognition unknown"]},{"year":2021,"claim":"Showed FATP4 controls macrophage lipid partitioning and inflammatory output, linking its ACS activity to ceramide production and IRE1α-dependent cytokine release.","evidence":"THP-1 knockdown and macrophage-specific knockout BMDMs with lipidomics, cytokine, and UPR analyses","pmids":["33900381"],"confidence":"Medium","gaps":["Mechanism connecting FATP4 lipids to selective IRE1α activation undefined","Single lab without independent replication"]},{"year":2023,"claim":"Defined a direct PLIN5-FATP4 interaction tethering lipid droplets to mitochondria to channel fatty acids into β-oxidation, establishing a contact-site role in fuel delivery.","evidence":"Reciprocal Co-IP, C-terminal domain mapping, contact-site imaging, and β-oxidation assays in myoblasts","pmids":["37290445"],"confidence":"High","gaps":["Mitochondrial pool of FATP4 versus ER pool not fully resolved","Regulation of the interaction beyond starvation/phosphorylation unclear"]},{"year":2024,"claim":"Established hepatic and intestinal FATP4 as drivers of systemic lipid pathology—via a phosphatidylcholine-PXR feedforward loop in liver and polar/neutral lipid balance in the ileum controlling plasma lipids.","evidence":"Hepatocyte- and enterocyte-specific knockouts plus AAV overexpression with lipidomics, RNA-seq, and PXR genetic epistasis","pmids":["39489412","38915276"],"confidence":"High","gaps":["Mechanism of PC-mediated PXR activation not structurally defined","Translation of mouse intestinal findings to human lipid disorders unaddressed"]},{"year":2023,"claim":"Linked FATP4 to cancer cell survival through MUFA-driven membrane composition conferring ferroptosis resistance and through ATG4B-stabilized autophagy.","evidence":"Lipidomics with overexpression/knockdown and ferroptosis assays in HCC; TAP/MS and reciprocal pulldown with ATG4B in lung cancer cells","pmids":["36924851","26662804"],"confidence":"Medium","gaps":["ATG4B interaction tested only in cancer cell lines without in vivo validation","Whether autophagy role depends on ACS activity unknown"]},{"year":null,"claim":"How FATP4's single acyl-CoA synthetase activity is differentially routed to distinct lipid fates (acylceramides, complex phospholipids, β-oxidation, PXR-activating PC) across tissues, and the structural basis of its substrate selectivity and protein partnerships, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No crystal/cryo-EM structure to explain VLCFA selectivity","Mechanism selecting biosynthetic versus catabolic acyl-CoA channeling unknown","Direct partners beyond PLIN5/ATG4B largely uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,2,5,16]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,16]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[4,9,15]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4,8,9,11]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[18]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,16,20,21]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,3,5,16]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[12]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14]}],"complexes":[],"partners":["PLIN5","ATG4B","NIPAL4","RPE65"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6P1M0","full_name":"Long-chain fatty acid transport protein 4","aliases":["Arachidonate--CoA ligase","Long-chain-fatty-acid--CoA ligase","Solute carrier family 27 member 4","Very long-chain acyl-CoA synthetase 4","ACSVL4"],"length_aa":643,"mass_kda":72.1,"function":"Mediates the levels of long-chain fatty acids (LCFA) in the cell by facilitating their transport across cell membranes (PubMed:10518211, PubMed:12556534, PubMed:20448275, PubMed:21395585, PubMed:22022213). Appears to be the principal fatty acid transporter in small intestinal enterocytes (PubMed:20448275). Also functions as an acyl-CoA ligase catalyzing the ATP-dependent formation of fatty acyl-CoA using LCFA and very-long-chain fatty acids (VLCFA) as substrates, which prevents fatty acid efflux from cells and might drive more fatty acid uptake (PubMed:22022213, PubMed:24269233). Plays a role in the formation of the epidermal barrier. Required for fat absorption in early embryogenesis (By similarity). Probably involved in fatty acid transport across the blood barrier (PubMed:21395585). Indirectly inhibits RPE65 via substrate competition and via production of VLCFA derivatives like lignoceroyl-CoA. Prevents light-induced degeneration of rods and cones (By similarity)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q6P1M0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC27A4","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000167114","cell_line_id":"CID001322","localizations":[{"compartment":"er","grade":3}],"interactors":[{"gene":"C9ORF16","stoichiometry":0.2},{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001322","total_profiled":1310},"omim":[{"mim_id":"608649","title":"ICHTHYOSIS PREMATURITY SYNDROME; IPS","url":"https://www.omim.org/entry/608649"},{"mim_id":"604196","title":"SOLUTE CARRIER FAMILY 27 (FATTY ACID TRANSPORTER), MEMBER 6; SLC27A6","url":"https://www.omim.org/entry/604196"},{"mim_id":"604194","title":"SOLUTE CARRIER FAMILY 27 (FATTY ACID TRANSPORTER), MEMBER 4; SLC27A4","url":"https://www.omim.org/entry/604194"},{"mim_id":"604193","title":"SOLUTE CARRIER FAMILY 27 (FATTY ACID TRANSPORTER), MEMBER 3; SLC27A3","url":"https://www.omim.org/entry/604193"},{"mim_id":"603314","title":"SOLUTE CARRIER FAMILY 27 (FATTY ACID TRANSPORTER), MEMBER 5; SLC27A5","url":"https://www.omim.org/entry/603314"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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Extracts from skin and intestine of FATP4 null mice showed reduced esterification specifically for C24:0 but not C16:0 or C18:1, suggesting FATP4 preferentially activates very long chain fatty acids in vivo.\",\n      \"method\": \"Affinity purification of FLAG-tagged FATP4, kinetic enzymatic assays, acyl-CoA synthetase activity in tissue extracts from knockout mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — purified protein with kinetic analysis plus corroborating knockout tissue data, multiple orthogonal methods\",\n      \"pmids\": [\"15653672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Epidermal keratinocyte-specific inactivation of Fatp4 reproduces the hyperproliferative hyperkeratosis and disturbed epidermal barrier seen in global Fatp4 knockouts, establishing that intrinsic Fatp4 deficiency in keratinocytes (not secondary loss in other organs) is responsible for the epidermal structural abnormalities.\",\n      \"method\": \"Conditional keratinocyte-specific Fatp4 knockout (Cre-lox), histology, epidermal barrier assays\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined tissue-specific phenotype, corroborated by rescue experiments in other studies\",\n      \"pmids\": [\"16354193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"FATP4 localizes to the endoplasmic reticulum (not the plasma membrane), and its enhancement of cellular fatty acid uptake is dependent on its acyl-CoA synthetase enzymatic activity; ER-localized FATP4 drives fatty acid uptake indirectly by esterification (metabolic trapping) rather than by direct translocation at the plasma membrane.\",\n      \"method\": \"Immunofluorescence localization, quantitative fatty acid uptake assays at single-cell level, enzymatic activity mutant analysis, expression of mitochondrial acyl-CoA synthetase as control\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — subcellular localization with functional consequence, activity-dependent uptake assay, replicated across multiple labs\",\n      \"pmids\": [\"17062637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Keratinocyte-specific expression of FATP4 rescues the neonatally lethal skin phenotype of Fatp4-/- mice, while expression of an FATP4 variant with mutations in the acyl-CoA synthetase domain fails to rescue, establishing that the acyl-CoA synthetase activity of FATP4 in suprabasal keratinocytes is necessary for normal skin development and cornified envelope formation.\",\n      \"method\": \"Transgenic rescue experiments (wild-type and ACS-domain mutant FATP4), tetraploid aggregation, phenotypic analysis of skin barrier\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structure-function rescue with active site mutant, multiple transgenic lines tested\",\n      \"pmids\": [\"17401141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Independent overexpression of FATP4 in rat skeletal muscle increases fatty acid transport; FATP4 is 1.7-fold more effective than FABPpm and FATP1 at enhancing fatty acid transport. All transporters increased long chain fatty acid oxidation, but FABPpm and FAT/CD36 had 3-fold greater effects on oxidation than FATP1 and FATP4. FATP4 overexpression did not alter rates of fatty acid esterification into triacylglycerols.\",\n      \"method\": \"In vivo electroporation-mediated overexpression in rat skeletal muscle, fatty acid transport assays, oxidation and esterification measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo overexpression with defined metabolic readouts, single lab\",\n      \"pmids\": [\"19380575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"FATP4-deficient epidermis exhibits increased expression of EGF family members (Ereg, Areg, Epgn) associated with elevated EGFR activation and downstream STAT3 signaling in suprabasal cells; pharmacological inhibition of EGFR or STAT3 attenuated STAT3 activation and partially suppressed skin thickening and barrier abnormalities, placing FATP4 activity upstream of EGFR-STAT3 signaling in skin development.\",\n      \"method\": \"Gene expression profiling in Fatp4 mutant skin, EGFR/STAT3 activation assays, pharmacological inhibition (Tyrphostin AG1478, curcumin) with phenotypic readout\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via pharmacological inhibition with cellular phenotype, single lab\",\n      \"pmids\": [\"20513444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FATP4 localizes to the endoplasmic reticulum (not plasma membrane) in C2C12 muscle cells; stable FATP4 overexpression doubles acyl-CoA synthetase activity and cellular oleate uptake. Insulin treatment increases acyl-CoA synthetase activity within minutes in a wortmannin-sensitive manner, and affinity-purified FATP4 from insulin-treated cells shows enhanced enzyme activity, suggesting insulin regulation of FATP4 enzymatic activity as a mechanism for insulin-stimulated fatty acid uptake.\",\n      \"method\": \"Stable overexpression, acyl-CoA synthetase activity assays, subcellular fractionation and immunofluorescence, insulin treatment with wortmannin inhibition, affinity purification of FATP4 from insulin-treated cells\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzyme activity assay with purified protein from treated cells, localization confirmed by two methods, single lab\",\n      \"pmids\": [\"21750264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FATP2 and FATP4 localize to the ER in HuH7 and HepG2 hepatoma cells; overexpression of FATP4 increases acyl-CoA synthetase activity and enhances uptake of [3H]-oleic acid and fluorescent Bodipy-C12 fatty acid, consistent with ER-based metabolic trapping as the mechanism for FA uptake enhancement.\",\n      \"method\": \"Immunofluorescence localization, overexpression, acyl-CoA synthetase activity assays, radiolabeled and fluorescent fatty acid uptake assays, quantitative FACS\",\n      \"journal\": \"International journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal uptake assays plus localization, single lab\",\n      \"pmids\": [\"22022213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Adipocyte-specific Fatp4 knockout mice show no change in fatty acid uptake into adipose tissue under standard conditions, establishing that FATP4 is not required for fatty acid uptake in adipocytes. Under high-fat diet, Fatp4-deficient adipocytes show altered metabolism of complex lipids (decreased phospholipids, sphingomyelin, and cholesteryl esters) with adipose hypertrophy.\",\n      \"method\": \"Adipocyte-specific Cre-lox knockout, radiolabeled fatty acid uptake assays, lipidomics, histology, metabolic phenotyping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — negative result for FA uptake with direct assay in tissue-specific KO, positive lipidomic result, multiple methods\",\n      \"pmids\": [\"21808061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FATP1 and ACSVL4/FATP4 both localize to the ER (not plasma membrane) in 3T3-L1 adipocytes as confirmed by confocal microscopy and subcellular fractionation; stable overexpression increases acyl-CoA synthetase activity and fatty acid uptake. Insulin increases fatty acid uptake without changing the ER localization of FATP1 or FATP4.\",\n      \"method\": \"Retroviral stable overexpression, confocal microscopy, subcellular fractionation, acyl-CoA synthetase activity assays, fatty acid uptake assays, insulin treatment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — localization confirmed by two orthogonal methods, functional assays, single lab\",\n      \"pmids\": [\"23024797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FATP4 was identified as a negative regulator of RPE65 isomerase activity; FATP4 inhibits synthesis of 11-cis-retinol (11cROL) in the visual cycle through two mechanisms: (1) competition with RPE65 for substrate, and (2) production of lignoceroyl (C24:0)-CoA which inhibits 11cROL synthesis. FATP4-deficient RPE shows significantly higher RPE65 isomerase activity, faster 11-cis-retinaldehyde regeneration, and faster rod light sensitivity recovery, but increased accumulation of cytotoxic all-trans retinaldehyde and hypersusceptibility to light-induced photoreceptor degeneration.\",\n      \"method\": \"Expression screening of bovine RPE cDNA library, FATP4-deficient mice, isomerase activity assays, retinoid analysis, electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including enzymatic activity, substrate competition assay, and in vivo functional validation in knockout mice\",\n      \"pmids\": [\"23407971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FATP4 and ichthyin (NIPAL4 product) show close proximity interaction in the upper stratum granulosum of normal epidermis by proximity ligation assay. In IPS skin lacking FATP4, ichthyin expression is reduced; conversely, NIPAL4-mutant skin shows increased FATP4 staining, suggesting mutual interdependence in epidermal lipid processing.\",\n      \"method\": \"Immunofluorescence, proximity ligation assay (PLA) in human skin biopsies and organotypic epidermis with siRNA silencing\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proximity ligation assay confirms interaction, with siRNA corroboration in two models, single lab\",\n      \"pmids\": [\"23290633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SLC27A4 directly interacts with ATG4B (a cysteine protease required for autophagy) in lung cancer cell lines, as shown by co-immunoprecipitation and GST-pull down assays; SLC27A4 stabilizes ATG4B protein and maintains its intracellular concentration, promoting rapid ATG4B-mediated autophagy in response to chemotherapy stress.\",\n      \"method\": \"Tandem affinity purification/mass spectrometry (TAP/MS), co-immunoprecipitation, GST-pulldown, siRNA knockdown with autophagy and drug sensitivity readouts\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reciprocal pulldown confirms interaction, functional siRNA data, but cancer cell line context and single lab\",\n      \"pmids\": [\"26662804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ETEC K88 challenge reduces FATP4 protein expression in intestinal epithelial cells via phosphorylation of ERK1/2 and PPARγ (ERK1/2-PPARγ pathway), impairing FATP4-dependent long-chain fatty acid (LCFA) uptake; gene knockdown and overexpression confirmed FATP4 as the responsible transporter for LCFA (C16:0) but not medium-chain fatty acid (C12:0) uptake in IPEC-J2 cells.\",\n      \"method\": \"In vivo piglet model, polarized IPEC-J2 cell model, FATP4 knockdown and overexpression, ERK1/2 inhibitor (U0126) and PPARγ antagonist (T0070907), BODIPY-labeled fatty acid uptake assays\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway placement via pharmacological inhibitors and gene KD/OE with defined uptake readout, single lab\",\n      \"pmids\": [\"31281267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FATP4 exhibits acyl-CoA synthetase activity toward ω-hydroxy fatty acids, intermediates in the acylceramide synthetic pathway; Fatp4 knockout mice show severely reduced total acylceramide levels (~10% of wild type), decreased and shortened saturated non-acylated ceramides, and reduced ELOVL1 elongase expression, establishing FATP4 as the acyl-CoA synthetase responsible for acylceramide synthesis required for epidermal permeability barrier formation.\",\n      \"method\": \"In vitro ACS activity assay with ω-hydroxy fatty acid substrate, Fatp4 KO mice lipidomics, siRNA knockdown in human keratinocytes, ELOVL1 expression analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic activity with specific substrate plus KO mouse lipidomics plus human cell knockdown, multiple orthogonal methods\",\n      \"pmids\": [\"31974308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FATP4 inactivation in macrophages (THP-1 knockdown and bone marrow-derived macrophages from Fatp4M-/- mice) causes a metabolic shift towards triacylglycerides, decreases ceramide levels, and attenuates M1 activation- or ER stress-induced pro-inflammatory cytokine release (IL-8, TNF-α, IL-12). FATP4 deficiency specifically attenuates tunicamycin-induced activation of IRE1α but not other unfolded protein response pathways.\",\n      \"method\": \"siRNA knockdown in THP-1-derived macrophages, macrophage-specific Fatp4-KO mice (BMDMs), lipidomics, cytokine measurements, UPR pathway analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two complementary KD/KO models with lipidomic and functional readouts, single lab\",\n      \"pmids\": [\"33900381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PLIN5 interacts with FATP4 at lipid droplet-mitochondria contact sites; the C-terminal domains of PLIN5 and FATP4 constitute a minimal protein interaction sufficient to induce organelle contacts. Phosphorylation of PLIN5 upon starvation promotes LD-to-mitochondria fatty acid trafficking and β-oxidation, requiring an intact PLIN5 mitochondrial tethering domain and functional FATP4 on mitochondria for conversion of fatty acids to acyl-CoAs.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping (C-terminal interaction), organelle contact site imaging, starvation/phosphorylation experiments in human and murine myoblasts, β-oxidation assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP with domain mapping, functional contact site induction, multiple cell models, β-oxidation readout\",\n      \"pmids\": [\"37290445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SLC27A4 overexpression promotes selective uptake of mono-unsaturated fatty acids (MUFAs) in HCC cells, leading to elevated MUFA-containing phosphatidylcholine and phosphatidylethanolamine, which confers resistance to lipid peroxidation and ferroptosis; SLC27A4 silencing sensitizes HCC cells to sorafenib both in vitro and in vivo.\",\n      \"method\": \"Lipidomic analysis, SLC27A4 overexpression and siRNA knockdown, ferroptosis assays, xenograft mouse model\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lipidomics plus in vitro/in vivo KD with defined ferroptosis readout, single lab\",\n      \"pmids\": [\"36924851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hepatocyte-specific SLC27A4 deletion ameliorates NAFLD in mice; SLC27A4 overexpression increases hepatic phosphatidylcholine (PC) accumulation, which activates pregnane X receptor (PXR) signaling and further induces SLC27A4 expression forming a feedforward loop. PXR overexpression reverses the protective effect of Slc27a4 deletion, while PXR deficiency reduces the effect of Slc27a4 overexpression on NAFLD.\",\n      \"method\": \"AAV-mediated liver overexpression, hepatocyte-specific Cre-lox KO, lipidomics, RNA-seq, PXR genetic epistasis (overexpression and KO crosses), biochemical and histological analysis\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with gain- and loss-of-function for both SLC27A4 and PXR, lipidomic mechanism, multiple dietary models\",\n      \"pmids\": [\"39489412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Enterocyte-specific Fatp4 knockout mice show a metabolic shift from very long-chain to long-chain fatty acids and from polar lipids (ceramides, sphingomyelin, phosphatidylcholine) to neutral lipids predominantly in the ileum, resulting in elevated plasma triglycerides, chylomicrons, and lipoproteins after fat loading or high-fat feeding, establishing FATP4's role in controlling intestinal lipid processing and blood lipid levels.\",\n      \"method\": \"Villin-Cre enterocyte-specific Fatp4 KO mice, lipidomics of intestinal segments, plasma lipid and lipoprotein measurements after oral fat loading and chronic HFHC feeding\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tissue-specific KO with detailed lipidomics and multiple dietary challenges, single lab\",\n      \"pmids\": [\"38915276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"sEV-NAMPT activates NF-κB through TLR4, leading to elevated SLC27A4 expression; SLC27A4 then increases intracellular triacylglycerol (TG) and dihydroxyacetone phosphate (DHAP) levels, linking lipid metabolism to glycolysis by facilitating conversion of glycerol-3-phosphate to DHAP via lipolysis of TG.\",\n      \"method\": \"Mass spectrometry protein analysis of HCC-derived sEV, NF-κB signaling assays, lipidomic and metabolomic analysis, SLC27A4 knockdown/overexpression, hepatic lipase activity assays\",\n      \"journal\": \"Journal of extracellular vesicles\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lipidomics plus metabolomics with KD/OE and upstream signaling pathway, single lab\",\n      \"pmids\": [\"40237223\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC27A4/FATP4 is an integral membrane very long-chain acyl-CoA synthetase localized primarily to the endoplasmic reticulum (and mitochondria in some contexts) that drives cellular fatty acid uptake indirectly through metabolic trapping via esterification rather than direct plasma membrane translocation; in skin, its ACS activity toward ω-hydroxy fatty acids is essential for acylceramide synthesis and epidermal permeability barrier formation (loss causes ichthyosis prematurity syndrome); in the RPE it inhibits RPE65 isomerase activity by substrate competition and via C24:0-CoA production; it interacts with PLIN5 at lipid droplet-mitochondria contact sites to channel fatty acids to β-oxidation; in macrophages its ACS activity channels fatty acids into ceramides/phospholipids, and loss shifts metabolism toward triacylglycerides and suppresses pro-inflammatory cytokine release; in liver it drives phosphatidylcholine accumulation that activates PXR in a feedforward loop promoting steatosis; and in the intestine it controls the balance between polar and neutral lipids in the ileum to regulate plasma lipid levels.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC27A4 (FATP4) is an endoplasmic reticulum-localized very long-chain acyl-CoA synthetase that governs cellular fatty acid handling by esterifying fatty acids to acyl-CoAs, thereby driving fatty acid uptake indirectly through metabolic trapping rather than direct plasma-membrane translocation [#0, #4]. Its enzyme is biased toward very long-chain substrates (e.g. C24:0) over long-chain fatty acids, is insensitive to triacsin C, and is feedback-inhibited by acyl-CoA [#0, #2]. ER residence with activity-dependent uptake enhancement has been confirmed across muscle, hepatoma, and adipocyte cell models [#4, #8, #9, #11]. In skin, FATP4 acyl-CoA synthetase activity in suprabasal keratinocytes is essential for epidermal permeability barrier formation: it activates \\u03c9-hydroxy fatty acids for acylceramide synthesis, and its loss abolishes acylceramides and causes hyperproliferative hyperkeratosis with a defective barrier, downstream of which EGFR-STAT3 signaling is aberrantly activated [#1, #3, #5, #16, #7]. Beyond skin, FATP4 channels fatty acids into distinct lipid pools in a tissue-specific manner\\u2014partitioning toward complex/polar lipids in adipocytes, macrophages, and enterocytes\\u2014so that its loss shifts metabolism toward neutral lipids (triacylglycerides) and alters inflammatory output and plasma lipid levels [#10, #17, #21]. It interacts with PLIN5 at lipid droplet-mitochondria contact sites to supply acyl-CoAs for \\u03b2-oxidation [#18], negatively regulates RPE65 isomerase activity in the visual cycle by substrate competition and C24:0-CoA production [#12], and in liver drives phosphatidylcholine accumulation that activates PXR in a feedforward loop promoting steatosis [#20]. In cancer contexts it has been linked to MUFA-dependent ferroptosis resistance and to ATG4B-mediated autophagy [#19, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established that FATP4 is an enzyme\\u2014a very long-chain acyl-CoA synthetase\\u2014rather than a passive transporter, defining its core biochemical activity.\",\n      \"evidence\": \"Transfection of FATP4 cDNA into COS1 cells with acyl-CoA synthetase activity assays on membrane extracts\",\n      \"pmids\": [\"11404000\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define subcellular site of activity\", \"Did not establish physiological substrate preference in vivo\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated an essential in vivo function in epidermal barrier formation, linking FATP4 loss to defective ceramide fatty acid composition.\",\n      \"evidence\": \"Targeted Fatp4 knockout mice with histology and epidermal ceramide lipid analysis\",\n      \"pmids\": [\"12821645\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Could not distinguish keratinocyte-intrinsic from systemic effects\", \"Molecular target lipid in ceramide synthesis not yet defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved substrate specificity and confirmed enzymatic identity using purified protein plus knockout tissue, showing preferential activation of very long-chain fatty acids in vivo.\",\n      \"evidence\": \"Affinity-purified FLAG-FATP4 kinetics and acyl-CoA synthetase assays in knockout skin/intestine extracts\",\n      \"pmids\": [\"15653672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address localization\", \"Mechanism of feedback inhibition not structurally defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that FATP4 enhances fatty acid uptake indirectly via ER-based metabolic trapping (esterification), settling the transporter-versus-enzyme question of how uptake is driven.\",\n      \"evidence\": \"Immunofluorescence localization, single-cell uptake assays, and ACS-activity mutant analysis\",\n      \"pmids\": [\"17062637\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not rule out tissue-specific plasma-membrane pools\", \"Quantitative contribution to whole-body FA flux unaddressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed keratinocyte-intrinsic FATP4 deficiency suffices for the skin phenotype and that its ACS catalytic activity is required, linking enzyme function directly to barrier development.\",\n      \"evidence\": \"Keratinocyte-specific conditional knockout and transgenic rescue with wild-type versus ACS-domain mutant FATP4\",\n      \"pmids\": [\"16354193\", \"17401141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lipid substrate in keratinocytes not yet identified\", \"Downstream signaling consequences not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placed FATP4 activity upstream of EGFR-STAT3 signaling, connecting a metabolic lipid defect to a proliferative signaling cascade in skin.\",\n      \"evidence\": \"Expression profiling in mutant skin plus pharmacological EGFR/STAT3 inhibition with phenotypic rescue\",\n      \"pmids\": [\"20513444\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal lipid linking FATP4 loss to EGF ligand induction unidentified\", \"Pharmacological inhibitors lack genetic confirmation\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Generalized ER localization and metabolic-trapping uptake mechanism across muscle, hepatoma, and adipocyte cells, and linked insulin to acute regulation of FATP4 enzymatic activity.\",\n      \"evidence\": \"Stable overexpression, fractionation/confocal localization, ACS and FA-uptake assays with insulin/wortmannin treatment\",\n      \"pmids\": [\"21750264\", \"22022213\", \"23024797\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of insulin-induced activity increase not defined\", \"Phosphorylation or modification of FATP4 not directly demonstrated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated FATP4 is dispensable for adipocyte fatty acid uptake but shapes complex lipid metabolism, refining the view that its role is biosynthetic partitioning rather than bulk uptake.\",\n      \"evidence\": \"Adipocyte-specific knockout with radiolabeled uptake assays and lipidomics under high-fat diet\",\n      \"pmids\": [\"21808061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundant transporters compensating for uptake unidentified\", \"Mechanism linking loss to adipose hypertrophy unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified FATP4 as a negative regulator of the RPE65 visual cycle isomerase, expanding its role beyond bulk lipid metabolism to enzyme-level regulation via substrate competition and product (C24:0-CoA) inhibition.\",\n      \"evidence\": \"Expression cloning, FATP4-deficient RPE isomerase and retinoid analyses, and electrophysiology\",\n      \"pmids\": [\"23407971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physical interaction with RPE65 not established\", \"Relative weight of competition versus C24:0-CoA inhibition unquantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Provided in situ evidence that FATP4 functions in proximity to NIPAL4/ichthyin in epidermis, implicating a coordinated lipid-processing module in barrier formation.\",\n      \"evidence\": \"Proximity ligation assay in human skin and organotypic epidermis with siRNA silencing\",\n      \"pmids\": [\"23290633\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PLA proximity does not prove direct binding\", \"Functional consequence of the interaction not biochemically defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Pinpointed the biochemical substrate explaining the skin phenotype: FATP4 activates \\u03c9-hydroxy fatty acids for acylceramide synthesis essential for the permeability barrier.\",\n      \"evidence\": \"In vitro ACS assay with \\u03c9-hydroxy fatty acid substrate, knockout mouse lipidomics, and human keratinocyte knockdown\",\n      \"pmids\": [\"31974308\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism coupling FATP4 to ELOVL1 expression unclear\", \"Structural basis of \\u03c9-hydroxy substrate recognition unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed FATP4 controls macrophage lipid partitioning and inflammatory output, linking its ACS activity to ceramide production and IRE1\\u03b1-dependent cytokine release.\",\n      \"evidence\": \"THP-1 knockdown and macrophage-specific knockout BMDMs with lipidomics, cytokine, and UPR analyses\",\n      \"pmids\": [\"33900381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting FATP4 lipids to selective IRE1\\u03b1 activation undefined\", \"Single lab without independent replication\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a direct PLIN5-FATP4 interaction tethering lipid droplets to mitochondria to channel fatty acids into \\u03b2-oxidation, establishing a contact-site role in fuel delivery.\",\n      \"evidence\": \"Reciprocal Co-IP, C-terminal domain mapping, contact-site imaging, and \\u03b2-oxidation assays in myoblasts\",\n      \"pmids\": [\"37290445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mitochondrial pool of FATP4 versus ER pool not fully resolved\", \"Regulation of the interaction beyond starvation/phosphorylation unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established hepatic and intestinal FATP4 as drivers of systemic lipid pathology\\u2014via a phosphatidylcholine-PXR feedforward loop in liver and polar/neutral lipid balance in the ileum controlling plasma lipids.\",\n      \"evidence\": \"Hepatocyte- and enterocyte-specific knockouts plus AAV overexpression with lipidomics, RNA-seq, and PXR genetic epistasis\",\n      \"pmids\": [\"39489412\", \"38915276\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of PC-mediated PXR activation not structurally defined\", \"Translation of mouse intestinal findings to human lipid disorders unaddressed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked FATP4 to cancer cell survival through MUFA-driven membrane composition conferring ferroptosis resistance and through ATG4B-stabilized autophagy.\",\n      \"evidence\": \"Lipidomics with overexpression/knockdown and ferroptosis assays in HCC; TAP/MS and reciprocal pulldown with ATG4B in lung cancer cells\",\n      \"pmids\": [\"36924851\", \"26662804\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ATG4B interaction tested only in cancer cell lines without in vivo validation\", \"Whether autophagy role depends on ACS activity unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FATP4's single acyl-CoA synthetase activity is differentially routed to distinct lipid fates (acylceramides, complex phospholipids, \\u03b2-oxidation, PXR-activating PC) across tissues, and the structural basis of its substrate selectivity and protein partnerships, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No crystal/cryo-EM structure to explain VLCFA selectivity\", \"Mechanism selecting biosynthetic versus catabolic acyl-CoA channeling unknown\", \"Direct partners beyond PLIN5/ATG4B largely uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 2, 5, 16]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 16]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [4, 9, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4, 8, 9, 11]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 16, 20, 21]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 3, 5, 16]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PLIN5\", \"ATG4B\", \"NIPAL4\", \"RPE65\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}