{"gene":"OSBPL8","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2007,"finding":"ORP8 localizes to the endoplasmic reticulum via its C-terminal transmembrane span and binds 25-hydroxycholesterol, identifying it as an ER oxysterol-binding protein. Silencing ORP8 in THP-1 macrophages increased ABCA1 expression and cholesterol efflux to lipid-free apolipoprotein A-I; the effect was partially attenuated by mutation of the DR4 element in the ABCA1 promoter and synergized with LXR agonist treatment, indicating ORP8 negatively regulates ABCA1 transcription involving both LXR and E-box functions.","method":"RNA interference (siRNA), ABCA1 promoter-luciferase reporter assays, cholesterol efflux assays, ligand binding studies","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi knockdown with defined molecular readout (ABCA1 reporter), single lab with multiple orthogonal methods (binding assay, luciferase reporter, efflux assay)","pmids":["17991739"],"is_preprint":false},{"year":2011,"finding":"ORP8 binds cholesterol in vitro (in addition to 25-hydroxycholesterol). ORP8 overexpression in mouse liver reduced nuclear SREBP-1 and SREBP-2 and their target gene mRNAs, and suppressed cholesterol biosynthesis. Yeast two-hybrid, BiFC, and co-immunoprecipitation identified nuclear pore component Nup62 as a direct interaction partner of ORP8; ORP8 and Nup62 co-localize at the nuclear envelope, and depletion of Nup62 inhibited the effect of ORP8 overexpression on nSREBPs.","method":"In vitro cholesterol binding, adenoviral overexpression in mouse liver, [3H]acetate pulse-labeling, yeast two-hybrid, bimolecular fluorescence complementation (BiFC), co-immunoprecipitation, confocal immunofluorescence, Nup62 RNAi","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (BiFC, Co-IP, yeast two-hybrid, in vivo overexpression), single lab","pmids":["21698267"],"is_preprint":false},{"year":2012,"finding":"ORP8 silencing in RAW264.7 macrophages increased expression and altered subcellular distribution of its interaction partner Nup62 (including intranuclear localization), enhanced cell migration, and promoted a more pronounced microtubule cytoskeleton. ORP8 competed with Exo70 for binding to Nup62, and Nup62 knockdown abolished the migration-enhancing effect of ORP8 silencing, placing Nup62 downstream of ORP8 in migration control.","method":"Stable shRNA lentiviral knockdown, microarray transcriptomics, confocal microscopy, migration assays, Nup62 RNAi epistasis","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (double KD), migration phenotype, interaction competition assay; single lab","pmids":["22683860"],"is_preprint":false},{"year":2014,"finding":"Yeast two-hybrid screening followed by pulldown and co-immunoprecipitation identified SPAG5/Astrin as an interaction partner of ORP8. Overexpressed ORP8 recruited SPAG5 onto ER membranes in interphase cells. ORP8 overexpression or 25-hydroxycholesterol treatment caused G2/M accumulation in HepG2 cells; ORP8 knockdown strongly inhibited the oxysterol-induced G2/M arrest, and SPAG5 knockdown reduced the cell-cycle effects of both ORP8 overexpression and 25-OHC, placing SPAG5 downstream of ORP8.","method":"Yeast two-hybrid, pulldown, co-immunoprecipitation, flow cytometry cell cycle analysis, RNAi knockdown epistasis","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP/pulldown, genetic epistasis with defined cell-cycle phenotype; single lab","pmids":["24424245"],"is_preprint":false},{"year":2015,"finding":"ORP5 and ORP8 are ER integral membrane proteins that tether the ER to the plasma membrane via PH domain interaction with PI4P. Their OSBP-related domains (ORDs) carry either PI4P or phosphatidylserine (PS) and exchange these lipids between bilayers, mediating PI4P/PS countertransport: delivering PI4P to ER-localized Sac1 phosphatase for degradation and PS from ER to PM. Gain- and loss-of-function experiments showed these activities control PM PI4P levels and selectively enrich PS at the PM.","method":"Gain- and loss-of-function experiments, lipid transfer assays, subcellular fractionation, imaging of ER-PM contacts","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro lipid transfer assays, gain/loss-of-function, mechanistically defined countertransport activity; replicated by multiple subsequent labs","pmids":["26206935"],"is_preprint":false},{"year":2015,"finding":"ORP8 overexpression triggered apoptosis in HCC cells coinciding with relocation of cytoplasmic Fas to the cell plasma membrane and FasL upregulation. ORP8-induced Fas translocation was p53-dependent, and FasL induction occurred via the ER stress response.","method":"ORP8 overexpression in HCC cell lines and primary cells, co-culture with T cells/Jurkat cells, western blot, confocal microscopy, xenograft tumor model","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression with defined apoptotic phenotype, p53 dependency shown, multiple cell systems; single lab","pmids":["25596532"],"is_preprint":false},{"year":2016,"finding":"In addition to ER-PM contact sites, ORP5 and ORP8 localize to ER-mitochondria contacts (MAM) and interact physically with the outer mitochondrial membrane protein PTPIP51. A functional lipid transfer (ORD) domain was required for this MAM localization. ORP5/ORP8 depletion caused defects in mitochondria morphology and respiratory function.","method":"Confocal and electron microscopy, co-immunoprecipitation with PTPIP51, domain deletion analysis, mitochondrial respiration assays, RNAi knockdown","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain requirement experiment, functional respiratory readout, replicated by later MAM studies","pmids":["27113756"],"is_preprint":false},{"year":2017,"finding":"The pleckstrin homology (PH) domain of ORP8 mediates recruitment to ER-PM contact sites via binding to PtdIns(4,5)P2, not PtdIns(4)P. The ORD of ORP8 can extract and transport multiple phosphoinositides in vitro. Knockdown of both ORP5 and ORP8 increases PM PtdIns(4,5)P2 levels with little effect on PtdIns(4)P, indicating PtdIns(4,5)P2 can serve as a co-exchanger for cargo lipid transport by ORP8.","method":"In vitro lipid extraction/transport assays with purified ORD, PM recruitment assays, PH domain binding studies, siRNA double knockdown with lipid level measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro lipid transport assay with purified domain, cellular knockdown with quantitative lipid readout; single lab but multiple orthogonal methods","pmids":["28970484"],"is_preprint":false},{"year":2020,"finding":"ORP8 overexpression in non-small cell lung cancer cells induced apoptosis via release of cytochrome c from mitochondria into the cytoplasm.","method":"ORP8 overexpression, western blot and confocal microscopy for cytochrome c release, MTS/anchorage-independent growth assays","journal":"Oncology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single overexpression experiment, single lab, limited mechanistic dissection beyond cytochrome c release","pmids":["32323800"],"is_preprint":false},{"year":2022,"finding":"ORP5 and ORP8 localize to MAM subdomains enriched in phosphatidic acid and control lipid droplet (LD) biogenesis at these sites. ORP5/8 regulate seipin recruitment to MAM-LD contacts; loss of ORP5/8 impairs LD biogenesis, and intact ER-mitochondria contact sites are required for this ORP5/8 function.","method":"Fluorescence microscopy, siRNA knockdown, seipin localization assays, LD biogenesis quantification, ER-mitochondria contact site disruption","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cellular phenotype (LD biogenesis defect), mechanistic link to seipin recruitment, contact site requirement demonstrated; single lab","pmids":["35969857"],"is_preprint":false},{"year":2023,"finding":"ORP8 functions as a lipophagy receptor by localizing to lipid droplets and directly interacting with phagophore-anchored LC3/GABARAPs to mediate LD encapsulation by autophagosomes. This function is independent of ORP8's lipid transporter activity. Upon lipophagy induction, AMPK phosphorylates ORP8, enhancing its affinity for LC3/GABARAPs. ORP8 deletion or disruption of the ORP8-LC3/GABARAP interaction causes LD and triglyceride accumulation; ORP8 overexpression alleviates liver lipid accumulation in ob/ob mice, and Osbpl8−/− mice show liver lipid clearance defects.","method":"Co-immunoprecipitation (ORP8-LC3/GABARAP), AMPK phosphorylation assays, ORP8 KO mice, ob/ob mouse ORP8 overexpression, lipid transfer domain mutants, LD and triglyceride quantification","journal":"Protein & cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, genetic KO mouse model, AMPK phosphorylation mechanistically linked, lipid-transfer-independent function demonstrated by domain mutant, replicated in two in vivo models","pmids":["37707322"],"is_preprint":false},{"year":2023,"finding":"Crystal structure of the ORP8 lipid transport domain (ORD8) was solved, revealing a β-barrel fold with anti-parallel β-strands and a large cavity (~1860 Å3) as the lipid-binding site. The lid region is required for stable lipid binding and slows transport while stabilizing cargo; fluorescence assays showed differential transport efficiencies for PS versus PI4P.","method":"X-ray crystallography, computer docking simulations, fluorescence lipid transport assays, comparative experiments between lid-deleted and full-length ORD8","journal":"Cells","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with functional validation (fluorescence transport assay, lid mutant), single lab but multiple orthogonal methods","pmids":["37566053"],"is_preprint":false},{"year":2023,"finding":"STIM1-formed ER-PM junctions are required for PI4P/PS exchange by ORP5 and ORP8. ORP5 and ORP8 operate as a rheostat setting junctional PI4P/PtdSer ratio with reciprocal modes: ORP5 sets low and ORP8 sets high junctional PI4P/PtdSer ratio. This ratio controls STIM1-STIM1 and STIM1-Orai1 interactions, SERCA pump activity, Ca2+ oscillation patterns, and NFAT nuclear translocation. Targeting the ORDs to the STIM1 ER subdomain reversed ORP5/ORP8 function.","method":"Targeted ORD domain expression at PM vs ER subdomains, targeted PtdSer-specific PLA1a1, Ca2+ imaging, NFAT translocation assays, STIM1 interaction measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional readouts (Ca2+ signaling, NFAT, STIM1 interactions), domain-swap experiments; single lab","pmids":["37607230"],"is_preprint":false},{"year":2023,"finding":"Sec22b co-precipitates with ORP8 at ER-phagosome membrane contact sites. Wild-type but not lipid-transfer-mutant ORP8 rescues phagosomal PI4P levels and reduces antigen degradation in Sec22b knockdown cells, and restores phagolysosome fusion, establishing that ORP8's PS/PI4P exchange activity downstream of Sec22b tethering controls phagosome maturation.","method":"Co-immunoprecipitation (Sec22b–ORP8), siRNA knockdown, phagosomal lipid quantification, antigen degradation assays, phagolysosome fusion assays with ORP8 mutant rescue","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, functional rescue with lipid-transfer mutant establishing enzymatic requirement, epistasis; single lab","pmids":["37794132"],"is_preprint":false},{"year":2023,"finding":"ORP8 overexpression in renal cell carcinoma cells accelerated ubiquitin-mediated proteasomal degradation of Stathmin1, leading to increased microtubule polymerization and suppression of RCC cell growth, migration, and invasion.","method":"ORP8 overexpression and knockdown, proteasome inhibitor experiments, western blot for Stathmin1, microtubule polymerization assays, functional cell assays","journal":"Experimental cell research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — overexpression phenotype with mechanistic proposal (ubiquitin-proteasome), single lab, limited biochemical dissection of direct vs indirect effect","pmids":["37054771"],"is_preprint":false},{"year":2025,"finding":"Osbpl8 remodels lipid metabolism in macrophages by inhibiting excessive IRE1α-XBP1-related ER stress. Osbpl8 delivered via extracellular vesicles from anti-inflammatory BMDMs suppressed inflammatory responses and lipotoxicity in hepatocytes during MASH.","method":"LC-MS/MS proteomic identification, shRNA knockdown, palmitic acid lipotoxicity model, IRE1α-XBP1 pathway markers, AAV-shRNA in vivo","journal":"Molecular medicine (Cambridge, Mass.)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanism inferred from pathway markers (IRE1α-XBP1), limited direct mechanistic dissection of how ORP8 affects ER stress","pmids":["40448016"],"is_preprint":false},{"year":2026,"finding":"OSBPL8 recruits GPX1 to the ER membrane, where GPX1 directly reduces peroxidized phosphatidic acid (PA-OOH) generated by ROS. This GPX1-OSBPL8 axis drives a noncanonical ferroptosis pathway at the ER (distinct from GPX4-dependent plasma membrane ferroptosis); ROS-driven lipid peroxidation accumulates at the ER before plasma membrane rupture. Knockdown of either OSBPL8 or GPX1 promotes ROS-induced ferroptosis and suppresses tumor growth.","method":"Co-immunoprecipitation (GPX1-OSBPL8), subcellular fractionation (ER lipid peroxidation), siRNA knockdown, in vivo tumor growth assays, lipidomics (PA peroxidation)","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — Co-IP establishing direct interaction, organelle-specific lipid peroxidation biochemistry, in vitro and in vivo knockdown with defined ferroptosis phenotype, published in high-rigor venue","pmids":["41720096"],"is_preprint":false},{"year":2025,"finding":"Glycosphingolipids (GM3 and SM4) are required to maintain ORP8 (and ORP5) localization to ER-PM membrane contact sites. Genetic deletion or pharmacological inhibition of GM3/SM4 biosynthetic enzymes displaced PI4KIIIα and its adaptor EFR3A from the PM, reducing PM PI4P content and disrupting ORP8 PM interactions, consequently reducing PS transport to the PM.","method":"High-resolution imaging, genetic deletion and pharmacological inhibition of GSL biosynthesis enzymes, quantitative lipid measurements (PI4P, PS)","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 2 / Weak — imaging and genetic perturbation, mechanistic link established but preprint (not peer-reviewed), single lab","pmids":["bio_10.1101_2025.09.26.678863"],"is_preprint":true}],"current_model":"OSBPL8/ORP8 is an ER-anchored lipid transfer protein that countertransports phosphatidylserine (PS) from the ER to the plasma membrane in exchange for PI4P (which is delivered to Sac1 for degradation) at ER-PM contact sites; it also transfers PS at ER-mitochondria contacts (MAMs) where it interacts with PTPIP51 and controls mitochondrial morphology and respiration, orchestrates lipid droplet biogenesis at MAMs by regulating seipin recruitment, functions as a lipophagy receptor on LDs by directly binding LC3/GABARAPs in an AMPK-phosphorylation-dependent manner, recruits GPX1 to the ER to reduce peroxidized phosphatidic acid as part of a noncanonical ferroptosis pathway, and in the nucleus/nuclear envelope interacts with Nup62 to modulate SREBP activity, macrophage migration, and cell-cycle progression via SPAG5."},"narrative":{"mechanistic_narrative":"OSBPL8 (ORP8) is an ER-anchored lipid transfer protein that establishes and exploits membrane contact sites to countertransport phospholipids and thereby control plasma membrane lipid identity, organelle physiology, and lipid catabolism [PMID:26206935, PMID:27113756]. Anchored in the ER through a C-terminal transmembrane span, it tethers the ER to the plasma membrane via a PH domain that engages PM phosphoinositides, while its OSBP-related domain (ORD) extracts and exchanges phosphatidylserine for PI4P, delivering PI4P to ER Sac1 for degradation and enriching PS at the PM [PMID:26206935, PMID:28970484]. The ORD adopts a β-barrel fold with a large lipid-binding cavity whose lid stabilizes cargo and tunes the relative transport efficiency of PS versus PI4P [PMID:37566053]. At ER–plasma membrane junctions ORP8 sets a high PI4P/PS ratio that, opposite ORP5, governs STIM1–Orai1 coupling, Ca2+ oscillations, and downstream NFAT translocation [PMID:37607230], and the same exchange activity acts downstream of Sec22b tethering at ER–phagosome contacts to control phagosome maturation and antigen degradation [PMID:37794132]. Beyond the PM, ORP8 localizes to ER–mitochondria contacts where it binds PTPIP51 and maintains mitochondrial morphology and respiration [PMID:27113756], and it organizes phosphatidic-acid–rich MAM subdomains to recruit seipin and drive lipid droplet biogenesis [PMID:35969857]. Independently of its transfer activity, ORP8 serves as a lipophagy receptor on lipid droplets by directly binding LC3/GABARAPs in an AMPK-phosphorylation–dependent manner, controlling triglyceride clearance in vivo [PMID:37707322]. ORP8 also recruits GPX1 to the ER to reduce peroxidized phosphatidic acid as part of a noncanonical, ER-localized ferroptosis pathway [PMID:41720096], and at the nuclear envelope it interacts with Nup62 to modulate SREBP-driven lipid biosynthesis [PMID:21698267].","teleology":[{"year":2007,"claim":"Established ORP8 as an ER-resident oxysterol-binding protein and linked it to cholesterol homeostasis by showing it negatively regulates ABCA1-dependent cholesterol efflux.","evidence":"siRNA knockdown in THP-1 macrophages with ABCA1 promoter-luciferase reporters, cholesterol efflux and ligand binding assays","pmids":["17991739"],"confidence":"Medium","gaps":["Mechanism connecting ER-localized ORP8 to ABCA1 transcription not resolved","Direct lipid transfer activity not yet demonstrated"]},{"year":2011,"claim":"Identified Nup62 as a direct partner and connected ORP8 to SREBP-controlled lipogenesis, providing a nuclear-envelope route by which ORP8 suppresses cholesterol biosynthesis.","evidence":"Yeast two-hybrid, BiFC, Co-IP, adenoviral overexpression in mouse liver with [3H]acetate labeling and Nup62 RNAi","pmids":["21698267"],"confidence":"Medium","gaps":["How ORP8-Nup62 binding mechanistically lowers nuclear SREBP is unclear","Lipid-transfer dependence of the SREBP effect not tested"]},{"year":2012,"claim":"Showed ORP8 controls macrophage migration through the same Nup62 partner, competing with Exo70 and placing Nup62 downstream of ORP8.","evidence":"Stable shRNA knockdown, microarray, migration assays and Nup62 RNAi epistasis in RAW264.7 cells","pmids":["22683860"],"confidence":"Medium","gaps":["Direct biochemistry of ORP8/Exo70/Nup62 competition not structurally defined","Link between migration and lipid transfer activity untested"]},{"year":2014,"claim":"Linked ORP8 to cell-cycle control by identifying SPAG5/Astrin as a partner recruited to ER membranes and mediating oxysterol-induced G2/M arrest.","evidence":"Yeast two-hybrid, pulldown/Co-IP, flow cytometry cell-cycle analysis and RNAi epistasis in HepG2 cells","pmids":["24424245"],"confidence":"Medium","gaps":["Mechanism by which ER-tethered SPAG5 alters the cell cycle unknown","Relationship to ORP8 lipid-transfer function not addressed"]},{"year":2015,"claim":"Defined the core biochemical activity: ORP8 (with ORP5) tethers ER to PM and performs PI4P/PS countertransport, establishing it as a lipid transfer protein that shapes PM phosphoinositide and PS content.","evidence":"In vitro lipid transfer assays, gain/loss-of-function, subcellular fractionation and ER-PM contact imaging","pmids":["26206935"],"confidence":"High","gaps":["In vivo physiological consequences of altered PM PS not yet mapped","Structural basis of cargo selectivity not resolved at this stage"]},{"year":2016,"claim":"Extended ORP8 function to ER-mitochondria contacts, showing PTPIP51 binding and an ORD requirement for MAM localization with consequences for mitochondrial morphology and respiration.","evidence":"Confocal/EM imaging, reciprocal Co-IP with PTPIP51, domain-deletion analysis and respiration assays with RNAi","pmids":["27113756"],"confidence":"High","gaps":["Lipid species transferred at MAMs not directly demonstrated","Causal chain from lipid transfer to respiratory defect unclear"]},{"year":2017,"claim":"Refined the recruitment mechanism, showing ORP8's PH domain binds PtdIns(4,5)P2 and that PtdIns(4,5)P2 can serve as a co-exchanger for cargo transport.","evidence":"In vitro lipid extraction/transport with purified ORD, PM recruitment and PH-domain binding assays, double siRNA with lipid measurements","pmids":["28970484"],"confidence":"High","gaps":["Relative in vivo contribution of PI4P vs PIP2 co-exchange not quantified","Regulation of PH-domain engagement unknown"]},{"year":2022,"claim":"Connected ORP8's MAM activity to lipid droplet biogenesis by showing it regulates seipin recruitment at phosphatidic-acid-rich MAM subdomains.","evidence":"Fluorescence microscopy, siRNA knockdown, seipin localization and LD biogenesis quantification with contact-site disruption","pmids":["35969857"],"confidence":"Medium","gaps":["Direct molecular interaction between ORP8 and seipin not established","Lipid flux driving seipin recruitment not measured"]},{"year":2023,"claim":"Revealed a transfer-independent role as a lipophagy receptor, with AMPK phosphorylation enhancing direct LC3/GABARAP binding to drive LD autophagy and triglyceride clearance in vivo.","evidence":"Co-IP of ORP8-LC3/GABARAP, AMPK phosphorylation assays, ORP8 KO and ob/ob overexpression mice, lipid-transfer domain mutants","pmids":["37707322"],"confidence":"High","gaps":["Phosphosite-resolved structural basis of LC3 binding not fully defined","Coordination between lipophagy and transfer functions on the same LD unclear"]},{"year":2023,"claim":"Provided the structural framework for cargo handling by solving the ORD8 β-barrel and showing the lid stabilizes cargo and differentiates PS from PI4P transport.","evidence":"X-ray crystallography, docking and fluorescence lipid transport assays comparing lid-deleted and full-length ORD8","pmids":["37566053"],"confidence":"High","gaps":["Conformational dynamics during membrane extraction not captured","Structure of full-length membrane-embedded ORP8 unavailable"]},{"year":2023,"claim":"Showed ORP8 acts as a rheostat at STIM1-organized ER-PM junctions, setting a high PI4P/PS ratio that tunes store-operated Ca2+ entry and NFAT signaling.","evidence":"Targeted ORD expression, PtdSer-specific PLA1a1, Ca2+ imaging, NFAT translocation and STIM1 interaction measurements","pmids":["37607230"],"confidence":"Medium","gaps":["Direct ORP8-STIM1 physical relationship not defined","Quantitative lipid-ratio thresholds for Ca2+ effects not established"]},{"year":2023,"claim":"Demonstrated ORP8's PS/PI4P exchange operates at ER-phagosome contacts downstream of Sec22b to control phagosome maturation and antigen degradation.","evidence":"Co-IP of Sec22b-ORP8, siRNA knockdown, phagosomal lipid quantification and rescue with lipid-transfer mutant","pmids":["37794132"],"confidence":"Medium","gaps":["How Sec22b recruits ORP8 mechanistically unclear","Generality across phagocyte types untested"]},{"year":2026,"claim":"Uncovered a noncanonical ferroptosis role: ORP8 recruits GPX1 to the ER to reduce peroxidized phosphatidic acid, defining an ER-localized lipid-peroxidation defense distinct from GPX4 at the PM.","evidence":"Co-IP of GPX1-OSBPL8, subcellular fractionation, lipidomics, siRNA knockdown and in vivo tumor growth assays","pmids":["41720096"],"confidence":"High","gaps":["Whether lipid-transfer activity contributes to GPX1 recruitment unclear","Interplay with the canonical GPX4 pathway not fully mapped"]},{"year":null,"claim":"How ORP8's many spatially distinct functions — PM/MAM/phagosome lipid exchange, lipophagy, GPX1-mediated peroxide defense, and nuclear SREBP control — are coordinated and regulated within a single cell remains unresolved.","evidence":"No single study integrates the contact-site, autophagy, ferroptosis, and transcriptional roles","pmids":[],"confidence":"Low","gaps":["No unifying regulatory logic for partitioning ORP8 among its sites","Post-translational switches beyond AMPK phosphorylation not characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,1,4,7,11]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[4,7,11,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,6,13]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[10]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,4,6,16]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,7,12]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[6,9]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[9,10]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[4,9,10]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[10]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,7]}],"complexes":[],"partners":["PTPIP51","NUP62","SPAG5","LC3","GABARAP","SEC22B","GPX1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BZF1","full_name":"Oxysterol-binding protein-related protein 8","aliases":[],"length_aa":889,"mass_kda":101.2,"function":"Lipid transporter involved in lipid countertransport between the endoplasmic reticulum and the plasma membrane: specifically exchanges phosphatidylserine with phosphatidylinositol 4-phosphate (PI4P), delivering phosphatidylserine to the plasma membrane in exchange for PI4P, which is degraded by the SAC1/SACM1L phosphatase in the endoplasmic reticulum. Binds phosphatidylserine and PI4P in a mutually exclusive manner (PubMed:26206935). Binds oxysterol, 25-hydroxycholesterol and cholesterol (PubMed:17428193, PubMed:17991739, PubMed:21698267)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q9BZF1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/OSBPL8","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000091039","cell_line_id":"CID000414","localizations":[{"compartment":"er","grade":3},{"compartment":"cell_contact","grade":2},{"compartment":"membrane","grade":2},{"compartment":"vesicles","grade":2}],"interactors":[{"gene":"CAPZB","stoichiometry":0.2},{"gene":"COPB2","stoichiometry":0.2},{"gene":"COPE","stoichiometry":0.2},{"gene":"CSNK2A1","stoichiometry":0.2},{"gene":"CSNK2A2","stoichiometry":0.2},{"gene":"CSNK2B","stoichiometry":0.2},{"gene":"EMC4","stoichiometry":0.2},{"gene":"GLG1","stoichiometry":0.2},{"gene":"ESYT1","stoichiometry":0.2},{"gene":"ERLIN2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000414","total_profiled":1310},"omim":[{"mim_id":"606736","title":"OXYSTEROL-BINDING PROTEIN-LIKE PROTEIN 8; OSBPL8","url":"https://www.omim.org/entry/606736"},{"mim_id":"606733","title":"OXYSTEROL-BINDING PROTEIN-LIKE PROTEIN 5; OSBPL5","url":"https://www.omim.org/entry/606733"},{"mim_id":"605704","title":"VAMP-ASSOCIATED PROTEIN B AND C; VAPB","url":"https://www.omim.org/entry/605704"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/OSBPL8"},"hgnc":{"alias_symbol":["OSBP10","ORP8","MST120","MSTP120"],"prev_symbol":[]},"alphafold":{"accession":"Q9BZF1","domains":[{"cath_id":"2.30.29.30","chopping":"133-274","consensus_level":"high","plddt":78.7791,"start":133,"end":274},{"cath_id":"2.40.160.120","chopping":"379-722","consensus_level":"high","plddt":90.2944,"start":379,"end":722},{"cath_id":"-","chopping":"732-769","consensus_level":"medium","plddt":94.1058,"start":732,"end":769}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BZF1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BZF1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BZF1-F1-predicted_aligned_error_v6.png","plddt_mean":70.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=OSBPL8","jax_strain_url":"https://www.jax.org/strain/search?query=OSBPL8"},"sequence":{"accession":"Q9BZF1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BZF1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BZF1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BZF1"}},"corpus_meta":[{"pmid":"26206935","id":"PMC_26206935","title":"INTRACELLULAR TRANSPORT. PI4P/phosphatidylserine countertransport at ORP5- and ORP8-mediated ER-plasma membrane contacts.","date":"2015","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/26206935","citation_count":513,"is_preprint":false},{"pmid":"27113756","id":"PMC_27113756","title":"ORP5/ORP8 localize to endoplasmic reticulum-mitochondria contacts and are involved in mitochondrial function.","date":"2016","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/27113756","citation_count":237,"is_preprint":false},{"pmid":"28970484","id":"PMC_28970484","title":"ORP5 and ORP8 bind phosphatidylinositol-4, 5-biphosphate (PtdIns(4,5)P 2) and regulate its level at the plasma membrane.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/28970484","citation_count":159,"is_preprint":false},{"pmid":"17991739","id":"PMC_17991739","title":"OSBP-related protein 8 (ORP8) suppresses ABCA1 expression and cholesterol efflux from macrophages.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17991739","citation_count":111,"is_preprint":false},{"pmid":"35969857","id":"PMC_35969857","title":"ORP5 and ORP8 orchestrate lipid droplet biogenesis and maintenance at ER-mitochondria contact sites.","date":"2022","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/35969857","citation_count":93,"is_preprint":false},{"pmid":"37707322","id":"PMC_37707322","title":"ORP8 acts as a lipophagy receptor to mediate lipid droplet turnover.","date":"2023","source":"Protein & cell","url":"https://pubmed.ncbi.nlm.nih.gov/37707322","citation_count":68,"is_preprint":false},{"pmid":"21698267","id":"PMC_21698267","title":"OSBP-related protein 8 (ORP8) regulates plasma and liver tissue lipid levels and interacts with the nucleoporin Nup62.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21698267","citation_count":53,"is_preprint":false},{"pmid":"25596532","id":"PMC_25596532","title":"Oxysterol-binding protein-related protein 8 (ORP8) increases sensitivity of hepatocellular carcinoma cells to Fas-mediated apoptosis.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25596532","citation_count":36,"is_preprint":false},{"pmid":"32570981","id":"PMC_32570981","title":"ORP5 and ORP8: Sterol Sensors and Phospholipid Transfer Proteins at Membrane Contact Sites?","date":"2020","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/32570981","citation_count":26,"is_preprint":false},{"pmid":"22683860","id":"PMC_22683860","title":"Silencing of OSBP-related protein 8 (ORP8) modifies the macrophage transcriptome, nucleoporin p62 distribution, and migration capacity.","date":"2012","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/22683860","citation_count":25,"is_preprint":false},{"pmid":"23554939","id":"PMC_23554939","title":"Osbpl8 deficiency in mouse causes an elevation of high-density lipoproteins and gender-specific alterations of lipid metabolism.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23554939","citation_count":21,"is_preprint":false},{"pmid":"37607230","id":"PMC_37607230","title":"PtdSer as a signaling lipid determined by privileged localization of ORP5 and ORP8 at ER/PM junctional foci to determine PM and ER PtdSer/PI(4)P ratio and cell function.","date":"2023","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/37607230","citation_count":17,"is_preprint":false},{"pmid":"24424245","id":"PMC_24424245","title":"OSBP-related protein 8 (ORP8) interacts with Homo sapiens sperm associated antigen 5 (SPAG5) and mediates oxysterol interference of HepG2 cell cycle.","date":"2014","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/24424245","citation_count":16,"is_preprint":false},{"pmid":"32323800","id":"PMC_32323800","title":"ORP8 induces apoptosis by releasing cytochrome c from mitochondria in non‑small cell lung cancer.","date":"2020","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/32323800","citation_count":15,"is_preprint":false},{"pmid":"37794132","id":"PMC_37794132","title":"Sec22b regulates phagosome maturation by promoting ORP8-mediated lipid exchange at endoplasmic reticulum-phagosome contact sites.","date":"2023","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/37794132","citation_count":9,"is_preprint":false},{"pmid":"25347070","id":"PMC_25347070","title":"Orp8 deficiency in bone marrow-derived cells reduces atherosclerotic lesion progression in LDL receptor knockout mice.","date":"2014","source":"PloS 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phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41027151","citation_count":3,"is_preprint":false},{"pmid":"41720096","id":"PMC_41720096","title":"A GPX1-OSBPL8 axis mediates noncanonical in vivo ferroptosis and cancer growth suppression.","date":"2026","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/41720096","citation_count":2,"is_preprint":false},{"pmid":"37054771","id":"PMC_37054771","title":"ORP8 inhibits renal cell carcinoma progression by accelerating Stathmin1 degradation and microtubule polymerization.","date":"2023","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/37054771","citation_count":1,"is_preprint":false},{"pmid":"39761801","id":"PMC_39761801","title":"Gender difference in the association of OSBPL8 polymorphisms with nephrolithiasis within a Chinese cohort.","date":"2025","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/39761801","citation_count":1,"is_preprint":false},{"pmid":"42149290","id":"PMC_42149290","title":"The GPX1-OSBPL8 axis: integrating ER ferroptosis and apoptotic signaling.","date":"2026","source":"Apoptosis : an international journal on programmed cell death","url":"https://pubmed.ncbi.nlm.nih.gov/42149290","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.26.678863","title":"Glycosphingolipids Regulate Phosphatidylserine Transport at ER–PM Contact Sites","date":"2025-09-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.26.678863","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14187,"output_tokens":5256,"usd":0.0607,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13634,"output_tokens":4697,"usd":0.092798,"stage2_stop_reason":"end_turn"},"total_usd":0.153498,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"ORP8 localizes to the endoplasmic reticulum via its C-terminal transmembrane span and binds 25-hydroxycholesterol, identifying it as an ER oxysterol-binding protein. Silencing ORP8 in THP-1 macrophages increased ABCA1 expression and cholesterol efflux to lipid-free apolipoprotein A-I; the effect was partially attenuated by mutation of the DR4 element in the ABCA1 promoter and synergized with LXR agonist treatment, indicating ORP8 negatively regulates ABCA1 transcription involving both LXR and E-box functions.\",\n      \"method\": \"RNA interference (siRNA), ABCA1 promoter-luciferase reporter assays, cholesterol efflux assays, ligand binding studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi knockdown with defined molecular readout (ABCA1 reporter), single lab with multiple orthogonal methods (binding assay, luciferase reporter, efflux assay)\",\n      \"pmids\": [\"17991739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ORP8 binds cholesterol in vitro (in addition to 25-hydroxycholesterol). ORP8 overexpression in mouse liver reduced nuclear SREBP-1 and SREBP-2 and their target gene mRNAs, and suppressed cholesterol biosynthesis. Yeast two-hybrid, BiFC, and co-immunoprecipitation identified nuclear pore component Nup62 as a direct interaction partner of ORP8; ORP8 and Nup62 co-localize at the nuclear envelope, and depletion of Nup62 inhibited the effect of ORP8 overexpression on nSREBPs.\",\n      \"method\": \"In vitro cholesterol binding, adenoviral overexpression in mouse liver, [3H]acetate pulse-labeling, yeast two-hybrid, bimolecular fluorescence complementation (BiFC), co-immunoprecipitation, confocal immunofluorescence, Nup62 RNAi\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (BiFC, Co-IP, yeast two-hybrid, in vivo overexpression), single lab\",\n      \"pmids\": [\"21698267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ORP8 silencing in RAW264.7 macrophages increased expression and altered subcellular distribution of its interaction partner Nup62 (including intranuclear localization), enhanced cell migration, and promoted a more pronounced microtubule cytoskeleton. ORP8 competed with Exo70 for binding to Nup62, and Nup62 knockdown abolished the migration-enhancing effect of ORP8 silencing, placing Nup62 downstream of ORP8 in migration control.\",\n      \"method\": \"Stable shRNA lentiviral knockdown, microarray transcriptomics, confocal microscopy, migration assays, Nup62 RNAi epistasis\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (double KD), migration phenotype, interaction competition assay; single lab\",\n      \"pmids\": [\"22683860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Yeast two-hybrid screening followed by pulldown and co-immunoprecipitation identified SPAG5/Astrin as an interaction partner of ORP8. Overexpressed ORP8 recruited SPAG5 onto ER membranes in interphase cells. ORP8 overexpression or 25-hydroxycholesterol treatment caused G2/M accumulation in HepG2 cells; ORP8 knockdown strongly inhibited the oxysterol-induced G2/M arrest, and SPAG5 knockdown reduced the cell-cycle effects of both ORP8 overexpression and 25-OHC, placing SPAG5 downstream of ORP8.\",\n      \"method\": \"Yeast two-hybrid, pulldown, co-immunoprecipitation, flow cytometry cell cycle analysis, RNAi knockdown epistasis\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP/pulldown, genetic epistasis with defined cell-cycle phenotype; single lab\",\n      \"pmids\": [\"24424245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ORP5 and ORP8 are ER integral membrane proteins that tether the ER to the plasma membrane via PH domain interaction with PI4P. Their OSBP-related domains (ORDs) carry either PI4P or phosphatidylserine (PS) and exchange these lipids between bilayers, mediating PI4P/PS countertransport: delivering PI4P to ER-localized Sac1 phosphatase for degradation and PS from ER to PM. Gain- and loss-of-function experiments showed these activities control PM PI4P levels and selectively enrich PS at the PM.\",\n      \"method\": \"Gain- and loss-of-function experiments, lipid transfer assays, subcellular fractionation, imaging of ER-PM contacts\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro lipid transfer assays, gain/loss-of-function, mechanistically defined countertransport activity; replicated by multiple subsequent labs\",\n      \"pmids\": [\"26206935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ORP8 overexpression triggered apoptosis in HCC cells coinciding with relocation of cytoplasmic Fas to the cell plasma membrane and FasL upregulation. ORP8-induced Fas translocation was p53-dependent, and FasL induction occurred via the ER stress response.\",\n      \"method\": \"ORP8 overexpression in HCC cell lines and primary cells, co-culture with T cells/Jurkat cells, western blot, confocal microscopy, xenograft tumor model\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression with defined apoptotic phenotype, p53 dependency shown, multiple cell systems; single lab\",\n      \"pmids\": [\"25596532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In addition to ER-PM contact sites, ORP5 and ORP8 localize to ER-mitochondria contacts (MAM) and interact physically with the outer mitochondrial membrane protein PTPIP51. A functional lipid transfer (ORD) domain was required for this MAM localization. ORP5/ORP8 depletion caused defects in mitochondria morphology and respiratory function.\",\n      \"method\": \"Confocal and electron microscopy, co-immunoprecipitation with PTPIP51, domain deletion analysis, mitochondrial respiration assays, RNAi knockdown\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain requirement experiment, functional respiratory readout, replicated by later MAM studies\",\n      \"pmids\": [\"27113756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The pleckstrin homology (PH) domain of ORP8 mediates recruitment to ER-PM contact sites via binding to PtdIns(4,5)P2, not PtdIns(4)P. The ORD of ORP8 can extract and transport multiple phosphoinositides in vitro. Knockdown of both ORP5 and ORP8 increases PM PtdIns(4,5)P2 levels with little effect on PtdIns(4)P, indicating PtdIns(4,5)P2 can serve as a co-exchanger for cargo lipid transport by ORP8.\",\n      \"method\": \"In vitro lipid extraction/transport assays with purified ORD, PM recruitment assays, PH domain binding studies, siRNA double knockdown with lipid level measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro lipid transport assay with purified domain, cellular knockdown with quantitative lipid readout; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"28970484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ORP8 overexpression in non-small cell lung cancer cells induced apoptosis via release of cytochrome c from mitochondria into the cytoplasm.\",\n      \"method\": \"ORP8 overexpression, western blot and confocal microscopy for cytochrome c release, MTS/anchorage-independent growth assays\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single overexpression experiment, single lab, limited mechanistic dissection beyond cytochrome c release\",\n      \"pmids\": [\"32323800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ORP5 and ORP8 localize to MAM subdomains enriched in phosphatidic acid and control lipid droplet (LD) biogenesis at these sites. ORP5/8 regulate seipin recruitment to MAM-LD contacts; loss of ORP5/8 impairs LD biogenesis, and intact ER-mitochondria contact sites are required for this ORP5/8 function.\",\n      \"method\": \"Fluorescence microscopy, siRNA knockdown, seipin localization assays, LD biogenesis quantification, ER-mitochondria contact site disruption\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cellular phenotype (LD biogenesis defect), mechanistic link to seipin recruitment, contact site requirement demonstrated; single lab\",\n      \"pmids\": [\"35969857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ORP8 functions as a lipophagy receptor by localizing to lipid droplets and directly interacting with phagophore-anchored LC3/GABARAPs to mediate LD encapsulation by autophagosomes. This function is independent of ORP8's lipid transporter activity. Upon lipophagy induction, AMPK phosphorylates ORP8, enhancing its affinity for LC3/GABARAPs. ORP8 deletion or disruption of the ORP8-LC3/GABARAP interaction causes LD and triglyceride accumulation; ORP8 overexpression alleviates liver lipid accumulation in ob/ob mice, and Osbpl8−/− mice show liver lipid clearance defects.\",\n      \"method\": \"Co-immunoprecipitation (ORP8-LC3/GABARAP), AMPK phosphorylation assays, ORP8 KO mice, ob/ob mouse ORP8 overexpression, lipid transfer domain mutants, LD and triglyceride quantification\",\n      \"journal\": \"Protein & cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, genetic KO mouse model, AMPK phosphorylation mechanistically linked, lipid-transfer-independent function demonstrated by domain mutant, replicated in two in vivo models\",\n      \"pmids\": [\"37707322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Crystal structure of the ORP8 lipid transport domain (ORD8) was solved, revealing a β-barrel fold with anti-parallel β-strands and a large cavity (~1860 Å3) as the lipid-binding site. The lid region is required for stable lipid binding and slows transport while stabilizing cargo; fluorescence assays showed differential transport efficiencies for PS versus PI4P.\",\n      \"method\": \"X-ray crystallography, computer docking simulations, fluorescence lipid transport assays, comparative experiments between lid-deleted and full-length ORD8\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with functional validation (fluorescence transport assay, lid mutant), single lab but multiple orthogonal methods\",\n      \"pmids\": [\"37566053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STIM1-formed ER-PM junctions are required for PI4P/PS exchange by ORP5 and ORP8. ORP5 and ORP8 operate as a rheostat setting junctional PI4P/PtdSer ratio with reciprocal modes: ORP5 sets low and ORP8 sets high junctional PI4P/PtdSer ratio. This ratio controls STIM1-STIM1 and STIM1-Orai1 interactions, SERCA pump activity, Ca2+ oscillation patterns, and NFAT nuclear translocation. Targeting the ORDs to the STIM1 ER subdomain reversed ORP5/ORP8 function.\",\n      \"method\": \"Targeted ORD domain expression at PM vs ER subdomains, targeted PtdSer-specific PLA1a1, Ca2+ imaging, NFAT translocation assays, STIM1 interaction measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional readouts (Ca2+ signaling, NFAT, STIM1 interactions), domain-swap experiments; single lab\",\n      \"pmids\": [\"37607230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Sec22b co-precipitates with ORP8 at ER-phagosome membrane contact sites. Wild-type but not lipid-transfer-mutant ORP8 rescues phagosomal PI4P levels and reduces antigen degradation in Sec22b knockdown cells, and restores phagolysosome fusion, establishing that ORP8's PS/PI4P exchange activity downstream of Sec22b tethering controls phagosome maturation.\",\n      \"method\": \"Co-immunoprecipitation (Sec22b–ORP8), siRNA knockdown, phagosomal lipid quantification, antigen degradation assays, phagolysosome fusion assays with ORP8 mutant rescue\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, functional rescue with lipid-transfer mutant establishing enzymatic requirement, epistasis; single lab\",\n      \"pmids\": [\"37794132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ORP8 overexpression in renal cell carcinoma cells accelerated ubiquitin-mediated proteasomal degradation of Stathmin1, leading to increased microtubule polymerization and suppression of RCC cell growth, migration, and invasion.\",\n      \"method\": \"ORP8 overexpression and knockdown, proteasome inhibitor experiments, western blot for Stathmin1, microtubule polymerization assays, functional cell assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — overexpression phenotype with mechanistic proposal (ubiquitin-proteasome), single lab, limited biochemical dissection of direct vs indirect effect\",\n      \"pmids\": [\"37054771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Osbpl8 remodels lipid metabolism in macrophages by inhibiting excessive IRE1α-XBP1-related ER stress. Osbpl8 delivered via extracellular vesicles from anti-inflammatory BMDMs suppressed inflammatory responses and lipotoxicity in hepatocytes during MASH.\",\n      \"method\": \"LC-MS/MS proteomic identification, shRNA knockdown, palmitic acid lipotoxicity model, IRE1α-XBP1 pathway markers, AAV-shRNA in vivo\",\n      \"journal\": \"Molecular medicine (Cambridge, Mass.)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanism inferred from pathway markers (IRE1α-XBP1), limited direct mechanistic dissection of how ORP8 affects ER stress\",\n      \"pmids\": [\"40448016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"OSBPL8 recruits GPX1 to the ER membrane, where GPX1 directly reduces peroxidized phosphatidic acid (PA-OOH) generated by ROS. This GPX1-OSBPL8 axis drives a noncanonical ferroptosis pathway at the ER (distinct from GPX4-dependent plasma membrane ferroptosis); ROS-driven lipid peroxidation accumulates at the ER before plasma membrane rupture. Knockdown of either OSBPL8 or GPX1 promotes ROS-induced ferroptosis and suppresses tumor growth.\",\n      \"method\": \"Co-immunoprecipitation (GPX1-OSBPL8), subcellular fractionation (ER lipid peroxidation), siRNA knockdown, in vivo tumor growth assays, lipidomics (PA peroxidation)\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — Co-IP establishing direct interaction, organelle-specific lipid peroxidation biochemistry, in vitro and in vivo knockdown with defined ferroptosis phenotype, published in high-rigor venue\",\n      \"pmids\": [\"41720096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Glycosphingolipids (GM3 and SM4) are required to maintain ORP8 (and ORP5) localization to ER-PM membrane contact sites. Genetic deletion or pharmacological inhibition of GM3/SM4 biosynthetic enzymes displaced PI4KIIIα and its adaptor EFR3A from the PM, reducing PM PI4P content and disrupting ORP8 PM interactions, consequently reducing PS transport to the PM.\",\n      \"method\": \"High-resolution imaging, genetic deletion and pharmacological inhibition of GSL biosynthesis enzymes, quantitative lipid measurements (PI4P, PS)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 / Weak — imaging and genetic perturbation, mechanistic link established but preprint (not peer-reviewed), single lab\",\n      \"pmids\": [\"bio_10.1101_2025.09.26.678863\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"OSBPL8/ORP8 is an ER-anchored lipid transfer protein that countertransports phosphatidylserine (PS) from the ER to the plasma membrane in exchange for PI4P (which is delivered to Sac1 for degradation) at ER-PM contact sites; it also transfers PS at ER-mitochondria contacts (MAMs) where it interacts with PTPIP51 and controls mitochondrial morphology and respiration, orchestrates lipid droplet biogenesis at MAMs by regulating seipin recruitment, functions as a lipophagy receptor on LDs by directly binding LC3/GABARAPs in an AMPK-phosphorylation-dependent manner, recruits GPX1 to the ER to reduce peroxidized phosphatidic acid as part of a noncanonical ferroptosis pathway, and in the nucleus/nuclear envelope interacts with Nup62 to modulate SREBP activity, macrophage migration, and cell-cycle progression via SPAG5.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"OSBPL8 (ORP8) is an ER-anchored lipid transfer protein that establishes and exploits membrane contact sites to countertransport phospholipids and thereby control plasma membrane lipid identity, organelle physiology, and lipid catabolism [#4, #6]. Anchored in the ER through a C-terminal transmembrane span, it tethers the ER to the plasma membrane via a PH domain that engages PM phosphoinositides, while its OSBP-related domain (ORD) extracts and exchanges phosphatidylserine for PI4P, delivering PI4P to ER Sac1 for degradation and enriching PS at the PM [#4, #7]. The ORD adopts a β-barrel fold with a large lipid-binding cavity whose lid stabilizes cargo and tunes the relative transport efficiency of PS versus PI4P [#11]. At ER–plasma membrane junctions ORP8 sets a high PI4P/PS ratio that, opposite ORP5, governs STIM1–Orai1 coupling, Ca2+ oscillations, and downstream NFAT translocation [#12], and the same exchange activity acts downstream of Sec22b tethering at ER–phagosome contacts to control phagosome maturation and antigen degradation [#13]. Beyond the PM, ORP8 localizes to ER–mitochondria contacts where it binds PTPIP51 and maintains mitochondrial morphology and respiration [#6], and it organizes phosphatidic-acid–rich MAM subdomains to recruit seipin and drive lipid droplet biogenesis [#9]. Independently of its transfer activity, ORP8 serves as a lipophagy receptor on lipid droplets by directly binding LC3/GABARAPs in an AMPK-phosphorylation–dependent manner, controlling triglyceride clearance in vivo [#10]. ORP8 also recruits GPX1 to the ER to reduce peroxidized phosphatidic acid as part of a noncanonical, ER-localized ferroptosis pathway [#16], and at the nuclear envelope it interacts with Nup62 to modulate SREBP-driven lipid biosynthesis [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established ORP8 as an ER-resident oxysterol-binding protein and linked it to cholesterol homeostasis by showing it negatively regulates ABCA1-dependent cholesterol efflux.\",\n      \"evidence\": \"siRNA knockdown in THP-1 macrophages with ABCA1 promoter-luciferase reporters, cholesterol efflux and ligand binding assays\",\n      \"pmids\": [\"17991739\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting ER-localized ORP8 to ABCA1 transcription not resolved\", \"Direct lipid transfer activity not yet demonstrated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified Nup62 as a direct partner and connected ORP8 to SREBP-controlled lipogenesis, providing a nuclear-envelope route by which ORP8 suppresses cholesterol biosynthesis.\",\n      \"evidence\": \"Yeast two-hybrid, BiFC, Co-IP, adenoviral overexpression in mouse liver with [3H]acetate labeling and Nup62 RNAi\",\n      \"pmids\": [\"21698267\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How ORP8-Nup62 binding mechanistically lowers nuclear SREBP is unclear\", \"Lipid-transfer dependence of the SREBP effect not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed ORP8 controls macrophage migration through the same Nup62 partner, competing with Exo70 and placing Nup62 downstream of ORP8.\",\n      \"evidence\": \"Stable shRNA knockdown, microarray, migration assays and Nup62 RNAi epistasis in RAW264.7 cells\",\n      \"pmids\": [\"22683860\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemistry of ORP8/Exo70/Nup62 competition not structurally defined\", \"Link between migration and lipid transfer activity untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked ORP8 to cell-cycle control by identifying SPAG5/Astrin as a partner recruited to ER membranes and mediating oxysterol-induced G2/M arrest.\",\n      \"evidence\": \"Yeast two-hybrid, pulldown/Co-IP, flow cytometry cell-cycle analysis and RNAi epistasis in HepG2 cells\",\n      \"pmids\": [\"24424245\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which ER-tethered SPAG5 alters the cell cycle unknown\", \"Relationship to ORP8 lipid-transfer function not addressed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the core biochemical activity: ORP8 (with ORP5) tethers ER to PM and performs PI4P/PS countertransport, establishing it as a lipid transfer protein that shapes PM phosphoinositide and PS content.\",\n      \"evidence\": \"In vitro lipid transfer assays, gain/loss-of-function, subcellular fractionation and ER-PM contact imaging\",\n      \"pmids\": [\"26206935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo physiological consequences of altered PM PS not yet mapped\", \"Structural basis of cargo selectivity not resolved at this stage\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended ORP8 function to ER-mitochondria contacts, showing PTPIP51 binding and an ORD requirement for MAM localization with consequences for mitochondrial morphology and respiration.\",\n      \"evidence\": \"Confocal/EM imaging, reciprocal Co-IP with PTPIP51, domain-deletion analysis and respiration assays with RNAi\",\n      \"pmids\": [\"27113756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lipid species transferred at MAMs not directly demonstrated\", \"Causal chain from lipid transfer to respiratory defect unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Refined the recruitment mechanism, showing ORP8's PH domain binds PtdIns(4,5)P2 and that PtdIns(4,5)P2 can serve as a co-exchanger for cargo transport.\",\n      \"evidence\": \"In vitro lipid extraction/transport with purified ORD, PM recruitment and PH-domain binding assays, double siRNA with lipid measurements\",\n      \"pmids\": [\"28970484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo contribution of PI4P vs PIP2 co-exchange not quantified\", \"Regulation of PH-domain engagement unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected ORP8's MAM activity to lipid droplet biogenesis by showing it regulates seipin recruitment at phosphatidic-acid-rich MAM subdomains.\",\n      \"evidence\": \"Fluorescence microscopy, siRNA knockdown, seipin localization and LD biogenesis quantification with contact-site disruption\",\n      \"pmids\": [\"35969857\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular interaction between ORP8 and seipin not established\", \"Lipid flux driving seipin recruitment not measured\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed a transfer-independent role as a lipophagy receptor, with AMPK phosphorylation enhancing direct LC3/GABARAP binding to drive LD autophagy and triglyceride clearance in vivo.\",\n      \"evidence\": \"Co-IP of ORP8-LC3/GABARAP, AMPK phosphorylation assays, ORP8 KO and ob/ob overexpression mice, lipid-transfer domain mutants\",\n      \"pmids\": [\"37707322\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphosite-resolved structural basis of LC3 binding not fully defined\", \"Coordination between lipophagy and transfer functions on the same LD unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided the structural framework for cargo handling by solving the ORD8 β-barrel and showing the lid stabilizes cargo and differentiates PS from PI4P transport.\",\n      \"evidence\": \"X-ray crystallography, docking and fluorescence lipid transport assays comparing lid-deleted and full-length ORD8\",\n      \"pmids\": [\"37566053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational dynamics during membrane extraction not captured\", \"Structure of full-length membrane-embedded ORP8 unavailable\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed ORP8 acts as a rheostat at STIM1-organized ER-PM junctions, setting a high PI4P/PS ratio that tunes store-operated Ca2+ entry and NFAT signaling.\",\n      \"evidence\": \"Targeted ORD expression, PtdSer-specific PLA1a1, Ca2+ imaging, NFAT translocation and STIM1 interaction measurements\",\n      \"pmids\": [\"37607230\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ORP8-STIM1 physical relationship not defined\", \"Quantitative lipid-ratio thresholds for Ca2+ effects not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated ORP8's PS/PI4P exchange operates at ER-phagosome contacts downstream of Sec22b to control phagosome maturation and antigen degradation.\",\n      \"evidence\": \"Co-IP of Sec22b-ORP8, siRNA knockdown, phagosomal lipid quantification and rescue with lipid-transfer mutant\",\n      \"pmids\": [\"37794132\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How Sec22b recruits ORP8 mechanistically unclear\", \"Generality across phagocyte types untested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Uncovered a noncanonical ferroptosis role: ORP8 recruits GPX1 to the ER to reduce peroxidized phosphatidic acid, defining an ER-localized lipid-peroxidation defense distinct from GPX4 at the PM.\",\n      \"evidence\": \"Co-IP of GPX1-OSBPL8, subcellular fractionation, lipidomics, siRNA knockdown and in vivo tumor growth assays\",\n      \"pmids\": [\"41720096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether lipid-transfer activity contributes to GPX1 recruitment unclear\", \"Interplay with the canonical GPX4 pathway not fully mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ORP8's many spatially distinct functions — PM/MAM/phagosome lipid exchange, lipophagy, GPX1-mediated peroxide defense, and nuclear SREBP control — are coordinated and regulated within a single cell remains unresolved.\",\n      \"evidence\": \"No single study integrates the contact-site, autophagy, ferroptosis, and transcriptional roles\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying regulatory logic for partitioning ORP8 among its sites\", \"Post-translational switches beyond AMPK phosphorylation not characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 1, 4, 7, 11]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [4, 7, 11, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 6, 13]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 4, 6, 16]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 7, 12]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [9, 10]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [4, 9, 10]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PTPIP51\", \"Nup62\", \"SPAG5\", \"LC3\", \"GABARAP\", \"Sec22b\", \"GPX1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}