Affinage

OSBPL9

Oxysterol-binding protein-related protein 9 · UniProt Q96SU4

Round 2 corrected
Length
736 aa
Mass
83.2 kDa
Annotated
2026-04-29
45 papers in source corpus 10 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

OSBPL9 (ORP9) is a lipid transfer protein that shuttles cholesterol and phosphatidylserine between the ER and trans-Golgi/TGN or damaged lysosomes, thereby maintaining secretory pathway integrity and enabling rapid lysosomal membrane repair. The long isoform (ORP9L) partitions between the Golgi via a PI4P-binding PH domain and the ER via a FFAT motif–mediated interaction with VAP-A; disruption of either determinant collapses ER–Golgi trafficking and causes Golgi fragmentation (PMID:15212954, PMID:19129476). Upon lysosomal membrane damage, PI4K2A-generated PI4P recruits ORP9 together with OSBP, ORP10, and ORP11 to establish ER–lysosome contact sites that deliver phosphatidylserine and cholesterol for membrane repair (PITT pathway) (PMID:36071159). OSBPL9 transcription is upregulated during ER stress through the IRE1α branch of the unfolded protein response (PMID:32161797).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2001 Medium

    Identification of OSBPL9 as one of 12 human ORP family members established that it carries a conserved C-terminal sterol-binding domain and an N-terminal PH domain, framing it as a candidate lipid-binding/transfer protein.

    Evidence Bioinformatics, cDNA cloning, and RT-PCR across human tissues

    PMID:11483621 PMID:11735225

    Open questions at the time
    • No ligand binding or lipid transfer activity demonstrated
    • Subcellular localization not determined experimentally
  2. 2004 High

    Demonstration that ORP9L localizes to the Golgi via its PH domain and to the ER via VAP-A/FFAT interaction revealed how the protein bridges two compartments and showed that loss of either targeting determinant disrupts ER-Golgi transport.

    Evidence FFAT-motif mutagenesis, fluorescence co-localization, dominant-negative overexpression causing ER vacuolation and ERGIC-53 retention

    PMID:15212954

    Open questions at the time
    • Lipid cargo transferred by ORP9 not yet identified
    • Whether PH domain binds PI4P specifically was not tested
  3. 2009 High

    In vitro reconstitution showed ORP9L transfers cholesterol between liposomes in a PI4P-dependent manner, while RNAi depletion caused Golgi fragmentation and cholesterol accumulation in endosomes/lysosomes, establishing ORP9 as a bona fide cholesterol transfer protein essential for secretory pathway integrity.

    Evidence Liposome cholesterol transfer assay, RNAi knockdown, VSV-G transport assay, inducible dominant-negative expression

    PMID:19129476

    Open questions at the time
    • Whether ORP9 transfers lipids other than cholesterol was not addressed
    • Structural basis of PI4P-dependent lipid exchange not resolved
  4. 2009 Medium

    Identification of miR-125a-5p as a post-transcriptional regulator of OSBPL9 in oxLDL-stimulated macrophages linked ORP9 expression levels to inflammatory lipid handling.

    Evidence Luciferase reporter assay confirming 3ʹUTR targeting, cytokine and lipid-uptake measurements in monocyte-derived macrophages

    PMID:19377067

    Open questions at the time
    • Direct contribution of ORP9 reduction (versus other miR-125a-5p targets) to the anti-inflammatory phenotype not isolated
    • In vivo relevance not tested
  5. 2018 Medium

    Placing OSBPL9 transcriptional upregulation downstream of the IRE1α branch of the UPR connected ORP9 to ER stress signaling, suggesting a homeostatic feedback role for lipid transfer during ER stress.

    Evidence piggyBac trap reporter, endogenous mRNA RT-qPCR, pharmacological inhibition of IRE1α (4μ8C, toyocamycin) versus PERK (GSK2656157)

    PMID:32161797

    Open questions at the time
    • Transcription factor downstream of IRE1α that drives OSBPL9 expression not identified
    • Functional consequence of ORP9 upregulation during ER stress not tested
  6. 2022 High

    Discovery of the PITT pathway showed that upon lysosomal membrane damage, PI4K2A-generated PI4P recruits ORP9 (with OSBP, ORP10, ORP11) to form ER–lysosome contacts that deliver phosphatidylserine and cholesterol for rapid membrane repair, broadening ORP9's role from ER–Golgi to ER–lysosome lipid transfer.

    Evidence Unbiased proteomics of LMP-induced recruitment, live-cell imaging, lipid transfer assays, genetic depletion with lysosomal repair readouts

    PMID:36071159

    Open questions at the time
    • Relative contributions of ORP9 versus OSBP versus ORP10/11 not fully deconvolved
    • Whether ORP9 acts as a PS or cholesterol transporter (or both) at lysosomes not resolved in isolation
    • In vivo physiological relevance of the PITT pathway not yet demonstrated in animal models
  7. 2025 Low

    A homozygous nonsense OSBPL9 variant in a consanguineous family with cerebral ventriculomegaly, cerebellar hypoplasia, and arthrogryposis provided human genetic evidence that loss of ORP9 causes a severe neurodevelopmental syndrome.

    Evidence Whole exome sequencing and homozygosity mapping in affected fetuses

    PMID:40182349

    Open questions at the time
    • Single family with no functional cellular rescue or animal model validation
    • Mechanism linking ORP9 loss to brain and joint malformations unknown
    • Not independently replicated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ORP9 lipid transfer activity is coordinated with its ORP partners (OSBP, ORP10, ORP11) at different membrane contact sites, and whether its upregulation during ER stress is functionally protective, remain open questions.
  • No high-resolution structure of ORP9 ORD domain with bound lipid
  • Tissue-specific roles of ORP9 in vivo not characterized
  • Functional validation of the human disease link is lacking

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008289 lipid binding 3 GO:0140104 molecular carrier activity 2
Localization
GO:0005783 endoplasmic reticulum 2 GO:0005794 Golgi apparatus 2 GO:0005764 lysosome 1
Pathway
R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-1430728 Metabolism 2 R-HSA-8953897 Cellular responses to stimuli 1
Partners
ORP10ORP11OSBPPI4K2AVAPA

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 OSBPL9 (ORP9) was identified as a member of the 12-gene human oxysterol-binding protein-related protein (ORP) family, characterized by a conserved C-terminal OSBP-type sterol-binding domain (containing the EQVSHHPP signature) and an N-terminal pleckstrin homology (PH) domain. Phylogenetic analysis grouped ORP9 within a distinct subfamily, and RT-PCR confirmed its expression across human tissues. Bioinformatics/data mining, cDNA cloning, RT-PCR, cladistic analysis Genomics Medium 11483621 11735225
2004 ORP9L (OSBPL9 long isoform) localizes to the Golgi apparatus via its PH domain and to the ER via interaction with VAP-A through a conserved FFAT motif (E-F/Y-F/Y-DA). Mutation of the FFAT motif in ORP9L (FY→AA) abolished ER localization and caused retention of ORP9L on large vesicular Golgi-COPII hybrid structures. Overexpression of ORP9S (dominant negative, lacking PH domain) or ORP9L caused ER vacuolation and retention of ERGIC-53/p58 in the ER, demonstrating that VAP-A binding and PH domain together are required for proper ORP9 partitioning between ER and Golgi. Mutation analysis, fluorescence microscopy (co-localization), inducible overexpression, dominant-negative constructs Experimental cell research High 15212954
2009 ORP9L (OSBPL9) mediates PI4P-dependent cholesterol transport between liposomes in vitro, analogous to OSBP. ORP9L partitions between the trans-Golgi/TGN (via PI4P-binding PH domain) and the ER (via VAP interaction). RNAi depletion of ORP9L caused Golgi fragmentation, inhibition of VSV-G transport from the ER, and accumulation of cholesterol in endosomes/lysosomes. Inducible overexpression of ORP9S (dominant negative) caused complete cessation of protein transport and cell growth inhibition. These results establish ORP9 as a cholesterol transfer protein maintaining early secretory pathway integrity. In vitro liposome cholesterol transport assay, RNAi knockdown, inducible overexpression, fluorescence microscopy, VSV-G transport assay Molecular biology of the cell High 19129476
2009 MicroRNA-125a-5p was identified as a post-transcriptional regulator of ORP9 (OSBPL9) expression in oxLDL-stimulated human monocyte-derived macrophages. Bioinformatics predicted ORP9 as a miR-125a-5p target, confirmed by luciferase reporter assay. miR-125a-5p overexpression decreased ORP9 expression and mediated reduced lipid uptake and decreased secretion of inflammatory cytokines (IL-2, IL-6, TNF-α, TGF-β) in oxLDL-stimulated macrophages. Luciferase reporter assay, microarray, TaqMan RT-PCR, cytokine measurement, lipid uptake assay Cardiovascular research Medium 19377067
2018 OSBPL9 was identified as a novel ER stress-responsive gene. Using a piggyBac trap vector system, OSBPL9 promoter activity was induced by the ER stress agent thapsigargin. Endogenous OSBPL9 mRNA was confirmed to be upregulated by thapsigargin. This upregulation was repressed by IRE1α inhibitors (4μ8C and toyocamycin) but not significantly by the PERK inhibitor GSK2656157, placing OSBPL9 induction downstream of the IRE1α branch of the unfolded protein response. piggyBac trap vector/reporter system, RT-qPCR of endogenous mRNA, pharmacological inhibitors of IRE1α and PERK Biology methods & protocols Medium 32161797
2018 OSBPL9 (ORP9) was identified as a molecular interaction partner of hNOT-1/ALG3-1 by yeast two-hybrid screening, providing experimental evidence for an in vivo protein-protein interaction between hNOT/ALG3 and OSBPL9, consistent with a role in ER-associated molecular networks involving OSBPs and their targets. Yeast two-hybrid screening Human molecular genetics Low 29547901
2019 OSBPL9 and OSBPL11 were validated as interactors of the Zika virus (ZIKV) and Japanese encephalitis virus (JEV) non-structural protein NS5 by EGFP immunoprecipitation with label-free quantitative mass spectrometry, suggesting a role for these lipid-shuttling proteins in flavivirus replication. EGFP immunoprecipitation, label-free quantitative mass spectrometry Journal of proteome research Low 31199156
2022 Upon lysosomal membrane permeabilization (LMP), ORP9 (OSBPL9) is recruited to damaged lysosomes as part of the phosphoinositide-initiated membrane tethering and lipid transport (PITT) pathway. PI4K2A accumulates on damaged lysosomes generating PI4P, which recruits ORP9 along with ORP10, ORP11, and OSBP to form extensive new ER-lysosome membrane contact sites. ORP9 then catalyzes ER-to-lysosome transfer of phosphatidylserine and cholesterol to support rapid lysosomal membrane repair. Unbiased proteomics of LMP-induced recruitment, live-cell imaging, lipid transfer assays, genetic depletion with lysosomal repair readouts Nature High 36071159
2025 A homozygous nonsense variant in OSBPL9 (c.615_616insTAA; p.Pro206*) was identified in fetuses with cerebral ventriculomegaly, cerebellar hypoplasia, and arthrogryposis multiplex in a consanguineous family, establishing loss of OSBPL9 function as causing a severe neurodevelopmental/structural malformation syndrome with autosomal recessive inheritance. Protein network analysis (STRING) identified close interactions between OSBPL9 and OSBP, PI4K2A, PIP5K1C, PI4KA, and CERT1, proteins involved in sphingomyelin, sterol, and phosphatidylinositol metabolism. Whole exome sequencing, chromosomal microarray homozygosity mapping, protein network analysis Cureus Low 40182349

Source papers

Stage 0 corpus · 45 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2009 Defining the human deubiquitinating enzyme interaction landscape. Cell 1282 19615732
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2009 A genome-wide RNAi screen identifies multiple synthetic lethal interactions with the Ras oncogene. Cell 843 19490893
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2005 Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome research 409 16344560
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2017 Genome-wide CRISPR screen identifies HNRNPL as a prostate cancer dependency regulating RNA splicing. Proceedings of the National Academy of Sciences of the United States of America 282 28611215
2022 A phosphoinositide signalling pathway mediates rapid lysosomal repair. Nature 278 36071159
2009 MicroRNA-125a-5p partly regulates the inflammatory response, lipid uptake, and ORP9 expression in oxLDL-stimulated monocyte/macrophages. Cardiovascular research 268 19377067
2009 Lys-N and trypsin cover complementary parts of the phosphoproteome in a refined SCX-based approach. Analytical chemistry 226 19413330
2018 An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein interactions and subcellular localizations. Nature communications 201 29568061
2020 UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination. Nature cell biology 168 32807901
2009 Gene-centric association signals for lipids and apolipoproteins identified via the HumanCVD BeadChip. American journal of human genetics 164 19913121
2001 The OSBP-related protein family in humans. Journal of lipid research 158 11483621
2009 Oxysterol binding protein-related Protein 9 (ORP9) is a cholesterol transfer protein that regulates Golgi structure and function. Molecular biology of the cell 156 19129476
2020 A High-Density Human Mitochondrial Proximity Interaction Network. Cell metabolism 148 32877691
2019 Mapping the proximity interaction network of the Rho-family GTPases reveals signalling pathways and regulatory mechanisms. Nature cell biology 137 31871319
2001 A family of 12 human genes containing oxysterol-binding domains. Genomics 115 11735225
2021 Protein interaction landscapes revealed by advanced in vivo cross-linking-mass spectrometry. Proceedings of the National Academy of Sciences of the United States of America 113 34349018
2018 Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei. Molecular & cellular proteomics : MCP 101 30021884
2004 VAMP-associated protein-A regulates partitioning of oxysterol-binding protein-related protein-9 between the endoplasmic reticulum and Golgi apparatus. Experimental cell research 89 15212954
2021 SARS-CoV-2-host proteome interactions for antiviral drug discovery. Molecular systems biology 86 34709727
2017 Assembly of the WHIP-TRIM14-PPP6C Mitochondrial Complex Promotes RIG-I-Mediated Antiviral Signaling. Molecular cell 68 29053956
2009 OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism. Journal of molecular medicine (Berlin, Germany) 51 19554302
2017 Targeted next generation sequencing identifies somatic mutations and gene fusions in papillary thyroid carcinoma. Oncotarget 38 28507274
2019 Analysis of the Zika and Japanese Encephalitis Virus NS5 Interactomes. Journal of proteome research 25 31199156
2013 A candidate gene analysis of canine hypoadrenocorticism in 3 dog breeds. The Journal of heredity 21 23997205
2015 Differentially expressed gene transcripts using RNA sequencing from the blood of immunosuppressed kidney allograft recipients. PloS one 20 25946140
2017 Multicellular tumor spheroids of human uveal melanoma induce genes associated with anoikis resistance, lipogenesis, and SSXs. Molecular vision 17 29033534
2017 Expression differences of genes in the PI3K/AKT, WNT/b-catenin, SHH, NOTCH and MAPK signaling pathways in CD34+ hematopoietic cells obtained from chronic phase patients with chronic myeloid leukemia and from healthy controls. Clinical & translational oncology : official publication of the Federation of Spanish Oncology Societies and of the National Cancer Institute of Mexico 13 28905209
2018 Molecular partners of hNOT/ALG3, the human counterpart of the Drosophila NOT and yeast ALG3 gene, suggest its involvement in distinct cellular processes relevant to congenital disorders of glycosylation, cancer, neurodegeneration and a variety of further pathologies. Human molecular genetics 9 29547901
2018 A highly sensitive trap vector system for isolating reporter cells and identification of responsive genes. Biology methods & protocols 9 32161797
2020 Identification of Novel Potential Type 2 Diabetes Genes Mediating β-Cell Loss and Hyperglycemia Using Positional Cloning. Frontiers in genetics 8 33133152
2024 Discovering ferroptosis-associated tumor antigens and ferroptosis subtypes in pancreatic adenocarcinoma to facilitate mRNA vaccine development. Heliyon 5 38463885
2021 Long tracks of homozygosity predict the severity of alcohol use disorders in an American Indian population. Molecular psychiatry 4 33398086
2025 Identification of Key Biomarkers Related to Lipid Metabolism in Acute Pancreatitis and Their Regulatory Mechanisms Based on Bioinformatics and Machine Learning. Biomedicines 2 41007695
2024 Sarcomatoid Morphology in Pediatric Langerhans Cell Neoplasm Does Not Always Predict Aggressive Clinical Course. Pediatric and developmental pathology : the official journal of the Society for Pediatric Pathology and the Paediatric Pathology Society 1 39340393
2025 The First Known Case Report of a Novel Homozygous Nonsense Variant in the OSBPL9 Gene Associated With Fetal Cerebral Ventriculomegaly, Cerebellar Hypoplasia, and Arthrogryposis Multiplex. Cureus 0 40182349