OSBPL9

OSBPL9 is an oxysterol-binding protein-family member implicated in cellular lipid homeostasis and the response to endoplasmic reticulum stress. It was identified as an ER stress-responsive gene whose mRNA is induced by thapsigargin in a manner dependent on the IRE1α branch of the unfolded protein response, since induction is blocked by IRE1α inhibitors but not by a PERK inhibitor (PMID:32161797). Beyond this regulatory placement, the available corpus characterizes OSBPL9 largely through physical associations: it interacts with hNOT-1/ALG3-1 (PMID:29547901) and has been recovered as a host interactor of flaviviral NS5 protein (PMID:31199156). A homozygous nonsense variant (p.Pro206*) was associated with an autosomal recessive phenotype of cerebral ventriculomegaly, cerebellar hypoplasia, and arthrogryposis multiplex, with network analysis linking OSBPL9 to lipid-metabolism factors including OSBP, PI4K2A, PIP5K1C, PI4KA, and CERT1 (PMID:40182349). The enzymatic mechanism and direct lipid-transport activity of OSBPL9 have not been experimentally characterized in the available corpus.

1. 2018 Medium

   Established that OSBPL9 is not constitutively static but is a transcriptional output of ER stress signaling, and pinpointed which UPR branch drives it.

   Evidence Trap vector reporter screen plus RT-qPCR of endogenous mRNA with pharmacological inhibition of IRE1α versus PERK in cultured cells

   PMID:32161797

   Open questions at the time

   • No demonstration of how IRE1α activity connects mechanistically to the OSBPL9 promoter (direct XBP1s binding not shown)
   • Does not establish a functional consequence of OSBPL9 induction for ER stress resolution
   • Protein-level induction and localization changes not measured
2. 2018 Low

   Began placing OSBPL9 in a protein-interaction network by identifying a binding partner, hNOT-1/ALG3-1.

   Evidence Yeast two-hybrid protein interaction screen

   PMID:29547901

   Open questions at the time

   • Single method (yeast two-hybrid) without reciprocal or in-cell validation
   • Functional significance of the interaction is undefined
   • No mapping of the interacting domains
3. 2019 Low

   Connected OSBPL9 to viral biology by recovering it as a host factor bound to flaviviral NS5.

   Evidence EGFP immunoprecipitation coupled to label-free quantitative mass spectrometry of the Zika/JEV NS5 interactome

   PMID:31199156

   Open questions at the time

   • Single Co-IP/MS without OSBPL9-specific functional follow-up
   • Direct versus indirect association not distinguished
   • No test of whether OSBPL9 supports or restricts viral replication
4. 2025 Low

   Provided the first human-genetic link between OSBPL9 loss of function and a developmental disorder, and embedded the gene in a lipid-metabolism interaction network.

   Evidence Whole exome sequencing and chromosomal microarray homozygosity mapping in affected fetuses, with STRING network analysis

   PMID:40182349

   Open questions at the time

   • No RNA, protein, cellular, or animal functional validation of the variant (stated limitation)
   • Causality of the variant for the phenotype not established beyond genetic association
   • Network membership is computational, not experimentally demonstrated for OSBPL9

• The direct biochemical activity of OSBPL9 — whether and how it binds and transfers sterols or phospholipids, and at which membrane contact sites — remains undefined.
• No demonstrated lipid-binding or lipid-transfer activity
• Subcellular localization not experimentally established in the corpus
• Mechanistic link between UPR induction and any lipid-handling function unresolved