SORT1

SORT1 encodes sortilin, a type-I transmembrane sorting receptor that governs the intracellular trafficking and secretion of multiple ligands and was originally identified as the 100-kDa neurotensin receptor, the first transmembrane neuropeptide receptor outside the G-protein-coupled receptor superfamily (PMID:9756851). Sortilin matures by furin cleavage of a 110-kDa precursor into a higher-affinity 100-kDa form (PMID:9756851). In the liver, sortilin is a central regulator of plasma cholesterol: it binds apolipoprotein B100 in the Golgi to facilitate assembly and hepatic export of apoB100-containing lipoproteins (PMID:20816088), and acts as a high-affinity trans-Golgi network sorting receptor for PCSK9 to promote its secretion (PMID:24506872). Hepatic SORT1 expression is itself set by a causal noncoding regulatory variant (rs12740374) that creates a C/EBP binding site, with allele-specific CRISPR editing in primary hepatocytes and humanized mice confirming the variant controls SORT1 transcription and downstream LDL/VLDL levels (PMID:20686566, PMID:29097363). Beyond lipoprotein sorting, cell-surface sortilin binds and internalizes LDL by receptor-mediated endocytosis (PMID:23102784) and mediates uptake of SORT1-targeted peptide-drug conjugates in cancer cells (PMID:34751242, PMID:36145658). In the nervous system, progranulin signals retrogradely onto Sort1 on cerebellar climbing fibers to strengthen developing synaptic inputs and counteract synapse elimination (PMID:29398357), and SORT1 mRNA is subject to TDP-43/hnRNP-regulated alternative splicing of exon 17b that controls production of a truncated sortilin isoform implicated in FTLD-TDP (PMID:26614389).

1. 1998 High

   Established the molecular identity of sortilin as a non-GPCR transmembrane neurotensin receptor and defined furin cleavage as the maturation step that confers high-affinity ligand binding.

   Evidence Cloning from human brain cDNA, saturable neurotensin binding in transfected COS-7 cells, furin co-transfection, affinity labeling and immunolocalization

   PMID:9756851

   Open questions at the time

   • Did not address lipoprotein or PCSK9 sorting functions
   • Downstream signaling consequences of neurotensin binding not defined
2. 2010 High

   Showed that hepatic sortilin causally controls plasma LDL/VLDL and identified the causal noncoding regulatory mechanism behind a major lipid GWAS locus.

   Evidence siRNA knockdown and adenoviral overexpression in mouse liver, VLDL secretion assays, human expression QTL analysis identifying rs12740374 creating a C/EBP site

   PMID:20686566

   Open questions at the time

   • Direction of effect on secretion not fully reconciled across studies
   • Molecular cargo bound by sortilin not identified in this study
3. 2010 High

   Identified apoB100 as a direct sortilin cargo, providing the molecular mechanism for sortilin's control of hepatic lipoprotein export.

   Evidence Reciprocal Co-IP of sortilin with apoB100, gene-targeted knockout and hepatic overexpression in mice with plasma LDL/atherosclerosis readouts

   PMID:20816088

   Open questions at the time

   • Precise binding interface on apoB100/sortilin not mapped
   • Stoichiometry and Golgi trafficking itinerary not resolved
4. 2012 Medium

   Distinguished a cell-surface endocytic pool of sortilin that binds and internalizes LDL from intracellular sorting, while showing SORT1 missense variants are unlikely to cause autosomal dominant hypercholesterolemia.

   Evidence Wild-type and surface-retained mutant SORT1 constructs in HeLa T-REx cells, siRNA knockdown, cell-surface LDL binding/internalization assays

   PMID:23102784

   Open questions at the time

   • Single lab
   • Quantitative contribution of surface uptake versus secretory sorting to plasma LDL not established
5. 2014 High

   Defined sortilin as a high-affinity TGN sorting receptor for PCSK9, linking it mechanistically to a second arm of cholesterol regulation.

   Evidence TGN colocalization and binding assays, sortilin-knockout and overexpression mice, plasma PCSK9 ELISA, human cohort correlation

   PMID:24506872

   Open questions at the time

   • Binding interface not mapped at residue level
   • Whether sortilin escorts PCSK9 along a dedicated secretory route not defined
6. 2015 Medium

   Revealed that TDP-43 and an hnRNP network suppress SORT1 exon 17b inclusion, connecting RNA-binding-protein dysfunction in FTLD-TDP to production of a truncated sortilin isoform.

   Evidence RNA-binding protein knockdown/overexpression, minigene splicing assays, analysis of FTLD-TDP patient tissue

   PMID:26614389

   Open questions at the time

   • Functional consequence of the truncated isoform not biochemically characterized
   • Single lab
7. 2015 Medium

   Implicated a SORT1 missense mutation in essential tremor by impairing sortilin expression and reducing its partner p75NTR, linking sortilin to neuronal apoptosis pathways.

   Evidence Whole exome sequencing in a family, mutagenesis, cell-based expression, ELISA, apoptosis assays

   PMID:26297037

   Open questions at the time

   • Single family/single lab
   • Causality for the tremor phenotype not established beyond segregation
8. 2017 High

   Provided causal proof that the rs12740374 noncoding allele drives hepatic SORT1 transcription, closing the loop from regulatory variant to gene expression.

   Evidence Allele-specific CRISPR-Cas9 editing in primary human hepatocytes and locus-humanized mice with quantitative SORT1 mRNA readout

   PMID:29097363

   Open questions at the time

   • Effect quantified at mRNA level; protein and downstream lipid effects assessed indirectly
   • Transcription factor occupancy at the edited site not directly measured here
9. 2018 High

   Established progranulin-Sort1 retrograde signaling as a developmental synaptic mechanism strengthening climbing-fiber inputs and counteracting synapse elimination, independent of semaphorin 3A.

   Evidence Sort1 conditional knockout, electrophysiology of CF-PC synapses, in vivo cerebellar circuit analysis, genetic epistasis with Sema3A

   PMID:29398357

   Open questions at the time

   • Direct progranulin-sortilin binding not biochemically demonstrated in this study
   • Downstream signaling cascade in climbing fibers not defined
10. 2018 Medium

    Showed sortilin functions in cancer biology, regulating extracellular vesicle secretion and drug resistance in myeloma and mediating receptor-dependent uptake driving vasculogenic mimicry in solid tumors.

    Evidence siRNA silencing of SORT1 (and LAMP2), EV secretion and adhesion assays, fluorescent peptide-drug-conjugate uptake, 3D capillary-formation assays, xenografts

    PMID:34751242 PMID:34979567 PMID:36145658

    Open questions at the time

    • Mechanism coupling sortilin to EV biogenesis not resolved
    • Single-lab findings for each tumor context
11. 2018 Low

    Implicated SORT1 as a genetic risk factor for frontotemporal dementia, with variant enrichment in the β-propeller and predicted GRN-binding region.

    Evidence Whole-exome sequencing and rare-variant burden/meta-analysis in European cohorts

    PMID:29555433

    Open questions at the time

    • Genetic association without direct biochemical validation of individual variants
    • Effect of variants on GRN binding not experimentally tested

• How sortilin's distinct trafficking functions (apoB100/PCSK9 secretory sorting, surface LDL endocytosis, progranulin/neurotensin receptor signaling) are partitioned and regulated within a single cell remains unresolved.
• No structural model integrating multiple ligand-binding modes in the timeline
• Mechanism switching sortilin between secretory and endocytic roles unknown
• Functional consequence of the truncated splice isoform uncharacterized