Affinage

CLN8

Protein CLN8 · UniProt Q9UBY8

Length
286 aa
Mass
32.8 kDa
Annotated
2026-06-09
45 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CLN8 is an ER-resident transmembrane protein of the TRAM-LAG1-CLN8 (TLC) domain family that links lysosomal enzyme delivery and phospholipid metabolism, and whose loss causes neuronal ceroid lipofuscinosis: distinct mutations underlie human EPMR (R24G) and the murine mnd phenotype (PMID:10508524). The protein localizes to the ER and cycles to the ERGIC, with a C-terminal KKRP motif serving as an ER-retrieval signal whose mutation redirects CLN8 to the Golgi (PMID:10861296). Mechanistically, CLN8 acts as an ER cargo receptor for soluble lysosomal enzymes, binding them through its second luminal loop—an interaction abolished by disease mutations in this region—and shuttling them from the ER to the Golgi via COPII export and COPI retrieval signals in its cytosolic C-terminus, such that CLN8 deficiency depletes lysosomal enzymes and impairs lysosome biogenesis (PMID:30397314). This receptor function is executed within an obligate complex with CLN6 (the EGRESS complex), which operates as a single functional unit (PMID:32597833). Independently, CLN8 is a lysophosphatidylglycerol acyltransferase catalyzing an essential step in biosynthesis of the lysosomal phospholipid bis(monoacylglycero)phosphate (BMP) (PMID:39970228). CLN8 loss perturbs sphingolipid homeostasis, reducing ceramide synthase activity and ceramide species (PMID:23160995), and elevates PP2A activity through interaction with PP2A and its inhibitor I2PP2A (PMID:30453012). Downstream consequences include endo-lysosomal dysfunction with Golgi enlargement and lysosomal alkalinization (PMID:34021618), impaired autophagy (PMID:38763444), and ER stress and calcium-handling defects in disease models (PMID:21094208, PMID:21917311).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1999 High

    Established the genetic identity of CLN8, answering which gene underlies EPMR and the mnd neurodegenerative phenotype.

    Evidence Positional cloning and mutation analysis in human EPMR patients and mnd mice

    PMID:10508524

    Open questions at the time
    • Protein function unknown at this stage
    • No subcellular localization or biochemical activity defined
  2. 2000 High

    Defined CLN8 as an ER-resident protein cycling to the ERGIC and identified the KKRP C-terminal ER-retrieval signal, framing it as a trafficking/secretory pathway component.

    Evidence Confocal immunofluorescence, pulse-chase, and site-directed mutagenesis of the KKRP motif in multiple cell lines

    PMID:10861296

    Open questions at the time
    • Cargo or molecular activity not identified
    • Mechanism of retrieval beyond signal mapping unresolved
  3. 2002 Low

    Placed CLN8 in the TLC domain family, raising the hypothesis of a lipid-related ER function.

    Evidence Bioinformatic sequence and domain analysis

    PMID:12151215

    Open questions at the time
    • Computational prediction only, no experimental validation of lipid function in this work
    • Specific enzymatic activity not demonstrated
  4. 2009 Medium

    Linked CLN8 to cellular phenotypes of neuronal proliferation and survival, moving beyond localization toward functional consequence.

    Evidence Overexpression of wild-type/mutant CLN8 and siRNA silencing in neuronal cell models with proliferation and apoptosis assays

    PMID:19431184

    Open questions at the time
    • Molecular mechanism behind proliferation/survival role not defined
    • Single lab, cell-model based
  5. 2011 Medium

    Connected CLN8 loss to ER stress and impaired mitochondrial calcium handling, identifying stress pathways contributing to disease progression.

    Evidence ER stress marker profiling in Cln8mnd CNS and electrophysiology/Ca2+ imaging in mutant hippocampal neurons

    PMID:21094208 PMID:21917311

    Open questions at the time
    • Whether these are primary or downstream effects unresolved
    • Mechanistic link to CLN8 molecular function not established
  6. 2012 Medium

    Defined a physical interactome (VAPA, GATE16, STX8, BNIP3/3L) and linked CLN8 to ceramide synthase activation, implicating it in lipid metabolism and trafficking.

    Evidence Split-ubiquitin membrane yeast two-hybrid with Co-IP/co-localization validation; ceramide synthase activity assays and MS in CLN8-/- cells with CLN5 complementation

    PMID:23142642 PMID:23160995

    Open questions at the time
    • Direct enzymatic role versus indirect modulation of ceramide synthases unclear
    • Interactors validated only for a subset
  7. 2018 High

    Established CLN8's core molecular function as an ER cargo receptor for lysosomal enzymes and a regulator of PP2A activity, explaining lysosomal enzyme depletion in deficiency.

    Evidence Co-IP, luminal loop and COPII/COPI signal mutagenesis, lysosomal enzyme activity assays; Co-IP with PP2A/I2PP2A and cantharidin rescue in patient fibroblasts

    PMID:30397314 PMID:30453012

    Open questions at the time
    • Identity of full cargo repertoire incomplete
    • How PP2A modulation integrates with cargo receptor role unresolved
  8. 2020 High

    Demonstrated that CLN8 acts within an obligate CLN6-CLN8 (EGRESS) complex functioning as a single unit for ER-to-Golgi enzyme relay.

    Evidence Reciprocal Co-IP, CLN6 luminal-loop mutagenesis, enzyme trafficking assays, and CLN6/CLN8 double-knockout epistasis in mice

    PMID:32597833

    Open questions at the time
    • Stoichiometry and structure of the complex undetermined
    • Regulation of complex assembly unknown
  9. 2021 Medium

    Showed CLN8 loss disrupts endo-lysosomal dynamics, Golgi morphology, and lysosomal pH, and impairs dendritic development, connecting trafficking defects to neuronal phenotypes.

    Evidence shRNA knockdown with live pH imaging, vesicle tracking, Golgi morphometry, and dendritic morphology in primary neurons

    PMID:34021618

    Open questions at the time
    • Causal chain from enzyme depletion to dendritic deficits not fully traced
    • Single lab
  10. 2024 Medium

    Identified impaired autophagy as a secondary pathological event amenable to pharmacological correction in CLN8 disease.

    Evidence cln8-deficient zebrafish model with trehalose and SG2 rescue

    PMID:38763444

    Open questions at the time
    • Mechanistic link between cargo receptor loss and autophagy block not defined
    • Therapeutic relevance to mammals untested here
  11. 2025 High

    Resolved a direct catalytic activity for CLN8 as a lysophosphatidylglycerol acyltransferase in BMP biosynthesis, unifying its TLC-family identity with lysosomal phospholipid metabolism.

    Evidence In vitro acyltransferase reconstitution, lipidomics, and comparison with paralog TLCD1

    PMID:39970228

    Open questions at the time
    • How acyltransferase activity is reconciled with the cargo receptor role unresolved
    • In vivo contribution of BMP synthesis to disease not quantified

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CLN8's dual roles—enzyme cargo receptor in the EGRESS complex and LPG acyltransferase for BMP synthesis—are coordinated, and which is primary in driving neurodegeneration, remains unresolved.
  • No structural model integrating both functions
  • Relative disease contribution of each activity unmeasured
  • Substrate specificity in vivo undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0038024 cargo receptor activity 2 GO:0016740 transferase activity 1
Localization
GO:0005794 Golgi apparatus 3 GO:0005783 endoplasmic reticulum 2
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-9609507 Protein localization 2
Partners
BNIP3BNIP3LCLN6GATE16I2PP2APP2ASTX8VAPA
Complex memberships
EGRESS (CLN6-CLN8) complex

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 CLN8 encodes a novel putative transmembrane protein; a missense mutation (R24G) in EPMR patients and a frameshift insertion in mnd mice were identified as disease-causing, establishing CLN8 as the gene underlying these NCL phenotypes. Positional cloning, mutation analysis, sequence conservation analysis Nature genetics High 10508524
2000 CLN8 protein (~33 kDa) is an ER-resident protein that cycles between the ER and ERGIC; the C-terminal KKRP motif acts as an ER-retrieval signal, as mutation of KKRP redirects CLN8 to the Golgi; the mnd mutant protein is restricted to the ER, while the EPMR mutation (R24G) does not alter ER-ERGIC localization. Confocal immunofluorescence microscopy with organelle markers, western blotting, pulse-chase analysis, site-directed mutagenesis of KKRP retrieval signal, expression in BHK/HeLa/CHO cells Human molecular genetics High 10861296
2002 CLN8 was identified as a member of the TLC (TRAM-LAG1-CLN8) domain family, related to yeast Lag1p and mammalian TRAM, suggesting a conserved role in lipid sensing, ceramide synthesis, or lipid regulation in the ER. Bioinformatic sequence analysis and domain identification Trends in biochemical sciences Low 12151215
2004 In mouse hippocampal neurons, CLN8 localizes to the ER (consistent with non-neuronal cells); in polarized epithelial CaCo-2 cells, CLN8 shows basolateral targeting; brain fractionation shows endogenous Cln8 in light membrane fractions distinct from ER in polarized cells. Disease-causing mutations do not alter intracellular localization in neuronal or non-neuronal cells. Semliki Forest virus-mediated expression, immunofluorescence microscopy with subcellular markers, subcellular fractionation of mouse brain tissue, polarized epithelial cell targeting assay Journal of neuroscience research Medium 15160397
2009 CLN8 plays a role in cell proliferation during neuronal differentiation and in protection against cell death; expression of native CLN8 or mutant forms (including novel p.Lys61del and three previously described missense mutations) in neuronal cell models, validated by gene silencing, demonstrated these functions. Overexpression of wild-type and mutant CLN8 in neuronal cell models, gene silencing (siRNA knockdown), cell proliferation and apoptosis assays Human mutation Medium 19431184
2010 In CLN8(mnd) mice, ER stress markers are activated early and differentially across CNS regions: GRP78 upregulation and ATF6 activation occur presymptomatically in all regions; CHOP-dependent and caspase-12-dependent pathways are activated in a region-specific manner; NF-κB, TRAF2, TNF-α, and TNFR1 are also elevated, but ASK-1/JNK signaling is not activated. These ER stress responses contribute to CLN8(mnd) disease progression. Western blotting and immunohistochemistry for ER stress markers in Cln8mnd mouse CNS tissues at presymptomatic and symptomatic stages Neuroscience letters Medium 21094208
2011 In Cln8(mnd) hippocampal neurons, mitochondrial Ca2+ uptake is specifically impaired, reducing Ca2+ clearance efficiency; SERCA-mediated ER Ca2+ uptake and plasma membrane Ca2+ extrusion are unaffected. Cln8mnd neurons show increased vulnerability to excitotoxic glutamate-induced Ca2+ deregulation. Patch clamp, fluorescence Ca2+ imaging, caged Ca2+ photolysis in hippocampal slices and cultured neurons from Cln8mnd mice; pharmacological dissection of Ca2+ clearance pathways Cell calcium Medium 21917311
2012 CLN8 protein interacts with VAPA, c14orf1/hERG28, STX8, GATE16, BNIP3 and BNIP3L by split-ubiquitin membrane yeast two-hybrid screen; interactions with VAPA and GATE16 were validated by co-immunoprecipitation and co-localization in mammalian cells and CNS tissues, implicating CLN8 in lipid transport, vesicular trafficking, autophagy/mitophagy, and apoptosis. Split-ubiquitin membrane yeast two-hybrid (MYTH) screen, co-immunoprecipitation, co-localization immunofluorescence in mammalian cells and CNS tissue Biochimica et biophysica acta Medium 23142642
2012 CLN8-deficient cells show decreased ceramide synthase activity and reduced C16/C18:0/C24:0/C24:1 ceramide species (measured by MS), and CLN8 protein can complement defects in CLN5-deficient cells (growth, apoptosis), suggesting CLN8 and CLN5 are functionally related as activators of (dihydro)ceramide synthases. Ceramide synthase activity assay, mass spectrometry of ceramide species in CLN8-/- cells, complementation of CLN5-deficient cells by CLN8 overexpression Electrophoresis Medium 23160995
2018 CLN8 functions as an ER cargo receptor for lysosomal enzymes: it binds lysosomal enzymes via its second luminal loop (binding abolished by disease-causing mutations in this region), and traffics from ER to Golgi via COPII (export signal) and COPI (retrieval signal) interactions in its cytosolic C-terminus. CLN8 deficiency depletes soluble lysosomal enzymes and impairs lysosome biogenesis. Co-immunoprecipitation, domain mapping and mutagenesis (luminal loop, COPII/COPI signals), lysosomal enzyme activity assays, CLN8 knockdown/knockout with lysosomal functional readouts Nature cell biology High 30397314
2018 CLN8 interacts with PP2A and its inhibitor I2PP2A; CLN8-deficient patient fibroblasts show decreased phosphorylation of PP2A substrates Akt, S6 kinase, and GSK3β (reversed by PP2A inhibitor cantharidin), indicating elevated PP2A activity. Ceramide levels are reduced by ~60% in CLN8-deficient cells, but ER-to-Golgi ceramide transport is not impaired. Co-immunoprecipitation of CLN8 with PP2A/I2PP2A, phosphorylation assays in patient fibroblasts, cantharidin rescue experiment, NBD-C6-ceramide transport assay, ceramide quantification Biochimica et biophysica acta. Molecular basis of disease Medium 30453012
2020 CLN6 forms an obligate complex with CLN8 (termed EGRESS: ER-to-Golgi relaying of enzymes of the lysosomal system) to recruit and transport lysosomal enzymes from the ER to the Golgi; the second luminal loop of CLN6 is required for enzyme binding but not for CLN6-CLN8 interaction. Mice lacking both CLN6 and CLN8 do not show aggravated pathology compared to single knockouts, confirming the complex acts as a functional unit. Co-immunoprecipitation, domain mutagenesis (CLN6 luminal loop), lysosomal enzyme trafficking assays in vitro and in vivo, double-knockout mouse epistasis analysis The Journal of clinical investigation High 32597833
2021 CLN8 knockdown in neuronal and non-neuronal cells increases Golgi apparatus size, increases the number and speed of mobile endo-lysosomes, and causes lysosomal alkalinization (detected with mApple-LAMP1-pHluorin). In primary rat hippocampal neurons, CLN8 knockdown reduces dendritic complexity and size, establishing a role for CLN8 in endo-lysosomal dynamics and somatodendritic development. shRNA knockdown, live fluorescence imaging (mApple-LAMP1-pHluorin pH reporter), vesicle tracking, Golgi morphometry, dendritic morphology analysis in primary neurons Biology of the cell Medium 34021618
2024 CLN8 deficiency impairs autophagy in a zebrafish model; autophagy modulators trehalose and SG2 attenuate the pathological phenotype in cln8-deficient zebrafish larvae, establishing autophagy impairment as a secondary pathological event in CLN8 disease. Zebrafish cln8 knockout model, autophagy pathway analysis, pharmacological rescue with trehalose and SG2 Neurobiology of disease Medium 38763444
2025 CLN8 is a lysophosphatidylglycerol (LPG) acyltransferase that catalyzes an essential step in the biosynthesis of bis(monoacylglycero)phosphate (BMP), a phospholipid critical for lysosome function; this establishes CLN8 as a phospholipid remodeling enzyme within the TRAM-LAG1-CLN8 (TLC) domain protein family. In vitro acyltransferase activity assay, lipidomics, biochemical reconstitution of BMP biosynthesis, comparison with paralog TLCD1 (lysophosphatidylethanolamine acyltransferase) Science advances High 39970228

Source papers

Stage 0 corpus · 45 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 The neuronal ceroid lipofuscinoses in human EPMR and mnd mutant mice are associated with mutations in CLN8. Nature genetics 235 10508524
2002 TRAM, LAG1 and CLN8: members of a novel family of lipid-sensing domains? Trends in biochemical sciences 137 12151215
2005 A mutation in the CLN8 gene in English Setter dogs with neuronal ceroid-lipofuscinosis. Biochemical and biophysical research communications 103 15629147
2000 The neuronal ceroid lipofuscinosis CLN8 membrane protein is a resident of the endoplasmic reticulum. Human molecular genetics 92 10861296
2018 CLN8 is an endoplasmic reticulum cargo receptor that regulates lysosome biogenesis. Nature cell biology 87 30397314
2020 A CLN6-CLN8 complex recruits lysosomal enzymes at the ER for Golgi transfer. The Journal of clinical investigation 70 32597833
2011 Acyl chain specificity of ceramide synthases is determined within a region of 150 residues in the Tram-Lag-CLN8 (TLC) domain. The Journal of biological chemistry 57 22144673
2005 Mass spectrometric analysis reveals changes in phospholipid, neutral sphingolipid and sulfatide molecular species in progressive epilepsy with mental retardation, EPMR, brain: a case study. Journal of neurochemistry 53 16086686
2012 Genome-wide association study of N370S homozygous Gaucher disease reveals the candidacy of CLN8 gene as a genetic modifier contributing to extreme phenotypic variation. American journal of hematology 48 22388998
2012 CLN5 and CLN8 protein association with ceramide synthase: biochemical and proteomic approaches. Electrophoresis 46 23160995
2009 A novel CLN8 mutation in late-infantile-onset neuronal ceroid lipofuscinosis (LINCL) reveals aspects of CLN8 neurobiological function. Human mutation 45 19431184
2014 A CLN8 nonsense mutation in the whole genome sequence of a mixed breed dog with neuronal ceroid lipofuscinosis and Australian Shepherd ancestry. Molecular genetics and metabolism 42 24953404
2006 Novel mutations in CLN8 in Italian variant late infantile neuronal ceroid lipofuscinosis: Another genetic hit in the Mediterranean. Neurogenetics 38 16570191
2020 AAV9 Gene Therapy Increases Lifespan and Treats Pathological and Behavioral Abnormalities in a Mouse Model of CLN8-Batten Disease. Molecular therapy : the journal of the American Society of Gene Therapy 36 33010819
2004 Localization of wild-type and mutant neuronal ceroid lipofuscinosis CLN8 proteins in non-neuronal and neuronal cells. Journal of neuroscience research 35 15160397
2001 Turkish variant late infantile neuronal ceroid lipofuscinosis (CLN7) may be allelic to CLN8. European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society 34 11589000
2012 Identifying protein partners of CLN8, an ER-resident protein involved in neuronal ceroid lipofuscinosis. Biochimica et biophysica acta 30 23142642
2010 Different early ER-stress responses in the CLN8(mnd) mouse model of neuronal ceroid lipofuscinosis. Neuroscience letters 27 21094208
2009 Novel CLN8 mutations confirm the clinical and ethnic diversity of late infantile neuronal ceroid lipofuscinosis. Clinical genetics 27 19807737
2016 Neuronal ceroid lipofuscinosis (NCL) is caused by the entire deletion of CLN8 in the Alpenländische Dachsbracke dog. Molecular genetics and metabolism 26 28024876
2011 Deficient mitochondrial Ca(2+) buffering in the Cln8(mnd) mouse model of neuronal ceroid lipofuscinosis. Cell calcium 20 21917311
2007 A novel mutation of the CLN8 gene: is there a Mediterranean phenotype? Pediatric neurology 20 17560505
2018 Neuronal ceroid lipofuscinosis in Salukis is caused by a single base pair insertion in CLN8. Animal genetics 17 29446145
2001 Studies of homogenous populations: CLN5 and CLN8. Advances in genetics 15 11332769
2019 Neuronal ceroid lipofuscinosis in a German Shorthaired Pointer associated with a previously reported CLN8 nonsense variant. Molecular genetics and metabolism reports 14 31687336
2018 Neuronal ceroid lipofuscinosis related ER membrane protein CLN8 regulates PP2A activity and ceramide levels. Biochimica et biophysica acta. Molecular basis of disease 14 30453012
2021 The neuronal ceroid lipofuscinosis-related protein CLN8 regulates endo-lysosomal dynamics and dendritic morphology. Biology of the cell 13 34021618
1996 Genetic and physical mapping of the progressive epilepsy with mental retardation (EPMR) locus on chromosome 8p. Genome research 13 8743986
2021 miR-3074-5p/CLN8 pathway regulates decidualization in recurrent miscarriage. Reproduction (Cambridge, England) 12 34044364
2012 Phenotypic heterogeneity in consanguineous patients with a common CLN8 mutation. Pediatric neurology 11 22964447
2016 CLN8 disease caused by large genomic deletions. Molecular genetics & genomic medicine 8 28116333
2024 Targeting autophagy impairment improves the phenotype of a novel CLN8 zebrafish model. Neurobiology of disease 7 38763444
2023 A novel candidate gene CLN8 regulates fat deposition in avian. Journal of animal science and biotechnology 7 37121996
2021 CLN8 Mutations Presenting with a Phenotypic Continuum of Neuronal Ceroid Lipofuscinosis-Literature Review and Case Report. Genes 7 34201538
2019 Congenital CLN8 disease of neuronal ceroid lipofuscinosis: a novel phenotype. Revista de neurologia 7 30741402
2015 Novel missense mutation in CLN8 in late infantile neuronal ceroid lipofuscinosis: The first report of a CLN8 mutation in Japan. Brain & development 7 26443629
2001 Northern epilepsy syndrome (NES, CLN8)--MRI and electrophysiological studies. European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society 7 11588991
2019 The Neuronal Ceroid Lipofuscinoses-Linked Loss of Function CLN5 and CLN8 Variants Disrupt Normal Lysosomal Function. Neuromolecular medicine 6 30919163
2016 Exome sequencing identifies a novel homozygous CLN8 mutation in a Turkish family with Northern epilepsy. Acta neurologica Belgica 6 27844444
2020 Status dystonicus associated with CLN8 disease. Brain & development 5 33358637
2025 TRAM-LAG1-CLN8 family proteins are acyltransferases regulating phospholipid composition. Science advances 4 39970228
2022 CLN8 Gene Compound Heterozygous Variants: A New Case and Protein Bioinformatics Analyses. Genes 4 36011304
2022 Sex-split analysis of pathology and motor-behavioral outcomes in a mouse model of CLN8-Batten disease reveals an increased disease burden and trajectory in female Cln8mnd mice. Orphanet journal of rare diseases 4 36369162
2024 Two compound heterozygous variants in the CLN8 gene are responsible for neuronal cereidolipofuscinoses disorder in a child: a case report. Frontiers in pediatrics 1 38751748
2026 TRAM-LAG1-CLN8 domain-containing protein TMEM56 regulates cell migration by changing intracellular ceramide levels. BMC biology 0 42087192

Missed literature

Know a paper Affinage missed for CLN8? Flag it for the maintainers and the community.

No submissions yet.