Affinage

CLN8

Protein CLN8 · UniProt Q9UBY8

Length
286 aa
Mass
32.8 kDa
Annotated
2026-04-28
44 papers in source corpus 14 papers cited in narrative 14 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CLN8 is an ER-resident transmembrane protein that serves dual roles as a lysophosphatidylglycerol acyltransferase essential for bis(monoacylglycero)phosphate (BMP) biosynthesis and as an ER cargo receptor for lysosomal enzymes, thereby governing lysosome biogenesis and function (PMID:39970228, PMID:30397314). CLN8 forms the EGRESS complex with CLN6, which recruits soluble lysosomal enzymes at the ER via its second luminal loop and mediates their COPII/COPI-dependent export to the Golgi; disease-causing mutations in this loop abolish enzyme binding and deplete lysosomal enzymes (PMID:30397314, PMID:32597833). CLN8 also interacts with PP2A/I2PP2A to regulate ceramide levels and downstream Akt/S6K/GSK3β signaling, and its loss impairs mitochondrial calcium buffering, autophagy, and neuronal viability (PMID:30453012, PMID:21917311, PMID:38763444). Loss-of-function mutations in CLN8 cause neuronal ceroid lipofuscinosis (Batten disease), a neurodegenerative lysosomal storage disorder (PMID:10508524).

Mechanistic history

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

    Positional cloning identified CLN8 as a novel transmembrane protein whose mutations cause progressive epilepsy with mental retardation (EPMR) in humans and motor neuron degeneration in mnd mice, establishing CLN8 as a neuronal ceroid lipofuscinosis gene.

    Evidence Positional cloning and mutation screening in human EPMR families and mnd mice

    PMID:10508524

    Open questions at the time
    • Protein function entirely unknown at this stage
    • Subcellular localization not determined
    • No mechanistic connection to lipofuscin storage
  2. 2000 High

    Determination that CLN8 is an ER-resident protein recycling through the ERGIC via a C-terminal KKRP retrieval signal established the ER as its primary site of action and suggested involvement in ER-to-Golgi trafficking.

    Evidence Confocal immunofluorescence, pulse-chase, site-directed mutagenesis of KKRP motif

    PMID:10861296

    Open questions at the time
    • Cargo being trafficked unknown
    • Enzymatic activity not addressed
    • Neuronal localization not yet confirmed
  3. 2004 Medium

    Confirmation of ER localization in primary hippocampal neurons, and the finding that disease mutations do not mislocalize CLN8, indicated that pathogenesis arises from loss of CLN8 function rather than mislocalization.

    Evidence Viral expression in primary neurons, subcellular fractionation of mouse brain

    PMID:15160397

    Open questions at the time
    • Functional activity of CLN8 at the ER still unknown
    • Brain fractionation placed endogenous Cln8 in non-ER light membranes, suggesting additional compartments
  4. 2011 Medium

    Two parallel discoveries linked CLN8 to ceramide metabolism and to mitochondrial calcium handling: CLN8-deficient cells showed reduced ceramide synthase activity and decreased ceramide species, while Cln8mnd neurons exhibited impaired mitochondrial Ca²⁺ uptake, revealing downstream consequences of CLN8 loss.

    Evidence Mass spectrometry lipidomics and co-IP with ceramide synthase; patch-clamp and Ca²⁺ imaging in Cln8mnd hippocampal neurons

    PMID:21917311 PMID:23160995

    Open questions at the time
    • Whether CLN8 directly catalyzes ceramide synthesis or acts indirectly was unclear
    • Relationship between ceramide deficiency and mitochondrial Ca²⁺ defect not established
    • Single-lab findings for each
  5. 2012 Medium

    Identification of CLN8 physical interactors including VAPA, GATE16/GABARAPL2, and BNIP3/BNIP3L expanded the functional network to ER–organelle contacts and autophagy-related pathways.

    Evidence Split-ubiquitin membrane yeast two-hybrid screen validated by co-IP and co-localization in mammalian cells and CNS tissue

    PMID:23142642

    Open questions at the time
    • Functional significance of VAPA and GATE16 interactions not tested by loss-of-function
    • Y2H-derived interactions require further in vivo validation
    • No direct link to lysosomal enzyme trafficking yet
  6. 2018 High

    A breakthrough study revealed CLN8 functions as an ER cargo receptor for lysosomal enzymes, with its second luminal loop directly binding enzymes and its cytosolic C-terminus engaging COPII/COPI machinery; this explained how CLN8 loss depletes lysosomes of soluble enzymes and impairs lysosome biogenesis.

    Evidence Co-IP, mutagenesis of export/retrieval signals and luminal loop, CLN8 KO/KD with lysosomal enzyme quantification and trafficking assays

    PMID:30397314

    Open questions at the time
    • Whether CLN8 acts alone or requires a co-receptor was unknown
    • Enzymatic activity of CLN8 itself not addressed
    • Selectivity mechanism for different lysosomal enzymes not defined
  7. 2018 Medium

    The discovery that CLN8 interacts with PP2A and its inhibitor I2PP2A, with CLN8 deficiency increasing PP2A activity and reducing Akt/S6K/GSK3β phosphorylation, provided a signaling axis linking CLN8 to cell survival regulation independent of its cargo receptor role.

    Evidence Co-IP of CLN8–PP2A/I2PP2A, phospho-western blotting, pharmacological rescue with cantharidin in patient fibroblasts

    PMID:30453012

    Open questions at the time
    • Relationship between PP2A regulation and lysosomal enzyme trafficking not clarified
    • Single-lab observation
    • Whether PP2A interaction is direct or bridged through a common complex unclear
  8. 2020 High

    Demonstration that CLN6 and CLN8 form an obligate complex (EGRESS) that jointly recruits lysosomal enzymes at the ER resolved how ER cargo reception is organized; epistasis analysis in double-KO mice confirmed they act in the same pathway.

    Evidence Reciprocal co-IP, CLN6 luminal loop mutagenesis, trafficking assays, CLN6/CLN8 double-knockout mice

    PMID:32597833

    Open questions at the time
    • Stoichiometry and structure of the EGRESS complex unknown
    • How EGRESS distinguishes different lysosomal enzymes from other ER cargo not defined
    • Whether additional ER factors participate in the complex
  9. 2021 Medium

    CLN8 knockdown in primary neurons caused Golgi expansion, altered endo-lysosome dynamics, lysosomal alkalinization, and dendritic atrophy, providing a cellular phenotype linking CLN8 loss to neuronal morphology defects.

    Evidence siRNA knockdown with live-cell LAMP1-pHluorin imaging and dendritic morphometry in rat hippocampal neurons

    PMID:34021618

    Open questions at the time
    • Whether Golgi expansion is a direct consequence of impaired ER-to-Golgi trafficking or secondary
    • No rescue experiment reported
    • Mechanism of dendritic simplification not established
  10. 2024 Medium

    CLN8 dysfunction was shown to impair autophagy in vivo, and pharmacological enhancement of autophagy with trehalose/SG2 attenuated pathology in CLN8-deficient zebrafish, establishing autophagy as a therapeutically relevant downstream pathway.

    Evidence CLN8 loss-of-function zebrafish model with autophagy analysis and pharmacological rescue

    PMID:38763444

    Open questions at the time
    • Molecular step at which autophagy is blocked not defined
    • Whether autophagy impairment is secondary to lysosomal enzyme depletion or an independent function of CLN8
    • Relevance to mammalian disease models not yet tested
  11. 2025 High

    Biochemical reconstitution demonstrated that CLN8 is a lysophosphatidylglycerol acyltransferase catalyzing a critical step in BMP biosynthesis, revealing for the first time a direct enzymatic activity for CLN8 and explaining its requirement for lysosome membrane lipid homeostasis.

    Evidence In vitro acyltransferase assay with substrate/product identification by lipidomics

    PMID:39970228

    Open questions at the time
    • How acyltransferase activity is coordinated with the EGRESS cargo receptor function is unknown
    • Structural basis of dual function not resolved
    • Whether BMP deficiency or enzyme depletion is the primary driver of NCL pathology remains open

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown how CLN8 integrates its dual roles as an acyltransferase for BMP biosynthesis and as an ER cargo receptor within the EGRESS complex, whether these functions are separable, and which activity is the primary driver of neurodegeneration in NCL.
  • No structure of CLN8 or the EGRESS complex
  • Relative contribution of BMP deficiency vs. lysosomal enzyme depletion to disease not dissected
  • Cell-type-specific functions in neurons vs. glia not resolved

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:0005783 endoplasmic reticulum 3
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-1430728 Metabolism 2 R-HSA-9609507 Protein localization 2 R-HSA-9612973 Autophagy 1
Partners
BNIP3LCLN6GABARAPL2I2PP2APP2ASTX8VAPA
Complex memberships
EGRESS complex (CLN6-CLN8)

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 CLN8 encodes a novel putative transmembrane protein of 286 amino acids; a missense mutation (R24G) in human EPMR patients and a 1-bp insertion causing frameshift/truncation in mnd mice were identified as disease-causing mutations in orthologous CLN8 genes. Positional cloning, sequence analysis, mutation screening Nature genetics High 10508524
2000 CLN8 protein is an ER-resident transmembrane protein (~33 kDa) that recycles between the ER and ER-Golgi intermediate compartment (ERGIC); the C-terminal KKRP motif functions as an ER retrieval signal, and mutation of this signal redirects CLN8 to the Golgi apparatus. Western blotting, pulse-chase analysis, confocal immunofluorescence microscopy with organelle-specific antibodies, site-directed mutagenesis of KKRP signal Human molecular genetics High 10861296
2002 CLN8 is identified as a member of the TLC (TRAM-LAG1-CLN8) domain family, related to yeast Lag1p and mammalian TRAM, implicating the protein in ceramide synthesis, lipid regulation, or protein translocation at the ER. Bioinformatic sequence analysis and domain family identification Trends in biochemical sciences Low 12151215
2004 CLN8 localizes to the ER in mouse hippocampal primary neurons; CLN8 shows basolateral targeting in polarized epithelial CaCo-2 cells; endogenous mouse Cln8 is found in light membrane fractions distinct from ER in brain fractionation; disease mutations do not alter intracellular localization of CLN8 in neuronal or non-neuronal cells. Semliki Forest virus-mediated expression, immunofluorescence microscopy with subcellular markers, subcellular fractionation of mouse brain tissue 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 patient-mutation CLN8 proteins in neuronal cell models and gene silencing both impaired proliferation and increased cell death during neuronal differentiation. Overexpression of wild-type and mutant CLN8 in neuronal cell models, siRNA gene silencing, cell proliferation and cell death assays Human mutation Medium 19431184
2011 CLN8-deficient (CLN8−/−) cells have decreased ceramide synthase activity and reduced C16/C18:0/C24:0/C24:1 ceramide species; CLN8 protein functionally complements CLN5-deficient cells, correcting growth and apoptosis defects; CLN8 protein was found to interact with ceramide synthase complex. Mass spectrometry-based ceramide species quantification, co-immunoprecipitation, complementation assays in CLN5-deficient fibroblasts Electrophoresis Medium 23160995
2011 In Cln8mnd hippocampal neurons, clearance of large Ca2+ loads is inefficient due to impaired mitochondrial Ca2+ uptake; neither SERCA-mediated ER Ca2+ uptake nor plasma membrane Ca2+ extrusion is affected by the Cln8 mutation. Patch clamp electrophysiology, fluorescence Ca2+ imaging, caged Ca2+ photolysis in hippocampal slices and cultured neurons Cell calcium Medium 21917311
2012 CLN8 protein interacts with VAPA, c14orf1/hERG28, STX8, GATE16, BNIP3, and BNIP3L; interactions with VAPA and GATE16 were validated by co-immunoprecipitation and co-localization assays in mammalian cells and confirmed in CNS tissues. Split-ubiquitin membrane yeast two-hybrid (MYTH) screen with human brain cDNA library, co-immunoprecipitation, co-localization assays, CNS tissue co-staining Biochimica et biophysica acta Medium 23142642
2018 CLN8 functions as an ER cargo receptor for lysosomal enzymes, mediating their ER-to-Golgi transfer via interaction with the COPII (export) and COPI (retrieval) machineries through specific signals in its cytosolic C-terminus; the second luminal loop of CLN8 binds lysosomal enzymes and is required for this interaction; CLN8 deficiency depletes soluble enzymes from lysosomes, impairing lysosome biogenesis; disease-causing mutations in the second luminal loop abolish enzyme binding. Co-immunoprecipitation, trafficking assays, mutagenesis of export/retrieval signals and luminal loop, CLN8 knockout/knockdown with lysosomal enzyme quantification Nature cell biology High 30397314
2018 CLN8 interacts with PP2A and its inhibitor I2PP2A; CLN8 deficiency leads to increased PP2A phosphatase activity (reduced phosphorylation of Akt, S6 kinase, GSK3β substrates) in patient fibroblasts; ceramide levels are reduced by ~60% in CLN8-deficient cells; transport of ceramide from ER to Golgi is not affected by CLN8 deficiency. Co-immunoprecipitation of CLN8 with PP2A/I2PP2A, phospho-western blotting, pharmacological rescue with cantharidin, NBD-ceramide trafficking assay, lipidomics 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) that recruits lysosomal enzymes at the ER for Golgi transfer; the second luminal loop of CLN6 is required for binding lysosomal enzymes but not for interaction with CLN8; CLN6 deficiency reduces ER export of lysosomal enzymes; mice lacking both CLN6 and CLN8 show no aggravated pathology compared to single knockouts, confirming both proteins act in the same functional unit. Co-immunoprecipitation, mutagenesis of CLN6 luminal loop, trafficking assays, lysosomal enzyme quantification, CLN6/CLN8 double-knockout mice with epistasis analysis The Journal of clinical investigation High 32597833
2021 CLN8 knockdown increases Golgi apparatus size, increases number and speed of mobile endo-lysosomes, causes lysosomal alkalisation, and reduces complexity/size of the somatodendritic compartment in primary rat hippocampal neurons. CLN8 siRNA knockdown, live-cell fluorescence imaging of endo-lysosomes (mApple-LAMP1-pHluorin), confocal microscopy of Golgi, dendritic morphometry in primary neurons Biology of the cell Medium 34021618
2024 CLN8 dysfunction impairs autophagy; treatment with autophagy modulators trehalose and SG2 attenuates the pathological phenotype in CLN8-deficient zebrafish larvae. CLN8-deficient zebrafish model (loss-of-function), autophagy pathway analysis, pharmacological rescue with trehalose and SG2 Neurobiology of disease Medium 38763444
2025 CLN8 is a lysophosphatidylglycerol acyltransferase that catalyzes an essential step in the biosynthesis of bis(monoacylglycero)phosphate (BMP), a phospholipid critical for lysosome function; this enzymatic activity is demonstrated for the human CLN8 protein. In vitro acyltransferase assay, lipidomics, biochemical reconstitution Science advances High 39970228

Source papers

Stage 0 corpus · 44 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 234 10508524
2002 TRAM, LAG1 and CLN8: members of a novel family of lipid-sensing domains? Trends in biochemical sciences 136 12151215
2005 A mutation in the CLN8 gene in English Setter dogs with neuronal ceroid-lipofuscinosis. Biochemical and biophysical research communications 102 15629147
2000 The neuronal ceroid lipofuscinosis CLN8 membrane protein is a resident of the endoplasmic reticulum. Human molecular genetics 91 10861296
2018 CLN8 is an endoplasmic reticulum cargo receptor that regulates lysosome biogenesis. Nature cell biology 86 30397314
2020 A CLN6-CLN8 complex recruits lysosomal enzymes at the ER for Golgi transfer. The Journal of clinical investigation 68 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 55 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 45 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 41 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 35 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 24 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 16 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 13 31687336
2018 Neuronal ceroid lipofuscinosis related ER membrane protein CLN8 regulates PP2A activity and ceramide levels. Biochimica et biophysica acta. Molecular basis of disease 13 30453012
1996 Genetic and physical mapping of the progressive epilepsy with mental retardation (EPMR) locus on chromosome 8p. Genome research 13 8743986
2021 The neuronal ceroid lipofuscinosis-related protein CLN8 regulates endo-lysosomal dynamics and dendritic morphology. Biology of the cell 12 34021618
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
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
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
2019 The Neuronal Ceroid Lipofuscinoses-Linked Loss of Function CLN5 and CLN8 Variants Disrupt Normal Lysosomal Function. Neuromolecular medicine 4 30919163
2025 TRAM-LAG1-CLN8 family proteins are acyltransferases regulating phospholipid composition. Science advances 3 39970228
2022 CLN8 Gene Compound Heterozygous Variants: A New Case and Protein Bioinformatics Analyses. Genes 3 36011304
2024 Two compound heterozygous variants in the CLN8 gene are responsible for neuronal cereidolipofuscinoses disorder in a child: a case report. Frontiers in pediatrics 0 38751748