Affinage

EPM2A

Laforin, isoform 9 · UniProt B3EWF7

Length
344 aa
Mass
35.2 kDa
Annotated
2026-06-09
54 papers in source corpus 12 papers cited in narrative 12 extracted findings
Cross-family judge faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

Laforin (EPM2A) is a dual-specificity phosphatase that safeguards glycogen quality control and intracellular proteostasis, with loss of function producing the neurodegenerative epilepsy Lafora disease (PMID:12019206). The protein is built from a carbohydrate-binding domain and a dual-specificity phosphatase domain, and disease mutations partition into folding/aggregation mutants in the phosphatase domain and localization-altering mutants in the carbohydrate-binding domain (PMID:12019207). Cytoplasmic/ER-localized laforin is the disease-relevant species, and its function is required to prevent the formation of insoluble Lafora inclusion bodies that accumulate ubiquitin and drive non-apoptotic neurodegeneration, ataxia, and myoclonic seizures (PMID:12019206, PMID:14722920). Laforin partners with the malin ubiquitin ligase, serving as both an interactor and substrate, and with EPM2AIP1; its activity is further tuned by alternatively spliced isoforms that form homo- and heterodimers, where the catalytically inactive laf317 isoform acts as a dominant-negative regulator and cannot bind glycogen (PMID:12782127, PMID:18617530, PMID:22036712). Critically, the phosphatase activity itself is dispensable for disease prevention: a phosphatase-dead laforin still blocks Lafora body formation and restores macroautophagy in Epm2a-null mice, establishing that the pathogenic defect is failure of the laforin-malin complex to control abnormal glycogen and engage proteolytic systems rather than loss of glycogen dephosphorylation per se (PMID:24430976). Consistent with this, the protein-interaction-defective N163D mutant retains near-normal catalytic activity yet causes disease (PMID:30041081). Beyond glycogen handling, laforin dephosphorylates GSK-3β and represses Wnt signaling, and its inactivation promotes lymphomagenesis, indicating a tumor-suppressive role (PMID:16959610).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2002 High

    Establishing that loss of laforin causes the cardinal features of Lafora disease answered whether EPM2A is causally responsible for the neuropathology rather than merely associated with it.

    Evidence Epm2a knockout mouse with histopathology, EEG, and behavioral readouts

    PMID:12019206

    Open questions at the time
    • Did not define the molecular substrate or biochemical mechanism linking phosphatase loss to inclusion-body formation
    • Mechanism of non-apoptotic neurodegeneration unresolved
  2. 2002 Medium

    Resolving the two-domain architecture and how distinct mutations behave clarified that laforin pathology arises through separable defects in carbohydrate binding versus protein folding/degradation.

    Evidence Expression of CBD and DSPD mutants in HeLa cells with fluorescence localization

    PMID:12019207

    Open questions at the time
    • Localization-based inference of polysome affinity not biochemically confirmed
    • Functional consequence of nuclear re-localization unknown
  3. 2003 Medium

    Identifying EPM2AIP1 as a direct partner began to place laforin in a protein-interaction network rather than as a solitary enzyme.

    Evidence Yeast two-hybrid screen, co-immunoprecipitation, co-localization

    PMID:12782127

    Open questions at the time
    • Functional role of the EPM2AIP1 interaction not established
    • No reciprocal endogenous validation
  4. 2004 Medium

    Pinpointing the ER-localized cytoplasmic isoform as disease-relevant established which laforin pool must retain function to prevent disease.

    Evidence Isoform-specific frameshift mutation with localization and phosphatase activity assays

    PMID:14722920

    Open questions at the time
    • Did not test whether activity or localization is the decisive variable in vivo
    • Single-mutation inference
  5. 2006 Medium

    Showing laforin dephosphorylates GSK-3β and represses Wnt extended its role beyond neuropathology to a tumor-suppressive signaling function.

    Evidence Genetic loss-of-function in transgenic mice, overexpression/shRNA, tumor growth assays

    PMID:16959610

    Open questions at the time
    • Relationship between Wnt repression and glycogen/Lafora pathology unclear
    • Single lab, GSK-3β as direct substrate not structurally confirmed
  6. 2008 High

    Defining isoform dimerization and malin substrate relationships revealed an autoregulatory layer in which an inactive isoform acts as a dominant-negative.

    Evidence In vitro phosphatase and glycogen-binding assays, co-IP with malin, isoform overexpression

    PMID:18617530

    Open questions at the time
    • Physiological abundance and regulation of laf317 in vivo not established
    • Structural basis of dimerization unresolved
  7. 2008 Medium

    Demonstrating that mutant laforins are insoluble, ubiquitinated aggregates that exacerbate ER stress connected loss of function to proteostatic toxicity, and showed chemical chaperones can mitigate it.

    Evidence Mutant transfection in neuronal cells with solubility, ubiquitination, ER stress, and apoptosis assays plus 4-phenylbutyrate rescue

    PMID:19403557

    Open questions at the time
    • Overexpression-based aggregation may not reflect endogenous levels
    • Causal link from ER stress to neurodegeneration in vivo not shown
  8. 2011 Medium

    Characterizing additional splice variants as malin substrates that form inactive heterodimers reinforced alternative splicing as an antagonistic regulator of laforin function.

    Evidence Ectopic expression, localization, co-IP with malin, in vitro phosphatase assays

    PMID:22036712

    Open questions at the time
    • Endogenous expression and tissue distribution of variants unverified
    • Functional significance in disease unclear
  9. 2014 High

    Showing a phosphatase-dead laforin still prevents Lafora bodies and restores autophagy overturned the assumption that glycogen dephosphorylation is the protective activity, refocusing pathogenesis on the laforin-malin complex and proteolytic control.

    Evidence Transgenic rescue of Epm2a-/- mice with WT or C265S laforin, histopathology and autophagy assays

    PMID:24430976

    Open questions at the time
    • The non-catalytic protective activity not molecularly defined
    • How the complex controls glycogen structure mechanistically unresolved
  10. 2018 Medium

    A catalytically intact but interaction-defective patient mutation confirmed that protein-protein interaction capacity, not phosphatase activity, is critical for laforin function.

    Evidence Recombinant N163D protein with phosphatase, stability, and binding-partner assays

    PMID:30041081

    Open questions at the time
    • Specific lost interaction(s) driving disease not identified
    • Single-patient, single-lab characterization
  11. 2025 Medium

    Demonstrating that laforin overexpression paradoxically generates Lafora bodies independent of enzymatic activity exposed a dosage-sensitive glycogen quality-control biology not captured by loss-of-function models.

    Evidence AAV9 overexpression in mice with enzymatic mutants and DRG/brain histopathology

    PMID:41825228

    Open questions at the time
    • Mechanism of dosage-dependent Lafora body induction unknown
    • Relevance of species-mismatch effect to human biology unclear
  12. 2025 Medium

    Showing lithium's inverted effect on glycogen synthase in Epm2a-null mice linked laforin-malin deficiency to altered control of glycogen synthase phosphorylation state.

    Evidence Lithium treatment of Epm2a-/- mice with glycogen synthase phosphorylation and Lafora body assays

    PMID:40258565

    Open questions at the time
    • Direct enzymatic link between laforin and glycogen synthase phosphorylation not established
    • Mechanism of inversion unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • The non-catalytic molecular activity by which the laforin-malin complex controls glycogen structure and engages autophagy/proteasome systems remains undefined.
  • No defined molecular mechanism for the protective non-phosphatase function
  • Structural basis of the laforin-malin complex unresolved
  • Dosage-sensitive and synthase-related effects mechanistically unexplained

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016787 hydrolase activity 3 GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005783 endoplasmic reticulum 2 GO:0005829 cytosol 2
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-162582 Signal Transduction 1 R-HSA-9612973 Autophagy 1
Partners
EPM2AIP1GSK3BNHLRC1
Complex memberships
laforin-malin complex

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 Laforin (EPM2A gene product) is a dual-specificity phosphatase; targeted disruption of Epm2a in mice causes formation of Lafora inclusion bodies (positive for ubiquitin and advanced glycation end-products in neurons), widespread neurodegeneration via a non-apoptotic mechanism (swelling of ER, Golgi, mitochondria without apoptotic bodies or DNA fragmentation), ataxia, spontaneous myoclonic seizures, and EEG epileptiform activity. Epm2a knockout mouse model (gene targeting), histopathology, EEG, behavioral testing Human molecular genetics High 12019206
2002 Laforin contains two functional domains: a carbohydrate-binding domain (CBD, exon 1) and a dual-specificity phosphatase domain (DSPD, exons 3–4). Missense mutations in DSPD (T194I, G279S, Y294N) cause formation of ubiquitin-positive cytoplasmic aggregates (folding mutants targeted for degradation), while CBD mutants (W32G, R108C) re-localize laforin from cytoplasm to both cytoplasm and nucleus, suggesting diminished affinity for polysomes. Expression of mutant proteins in HeLa cells, subcellular localization by fluorescence microscopy Human molecular genetics Medium 12019207
2003 Laforin interacts with EPM2AIP1 (a novel brain-expressed protein); interaction confirmed by yeast two-hybrid screen and co-immunoprecipitation of in vivo-transfected proteins; subcellular co-localization also demonstrated. Yeast two-hybrid screen, co-immunoprecipitation, subcellular co-localization Genomics Medium 12782127
2004 The cytoplasmic isoform of laforin (laf331, localized to the endoplasmic reticulum) is the disease-relevant isoform: a mutation (c.950insT, Q319fs) specific to this isoform drastically reduces phosphatase activity while maintaining ER localization, establishing that cytoplasmic laforin function is required for disease prevention. Mutation identification, subcellular localization assay, phosphatase activity assay Human mutation Medium 14722920
2006 Laforin acts as a phosphatase for GSK-3β and functions as a repressor in the Wnt signaling pathway; inactivation of Epm2a leads to increased Wnt signaling and lymphomagenesis in an immunocompromised host. Insertional mutation and epigenetic silencing in TCR transgenic mice, overexpression and shRNA knockdown, tumor growth assays Cancer cell Medium 16959610
2008 The two laforin isoforms (laf331 and laf317) interact with each other forming homo- and heterodimers with distinct activities: laf331 homodimer has robust phosphatase activity; laf317 homodimer and laf331–laf317 heterodimer lack phosphatase activity. Laf331 binds glycogen only as a monomer; laf317 cannot bind glycogen. Both isoforms interact with and serve as substrates for the malin ubiquitin ligase, with malin showing higher affinity for laf331. Disease mutations specific to laf331 abolish laf317–laf331 heterodimerization but not laf331 homodimerization, suggesting laf317 can act as a dominant-negative regulator. In vitro phosphatase assays, glycogen-binding assays, co-immunoprecipitation, overexpression of isoforms Human molecular genetics High 18617530
2008 Mutant laforin proteins encoded by missense mutations and deletions in EPM2A are unstable, insoluble, ubiquitinated, and accumulate in aggresome-like structures; these aggregates exacerbate ER stress and sensitize neuronal cells to apoptosis induced by ER stressors. Chemical chaperone 4-phenylbutyrate increases mutant solubility and reduces ER stress-induced apoptosis. Transfection of mutant EPM2A constructs in neuronal cell lines, solubility assays, ubiquitination assays, ER stress assays (thapsigargin), apoptosis assays Human molecular genetics Medium 19403557
2011 Three novel EPM2A splice variants encode five distinct proteins with unique subcellular localizations; these novel isoforms interact with and serve as substrates for malin ubiquitin ligase. Two phosphatase-active isoforms form an inactive heterodimer in vitro, suggesting antagonistic regulation of EPM2A function by alternative splicing. Ectopic expression in cell lines, subcellular localization, co-immunoprecipitation with malin, in vitro phosphatase assays Genomics Medium 22036712
2014 The phosphatase activity of laforin is dispensable for preventing Lafora disease: expression of phosphatase-dead laforin (C265S mutant) in Epm2a−/− mice fully blocks Lafora body formation and restores impaired macroautophagy, indicating the critical pathogenic process is control of abnormal glycogen accumulation through the laforin–malin complex acting on intracellular proteolytic systems, not glycogen dephosphorylation per se. Transgenic rescue of Epm2a−/− mice with wild-type or C265S phosphatase-dead laforin; histopathology for Lafora bodies; autophagy assays Brain : a journal of neurology High 24430976
2018 The laforin N163D mutation, found in a slow-progression LD patient, exhibits near wild-type phosphatase activity and protein stability but shows severe impairment in interactions with previously identified laforin binding partners, suggesting protein–protein interaction capacity (not just phosphatase activity) is critical for laforin function. Recombinant protein expression, phosphatase activity assay, protein stability assay, binding partner interaction assays Epilepsy research Medium 30041081
2025 Laforin overexpression paradoxically causes Lafora body formation, occurring independently of laforin's and malin's enzymatic activities, first and dominantly in dorsal root ganglia; the effect is stronger with human laforin expressed in mice (species mismatch) and is time-dependent, revealing a novel biology of laforin in glycogen quality control. AAV9-mediated overexpression of laforin in mice, histopathology for Lafora bodies in DRG and brain, enzymatic activity mutant analysis Neurotherapeutics Medium 41825228
2025 Lithium treatment of Epm2a−/− mice causes glycogen synthase dephosphorylation (activation, opposite to its effect in normal rat brain) and increased Lafora body formation in hearts (100%) and brains (40%) of treated mice, indicating that laforin-malin complex deficiency inverts lithium's effect on glycogen synthase phosphorylation state. Lithium treatment of Epm2a−/− knockout mice, glycogen synthase phosphorylation assays, Lafora body quantification Neuroscience letters Medium 40258565

Source papers

Stage 0 corpus · 54 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Targeted disruption of the Epm2a gene causes formation of Lafora inclusion bodies, neurodegeneration, ataxia, myoclonus epilepsy and impaired behavioral response in mice. Human molecular genetics 201 12019206
2003 Efflux pump Lde is associated with fluoroquinolone resistance in Listeria monocytogenes. Antimicrobial agents and chemotherapy 106 12543681
2013 NVP-LDE-225 (Erismodegib) inhibits epithelial-mesenchymal transition and human prostate cancer stem cell growth in NOD/SCID IL2Rγ null mice by regulating Bmi-1 and microRNA-128. Oncogenesis 92 23567619
2013 NPV-LDE-225 (Erismodegib) inhibits epithelial mesenchymal transition and self-renewal of glioblastoma initiating cells by regulating miR-21, miR-128, and miR-200. Neuro-oncology 86 23482671
2009 Lafora progressive myoclonus epilepsy: a meta-analysis of reported mutations in the first decade following the discovery of the EPM2A and NHLRC1 genes. Human mutation 80 19267391
2002 Genotype-phenotype correlations for EPM2A mutations in Lafora's progressive myoclonus epilepsy: exon 1 mutations associate with an early-onset cognitive deficit subphenotype. Human molecular genetics 69 12019207
2003 Metabolism of a cholesterol-rich microemulsion (LDE) in patients with multiple myeloma and a preliminary clinical study of LDE as a drug vehicle for the treatment of the disease. Cancer chemotherapy and pharmacology 61 14574458
2000 Mutational spectrum of the EPM2A gene in progressive myoclonus epilepsy of Lafora: high degree of allelic heterogeneity and prevalence of deletions. European journal of human genetics : EJHG 48 11175283
2006 Epm2a suppresses tumor growth in an immunocompromised host by inhibiting Wnt signaling. Cancer cell 44 16959610
2005 Lafora progressive Myoclonus Epilepsy mutation database-EPM2A and NHLRC1 (EPM2B) genes. Human mutation 43 16134145
1997 Expression of CD1 and HLA-DR by Langerhans cells (LC) in oral lichenoid drug eruptions (LDE) and idiopathic oral lichen planus (LP). Journal of oral pathology & medicine : official publication of the International Association of Oral Pathologists and the American Academy of Oral Pathology 36 9176792
2010 Novel mutations in EPM2A and NHLRC1 widen the spectrum of Lafora disease. Epilepsia 35 20738377
2014 The phosphatase activity of laforin is dispensable to rescue Epm2a-/- mice from Lafora disease. Brain : a journal of neurology 34 24430976
2003 Identification of a novel protein interacting with laforin, the EPM2a progressive myoclonus epilepsy gene product. Genomics 33 12782127
2000 Identification of new and common mutations in the EPM2A gene in Lafora disease. Neurology 33 10668720
2017 Phase II study of paclitaxel associated with lipid core nanoparticles (LDE) as third-line treatment of patients with epithelial ovarian carcinoma. Medical oncology (Northwood, London, England) 32 28756613
2001 Regional and developmental expression of Epm2a gene and its evolutionary conservation. Biochemical and biophysical research communications 32 11355878
2004 Loss of function of the cytoplasmic isoform of the protein laforin (EPM2A) causes Lafora progressive myoclonus epilepsy. Human mutation 29 14722920
2017 Pharmacodynamic and pharmacokinetic neoadjuvant study of hedgehog pathway inhibitor Sonidegib (LDE-225) in men with high-risk localized prostate cancer undergoing prostatectomy. Oncotarget 24 29262631
2009 Deletions and missense mutations of EPM2A exacerbate unfolded protein response and apoptosis of neuronal cells induced by endoplasm reticulum stress. Human molecular genetics 24 19403557
2008 Cooperation between prokaryotic (Lde) and eukaryotic (MRP) efflux transporters in J774 macrophages infected with Listeria monocytogenes: studies with ciprofloxacin and moxifloxacin. Antimicrobial agents and chemotherapy 21 18573933
2012 Expression of efflux pump gene lde in ciprofloxacin-resistant foodborne isolates of Listeria monocytogenes. Microbiology and immunology 20 22943162
2017 Molecular modeling study on resistance of WT/D473H SMO to antagonists LDE-225 and LEQ-506. Pharmacological research 18 29175550
2008 Modulation of functional properties of laforin phosphatase by alternative splicing reveals a novel mechanism for the EPM2A gene in Lafora progressive myoclonus epilepsy. Human molecular genetics 18 18617530
1999 Isolation and characterization of mouse homologue for the human epilepsy gene, EPM2A. Biochemical and biophysical research communications 17 10092504
2021 Cholesterol-rich nanoemulsion (LDE) as a novel drug delivery system to diagnose, delineate, and treat human glioblastoma. Materials science & engineering. C, Materials for biological applications 16 33812612
2007 Founder effect with variable age at onset in Arab families with Lafora disease and EPM2A mutation. Epilepsia 16 17509003
2014 Late onset Lafora disease and novel EPM2A mutations: breaking paradigms. Epilepsy research 15 25246353
2008 Lafora disease in the Indian population: EPM2A and NHLRC1 gene mutations and their impact on subcellular localization of laforin and malin. Human mutation 15 18311786
2024 Gene therapy for Lafora disease in the Epm2a-/- mouse model. Molecular therapy : the journal of the American Society of Gene Therapy 13 38796707
2021 A novel gene therapy for neurodegenerative Lafora disease via EPM2A-loaded DLinDMA lipoplexes. Nanomedicine (London, England) 13 33960213
2016 Late-onset Lafora disease with prominent parkinsonism due to a rare mutation in EPM2A. Neurology. Genetics 13 27574708
2001 Mutation screening for Japanese Lafora's disease patients: identification of novel sequence variants in the coding and upstream regulatory regions of EPM2A gene. Molecular and cellular probes 13 11735300
2016 PDE7B, NMBR and EPM2A Variants and Schizophrenia: A Case-Control and Pharmacogenetics Study. Neuropsychobiology 11 27092952
2003 Two novel mutations in the EPM2A gene in a Korean patient with Lafora's progressive myoclonus epilepsy. Journal of human genetics 11 12560877
2001 In vitro cytotoxicity of the LDE: daunorubicin complex in acute myelogenous leukemia blast cells. Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas 10 11593299
2003 Bioptically demonstrated Lafora disease without EPM2A mutation: a clinical and neurophysiological study of two sisters. Clinical neurology and neurosurgery 9 14643920
2013 Formulation and evaluation of cholesterol-rich nanoemulsion (LDE) for drug delivery potential of cholesteryl-maleoyl-5-fluorouracil. Pharmaceutical development and technology 8 24266739
2011 Four novel and two recurrent NHLRC1 (EPM2B) and EPM2A gene mutations leading to Lafora disease in six Turkish families. Epilepsy research 8 22047982
2023 Epm2aR240X knock-in mice present earlier cognitive decline and more epileptic activity than Epm2a-/- mice. Neurobiology of disease 7 37059210
2018 A novel EPM2A mutation yields a slow progression form of Lafora disease. Epilepsy research 7 30041081
1994 The metabolism of a series of ester pro-drugs by NCTC 2544 cells, skin homogenate and LDE testskin. The Journal of pharmacy and pharmacology 7 7714720
2025 Advances in gene therapy for Lafora disease: Intravenous recombinant adeno-associated virus-mediated delivery of EPM2A and EPM2B genes. Clinical and translational medicine 5 41169091
2011 Identification and characterization of novel splice variants of the human EPM2A gene mutated in Lafora progressive myoclonus epilepsy. Genomics 5 22036712
2023 MiR-95-3p/EPM2A/MMP2 contributes to the pathogenesis of severe preeclampsia through the regulation of trophoblast biological behaviour. Archives of biochemistry and biophysics 3 37030589
2022 Novel mutation of EPM2A causes progressive myoclonic epilepsy: a case report. Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology 3 35257260
2020 A novel compound heterozygous EPM2A mutation in a Chinese boy with Lafora disease. Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology 3 32342326
2024 Integrated aerobic exercise with LDE-docetaxel treatment: a novel approach to combat prostate cancer progression. Scientific reports 2 38671015
2026 Lafora disease gene therapy: EPM2A but not EPM2B overexpression results in Lafora body formation. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 1 41825228
2023 Gene replacement therapy for Lafora disease in the Epm2a mouse model. bioRxiv : the preprint server for biology 1 38168354
2022 EPM2A acts as a protective factor in prostate cancer, evidence from a real-world patient cohort. Frontiers in pharmacology 1 36199693
2021 A novel deletion mutation in EPM2A underlies progressive myoclonic epilepsy (Lafora body disease) in a Pakistani family. Neurology Asia 1 34733372
2025 Lithium exacerbates Lafora body formation in the Epm2a-/- Lafora disease mouse model. Neuroscience letters 0 40258565
2024 Identification of biallelic intronic EPM2A mutations in a Lafora disease kindred. Journal of human genetics 0 39558147

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