From The Cover: Insights into Lafora disease: Malin is an E3 ubiquitin ligase that ubiquitinates and promotes the degradation of laforin

Department of Pharmacology, School of Medicine, University of California at San Diego, La Jolla, CA 92093-0721, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/2005; 102(24):8501-6. DOI: 10.1073/pnas.0503285102
Source: PubMed


Lafora disease (LD) is a fatal form of progressive myoclonus epilepsy caused by recessive mutations in either a gene encoding a dual-specificity phosphatase, known as laforin, or a recently identified gene encoding the protein known as malin. Here, we demonstrate that malin is a single subunit E3 ubiquitin (Ub) ligase and that its RING domain is necessary and sufficient to mediate ubiquitination. Additionally, malin interacts with and polyubiquitinates laforin, leading to its degradation. Missense mutations in malin that are present in LD patients abolish its ability to polyubiquitinate and signal the degradation of laforin. Our results demonstrate that laforin is a physiologic substrate of malin, and we propose possible models to explain how recessive mutations in either malin or laforin result in LD. Furthermore, these data distinguish malin as an E3 Ub ligase whose activity is necessary to prevent a neurodegenerative disease that involves formation of nonproteinacious inclusion bodies.

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Available from: Jack E Dixon, Jul 28, 2015
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    • "The symptoms of LD include the disease defining myoclonic epilepsy, ataxia, dementia and cognitive defects [1] [2]. Being an autosomal recessive disorder, LD is caused by mutations in both copies of either the EPM2A gene coding for the protein phosphatase laforin [3] [4] or the NHLRC1 gene coding for an E3 ubiquitin ligase named malin [5] [6]. Studies have revealed that laforin and malin are recruited to aggresomes upon proteasomal impairment, and as a functional complex, promote the degradation of cytotoxic misfolded proteins [7] [8]. "
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    ABSTRACT: Lafora disease (LD) is an autosomal recessive, progressive, and fatal form of a neurodegenerative disorder characterized by the presence of Lafora polyglucosan bodies. LD is caused by defects in either the laforin protein phosphatase or the malin E3 ubiquitin ligase. Laforin and malin were shown play key roles in proteolytic processes, unfolded stress response, and glycogen metabolism. Therefore, the LD proteins laforin and malin are thought to function as pro-survival factors and their loss thus could result in neurodegeneration. To understand the molecular pathway leading to the cell death in LD, in the present study, we investigated the possible role of LD proteins in the p53-mediated cell death pathway. We show that loss of laforin or malin results in the increased level and activity of p53, both in cellular and animal models of LD, and that this is primarily due to the increased levels of Hipk2, a proapoptotic activator of p53. Overexpression of laforin or malin confers protection against Hipk2-mediated cell death by targeting the Hipk2 to the cytoplasmic compartment. Taken together, our study strengthens the notion that laforin and malin are pro-survival factors, and that the activation of Hipk2-p53 cell death pathway might underlie neurodegeneration in LD. Copyright © 2015. Published by Elsevier Inc.
    Biochemical and Biophysical Research Communications 06/2015; 464(1). DOI:10.1016/j.bbrc.2015.06.018 · 2.30 Impact Factor
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    • "Lafora disease (LD) is a rare form of inherited progressive myoclonus epilepsy (OMIM#254780; ORPHA501). Recessive mutations in either the EPM2A gene encoding a dual-specificity phosphatase known as laforin (OMIM 607566) (Minassian et al., 1998; Serratosa et al., 1999) or in the EPM2B/NHLRC1 gene encoding malin (OMIM 608072), an E3 ubiquitin ligase (Chan et al., 2003; Gentry et al., 2005; Gomez-Abad et al., 2005; Singh et al., 2005, 2006) are responsible for the disease, although the existence of a third, minor locus has also been postulated (Chan et al., 2004). Patients with LD develop progressive myoclonus epilepsy that usually starts in adolescence and includes absence, visual, myoclonic, and tonic-clonic seizures accompanied by rapid neurologic degeneration, including ataxia, dementia, dysarthria, amaurosis, respiratory failure, and a final vegetative state and death, usually within 10 years of onset (Lafora, 1911; Van Heycop Ten Ham, 1974; Berkovic et al., 1986, 1991; Roger et al., 1992; Acharya et al., 1995). "
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    ABSTRACT: Lafora disease is a rare form of inherited progressive myoclonus epilepsy caused by mutations in the EPM2A gene encoding laforin, or in the EPM2B gene, which encodes malin. It is characterized by the presence of polyglucosan inclusion bodies (Lafora bodies) in brain and other tissues. Genetically engineered mice lacking expression of either the laforin (Epm2a(-/-) ) or malin (Epm2b(-/-) ) genes display a number of neurological and behavioral abnormalities that resemble those found in patients suffering from Lafora disease; of these, both Epm2a(-/-) and Epm2b(-/-) mice have shown altered motor activity, impaired motor coordination, episodic memory deficits, and different degrees of spontaneous epileptic activity. In this study, we analyze the sensitivity of Epm2a(-/-) and Epm2b(-/-) mice to the convulsant drug pentylenetetrazol (PTZ), an antagonist of the γ-aminobutyric acid type A (GABAA) receptor, commonly used to induce epileptic tonic-clonic seizures in laboratory animals. PTZ-induced epileptic activity, including myoclonic jerks and tonic-clonic seizures, was analyzed in 2 age groups of mice comprising representative samples of young adult and aged mice, after administration of PTZ at sub-convulsive and convulsive doses. Epm2a(-/-) and Epm2b(-/-) mice showed a lower convulsive threshold after PTZ injections at sub-convulsive doses. A lower convulsive threshold and shorter latencies to develop epileptic seizures were observed after PTZ injections at convulsive doses. Different patterns of generalized seizures and of discharges were observed in Epm2a(-/-) and Epm2b(-/-) mice. Epm2a(-/-) and Epm2b(-/-) mice present an increased sensitivity to the convulsant agent PTZ that may reflect different degrees of increased GABAA receptor-mediated hyperexcitability.
    Frontiers in Neuroscience 09/2014; 8:291. DOI:10.3389/fnins.2014.00291 · 3.66 Impact Factor
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    • "EPM2B encodes malin, an E3-ubiquitin ligase of the RING type. Data from multiple labs demonstrate that malin and laforin physically interact and that this interaction is required for ubiquitination of laforin itself [21] and other glycogen-related substrates such as the muscle isoform of glycogen synthase (MGS) [22], glycogen debranching enzyme (GDE) [23], and the glycogenic regulatory subunits of PP1 (type 1 protein phosphatase) both R5/PTG (Protein Targeting to Glycogen) as well as R6 [24], [25]. The implication of laforin and malin in glycogen metabolism - either by means of a direct glycogen dephosphorylation executed by laforin, by the ubiquitination of glycogenic regulators through the laforin-malin complex, or by a balanced participation of both processes - has guided research in LD over the last several years. "
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    ABSTRACT: Laforin, encoded by a gene that is mutated in Lafora Disease (LD, OMIM 254780), is a modular protein composed of a carbohydrate-binding module and a dual-specificity phosphatase domain. Laforin is the founding member of the glucan-phosphatase family and regulates the levels of phosphate present in glycogen. Multiple reports have described the capability of laforin to form dimers, although the function of these dimers and their relationship with LD remains unclear. Recent evidence suggests that laforin dimerization depends on redox conditions, suggesting that disulfide bonds are involved in laforin dimerization. Using site-directed mutagenesis we constructed laforin mutants in which individual cysteine residues were replaced by serine and then tested the ability of each protein to dimerize using recombinant protein as well as a mammalian cell culture assay. Laforin-Cys329Ser was the only Cys/Ser mutant unable to form dimers in both assays. We also generated a laforin truncation lacking the last three amino acids, laforin-Cys329X, and this truncation also failed to dimerize. Interestingly, laforin-Cys329Ser and laforin-Cys329X were able to bind glucans, and maintained wild type phosphatase activity against both exogenous and biologically relevant substrates. Furthermore, laforin-Cys329Ser was fully capable of participating in the ubiquitination process driven by a laforin-malin complex. These results suggest that dimerization is not required for laforin phosphatase activity, glucan binding, or for the formation of a functional laforin-malin complex. Cumulatively, these results suggest that cysteine 329 is specifically involved in the dimerization process of laforin. Therefore, the C329S mutant constitutes a valuable tool to analyze the physiological implications of laforin's oligomerization.
    PLoS ONE 07/2013; 8(7):e69523. DOI:10.1371/journal.pone.0069523 · 3.23 Impact Factor
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