Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy

Hannes Lohi, Leonarda Ianzano, Xiao Chu Zhao, Elayne M. Chan, Julie Turnbull, Stephen W. Scherer, Cameron A. Ackerley, Berge A. Minassian

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

Lafora progressive myoclonus epilepsy, caused by defective laforin or malin, insidiously present in normal teenagers with cognitive decline, followed by rapidly intractable epilepsy, dementia and death. Pathology reveals neurodegeneration with neurofibrillary tangle formation and Lafora bodies (LBs). LBs are deposits of starch-like polyglucosans, insufficiently branched and hence insoluble glycogen molecules resulting from glycogen synthase (GS) overactivity relative to glycogen branching enzyme activity. We previously made the unexpected observation that laforin, in the absence of which polyglucosans accumulate, specifically binds polyglucosans. This suggested that laforin's role is to detect polyglucosan appearances during glycogen synthesis and to initiate mechanisms to downregulate GS. Glycogen synthase kinase 3 (GSK3) is the principal inhibitor of GS. Dephosphorylation of GSK3 at Ser 9 activates GSK3 to inhibit GS through phosphorylation at multiple sites. Glucose-6-phosphate is a potent allosteric activator of GS. Glucose-6-phosphate levels are high when the amount of glucose increases and its activation of GS overrides any phospho-inhibition. Here, we show that laforin is a GSK3 Ser 9 phosphatase, and therefore capable of inactivating GS through GSK3. We also show that laforin interacts with malin and that malin is an E3 ubiquitin ligase that binds GS. We propose that laforin, in response to appearance of polyglucosans, directs two negative feedback pathways: polyglucosan-laforin-GSK3-GS to inhibit GS activity and polyglucosan-laforin-malin-GS to remove GS through proteasomal degradation.

Original languageEnglish (US)
Pages (from-to)2727-2736
Number of pages10
JournalHuman Molecular Genetics
Volume14
Issue number18
DOIs
StatePublished - Sep 15 2005

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Progressive Myoclonic Epilepsy
Glycogen Synthase Kinase 3
Glycogen Synthase
Ubiquitination
Glucose-6-Phosphate
Glycogen
Lafora Disease
1,4-alpha-Glucan Branching Enzyme
Neurofibrillary Tangles
Ubiquitin-Protein Ligases
polyglucosan
Phosphoric Monoester Hydrolases
Starch

ASJC Scopus subject areas

  • Genetics

Cite this

Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy. / Lohi, Hannes; Ianzano, Leonarda; Zhao, Xiao Chu; Chan, Elayne M.; Turnbull, Julie; Scherer, Stephen W.; Ackerley, Cameron A.; Minassian, Berge A.

In: Human Molecular Genetics, Vol. 14, No. 18, 15.09.2005, p. 2727-2736.

Research output: Contribution to journalArticle

Lohi, H, Ianzano, L, Zhao, XC, Chan, EM, Turnbull, J, Scherer, SW, Ackerley, CA & Minassian, BA 2005, 'Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy', Human Molecular Genetics, vol. 14, no. 18, pp. 2727-2736. https://doi.org/10.1093/hmg/ddi306
Lohi, Hannes ; Ianzano, Leonarda ; Zhao, Xiao Chu ; Chan, Elayne M. ; Turnbull, Julie ; Scherer, Stephen W. ; Ackerley, Cameron A. ; Minassian, Berge A. / Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy. In: Human Molecular Genetics. 2005 ; Vol. 14, No. 18. pp. 2727-2736.
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AU - Turnbull, Julie

AU - Scherer, Stephen W.

AU - Ackerley, Cameron A.

AU - Minassian, Berge A.

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AB - Lafora progressive myoclonus epilepsy, caused by defective laforin or malin, insidiously present in normal teenagers with cognitive decline, followed by rapidly intractable epilepsy, dementia and death. Pathology reveals neurodegeneration with neurofibrillary tangle formation and Lafora bodies (LBs). LBs are deposits of starch-like polyglucosans, insufficiently branched and hence insoluble glycogen molecules resulting from glycogen synthase (GS) overactivity relative to glycogen branching enzyme activity. We previously made the unexpected observation that laforin, in the absence of which polyglucosans accumulate, specifically binds polyglucosans. This suggested that laforin's role is to detect polyglucosan appearances during glycogen synthesis and to initiate mechanisms to downregulate GS. Glycogen synthase kinase 3 (GSK3) is the principal inhibitor of GS. Dephosphorylation of GSK3 at Ser 9 activates GSK3 to inhibit GS through phosphorylation at multiple sites. Glucose-6-phosphate is a potent allosteric activator of GS. Glucose-6-phosphate levels are high when the amount of glucose increases and its activation of GS overrides any phospho-inhibition. Here, we show that laforin is a GSK3 Ser 9 phosphatase, and therefore capable of inactivating GS through GSK3. We also show that laforin interacts with malin and that malin is an E3 ubiquitin ligase that binds GS. We propose that laforin, in response to appearance of polyglucosans, directs two negative feedback pathways: polyglucosan-laforin-GSK3-GS to inhibit GS activity and polyglucosan-laforin-malin-GS to remove GS through proteasomal degradation.

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