Sequestration of chaperones and proteasome into Lafora bodies and proteasomal dysfunction induced by Lafora disease-associated mutations of malin.
Lafora disease (LD) is an autosomal recessive progressive myoclonic epilepsy characterized by the presence of intracellular polyglucosan inclusions commonly known as Lafora bodies in many tissues, including the brain, liver and skin. The disease is caused by mutations in either EPM2A gene, encoding the protein phosphatase, laforin, or EPM2B gene, encoding the ubiquitin ligase, malin. But how mutations in these two genes cause disease pathogenesis is poorly understood. In this study, we show that the Lafora bodies in the axillary skin and brain stain positively for the ubiquitin, the 20S proteasome and the molecular chaperones Hsp70/Hsc70. Interestingly, mutant malins that are misfolded also frequently colocalizes with Lafora bodies in the skin biopsy sample of the respective LD patient. The expression of disease-causing mutations of malin in Cos-7 cells results in the formation of the profuse cytoplasmic aggregates that colocalize with the Hsp70/Hsc70 chaperones and the 20S proteasome. The mutant malin expressing cells also exhibit proteasomal dysfunction and cell death. Overexpression of Hsp70 decreases the frequency of the mutant malin aggregation and protects from mutant malin-induced cell death. These findings suggest that Lafora bodies consist of abnormal proteins, including mutant malin, targeted by the chaperones or the proteasome for their refolding or clearance, and failure of these quality control systems could lead to LD pathogenesis. Our data also indicate that the Hsp70 chaperone could be a potential therapeutic target of LD.
Rao
Sudheendra N R
SN
Cellular and Molecular Neuroscience Laboratory, National Brain Research Centre, Manesar, Gurgaon, India.
Maity
Ranjan
R
Sharma
Jaiprakash
J
Dey
Parthanarayan
P
Shankar
Susarla Krishna
SK
Satishchandra
Parthasarathy
P
Jana
Nihar Ranjan
NR
D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics*; D016923:Cell Death; D002522:Chlorocebus aethiops; D005455:Fluorescent Antibody Technique; D005936:Glucans / Q000235:genetics; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism* / Q000473:pathology; D020192:Lafora Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
D002352:Carrier Proteins; C483189:EPM2AIP1 protein, human; D005936:Glucans; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D025801:Ubiquitin; C083094:polyglucosan; C478960:NHLRC1 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex