Human Molecular Genetics Advance Access published online on April 29, 2009
Human Molecular Genetics, doi:10.1093/hmg/ddp196
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Deletions and Missense Mutations of EPM2A Exacerbate Unfolded Protein Response and Apoptosis of Neuronal Cells Induced by Endoplasm Reticulum Stress
1 Division of Immunotherapy, Section of General Surgery, Department of Surgery, University of Michigan, Ann Arbor, MI 48109 2 Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109 3 Department of Pathology, University of Michigan, Ann Arbor, MI 48109 4 Department of Pathology, The Ohio State University Medical Center, Columbus, OH 43210
* To whom correspondence should be addressed. BSRB 1810, 109 Zina Pitcher Place, Department of Surgery and Pathology, University of Michigan, Ann Arbor, MI 48109. Tel: 734-615-3464, Fax: 734-763-2162. email: panz{at}umich.edu
Received March 9, 2009; Revised April 27, 2009; Accepted April 27, 2009
The majority of the Lafora's disease (LD) is caused by defect in the EPM2A gene, including missense and nonsense mutations and deletions. These defects mainly occur in the carbohydrate-binding domain (CBD) and. How these mutations cause neuronal defects is under active investigation. Here, we report that the mutant proteins encoded by all missense mutations and most deletions tested are unstable, insoluble, ubiquitinated, and are accumulated in aggresome-like structures. The effect of apparent "gain-of-function" mutations can be corrected by co-transfection of wild-type EPM2A cDNA, which is consistent with the recessive nature of these mutations in LD patients. In a neuronal cell line, these mutant aggregates exacerbate endoplasm reticulum (ER) stress and make the cells susceptible to the apoptosis induced by ER stressor, thapsigargin. The chemical chaperon, 4-phenylbutyrate (4-PBA), increased the mutant solubility, reduced the ER stress, and dulled the sensitivity of mutant neuronal cells to apoptosis induced by thapsigargin and the mutant laforin proteins. The increased sensitivity to ER stress-induced apoptosis may contribute to LD pathogenesis.
Yan Liu and Yin Wang contributed equally to the study