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First published online 12 September 2006
doi: 10.1242/jcs.03163

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Characterization of erasin (UBXD2): a new ER protein that promotes ER-associated protein degradation

Jing Liang^1,2,*,, Chaobo Yin^2,*, Howard Doong², Shengyun Fang^1,2, Corrine Peterhoff³, Ralph A. Nixon³ and Mervyn J. Monteiro^1,2,

¹ Graduate Program in Molecular Medicine, and Institute for Neurodegenerative Diseases, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201, USA
² Medical Biotechnology Center, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201, USA
³ Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY 10962, USA

Author for correspondence (e-mail: monteiro{at}umbi.umd.edu)

Accepted 11 July 2006

Ubiquitin regulator-X (UBX) is a discrete protein domain that binds p97/valosin-containing protein (VCP), a molecular chaperone involved in diverse cell processes, including endoplasmic-reticulum-associated protein degradation (ERAD). Here we characterize a human UBX-containing protein, UBXD2, that is highly conserved in mammals, which we have renamed erasin. Biochemical fractionation, immunofluorescence and electron microscopy, and protease protection experiments suggest that erasin is an integral membrane protein of the endoplasmic reticulum and nuclear envelope with both its N- and C-termini facing the cytoplasm or nucleoplasm. Localization of GFP-tagged deletion derivatives of erasin in HeLa cells revealed that a single 21-amino-acid sequence located near the C-terminus is necessary and sufficient for localization of erasin to the endoplasmic reticulum. Immunoprecipitation and GST-pulldown experiments confirmed that erasin binds p97/VCP via its UBX domain. Additional immunoprecipitation assays indicated that erasin exists in a complex with other p97/VCP-associated factors involved in ERAD. Overexpression of erasin enhanced the degradation of the ERAD substrate CD3, whereas siRNA-mediated reduction of erasin expression almost completely blocked ERAD. Erasin protein levels were increased by endoplasmic reticulum stress. Immunohistochemical staining of brain tissue from patients with Alzheimer's disease and control subjects revealed that erasin accumulates preferentially in neurons undergoing neurofibrillary degeneration in Alzheimer's disease. These results suggest that erasin may be involved in ERAD and in Alzheimer's disease.

Key words: Endoplasmic reticulum, UBXD2, Membrane topology, p97/VCP, ER-associated protein degradation, Alzheimer's disease

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