Essential role of the unfolded protein response regulator GRP78/BiP in protection from neuronal apoptosis.
Neurodegenerative diseases are often associated with dysfunction in protein quality control. The endoplasmic reticulum (ER), a key site for protein synthesis, senses stressful conditions by activating the unfolded protein response (UPR). In this study we report the creation of a novel mouse model in which GRP78/BiP, a major ER chaperone and master regulator of UPR, is specifically eliminated in Purkinje cells (PCs). GRP78-depleted PCs activate UPR including the induction of GRP94, PDI, CHOP and GADD34, feedback suppression of eIF2alpha phosphorylation and apoptotic cell death. In contrast to current models of protein misfolding in which an abnormal accumulation of ubiquitinated protein is prominent, cytosolic ubiquitin staining is dramatically reduced in GRP78-null PCs. Ultrastructural evaluation reveals that the ER shows prominent dilatation with focal accumulation of electron-dense material within the ER. The mice show retarded growth and severe motor coordination defect by week 5 and cerebellar atrophy by week 13. Our studies uncover a novel link between GRP78 depletion and reduction in cytosolic ubiquitination and establish a novel mouse model of accelerated cerebellar degeneration with basic and clinical applications.
Wang
M
M
Department of Biochemistry and Molecular Biology, USC/Norris Comprehensive Cancer Center, University of Southern California Keck School of Medicine, Los Angeles, CA 90089-9176, USA.
Ye
R
R
Barron
E
E
Baumeister
P
P
Mao
C
C
Luo
S
S
Fu
Y
Y
Luo
B
B
Dubeau
L
L
Hinton
D R
DR
Lee
A S
AS
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001522:Behavior, Animal / Q000502:physiology; D064026:Calbindins; D037281:Calnexin / Q000378:metabolism; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D019636:Neurodegenerative Diseases / Q000378:metabolism / Q000473:pathology; D011689:Purkinje Cells / Q000166:cytology / Q000502:physiology*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D025801:Ubiquitin / Q000378:metabolism; D056811:Unfolded Protein Response
D064026:Calbindins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D064030:S100 Calcium Binding Protein G; D025801:Ubiquitin; D037281:Calnexin