title: A novel beta-site amyloid precursor protein cleaving enzyme (BACE) isoform regulated by nonsense-mediated mRNA decay and proteasome-dependent degradation.
abstract: Proteolytic cleavage of amyloid beta-peptide (Abeta) from amyloid precursor protein (APP) is a key event in the pathogenesis of Alzheimer's disease. Beta-site amyloid precursor protein cleaving enzyme (BACE) cleaves the APP at the N-terminus of Abeta. We investigated whether particular stress conditions modify the expression and activity of BACE, and found that treatment of human neuroblastoma cells with protein synthesis inhibitors induced expression of a novel splice variant of BACE. This unusual transcript, I-127, is produced by usage of an internal splicing donor site in exon 3. The splicing event leads to a premature termination codon, as well as elimination of one of two conserved aspartic protease active sites, a transmembrane domain, and a C-terminal cytoplasmic tail from BACE. Low levels of this mRNA were found in the human brain. When expressed in cells, I-127 had no effect on Abeta secretion and was retained in the endoplasmic reticulum without propeptide removal. It was also unstable with a turnover t(1/2) of approximately 2h; normal BACE had a turnover t(1/2) of approximately 8h. Finally, I-127 was degraded in a proteasome-dependent manner. Thus, I-127 is regulated by both nonsense-mediated mRNA decay (NMD) and proteasome-dependent degradation.
authors.affiliation: Division of Demyelinating Disease and Aging, National Institute of Neuroscience, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan. tanahash@kenroku.kanazawa-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tanahashi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tabira
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017398:Alternative Splicing / Q000235:genetics; D000544:Alzheimer Disease / Q000201:enzymology* / Q000235:genetics* / Q000503:physiopathology; D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000096:biosynthesis; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D001921:Brain / Q000201:enzymology / Q000503:physiopathology; D002460:Cell Line; D045744:Cell Line, Tumor; D018389:Codon, Nonsense / Q000235:genetics; D017124:Conserved Sequence / Q000235:genetics; D004789:Enzyme Activation / Q000235:genetics; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D020871:RNA Stability / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D018389:Codon, Nonsense; D007527:Isoenzymes; D012333:RNA, Messenger; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D046988:Proteasome Endopeptidase Complex