title: Altered processing of amyloid precursor protein in cells undergoing apoptosis.
abstract: Altered proteolysis of amyloid precursor protein is an important determinant of pathology development in Alzheimer's disease. Here, we describe the detection of two novel fragments of amyloid precursor protein in H4 neuroglioma cells undergoing apoptosis. Immunoreactivity of these 25-35 kDa fragments to two different amyloid precursor protein antibodies suggests that they contain the amyloid-β region and an epitope near the C-terminus of amyloid precursor protein. Generation of these fragments is associated with cleavage of caspase-3 and caspase-7, suggesting activation of these caspases. Studies in neurons undergoing DNA damage-induced apoptosis also showed similar results. Inclusion of caspase inhibitors prevented the generation of these novel fragments, suggesting that they are generated by a caspase-dependent mechanism. Molecular weight prediction and immunoreactivity of the fragments generated suggested that such fragments could not be generated by cleavage at any previously identified caspase, secretase, or calpain site on amyloid precursor protein. Bioinformatic analysis of the amino acid sequence of amyloid precursor protein revealed that fragments fitting the observed size and immunoreactivity could be generated by either cleavage at a novel, hitherto unidentified, caspase site or at a previously identified matrix metalloproteinase site in the extracellular domain. Proteolytic cleavage at any of these sites leads to a decrease in the generation of α-secretase cleaved secreted APP, which has both anti-apoptotic and neuroprotective properties, and thus may contribute to neurodegeneration in Alzheimer's disease.
authors.affiliation: USF Health Byrd Alzheimer's Institute, University of South Florida, Tampa, Florida, United States of America.
authors.forename: Tina
authors.initials: T
authors.lastname: Fiorelli
authors.forename: Lisa
authors.initials: L
authors.lastname: Kirouac
authors.forename: Jaya
authors.initials: J
authors.lastname: Padmanabhan
mesh_terms: D016229:Amyloid beta-Peptides / Q000096:biosynthesis; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002166:Camptothecin / Q000494:pharmacology; D053148:Caspase 3 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D053179:Caspase 7 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D019295:Computational Biology; D004249:DNA Damage; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011247:Pregnancy; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D010446:Peptide Fragments; D034741:RNA, Small Interfering; D053148:Caspase 3; D053179:Caspase 7; D002166:Camptothecin