Early and late events induced by polyQ-expanded proteins: identification of a common pathogenic property of polYQ-expanded proteins.
To find a common pathogenetic trait induced by polyQ-expanded proteins, we have used a conditional expression system in PC12 cells to tune the expression of these proteins and analyze the early and late consequences of their expression. We find that expression for 3 h of a polyQ-expanded protein stimulates cellular reactive oxygen species (ROS) levels and significantly reduces the mitochondrial electrochemical gradient. 24-36 h later, ROS induce DNA damage and activation of the checkpoint kinase, ATM. DNA damage signatures are reversible and persist as long as polyQ-expanded proteins are expressed. Transcription of neural and stress response genes is down-regulated in these cells. Selective inhibition of ATM or histone deacetylase rescues transcription and restores the expression of silenced genes. Eventually, after 1 week, the expression of polyQ-expanded protein also induces endoplasmic reticulum stress. As to the primary mechanism responsible for ROS generation, we find that polyQ-expanded proteins, including native Ataxin-2 and Huntingtin, are selectively sequestered in the lipid raft membrane compartment and interact with gp91, the membrane NADPH-oxidase subunit. Selective inhibition of NADPH oxidase or silencing of H-Ras signaling dissolves the aggregates and eliminates DNA damage. We suggest that targeting of the polyQ-expanded proteins to the lipid rafts activates the resident NADPH oxidase. This triggers a signal linking H-Ras, ROS, and ERK1/2 that maintains and propagates the ROS wave to the nucleus. This mechanism may represent the common pathogenetic signature of all polyQ-expanded proteins independently of the specific context or the function of the native wild type protein.
Department of Molecular and Cellular Biology and Pathology, School of Medicine, Federico II University of Naples, Naples 80131 Italy.
Alessandra
A
Bertoni
Paola
P
Giuliano
Mario
M
Galgani
Deborah
D
Rotoli
Luca
L
Ulianich
Annagrazia
A
Adornetto
Maria Rosaria
MR
Santillo
Antonio
A
Porcellini
Vittorio Enrico
VE
Avvedimento
D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D000067528:Ataxins; D018797:Cell Cycle Proteins; D004249:DNA Damage; D004268:DNA-Binding Proteins; D006655:Histone Deacetylases; D006801:Humans; D000071058:Huntingtin Protein; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
D000067528:Ataxins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C086055:HTT protein, human; C506812:Htt protein, mouse; C499524:Htt protein, rat; D000071058:Huntingtin Protein; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D017382:Reactive Oxygen Species; D025521:Tumor Suppressor Proteins; C097188:polyglutamine; C056558:CYBB protein, human; C488842:Cybb protein, mouse; C500593:Cybb protein, rat; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D006655:Histone Deacetylases; D016283:Proto-Oncogene Proteins p21(ras)