Interaction of stress proteins with misfolded keratins.
Misfolded and aggregated proteins are a characteristic feature of a variety of chronic diseases. Examples include neurofibrillary tangles in Alzheimer disease, Lewy bodies in Parkinson disease and Mallory bodies (MBs) in chronic liver diseases, particularly alcoholic and non-alcoholic steatohepatitis (ASH and NASH). MB formation is at least in part the result of chronic oxidative cell stress in hepatocytes and can be induced in mice by long-term intoxication with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Proteomic analysis revealed that MBs consist of ubiquitinated keratins and the stress proteins Hsp70, Hsp25, and p62. Furthermore, marked overexpression of clusterin, which shares functional properties with small heat shock proteins, was identified by gene expression profiling of DDC-treated mice livers. To investigate whether clusterin has a function in the stress response to misfolded keratins, we performed transfection studies utilizing expression constructs encoding ubiquitin, p62, Hsp27, clusterin, keratin 8, and keratin 18. Ubiquitin was found in a strong and constant association with keratin aggregates, whereas binding of p62 to keratin was variable. Hsp27 did not colocalize with keratin aggregates under these experimental conditions. In contrast, clusterin associated with misfolded keratin only if its signal peptide was deleted and its secretion inhibited. This suggests that clusterin has ability to bind misfolded proteins, including keratins but its physiological function is restricted to the extracellular space. The extracellular localization of clusterin was underlined by immunohistochemical studies in Alzheimer disease brains, where clusterin was constantly found in association with amyloid plaques; in contrast, cytoplasmic inclusions such as neurofibrillary tangles as well as MBs in ASH were negative. Furthermore, we found clusterin in association with elastic fibers in the extracellular matrix in several chronic liver diseases, including ASH and alpha1-antitrypsin deficiency, implying a possible role of clusterin in liver fibrosis.
Janig
Elke
E
Institute of Pathology, Medical University of Graz, Auenbruggerplatz 25, A-8036 Graz, Austria.
Stumptner
Cornelia
C
Fuchsbichler
Andrea
A
Denk
Helmut
H
Zatloukal
Kurt
K
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000544:Alzheimer Disease / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D051152:Clusterin; D006224:Cricetinae; D003412:Cricetulus; D006023:Glycoproteins / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007633:Keratins / Q000378:metabolism*; D008108:Liver Diseases, Alcoholic / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D017510:Protein Folding; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C495242:CLU protein, human; C495243:Clu protein, mouse; D051152:Clusterin; D006023:Glycoproteins; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin; D007633:Keratins