Inhibition of proteasomes induces accumulation, phosphorylation, and recruitment of HSP27 and alphaB-crystallin to aggresomes.
Molecular chaperones and the ubiquitin-proteasome pathway are known to participate in the quality control of proteins in cells. In this study, we examined the responses of small heat shock proteins to proteasome inhibitors to clarify their roles under conditions where misfolded proteins are abnormally accumulated. HSP27 and alphaB-crystallin accumulated in both soluble and, more prominently, insoluble fractions after exposure to MG-132, a proteasome inhibitor. Enhanced expression of mRNAs for HSP27 and alphaB-crystallin was observed, suggesting transcriptional activation. Phosphorylation of HSP27 and alphaB-crystallin in cells treated with MG-132 was enhanced concomitantly with activation of p38 and p44/42 MAP kinase pathways. Immunofluorescence analysis revealed that exposure to proteasome inhibitors induced the formation of aggresomes in U373 MG cells, to which HSP27 and alphaB-crystallin were recruited. However, phosphorylation was not required for this accumulation in aggresomes. Thus, HSP27 and alphaB-crystallin are increased, phosphorylated and localized in aggresomes when proteasome activity is inhibited.
Ito
Hidenori
H
Department of Biochemistry, Institute for Developmental Research, Aichi Human Service Center, Kamiya, Kasugai, 480-0392, Japan. itohide@inst-hsc.pref.aichi.jp
Kamei
Keiko
K
Iwamoto
Ikuko
I
Inaguma
Yutaka
Y
García-Mata
Rafael
R
Sztul
Elizabeth
E
Kato
Kanefusa
K
D015152:Blotting, Northern; D015153:Blotting, Western; D003459:Crystallins / Q000737:chemistry*; D003546:Cysteine Endopeptidases; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D006801:Humans; D007150:Immunohistochemistry; D007976:Leupeptins / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009363:Neoplasm Proteins / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured
D003459:Crystallins; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D007976:Leupeptins; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde