title: Translocation of small heat shock proteins to the actin cytoskeleton upon proteasomal inhibition.
abstract: The role of small heat shock proteins (sHsps) as molecular chaperones is still poorly understood. We therefore investigated the effect of proteasomal inhibition on sHsps in the rat cardiac myoblast cell line H9c2. Proteasomes are responsible for controlled degradation of intracellular proteins. Inhibition of their activities leads to accumulation of unfolded proteins, which can form insoluble "aggresomes" together with proteasomes and heat shock proteins Hsp70 and Hsp90. We here report that upon proteasome inhibition, alpha B-crystallin and Hsp25 translocate from the detergent-soluble cytosolic fraction to the detergent-insoluble nuclear/cytoskeletal fraction. Although phosphorylation of both alpha B-crystallin and Hsp25 is induced, this does not seem to be essential for the translocation. Immunocytochemistry revealed that alpha B-crystallin and Hsp25, which show a diffuse cytoplasmic staining in unstressed H9c2 cells, colocalize with F-actin upon proteasomal inhibition. After transfection in H9c2 cells, other sHsps (alpha A-crystallin, Hsp20, HspB2 and HspB3) showed similar translocation to the actin cytoskeleton. The redistribution of sHsps upon proteasomal inhibition may reflect a mechanism by which cells are protected from damaged intracellular proteins by sequestering them on the cytoskeleton.
authors.affiliation: Department of Biochemistry, Faculty of Science, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Pauline
authors.initials: P
authors.lastname: Verschuure
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Croes
authors.forename: Paul R L A
authors.initials: PR
authors.lastname: van den IJssel
authors.forename: Roy A
authors.initials: RA
authors.lastname: Quinlan
authors.forename: Wilfried W
authors.initials: WW
authors.lastname: de Jong
authors.forename: Wilbert C
authors.initials: WC
authors.lastname: Boelens
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D003459:Crystallins / Q000378:metabolism; D003546:Cysteine Endopeptidases; D003599:Cytoskeleton / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007976:Leupeptins / Q000502:physiology; D018832:Molecular Chaperones / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D046988:Proteasome Endopeptidase Complex; D021381:Protein Transport; D051381:Rats; D022502:Stress Fibers / Q000378:metabolism
chemical_list: D000199:Actins; D003459:Crystallins; D006360:Heat-Shock Proteins; D007976:Leupeptins; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde