Regulation of stress-induced intracellular sorting and chaperone function of Hsp27 (HspB1) in mammalian cells
- 12 October 2007
- journal article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 407 (3), 407-417
- https://doi.org/10.1042/bj20070195
Abstract
In vitro, small Hsps (heat-shock proteins) have been shown to have chaperone function capable of keeping unfolded proteins in a form competent for Hsp70-dependent refolding. However, this has never been confirmed in living mammalian cells. In the present study, we show that Hsp27 (HspB1) translocates into the nucleus upon heat shock, where it forms granules that co-localize with IGCs (interchromatin granule clusters). Although heat-induced changes in the oligomerization status of Hsp27 correlate with its phosphorylation and nuclear translocation, Hsp27 phosphorylation alone is not sufficient for effective nuclear translocation of HspB1. Using firefly luciferase as a heat-sensitive reporter protein, we demonstrate that HspB1 expression in HspB1-deficient fibroblasts enhances protein refolding after heat shock. The positive effect of HspB1 on refolding is completely diminished by overexpression of Bag-1 (Bcl-2-associated athanogene), the negative regulator of Hsp70, consistent with the idea of HspB1 being the substrate holder for Hsp70. Although HspB1 and luciferase both accumulate in nuclear granules after heat shock, our results suggest that this is not related to the refolding activity of HspB1. Rather, granular accumulation may reflect a situation of failed refolding where the substrate is stored for subsequent degradation. Consistently, we found 20S proteasomes concentrated in nuclear granules of HspB1 after heat shock. We conclude that HspB1 contributes to an increased chaperone capacity of cells by binding unfolded proteins that are hereby kept competent for refolding by Hsp70 or that are sorted to nuclear granules if such refolding fails.This publication has 53 references indexed in Scilit:
- Proteasomes degrade proteins in focal subdomains of the human cell nucleusJournal of Cell Science, 2005
- Mimicking phosphorylation of the small heat‐shock protein αB‐crystallin recruits the F‐box protein FBX4 to nuclear SC35 specklesEuropean Journal of Biochemistry, 2004
- Heat stress-induced localization of small heat shock proteins in mouse myoblasts: intranuclear lamin A/C speckles as target for αB-crystallin and Hsp25Experimental Cell Research, 2004
- Nuclear speckle localisation of the small heat shock protein ?B-crystallin and its inhibition by the R120G cardiomyopathy-linked mutationExperimental Cell Research, 2003
- Interaction between αB-crystallin and the human 20S proteasomal subunit C8/α7Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 2001
- αB-crystallin and hsp25 in neonatal cardiac cells — differences in cellular localization under stress conditionsEuropean Journal of Cell Biology, 1998
- Dynamics of proteasome distribution in living cellsThe EMBO Journal, 1997
- Cells Overexpressing Hsp27 Show Accelerated Recovery from Heat-Induced Nuclear-Protein AggregationBiochemical and Biophysical Research Communications, 1994
- Intracellular distribution of 73 000 and 72 000 dalton heat shock proteins in HeLa cellsInternational Journal of Hyperthermia, 1986
- Molecular weight estimations of proteins by electrophoresis in polyacrylamide gels of graded porosityFEBS Letters, 1972