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Bryantsev A, Kurchashova S, Golyshev S, Polyakov V, Wunderink H, Kanon B, Budagova K, Kabakov A, Kampinga H. Regulation of stress-induced intracellular sorting and chaperone function of Hsp27 (HspB1) in mammalian cells. Biochem J 2007; 407:407-17. [PMID: 17650072 PMCID: PMC2275061 DOI: 10.1042/bj20070195] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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.
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Affiliation(s)
- Anton L. Bryantsev
- *Department of Electron Microscopy, Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119992, Russia
| | - Svetlana Yu. Kurchashova
- *Department of Electron Microscopy, Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119992, Russia
| | - Sergey A. Golyshev
- *Department of Electron Microscopy, Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119992, Russia
| | - Vladimir Yu. Polyakov
- *Department of Electron Microscopy, Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119992, Russia
| | - Herman F. Wunderink
- †Department of Cell Biology, Section Radiation and Stress Cell Biology, University Medical Center Groningen, University of Groningen, 9791 AV, Groningen, The Netherlands
| | - Bart Kanon
- †Department of Cell Biology, Section Radiation and Stress Cell Biology, University Medical Center Groningen, University of Groningen, 9791 AV, Groningen, The Netherlands
| | - Karina R. Budagova
- ‡Department of Radiation Biochemistry, Medical Radiology Research Center, Obninsk, 249036, Russia
| | - Alexander E. Kabakov
- ‡Department of Radiation Biochemistry, Medical Radiology Research Center, Obninsk, 249036, Russia
| | - Harm H. Kampinga
- †Department of Cell Biology, Section Radiation and Stress Cell Biology, University Medical Center Groningen, University of Groningen, 9791 AV, Groningen, The Netherlands
- To whom correspondence should be addressed (email )
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