Knock Down of Heat Shock Protein 27 (HspB1) Induces Degradation of Several Putative Client Proteins

Hsp27 belongs to the heat shock protein family and displays chaperone properties in stress conditions by holding unfolded polypeptides, hence avoiding their inclination to aggregate. Hsp27 is often referenced as an anti-cancer therapeutic target, but apart from its well-described ability to interfere with different stresses and apoptotic processes, its role in non-stressed conditions is still not well defined. In the present study we report that three polypeptides (histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3) were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. In addition, these proteins interacted with Hsp27 complexes of different native size. Altogether, these findings suggest that HDAC6, STAT2 and procaspase-3 are client proteins of Hsp27. Hence, in non stressed cancerous cells, the structural organization of Hsp27 appears to be a key parameter in the regulation by this chaperone of the level of specific polypeptides through client-chaperone type of interactions

Heat shock protein 27 prevents cellular polyglutamine toxicity and suppresses the increase of reactive oxygen species caused by huntingtin

Neuronal loss and intraneuronal protein aggregates are characteristics of Huntington’s disease (HD), which is one of 10 known neurodegenerative disorders caused by an expanded polyglutamine [poly(Q)] tract in the disease protein. N-terminal fragments of mutant huntingtin produce intracellular aggregates and cause toxicity. Several studies have shown that chaperones suppress poly(Q) aggregation and toxicity/cell death, but the mechanisms by which they prevent poly(Q)-mediated cell death remain unclear. In the present study, we identified heat shock protein 27 (HSP27) as a suppressor of poly(Q) mediated cell death, using a cellular model of HD. In contrast to HSP40/70 chaperones, we showed that HSP27 suppressed poly(Q) death without suppressing poly(Q) aggregation. We tested the hypotheses that HSP27 may reduce poly(Q)-mediated cell death either by binding cytochrome c and inhibiting the mitochondrial death pathway or by protecting gainst reactive oxygen species (ROS). While poly(Q)-induced cell death was reduced by inhibiting cytochrome c (cyt c) release from mitochondria, protection by HSP27 was regulated by its phosphorylation status and was independent of its ability to bind to cyt c. However, we observed that mutant huntingtin caused increased levels of ROS in neuronal and non-neuronal cells. ROS contributed to cell death because both N-acetyl-L-cysteine and glutathione in its reduced form suppressed poly(Q)-mediated cell death. HSP27 decreased ROS in cells expressing mutant huntingtin, suggesting that this chaperone protects cells against oxidative stress. We propose that a poly(Q) mutation can induce ROS that directly contribute to cell death and that HSP27 is an antagonist of this process

Protection against heat and staurosporine mediated apoptosis by the HSV-1 US11 protein

AbstractUS11 protein, one of herpes simplex virus type 1 (HSV-1) true late gene products, plays a role in the virally induced post-transcriptional control of gene expression. In addition, US11 expression also interferes with the cellular response to HSV-1 infection that can lead to apoptosis. We have previously shown that US11 expression enhanced the recovery of cellular protein synthesis and increased cell survival in response to thermal stress. Since heat shock can activate apoptosis, we tested for a possible anti-apoptotic behavior of US11. Here, we show that, in HeLa cells, US11 expression strongly reduced heat induced apoptosis, a phenomenon independent of Hsp expression and characterized by a delayed cytochrome c efflux from mitochondria and reduced caspase 3 activation. Moreover, US11 expression also protected against staurosporine induced apoptosis. Hence, our results favor an anti-apoptotic activity of US11 polypeptide that appears to be located at the level of mitochondria or upstream signaling pathways

Analysis of oxidative events induced by expanded polyglutamine huntingtin exon 1 that are differentially restored by expression of heat shock proteins or treatment with an antioxidant

We recently reported that the transient expression of polyglutamine tracts of various size in exon 1 of the huntingtin polypeptide (httExl) generated abnormally high levels of intracellular reactive oxygen species that directly contributed to cell death. Here, we compared the protection generated by heat shock proteins to that provided by the antioxidant agent N-acetyl-L-cysteine. In cells expressing httExl with 72 glutamine repeats (httEx1-72Q), the overexpression of Hsp27 or Hsp70 plus Hdj-1(Hsp40) or treatment of the cells with N-acetyl-L-cysteine inhibited not only mitochondrial membrane potential disruption but also the increase in reactive oxygen species, nitric oxide and protein oxidation. However, only heat shock proteins and not N-acetyl-L-cysteine reduced the size of the inclusion bodies formed by httExl-72Q. In cells expressing httExl polypeptide with 103 glutamine repeats (httEx1-103Q), heat shock proteins neither decreased oxidative damage nor reduced the size of the inclusions. In contrast, N-acetyl-L-cysteine still efficiently decreased the oxidative damage induced by httExl-103Q polypeptide without altering the inclusions. N-Acetyl-L-cysteine was inactive with regard to proteasome inhibition, whereas heat shock proteins partially restored the caspase-like activity of this protease. These observations suggest some relationships between the presence of inclusion bodies and the oxidative damage induced by httExl-polyQ