Hepatitis C virus inhibitor synergism suggests multistepinteractions between heat-shock protein 90 and hepatitis Cvirus replication

AIM: To address the effect of heat-shock protein 90(HSP90) inhibitors on the release of the hepatitis C virus(HCV), a cell culture-derived HCV(JFH1/HCVcc) from Huh-7 cells was examined.METHODS: We quantified both the intracellular and extracellular(culture medium) levels of the components(RNA and core) of JFH-1/HCVcc. The intracellular HCV RNA and core levels were determined after the JFH1/HCVcc-infected Huh-7 cells were treated with radicicol for 36 h. The extracellular HCV RNA and core protein levels were determined from the medium of the last 24 h of radicicol treatment. To determine the possible role of the HSP90 inhibitor in HCV release, we examined the effect of a combined application of low doses of the HSP90 inhibitor radicicol and the RNA replication inhibitors cyclosporin A(Cs A) or interferon. Finally, we statistically examined the combined effect of radicicoland Cs A using the combination index(CI) and graphical representation proposed by Chou and Talalay.RESULTS: We found that the HSP90 inhibitors had greater inhibitory effects on the HCV RNA and core protein levels measured in the medium than inside the cells. This inhibitory effect was observed in the presence of a low level of a known RNA replication inhibitor(Cs A or interferon-α). Treating the cells with a combination of radicicol and cyclosporin A for 24 h resulted in significant synergy(CI < 1) that affected the release of both the viral RNA and the core protein. CONCLUSION: In addition to having an inhibitory effect on RNA replication, HSP90 inhibitors may interfere with an HCV replication step that occurs after the synthesis of viral RNA, such as assembly and release.

PGK1-coupled HSP90 stabilizes GSK3βexpression to regulate the stemness of breast cancer stem cells

Objective:Glycogen synthase kinase-3β(GSK3β)has been recognized as a suppressor of Wnt/β-catenin signaling,which is critical for the stemness maintenance of breast cancer stem cells.However,the regulatory mechanisms of GSK3βprotein expression remain elusive.Methods:Co-immunoprecipitation and mass spectral assays were performed to identify molecules binding to GSK3β,and to characterize the interactions of GSK3β,heat shock protein 90(Hsp90),and co-chaperones.The role of PGK1 in Hsp90 chaperoning GSK3βwas evaluated by constructing 293T cells stably expressing different domains/mutants of Hsp90α,and by performing a series of binding assays with bacterially purified proteins and clinical specimens.The influences of Hsp90 inhibitors on breast cancer stem cell stemness were investigated by Western blot and mammosphere formation assays.Results:We showed that GSK3βwas a client protein of Hsp90.Hsp90,which did not directly bind to GSK3β,interacted with phosphoglycerate kinase 1 via its C-terminal domain,thereby facilitating the binding of GSK3βto Hsp90.GSK3β-bound PGK1 interacted with Hsp90 in the“closed”conformation and stabilized GSK3βexpression in an Hsp90 activity-dependent manner.The Hsp90 inhibitor,17-AAG,rather than HDN-1,disrupted the interaction between Hsp90 and PGK1,and reduced GSK3βexpression,resulting in significantly reduced inhibition ofβ-catenin expression,to maintain the stemness of breast cancer stem cells.Conclusions:Our findings identified a novel regulatory mechanism of GSK3βexpression involving metabolic enzyme PGK1-coupled Hsp90,and highlighted the potential for more effective cancer treatment by selecting Hsp90 inhibitors that do not affect PGK1-regulated GSK3βexpression.

Discovery and development of natural heat shock protein 90 inhibitors in cancer treatment

Heat shock protein 90(Hsp90)is a highly conserved molecular chaperone that plays a vital role in the signal transduction of cancers.Hsp90 inhibitors are able to inhibit Hsp90 or the complex of Hsp90 and co-chaperones resulting in the degradation of Hsp90-dependent client proteins through the ubiqui tina tion-proteasome pathway,thereby leading to the growth inhibition of tumor cells.This review will briefy discuss the molecular structure and biological function of Hsp90,and focus on a summary of recent progress in the development and testing of natural Hsp90 inhibitors and their different means by which they interact with Hsp90.

Hsp90βis critical for the infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome(SFTS)caused by the SFTS virus(SFTSV)is an emerging disease in East Asia with a fatality rate of up to 30%.However,the viral-host interaction of SFTSV remains largely unknown.The heat-shock protein 90(Hsp90)family consists of highly conserved chaperones that fold and remodel proteins and has a broad impact on the infection of many viruses.Here,we showed that Hsp90 is an important host factor involved in SFTSV infection.Hsp90 inhibitors significantly reduced SFTSV replication,viral protein expression,and the formation of inclusion bodies consisting of nonstructural proteins(NSs).Among viral proteins,NSs appeared to be the most reduced when Hsp90 inhibitors were used,and further analysis showed that their translation was affected.Co-immunoprecipitation of NSs with four isomers of Hsp90 showed that Hsp90βspecifically interacted with them.Knockdown of Hsp90βexpression also inhibited replication of SFTSV.These results suggest that Hsp90βplays a critical role during SFTSV infection and could be a potential target for the development of drugs against SFTS.

Construction of Hsp90β gene specific silencing plasmid and its transfection efficiency

The purpose of this work was to construct the plasmid that could direct the synthesis of siRNA-like transcripts and thus mediate strong and specific repression of human heat shock protein 90β(Hsp90β)gene expression and to compare the transfection efficiency of the plasmids in varying conditions of transfection.Three 64 nt oligos corresponding to different regions of the target gene were chemically synthesized and annealed and were then ligated with pSUPER EGFP1 plasmid and double-digested with HindIII and BglII.Recombinant plasmids were transformed into Escherichia coli,DH5a,and the colonies were picked and grown in the Amp-agarose.The presence of positive clones was checked by the means of endodigestion and sequencing.Three cell strains,HepG2,Human umbilicus vein endothelium cells(HUVEC)and HeK293,were cultured.Then the plasmids were transfected into the cells at different ratios of plasmid to Lipofectamine.The transfection efficiency was measured by detection of enhanced green fluorescence protein(EGFP).The presence of positive recombinant clones were verified by double-digestion and sequencing.The bases inserted into the plasmids were correct and the positive colonies were named pSuper-Hsp90β1,pSuper-Hsp90β2 and pSuper-Hsp90β3.After optimizing the ratio of plasmid to Lipofectamine,we achieved high transfection efficiency in HeK293 cells.Transfection efficiency was still low in the HepG2 cells.In conclusion,the si-RNA-synthesizing plasmids targeting Hsp90βwere constructed and transfected into cells with different transfection efficiency.

Homeopathic Thuja 30C ameliorates benzo(a)pyreneinduced DNA damage,stress and viability of perfused lung cells of mice in vitro

OBJECTIVE： To examine if the ultra-highly diluted homeopathic remedy Thuja 30C can ameliorate benzo（a）pyrene （BaP）-induced DNA damage, stress and viability of perfused lung cells of Swiss albino mice in vitro. METHODS： Perfused normal lung cells from mice were cultured in 5% Roswell Park Memorial Institute medium and exposed to BaP, a potent carcinogen, at the half maximal inhibitory concentration dose （2.2 μmol/L） for 24 h. Thereafter, the intoxicated cells were either treated with Thuja 30C （used against tumor or cancer） or its vehicle media, succussed alcohol 30C. Relevant parameters of study involving reactive oxygen species （ROS） accumulation, total glutathione （GSH） content, and generations of heat shock protein （hsp）-90 were measured; the cell viability and other test parameters were measured after treatment with either Thuja 30C or its vehicle media. Circular dichroism spectroscopy was performed to examine if Thuja 30C directly interacted with calf thymus DNA as target. For ascertaining if DNA damaged by BaP could be partially repaired and restituted by the remedy, 4＇,6-diamidino-2-phenylindole staining was performed. RESULTS： Thuja 30C increased cell viability of BaP-intoxicated cells significantly, as compared to drug-untreated or drug-vehicle control. A minimal dose of Thuja 30C significantly inhibited BaP-induced stress level, by down-regulating ROS and hsp-90, and increasing GSH content. Thuja 30C itself had no DNA-damaging effect, and no direct drug-DNA interaction. However, it showed quite striking ability to repair DNA damage caused by BaP. CONCLUSION： Thuja 30C ameliorates BaP-induced toxicity, stress and DNA damage in perfused lung cells of mice and it apparently has no effect on normal lung cells.

Dissecting the Heat Stress Response in Chlamydomonas by Pharmaceutical and RNAi Approaches Reveals Conserved and Novel Aspects

To study how conserved fundamental concepts of the heat stress response （HSR） are in photosynthetic eukaryotes, we applied pharmaceutical and antisense/amiRNA approaches to the unicellular green alga Chlamydomonas reinhardtii. The Chlamydomonas HSR appears to be triggered by the accumulation of unfolded proteins, as it was induced at ambient temperatures by feeding cells with the arginine analog canavanine. The protein kinase inhibitor staurosporine strongly retarded the HSR, demonstrating the importance of phosphorylation during activation of the HSR also in Chlamydomonas. While the removal of extracellular calcium by the application of EGTA and BAPTA inhibited the HSR in moss and higher plants, only the addition of BAPTA, but not of EGTA, retarded the HSR and impaired thermotoler- ance in Chlamydomonas. The addition of cycloheximide, an inhibitor of cytosolic protein synthesis, abolished the attenu- ation of the HSR, indicating that protein synthesis is necessary to restore proteostasis. HSP90 inhibitors induced a stress response when added at ambient conditions and retarded attenuation of the HSR at elevated temperatures. In addition, we detected a direct physical interaction between cytosolic HSP90A/HSP70A and heat shock factor 1, but surprisingly this interaction persisted after the onset of stress. Finally, the expression of antisense constructs targeting chloroplast HSP70B resulted in a delay of the cell＇s entire HSR, thus suggesting the existence of a retrograde stress signaling cascade that is desensitized in HSP7OB-antisense strains.