Heat shock resistance conferred by expression of the human HSP27 gene in rodent cells

Heat shock induces in cells the synthesis of specific proteins called heat shock proteins (HSPs) and a transient state of thermotolerance. The putative role of one of the HSPs, HSP27, as a protective molecule during thermal stress has been directly assessed by measuring the resistance to hyperthermia of Chinese hamster and mouse cells transfected with the human HSP27 gene contained in plasmid pHS2711. One- and two-dimensional gel electrophoresis of [3H]leucine- and [32P]orthophosphate-labeled proteins, coupled with immunological analysis using Ha27Ab and Hu27Ab, two rabbit antisera that specifically recognize the hamster and the human HSP27 protein respectively, were used to monitor expression and inducibility of the transfected and endogenous proteins. The human HSP27 gene cloned in pHS2711 is constitutively expressed in rodent cells, resulting in accumulation of the human HSP27 and all phosphorylated derivatives. No modification of the basal or heat-induced expression of endogenous HSPs is detected. The presence of additional HSP27 protein provides immediate protection against heat shock administered 48 h after transfection and confers a permanent thermoresistant phenotype to stable transfectant Chinese hamster and mouse cell lines. Mild heat treatment of the transfected cells results in an induction of the full complement of the endogenous heat shock proteins and a small increase in thermoresistance, but the level attained did not surpass that of heat-induced thermotolerant control cells. These results indicate that elevated levels of HSP27 is sufficient to give protection from thermal killing. It is concluded that HSP27 plays a major role in the increased thermal resistance acquired by cells after exposure to HSP inducers.     

Folding of the striated muscle myosin motor domain

We have investigated the folding of the myosin motor domain using a chimera of an embryonic striated muscle myosin II motor domain fused on its COOH terminus to a thermal stable, fast folding variant of green fluorescent protein (GFP). In in vitro expression assays, the GFP domain of the chimeric protein, S1(795)GFP, folds rapidly enabling us to monitor the folding of the motor domain using fluorescence. The myosin motor domain folds very slowly and transits through multiple intermediates that are detectable by gel filtration chromatography. The distribution of the nascent protein among these intermediates is strongly dependent upon temperature. At 25 degrees C and above the predominant product is an aggregate of S1(795)GFP or a complex with other lysate proteins. At 0 degrees C, the motor domain folds slowly via an energy independent pathway. The unusual temperature dependence and slow rate suggests that folding of the myosin motor is highly susceptible to off-pathway interactions and aggregation. Expression of the S1(795)GFP in the C2C12 muscle cell line yields a folded and functionally active protein that exhibits Mg(2+)ATP-sensitive actin-binding and myosin motor activity. In contrast, expression of S1(795)GFP in kidney epithelial cell lines (human 293 and COS 7 cells) results in an inactive and aggregated protein. The results of the in vitro folding assay suggest that the myosin motor domain does not fold spontaneously under physiological conditions and probably requires cytosolic chaperones. The expression studies support this conclusion and demonstrate that these factors are optimized in muscle cells.     

Specific protein homeostatic functions of small heat‐shock proteins increase lifespan

During aging, oxidized, misfolded, and aggregated proteins accumulate in cells, while the capacity to deal with protein damage declines severely. To cope with the toxicity of damaged proteins, cells rely on protein quality control networks, in particular proteins belonging to the family of heat‐shock proteins (HSPs). As safeguards of the cellular proteome, HSPs assist in protein folding and prevent accumulation of damaged, misfolded proteins. Here, we compared the capacity of all Drosophila melanogaster small HSP family members for their ability to assist in refolding stress‐denatured substrates and/or to prevent aggregation of disease‐associated misfolded proteins. We identified CG14207 as a novel and potent small HSP member that exclusively assisted in HSP70‐dependent refolding of stress‐denatured proteins. Furthermore, we report that HSP67BC, which has no role in protein refolding, was the most effective small HSP preventing toxic protein aggregation in an HSP70‐independent manner. Importantly, overexpression of both CG14207 and HSP67BC in Drosophila leads to a mild increase in lifespan, demonstrating that increased levels of functionally diverse small HSPs can promote longevity in vivo.     

Rapid protein-folding assay using green fluorescent protein.

Formation of the chromophore of green fluorescent protein (GFP) depends on the correct folding of the protein. We constructed a "folding reporter" vector, in which a test protein is expressed as an N-terminal fusion with GFP. Using a test panel of 20 proteins, we demonstrated that the fluorescence of Escherichia coli cells expressing such GFP fusions is related to the productive folding of the upstream protein domains expressed alone. We used this fluorescent indicator of protein folding to evolve proteins that are normally prone to aggregation during expression in E. coli into closely related proteins that fold robustly and are fully soluble and functional. This approach to improving protein folding does not require functional assays for the protein of interest and provides a simple route to improving protein folding and expression by directed evolution.     

Expression and distribution of HSP27 in response to G418 in different human breast cancer cell lines

Heat shock proteins (HSPs) play an important role in folding, intracellular localization and degradation of cellular proteins. However, the cellular role of HSP27 is not completely understood. The conflicting results have been reported regarding stress-induced nuclear translocation of HSP27. In this study, human breast cancer cells transiently and stably expressing HSP27–EGFP chimera were utilized to observe the intracellular localization of HSP27. The data show that the transient and stable expression of HSP27–EGFP displayed distinguishingly cellular localization. The nuclear translocalization of HSP27–EGFP was correlated with the presence of G418. Experiments carried out with different human breast cancer cell lines revealed clearly different distribution patterns of endogenous HSP27. The subcellular distribution of endogenous HSP27 appeared diffuse throughout the cytoplasm in MDA435 cells. In MCF-7 and SKBR3 cells, the accumulation of the protein was distinctly seen along the cell membrane and around nucleus. Moreover, the nuclear translocation of endogenous HSP27 was stimulated by G418 only in MDA435 cells, but not in MCF-7 and SKBR3 cells. Overexpression of HSP27 has been associated with resistance to cisplatin and doxorubicin. The correlation of the expression pattern of HSP27 with the drug resistance may need to be investigated. Further studies on the intracellular function of HSP27 may take into account its interaction proteins in the cells. It may provide useful information for the identification of sensitivity of carcinoma cells to the chemotherapeutic drugs and development of more specific agents to circumvent HSP27.     

Green fluorescent protein expression triggers proteome changes in breast cancer cells

Green fluorescent protein (GFP) is the most commonly used reporter of expression in cell biology despite evidence that it affects the cell physiology. The molecular mechanism of GFP-associated modifications has been largely unexplored. In this paper we investigated the proteome modifications following stable expression of GFP in breast cancer cells (MDA-MB-231). A combination of three different proteome analysis methods (2-DE, iTRAQ, label-free) was used to maximise proteome coverage. We found that GFP expression induces changes in expression of proteins that are associated with protein folding, cytoskeletal organisation and cellular immune response. In view of these findings, the use of GFP as a cell reporter should be carefully monitored.     

Reporter mice express green fluorescent protein at initiation of meiosis in spermatocytes

Transgenic mice were generated using a heat shock protein 2 (Hspa2) gene promoter to express green fluorescent protein (GFP) at the beginning of meiotic prophase I in spermatocytes. Expression was confirmed in four lines by in situ fluorescence, immunohistochemistry, western blotting, and PCR assays. The expression and distribution of the GFP and HSPA2 proteins co‐localized in spermatocytes and spermatids in three lines, but GFP expression was variegated in one line (F46), being present in some clones of meiotic and post‐meiotic germ cells and not in others. Fluorescence activated cell sorting (FACS) was used to isolate purified populations of spermatocytes and spermatids. Although bisulfite sequencing revealed differences in the DNA methylation patterns in the promoter regions of the transgene of the variegated expressing GFP line, a uniformly expressing GFP reporter line, and the Hspa2 gene, these differences did not correlate with variegated expression. The Hspa2‐GFP reporter mice provide a novel tool for studies of meiosis by allowing detection of GFP in situ and in isolated spermatogenic cells. They will allow sorting of meiotic and post‐meiotic germ cells for characterization of molecular features and correlation of expression of GFP with stage‐specific spermatogenic cell proteins and developmental events. genesis 52:976–984, 2014. © 2014 Wiley Periodicals, Inc.     

Use of Green Fluorescent Protein in mouse embryos

Green Fluorescent Protein (GFP) has rapidly been established as a versatile and powerful cell marker in many organisms. Initial problems in using it in mammalian cells were solved by introducing mutations to increase its solubility at higher temperatures, such that GFP has now been used as a reporter in both gene expression and cell lineage studies, and to localize proteins within mammalian cells. GFP has two unique advantages: (i) the protein becomes fluorescent in an autocatalytic reaction, so that it can be introduced into any cell type simply as a cDNA or mRNA, or as protein; (ii) it is "bright" enough to be visualized in living cells under conditions that do not cause photodamage to the cells. In this article we outline the ways in which we have used GFP mRNA and cDNA in our studies of mouse cell lineages, and to characterize the behavior of proteins within the embryos.     

Engineering and characterization of a superfolder green fluorescent protein

Existing variants of green fluorescent protein (GFP) often misfold when expressed as fusions with other proteins. We have generated a robustly folded version of GFP, called 'superfolder' GFP, that folds well even when fused to poorly folded polypeptides. Compared to 'folding reporter' GFP, a folding-enhanced GFP containing the 'cycle-3' mutations and the 'enhanced GFP' mutations F64L and S65T, superfolder GFP shows improved tolerance of circular permutation, greater resistance to chemical denaturants and improved folding kinetics. The fluorescence of Escherichia coli cells expressing each of eighteen proteins from Pyrobaculum aerophilum as fusions with superfolder GFP was proportional to total protein expression. In contrast, fluorescence of folding reporter GFP fusion proteins was strongly correlated with the productive folding yield of the passenger protein. X-ray crystallographic structural analyses helped explain the enhanced folding of superfolder GFP relative to folding reporter GFP.     

Chaperone-mediated hierarchical control in targeting misfolded proteins to aggresomes

Protein misfolding is a common event in living cells. Molecular chaperones not only assist protein folding; they also facilitate the degradation of misfolded polypeptides. When the intracellular degradative capacity is exceeded, juxtanuclear aggresomes are formed to sequester misfolded proteins. Despite the well-established role of chaperones in both protein folding and degradation, how chaperones regulate the aggregation process remains controversial. Here we investigate the molecular mechanisms underlying aggresome formation in mammalian cells. Analysis of the chaperone requirements for the fate of misfolded proteins reveals an unexpected role of heat shock protein 70 (Hsp70) in promoting aggresome formation. This proaggregation function of Hsp70 relies on the interaction with the cochaperone ubiquitin ligase carboxyl terminal of Hsp70/Hsp90 interacting protein (CHIP). Disrupting Hsp70-CHIP interaction prevents the aggresome formation, whereas a dominant-negative CHIP mutant sensitizes the aggregation of misfolded protein. This accelerated aggresome formation also relies on the stress-induced cochaperone Bcl2-associated athanogene 3. Our results indicate that a hierarchy of cochaperone interaction controls different aspects of the intracellular protein triage decision, extending the function of Hsp70 from folding and degradation to aggregation.     

Heat shock protein 27 expression in the human testis showing normal and abnormal spermatogenesis

Heat shock proteins (HSPs) are molecular chaperones involved in protein folding, assembly and transport, and which play critical roles in the regulation of cell growth, survival and differentiation. We set out to test the hypothesis that HSP27 protein is expressed in the human testes and its expression varies with the state of spermatogenesis. HSP27 expression was examined in 30 human testicular biopsy specimens (normal spermatogenesis, maturation arrest and Sertoli cell only syndrome, 10 cases each) using immunofluorescent methods. The biopsies were obtained from patients undergoing investigations for infertility. The seminiferous epithelium of the human testes showing normal spermatogenesis had a cell type-specific expression of HSP27. HSP27 expression was strong in the cytoplasm of the Sertoli cells, spermatogonia, and Leydig cells. Alternatively, the expression was moderate in the spermatocytes, weak in the spermatids and absent in the spermatozoa. In testes showing maturation arrest, HSP27 expression was strong in the Sertoli cells, weak in the spermatogonia, and spermatocytes. It was absent in the spermatids and Leydig cells. In Sertoli cell only syndrome, HSP27 expression was strong in the Sertoli cells and absent in the Leydig cells. We report for the first time the expression patterns of HSP27 in the human testes and show differential expression during normal spermatogenesis, indicating a possible role in this process. The altered expression of this protein in testes showing abnormal spermatogenesis may be related to the pathogenesis of male infertility.     

A Cre‐inducible fluorescent reporter for observing apical membrane dynamics

The ability to image living tissues with fluorescent proteins has revolutionized the fields of cell and developmental biology. Fusions between fluorescent proteins and various polypeptides are allowing scientists to image tissues with sub‐cellular resolution. Here, we describe the generation and activity of a genetically engineered mouse line expressing a fusion between the green fluorescent protein (GFP) and the apically localized protein Crumbs3 (Crb3). This reporter drives Cre‐inducible expression of Crb3–GFP under control of the EF1a regulatory domains. The fusion protein is broadly expressed in embryonic and adult tissues and shows apical restriction in the majority of epithelial cell types. It displays a variably penetrant gain of function activity in the neural tube. However, in several cell types, over‐expression of Crb3 does not appear to have any effect on normal development or maintenance. Detailed analysis of kidneys expressing this reporter indicates normal morphology and function highlighting the utility for live imaging. Thus, the EF1a^Crb3–GFP mouse line will be of broad use for studying membrane and/or tissue dynamics in living tissues. genesis 53:285–293, 2015. © 2015 Wiley Periodicals, Inc.     

Comparison of ES cell fate in sandwiched aggregates and co-cultured aggregates during blastocyst formation by monitored GFP expression

Markers and the means to detect them are required to monitor the fate of living cells. However, few suitable markers for living cells were known until a green fluorescent protein (GFP) was discovered. We have established mouse embryonic stem (ES) cell lines that express mutant GFP under the chicken beta-actin (CAG) promoter. Using these cell lines, we were able to follow the migration of ES cells during blastocyst formation both in sandwiching and coculture methods, even if only a single ES cell was used. Furthermore, the contribution of ES cells to the inner cell mass (ICM) was easily estimated at the blastocyst stage. We compared sandwiching with coculture aggregation relative to the contribution of the ES cell in the ICM, and the results indicated that there was no difference in the ratios of chimeric embryos having ICM contributed from cultured ES cells. Furthermore, an aggregated single ES cell was able to contribute three or four cells to the ICM at the blastocyst stage. Thus we conclude that one, instead of two, embryos is enough to make aggregation with ES cells, and a single ES cell attached to an embryo is enough to produce germline chimeras. Moreover, we could clearly observe single cell fate during blastocyst formation. This suggests that our established cell line can be used for monitoring single cell fate in vivo. In addition, we have shown that up to five doses of 30 sec of UV irradiation using GFP filters have no effect on the embryonic development.     

Translation‐coupled protein folding assay using a protease to monitor the folding status

Protein folding is an essential prerequisite for proteins to execute nearly all cellular functions. There is a growing demand for a simple and robust method to investigate protein folding on a large‐scale under the same conditions. We previously developed a global folding assay system, in which proteins translated using an Escherichia coli‐based cell‐free translation system are centrifuged to quantitate the supernatant fractions. Although the assay is based on the assumption that the supernatants contain the folded native states, the supernatants also include nonnative unstructured proteins. In general, proteases recognize and degrade unstructured proteins, and thus we used a protease to digest the unstructured regions to monitor the folding status. The addition of Lon protease during the translation of proteins unmasked subfractions, not only in the soluble fractions but also in the aggregation‐prone fractions. We translated ～90 E. coli proteins in the protease‐inclusion assay, in the absence and presence of chaperones. The folding assay, which sheds light on the molecular mechanisms underlying the aggregate formation and the chaperone effects, can be applied to a large‐scale analysis.     

Systematic identification of the HSP90 candidate regulated proteome

HSP90 is a central player in the folding and maturation of many proteins. More than two hundred HSP90 clients have been identified by classical biochemical techniques including important signaling proteins with high relevance to human cancer pathways. HSP90 inhibition has thus become an attractive therapeutic concept and multiple molecules are currently in clinical trials. It is therefore of fundamental biological and medical importance to identify, ideally, all HSP90 clients and HSP90 regulated proteins. To this end, we have taken a global and a chemical proteomic approach in geldanamycin treated cancer cell lines using stable isotope labeling with amino acids in cell culture and quantitative mass spectrometry. We identified >6200 proteins in four different human cell lines and ~1600 proteins showed significant regulation upon drug treatment. Gene ontology and pathway/network analysis revealed common and cell-type specific regulatory effects with strong connections to unfolded protein binding and protein kinase activity. Of the 288 identified protein kinases, 98 were geldanamycin treatment including >50 kinases not formerly known to be regulated by HSP90. Protein turn-over measurements using pulsed stable isotope labeling with amino acids in cell culture showed that protein down-regulation by HSP90 inhibition correlates with protein half-life in many cases. Protein kinases show significantly shorter half lives than other proteins highlighting both challenges and opportunities for HSP90 inhibition in cancer therapy. The proteomic responses of the HSP90 drugs geldanamycin and PU-H71 were highly similar suggesting that both drugs work by similar molecular mechanisms. Using HSP90 immunoprecipitation, we validated several kinases (AXL, DDR1, TRIO) and other signaling proteins (BIRC6, ISG15, FLII), as novel clients of HSP90. Taken together, our study broadly defines the cellular proteome response to HSP90 inhibition and provides a rich resource for further investigation relevant for the treatment of cancer.     

Beneficial effects of curcumin on GFAP filament organization and down-regulation of GFAP expression in an in vitro model of Alexander disease

Heterozygous mutations of the GFAP gene are responsible for Alexander disease, a neurodegenerative disorder characterized by intracytoplasmic Rosenthal fibers (RFs) in dystrophic astrocytes. In vivo and in vitro models have shown co-localization of mutant GFAP proteins with the small heat shock proteins (sHSPs) HSP27 and alphaB-crystallin, ubiquitin and proteasome components. Results reported by several recent studies agree on ascribing an altered cytoskeletal pattern to mutant GFAP proteins, an effect which induces mutant proteins accumulation, leading to impaired proteasome function and autophagy induction. On the basis of the protective role shown by both these small heat shock proteins (sHSPs), and on the already well established neuroprotective effects of curcumin in several diseases, we have investigated the effects of this compound in an in vitro model of Alexander disease, consisting in U251-MG astrocytoma cells transiently transfected with a construct encoding for GFAP carrying the p.R239C mutation in frame with the reporter green fluorescent protein (GFP). In particular, depending on the dose used, we have observed that curcumin is able to induce both HSP27 and alphaB-crystallin, to reduce expression of both RNA and protein of endogenous GFAP, to induce autophagy and, finally, to rescue the filamentous organization of the GFAP mutant protein, thus suggesting a role of this spice in counteracting the pathogenic effects of GFAP mutations.     

Plant-adapted green fluorescent protein is a versatile vital reporter for gene expression, protein localization and mitosis in the filamentous fungus, Aspergillus nidulans

Green fluorescent protein (GFP) is a useful reporter to follow the in vivo behaviour of proteins, but the wild-type gfp gene does not function in many organisms, including many plants and filamentous fungi. We show that codon-modified forms of gfp , produced for use in plants, function effectively in Aspergillus nidulans both as gene expression reporters and as vital reporters for protein location. To demonstrate the use of these modified gfp s as reporter genes we have used fluorescence to follow ethanol-induced GFP expression from the alcA promoter. Translational fusions with the modified gfp were used to follow protein location in living cells; plant ER-retention signals targeted GFP to the endoplasmic reticulum, whereas fusion to the GAL4 DNA-binding domain targeted it to the nucleus. Nuclear-targeted GFP allowed real-time observation of nuclear movement and division. These modified gfp genes should provide useful markers to follow gene expression, organelle behaviour and protein trafficking in real time.     

Association of heat shock protein 70 with enterovirus capsid precursor P1 in infected human cells.

Members of the human heat shock (HSP) family of related proteins are involved in the intracellular folding, transport, and assembly of proteins and protein complexes. We have observed that human heat shock protein 70 (HSP70) is associated with the capsid precursor P1 of poliovirus and coxsackievirus B1 in infected HeLa cells. Antiserum generated against HSP70 coimmunoprecipitated the poliovirus protein P1, an intermediate in capsid assembly. Similarly, alpha-virion serum coimmunoprecipitated HSP70 from virus-infected cell extracts, but not from mock-infected cell extracts. The HSP70-P1 complex was stable in high-salt medium but was sensitive to incubation with 2 mM ATP, which is a characteristic of other known functional complexes between HSP70 and cellular proteins. The P1 in the complex was predominantly newly synthesized, and the half-life of complexed P1 was nearly twice as long as that of total P1. The HSP70-P1 complex was found to sediment at 3S to 6S, suggesting that it may be part of, or a precursor to, the "5S promoter particles" thought to be an assembly intermediate of picornaviruses. The finding that HSP70 was associated with the capsid precursors of at least two enteroviruses may suggest a functional role of these complexes in the viral life cycles.