Naturally occurring transposable elements disrupt hsp70 promoter function in Drosophila melanogaster

Naturally occurring transposable element (TE) insertions that disrupt Drosophila promoters are correlated with modified promoter function and are posited to play a significant role in regulatory evolution, but their phenotypes have not been established directly. To establish the functional consequences of these TE insertions, we created constructs with either TE-bearing or TE-lacking hsp70 promoters fused to a luciferase reporter gene and assayed luciferase luminescence in transiently transfected Drosophila cells. Each of the four TEs reduces luciferase signal after heat shock and heat inducibility of the hsp70 promoter. To test if the differences in hsp70 promoter activity are TE-sequence dependent, we replaced each of the TEs with multiple intergenic sequences of equal length. These replacement insertions similarly reduced luciferase signal, suggesting that the TEs affect hsp70 promoter function by altering promoter architecture. These results are consistent with differences in Hsp70 expression levels, inducible thermotolerance, and fecundity previously associated with the TEs. That two different varieties of TEs in two different hsp70 genes have common effects suggests that TE insertion represents a general mechanism through which selection manipulates hsp70 gene expression.     

Differential heat shock gene hsp70-1 response to toxicants revealed by in vivo study of lungs in transgenic mice

Members of heat shock proteins (Hsp70) family have been considered to respond to a large variety of stressful conditions. But it was suggested that, in pulmonary cells, Hsp response depends more closely on the type of stimulus. The lungs are critical organs potentially subjected to air pollution affecting respiratory function and, therefore, these organs are of particular interest with regard to the stress response. To investigate the stress dependence of Hsp70 response in lungs, we created transgenic mice where the firefly luciferase reporter gene is under the control of the murine hsp70-1 promoter and exposed them to different sublethal toxic conditions. For each condition, the level of transgene induction and pulmonary toxicity were assessed. We found that hsp70-1 promoter was stimulated by heat shock and cadmium but not by ozone, paraquat, and parathion, even if these chemicals induced respiratory distress and lung inflammation. Similar observations were made when expression of the endogenous hsp70-1 gene was analyzed, indicating that our transgenic model was accurately detecting hsp70-1 induction. Thereby, it appeared that hsp70-1 response is selective and depends on signaling pathways triggered by the toxicants rather than by their pathologic toxicity per se. Furthermore, because all the chemicals used in our study have been previously described to increase the level of oxidative stress, it indicates that there is no direct and simple correlation between hsp70-1 response and the level of oxidative stress, but more specific oxidative patterns should be involved in Hsp regulation.     

A new method for manipulating transgenes: engineering heat tolerance in a complex, multicellular organism

BACKGROUND: Heat-shock proteins (hsps) are thought to protect cells against stresses, especially due to elevated temperatures. But while genetic manipulation of hsp gene expression can protect microorganisms and cultured metazoan cells against lethal stress, this has so far not been demonstrated in multicellular organisms. Testing whether expression of an hsp transgene contributes to increased stress tolerance is complicated by a general problem of transgene analysis: if the transgene cannot be targeted to a precise site in the genome, newly observed phenotypes may be due to either the action of the transgene or mutations caused by the transgene insertion. RESULTS: To study the relationship between heat tolerance and hsp expression in Drosophila melanogaster, we have developed a novel method for transgene analysis, based upon the site-specific FLP recombinase. The method employs site-specific sister chromatid exchange to create an allelic series of transgene insertions that share the same integration site, but differ in transgene copy number. Phenotypic differences between members of this series can be confidently attributed to the transgenes. Using such an allelic series and a novel thermotolerance assay for Drosophila embryos, we investigated the role of the 70 kD heat-shock protein, Hsp 70, in thermotolerance. At early embryonic stages, Hsp70 accumulation was rate-limiting for thermotolerance, and elevated Hsp70 expression increased survival at extreme temperatures. CONCLUSION: Our results provide an improved method for analyzing transgenes and demonstrate that, in Drosophila, Hsp70 is a critical thermotolerance factor. They show, moreover, that manipulating the expression of a single hsp can be sufficient to improve the stress tolerance of a complex multicellular organism.     

Involvement of heat shock protein-70 in the mechanism of hydrogen peroxide-induced DNA damage: the role of lysosomes and iron

Heat shock protein-70 (Hsp70) is the main heat-inducible member of the 70-kDa family of chaperones that assist cells in maintaining proteins functional under stressful conditions. In the present investigation, the role of Hsp70 in the molecular mechanism of hydrogen peroxide-induced DNA damage to HeLa cells in culture was examined. Stably transfected HeLa cell lines, overexpressing or lacking Hsp70, were created by utilizing constitutive expression of plasmids containing the functional hsp70 gene or hsp70-siRNA, respectively. Compared to control cells, the Hsp70-overexpressing ones were significantly resistant to hydrogen peroxide-induced DNA damage, while Hsp70-depleted cells showed an enhanced sensitivity. In addition, the "intracellular calcein-chelatable iron pool" was determined in the presence or absence of Hsp70 and found to be related to the sensitivity of nuclear DNA to H(2)O(2). It seems likely that the main action of Hsp70, at least in this system, is exerted at the lysosomal level, by protecting the membranes of these organelles against oxidative stress-induced destabilization. Apart from shedding additional light on the mechanistic details behind the action of Hsp70 during oxidative stress, our results indicate that modulation of cellular Hsp70 may represent a way to make cancer cells more sensitive to normal host defense mechanisms or chemotherapeutic drug treatment.     

Genetic evidence for a functional relationship between Hsp104 and Hsp70.

The phenotypes of single Hsp104 and Hsp70 mutants of the budding yeast Saccharomyces cerevisiae provide no clue that these proteins are functionally related. Mutation of the HSP104 gene severely reduces the ability of cells to survive short exposures to extreme temperatures (thermotolerance) but has no effect on growth rates. On the other hand, mutations in the genes that encode Hsp70 proteins have significant effects on growth rates but do not reduce thermotolerance. The absence of a thermotolerance defect in S. cerevisiae Hsp70 mutants is puzzling, since the protein clearly plays an important role in thermotolerance in a variety of other organisms. In this report, examination of the phenotypes of combined Hsp104 and Hsp70 mutants uncovers similarities in the functions of Hsp104 and Hsp70 not previously apparent. In the absence of the Hsp104 protein, Hsp70 is very important for thermotolerance in S. cerevisiae, particularly at very early times after a temperature upshift. Similarly, Hsp104 plays a substantial role in vegetative growth under conditions of decreased Hsp70 protein levels. These results suggest a close functional relationship between Hsp104 and Hsp70.     

Role of inducible heat shock protein 70 in radiation-induced cell death

We previously demonstrated the protective effect of inducible heat shock protein 70 (Hsp70) against gamma radiation. Herein, we extend our studies on the possible role of Hsp70 to ionizing radiation-induced cell cycle regulation. The growth rate of inducible hsp70-transfected cells was 2-3 hours slower than that of control cells. Flow cytometric analysis of cells at G1 phase synchronized by serum starvation also showed the growth delay in the Hsp70-overexpressing cells. In addition, reduced cyclin D1 and Cdc2 levels and increased dephosphorylated phosphoretinoblastoma (pRb) were observed in inducible hsp70-transfected cells, which were probably responsible for the reduction of cell growth. To find out if inducible Hsp70-mediated growth delay affected radiation-induced cell cycle regulation, flow cytometric and molecular analyses of cell cycle regulatory proteins and their kinase were performed. The radiation-induced G2/M arrest was found to be inhibited by Hsp70 overexpression and reduced p21Waf induction and its kinase activity by radiation in the Hsp70-transfected cells. In addition, radiation-induced cyclin A or B1 expressions together with their kinase activities were also inhibited by inducible Hsp70, which represented reduced mitotic cell death. Indeed, hsp70 transfectants showed less induction of radiation-induced apoptosis. When treated with nocodazole, radiation-induced mitotic arrest was inhibited by inducible Hsp70. These results strongly suggested that inducible Hsp70 modified growth delay (increased G1 phase) and reduced G2/M phase arrest, subsequently resulting in inhibition of radiation-induced cell death.     

Loss of Hsp70 in Drosophila is pleiotropic, with effects on thermotolerance, recovery from heat shock and neurodegeneration

The heat-shock response is a programmed change in gene expression carried out by cells in response to environmental stress, such as heat. This response is universal and is characterized by the synthesis of a small group of conserved protein chaperones. In Drosophila melanogaster the Hsp70 chaperone dominates the profile of protein synthesis during the heat-shock response. We recently generated precise deletion alleles of the Hsp70 genes of D. melanogaster and have used those alleles to characterize the phenotypes of Hsp70-deficient flies. Flies with Hsp70 deletions have reduced thermotolerance. We find that Hsp70 is essential to survive a severe heat shock, but is not required to survive a milder heat shock, indicating that a significant degree of thermotolerance remains in the absence of Hsp70. However, flies without Hsp70 have a lengthened heat-shock response and an extended developmental delay after a non-lethal heat shock, indicating Hsp70 has an important role in recovery from stress, even at lower temperatures. Lack of Hsp70 also confers enhanced sensitivity to a temperature-sensitive lethal mutation and to the neurodegenerative effects produced by expression of a human polyglutamine disease protein.     

Characterization of a heat-shock-inducible hsp70 gene of the green alga Volvox carteri

The green alga Volvox carteri possesses several thousand cells, but just two cell types: large reproductive cells called gonidia, and small, biflagellate somatic cells. Gonidia are derived from large precursor cells that are created during embryogenesis by asymmetric cell divisions. The J domain protein GlsA (Gonidialess A) is required for these asymmetric divisions and is believed to function with an Hsp70 partner. As a first step toward identifying this partner, we cloned and characterized V. carteri hsp70A, which is orthologous to HSP70A of the related alga Chlamydomonas reinhardtii. Like HSP70A, V. carteri hsp70A contains multiple heat shock elements (HSEs) and is highly inducible by heat shock. Consistent with these properties, Volvox transformants that harbor a glsA antisense transgene that is driven by an hsp70A promoter fragment express Gls phenotypes that are temperature-dependent. hsp70A appears to be the only gene in the genome that encodes a cytoplasmic Hsp70, so we conclude that Hsp70A is clearly the best candidate to be the chaperone that participates with GlsA in asymmetric cell division.     

HERITABILITY OF EXPRESSION OF THE 70KD HEAT-SHOCK PROTEIN IN DROSOPHILA MELANOGASTER AND ITS RELEVANCE TO THE EVOLUTION OF THERMOTOLERANCE

The principle inducible heat-shock protein of Drosophila melanogaster, Hsp70, contributes to thermotolerance throughout the entire life cycle of the species but may also reduce fitness in some life stages. In principle, selection might maximize the benefits of Hsp70 expression relative to its costs by adjusting the magnitude of Hsp70 expression for each life-cycle stage independently. Therefore we examined whether the magnitude of Hsp70 expression varied during the life cycle and the relationship of this variation to several life-history traits. For 28 isofemale lines derived from a single natural population, estimates of heritable variation in Hsp70 expression ranged between 0.25 and 0.49, and the association among variation in first- and third-instar larvae and in adults correlated highly. Thus, Hsp70 expression is genetically coupled at these developmental stages. A line engineered with extra copies of the hsp70 gene produced more Hsp70 and survived heat shock much better than did a control strain. Among natural lines, Hsp70 expression was only weakly related to tolerance of heat shock and to larva-to-adult survival and developmental time at permissive temperatures. Additionally, lines with high adult survival developed slowly as larvae, which is a possible trade-off. These and other findings suggest that trade-offs may maintain quantitative variation both in heat-shock protein expression and in life-history traits that associate with thermotolerance.     

Small heat-shock protein Hsp9 has dual functions in stress adaptation and stress-induced G2-M checkpoint regulation via Cdc25 inactivation in Schizosaccharomyces pombe

The small heat-shock protein Hsp9 from Schizosaccharomyces pombe was previously reported to be a homologue of Saccharomyces cerevisiae HSP12. Although Hsp9 is expressed in response to heat shock and nutritional limitation, its function is still not completely understood. Here, we explored the biological function of Hsp9 in S. pombe. The hsp9 gene might play a role in stress adaptation; hsp9 deletion caused heat sensitivity and overexpression induced heat tolerance. In addition, Hsp9 also contribute to cell cycle regulation in the nucleus. Δhsp9 cells grew more quickly and were shorter in length than wild-type cells. Moreover, Δhsp9 cells did not achieve checkpoint arrest under stress conditions, leading to cell death, and exhibited a short doubling time and short G2 phase. Overexpression of hsp9 induced cell cycle delay, increased the population of G2 phase cells, and rescued the phenotypes of cdc2-33, cdc25-22, Δrad24, and Δrad25 mutants, suggesting that Hsp9 probably regulates Cdc2 phosphorylation by modulating the Cdc25 activity. Indeed, immunoprecipitation experiments revealed that Hsp9 is associated with 14-3-3 and Cdc25. In Δhsp9 cells, the association of 14-3-3 with Cdc25 was weakened and Cdc2 phosphorylaton was reduced. Together, our data suggest that Hsp9 has dual functions in stress adaptation and regulating a G2-M checkpoint by the Cdc25 inactivation; this differs from S. cerevisiae HSP12, which maintains cell membrane stability under stress conditions.     

Hsp27 protects mitochondria of thermotolerant cells against apoptotic stimuli

Enhanced cell survival and resistance to apoptosis during thermotolerance correlates with an increased expression of heat shock proteins (Hsps). Here we present additional evidence in support of the hypothesis that the induction of Hsp27 and Hsp72 during acquired thermotolerance in Jurkat T-lymphocytes prevents apoptosis. In thermotolerant cells, Hsp27 was shown to associate with the mitochondrial fraction, and inhibition of Hsp27 induction during thermotolerance in cells transfected with hsp27 antisense potentiated mitochondrial cytochrome c release after exposure to various apoptotic stimuli, despite the presence of elevated levels of Hsp72. Caspase activation and apoptosis were inhibited under these conditions. In vitro studies revealed that recombinant Hsp72 more efficiently blocked cytochrome c-mediated caspase activation than did recombinant Hsp27. A model is presented for the inhibition of apoptosis during thermotolerance in which Hsp27 preferentially blocks mitochondrial cytochrome c release, whereas Hsp72 interferes with apoptosomal caspase activation.     

Heat shock proteins Hsp70-1 and Hsp70-3 Are necessary and sufficient to prevent arsenite-induced dysmorphology in mouse embryos.

Heat Shock Proteins (HSPs) represent a variety of protein families that are induced by stressors such as heat and toxicants, and the induction of HSPs in the organogenesis stage rodent embryo is well established. It has been proposed that thermotolerance and chemotolerance result from expression of the HSPs. However, whether these proteins function to prevent dysmorphogenesis and which family members serve this function are unknown. Therefore, we evaluated the specific ability of stress-inducible Hsp70-1 and Hsp70-3 to prevent arsenite-induced dysmorphology in the cultured mouse embryo using gain- and loss-of-function models. Loss of HSP function was accomplished by injecting antisense oligonucleotides directed against hsp70-1 and hsp 70-3 mRNAs into the amniotic cavity of cultured Day 9 mouse embryos. Suppression of hsp70-1 and hsp70-3 expression resulted in an up to six-fold increase in the incidence of arsenite-induced neural tube defects. Gain of HSP function was accomplished by microinjecting a transgene with a constitutive promotor driving expression of the hsp70-1 coding region, and resulted in a decreased incidence of arsenite-induced neural tube defects. These results indicate that Hsp70-1 and Hsp70-3 are both necessary and sufficient for preventing arsenite-induced dysmorphology in early-somite staged mouse embryos. Mol. Reprod. Dev. 59:285-293, 2001.     

Modified expression of a carrot small heat shock protein gene, hsp17. 7, results in increased or decreased thermotolerancedouble dagger

We have determined that one small heat shock protein gene, encoding Hsp17.7, plays an important role in the ability of carrot cells and plants to survive thermal stress. Transgenic cells and regenerated plants were generated in which the carrot Hsp17.7 gene was either constitutively expressed (denoted CaS lines) or expressed as a heat inducible antisense RNA (denoted AH lines). Thermotolerance measurements demonstrated that CaS lines were more thermotolerant than vector controls and AH antisense lines were less thermo- tolerant than vector controls. RNA analysis demonstrated that Hsp17. 7 mRNA was detectable, but not abundant, prior to heat shock in CaS cells, but not in vector control cells. Conversely, RNA analysis of antisense cells showed that, after heat shock, the amounts of mRNA for Hsp17.7 was moderately less abundant in AH cells than in vector controls. Analysis of protein synthesis in CaS cells did not indicate substantial synthesis or accumulation of Hsp17.7, or any small Hsp, at 23 degrees C. However, in the most thermotolerant line, protein synthesis was maintained at a higher rate than in other cell lines at a more extreme heat shock (42 degrees C). In contrast, antisense AH cells showed reduced synthesis of many Hsp, large and small. These results suggest that the Hsp17.7 gene plays a critical, although as yet not understood, role in thermotolerance in carrot. This represents the first demonstration of the ability to both increase and decrease thermotolerance by the manipulation of expression of a single gene.     

Thermotolerance and nuclear protein aggregation: Protection against initial damage or better recovery?

Heat-induced nuclear protein aggregation and subsequent disaggregation were measured in nonpreheated and preheated (thermotolerant) HeLa S3 cells. The effect of thermotolerance on the formation of and recovery from heat-induced nuclear protein aggregates was related to the cellular levels of hsp27, hsp60, hsp70, hsc70, and hsp90. Cells heated at different time points after the thermotolerance trigger showed various levels of protection against heat-induced nuclear protein aggregation. This protection, however, did not parallel the development and decay of thermotolerance on cell survival. The protection was maximal when the thermotolerance level already had started to decay. The level of protection against nuclear protein aggregation did however parallel the cellular level of hsp70 indicating that hsp70 may be involved in this process. At all stages during the development and decay, thermotolerant cells showed a more rapid recovery (disaggregation) from the heat-induced nuclear protein aggregates than non-thermotolerant cells. The rates of disaggregation during development and decay of thermotolerance paralleled the cellular levels of hsp27 suggesting that hsp27 is somehow involved in this recovery process from heat-induced nuclear protein aggregates. The total cellular levels of none of the individual hsp's completely correlate with development and decay of thermotolerance, indicating that overexpression of any of these hsp's alone does not determine the level of thermotolerance. Clonogenic cell survival paralleled the rates of disaggregation, leading to the notion that recovery processes are the most important determinant for the thermotolerant state of HeLa S3 cells. The best corelation with clonogenic survival was found when both initial aggregation and subsequent disaggregation were taken into account, suggesting that the combined action of various hsp's in these two processes have to be included in thermotolerance development and decay. © 1995 Wiley-Liss, Inc.