Heat shock gene expression in Xenopus laevis A6 cells in response to heat shock and sodium arsenite treatments

Continuous exposure of a Xenopus laevis kidney epithelial cell line, A6, to either heat shock (33 degrees C) or sodium arsenite (50 microM) resulted in transient but markedly different temporal patterns of heat-shock protein (HSP) synthesis and HSP 70 and 30 mRNA accumulation. Heat-shock-induced synthesis of HSPs was detectable within 1 h and reached maximum levels by 2-3 h. While sodium arsenite induced the synthesis of some HSPs within 1 h, maximal HSP synthesis did not occur until 12 h. The pattern of HSP 70 and 30 mRNA accumulation was similar to the response observed at the protein level. During recovery from heat shock, a coordinate decline in HSPs and HSP 70 and 30 mRNA was observed. During recovery from sodium arsenite, a similar phenomenon occurred during the initial stages. However, after 6 h of recovery, HSP 70 mRNA levels persisted in contrast to the declining HSP 30 mRNA levels. Two-dimensional polyacrylamide gel electrophoresis revealed the presence of 5 HSPs in the HSP 70 family, of which two were constitutive, and 16 different stress-inducible proteins in the HSP 30 family. In conclusion, heat shock and sodium arsenite induce a similar set of HSPs but maximum synthesis of the HSP is temporally separated by 12-24 h.     

Heat and sodium arsenite act synergistically on the induction of heat shock gene expression in Xenopus laevis A6 cells

Heat shock protein (HSP) synthesis was studied in the Xenopus epithelial cell line A6 in response to heat and sodium arsenite, either singly or together. Temperatures of 33-35 degrees C consistently brought about the synthesis of HSPs at 87, 73, 70, 54, 31, and 30 kilodaltons (kDa), whereas sodium arsenite at 25-100 microM induced the synthesis of HSPs at 73 and 70 kDa. In cultures exposed to 10 microM sodium arsenite at 30 degrees C, HSP synthesis in the 68- to 73-kDa and 29- to 31-kDa regions was much greater than the HSP synthesis in response to each treatment individually. RNA dot blot analysis using homologous genomic subclones revealed that heat shock induced the accumulation of HSP 70 and 30 mRNAs. The sizes of the HSP 70 and 30 mRNAs determined by Northern hybridization were 2.7 and 1.5 kilobases, respectively. Sodium arsenite (10-100 microM) also induced the accumulation of both HSP 70 and 30 mRNAs. Finally, a mild heat shock (30 degrees C) plus a low concentration of sodium arsenite (10 microM) acted synergistically on HSP 70 and 30 mRNA accumulation in A6 cells. Thus sodium arsenite and heat act synergistically at the level of both HSP synthesis and HSP mRNA accumulation.     

induction of heat shock response and acquisition of thermotolerance in callus cultures of Gerbera jamesonii

Summary The heat shock (HS) response in callus cultures of the ornamental plant Gerbera jamesonii H. Bolus var. hybrida was analyzed. A HS at 35° C or 40° C for 4 h induced (a) the synthesis of several heat shock proteins (HSPs), especially in the small molecular weight range and some spots corresponding to HSP70 components, and (b) an increase in the steady state levels of some specific mRNAs. At the nonstressing temperature (26° C), a sustainable level of translation for HSP70 was indeed carried out, as confirmed by immunological analysis with a monoclonal antibody against cotton HSP70. The steady state levels of mRNAs measured before and after a HS by Northern hybridization showed an increase with the heterologous probes HSP17.4, HSP17.6, and HSP21, whereas the probes HSC70 and HSP70 did not show any difference between the levels of control and HS-mRNAs. A pretreatment at 35° C, which induced a set of HSPs in the callus cultures, decreased the cell damage upon exposure to a temperature of 45° C as determined either with a regrowth test or by the tetrazolium reduction assay. Typically, as with the whole plants, callus of Gerbera jamesonii possessed the ability to respond to HS both by inducing HSPs and by developing an acquired thermotolerance.     

Heat-shock proteins during pollen development in maize

In contrast to sporophytic tissues, mature pollen of higher plants does not synthesize the typical set of heat-shock proteins (HSPs) in response to a marked temperature upshift. Immature grains, however, seem able to do so, at least partially. We investigated the characteristics of HSP synthesis throughout the male gametophytic phase in maize and compared gametophytic and sporophytic heat-shock responses. One-dimensional Sodium dodecyl sulfate-polyacryl-amide gel electrophoresis technique (SDS-PAGE) of newly synthesized proteins revealed that immature pollen synthesizes HSPs, some of which are not induced in sporophytic tissues. The heat-shock response appeared to be related to microgametophytic developmental stages. The strongest response was found in uninucleate microspores: at this stage, in addition to the sporophytic 102, 84, 72, and 18 kD HSPs, three other polypeptides of 74, 56, and 46 kD were observed. In the binucleate and trinucleate stages, only a reduced synthesis of few HSPs could be induced, and differences between genotypes were observed. In germinating pollen, HSP synthesis was not induced under a voriety of heat-stress conditions; however, the consti-tutive synthesis of two polypeptides of the same molecular weight, 72 and 64 kD, as two HSPs was observed. The biological significance of these results is discussed.     

Proteomic analysis of altered protein expression in skeletal muscle of rats in a hypermetabolic state induced by burn sepsis

mRNA profiling has been extensively used to study muscle wasting. mRNA level changes may not reflect that of proteins, especially in catabolic muscle where there is decreased synthesis and increased degradation. As sepsis is often associated with burn injury, and burn superimposed by sepsis has been shown to result in significant loss of lean tissues, we characterized changes in the skeletal-muscle proteome of rats subjected to a cutaneous burn covering 20% of the total body surface area, followed 2 days later by sepsis induced by CLP (caecal ligation and puncture). EDL (extensor digitorum longus) muscles were dissected from Burn-CLP animals (n=4) and controls (sham-burned and sham-CLP-treated, n=4). Burn-CLP injury resulted in a rapid loss of EDL weight, increased ubiquitin-conjugated proteins and increased protein carbonyl groups. EDL protein profiles were obtained by two-dimensional gel electrophoresis using two immobilized pH gradient strips with overlapping pH range covering a pH 3-8 range. Seventeen spots were significantly altered in the Burn-CLP compared with the control group, representing 15 different proteins identified by peptide mass fingerprinting. The identities of three proteins including transferrin were further confirmed by liquid chromatography-tandem MS. The significant changes in transferrin and HSP27 (heat-shock protein 27) were verified by Western-blot analysis. HSP60, HSP27 and HSPbeta6 were down-regulated, along with HSP70, as detected by Western blotting. Six metabolic enzymes related to energy production were also down-regulated. A simultaneous decrease in chaperone proteins and metabolic enzymes could decrease protein synthesis. Furthermore, decreased HSPs could increase oxidative damage, thus accelerating protein degradation. Using cultured C2C12 myotubes, we showed that H2O2-induced protein degradation in vitro could be partially attenuated by prior heat-shock treatment, consistent with a protective role of HSP70 and/or other HSPs against proteolysis.     

Developmental regulation of heat shock protein synthesis and HSP 70 RNA accumulation during postimplantation rat embryogenesis

Exposure of postimplantation rat embryos on days 9, 10, 11, and 12 of gestation to an in vitro heat shock of 43 degrees C for 30 min results in the induction of heat shock proteins (HSPs) in day 9 and 10 embryos, a severely attenuated response in day 11 embryos, and no detectable response in day 12 embryos. The heat shock response in day 9 embryos (presomite stage) is characterized by the synthesis of HSPs with molecular weights of 28-78 kDa. In heat shocked day 10 embryos, two additional HSPs are induced (34 and 82 kDa). In addition, two HSPs present on day 9 are absent on day 10. In day 11 heat shocked embryos, only three HSPs (31, 39, and 69 kDa) are induced, while in day 12 embryos no detectable HSPs are induced. Northern blot analysis of HSP 70 RNA levels indicates that the accumulation of this RNA, but not actin RNA, varies depending on developmental stage at the time of exposure to heat as well as the duration of the heat shock. Day 9 embryos exhibit the most pronounced accumulation of HSP 70 RNA while embryos on days 10-12 exhibit an increasingly attenuated accumulation of HSP 70 RNA, particularly after the more acute exposures (43 degrees C for 30 or 60 min). Thus, the ability to synthesize HSP 70 and to accumulate HSP 70 RNA changes dramatically as rat embryos develop from day 9 to day 12 (presomite to 31-35 somite stages).     

Preferential translation of heat shock mRNAs in HeLa cells deficient in protein synthesis initiation factors eIF-4E and eIF-4 gamma.

Expression of antisense RNA against eukaryotic translation initiation factor 4E (eIF-4E) in HeLa cells causes a reduction in the levels of both eIF-4E and eIF-4 gamma (p220) and a concomitant decrease in the rates of both cell growth and protein synthesis (De Benedetti, A., Joshi-Barve, S., Rinker-Schaffer, C., and Rhoads, R. E. (1991) Mol. Cell Biol. 11, 5435-5445). The synthesis of most proteins in the antisense RNA-expressing cells (AS cells) is decreased, but certain proteins continue to be synthesized. In the present study, we identified many of these as stress-inducible or heat shock proteins (HSPs). By mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by reactivity with monoclonal antibodies generated against human HSPs, four of these were shown to be HSP 90, HSP 70, HSP 65, and HSP 27. The steady-state levels of HSP 90, 70, and 27 were elevated in relation to total protein in AS cells. Pulse labeling and immunoprecipitation indicated that HSP 90 and HSP 70 were synthesized more rapidly in AS cells than in control cells. The accelerated synthesis of HSPs in the AS cells was not due, however, to increased mRNA levels; the levels of HSP 90 and 70 mRNAs either remained the same or decreased after induction of antisense RNA expression. Actin mRNA, a typical cellular mRNA, was found on high polysomes in control cells but shifted to smaller polysomes in AS cells, as expected from the general decrease in translational initiation caused by eIF-4E and eIF-4 gamma depletion. HSP 90 and 70 mRNAs showed the opposite behavior; they were associated with small polysomes in control cells but shifted to higher polysomes in AS cells. These results demonstrate that HSP mRNAs have little or no requirement in vivo for the cap-recognition machinery and suggest that these mRNAs may utilize an alternative, cap-independent mechanism of translational initiation.     

Recovery from Heat Shock in Heat-Tolerant and Nontolerant Variants of Creeping Bentgrass

Recovery from the heat-shock response was tested in heat-tolerant (selected bentgrass [SB]) and nontolerant (nonselected bentgrass [NSB]) variants of creeping bentgrass (Agrostis palustris Huds.) SB increased incorporation of radioactive amino acids into protein 2 h earlier than NSB when leaf blades were incubated at the recovery temperature following heat shock. Electrophoresis indicated that heat-shock protein (HSP) synthesis decreased and normal protein synthesis increased at 4 h in SB and at 6 to 8 h in NSB. Increased synthesis of normal proteins was not due to increased abundance of normal mRNAs, which were equivalent in SB and NSB at 4 h. But at 4 h, more of the normal mRNA population was associated with polysomes in SB than in NSB. Synthesis of HSP70 and HSP18 decreased earlier in SB than in NSB. The decreased synthesis of these HSPs appeared to be correlated with decreased mRNA abundance. But at 4 h, some of the HSP18 mRNA may have been associated with heat-shock granules in SB. Synthesis of HSP25 continued through the 8-h recovery in both variants. Although the abundance of HSP25 was equivalent in SB and NSB during heat shock and recovery, more HSP25 mRNA was associated with polysomes in SB than in NSB.     

Differential expression of heat-shock proteins and spontaneous synthesis of HSP70 during the life cycle of Blastocladiella emersonii

The heat-shock response in Blastocladiella emersonii is dependent on the developmental stage. Cells exposed to elevated temperatures at different stages of the life cycle (sporulation, germination or growth) show a differential synthesis of heat-shock proteins (hsps). Of a total of 22 polypeptides induced, particular subsets of hsps appear in each phase, demonstrating a non-coordinate heat-shock gene expression. In contrast, heat-shock-related proteins (hsp76, hsp70, hsp39a) are spontaneously expressed at a high level during sporulation. By the criteria of two-dimensional gel electrophoresis and partial proteolysis mapping, the 70,000-Da protein, whose synthesis is induced spontaneously during sporulation, is indistinguishable from the heat-inducible hsp70. The techniques of in vitro translation, and Northern analysis using a Drosophila hsp70 probe, demonstrated that enhanced synthesis of hsp70, which occurs during heat-shock treatment and spontaneously during sporulation, is associated with an accumulation of hsp70 mRNA. These observations suggest that hsp70 gene expression is induced during sporulation.     

Alpha-lipoic acid does not alter stress protein response to acute exercise in diabetic brain

Heat shock proteins (HSPs) are molecular chaperones which may act protective in cerebrovascular insults and peripheral diabetic neuropathy. We hypothesized that alpha-lipoic acid (LA), a natural thiol antioxidant, may enhance brain HSP response in diabetes. Rats with or without streptozotocin-induced diabetes were treated with LA or saline for 8 weeks. Half of the rats were subjected to exhaustive exercise to investigate HSP induction, and the brain tissue was analyzed. Diabetes increased constitutive HSC70 mRNA, and decreased HSP90 and glucose-regulated protein 75 (GRP75) mRNA without affecting protein levels. Exercise increased HSP90 protein and mRNA, and also GRP75 and heme oxygenase-1 (HO-1) mRNA only in non-diabetic animals. LA had no significant effect on brain HSPs, although LA increased HSC70 and HO-1 mRNA in diabetic animals and decreased HSC70 mRNA in non-diabetic animals. Eukaryotic translation elongation factor-2, essential for protein synthesis, was decreased by diabetes and suggesting a mechanism for the impaired HSP response related to translocation of the nascent chain during protein synthesis. LA supplementation does not offset the adverse effects of diabetes on brain HSP mRNA expression. Diabetes may impair HSP translation through elongation factors related to nascent chain translocation and subsequent responses to acute stress.     

Thermotolerance and the heat-shock response in Candida albicans

At elevated temperatures, yeast cells of Candida albicans synthesized nine heat-shock proteins (HSPs) with apparent molecular masses of 98, 85, 81, 76, 72, 54, 34, 26 and 18 kDa. The optimum temperature for the heat-shock response was 45 degrees C although HSPs were detected throughout the range 41-46 degrees C. Protein synthesis was not observed in cells kept at 48 degrees C. Yeast cells survived exposure to an otherwise lethal temperature of 55 degrees C when they had previously been exposed to 45 degrees C. The thermotolerance induced during incubation at 45 degrees C required protein synthesis, since protection was markedly reduced by trichodermin. Mercury ions induced a set of three stress proteins, one of which corresponded in size to an HSP, and cadmium ions evoked one stress protein seemingly unrelated to the HSPs observed after temperature shift.