Characterization of goldfish heat shock protein-30 induced upon severe heat shock in cultured cells

Transient heat release during induced mitochondrial proton uncoupling

Non-shivering thermogenesis through mitochondrial proton uncoupling is one of the dominant thermoregulatory mechanisms crucial for normal cellular functions. The metabolic pathway for intracellular temperature rise has widely been considered as steady-state substrate oxidation. Here, we show that a transient proton motive force (pmf) dissipation is more dominant than steady-state substrate oxidation in stimulated thermogenesis. Using transient intracellular thermometry during stimulated proton uncoupling in neurons of Aplysia californica, we observe temperature spikes of ~7.5 K that decay over two time scales: a rapid decay of ~4.8 K over ~1 s followed by a slower decay over ~17 s. The rapid decay correlates well in time with transient electrical heating from proton transport across the mitochondrial inner membrane. Beyond ~33 s, we do not observe any heating from intracellular sources, including substrate oxidation and pmf dissipation. Our measurements demonstrate the utility of transient thermometry in better understanding the thermochemistry of mitochondrial metabolism.

The expression and function of hsp30-like small heat shock protein genes in amphibians, birds, fish, and reptiles

Small heat shock proteins (sHSPs) are a superfamily of molecular chaperones with important roles in protein homeostasis and other cellular functions. Amphibians, reptiles, fish and birds have a shsp gene called hsp30, which was also referred to as hspb11 or hsp25 in some fish and bird species. Hsp30 genes, which are not found in mammals, are transcribed in response to heat shock or other stresses by means of the heat shock factor that is activated in response to an accumulation of unfolded protein. Amino acid sequence analysis revealed that representative HSP30s from different classes of non-mammalian vertebrates were distinct from other sHSPs including HSPB1/HSP27. Studies with amphibian and fish recombinant HSP30 determined that they were molecular chaperones since they inhibited heat- or chemically-induced aggregation of unfolded protein. During non-mammalian vertebrate development, hsp30 genes were differentially expressed in selected tissues. Also, heat shock-induced stage-specific expression of hsp30 genes in frog embryos was regulated at the level of chromatin structure. In adults and/or tissue culture cells, hsp30 gene expression was induced by heat shock, arsenite, cadmium or proteasomal inhibitors, all of which enhanced the production of unfolded/damaged protein. Finally, immunocytochemical analysis of frog and chicken tissue culture cells revealed that proteotoxic stress-induced HSP30 accumulation co-localized with aggresome-like inclusion bodies. The congregation of damaged protein in aggresomes minimizes the toxic effect of aggregated protein dispersed throughout the cell. The current availability of probes to detect the presence of hsp30 mRNA or encoded protein has resulted in the increased use of hsp30 gene expression as a marker of proteotoxic stress in non-mammalian vertebrates.

Isolation and characterization of a genomic fosmid clone containing hspb1 (hsp27) from the Pacific bluefin tuna Thunnus orientalis

We constructed a fosmid library of genomic DNA from the Pacific bluefin tuna Thunnus orientalis and isolated a clone containing the complete gene hspb1 (hsp27) from the library. To screen the library, we first obtained a full-length hspb1 cDNA by RACE-PCR. This cDNA encodes a putative protein of 202 amino acids. Phylogenetic analysis indicated that the protein belongs to the Hsp27 family. Northern blot analysis demonstrated that the gene transcript was expressed in tuna muscle tissues. Using a combination of PCR screening and colony hybridization, we isolated a 39,422-bp fosmid clone containing hspb1 from an arrayed library. Sequence alignment showed that hspb1 contains three exons and two introns. Comparative genomic analysis revealed that hspb1 lies in a region of conserved synteny in the genomes of fish and human. Our finding of conserved regions within and around hspb1 in fish species will help to identify functional elements such as promoter regions.

Ligand-dependent transcriptional activities of four torafugu pufferfish Takifugu rubripes peroxisome proliferator-activated receptors

Structural and functional properties were investigated for four peroxisome proliferator-activated receptors (PPARs), PPARalpha1, PPARalpha2, PPARbeta, and PPARgamma, from torafugu pufferfish Takifugu rubripes and determined for their transcriptional activity by the reporter assay using reporter plasmids containing three copies of the acyl-CoA oxidase PPAR response element. Although torafugu PPARs showed a high similarity in the primary structure to other vertebrate counterparts, torafugu PPARalpha2 and gamma contained additional sequences of 21 and 28 amino acids, respectively, as in the case of other teleost fish species when compared with African clawed frog counterparts. The transcriptional activity of torafugu PPARalpha1 was enhanced 4.5- and 11.5-fold by Wy-14643 and 5,8,11,14-eicosatetraynoic acid (ETYA) each at 10 microM, respectively, whereas that of PPARalpha2, 4.5- and 7.3-fold at the same concentration of the respective ligands, respectively. The activities of torafugu PPARalpha1 and alpha2 were also enhanced 5.6- and 6.3-fold by ETYA at 1 microM, respectively, but not by Wy-14643 at this concentration. Furthermore, the activities of the two torafugu PPARalphas were enhanced 4.3- and 7.6-fold by arachidonic acid, 4.4- and 5.2-fold by docosahexaenoic acid, and 6.7- and 8.0-fold by eicosapentaenoic acid each at 50 microM, respectively. On the other hand, the activities of torafugu PPARbeta and gamma were not changed by Wy-14643, ETYA, rosiglitazone, nor PUFAs. These results suggest that the activities of torafugu PPARbeta and gamma require undefined ligands. Alternatively, the molecular mechanisms involved in their activation are different from those of other vertebrates.

The identification of heat shock protein genes in goldfish (Carassius auratus) and their expression in a complex environment in Gaobeidian Lake, Beijing, China

The enhanced expression of heat shock proteins (HSPs) can be detected in response to high temperatures, as well as to many kinds of stressors, including pollutants. Partial cDNA sequences encoding HSP30, HSP70, HSP90 beta, and heat shock cognate (HSC) 70, and full-length cDNA sequences encoding HSP27, HSP47 and HSP60 were cloned from goldfish (Carassius auratus). The expression of these genes was investigated in goldfish inhabiting Gaobeidian Lake in Beijing, China. The water of this lake is moderately polluted and has a higher temperature due to the water being used as a coolant in the nearby thermal power plant. All HSP sequences tested were highly conserved compared with their corresponding genes in other species. A significant up-regulation in HSP30 and HSP70 transcripts was exhibited in goldfish collected in winter in Gaobeidian Lake. The up-regulation in HSP27 and HSP90 beta transcript, as well as HSP30, was observed on the day of collection in summer. The up-regulation of these HSPs suggested that fish under these specific environmental conditions were experiencing a complex stress process. The expression of HSP30 was found to be more prominent among the fishes in Gaobeidian Lake than at the cleaner reference site (Huairou Reservoir). In the latter case, the HSP30 expression was almost non-detectable, suggesting the possibility of using it as a biomarker for complex environmental pollution.

Temperature increase results in oxidative stress in goldfish tissues. 2. Antioxidant and associated enzymes

Activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione-S-transferase (GST), glutathione reductase (GR), and glucose-6-phophate dehydrogenase (G6PDH) were measured in four tissues of goldfish, Carassius auratus L., over 1-12 h of high temperature (35 degrees C) exposure followed by 4 or 24 h of lower temperature (21 degrees C) recovery. SOD activity was strongly affected by heat shock, increasing 4-fold in brain, liver, and kidney, but was mainly reversed at recovery. In some tissues, activities of SOD, catalase, GPx, and G6PDH decreased significantly after 1 h heat shock exposure suggesting that thermal inactivation possibly occurred, but were renewed at further exposure. In many cases, 4 h of return to the initial temperature decreased enzyme activities. High correlation coefficients between SOD activities and levels of lipid peroxidation products suggest that these products might be involved in up-regulation of antioxidant defense. Several enzymes (SOD, GST, GR) responded to stress in coordinated manner.

Temperature increase results in oxidative stress in goldfish tissues. 1. Indices of oxidative stress

Levels of lipid peroxides (LOOH), thiobarbituric-acid reactive substances (TBARS), protein carbonyls and low- and high-molecular weight thiols were measured in brain, liver, kidney, and white muscle of goldfish, Carassius auratus L., over 1-12 h of high temperature (35 degrees C) exposure followed by 4 or 24 h of lower (21 degrees C) temperature recovery. LOOH and TBARS contents increased during heat shock exposure with a maximal rise of 20-fold for liver TBARS, but both mainly reversed at recovery. Protein carbonyl content was unaffected by heat shock but rose in brain, liver, and kidney during recovery. Low-molecular weight thiol concentrations unexpectedly increased up to approximately 4-fold in brain, kidney and muscle under heat shock and remained high during recovery. Protein thiol contents also rose in liver and muscle during high temperature exposure by 2- and 3-fold, respectively, and decreased to control values or below in all tissues at late recovery. Low- and high-molecular weight thiol levels inversely correlated in liver (R2=0.87) suggesting that the former was used to reduce the latter over the experiment. It is concluded that the redox balance in goldfish tissues is strictly maintained probably contributing to the high tolerance of this species to heat shock.