Comparison of regulatory and structural regions of the Xenopus laevis small heat-shock protein-encoding gene family

The avian-specific small heat shock protein HSP25 is a constitutive protector against environmental stresses during blastoderm dormancy

Small heat shock proteins (sHSPs) range in size from 12 to 42 kDa and contain an α-crystalline domain. They have been proposed to play roles in the first line of defence against various stresses in an ATP-independent manner. In birds, a newly oviposited blastoderm can survive several weeks in a dormant state in low-temperature storage suggesting that blastoderm cells are basically tolerant of environmental stress. However, sHSPs in the stress-tolerant blastoderm have yet to be investigated. Thus, we characterised the expression and function of sHSPs in the chicken blastoderm. We found that chicken HSP25 was expressed especially in the blastoderm and was highly upregulated during low-temperature storage. Multiple alignments, phylogenetic trees, and expression in the blastoderms of Japanese quail and zebra finch showed homologues of HSP25 were conserved in other avian species. After knockdown of chicken HSP25, the expression of pluripotency marker genes decreased significantly. Furthermore, loss of function studies demonstrated that chicken HSP25 is associated with anti-apoptotic, anti-oxidant, and pro-autophagic effects in chicken blastoderm cells. Collectively, these results suggest avian HSP25 could play an important role in association with the first line of cellular defences against environmental stress and the protection of future embryonic cells in the avian blastoderm.

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.

Expression and localization of the Xenopus laevis small heat shock protein, HSPB6 (HSP20), in A6 kidney epithelial cells

Small heat shock proteins (sHSPs) are molecular chaperones that bind to unfolded protein, inhibit the formation of toxic aggregates and facilitate their refolding and/or degradation. Previously, the only sHSPs that have been studied in detail in the model frog system, Xenopus laevis, were members of the HSP30 family and HSPB1 (HSP27). We now report the analysis of X. laevis HSPB6, an ortholog of mammalian HSPB6. X. laevis HSPB6 cDNA encodes a 168 aa protein that contains an α-crystallin domain, a polar C-terminal extension and some possible phosphorylation sites. X. laevis HSPB6 shares 94% identity with a X. tropicalis HSPB6, 65% with turtle, 59% with humans, 49% with zebrafish and only 50% and 43% with X. laevis HSPB1 and HSP30C, respectively. Phylogenetic analysis revealed that X. laevis HSPB6 grouped more closely with mammalian and reptilian HSPB6s than with fish HSPB6. X. laevis recombinant HSPB6 displayed molecular chaperone properties since it had the ability to inhibit heat-induced aggregation of citrate synthase. Immunoblot analysis determined that HSPB6 was present constitutively in kidney epithelial cells and that heat shock treatment did not upregulate HSPB6 levels. While treatment with the proteasomal inhibitor, MG132, resulted in a 2-fold increase in HSPB6 levels, exposure to cadmium chloride produced a slight increase in HSPB6. These findings were in contrast to HSP70, which was enhanced in response to all three stressors. Finally, immunocytochemical analysis revealed that HSPB6 was present in the cytoplasm in the perinuclear region with some in the nucleus.

Withaferin A induces proteasome inhibition, endoplasmic reticulum stress, the heat shock response and acquisition of thermotolerance

In the present study, withaferin A (WA), a steroidal lactone with anti-inflammatory and anti-tumor properties, inhibited proteasome activity and induced endoplasmic reticulum (ER) and cytoplasmic HSP accumulation in Xenopus laevis A6 kidney epithelial cells. Proteasomal inhibition by WA was indicated by an accumulation of ubiquitinated protein and a decrease in chymotrypsin-like activity. Additionally, immunoblot analysis revealed that treatment of cells with WA induced the accumulation of HSPs including ER chaperones, BiP and GRP94, as well as cytoplasmic/nuclear HSPs, HSP70 and HSP30. Furthermore, WA-induced an increase in the relative levels of the protein kinase, Akt, while the levels of actin were unchanged compared to control. Northern blot experiments determined that WA induced an accumulation in bip, hsp70 and hsp30 mRNA but not eIF-1α mRNA. Interestingly, WA acted synergistically with mild heat shock to enhance HSP70 and HSP30 accumulation to a greater extent than the sum of both stressors individually. This latter phenomenon was not observed with BiP or GRP94. Immunocytochemical analysis indicated that WA-induced BiP accumulation occurred mainly in the perinuclear region in a punctate pattern, while HSP30 accumulation occurred primarily in a granular pattern in the cytoplasm with some staining in the nucleus. Prolonged exposure to WA resulted in disorganization of the F-actin cytoskeleton as well as the production of relatively large HSP30 staining structures that co-localized with F-actin. Finally, prior exposure of cells to WA treatment, which induced the accumulation of HSPs conferred a state of thermal protection since it protected the F-actin cytoskeleton against a subsequent cytotoxic thermal challenge.

Sodium arsenite and cadmium chloride induction of proteasomal inhibition and HSP accumulation in Xenopus laevis A6 kidney epithelial cells

Sodium arsenite (NA) and cadmium chloride (CdCl(2)) are relatively abundant environmental toxicants that have multiple toxic effects including carcinogenesis, dysfunction of gene regulation and DNA and protein damage. In the present study, treatment of Xenopus laevis A6 kidney epithelial cells with concentrations of NA (20-30 μM) or CdCl(2) (100-200 μM) that induced HSP30 and HSP70 accumulation also produced an increase in the relative levels of ubiquitinated protein. Actin protein levels were unchanged in these experiments. In time course experiments, the levels of ubiquitinated protein and HSPs increased over a 24h exposure to NA or CdCl(2). Furthermore, treatment of cells with NA or CdCl(2) reduced the relative levels of proteasome chymotrypsin (CT)-like activity compared to control. Interestingly, pretreatment of cells with the HSP accumulation inhibitor, KNK437, prior to NA or CdCl(2) exposure decreased the relative levels of ubiquitinated protein as well as HSP30 and HSP70. A similar finding was made with ubiquitinated protein induced by proteasomal inhibitors, MG132 and celastrol, known to induce HSP accumulation in A6 cells. However, the NA- or CdCl(2)-induced decrease in proteasome CT-like activity was not altered by KNK437 pretreatment. This study has shown for the first time in poikilothermic vertebrates that NA and CdCl(2) can inhibit proteasomal activity and that there is a possible association between HSP accumulation and the mechanism of protein ubiquitination.

Comparison of the effect of heat shock factor inhibitor, KNK437, on heat shock- and chemical stress-induced hsp30 gene expression in Xenopus laevis A6 cells

In this study, we compared the effect of KNK437 (N-formyl-3, 4-methylenedioxy-benzylidene-gamma-butyrolactam), a benzylidene lactam compound, on heat shock and chemical stressor-induced hsp30 gene expression in Xenopus laevis A6 kidney epithelial cells. Previously, KNK437 was shown to inhibit HSE-HSF1 binding activity and heat-induced hsp gene expression. In the present study, Northern and Western blot analysis revealed that pretreatment of A6 cells with KNK437 inhibited hsp30 mRNA and HSP30 and HSP70 protein accumulation induced by chemical stressors including sodium arsenite, cadmium chloride and herbimycin A. In A6 cells subjected to sodium arsenite, cadmium chloride, herbimycin A or a 33 degrees C heat shock treatment, immunocytochemistry and confocal microscopy revealed that HSP30 accumulated primarily in the cytoplasm. However, incubation of A6 cells at 35 degrees C resulted in enhanced HSP30 accumulation in the nucleus. Pre-treatment with 100 microM KNK437 completely inhibited HSP30 accumulation in A6 cells heat shocked at 33 or 35 degrees C as well as cells treated with 10 microM sodium arsenite, 100 microM cadmium chloride or 1 microg/mL herbimycin A. These results show that KNK437 is effective at inhibiting both heat shock- and chemical stress-induced hsp gene expression in amphibian cells.

Genome-wide analysis and expression profiling of the small heat shock proteins in zebrafish

Small Heat Shock Proteins (sHSPs) have important roles in preventing disease and promoting resistance to environmental stressors. Mutations in any one of a number of sHSPs, including HSP27 (HSPB1), HSP22 (HSPB8), alphaA-crystallin (HSPB4), or alphaB-crystallin (HSPB5) can result in neuronal degeneration, myopathy, and/or cataract in humans. Ten sHSPs are known in humans, and thirteen have been identified in teleost fish. Here we report the identification of thirteen zebrafish sHSPs. Using a combination of phylogenetic analysis and analysis of synteny, we have determined that ten are likely orthologs of human sHSPs. We have used quantitative RT-PCR to determine the relative expression levels of all thirteen sHSPs during development and in response to heat shock. Our findings indicate that most of the zebrafish sHSPs are expressed during development, and five of these genes are transcriptionally upregulated by heat shock at one or more stages of development.

Analysis of the expression and function of the small heat shock protein gene, hsp27, in Xenopus laevis embryos

In previous studies, the only small HSPs that have been studied in Xenopus laevis are members of the HSP30 family. We now report the analysis of Xenopus HSP27, a homolog of the human small HSP, HSP27. To date the presence of both hsp30 and hsp27 genes has been demonstrated only in minnow and chicken. Xenopus HSP27 cDNA encodes a 213 aa protein that contains an alpha-crystallin domain as well as a polar C-terminal extension. Xenopus HSP27 shares 71% identity with chicken HSP24 but only 19% identity with Xenopus HSP30C. Northern blot analysis revealed that Xenopus HSP27 gene expression was developmentally regulated. Constitutive and heat shock-induced hsp27 mRNA accumulation was first detectable at the early tailbud stage while HSP27 protein was detected at the tadpole stage. Furthermore, hsp27 mRNA was enriched in selected tissues under both control and heat shock conditions. Whole mount in situ hybridization analysis detected the presence of this message in the lens vesicle, heart, head, somites, and tail region. Purified recombinant HSP27 protein displayed molecular chaperone properties since it had the ability to inhibit heat-induced aggregation of target proteins including citrate synthase, malate dehydrogenase and luciferase. Thus, Xenopus HSP27, like HSP30, is a developmentally-regulated heat-inducible molecular chaperone.

Regulation and function of small heat shock protein genes during amphibian development

Small heat shock proteins (shsps) are molecular chaperones that are inducible by environmental stress such as elevated temperature or exposure to heavy metals or arsenate. Recent interest in shsps has been propelled by the finding that shsp synthesis or mutations are associated with various human diseases. While much is known about shsps in cultured cells, less is known about their expression and function during early animal development. In amphibian model systems, shsp genes are developmentally regulated under both normal and environmental stress conditions. For example, in Xenopus, the shsp gene family, hsp30, is repressed and not heat-inducible until the late neurula/early tailbud stage whereas other hsps are inducible at the onset of zygotic genome activation at the midblastula stage. Furthermore, these shsp genes are preferentially induced in selected tissues. Recent studies suggest that the developmental regulation of these shsp genes is controlled, in part, at the level of chromatin structure. Some shsps including Xenopus and Rana hsp30 are synthesized constitutively in selected tissues where they may function in the prevention of apoptosis. During environmental stress, amphibian multimeric shsps bind to denatured target protein, inhibittheir aggregation and maintain them in a folding-competent state until reactivated by other cellular chaperones. Phosphorylation of shsps appears to play a major role in the regulation of their function.

Evolutionary diversity of vertebrate small heat shock proteins

All vertebrates express multiple small heat shock proteins (sHsps), which are important components of the cellular chaperoning machinery and display a spectacular diversity of functions. This ranges from remodeling the cytoskeleton and inhibiting apoptosis to serving as structural proteins in eye lens and sperm tail. Most information is available for the 10 known mammalian sHsps, formally named HspB1-B10. Only three of them (Hsp27/B1, alphaA-crystallin/B4, alphaB-crystallin/B5) have been reported from nonmammalian vertebrates, while an apparent paralog, Hsp30/B11, is found in frogs and teleost fish. To reconstruct the evolutionary diversification of the sHsps in vertebrates, we searched for additional sHsps in genome, protein, and EST databases and sequenced some avian and amphibian sHsps (HspB2, Hsp30/B11). The urochordate Ciona intestinalis was included in the search, as the outgroup of vertebrates. Orthologs of seven mammalian sHsps were now found in other vertebrate classes. Two novel sHsps, named HspB11 and HspB12, were recognized in birds, and four novel sHsps, named HspB12-B15, in teleost fish. Secondary structure predictions of orthologous sHsps from different vertebrate classes indicate conservation of the beta-sandwich structure of the functionally important C-terminal "alpha-crystallin domain," while the N-terminal domains generally have alpha-helical structures, despite their pronounced sequence variation. The constructed chordate sHsp tree is supported by shared introns, indels, and diagnostic sequences. The tree distinguishes putative orthologous and paralogous relationships, which will facilitate the functional and structural comparison of the various vertebrate sHsps. The 15 recognized paralogous vertebrate sHsps reflect the period of extensive gene duplications early in vertebrate evolution. Eleven of these sHsps are grouped in a clade that might be specific for chordates. It is inferred that at least 13 intron insertions have occurred during the evolution of chordate sHsp genes, while a single ancient intron is maintained in some lineages, in line with the general trend of massive intron gain before or during early vertebrate radiation. Interesting is the occurrence of several head-to-head located pairs of chordate sHsp genes.

Molecular chaperone function of the Rana catesbeiana small heat shock protein, hsp30

Eukaryotic small heat shock proteins (shps) act as molecular chaperones by binding to denaturing proteins, preventing their heat-induced aggregation and maintaining their solubility until they can be refolded back to their normal state by other chaperones. In this study we report on the functional characterization of a developmentally regulated shsp, hsp30, from the American bullfrog, Rana catesbeiana. An expression vector containing the open reading frame of the hsp30 gene was expressed in Escherichia coli. Purified recombinant hsp30 was recovered as multimeric complexes and was composed of a mixture of alpha-helical and beta-sheet-like structures as determined by circular dichroism analysis. Hsp30 displayed chaperone activity since it inhibited heat-induced aggregation of citrate synthase. Furthermore hsp30 maintained heat-treated luciferase in a folding competent state. For example, heat denatured luciferase when microinjected into Xenopus oocytes did not regain enzyme activity whereas luciferase heat denatured with hsp30 regained 100% enzyme activity. Finally, hsp30 protected the DNA restriction endonuclease, PstI, from heat inactivation. PstI incubated alone at 42 degrees C lost its enzymatic function after 1 h whereas PstI supplemented with hsp30 accurately digested plasmid DNA after 4 h at the elevated temperature. These results clearly indicate a molecular chaperone role for R. catesbeiana hsp30.

Hsp25, a member of the Hsp30 family, promotes inclusion formation in response to stress

Protein aggregates are oligomeric complexes of misfolded proteins, and serve as the seeds of inclusion bodies termed aggresomes in the cells. Heat shock proteins (Hsps) prevent misfolding and aggregate formation. Here, we found that only avian Hsp25 dominantly accumulated in the aggresomes induced by proteasome inhibition. Molecular cloning of chicken Hsp25 (cHsp25) revealed that it belongs to the Hsp30 family, which is a subfamily of the alpha-crystallin/small Hsp gene family. Unexpectedly, overexpression of cHsp25 into HeLa cells promoted inclusion formation whereas overexpression of mouse Hsp27 and its chicken homologue did not. These results suggest that cHsp25 acts differently from other small Hsps on protein aggregates.

Expression and function of small heat shock protein genes during Xenopus development

The hsp30 small heat shock protein family is a stress-inducible group of molecular chaperones in the frog, Xenopus laevis. Hsp30 genes are intronless and present in clusters. Expression of these genes are developmentally regulated likely at the level of chromatin structure. Also heat-induced hsp30 transcripts and protein are enriched in selected embryonic tissues. In vitro studies revealed that multimeric hsp30 binds to heat denatured target protein, inhibits their aggregation and maintains them in a folding-competent state until reactivated by other cellular chaperones. Finally optimal chaperone activity and secondary structure of hsp30 can be inhibited by phosphorylation or mutagenesis of the C-terminal end.

Effect of histone deacetylase inhibitors on heat shock protein gene expression during Xenopus development

We examined the effect of histone deacetylase inhibitors (HDIs), trichostatin A (TSA), valproic acid (VPA), and sodium butyrate (NaB) on heat shock protein (hsp) gene expression during early Xenopus laevis development. HDIs enhance histone acetylation and result in the relief of repressed chromatin domains and ultimately increase the accessibility of transcription factors to target cis-acting regulatory sites. Treatment of embryos with HDIs enhanced the heat shock-induced accumulation of hsp70 mRNA in post-midblastula stage embryos. No effect was observed with actin mRNA or other hsp70 family members including heat shock cognate 70 and immunoglobulin binding protein. Normally, hsp30 genes are not heat-inducible until the late neurula or early tailbud stage of development. Treatment with HDIs resulted in heat-induced expression of hsp30 genes at the gastrula stage with enhanced heat-induced accumulation in neurula and tailbud stages. HDI treatment alone did not induce the accumulation of hsp70 or hsp30 mRNA. Whole-mount in situ hybridization verified the RNA blot analyses and additionally revealed that TSA treatment did not result in any major alterations in the spatial pattern of stress-induced hsp70 or hsp30 mRNA accumulation in early embryos. This study suggests that the states of Xenopus hsp70 and 30 chromatin are subject to repression beyond the midblastula transition.

Enhanced accumulation of constitutive heat shock protein mRNA is an initial response of eye tissue to mild hyperthermia in vivo in adult Xenopus laevis

We have examined the effect of mild hyperthermia in vivo on heat shock transcription factor (HSF) binding activity and heat shock protein (hsp) gene expression in eye tissue of adult Xenopus laevis. A specific interaction between HSF and a synthetic oligonucleotide corresponding to the proximal heat shock element of the Xenopus hsp70B gene was greatly enhanced in eyes from hyperthermic animals compared with controls. Given these results, we examined the effect of hyperthermia in vivo on the expression of five hsp genes (hsp70, hsc70, BiP, hsp90, and hsp30) in eye tissue. Interestingly, at 28 degrees C constitutively expressed hsp genes hsc70, BiP, and hsp90 were strongly enhanced, with further accumulation at 30 degrees C. However, hsp70 and hsp30 mRNA accumulation were not detectable at 28 degrees C but were strongly induced at 30 degrees C. No enhancement of the relative levels of cytoskeletal actin mRNA was observed in the eye tissue of hyperthermic animals. These results suggest that one of the primary responses of eye tissue to hyperthermia in vivo is in the elevation of mRNAs encoding a set of constitutively expressed molecular chaperones.

Mutation or deletion of the C-terminal tail affects the function and structure of Xenopus laevis small heat shock protein, hsp30

Small heat shock proteins (shsps) act as molecular chaperones by preventing heat-induced aggregation and unfolding of cellular proteins by a mechanism that is still unclear. Previously we found that the C-terminal end of Xenopus shsp, hsp30C (30C), was essential for optimal chaperone activity. Examination of the C-terminal tail of 30C revealed that it had a net negative charge. Involvement of this negative charge in chaperone activity was assessed by the creation of two mutants, D209G (Asp converted to the more neutrally charged and less polar Gly at position 209) and D209/213G (Asp to Gly at position 209 and 213). Compared to 30C and D209G, D209/213G was impaired in inhibiting heat-induced citrate synthase aggregation. In rabbit reticulocyte lysate and Xenopus oocyte microinjection refolding assays the mutants were not as efficient as 30C in maintaining heat-treated luciferase in a folding competent state. Circular dichroism analysis revealed that D209G was similar in secondary structure to 30C whereas D209/213G displayed a loss of alpha-helical-like and beta-sheet structure. Also, C-terminal truncation of 30C or 30D (an hsp30 isoform) resulted in a loss of secondary structure and function. This study clearly shows that mutation of aspartic acid residues in the C-terminal end of hsp30 or its truncation disrupts secondary structure and impairs its chaperone activity.

Xenopus small heat shock proteins, Hsp30C and Hsp30D, maintain heat- and chemically denatured luciferase in a folding-competent state

In this study we characterized the chaperone functions of Xenopus recombinant Hsp30C and Hsp30D by using an in vitro rabbit reticulocyte lysate (RRL) refolding assay system as well as a novel in vivo Xenopus oocyte microinjection assay. Whereas heat- or chemically denaturated luciferase (LUC) did not regain significant enzyme activity when added to RRL or microinjected into Xenopus oocytes, compared with native LUC, denaturation of LUC in the presence of Hsp30C resulted in a reactivation of enzyme activity up to 80-100%. Recombinant Hsp30D, which differs from Hsp30C by 19 amino acids, was not as effective as its isoform in preventing LUC aggregation or maintaining it in a folding-competent state. Removal of the first 17 amino acids from the N-terminal region of Hsp30C had little effect on its ability to maintain LUC in a folding-competent state. However, deletion of the last 25 residues from the C-terminal end dramatically reduced Hsp30C chaperone activity. Coimmunoprecipitation and immunoblot analyses revealed that Hsp30C remained associated with heat-denatured LUC during incubation in reticulocyte lysate and that the C-terminal mutant exhibited reduced affinity for unfolded LUC. Finally, we found that Hsc70 present in RRL interacted only with heat-denatured LUC bound to Hsp30C. These findings demonstrate that Xenopus Hsp30 can maintain denatured target protein in a folding-competent state and that the C-terminal end is involved in this function.

Functional characterization of Xenopus small heat shock protein, Hsp30C: the carboxyl end is required for stability and chaperone activity

Small heat shock proteins protect cells from stress presumably by acting as molecular chaperones. Here we report on the functional characterization of a developmentally regulated, heat-inducible member of the Xenopus small heat shock protein family, Hsp30C. An expression vector containing the open reading frame of the Hsp30C gene was expressed in Escherichia coli. These bacterial cells displayed greater thermoresistance than wild type or plasmid-containing cells. Purified recombinant protein, 30C, was recovered as multimeric complexes which inhibited heat-induced aggregation of either citrate synthase or luciferase as determined by light scattering assays. Additionally, 30C attenuated but did not reverse heat-induced inactivation of enzyme activity. In contrast to an N-terminal deletion mutant, removal of the last 25 amino acids from the C-terminal end of 30C severely impaired its chaperone activity. Furthermore, heat-treated concentrated solutions of the C-terminal mutant formed nonfunctional complexes and precipitated from solution. Immunoblot and gel filtration analysis indicated that 30C binds with and maintains the solubility of luciferase preventing it from forming heat-induced aggregates. Coimmunoprecipitation experiments suggested that the carboxyl region is necessary for 30C to interact with target proteins. These results clearly indicate a molecular chaperone role for Xenopus Hsp30C and provide evidence that its activity requires the carboxyl terminal region.

Functional characterization of Xenopus small heat shock protein, Hsp30C: the carboxyl end is required for stability and chaperone activity

Small heat shock proteins protect cells from stress presumably by acting as molecular chaperones. Here we report on the functional characterization of a developmentally regulated, heat-inducible member of the Xenopus small heat shock protein family, Hsp30C. An expression vector containing the open reading frame of the Hsp30C gene was expressed in Escherichia coli. These bacterial cells displayed greater thermoresistance than wild type or plasmid-containing cells. Purified recombinant protein, 30C, was recovered as multimeric complexes which inhibited heat-induced aggregation of either citrate synthase or luciferase as determined by light scattering assays. Additionally, 30C attenuated but did not reverse heat-induced inactivation of enzyme activity. In contrast to an N-terminal deletion mutant, removal of the last 25 amino acids from the C-terminal end of 30C severely impaired its chaperone activity. Furthermore, heat-treated concentrated solutions of the C-terminal mutant formed nonfunctional complexes and precipitated from solution. Immunoblot and gel filtration analysis indicated that 30C binds with and maintains the solubility of luciferase preventing it from forming heat-induced aggregates. Coimmunoprecipitation experiments suggested that the carboxyl region is necessary for 30C to interact with target proteins. These results clearly indicate a molecular chaperone role for Xenopus Hsp30C and provide evidence that its activity requires the carboxyl terminal region.

Spatial pattern of constitutive and heat shock-induced expression of the small heat shock protein gene family, Hsp30, in Xenopus laevis tailbud embryos

We employed whole-mount in situ hybridization and immunohistochemistry to study the spatial pattern of hsp30 gene expression in normal and heatshocked embryos during Xenopus laevis development. Our findings revealed that hsp30 mRNA accumulation was present constitutively only in the cement gland of early and midtailbud embryos, while hsp30 protein was detected until at least the early tadpole stage. Heat shock-induced accumulation of hsp30 mRNA and protein was first observed in early and midtailbud embryos with preferential enrichment in the cement gland, somitic region, lens placode, and proctodeum. In contrast, cytoskeletal actin mRNA displayed a more generalized pattern of accumulation which did not change following heat shock. In heat shocked midtailbud embryos the enrichment of hsp30 mRNA in lens placode and somitic region was first detectable after 15 min of a 33 degrees C heatshock. The lowest temperature capable of inducing this pattern was 30 degrees C. Placement of embryos at 22 degrees C following a 1-h 33 degrees C heat shock resulted in decreased hsp30 mRNA in all regions with time, although enhanced hsp30 mRNA accumulation still persisted in the cement gland after 11 h compared to control. In late tailbud embryos the basic midtailbud pattern of hsp30 mRNA accumulation was enhanced with additional localization to the spinal cord as well as enrichment across the embryo surface. These studies demonstrate that hsp30 gene expression can be detected constitutively in the cement gland of tailbud embryos and that heat shock results in a preferential accumulation of hsp30 mRNA and protein in certain tissues.

Genealogy of the alpha-crystallin--small heat-shock protein superfamily

Sequences of 40 very diverse representatives of the alpha-crystallin-small heat-shock protein (alpha-Hsp) superfamily are compared. Their characteristic C-terminal 'alpha-crystallin domain' of 80-100 residues contains short consensus sequences that are highly conserved from prokaryotes to eukaryotes. There are, in addition, some positions that clearly distinguish animal from non-animal alpha-Hsps. The alpha-crystallin domain is predicted to consist of two hydrophobic beta-sheet motifs, separated by a hydrophilic region which is variable in length. Combination of a conserved alpha-crystallin domain with a variable N-terminal domain and C-terminal extension probably modulates the properties of the various alpha-Hsps as stress-protective and structural oligomeric proteins. Phylogeny reconstruction indicates that multiple alpha-Hsps were already present in the last common ancestor of pro- and eukaryotes. It is suggested that during eukaryote evolution, animal and non-animal alpha-Hsps originated from different ancestral gene copies. Repeated gene duplications gave rise to the multiple alpha-Hsps present in most organisms.

Effect of herbimycin A on hsp30 and hsp70 heat shock protein gene expression in Xenopus cultured cells

We have examined the effect of herbimycin A, a benzoquinoid ansamycin antibiotic, on the pattern of gene expression in amphibians. Exposure of Xenopus laevis A6 kidney epithelial cells to 1 µg/mL herbimycin A induced the synthesis of the heat shock proteins hsp30 and hsp70 as well as 33- and 45-kDa proteins. Enhanced synthesis of a 34-kDa protein appears to be specific to herbimycin A because its synthesis did not increase after heat shock (35°C). In addition, the synthesis of hsp30 and hsp70 induced by herbimycin A was accompanied by an increase in their mRNAs. Herbimycin A induced a transient accumulation of hsp30 and hsp70 mRNA, which peaked between 4 and 6 h. Finally, concurrent treatment of cells with 0.5 µg/mL herbimycin A and a mild heat shock of 27°C yielded a synergistic accumulation of hsp30 and hsp70 mRNA. These studies demonstrate that herbimycin A can induce the expression of a set of stress proteins in amphibians and that concurrent treatment with herbimycin A and mild heat shock has a synergistic effect on the accumulation of hsp30 and hsp70 mRNA. Key words: heat shock, heat shock proteins, Xenopus, herbimycin A, mRNA.

Isolation and characterization of a cDNA encoding a Xenopus immunoglobulin binding protein, BiP (grp78)

We have isolated a full-length cDNA clone encoding a Xenopus laevis immunoglobulin binding protein (BiP; also called glucose-regulated protein or grp78). The Bip cDNA sequence includes an open reading frame of 1,965 bp encoding a 655 amino acid protein with an N-terminal hydrophobic leader sequence and a C-terminal KDEL tetrapeptide which has been found in other lumenal proteins of the endoplasmic reticulum. The 3' untranslated region contains a polyadenylation and an adenylation control element (ACE) as well as a putative mRNA instability sequence. The Xenopus BiP amino acid sequence displayed high identity with BiP from other vertebrates including chicken (91.3%), rat (90.7%), and human (89.9%). Northern hybridization analysis demonstrated that BiP mRNA was present constitutively in the Xenopus A6 kidney epithelial cell line and that BiP mRNA levels could be enhanced by treatment of the cells with galactose-free media, 2-deoxyglucose, 2-deoxygalactose, glucosamine, tunicamycin, heat shock, dithiothreitol, and the calcium ionophore, A23187. Finally, while BiP mRNA was detected in all of the adult tissues examined, the relative level of BiP mRNA differed dramatically between organs. For example, relatively high levels of BiP mRNA were detected in liver with moderate levels in testis, ovary and heart and reduced levels in eye and muscle tissue.

Cloning and characterization of a cDNA encoding the collagen-binding stress protein hsp47 in zebrafish

Hsp47 is a major stress-inducible protein that is localized to the endoplasmic reticulum of avian and mammalian cells and is thought to act as a molecular chaperone specific for the processing of procollagen. Although hsp47 is coordinately expressed together with several collagen types, and vertebrate embryos are known to express collagen genes in complex spatial and temporal patterns, limited information is available regarding the function or regulation of hsp47 during early embryonic development. We have initiated an examination of hsp47 in the zebrafish, Danio rerio, which offers a number of features that make it attractive as a model developmental system with which to examine the expression and function of hsp47. A polymerase chain reaction (PCR)-based cloning strategy was used to isolate a hsp47 cDNA from an embryonic zebrafish cDNA library. The deduced translation product of the cDNA is a 404-amino-acid polypeptide that is 72% identical to chicken, 64% identical to mouse and rat, and 69% identical to human hsp47. The protein contains a typical hydrophobic signal sequence, an RDEL endoplasmic reticulum retention signal, and a serine protease inhibitor signature sequence, all of which are characteristic of hsp47 in higher vertebrates. Thus, it is likely that hsp47 in zebrafish is also localized to the endoplasmic reticulum and may play a similar role to its counterpart in higher vertebrates. Northern blot analysis revealed that the hsp47 gene is expressed at relatively low levels in embryos during normal development but is strongly induced following exposure to heat shock at the gastrula, midsomitogenesis, 2-day, and 3-day larval stages. The level of induction was much higher than has previously been reported in chicken and mouse cells.

Characterization of a Rana catesbeiana hsp30 gene and its expression in the liver of this amphibian during both spontaneous and thyroid hormone-induced metamorphosis

During metamorphosis, the Rana catesbeiana tadpole undergoes developmental changes in almost every tissue/organ. These changes prepare the ammonotelic, swimming larva for its transition to a ureotelic, terrestrial adult, and involve dramatic remodeling. The postembryonic changes in this tadpole are initiated by the thyroid hormones (TH) and result in the extensive degradation of proteins and degeneration of tissues characteristic of the larval phenotype and in the de novo synthesis of proteins characteristic of the adult phenotype. We questioned whether the drastic nature and abruptness of the TH-dependent, postembryonic changes occurring in the tissues of this tadpole might be perceived by the cells in some tissues as stressful and, therefore, cause them to express heat shock and/or stress-like proteins. To address this question, we isolated and characterized a Rana catesbeiana hsp30 gene and used sequences from it to determine if mRNAs encoded from it, or other members of this gene family, are expressed in tissues of tadpoles undergoing metamorphosis. Our results demonstrate that the liver of metamorphosing Rana catesbeiana tadpoles accumulate hsp30 mRNAs and express the heat shock proteins they encode. The fact that the expression of these hsp30s in the liver of these tadpoles is coincidental with the TH-induced expression of genes encoding the liver-specific urea cycle enzymes suggests that TH may influence, directly or indirectly, the expression of these hsp30 genes and, moreover, implies that the presence of one or more of these heat shock proteins may be necessary for the developmental transitions occurring in this organ.

Identification of members of the HSP30 small heat shock protein family and characterization of their developmental regulation in heat-shocked Xenopus laevis embryos

In the present study we have characterized the synthesis of members of the HSP30 family during Xenopus laevis development using a polyclonal antipeptide antibody derived from the carboxyl end of HSP30C. Two-dimensional PAGE/immunoblot analysis was unable to detect any heat-inducible small HSPs in cleavage, blastula, gastrula, or neurula stage embryos. However, heat-inducible accumulation of a single protein was first detectable in early tailbud embryos with an additional 5 HSPs at the late tailbud stage and a total of 13 small HSPs at the early tadpole stage. In the Xenopus A6 kidney epithelial cell line, a total of eight heat-inducible small HSPs were detected by this antibody. Comparison of the pattern of protein synthesis in embryos and somatic cells revealed a number of common and unique heat inducible proteins in Xenopus embryos and cultured kidney epithelial cells. To specifically identify the protein product of the HSP30C gene, we made a chimeric gene construct with the Xenopus HSP30C coding sequence under the control of a constitutive promoter. This construct was microinjected into fertilized eggs and resulted in the premature and constitutive synthesis of the HSP30C protein in gastrula stage embryos. Through a series of mixing experiments, we were able to specifically identify the protein encoded by the HSP30C gene in embryos and somatic cells and to conclude that HSP30C synthesis was first head-inducible at the early tailbud stage of development. The differential pattern of heat-inducible accumulation of members of the HSP30 family during Xenopus development suggests that these proteins may have distinct functions at specific embryonic stages during a stress response.

Involvement of differential gene expression and mRNA stability in the developmental regulation of the hsp 30 gene family in heat-shocked Xenopus laevis embryos

Four complete hsp 30 genes have been isolated from Xenopus laevis: hsp 30A, hsp 30B (a pseudogene), hsp 30C, and hsp 30D. The hsp 30A and hsp 30C genes are first heat inducible at the early tailbud stage, as determined by RNase protection and RT-PCR assays. In this study, we determined by RT-PCR that the hsp 30D gene was first heat inducible (33 degrees C for 1 h) at the mid-tailbud stage, approximately 1 day later in development than hsp 30A and hsp 30C. Furthermore, using Northern blot analysis, we detected the presence of very low levels of hsp 30 mRNA at the heat-shocked late blastula stage. The relative levels of these pre-tailbud (PTB) hsp 30 mRNAs increased at the gastrula and neurula stage followed by a dramatic enhancement in heat shocked tailbud and tadpole stage embryos (50- to 100- fold relative to late blastula). Interestingly, treatment of blastula or gastrula embryos at high temperatures (37 degrees C for 1 h) or with the protein synthesis inhibitor, cycloheximide, followed by heat shock, led to enhanced accumulation of the pre-tailbud (PTB) hsp 30 mRNAs. hsp 70, hsp 87, and actin messages were not stabilized at high temperatures or by cycloheximide treatment. Finally, hsp 30D mRNA was not detected by RT-PCR analysis of cycloheximide-treated, heat-shocked blastula stage embryos, confirming that it is not a member of the PTB hsp 30 mRNAs. This study indicates that differential gene expression and mRNA stability are involved in the regulation of hsp 30 gene expression during early Xenopus laevis development.

Expression of endogenous and microinjected hsp 30 genes in early Xenopus laevis embryos

In the present study, we have examined the regulation of expression of a newly isolated member of the hsp 30 gene family, hsp 30C. Using RT-PCR, we found that this gene was first heat-inducible at the tailbud stage of development. We also examined the expression of two microinjected modified hsp 30C gene constructs in Xenopus embryos. One of the constructs had 404 bp of hsp 30C 5'-flanking region, whereas the other had 3.6 kb. Both gene constructs had 1 kb of 3'-flanking region. RT-PCR assays were employed to detect the expression of these microinjected genes. The presence of extensive 5'- and 3'-flanking regions of the hsp 30C gene did not confer proper developmental regulation, since heat-inducible expression of both of the microinjected constructs was detectable at the midblastula stage. The premature expression of the microinjected hsp 30 gene was not a result of high plasmid copy number of the presence of plasmid DNA sequences. These results suggest that the microinjected genes contain all the cis-acting DNA sequences required for correct heat-inducible regulation but do not contain the elements required for the proper regulation of hsp 30 gene expression during development. It is possible that regulatory elements controlling the developmental expression of the hsp30 genes may reside upstream or downstream of the entire cluster.