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

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.

Cloning & sequence identification of Hsp27 gene and expression analysis of the protein on thermal stress in Lucilia cuprina

Hsp27, a highly conserved small molecular weight heat shock protein, is widely known to be developmentally regulated and heat inducible. Its role in thermotolerance is also implicated. This study is a sequel of our earlier studies to understand the molecular organization of heat shock genes/proteins and their role in development and thermal adaptation in a sheep pest, Lucilia cuprina (blowfly), which exhibits unusually high adaptability to a variety of environmental stresses, including heat and chemicals. In this report our aim was to understand the evolutionary relationship of Lucilia hsp27 gene/protein with those of other species and its role in thermal adaptation. We sequence characterized the Lchsp27 gene (coding region) and analyzed its expression in various larval and adult tissues under normal as well as heat shock conditions. The nucleotide sequence analysis of 678 bps long-coding region of Lchsp27 exhibited closest evolutionary proximity with Drosophila (90.09%), which belongs to the same order, Diptera. Heat shock caused significant enhancement in the expression of Lchsp27 gene in all the larval and adult tissues examined, however, in a tissue specific manner. Significantly, in Malpighian tubules, while the heat-induced level of hsp27 transcript (mRNA) appeared increased as compared to control, the protein level remained unaltered and nuclear localized. We infer that Lchsp27 may have significant role in the maintenance of cellular homeostasis, particularly, during summer months, when the fly remains exposed to high heat in its natural habitat.

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.

Distinct patterns of HSP30 and HSP70 degradation in Xenopus laevis A6 cells recovering from thermal stress

Heat shock proteins (HSPs) are molecular chaperones that assist in protein synthesis, folding and degradation and prevent stress-induced protein aggregation. In this study, we examined the pattern of accumulation of HSP30 and HSP70 in Xenopus laevis A6 kidney epithelial cells recovering from heat shock. Immunoblot analysis revealed the presence of elevated levels of HSP30 after 72h of recovery. However, the relative levels of HSP70 declined to near control levels after 24h. The relative levels of both hsp30 and hsp70 mRNA were reduced to low levels after 24h of recovery from heat shock. Pretreatment of cells with cycloheximide, a translational inhibitor, produced a rapid decline in HSP70 but not HSP30. The cycloheximide-associated decline of HSP70 was blocked by the proteasomal inhibitor, MG132, but had little effect on the relative level of HSP30. Also, treatment of cells with the phosphorylation inhibitor, SB203580, in addition to cycloheximide treatment enhanced the stability of HSP30 compared to cycloheximide alone. Immunocytochemical studies detected the presence of HSP30 accumulation in a granular pattern in the cytoplasm of recovering cells and its association with aggresome-like structures, which was enhanced in the presence of SB203580. This study has shown that the relative levels of heat shock-induced HSP30 persist during recovery in contrast to HSP70. While HSP70 is degraded by the ubiquitin-proteasome system, it is likely that the presence of HSP30 multimeric complexes that are known to associate with unfolded protein as well as its association with aggresome-like structures may delay its degradation.

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.

Small heat shock protein expression and functions during development

The expression of small heat shock proteins is tightly regulated during development in multiple organisms. As housekeeping proteins, small heat shock proteins help protect cells from apoptosis, stabilize the cytoskeleton and contribute to proteostasis. Consistently, depletion of one small heat shock protein is usually not detrimental due to a certain level of redundancy between the functions of each small heat shock protein. However, while their stress-induced expression is regulated by heat shock factors, their constitutive expression is under the control of other specific transcription factors, suggesting the existence of very specialized functions. This review focuses on the expression patterns and functions of small heat shock proteins in various organisms during development. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

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.

Proteasome inhibition induces hsp30 and hsp70 gene expression as well as the acquisition of thermotolerance in Xenopus laevis A6 cells

Previous studies have shown that inhibiting the activity of the proteasome leads to the accumulation of damaged or unfolded proteins within the cell. In this study, we report that proteasome inhibitors, lactacystin and carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), induced the accumulation of ubiquitinated proteins as well as a dose- and time-dependent increase in the relative levels of heat shock protein (HSP)30 and HSP70 and their respective mRNAs in Xenopus laevis A6 kidney epithelial cells. In A6 cells recovering from MG132 exposure, HSP30 and HSP70 levels were still elevated after 24 h but decreased substantially after 48 h. The activation of heat shock factor 1 (HSF1) may be involved in MG132-induced hsp gene expression in A6 cells since KNK437, a HSF1 inhibitor, repressed the accumulation of HSP30 and HSP70. Exposing A6 cells to simultaneous MG132 and mild heat shock enhanced the accumulation of HSP30 and HSP70 to a much greater extent than with each stressor alone. Immunocytochemical studies determined that HSP30 was localized primarily in the cytoplasm of lactacystin- or MG132-treated cells. In some cells treated with higher concentrations of MG132 or lactacystin, we observed in the cortical cytoplasm (1) relatively large HSP30 staining structures, (2) colocalization of actin and HSP30, and (3) cytoplasmic areas that were devoid of HSP30. Lastly, MG132 treatment of A6 cells conferred a state of thermotolerance such that they were able to survive a subsequent thermal challenge.

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.

Developmental expression patterns of the zebrafish small heat shock proteins

Small heat shock proteins (sHSPs), or alpha-crystallins, are low-molecular weight proteins found in every kingdom and nearly every species examined to date. Many, if not all, sHSPs act as molecular chaperones. Several also have functions independent of their chaperone activity, and at least a few are expressed in specific spatiotemporal patterns during embryonic and/or juvenile stages, suggesting specific roles during development. To date, however, no one has systematically characterized the expression patterns of all of the sHSPs during development in any organism. We have characterized the normal heat shock-induced expression patterns of all 13 zebrafish sHSPs during development. Seven of the sHSPs are expressed in a tissue-specific manner during development, and five are upregulated by heat shock. The results of these studies provide a foundation for analysis of sHSP function during normal development and their roles in protecting cells from the effects environmental stressors.

Expression of the small heat shock protein gene, hsp30, in Rana catesbeiana fibroblasts

In the present study, we examined the expression of the Rana catesbeiana small heat shock protein gene, hsp30, in an FT fibroblast cell line. Northern and western blot analyses revealed that hsp30 mRNA or HSP30 protein was not present constitutively but was strongly induced at a heat shock temperature of 35 degrees C. However, treatment of FT cells with sodium arsenite at concentrations that induced hsp gene expression in other amphibian systems caused cell death. Non-lethal concentrations of sodium arsenite (10 microM) induced only minimal accumulation of hsp30 mRNA or protein after 12 h. Immunocytochemical analyses employing laser scanning confocal microscopy detected the presence of heat-inducible HSP30, in a granular or punctate pattern. HSP30 was enriched in the nucleus with more diffuse localization in the cytoplasm. The nuclear localization of HSP30 was more prominent with continuous heat shock. These heat treatments did not alter FT cell shape or disrupt actin cytoskeletal organization. Also, HSP30 did not co-localize with the actin cytoskeleton.

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.

Examination of KNK437- and quercetin-mediated inhibition of heat shock-induced heat shock protein gene expression in Xenopus laevis cultured cells

We examined the effect of quercetin (3,3',4',5,7-pentahydroxyflavon) and KNK437 (N-formyl-3,4-methylenedioxy-benzylidene-gamma-butyrolactam), a benzylidene lactam compound, on heat-induced heat shock protein (hsp) gene expression in Xenopus laevis A6 kidney epithelial cells. In previous studies, both quercetin and KNK437 inhibited heat shock factor activity resulting in a repression of hsp mRNA and protein accumulation in human cultured cells. In this first study of the effect of these hsp gene expression inhibitors in a non-mammalian cell line, we report that both quercetin and KNK437 reduced the heat shock-induced accumulation of hsp30, hsp47 and hsp70 mRNA in X. laevis cultured cells. However, these inhibitors had no effect on the relative level of a non-heat shock protein mRNA, ef1alpha, in either control or heat shocked cells. Western blot and immunocytochemical analyses revealed that quercetin partially inhibited HSP30 protein accumulation. In contrast, HSP30 protein was not detectable in KNK437-treated cells. Finally, treatment of A6 cells with KNK437 inhibited the heat shock-induced acquisition of thermotolerance, as determined by preservation of actin filaments and cellular morphology using immunocytochemistry and laser scanning confocal microscopy.

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.

Examination of the expression of the heat shock protein gene, hsp110, in Xenopus laevis cultured cells and embryos

Eukaryotic organisms respond to various stresses with the synthesis of heat shock proteins (HSPs). HSP110 is a large molecular mass HSP that is part of the HSP70/DnaK superfamily. In this study, we have examined, for the first time, the expression of the hsp110 gene in Xenopus laevis cultured cells and embryos. Sequence analysis revealed that the protein encoded by the hsp110 cDNA exhibited 74% identity with its counterparts in mammals and only 27-29% with members of the Xenopus HSP70 family. Hsp110 mRNA and/or protein was detected constitutively in A6 kidney epithelial cells and was inducible by heat shock, sodium arsenite, and cadmium chloride. However, treatment with ethanol or copper sulfate had no detectable effect on hsp110 mRNA levels. Similar results were obtained for hsp70 mRNA except that it was inducible with ethanol. In Xenopus embryos, hsp110 mRNA was present constitutively during development. Heat shock-inducible accumulation of hsp110 mRNA occurred only after the midblastula stage. Whole mount in situ hybridization analysis revealed that hsp110 mRNA accumulation in control and heat shocked embryos was enriched in selected tissues. These studies demonstrate that Xenopus hsp110 gene expression is constitutive and stress inducible in cultured cells and developmentally- and tissue specifically-regulated during early embryogenesis.

Differential subcellular localization of members of the Toxoplasma gondii small heat shock protein family

The results of this study describe the identification and characterization of the Toxoplasma gondii alpha-crystallin/small heat shock protein (sHsp) family. By database (www.toxodb.org) search, five parasite sHsps (Hsp20, Hsp21, Hsp28, Hsp29, and the previously characterized Hsp30/Bag1) were identified. As expected, they share the homologous alpha-crystallin domain, which is the key characteristic of sHsps. However, the N-terminal segment of each protein contains unique characteristics in size and sequence. Most T. gondii sHsps are constitutively expressed in tachyzoites and fully differentiated bradyzoites, with the exception of Hsp30/Bag1. Interestingly, by subcellular localization we observed that T. gondii sHsps are located in different compartments. Hsp20 is located at the apical end of the cell, Hsp28 is located inside the mitochondrion, Hsp29 showed a membrane-associated labeling, and Hsp21 appeared throughout the cytosol of the parasites. These particular differences in the immunostaining patterns suggest that their targets and functions might be different.

Developmentally regulated gene expression of the small heat shock protein Hsp27 in zebrafish embryos

Mammalian small heat shock proteins including Hsp27 and alpha-B crystallin are constitutively expressed in various adult and embryonic tissues including skeletal and cardiac muscle. However, the function of these proteins during embryonic development is not understood, and information on their expression during the earliest stages of development is limited. We have recently demonstrated constitutive and stress inducible expression of a homologue of human Hsp27 in adult zebrafish, an important experimental model of vertebrate developmental processes. Here, we assessed the temporospatial dynamics of zebrafish Hsp27 (hsp27) and alpha-B crystallin (cryab) gene expression using reverse-transcriptase PCR (RT-PCR) and hsp27 expression by in situ hybridization. Our results reveal that initial upregulation of hsp27 expression occurs during early gastrulation. Expression of hsp27 is detected transiently in developing myotomes, lens and brain, and more persistently in developing heart. The constitutive expression level of hsp27 in embryos at some stages of development is considerably greater than that observed in unstressed adult tissues. Expression of hsp27 was also observed in all tissues examined in embryos recovering from heat stress. The pattern of expression observed for hsp27 overlaps partially, but not completely, with that reported for other heat shock proteins.

Examination of the stress-induced expression of the collagen binding heat shock protein, hsp47, in Xenopus laevis cultured cells and embryos

HSP47 is an endoplasmic reticulum (ER)-resident molecular chaperone involved in collagen production. This study examined the stress-induced pattern of hsp47 gene expression in Xenopus cultured cells and embryos. Sequence analysis revealed that protein encoded by the hsp47 cDNA exhibited 70-77% identity with fish, avian and mammalian HSP47. In A6 kidney epithelial cells hsp47 mRNA and HSP47 were present constitutively and inducible by heat shock but not ER stressors including tunicamycin and A23187, both of which enhanced BiP mRNA. Furthermore A23187 treatment inhibited constitutive accumulation of hsp47 mRNA and retarded heat-induced accumulation of hsp47 and hsp70 mRNA. Interestingly, hsp47 gene expression but not hsp70 or BiP mRNA accumulation was enhanced by treatment with a procollagen-specific stressor, beta-aminopropionitrile. In Xenopus embryos hsp47 mRNA was present constitutively throughout development. In tailbud embryos hsp47 mRNA was enriched in tissues associated with collagen production including notochord, somites and head region. Heat shock-induced accumulation of hsp47 mRNA was enhanced primarily in embryonic tissues already exhibiting hsp47 mRNA accumulation. These studies suggest that the pattern of Xenopus hsp47 gene expression is similar to hsp70 in response to heat shock but also displays unique features including a response to a procollagen-specific stressor and preferential expression in collagen-containing tissues.

Constitutive expression of heat shock protein p23 correlates with proneural territories in imaginal discs ofDrosophila melanogaster

2-DE followed by MALDI-TOF was used to purify and identify a Drosophila protein (catalogued as SSP 6002) that showed marked differences in the level of expression in the different imaginal discs of third instar larvae. Fingerprinting showed that the spot of interest was the heat shock 23 polypeptide (hsp23). We characterized the kinetics of its induction by heat shock in wing imaginal discs and raised an antiserum against the denatured protein, which recognizes a single unphosphorylated spot on 2-D gels. The difference in its expression in discs was corroborated by analyzing its level in the imaginal discs of postbithorax mutants. We also investigated the developmental expression of hsp23 in imaginal discs with antiserum raised against the native protein. Its spatial and temporal pattern of expression is related to the proneural territories and maintained even under heat shock conditions. In addition, its pattern of expression is regulated by transcription factors and signaling pathways (notch and epidermal growth factor receptor) involved in proneural specification.

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.

Hydrogen peroxide induces heat shock protein and proto-oncogene mRNA accumulation in Xenopus laevis A6 kidney epithelial cells

In this study, we examined the effect of hydrogen peroxide on the accumulation of various mRNAs encoding heat shock proteins (hsps) and proto-oncogenes in Xenopus A6 kidney epithelial cells. Hydrogen peroxide treatment enhanced the accumulation of hsp90, hsp70, hsp30, c-jun, c-fos, and actin mRNAs with distinct temporal patterns. Although hsp70, c-fos, and c-jun mRNA levels peaked at 1–2 h before declining, hsp30 and hsp90 mRNA levels were maximal at 4–6 h. Other mRNAs, including heat shock cognate hsc70, immunoglobulin binding protein, and ribosomal L8, were unaffected. Treatment of kidney cells with a combination of mild heat shock plus hydrogen peroxide resulted in a synergistic increase in the relative levels of both hsp70 and hsp30 mRNA, but not hsp90, c-fos, c-jun, or actin. This study suggests that analysis of hsp and proto-oncogene mRNA levels may be of value as molecular biomarkers of oxidative stress associated with various disease states and nephrotoxicity in kidney.Key words: Xenopus, kidney, mRNA, heat shock protein, hydrogen peroxide.

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 of the Hsp23 chaperone during Drosophila embryogenesis: association to distinct neural and glial lineages

Background

In addition to their strong induction following stress, small heat shock proteins (Hsp) are also expressed during development in a wide variety of organisms. However, the precise identity of cell(s) expressing these proteins and the functional contribution of small heat shock proteins in such developmental context remain to be determined. The present study provides a detailed description of the Drosophila small heat shock protein Hsp23 expression pattern during embryogenesis and evaluates its functional contribution to central nervous system development.

Results

Throughout embryogenesis, Hsp23 is expressed in a stage-specific manner by a restricted number of neuronal and glial lineages of the central nervous system. Hsp23 is also detected in the amnioserosa and within a single lateral chordotonal organ. Its expression within the MP2 lineage does not require the presence of a functional midline nor the activity of the Notch signaling pathway. Transactivation assays demonstrate that transcription factors implicated in the differentiation of the midline also regulate hsp23 promoter activity. Phenotypic analysis of a transgenic line exhibiting loss of Hsp23 expression in the central nervous system suggests that Hsp23 is not required for development and function of this tissue. Likewise, its overexpression does not cause deleterious effects, as development remains unaffected.

Conclusions

Based on the presented data, we suggest that the tightly regulated developmental expression of Hsp23 is not actively involved in cell differentiation and central nervous system development per se but rather reflects a putative role in preventive "pre-stress" neuroprotection or in non-vital process(es) common to the identified cell lineages.

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.

Stress-induced, tissue-specific enrichment of hsp70 mRNA accumulation in Xenopus laevis embryos

In this study, we have employed whole-mount, in situ hybridization to study the spatial pattern of hsc70 and hsp70 mRNA accumulation in normal and heat shocked embryos during Xenopus laevis development. Our findings revealed that hsc70 mRNA was constitutively present in a global fashion throughout the embryo and was not heat inducible. Accumulation of hsp70 mRNA, however, was detected only in heat shocked embryos. Furthermore, hsp70 mRNA accumulation was enriched in a tissue-specific manner in X. laevis tailbud embryos within 15 minutes of a 33 degrees C heat shock. Abundant levels of heat shock-induced hsp70 mRNA were detected in the head region, including the lens placode, the cement gland, and in the somitic region and proctodeum. Preferential heat-induced accumulation of hsp70 mRNA was first detected at a heat shock temperature of 30 degrees C. Placement of embryos at 22 degrees C after a 1-hour, 33 degrees C heat shock resulted in decreased hsp70 mRNA with time, but the message persisted in selected tissues, including the lens placode and somites. Treatment of tailbud embryos with either sodium arsenite or zinc chloride induced a tissue-specific enrichment of hsp70 mRNA in the lens placode and somitic region. These studies reveal the complex nature of the heat shock response in different embryonic tissues and suggest the presence of regulatory mechanisms that lead to a stressor-induced, tissue-specific enrichment of hsp70 mRNA.

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.