The small heat shock protein, HSP30, is associated with aggresome-like inclusion bodies in proteasomal inhibitor-, arsenite-, and cadmium-treated Xenopus kidney cells

Molecular evolution of the heat shock protein family and the role of HSP30 in immune response and wound healing in lampreys (Lethenteron reissneri)

Heat shock proteins (HSPs) are molecular chaperones that ubiquitously exist in various organisms and play essential roles in protein folding, transport, and expression. While most HSPs are highly conserved across species, a few HSPs are evolutionarily distinct in some species and may have unique functions. To explore the evolutionary history of the vertebrate HSP family, we identify members of the HSP family at the genome-wide level in lampreys (Lethenteron reissneri), a living representative of jawless vertebrates diverged from jawed vertebrates over 500 million years ago. The phylogenetic analysis reveals that the lamprey HSP family contains HSP90a1, HSP90a2, HSC70, HSP60, HSP30, HSP27, HSP17, and HSP10, which have a primitive status in the molecular evolution of vertebrate HSPs. Transcriptome analysis reveals the expression distribution of members of the HSP family in various tissues of lampreys. It is shown that HSP30, normally found in birds, amphibians, and fish, is also present in lampreys, with remarkable expansion of HSP30 gene copies in the lamprey genome. The transcription of HSP30 is significantly induced in leukocytes and heart of lampreys during various pathogens or poly(I:C) stimulation, indicating that HSP30 may be involved in the immune defense of lampreys in response to bacterial or viral infection. Immunohistochemistry demonstrates significantly increased HSP30 expression in subcutaneous muscle tissue after skin injury in lamprey models of wound repair. Furthermore, transcriptome analysis shows that ectopic expression of HSP30 in 3T3-L1 fibroblasts affect the expression of genes related to the PI3K-AKT signaling pathway, suggesting that HSP30 could serves as a negative regulator of fibrosis. These results indicate that HSP30 may play a critical role in facilitating the process of lamprey skin repair following injury. This study provides new insights into the origin and evolution of the HSP gene family in vertebrates and offers valuable clues to reveal the important role of HSP30 in immune defense and wound healing of lampreys.

Combination of Withaferin-A and CAPE Provides Superior Anticancer Potency: Bioinformatics and Experimental Evidence to Their Molecular Targets and Mechanism of Action

We have earlier reported anticancer activity in Withaferin A (Wi-A), a withanolide derived from Ashwagandha (Withania somnifera) and caffeic acid phenethyl ester (CAPE), an active compound from New Zealand honeybee propolis. Whereas Wi-A was cytotoxic to both cancer and normal cells, CAPE has been shown to cause selective death of cancer cells. In the present study, we investigated the efficacy of Wi-A, CAPE, and their combination to ovarian and cervical cancer cells. Both Wi-A and CAPE were seen to activate tumor suppressor protein p53 by downregulation of mortalin and abrogation of its interactions with p53. Downregulation of mortalin translated to compromised mitochondria integrity and function that affected poly ADP-ribose polymerase1 (PARP1); a key regulator of DNA repair and protein-target for Olaparib, drugs clinically used for treatment of breast, ovarian and cervical cancers)-mediated DNA repair yielding growth arrest or apoptosis. Furthermore, we also compared the docking capability of Wi-A and CAPE to PARP1 and found that both of these could bind to the catalytic domain of PARP1, similar to Olaparib. We provide experimental evidences that (i) Wi-A and CAPE cause inactivation of PARP1-mediated DNA repair leading to accumulation of DNA damage and activation of apoptosis signaling by multiple ways, and (ii) a combination of Wi-A and CAPE offers selective toxicity and better potency to cancer cells.

The proteostasis network and its decline in ageing

Ageing is a major risk factor for the development of many diseases, prominently including neurodegenerative disorders such as Alzheimer disease and Parkinson disease. A hallmark of many age-related diseases is the dysfunction in protein homeostasis (proteostasis), leading to the accumulation of protein aggregates. In healthy cells, a complex proteostasis network, comprising molecular chaperones and proteolytic machineries and their regulators, operates to ensure the maintenance of proteostasis. These factors coordinate protein synthesis with polypeptide folding, the conservation of protein conformation and protein degradation. However, sustaining proteome balance is a challenging task in the face of various external and endogenous stresses that accumulate during ageing. These stresses lead to the decline of proteostasis network capacity and proteome integrity. The resulting accumulation of misfolded and aggregated proteins affects, in particular, postmitotic cell types such as neurons, manifesting in disease. Recent analyses of proteome-wide changes that occur during ageing inform strategies to improve proteostasis. The possibilities of pharmacological augmentation of the capacity of proteostasis networks hold great promise for delaying the onset of age-related pathologies associated with proteome deterioration and for extending healthspan.

Effect of hemin, baicalein and heme oxygenase-1 (HO-1) enzyme activity inhibitors on Cd-induced accumulation of HO-1, HSPs and aggresome-like structures in Xenopus kidney epithelial cells

Cadmium is a highly toxic environmental pollutant that can cause many adverse effects including cancer, neurological disease and kidney damage. Aquatic amphibians are particularly susceptible to this toxicant as it was shown to cause developmental abnormalities and genotoxic effects. In mammalian cells, the accumulation of heme oxygenase-1 (HO-1), which catalyzes the breakdown of heme into CO, free iron and biliverdin, was reported to protect cells against potentially lethal concentrations of CdCl₂. In the present study, CdCl₂ treatment of A6 kidney epithelial cells, derived from the frog, Xenopus laevis, induced the accumulation of HO-1, heat shock protein 70 (HSP70) and HSP30 as well as an increase in the production of aggregated protein and aggresome-like structures. Treatment of cells with inhibitors of HO-1 enzyme activity, tin protoporphyrin (SnPP) and zinc protoporphyrin (ZnPP), enhanced CdCl₂-induced actin cytoskeletal disorganization and the accumulation of HO-1, HSP70, aggregated protein and aggresome-like structures. Treatment of cells with hemin and baicalein, which were previously shown to provide cytoprotection against various stresses, induced HO-1 accumulation in a concentration-dependent manner. Also, treatment of cells with hemin and baicalein suppressed CdCl₂-induced actin dysregulation and the accumulation of aggregated protein and aggresome-like structures. This cytoprotective effect was inhibited by SnPP. These results suggest that HO-1-mediated protection against CdCl₂ toxicity includes the maintenance of actin cytoskeletal and microtubular structure and the suppression of aggregated protein and aggresome-like structures.

Ultraviolet filters and heat shock proteins: effects in Chironomus riparius by benzophenone-3 and 4-methylbenzylidene camphor

Benzophenone-3 (BP3) and 4-methylbenzylidene camphor (4MBC) are common ultraviolet filters (UV filters), compounds considered as emergent contaminants, used in different products like plastics and personal care products. The levels of these compounds are rising in the wild, but the effects they have on invertebrates are poorly understood. Chironomus riparius is a benthic insect widely used in toxicology, and several studies have been previously performed in our laboratory to determine the effects these compounds have on this organism at the molecular level. We have shown that UV filters can alter the mRNA levels of heat shock protein 70 (Hsp70), one of the most studied heat shock proteins. Although these proteins are crucial for the survival of organisms, little data is available on the effects these emergent contaminants have on them, especially in invertebrates. Here, we analyzed the transcriptional activity of 12 genes covering the different groups of heat shock protein [Hsp10, Hsp17, Hsp21, Hsp22, Hsp23, Hsp24, Hsp27, Hsp34, Hsp40, Hsp60, Hsc70 (3), and Hsc70 (4)] in response to 0.1 and 1 mg/L concentrations of BP3 and 4MBC at 8 and 24 h. The results showed that some small Hsp (sHsp) genes were altered by these compounds, while the genes of proteins present in mitochondria, Hsp10 and Hsp60, did not change. sHsps are also involved in developmental processes, so the observed variations could be due to the endocrine disruption activity described for these compounds rather than to a stress response.

Effect of isothiocyanates, BITC and PEITC, on stress protein accumulation, protein aggregation and aggresome-like structure formation in Xenopus A6 kidney epithelial cells

Numerous studies have elucidated the health benefits of organosulfur compounds, known as isothiocyanates (ITCs), derived from cruciferous vegetables. As electrophiles, ITCs have the ability to directly bind and modify thiol-containing compounds such as glutathione and cellular protein, including tubulin. While the biochemical effects of ITCs have been well characterized, less information is available regarding their effects on the accumulation of stress-inducible heme oxygenase-1 (HO-1), heat shock proteins (HSPs) and the possible formation of aggregated protein due to thiol modification. The present study has examined the effect of the ITCs, benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), on the accumulation of HO-1, HSP70 and HSP30 in Xenopus laevis A6 kidney epithelial cells. Immunoblot analysis revealed that both BITC and PEITC induced the accumulation of HO-1 and HSP70 whereas HSP30 levels were enhanced only in cells treated with BITC. Immunocytochemistry determined that ITC treatment induced F-actin disorganization and membrane ruffling and enhanced accumulation of HO-1 in the cytoplasm. Additionally, BITC induced enhanced levels of ubiquitinated protein, aggregated protein, and the collapse and fragmentation of microtubules. In comparison, treatment of cells with the proteasomal inhibitor, MG132, induced the accumulation of all three stress proteins, aggregated protein and aggresome-like structures. Finally, cells pretreated with BITC inhibited the formation of MG132-induced aggresome-like structures in the perinuclear region. This latter finding suggests that BITC-induced microtubule fragmentation may impede the movement of aggregated protein via microtubules and their subsequent coalescence into aggresome-like structures in the perinuclear region.

Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells

Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.

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.