Hsp60D is essential for caspase-mediated induced apoptosis in Drosophila melanogaster

Molecular Chaperonin HSP60: Current Understanding and Future Prospects

Molecular chaperones are highly conserved across evolution and play a crucial role in preserving protein homeostasis. The 60 kDa heat shock protein (HSP60), also referred to as chaperonin 60 (Cpn60), resides within mitochondria and is involved in maintaining the organelle's proteome integrity and homeostasis. The HSP60 family, encompassing Cpn60, plays diverse roles in cellular processes, including protein folding, cell signaling, and managing high-temperature stress. In prokaryotes, HSP60 is well understood as a GroEL/GroES complex, which forms a double-ring cavity and aids in protein folding. In eukaryotes, HSP60 is implicated in numerous biological functions, like facilitating the folding of native proteins and influencing disease and development processes. Notably, research highlights its critical involvement in sustaining oxidative stress and preserving mitochondrial integrity. HSP60 perturbation results in the loss of the mitochondria integrity and activates apoptosis. Currently, numerous clinical investigations are in progress to explore targeting HSP60 both in vivo and in vitro across various disease models. These studies aim to enhance our comprehension of disease mechanisms and potentially harness HSP60 as a therapeutic target for various conditions, including cancer, inflammatory disorders, and neurodegenerative diseases. This review delves into the diverse functions of HSP60 in regulating proteo-homeostasis, oxidative stress, ROS, apoptosis, and its implications in diseases like cancer and neurodegeneration.

Zearalenone Does Not Show Genotoxic Effects in the Drosophila melanogaster Wing Spot Test, but It Induces Oxidative Imbalance, Development, and Fecundity Alterations

Zearalenone (ZEN) is a non-steroidal mycoestrogen produced by the Fusarium genus. ZEN and its metabolites compete with 17-beta estradiol for cytosolic estrogen receptors, causing reproductive alterations in vertebrates. ZEN has also been associated with toxic and genotoxic effects, as well as an increased risk for endometrial adenocarcinomas or hyperplasia, breast cancer, and oxidative damage, although the underlying mechanisms remain unclear. Previous studies have monitored cellular processes through levels of transcripts associated with Phase I Xenobiotic Metabolism (Cyp6g1 and Cyp6a2), oxidative stress (hsp60 and hsp70), apoptosis (hid, grim, and reaper), and DNA damage genes (Dmp53). In this study, we evaluated the survival and genotoxicity of ZEN, as well as its effects on emergence rate and fecundity in Drosophila melanogaster. Additionally, we determined levels of reactive oxygen species (ROS) using the D. melanogaster flare and Oregon R(R)-flare strains, which differ in levels of Cyp450 gene expression. Our results showed that ZEN toxicity did not increase mortality by more than 30%. We tested three ZEN concentrations (100, 200, and 400 μM) and found that none of the concentrations were genotoxic but were cytotoxic. Taking into account that it has previously been demonstrated that ZEN administration increased hsp60 expression levels and apoptosis gene transcripts in both strains, the data agree with an increase in ROS and development and fecundity alterations. Since Drosophila lacks homologous genes for mammalian estrogen receptors alpha and beta, the effects of this mycotoxin can be explained by a mechanism different from estrogenic activity.

Expression of the gonad-specific small heat shock protein, CfHSP20.2, in the spruce budworm, Choristoneura fumiferana (Clem.)

Small heat shock proteins (sHSPs) play important roles in insect development and stress resistance. However, the in vivo functions and mechanisms of action remain largely unknown or unclear for most members of the sHSPs in insects. This study investigated the expression of CfHSP20.2 in the spruce budworm, Choristoneura fumiferana (Clem.) under normal and heat-stress conditions. Under normal conditions, CfHSP20.2 transcript and protein were highly and constantly expressed in the testes of male larvae, pupae and young adults and in the ovaries of female late-stage pupae and adults. After adult eclosion, CfHSP20.2 remained highly and almost constantly expressed in the ovaries, but in contrast, was downregulated in the testes. Upon heat stress, CfHSP20.2 was upregulated in the gonads and non-gonadal tissues in both sexes. These results indicate that CfHSP20.2 expression is gonad-specific and heat-inducible. This provides evidence that the CfHSP20.2 protein plays important roles during reproductive development under normal environmental conditions, while under heat-stress conditions, it may also enhance the thermal tolerance of the gonads and non-gonadal tissues.

Mitochondria as a target and central hub of energy division during cold stress in insects

Temperature stress is one of the crucial factors determining geographical distribution of insect species. Most of them are active in moderate temperatures, however some are capable of surviving in extremely high as well as low temperatures, including freezing. The tolerance of cold stress is a result of various adaptation strategies, among others the mitochondria are an important player. They supply cells with the most prominent energy carrier—ATP, needed for their life processes, but also take part in many other processes like growth, aging, protection against stress injuries or cell death. Under cold stress, the mitochondria activity changes in various manner, partially to minimize the damages caused by the cold stress, partially because of the decline in mitochondrial homeostasis by chill injuries. In the response to low temperature, modifications in mitochondrial gene expression, mtDNA amount or phosphorylation efficiency can be observed. So far study also showed an increase or decrease in mitochondria number, their shape and mitochondrial membrane permeability. Some of the changes are a trigger for apoptosis induced via mitochondrial pathway, that protects the whole organism against chill injuries occurring on the cellular level. In many cases, the observed modifications are not unequivocal and depend strongly on many factors including cold acclimation, duration and severity of cold stress or environmental conditions. In the presented article, we summarize the current knowledge about insect response to cold stress focusing on the role of mitochondria in that process considering differences in results obtained in different experimental conditions, as well as depending on insect species. These differentiated observations clearly indicate that it is still much to explore.

Molecular characterization of eight ATP-dependent heat shock protein transcripts and their expression profiles in response to stresses in the spruce budworm, Choristoneura fumiferana (L.)

Heat shock proteins (HSPs) greatly contribute to insect stress tolerance and enhance survival and adaptation in severe environmental conditions. To investigate the potential roles of HSPs in the spruce budworm, Choristoneura fumiferana (L.), an important native pest of forests in North America, we found eight ATP-dependent HSP transcripts (CfHSPs). Based on molecular characteristics, the identified HSP genes were classified into HSP70 and HSP90 families, and phylogenetic results showed that they had orthologues in other insects. The transcript levels of these HSPs were measured using RT-qPCR under normal and stressful conditions in the laboratory. Under normal conditions, three HSP genes were consistently expressed in all life stages, whereas expression of the other five genes was dependent on the developmental stage. In the larvae, most CfHSP transcripts displayed similar expression levels among different tissues. Under heat shock conditions, one HSP70 gene and one HSP90 gene were upregulated in all life stages. One HSP70 gene was upregulated after cold injury in the larval stage. With starvation, HSP gene expression exhibited complex expression patterns; most of them were downregulated. These results suggest that the ATP-dependent HSPs have multiple roles during normal development as well as under stressful conditions including heat, cold injury and starvation.

Expression status of heat shock proteins in response to cold, heat, or insecticide exposure in the Colorado potato beetle Leptinotarsa decemlineata

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an agricultural pest that threatens the potato industry worldwide. This insect is widely regarded as one of the most difficult-to-control pests, as it can thrive in a wide range of temperature conditions and routinely develops resistance towards various insecticides. The molecular changes associated with response to these challenges have not been fully investigated in L. decemlineata. While differential expression and characterization of heat shock proteins (HSPs) in response to stress have been conducted in several insects, data regarding HSPs in L. decemlineata are limited. The overarching objective of this study consisted of evaluating the expression of various HSPs in L. decemlineata exposed to different temperatures or treated with the insecticides imidacloprid and chlorantraniliprole. Expression levels of HSP60, HSP70, HSP90, and HSP Beta-1 were evaluated by qRT-PCR and insect mortality was assessed using dsRNAs aimed at select HSP targets. Elevated HSP70 and HSP90 transcript levels were observed in heat-exposed L. decemlineata while downregulation of HSP70 transcript levels was measured in insects submitted to cold conditions. Chlorantraniliprole exposure was associated with reduced HSP Beta-1 transcript levels while no change in expression was monitored in insects exposed to imidacloprid. RNAi-based knockdown of HSP60 levels correlated with significant insect mortality 14 days after dsRNA injection. These results highlight the modulation of HSPs that occur in L. decemlineata exposed to fluctuating temperatures and position HSPs as interesting candidates in the identification of novel molecular leads that could be targeted to control this insect.

Suppression of induced but not developmental apoptosis in Drosophila by Ayurvedic Amalaki Rasayana and Rasa-Sindoor

Earlier we showed formulation-specific beneficial effects of dietary supplement of Ayurvedic Amalaki Rasayana (AR, a herbal formulation) and Rasa-Sindoor (RS, a mercury-based organo-metallic formulation) on various biological parameters in Drosophila, parallel to traditional Ayurvedic literature. These formulations also suppressed cell death and pathology in fly models of neurodegeneration. To understand basis of inhibition of apoptosis, we examined effects of AR and RS on induced and developmental apoptosis in Drosophila. Dietary AR or RS significantly reduced apoptosis induced by GMR-GAL4-, sev-GAL4- or hs-GAL4-directed expression of Rpr, Hid or Grim (RHG) proapoptotic proteins or by GMR-GAL4-directed DIAP1-RNAi, resulting in significant restoration of organism's viability and eye morphology. AR or RS supplement enhanced levels of inhibitor of apoptosis proteins, DIAP1 and DIAP2, and of Bancal/Hrb57A, while the levels of RHG proteins and of initiator Dronc and effecter Drice caspases were reduced in non-apoptotic wild type as well as in RHG over-expressing tissues. Levels of Dronc or Drice remained unaffected in cells developmentally destined to die so that developmental apoptosis occurred normally. Elevated levels of DIAPs and reduced levels of RHG proteins and caspases reflect a more robust physiological state of AR or RS fed organisms allowing them to tolerate greater insults without triggering the cell-death response. Such homeostatic effects of these Rasayanas seem to contribute to 'healthy ageing', one of their effects suggested in traditional Ayurvedic practices.

FUS Interacts with HSP60 to Promote Mitochondrial Damage

FUS-proteinopathies, a group of heterogeneous disorders including ALS-FUS and FTLD-FUS, are characterized by the formation of inclusion bodies containing the nuclear protein FUS in the affected patients. However, the underlying molecular and cellular defects remain unclear. Here we provide evidence for mitochondrial localization of FUS and its induction of mitochondrial damage. Remarkably, FTLD-FUS brain samples show increased FUS expression and mitochondrial defects. Biochemical and genetic data demonstrate that FUS interacts with a mitochondrial chaperonin, HSP60, and that FUS translocation to mitochondria is, at least in part, mediated by HSP60. Down-regulating HSP60 reduces mitochondrially localized FUS and partially rescues mitochondrial defects and neurodegenerative phenotypes caused by FUS expression in transgenic flies. This is the first report of direct mitochondrial targeting by a nuclear protein associated with neurodegeneration, suggesting that mitochondrial impairment may represent a critical event in different forms of FUS-proteinopathies and a common pathological feature for both ALS-FUS and FTLD-FUS. Our study offers a potential explanation for the highly heterogeneous nature and complex genetic presentation of different forms of FUS-proteinopathies. Our data also suggest that mitochondrial damage may be a target in future development of diagnostic and therapeutic tools for FUS-proteinopathies, a group of devastating neurodegenerative diseases.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two groups of common and devastating neurodegenerative diseases, characterized by losses of selected groups of neurons. Mutations in the FUS gene have been associated with ALS, whereas inclusion bodies containing the FUS protein have been discovered in both ALS and FTLD patients. However, the underlying pathogenic mechanisms of FUS in these diseases remain unclear. Here, we demonstrate that wild-type or ALS-associated mutant FUS can interact with mitochondrial chaperonin HSP60 and that HSP60 mediates FUS localization to mitochondria, leading to mitochondrial damage. Mitochondrial impairment may be an early event in FUS proteinopathies and represent a potential therapeutic target for treating these fatal diseases.

N -methyl- N -nitrosourea-induced retinal degeneration in mice

Mouse retinal degeneration models have been investigated for many years in the hope of understanding the mechanism of photoreceptor cell death. N -methyl- N -nitrosourea (MNU) has been previously shown to induce outer retinal degeneration in mice. After MNU was intraperitoneally injected in C57/BL mice, we observed a gradual decrease in the outer nuclear layer (ONL) thickness associated with photoreceptor outer segment loss, bipolar cell dendritic retraction and reactive gliosis. Reactive gliosis was confirmed by increased GFAP protein levels. More serious damage to the central retina as opposed to the peripheral retina was found in the MNU-induced retinal degeneration model. Retinal ganglion cells (RGC) appear to be spared for at least two months after MNU treatment. Following retinal vessel labelling, we observed vascular complexes in the distal vessels, indicating retinal vessel damage. In the remnant retinal photoreceptor of the MNU-treated mouse, concentrated colouring nuclei were detected by electron microscopy, together with the loss of mitochondria and displaced remnant synaptic ribbons in the photoreceptor. We also observed decreased mitochondrial protein levels and increased amounts of nitrosylation/nitration in the photoreceptors. The mechanism of MNU-induced apoptosis may result from oxidative stress or the loss of retinal blood supply. MNU-induced mouse retinal degeneration in the outer retina is a useful animal model for photoreceptor degeneration diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP).

Neurodegeneration caused by polyglutamine expansion is regulated by P-glycoprotein in Drosophila melanogaster

Trinucleotide CAG repeat disorders are caused by expansion of polyglutamine (polyQ) domains in certain proteins leading to fatal neurodegenerative disorders and are characterized by accumulation of inclusion bodies in the neurons. Clearance of these inclusion bodies holds the key to improve the disease phenotypes, which affects basic cellular processes such as transcription, protein degradation and cell signaling. In the present study, we show that P-glycoprotein (P-gp), originally identified as a causative agent of multidrug-resistant cancer cells, plays an important role in ameliorating the disease phenotype. Using a Drosophila transgenic strain that expresses a stretch of 127 glutamine repeats, we demonstrate that enhancing P-gp levels reduces eye degeneration caused by expression of polyQ, whereas reducing it increases the severity of the disease. Increase in polyQ inclusion bodies represses the expression of mdr genes, suggesting a functional link between P-gp and polyQ. P-gp up-regulation restores the defects in the actin organization and precise array of the neuronal connections caused by inclusion bodies. β-Catenin homolog, Armadillo, also interacts with P-gp and regulates the accumulation of inclusion bodies. These results thus show that P-gp and polyQ interact with each other, and changing P-gp levels can directly affect neurodegeneration.

Global transcriptome profiling of the pine shoot beetle, Tomicus yunnanensis (Coleoptera: Scolytinae)

Background

The pine shoot beetle Tomicus yunnanensis (Coleoptera: Scolytinae) is an economically important pest of Pinus yunnanensis in southwestern China. Developed resistance to insecticides due to chemical pesticides being used for a long time is a factor involved in its serious damage, which poses a challenge for management. In addition, highly efficient adaptation to divergent environmental ecologies results in this pest posing great potential threat to pine forests. However, the molecular mechanisms remain unknown as only limited nucleotide sequence data for this species is available.

Methodology/Principal Findings

In this study, we applied next generation sequencing (Illumina sequencing) to sequence the adult transcriptome of T. yunnanensis. A total of 51,822,230 reads were obtained. They were assembled into 140,702 scaffolds, and 60,031 unigenes. The unigenes were further functionally annotated with gene descriptions, Gene Ontology (GO), Clusters of Orthologous Groups (COG), and Kyoto Encyclopedia of Genes and Genome (KEGG). In total, 80,932 unigenes were classified into GO, 13,599 unigenes were assigned to COG, and 33,875 unigenes were found in KO categories. A biochemical pathway database containing 219 predicted pathways was also created based on the annotations. In depth analysis of the data revealed a large number of genes related to insecticides resistance and heat shock protein genes associated with environmental stress.

Conclusions/Significance

The results facilitate the investigations of molecular resistance mechanisms to insecticides and environmental stress. This study lays the foundation for future functional genomics studies of important biological questions of this pest.

The heat shock proteins as targets for radiosensitization and chemosensitization in cancer

The heat shock proteins (HSPs) represent a class of proteins which are induced under physiologic stress to promote cell survival in the face of endogenous or exogenous injury. HSPs function predominantly as molecular chaperones, maintaining their "client" proteins in the correct conformational state in order to withstand a biologic stressor. Elevated HSP expression is also found in a range of pathologic conditions, notably malignancy. Cancer cells exploit the pro-survival phenotype endowed by HSPs to bolster their proliferative potential. Consequently, developing means of abrogating HSP expression may provide a way to render cancer cells more susceptible to radiation or chemotherapy. Here, we review the members of the HSP class and their roles in malignancy. We focus on attempts to target these proteins, particularly the small HSPs, in developing potent radiation and chemotherapy sensitizers, as well as proposed mechanisms for this sensitization effect.

The developmentally active and stress-inducible noncoding hsromega gene is a novel regulator of apoptosis in Drosophila

The large nucleus limited noncoding hsromega-n RNA of Drosophila melanogaster is known to associate with a variety of heterogeneous nuclear RNA-binding proteins (hnRNPs) and certain other RNA-binding proteins to assemble the nucleoplasmic omega speckles. In this article, we show that RNAi-mediated depletion of this noncoding RNA dominantly suppresses apoptosis, in eye and other imaginal discs, triggered by induced expression of Rpr, Grim, or caspases (initiator as well as effector), all of which are key regulators/effectors of the canonical caspase-mediated cell death pathway. We also show, for the first time, a genetic interaction between the noncoding hsromega transcripts and the c-Jun N-terminal kinase (JNK) signaling pathway since downregulation of hsromega transcripts suppressed JNK activation. In addition, hsromega-RNAi also augmented the levels of Drosophila Inhibitor of Apoptosis Protein 1 (DIAP1) when apoptosis was activated. Suppression of induced cell death following depletion of hsromega transcripts was abrogated when the DIAP1-RNAi transgene was coexpressed. Our results suggest that the hsromega transcripts regulate cellular levels of DIAP1 via the hnRNP Hrb57A, which physically interacts with DIAP1, and any alteration in levels of the hsromega transcripts in eye disc cells enhances association between these two proteins. Our studies thus reveal a novel regulatory role of the hsromega noncoding RNA on the apoptotic cell death cascade through multiple paths. These observations add to the diversity of regulatory functions that the large noncoding RNAs carry out in the cells' life.