Bridging human chaperonopathies and microbial chaperonins

Genetic and structural insights into the functional importance of the conserved gly-met-rich C-terminal tails in bacterial chaperonins

E. coli chaperonin GroEL forms nano-cages for protein folding. Although the chaperonin-mediated protein folding mechanism is well understood, the role of the conserved glycine and methionine-rich carboxy-terminal residues remains unclear. Bacteria with multiple chaperonins always retain at least one paralogue having the gly-met-rich C-terminus, indicating an essential conserved function. Here, we observed a stronger selection pressure on the paralogues with gly-met-rich C-termini, consistent with their ancestral functional importance. E. coli GroEL variants having mutations in their C-termini failed to functionally replace GroEL, suggesting the functional significance of the gly-met-rich C-termini. Further, our structural modelling and normal mode analysis showed that the C-terminal region shuttles between two cavity-specific conformations that correlate with the client-protein-binding apical domains, supporting C-termini's role in client protein encapsulation. Therefore, employing phylogenetic, genetic, and structural tools, we demonstrate that the gly-met-rich C-termini are functionally significant in chaperonin-mediated protein folding function. Owing to the pathogenic roles of the chaperonins having non-canonical C-termini, future investigations on the client protein selectivity will enable understanding the disease-specific client protein folding pathways and treatment options.

Liver Mitochondrial Morphology and Gene Expression as Markers of Liver Reserve: Prognostic Implications for Native Liver Survival in Biliary Atresia

PURPOSE

Hepatocyte mitochondrial morphology and gene expression were compared between biliary atresia (BA), infantile cholestasis (IC), and normal liver (NL) as prognostic indicators.

METHODS

Specimens of liver at portoenterostomy (PE) for BA, from intrahepatic bile duct paucity patients for IC, and from choledochal cyst or hepatoblastoma patients for NL were collected prospectively (P) beginning in 2021 (P-BA = 11, P-IC = 9, P-NL = 7) and retrospectively (R) from paraffin-embedded tissue going back to 1981 (R-BA = 25, R-IC = 9, R-NL = 4). The P-cohort had transmission electron microscopy (TEM) to image mitochondria, immunoblotting for heat shock protein 60 (HSP60), and quantitative PCR (qPCR) for HSP60 and mitochondrial functional genes. Both cohorts had immunofluorescence for HSP60 quantified as a ratio to albumin-positive hepatocytes (ALB) with HSP60/ALB<1.0 as a cutoff limit using ImageJ.

RESULTS

HSP60 was significantly lower in BA/IC than NL on qPCR (BA: p < 0.01, IC: p < 0.05) and lower in BA than IC/NL on immunoblotting (p < 0.05). HSP60/ALB was significantly lower in BA than NL/IC (p < 0.001). Despite BA subjects being matched for types of BA and ages at PE, HSP60/ALB did not correlate with jaundice clearance (JC; T-Bil<1.2 mg/dL) but was significantly higher in native liver survivors (NLS) after PE compared with liver transplant (LTx) cases (p < 0.05) and significantly lower in LTx cases achieving JC than NLS achieving JC (p < 0.05). TEM showed BA had significantly more mitochondrial inclusion bodies (p < 0.05) and significantly larger cristae (p < 0.01) than IC/NL. qPCR in BA showed significant repression of mitochondrial functional genes for mRNA stabilization and energy facilitation.

CONCLUSION

HSP60/ALB correlates with NLS after PE for BA.

LEVEL OF EVIDENCE

II.

The response of heat shock proteins in honey bees to abiotic and biotic stressors

Honey bees, Apis mellifera, are the most important managed pollinators worldwide. They are highly impacted by various abiotic and biotic stressors, especially temperature extremes, which can lead to cellular damage and death. The induction of heat shock proteins (HSPs) has been recorded in honey bees as a response to various types of stressors. HSPs are classified into different gene families according to their molecular weights. HSPs play an important role in maintaining cellular protein homeostasis due to their contribution as molecular chaperones or co-chaperones. HSPs in honey bees have complex functions with induction even under normal colony conditions. Previous studies have suggested various functions of HSPs to protect cells from damage under exposure to environmental stressors, pollutants, and pathogens. Surprisingly, HSPs have also been found to play roles in larval development and age-related tasks. The expression of HSPs varies depending on tissue type, developmental stage, age, and stress period. This article reviews studies on HSPs (sHSPs, HSP40, HSP60, HSP70, and HSP90) in honey bees and highlights gaps in the available knowledge. This review is crucial for honey bee research, particularly in the face of climate change challenges.

Minimal Yet Powerful: The Role of Archaeal Small Heat Shock Proteins in Maintaining Protein Homeostasis

Small heat shock proteins (sHsp) are a ubiquitous group of ATP-independent chaperones found in all three domains of life. Although sHsps in bacteria and eukaryotes have been studied extensively, little information was available on their archaeal homologs until recently. Interestingly, archaeal heat shock machinery is strikingly simplified, offering a minimal repertoire of heat shock proteins to mitigate heat stress. sHsps play a crucial role in preventing protein aggregation and holding unfolded protein substrates in a folding-competent form. Besides protein aggregation protection, archaeal sHsps have been shown recently to stabilize membranes and contribute to transferring captured substrate proteins to chaperonin for refolding. Furthermore, recent studies on archaeal sHsps have shown that environment-induced oligomeric plasticity plays a crucial role in maintaining their functional form. Despite being prokaryotes, the archaeal heat shock protein repository shares several features with its highly sophisticated eukaryotic counterpart. The minimal nature of the archaeal heat shock protein repository offers ample scope to explore the function and regulation of heat shock protein(s) to shed light on their evolution. Moreover, similar structural dynamics of archaeal and human sHsps have made the former an excellent system to study different chaperonopathies since archaeal sHsps are more stable under in vitro experiments.

Heat shock proteins in cell signaling and cancer

Heat Shock Proteins (HSPs) and their co-chaperones have well-established roles in regulating proteostasis within the cell, the nature of which continues to emerge with further study. To date, HSPs have been shown to be integral to protein folding and re-folding, protein transport, avoidance of protein aggregation, and modulation of protein degradation. Many cell signaling events are mediated by the chemical modification of proteins post-translationally that can alter protein conformation and activity, although it is not yet known whether the changes in protein conformation induced by post-translational modifications (PTMs) are also dependent upon HSPs and their co-chaperones for subsequent protein re-folding. We discuss what is known regarding roles for HSPs and other molecular chaperones in cell signaling events with a focus on oncogenic signaling. We also propose a hypothesis by which Hsp70 and Hsp90 may co-operate to facilitate cell signaling events that may link PTMs with the cellular protein folding machinery.

Chaperonins in cancer: Expression, function, and migration in extracellular vesicles

The chaperonins CCT and Hsp60 are molecular chaperones, members of the chaperone system (CS). Chaperones are cytoprotective but if abnormal in quantity or quality they may cause diseases, the chaperonopathies. Here, recent advances in the understanding of CCT and Hsp60 in cancerology are briefly discussed, focusing on breast and brain cancers. CCT subunits, particularly CCT2, were increased in breast cancer cells and this correlated with tumor progression. Experimental induction of CCT2 increase was accompanied by an increase of CCT3, 4, and 5, providing another evidence for the interconnection between the members of the CS and the difficulties expected while manipulating one member with therapeutic purposes. Another in silico study demonstrated a direct correlation between the increase in the tumor tissue of the mRNA levels of all CCT subunits, except CCTB6, with bad prognosis. Studies with glioblastomas demonstrated an increase in the CCT subunits in the tumor tissue and in extracellular vesicles (EVs) derived from them. Expression levels of CCT1, 2, 6A, and 7 were the most increased and markers of bad prognosis, particularly CCT6A. A method for measuring Hsp60 and related miRNA in exosomes from blood of patients with glioblastomas or other brain tumors was discussed, and the results indicate that the triad Hsp60-related miRNAs-exosomes has potential regarding diagnosis and patient monitoring. All these data provide a strong foundation for future studies on the role played by chaperonins in carcinogenesis and for fully developing their theranostics applications along with exosomes.

Molecular mechanisms in chaperonopathies: clues to understanding the histopathological abnormalities and developing novel therapies

Molecular chaperones, many of which are heat shock proteins (Hsps), are components of the chaperoning system and when defective can cause disease, the chaperonopathies. Chaperone-gene variants cause genetic chaperonopathies, whereas in the acquired chaperonopathies the genes are normal, but their protein products are not, due to aberrant post-transcriptional mechanisms, e.g. post-translational modifications (PTMs). Since the chaperoning system is widespread in the body, chaperonopathies affect various tissues and organs, making these diseases of interest to a wide range of medical specialties. Genetic chaperonopathies are uncommon but the acquired ones are frequent, encompassing various types of cancer, and inflammatory and autoimmune disorders. The clinical picture of chaperonopathies is known. Much less is known on the impact that pathogenic mutations and PTMs have on the properties and functions of chaperone molecules. Elucidation of these molecular alterations is necessary for understanding the mechanisms underpinning the tissue and organ abnormalities occurring in patients. To illustrate this issue, we discuss structural-functional alterations caused by mutation in the chaperones CCT5 and HSPA9, and PTM effects on Hsp60. The data provide insights into what may happen when CCT5 and HSPA9 malfunction in patients, e.g. accumulation of cytotoxic protein aggregates with tissue destruction; or for Hsp60 with aberrant PTM, degradation and/or secretion of the chaperonin with mitochondrial damage. These and other possibilities are now open for investigation. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.