Caenorhabditis elegans chaperonin CCT/TRiC is required for actin and tubulin biogenesis and microvillus formation in intestinal epithelial cells

The CCT chaperonin and actin modulate the ER and RNA-binding protein condensation during oogenesis and maintain translational repression of maternal mRNA and oocyte quality

The regulation of maternal mRNAs is essential for proper oogenesis, the production of viable gametes, and to avoid birth defects and infertility. Many oogenic RNA-binding proteins have been identified with roles in mRNA metabolism, some of which localize to dynamic ribonucleoprotein granules and others that appear dispersed. Here, we use a combination of in vitro condensation assays and the in vivo Caenorhabditis elegans oogenesis model to characterize the properties of the conserved KH-domain MEX-3 protein and to identify novel regulators of MEX-3 and three other translational regulators. We demonstrate that MEX-3 undergoes phase separation and appears to have intrinsic gel-like properties in vitro. We also identify novel roles for the chaperonin-containing tailless complex polypeptide 1 (CCT) chaperonin and actin in preventing ectopic RNA-binding protein condensates in maturing oocytes that appear to be independent of MEX-3 folding. The CCT chaperonin and actin also oppose the expansion of endoplasmic reticulum sheets that may promote ectopic condensation of RNA-binding proteins. These novel regulators of condensation are also required for the translational repression of maternal mRNA which is essential for oocyte quality and fertility. The identification of this regulatory network may also have implications for understanding the role of hMex3 phase transitions in cancer.

The CCT chaperonin and actin modulate the ER and RNA-binding protein condensation during oogenesis to maintain translational repression of maternal mRNA and oocyte quality

The regulation of maternal mRNAs is essential for proper oogenesis, the production of viable gametes, and to avoid birth defects and infertility. Many oogenic RNA-binding proteins have been identified with roles in mRNA metabolism, some of which localize to dynamic ribonucleoprotein granules and others that appear dispersed. Here, we use a combination of in vitro condensation assays and the in vivo C. elegans oogenesis model to determine the intrinsic properties of the conserved KH-domain MEX-3 protein and to identify novel regulators of MEX-3 and the Lsm protein, CAR-1. We demonstrate that MEX-3 undergoes liquid-liquid phase separation and appears to have intrinsic gel-like properties in vitro . We also identify novel roles for the CCT chaperonin and actin in preventing ectopic RNA-binding protein condensates in maturing oocytes that appear to be independent of MEX-3 folding. CCT and actin also oppose the expansion of ER sheets that may promote ectopic condensation of RNA-binding proteins that are associated with de-repression of maternal mRNA. This regulatory network is essential to preserve oocyte quality, prevent infertility, and may have implications for understanding the role of hMex3 phase transitions in cancer.

Significance statement

The molecular mechanisms that regulate phase transitions of oogenic RNA-binding proteins are critical to elucidate but are not fully understood.We identify novel regulators of RNA-binding protein phase transitions in maturing oocytes that are required to maintain translational repression of maternal mRNAs and oocyte quality.This study is the first to elucidate a regulatory network involving the CCT chaperonin, actin, and the ER for phase transitions of RNA-binding proteins during oogenesis. Our findings for the conserved MEX-3 protein may also be applicable to better understanding the role of hMex3 phase transitions in cancer.

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.

Regulation of Epithelial and Endothelial Barriers by Molecular Chaperones

The integrity and permeability of epithelial and endothelial barriers depend on the formation of tight junctions, adherens junctions, and a junction-associated cytoskeleton. The establishment of this junction-cytoskeletal module relies on the correct folding and oligomerization of its protein components. Molecular chaperones are known regulators of protein folding and complex formation in different cellular compartments. Mammalian cells possess an elaborate chaperone network consisting of several hundred chaperones and co-chaperones. Only a small part of this network has been linked, however, to the regulation of intercellular adhesions, and the systematic analysis of chaperone functions at epithelial and endothelial barriers is lacking. This review describes the functions and mechanisms of the chaperone-assisted regulation of intercellular junctions. The major focus of this review is on heat shock protein chaperones, their co-chaperones, and chaperonins since these molecules are the focus of the majority of the articles published on the chaperone-mediated control of tissue barriers. This review discusses the roles of chaperones in the regulation of the steady-state integrity of epithelial and vascular barriers as well as the disruption of these barriers by pathogenic factors and extracellular stressors. Since cytoskeletal coupling is essential for junctional integrity and remodeling, chaperone-assisted assembly of the actomyosin cytoskeleton is also discussed.

MARC-3, a membrane-associated ubiquitin ligase, is required for fast polyspermy block in Caenorhabditis elegans

In many sexually reproducing organisms, oocytes are fundamentally fertilized with one sperm. In Caenorhabditis elegans, chitin layer formation after fertilization by the EGG complex is one of the mechanisms of polyspermy block, but other mechanisms remain unknown. Here, we demonstrate that MARC-3, a membrane-associated RING-CH-type ubiquitin ligase that localizes to the plasma membrane and cortical puncta in oocytes, is involved in fast polyspermy block. During polyspermy, the second sperm entry occurs within approximately 10 s after fertilization in MARC-3-deficient zygotes, whereas it occurs approximately 200 s after fertilization in egg-3 mutant zygotes defective in the chitin layer formation. MARC-3 also functions in the selective degradation of maternal plasma membrane proteins and the transient accumulation of endosomal lysine 63-linked polyubiquitin after fertilization. The RING-finger domain of MARC-3 is required for its in vitro ubiquitination activity and polyspermy block, suggesting that a ubiquitination-mediated mechanism sequentially regulates fast polyspermy block and maternal membrane protein degradation during the oocyte-to-embryo transition.

A hierarchical assembly pathway directs the unique subunit arrangement of TRiC/CCT

How the essential eukaryotic chaperonin TRiC/CCT assembles from eight distinct subunits into a unique double-ring architecture remains undefined. We show TRiC assembly involves a hierarchical pathway that segregates subunits with distinct functional properties until holocomplex (HC) completion. A stable, likely early intermediate arises from small oligomers containing CCT2, CCT4, CCT5, and CCT7, contiguous subunits that constitute the negatively charged hemisphere of the TRiC chamber, which has weak affinity for unfolded actin. The remaining subunits CCT8, CCT1, CCT3, and CCT6, which comprise the positively charged chamber hemisphere that binds unfolded actin more strongly, join the ring individually. Unincorporated late-assembling subunits are highly labile in cells, which prevents their accumulation and premature substrate binding. Recapitulation of assembly in a recombinant system demonstrates that the subunits in each hemisphere readily form stable, noncanonical TRiC-like HCs with aberrant functional properties. Thus, regulation of TRiC assembly along a biochemical axis disfavors the formation of stable alternative chaperonin complexes.

A genome-wide CRISPR screen identifies the CCT chaperonin as a critical regulator of vesicle trafficking

Vesicle trafficking is a fundamental cellular process that controls the transport of various proteins and cargos between cellular compartments in eukaryotes. Using a combination of genome-wide CRISPR screening in mammalian cells and RNAi screening in Caenorhabditis elegans, we identify chaperonin containing TCP-1 subunit 4 (CCT4) as a critical regulator of protein secretion and vesicle trafficking. In C. elegans, deficiency of cct-4 as well as other CCT subunits impairs the trafficking of endocytic markers in intestinal cells, and this defect resembles that of dyn-1 RNAi worms. Consistent with these findings, the silencing of CCT4 in human cells leads to defective endosomal trafficking, and this defect can be rescued by the dynamin activator Ryngo 1-23. These results suggest that the cytosolic chaperonin CCT may regulate vesicle trafficking by promoting the folding of dynamin in addition to its known substrate tubulin. Our findings establish an essential role for the CCT chaperonin in regulating vesicle trafficking, and provide new insights into the regulation of vesicle trafficking and the cellular function of the cytosolic chaperonin.

CCT6A knockdown suppresses osteosarcoma cell growth and Akt pathway activation in vitro

We assessed the role of the protein-coding gene chaperonin-containing TCP1 subunit 6A (CCT6A) in osteosarcoma, as this is currently unknown. Using data from the R2 online genomic analysis and visualization application, we found that CCT6A messenger ribonucleic acid (RNA) expression is increased in osteosarcoma tissue and cells. Transfection of CCT6A small interfering RNA into cultured osteosarcoma cells revealed that CCT6A knockdown attenuates cell growth, cell viability, cell survival, and induced apoptosis and cell cycle progression at the G0/G1 phases. Moreover, CCT6A knockdown downregulated phospho-protein kinase B (p-Akt), cyclinD1 and B-cell lymphoma-2, whereas upregulated Bcl-2-associated X-protein expression. Thus, CCT6A knockdown inhibits cell proliferation, induces cell apoptosis, and suppresses the Akt pathway.

Ubiquitination-coupled liquid phase separation regulates the accumulation of the TRIM family of ubiquitin ligases into cytoplasmic bodies

Many members of the tripartite motif (TRIM) family of ubiquitin ligases localize in spherical, membrane-free structures collectively referred to as cytoplasmic bodies (CBs) in a concentration-dependent manner. These CBs may function as aggresome precursors or storage compartments that segregate potentially harmful excess TRIM molecules from the cytosolic milieu. However, the manner in which TRIM proteins accumulate into CBs is unclear. In the present study, using TRIM32, TRIM5α and TRIM63 as examples, we demonstrated that CBs are in a liquid droplet state, resulting from liquid-liquid phase separation (LLPS). This finding is based on criteria that defines phase-separated structures, such as recovery after photobleaching, sensitivity to hexanediol, and the ability to undergo fusion. CB droplets, which contain cyan fluorescent protein (CFP)-fused TRIM32, were purified from HEK293 cells using a fluorescence-activated cell sorter and analyzed by LC-MS/MS. We found that in addition to TRIM32, these droplets contain a variety of endogenous proteins and enzymes including ubiquitin. Localization of ubiquitin within CBs was further verified by fluorescence microscopy. We also found that the activation of the intracellular ubiquitination cascade promotes the assembly of TRIM32 molecules into CBs, whereas inhibition causes suppression. Regulation is dependent on the intrinsic E3 ligase activity of TRIM32. Similar regulation by ubiquitination on the TRIM assembly was also observed with TRIM5α and TRIM63. Our findings provide a novel mechanical basis for the organization of CBs that couples compartmentalization through LLPS with ubiquitination.

Identification of a Prognostic Signature Composed of GPI, IL22RA1, CCT6A and SPOCK1 for Lung Adenocarcinoma Based on Bioinformatic Analysis of lncRNA-Mediated ceRNA Network and Sample Validation

Lung adenocarcinoma (LUAD) is one of the most common malignant tumors with high morbidity and mortality in China and worldwide. Long non-coding RNAs (lncRNAs) as the competing endogenous RNA (ceRNA) play an essential role in the occurrence and development of LUAD. However, identifying lncRNA-related biomarkers to improve the accuracy of LUAD prognosis remains to be determined. This study downloaded RNA sequence data from The Cancer Genome Atlas (TCGA) database and identified the differential RNAs by bioinformatics. A total of 214 lncRNA, 198 miRNA and 2989 mRNA were differentially identified between LUAD and adjacent nontumor samples. According to the ceRNA hypothesis, we constructed a lncRNA-miRNA-mRNA network including 95 protein-coding mRNAs, 7 lncRNAs and 15 miRNAs, and found 24 node genes in this network were significantly associated with the overall survival of LUAD patients. Subsequently, through LASSO regression and multivariate Cox regression analyses, a four-gene prognostic signature composed of GPI, IL22RA1, CCT6A and SPOCK1 was developed based on the node genes of the lncRNA-mediated ceRNA network, demonstrating high performance in predicting the survival and chemotherapeutic responses of low- and high-risk LUAD patients. Finally, independent prognostic factors were further analyzed and combined into a well-executed nomogram that showed strong potential for clinical applications. In summary, the data from the current study suggested that the four-gene signature obtained from analysis of lncRNA-mediated ceRNA could serve as a reliable biomarker for LUAD prognosis and evaluation of chemotherapeutic response.

The chaperonin CCT8 controls proteostasis essential for T cell maturation, selection, and function

T cells rely for their development and function on the correct folding and turnover of proteins generated in response to a broad range of molecular cues. In the absence of the eukaryotic type II chaperonin complex, CCT, T cell activation induced changes in the proteome are compromised including the formation of nuclear actin filaments and the formation of a normal cell stress response. Consequently, thymocyte maturation and selection, and T cell homeostatic maintenance and receptor-mediated activation are severely impaired. In the absence of CCT-controlled protein folding, Th2 polarization diverges from normal differentiation with paradoxical continued IFN-γ expression. As a result, CCT-deficient T cells fail to generate an efficient immune protection against helminths as they are unable to sustain a coordinated recruitment of the innate and adaptive immune systems. These findings thus demonstrate that normal T cell biology is critically dependent on CCT-controlled proteostasis and that its absence is incompatible with protective immunity.

Reducing INS-IGF1 signaling protects against non-cell autonomous vesicle rupture caused by SNCA spreading

Aging is associated with a gradual decline of cellular proteostasis, giving rise to devastating protein misfolding diseases, such as Alzheimer disease (AD) or Parkinson disease (PD). These diseases often exhibit a complex pathology involving non-cell autonomous proteotoxic effects, which are still poorly understood. Using Caenorhabditis elegans we investigated how local protein misfolding is affecting neighboring cells and tissues showing that misfolded PD-associated SNCA/α-synuclein is accumulating in highly dynamic endo-lysosomal vesicles. Irrespective of whether being expressed in muscle cells or dopaminergic neurons, accumulated proteins were transmitted into the hypodermis with increasing age, indicating that epithelial cells might play a role in remote degradation when the local endo-lysosomal degradation capacity is overloaded. Cell biological and genetic approaches revealed that inter-tissue dissemination of SNCA was regulated by endo- and exocytosis (neuron/muscle to hypodermis) and basement membrane remodeling (muscle to hypodermis). Transferred SNCA conformers were, however, inefficiently cleared and induced endo-lysosomal membrane permeabilization. Remarkably, reducing INS (insulin)-IGF1 (insulin-like growth factor 1) signaling provided protection by maintaining endo-lysosomal integrity. This study suggests that the degradation of lysosomal substrates is coordinated across different tissues in metazoan organisms. Because the chronic dissemination of poorly degradable disease proteins into neighboring tissues exerts a non-cell autonomous toxicity, this implies that restoring endo-lysosomal function not only in cells with pathological inclusions, but also in apparently unaffected cell types might help to halt disease progression.Abbreviations: AD: Alzheimer disease; BM: basement membrane; BWM: body wall muscle; CEP: cephalic sensilla; CLEM: correlative light and electron microscopy; CTNS-1: cystinosin (lysosomal protein) homolog; DA: dopaminergic; DAF-2: abnormal dauer formation; ECM: extracellular matrix; FLIM: fluorescence lifetime imaging microscopy; fps: frames per second; GFP: green fluorescent protein; HPF: high pressure freezing; IGF1: insulin-like growth factor 1; INS: insulin; KD: knockdown; LMP: lysosomal membrane permeabilization; MVB: multivesicular body; NOC: nocodazole; PD: Parkinson disease; RFP: red fluorescent protein; RNAi: RNA interference; sfGFP: superfolder GFP; SNCA: synuclein alpha; TEM: transmission electron microscopy; TNTs: tunneling nanotubes; TCSPC: time correlated single photon counting; YFP: yellow fluorescent protein.

Plasmodium chaperonin TRiC/CCT identified as a target of the antihistamine clemastine using parallel chemoproteomic strategy

The antihistamine clemastine inhibits multiple stages of the Plasmodium parasite that causes malaria, but the molecular targets responsible for its parasite inhibition were unknown. Here, we applied parallel chemoproteomic platforms to discover the mechanism of action of clemastine and identify that clemastine binds to the Plasmodium falciparum TCP-1 ring complex or chaperonin containing TCP-1 (TRiC/CCT), an essential heterooligomeric complex required for de novo cytoskeletal protein folding. Clemastine destabilized all eight P. falciparum TRiC subunits based on thermal proteome profiling (TPP). Further analysis using stability of proteins from rates of oxidation (SPROX) revealed a clemastine-induced thermodynamic stabilization of the Plasmodium TRiC delta subunit, suggesting an interaction with this protein subunit. We demonstrate that clemastine reduces levels of the major TRiC substrate tubulin in P. falciparum parasites. In addition, clemastine treatment leads to disorientation of Plasmodium mitotic spindles during the asexual reproduction and results in aberrant tubulin morphology suggesting protein aggregation. This clemastine-induced disruption of TRiC function is not observed in human host cells, demonstrating a species selectivity required for targeting an intracellular human pathogen. Our findings encourage larger efforts to apply chemoproteomic methods to assist in target identification of antimalarial drugs and highlight the potential to selectively target Plasmodium TRiC-mediated protein folding for malaria intervention.

Application of transcriptome analysis: Oxidative stress, inflammation and microtubule activity disorder caused by ammonia exposure may be the primary factors of intestinal microvilli deficiency in chicken

Ammonia (NH₃), an inhaled harmful gas, is not only an important volatile in fertilizer production and ranching, but also the main basic component of haze. However, the effect and mechanism of NH₃ on the intestines are still unclear. To investigate the intestinal toxicity of NH₃ inhalation, morphological changes, transcriptome profiles and oxidative stress indicators of jejunum in broiler chicken exposed to NH₃ for 42 days were examined. Results of morphological observation showed that NH₃ exposure caused deficiency of jejunal microvilli and neutrophil infiltration. Transcriptomics sequencing identified 677 differential expressed genes (DEGs) including 358 up-regulated genes and 319 down-regulated genes. Enrichment analysis of obtained DEGs by Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) found that biological functions and pathways affected by NH₃ included antioxidant function, inflammation, microtubule and nutrition transport. Relative genes validation and chemical detection confirmed that NH₃-induced oxidative stress by activating CYPs and inhibiting antioxidant enzymes promoted inflammatory response and decreased microtubule activity, thus destroying the balance of nutritional transporters. Our study perfects the injurious mechanism of NH₃ exposure and provides a new insight and method for environmental risk assessment.

1-Deoxydihydroceramide causes anoxic death by impairing chaperonin-mediated protein folding

Ischaemic heart disease and stroke are the most common causes of death worldwide. Anoxia, defined as the lack of oxygen, is commonly seen in both these pathologies and triggers profound metabolic and cellular changes. Sphingolipids have been implicated in anoxia injury, but the pathomechanism is unknown. Here we show that anoxia-associated injury causes accumulation of the non-canonical sphingolipid 1-deoxydihydroceramide (DoxDHCer). Anoxia causes an imbalance between serine and alanine resulting in a switch from normal serine-derived sphinganine biosynthesis to non-canonical alanine-derived 1-deoxysphinganine. 1-Deoxysphinganine is incorporated into DoxDHCer, which impairs actin folding via the cytosolic chaperonin TRiC, leading to growth arrest in yeast, increased cell death upon anoxia-reoxygenation in worms and ischaemia-reperfusion injury in mouse hearts. Prevention of DoxDHCer accumulation in worms and in mouse hearts resulted in decreased anoxia-induced injury. These findings unravel key metabolic changes during oxygen deprivation and point to novel strategies to avoid tissue damage and death.

A V0-ATPase-dependent apical trafficking pathway maintains the polarity of the intestinal absorptive membrane

Intestine function relies on the strong polarity of intestinal epithelial cells and the array of microvilli forming a brush border at their luminal pole. Combining a genetic RNA interference (RNAi) screen with in vivo super-resolution imaging in the Caenorhabditiselegans intestine, we found that the V0 sector of the vacuolar ATPase (V0-ATPase) controls a late apical trafficking step, involving Ras-related protein 11 (RAB-11)+ endosomes and the N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) synaptosome-associated protein 29 (SNAP-29), and is necessary to maintain the polarized localization of both apical polarity modules and brush border proteins. We show that the V0-ATPase pathway also genetically interacts with glycosphingolipids and clathrin in enterocyte polarity maintenance. Finally, we demonstrate that silencing of the V0-ATPase fully recapitulates the severe structural, polarity and trafficking defects observed in enterocytes from individuals with microvillus inclusion disease (MVID) and use this new in vivo MVID model to follow the dynamics of microvillus inclusions. Thus, we describe a new function for V0-ATPase in apical trafficking and epithelial polarity maintenance and the promising use of the C. elegans intestine as an in vivo model to better understand the molecular mechanisms of rare genetic enteropathies.

Dietary Restriction Extends Lifespan through Metabolic Regulation of Innate Immunity

Chronic inflammation predisposes to aging-associated disease, but it is unknown whether immunity regulation might be important for extending healthy lifespan. Here we show that in C. elegans, dietary restriction (DR) extends lifespan by modulating a conserved innate immunity pathway that is regulated by p38 signaling and the transcription factor ATF-7. Longevity from DR depends upon p38-ATF-7 immunity being intact but downregulated to a basal level. p38-ATF-7 immunity accelerates aging when hyperactive, influences lifespan independently of pathogen exposure, and is activated by nutrients independently of mTORC1, a major DR mediator. Longevity from reduced insulin/IGF-1 signaling (rIIS) also involves p38-ATF-7 downregulation, with signals from DAF-16/FOXO reducing food intake. We conclude that p38-ATF-7 is an immunometabolic pathway that senses bacterial and nutrient signals, that immunity modulation is critical for DR, and that DAF-16/FOXO couples appetite to growth regulation. These conserved mechanisms may influence aging in more complex organisms.

The role of the molecular chaperone CCT in protein folding and mediation of cytoskeleton-associated processes: implications for cancer cell biology

The chaperonin-containing tailless complex polypeptide 1 (CCT) is required in vivo for the folding of newly synthesized tubulin and actin proteins and is thus intrinsically connected to all cellular processes that rely on the microtubule and actin filament components of the cytoskeleton, both of which are highly regulated and dynamic assemblies. In addition to CCT acting as a protein folding oligomer, further modes of CCT action mediated either by the CCT oligomer itself or via CCT subunits in their monomeric forms can influence processes associated with assembled actin filaments and microtubules. Thus, there is an extended functional role for CCT with regard to its major folding substrates with a complex interplay between CCT as folding machine for tubulin/actin and as a modulator of processes involving the assembled cytoskeleton. As cell division, directed cell migration, and invasion are major drivers of cancer development and rely on the microtubule and actin filament components of the cytoskeleton, CCT activity is fundamentally linked to cancer. Furthermore, the CCT oligomer also folds proteins connected to cell cycle progression and interacts with several other proteins that are linked to cancer such as tumor-suppressor proteins and regulators of the cytoskeleton, while CCT monomer function can influence cell migration. Thus, understanding CCT activity is important for many aspects of cancer cell biology and may reveal new ways to target tumor growth and invasion.

TRiC/CCT Chaperonin: Structure and Function

The eukaryotic group II chaperonin TRiC/CCT assists the folding of 10% of cytosolic proteins including many key structural and regulatory proteins. TRiC plays an essential role in maintaining protein homeostasis, and dysfunction of TRiC is closely related to human diseases including cancer and neurodegenerative diseases. TRiC consists of eight paralogous subunits, each of which plays a specific role in the assembly, allosteric cooperativity, and substrate recognition and folding of this complex macromolecular machine. TRiC-mediated substrate folding is regulated through its ATP-driven conformational changes. In recent years, progresses have been made on the structure, subunit arrangement, conformational cycle, and substrate folding of TRiC. Additionally, accumulating evidences also demonstrate the linkage between TRiC oligomer or monomer and diseases. In this review, we focus on the TRiC structure itself, TRiC assisted substrate folding, TRiC and disease, and the potential therapeutic application of TRiC in various diseases.

Comparative genomic analysis of the human and nematode Caenorhabditis elegans uncovers potential reproductive genes and disease associations in humans

Reproduction is an important biological process. However, studies of human reproduction at the molecular level are limited due to the difficulty of performing in vivo studies. Hence, a mechanistic understanding of human reproduction remains still poor. Thus, it is important to use an alternative model organism for mechanistic studies of human reproduction. In this study, we used the nematode Caenorhabditis elegans as a model for studying human reproduction and identified 61 human and 535 worm reproductive genes through a combination of comparative genomic and Gene Ontology (GO) analyses. Interestingly, in terms of sex specificity, the number of male-specific genes was greater than the number of female-specific genes. Gene enrichment analysis identified biologically significant processes such as protein localization to cajal bodies/telomeres/nuclear bodies/chromosomes, helicase activity, pyrimidine biosynthesis, and determination of adult lifespan. Regarding the analysis of human reproductive diseases among the identified genes, 10 and 12 genes were identified in the human- and C. elegans-based analyses, respectively. In addition, RNA interference knockdown of a newly identified F52H2.6/DHCR24 gene increased brood size and ovulation/egg-laying rate in C. elegans. Therefore, gene identification, disease associations, and a proof-of-concept experiment using C. elegans will not only provide insights into mechanistic study of human reproduction, but also demonstrate the utility in studying human reproduction.

The structure and evolution of eukaryotic chaperonin-containing TCP-1 and its mechanism that folds actin into a protein spring

Actin is folded to its native state in eukaryotic cytosol by the sequential allosteric mechanism of the chaperonin-containing TCP-1 (CCT). The CCT machine is a double-ring ATPase built from eight related subunits, CCT1–CCT8. Non-native actin interacts with specific subunits and is annealed slowly through sequential binding and hydrolysis of ATP around and across the ring system. CCT releases a folded but soft ATP-G-actin monomer which is trapped 80 kJ/mol uphill on the folding energy surface by its ATP-Mg2+/Ca2+ clasp. The energy landscape can be re-explored in the actin filament, F-actin, because ATP hydrolysis produces dehydrated and more compact ADP-actin monomers which, upon application of force and strain, are opened and closed like the elements of a spring. Actin-based myosin motor systems underpin a multitude of force generation processes in cells and muscles. We propose that the water surface of F-actin acts as a low-binding energy, directional waveguide which is recognized specifically by the myosin lever-arm domain before the system engages to form the tight-binding actomyosin complex. Such a water-mediated recognition process between actin and myosin would enable symmetry breaking through fast, low energy initial binding events. The origin of chaperonins and the subsequent emergence of the CCT–actin system in LECA (last eukaryotic common ancestor) point to the critical role of CCT in facilitating phagocytosis during early eukaryotic evolution and the transition from the bacterial world. The coupling of CCT-folding fluxes to the cell cycle, cell size control networks and cancer are discussed together with directions for further research.

SFT-4/Surf4 control ER export of soluble cargo proteins and participate in ER exit site organization

Saegusa et al. report that the SFT-4/Surf4 cargo receptor homologs mediate export of soluble proteins such as lipoproteins from the ER. Efficient export of yolk proteins in C. elegans intestinal cells, or apoliprotein trafficking in human hepatocytes, requires SFT-4/Surf4 so that they may enhance secretion by maintaining ER exit site organization.

Lipoproteins regulate the overall lipid homeostasis in animals. However, the molecular mechanisms underlying lipoprotein trafficking remain poorly understood. Here, we show that SFT-4, a Caenorhabditis elegans homologue of the yeast Erv29p, is essential for the endoplasmic reticulum (ER) export of the yolk protein VIT-2, which is synthesized as a lipoprotein complex. SFT-4 loss strongly inhibits the ER exit of yolk proteins and certain soluble cargo proteins in intestinal cells. SFT-4 predominantly localizes at ER exit sites (ERES) and physically interacts with VIT-2 in vivo, which suggests that SFT-4 promotes the ER export of soluble proteins as a cargo receptor. Notably, Surf4, a mammalian SFT-4 homologue, physically interacts with apolipoprotein B, a very-low-density lipoprotein core protein, and its loss causes ER accumulation of apolipoprotein B in human hepatic HepG2 cells. Interestingly, loss of SFT-4 and Surf4 reduced the number of COPII-positive ERES. Thus, SFT-4 and Surf4 regulate the export of soluble proteins, including lipoproteins, from the ER and participate in ERES organization in animals.

Chaperonin-containing T‑complex protein 1 subunit 8 promotes cell migration and invasion in human esophageal squamous cell carcinoma by regulating α-actin and β-tubulin expression

The chaperonin-containing T‑complex protein 1 (CCT) has eight subunits, CCT 1-8, which are dysregulated in several types of cancer. To determine how subunit 8 (CCT8) influences the development of esophageal squamous cell carcinoma (ESCC), immunohistochemistry and western blot analysis were performed on 128 ESCC samples in the present study to measure the expression of CCT8. The prognostic value of CCT8 was analyzed using univariate and multivariate survival analyses. CCT8 knockdown in ESCC cells was performed and subsequently, the migration and invasion of ESCC cells was assessed. The results of immunohistochemistry and western blot analysis of ESCC tissue indicated that the expression of CCT8 in tumor tissues from patients with lymph node metastasis (LNM) was high whereas its expression in tissues from those without LNM was low. In addition, the overall survival rate of patients with high CCT8 expression was poor. It was demonstrated that CCT8 influenced the migration and invasion of ESCC cells by regulating α-actin and β-tubulin. Following CCT8 knockdown, cells were treated with cisplatin; it was demonstrated that α-actin and β-tubulin were downregulated and that cell apoptosis was enhanced. These data confirm that α-actin and β-tubulin are regulated by CCT8, and that increased CCT8 expression is associated with poor patient prognosis and cisplatin resistance in ESCC.

Reconsidering an active role for G-actin in cytoskeletal regulation

Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell. Many of these structures are highly dynamic and to maintain them, the cell relies on a large reserve of monomers. Classically, the G-actin pool has been thought of as homogenous. However, recent work has shown that actin monomers can exist in distinct groups that can be targeted to specific networks, where they drive and modify filament assembly in ways that can have profound effects on cellular behavior. This Review focuses on the potential factors that could create functionally distinct pools of actin monomers in the cell, including differences between the actin isoforms and the regulation of G-actin by monomer binding proteins, such as profilin and thymosin β4. Owing to difficulties in studying and visualizing G-actin, our knowledge over the precise role that specific actin monomer pools play in regulating cellular actin dynamics remains incomplete. Here, we discuss some of these unanswered questions and also provide a summary of the methodologies currently available for the imaging of G-actin.

Characterization and Expression Pattern Analysis of the T-Complex Protein-1 Zeta Subunit in Musca domestica L (Diptera)

Chaperonins, belonging to the T-complex protein-1 (TCP-1) family, assist in the correct folding of nascent and misfolded proteins. It is well-known that in mammals, the zeta subunit of the TCP-1 complex (TCP-1ζ) plays a vital role in the folding and assembly of cytoskeleta proteins. This study reported for the first time the cloning, characterization and expression pattern analysis of the TCP-1ζ from Musca domestica, which was named as MdTCP-1ζ. The MdTCP-1ζ cDNA is 1,803 bp long with a 1,596 bp open reading frame that encodes a protein with 531 bp amino acids. The analysis of the transcriptional profile of MdTCP-1ζ using qRT-PCR revealed relatively high expression in the salivary glands and trachea at the tissues while among the developmental stages. The highest expression was observed only in the eggs suggesting that the MdTCP-1ζ may play a role in embryonic development. The expression of MdTCP-1ζ was also significantly induced after exposure to short-term heat shock and infection by Escherichia coli, Staphylococcus aureus, or Candida albicans. This suggested that MdTCP-1ζ may take part in the immune responses of housefly and perhaps contribute to the protection against cellular injury.

Cellular Proteomes Drive Tissue-Specific Regulation of the Heat Shock Response

The heat shock response (HSR) is a cellular stress response that senses protein misfolding and restores protein folding homeostasis, or proteostasis. We previously identified an HSR regulatory network in Caenorhabditis elegans consisting of highly conserved genes that have important cellular roles in maintaining proteostasis. Unexpectedly, the effects of these genes on the HSR are distinctly tissue-specific. Here, we explore this apparent discrepancy and find that muscle-specific regulation of the HSR by the TRiC/CCT chaperonin is not driven by an enrichment of TRiC/CCT in muscle, but rather by the levels of one of its most abundant substrates, actin. Knockdown of actin subunits reduces induction of the HSR in muscle upon TRiC/CCT knockdown; conversely, overexpression of an actin subunit sensitizes the intestine so that it induces the HSR upon TRiC/CCT knockdown. Similarly, intestine-specific HSR regulation by the signal recognition particle (SRP), a component of the secretory pathway, is driven by the vitellogenins, some of the most abundant secretory proteins. Together, these data indicate that the specific protein folding requirements from the unique cellular proteomes sensitizes each tissue to disruption of distinct subsets of the proteostasis network. These findings are relevant for tissue-specific, HSR-associated human diseases such as cancer and neurodegenerative diseases. Additionally, we characterize organismal phenotypes of actin overexpression including a shortened lifespan, supporting a recent hypothesis that maintenance of the actin cytoskeleton is an important factor for longevity.

A Differentiation Transcription Factor Establishes Muscle-Specific Proteostasis in Caenorhabditis elegans

Safeguarding the proteome is central to the health of the cell. In multi-cellular organisms, the composition of the proteome, and by extension, protein-folding requirements, varies between cells. In agreement, chaperone network composition differs between tissues. Here, we ask how chaperone expression is regulated in a cell type-specific manner and whether cellular differentiation affects chaperone expression. Our bioinformatics analyses show that the myogenic transcription factor HLH-1 (MyoD) can bind to the promoters of chaperone genes expressed or required for the folding of muscle proteins. To test this experimentally, we employed HLH-1 myogenic potential to genetically modulate cellular differentiation of Caenorhabditis elegans embryonic cells by ectopically expressing HLH-1 in all cells of the embryo and monitoring chaperone expression. We found that HLH-1-dependent myogenic conversion specifically induced the expression of putative HLH-1-regulated chaperones in differentiating muscle cells. Moreover, disrupting the putative HLH-1-binding sites on ubiquitously expressed daf-21(Hsp90) and muscle-enriched hsp-12.2(sHsp) promoters abolished their myogenic-dependent expression. Disrupting HLH-1 function in muscle cells reduced the expression of putative HLH-1-regulated chaperones and compromised muscle proteostasis during and after embryogenesis. In turn, we found that modulating the expression of muscle chaperones disrupted the folding and assembly of muscle proteins and thus, myogenesis. Moreover, muscle-specific over-expression of the DNAJB6 homolog DNJ-24, a limb-girdle muscular dystrophy-associated chaperone, disrupted the muscle chaperone network and exposed synthetic motility defects. We propose that cellular differentiation could establish a proteostasis network dedicated to the folding and maintenance of the muscle proteome. Such cell-specific proteostasis networks can explain the selective vulnerability that many diseases of protein misfolding exhibit even when the misfolded protein is ubiquitously expressed.

Molecular chaperones protect proteins from misfolding and aggregation. In multi-cellular organisms, the composition and expression levels of chaperones vary between tissues. However, little is known of how such differential expression is regulated. We hypothesized that the cellular differentiation that regulates the cell-type specific expression program may be involved in establishing a cell-type specific chaperone network. To test this possibility, we addressed the myogenic commitment transcription factor HLH-1 (CeMyoD) that converts embryonic cells to muscle cells in Caenorhabditis elegans. We demonstrated that HLH-1 regulates the expression of muscle chaperones during muscle differentiation. Moreover, we showed that HLH-1-dependent expression of chaperones is required for embryonic development and muscle function. We propose that cellular differentiation results in cell-specific differences in the chaperone network that may be detrimental in terms of the susceptibility of neurons and muscle cells to protein misfolding diseases.

A novel function for the MAP kinase SMA-5 in intestinal tube stability

In vivo evidence links SMA-5 to the maintenance of the apical domain in the Caenorhabditis elegans intestine. sma-5 mutations induce morphological and biochemical changes of the intermediate filament system, demonstrating the close relationship between posttranslational modification and structural integrity of the evolutionarily conserved intestinal cytoskeleton.

Intermediate filaments are major cytoskeletal components whose assembly into complex networks and isotype-specific functions are still largely unknown. Caenorhabditis elegans provides an excellent model system to study intermediate filament organization and function in vivo. Its intestinal intermediate filaments localize exclusively to the endotube, a circumferential sheet just below the actin-based terminal web. A genetic screen for defects in the organization of intermediate filaments identified a mutation in the catalytic domain of the MAP kinase 7 orthologue sma-5(kc1). In sma-5(kc1) mutants, pockets of lumen penetrate the cytoplasm of the intestinal cells. These membrane hernias increase over time without affecting epithelial integrity and polarity. A more pronounced phenotype was observed in the deletion allele sma-5(n678) and in intestine-specific sma-5(RNAi). Besides reduced body length, an increased time of development, reduced brood size, and reduced life span were observed in the mutants, indicating compromised food uptake. Ultrastructural analyses revealed that the luminal pockets include the subapical cytoskeleton and coincide with local thinning and gaps in the endotube that are often enlarged in other regions. Increased intermediate filament phosphorylation was detected by two-dimensional immunoblotting, suggesting that loss of SMA-5 function leads to reduced intestinal tube stability due to altered intermediate filament network phosphorylation.

Intermediate Filaments and Polarization in the Intestinal Epithelium

The cytoplasmic intermediate filament cytoskeleton provides a tissue-specific three-dimensional scaffolding with unique context-dependent organizational features. This is particularly apparent in the intestinal epithelium, in which the intermediate filament network is localized below the apical terminal web region and is anchored to the apical junction complex. This arrangement is conserved from the nematode Caenorhabditis elegans to humans. The review summarizes compositional, morphological and functional features of the polarized intermediate filament cytoskeleton in intestinal cells of nematodes and mammals. We emphasize the cross talk of intermediate filaments with the actin- and tubulin-based cytoskeleton. Possible links of the intermediate filament system to the distribution of apical membrane proteins and the cell polarity complex are highlighted. Finally, we discuss how these properties relate to the establishment and maintenance of polarity in the intestine.

Noncentrosomal microtubules in C. elegans epithelia

The microtubule cytoskeleton has a dual contribution to cell organization. First, microtubules help displace chromosomes and provide tracks for organelle transport. Second, microtubule rigidity confers specific mechanical properties to cells, which are crucial in cilia or mechanosensory structures. Here we review the recently uncovered organization and functions of noncentrosomal microtubules in C. elegans epithelia, focusing on how they contribute to nuclear positioning and protein transport. In addition, we describe recent data illustrating how the microtubule and actin cytoskeletons interact to achieve those functions.

Interplay between redox and protein homeostasis

The subcellular compartments of eukaryotic cells are characterized by different redox environments. Whereas the cytosol, nucleus and mitochondria are more reducing, the endoplasmic reticulum represents a more oxidizing environment. As the redox level controls the formation of intra- and inter-molecular disulfide bonds, the folding of proteins is tightly linked to its environment. The proteostasis network of each compartment needs to be adapted to the compartmental redox properties. In addition to chaperones, also members of the thioredoxin superfamily can influence the folding of proteins by regulation of cysteine reduction/oxidation. This review will focus on thioredoxin superfamily members and chaperones of C. elegans, which play an important role at the interface between redox and protein homeostasis. Additionally, this review will highlight recent methodological developments on in vivo and in vitro assessment of the redox state and their application to provide insights into the high complexity of redox and proteostasis networks of C. elegans.

LIN-41 inactivation leads to delayed centrosome elimination and abnormal chromosome behavior during female meiosis in Caenorhabditis elegans

During oogenesis, two successive meiotic cell divisions occur without functional centrosomes because of the inactivation and subsequent elimination of maternal centrosomes during the diplotene stage of meiosis I. Despite being a conserved phenomenon in most metazoans, the means by which this centrosome behavior is controlled during female meiosis remain elusive. Here, we conducted a targeted RNAi screening in the Caenorhabditis elegans gonad to identify novel regulators of centrosome behavior during oogenesis. We screened 513 genes known to be essential for embryo production and directly visualized GFP-γ-tubulin to monitor centrosome behavior at all stages of oogenesis. In the screening, we found that RNAi-mediated inactivation of 33 genes delayed the elimination of GFP-γ-tubulin at centrosomes during oogenesis, whereas inactivation of nine genes accelerated the process. Depletion of the TRIM-NHL protein LIN-41 led to a significant delay in centrosome elimination and to the separation and reactivation of centrosomes during oogenesis. Upon LIN-41 depletion, meiotic chromosomes were abnormally condensed and pulled toward one of the two spindle poles around late pachytene even though the spindle microtubules emanated from both centrosomes. Overall, our work provides new insights into the regulation of centrosome behavior to ensure critical meiotic events and the generation of intact oocytes.

Chaperonin TRiC/CCT Modulates the Folding and Activity of Leukemogenic Fusion Oncoprotein AML1-ETO

AML1-ETO is the most common fusion oncoprotein causing acute myeloid leukemia (AML), a disease with a 5-year survival rate of only 24%. AML1-ETO functions as a rogue transcription factor, altering the expression of genes critical for myeloid cell development and differentiation. Currently, there are no specific therapies for AML1-ETO-positive AML. While known for decades to be the translational product of a chimeric gene created by the stable chromosome translocation t(8;21)(q22;q22), it is not known how AML1-ETO achieves its native and functional conformation or whether this process can be targeted for therapeutic benefit. Here, we show that the biosynthesis and folding of the AML1-ETO protein is facilitated by interaction with the essential eukaryotic chaperonin TRiC (or CCT). We demonstrate that a folding intermediate of AML1-ETO binds to TRiC directly, mainly through its β-strand rich, DNA-binding domain (AML-(1-175)), with the assistance of HSP70. Our results suggest that TRiC contributes to AML1-ETO proteostasis through specific interactions between the oncoprotein's DNA-binding domain, which may be targeted for therapeutic benefit.

Contribution of the Type II Chaperonin, TRiC/CCT, to Oncogenesis

The folding of newly synthesized proteins and the maintenance of pre-existing proteins are essential in sustaining a living cell. A network of molecular chaperones tightly guides the folding, intracellular localization, and proteolytic turnover of proteins. Many of the key regulators of cell growth and differentiation have been identified as clients of molecular chaperones, which implies that chaperones are potential mediators of oncogenesis. In this review, we briefly provide an overview of the role of chaperones, including HSP70 and HSP90, in cancer. We further summarize and highlight the emerging the role of chaperonin TRiC (T-complex protein-1 ring complex, also known as CCT) in the development and progression of cancer mediated through its critical interactions with oncogenic clients that modulate growth deregulation, apoptosis, and genome instability in cancer cells. Elucidation of how TRiC modulates the folding and function of oncogenic clients will provide strategies for developing novel cancer therapies.