Aneuploidy and proteotoxic stress in cancer.
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ABSTRACT:
SUBMITTER: Donnelly N
PROVIDER: S-EPMC4904904 | biostudies-other | 2015 Apr-Jun
REPOSITORIES: biostudies-other
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Project description:Gains or losses of entire chromosomes lead to aneuploidy, a condition tolerated poorly in all eukaryotes analyzed to date. How aneuploidy affects organismal and cellular physiology is poorly understood. We found that aneuploid budding yeast cells are under proteotoxic stress. Aneuploid strains are prone to aggregation of endogenous proteins as well as of ectopically expressed hard-to-fold proteins such as those containing polyglutamine (polyQ) stretches. Protein aggregate formation in aneuploid yeast strains is likely due to limiting protein quality-control systems, since the proteasome and at least one chaperone family, Hsp90, are compromised in many aneuploid strains. The link between aneuploidy and the formation and persistence of protein aggregates could have important implications for diseases such as cancer and neurodegeneration.
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Project description:BACKGROUND:The protein homeostasis (proteostasis) network maintains balanced protein synthesis, folding, transport, and degradation within a cell. Failure to maintain proteostasis is associated with aging and disease, leading to concerted efforts to study how the network responds to various proteotoxic stresses. This is often accomplished using ectopic overexpression of well-characterized, model misfolded protein substrates. However, how cells tolerate large-scale, diverse burden to the proteostasis network is not understood. Aneuploidy, the state of imbalanced chromosome content, adversely affects the proteostasis network by dysregulating the expression of hundreds of proteins simultaneously. Using aneuploid haploid yeast cells as a model, we address whether cells can tolerate large-scale, diverse challenges to the proteostasis network. RESULTS:Here we characterize several aneuploid Saccharomyces cerevisiae strains isolated from a collection of stable, randomly generated yeast aneuploid cells. These strains exhibit robust growth and resistance to multiple drugs which induce various forms of proteotoxic stress. Whole genome re-sequencing of the strains revealed this was not the result of genetic mutations, and transcriptome profiling combined with ribosome footprinting showed that genes are expressed and translated in accordance to chromosome copy number. In some strains, various facets of the proteostasis network are mildly upregulated without chronic activation of environmental stress response or heat shock response pathways. No severe defects were observed in the degradation of misfolded proteins, using model misfolded substrates of endoplasmic reticulum-associated degradation or cytosolic quality control pathways, and protein biosynthesis capacity was not impaired. CONCLUSIONS:We show that yeast strains of some karyotypes in the genetic background studied here can tolerate the large aneuploidy-associated burden to the proteostasis machinery without genetic changes, dosage compensation, or activation of canonical stress response pathways. We suggest that proteotoxic stress, while common, is not always an obligate consequence of aneuploidy, but rather certain karyotypes and genetic backgrounds may be able to tolerate the excess protein burden placed on the protein homeostasis machinery. This may help clarify how cancer cells are paradoxically both highly aneuploid and highly proliferative at the same time.
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Project description:The molecular mechanism responsible that determines cell fate after mitotic slippage is unclear. Here we investigate the post-mitotic effects of different mitotic aberrations--misaligned chromosomes produced by CENP-E inhibition and monopolar spindles resulting from Eg5 inhibition. Eg5 inhibition in cells with an impaired spindle assembly checkpoint (SAC) induces polyploidy through cytokinesis failure without a strong anti-proliferative effect. In contrast, CENP-E inhibition causes p53-mediated post-mitotic apoptosis triggered by chromosome missegregation. Pharmacological studies reveal that aneuploidy caused by the CENP-E inhibitor, Compound-A, in SAC-attenuated cells causes substantial proteotoxic stress and DNA damage. Polyploidy caused by the Eg5 inhibitor does not produce this effect. Furthermore, p53-mediated post-mitotic apoptosis is accompanied by aneuploidy-associated DNA damage response and unfolded protein response activation. Because Compound-A causes p53 accumulation and antitumour activity in an SAC-impaired xenograft model, CENP-E inhibitors could be potential anticancer drugs effective against SAC-impaired tumours.
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Project description:The protein homeostasis (proteostasis) network maintains balanced protein synthesis, folding, transport and degradation within a cell. Because failure to maintain proteostasis is associated with aging and disease, a concerted effort has been placed on studying how the proteostasis network responds to various stresses. Typically, this is accomplished using ectopic overexpression of well-characterized, model misfolded protein substrates; however, how cells tolerate large-scale, diverse burden to the proteostasis network is not understood. Aneuploidy, the state of imbalanced chromosome content, adversely affects the proteostasis network by dysregulating the expression of hundreds of proteins simultaneously. Using aneuploid yeast cells as a model, we address what compensatory adjustments enable cells to tolerate large-scale, diverse challenges to the proteostasis network. Here we show adapted aneuploid Saccharomyces cerevisiae strains that exhibit robust growth and enhanced stress tolerance associated with enhancement of translation, folding, and quality control systems without genetic changes or activation of canonical stress response pathways.
2020-08-17 | GSE140733 | GEO
Project description:Although severe stress can elicit toxicity, mild stress often elicits adaptations. Here we review the literature on stress-induced adaptations versus stress sensitization in models of neurodegenerative diseases. We also describe our recent findings that chronic proteotoxic stress can elicit adaptations if the dose is low but that high-dose proteotoxic stress sensitizes cells to subsequent challenges. In these experiments, long-term, low-dose proteasome inhibition elicited protection in a superoxide dismutase-dependent manner. In contrast, acute, high-dose proteotoxic stress sensitized cells to subsequent proteotoxic challenges by eliciting catastrophic loss of glutathione. However, even in the latter model of synergistic toxicity, several defensive proteins were upregulated by severe proteotoxicity. This led us to wonder whether high-dose proteotoxic stress can elicit protection against subsequent challenges in astrocytes, a cell type well known for their resilience. In support of this new hypothesis, we found that the astrocytes that survived severe proteotoxicity became harder to kill. The adaptive mechanism was glutathione dependent. If these findings can be generalized to the human brain, similar endogenous adaptations may help explain why neurodegenerative diseases are so delayed in appearance and so slow to progress. In contrast, sensitization to severe stress may explain why defenses eventually collapse in vulnerable neurons.
| S-EPMC3960953 | biostudies-literature
Project description:Through dynamic activities of conserved master transcription factors (mTFs), the unfolded protein response (UPR) relieves proteostasis imbalance of the endoplasmic reticulum (ER), a condition known as ER stress1,2. Because dysregulated UPR is lethal, the competence for fate changes of the UPR mTFs must be tightly controlled3,4. However, the molecular mechanisms underlying regulatory dynamics of mTFs remain largely elusive. Here, we identified the abscisic acid-related regulator G-class bZIP TF2 (GBF2) and the cis-regulatory element G-box as regulatory components of the plant UPR led by the mTFs, bZIP28 and bZIP60. We demonstrate that, by competing with the mTFs at G-box, GBF2 represses UPR gene expression. Conversely, a gbf2 null mutation enhances UPR gene expression and suppresses the lethality of a bzip28 bzip60 mutant in unresolved ER stress. By demonstrating that GBF2 functions as a transcriptional repressor of the UPR, we address the long-standing challenge of identifying shared signalling components for a better understanding of the dynamic nature and complexity of stress biology. Furthermore, our results identify a new layer of UPR gene regulation hinged upon an antagonistic mTFs-GFB2 competition for proteostasis and cell fate determination.
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Project description:The mechanisms by which cells adapt to proteotoxic stress are largely unknown, but are key to understanding how tumor cells, particularly in vivo, are largely resistant to proteasome inhibitors. Analysis of cancer cell lines, mouse xenografts and patient-derived tumor samples all showed an association between mitochondrial metabolism and proteasome inhibitor sensitivity. When cells were forced to use oxidative phosphorylation rather than glycolysis, they became proteasome-inhibitor resistant. This mitochondrial state, however, creates a unique vulnerability: sensitivity to the small molecule compound elesclomol. Genome-wide CRISPR-Cas9 screening showed that a single gene, encoding the mitochondrial reductase FDX1, could rescue elesclomol-induced cell death. Enzymatic function and nuclear-magnetic-resonance-based analyses further showed that FDX1 is the direct target of elesclomol, which promotes a unique form of copper-dependent cell death. These studies explain a fundamental mechanism by which cells adapt to proteotoxic stress and suggest strategies to mitigate proteasome inhibitor resistance.
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Project description:The regulation of protein synthesis is essential for maintaining cellular homeostasis, especially during stress responses, and its dysregulation could underlie the development of human diseases. The critical step during translation regulation is the phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α). Here we report the identification of a direct kinase of eIF2α, microtubule affinity-regulating kinase 2 (MARK2), which phosphorylates eIF2α in response to proteotoxic stress. The activity of MARK2 was confirmed in the cells lacking the 4 previously known eIF2α kinases. MARK2 itself was found to be a substrate of protein kinase C delta (PKCδ), which serves as a sensor for protein misfolding stress through a dynamic interaction with heat shock protein 90 (HSP90). Both MARK2 and PKCδ are activated via phosphorylation in proteotoxicity-associated neurodegenerative mouse models and in human patients with amyotrophic lateral sclerosis (ALS). These results reveal a PKCδ-MARK2-eIF2α cascade that may play a critical role in cellular proteotoxic stress responses and human diseases.
| S-EPMC7951919 | biostudies-literature
Project description:Leiomyosarcoma (LMS) is aggressive cancer with few therapeutic options. LMS cells are more sensitive to proteotoxic stress compared to normal smooth muscle cells. We used small compound 2c to induce proteotoxic stress and compare the transcriptomic adaptations of immortalized human uterine smooth muscle cells (HUtSMC) and LMS cells SK-UT-1. We found that the expression of the heat shock proteins (HSPs) gene family is upregulated with higher efficiency in normal cells. In contrast, the upregulation of BH3-only proteins is higher in LMS cells. HSF1, the master regulator of HSP transcription, is sequestered into transcriptionally incompetent nuclear foci only in LMS cells, which explains the lower HSP upregulation. We also found that several compounds can enhance the cell death response to proteotoxic stress. Specifically, when low doses were used, an inhibitor of salt-inducible kinases (SIKs) and the inhibitor of IRE1α, a key element of the unfolded protein response (UPR), support proteotoxic-induced cell death with strength in LMS cells and without effects on the survival of normal cells. Overall, our data provide an explanation for the higher susceptibility of LMS cells to proteotoxic stress and suggest a potential option for co-treatment strategies.
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Project description:Conditions of chronic stress are associated with genetic instability in many organisms, but the roles of stress responses in mutagenesis have so far been elucidated only in bacteria. Here, we present data demonstrating that the environmental stress response (ESR) in yeast functions in mutagenesis induced by proteotoxic stress. We show that the drug canavanine causes proteotoxic stress, activates the ESR, and induces mutagenesis at several loci in an ESR-dependent manner. Canavanine-induced mutagenesis also involves translesion DNA polymerases Rev1 and Pol? and non-homologous end joining factor Ku. Furthermore, under conditions of chronic sub-lethal canavanine stress, deletions of Rev1, Pol?, and Ku-encoding genes exhibit genetic interactions with ESR mutants indicative of ESR regulating these mutagenic DNA repair processes. Analyses of mutagenesis induced by several different stresses showed that the ESR specifically modulates mutagenesis induced by proteotoxic stress. Together, these results document the first known example of an involvement of a eukaryotic stress response pathway in mutagenesis and have important implications for mechanisms of evolution, carcinogenesis, and emergence of drug-resistant pathogens and chemotherapy-resistant tumors.
| S-EPMC3731204 | biostudies-literature