Promote Protein Misfolding Research Articles

Systems-wide analysis of glycoprotein conformational changes by limited deglycosylation assay

A new method to probe the conformational changes of glycoproteins on a systems-wide scale, termed limited deglycosylation assay (LDA), is described. The method measures the differential rate of deglycosylation of N-glycans on natively folded proteins by the common peptide:N-glycosidase F (PNGase F) enzyme which in turn informs on their spatial presentation and solvent exposure on the protein surface hence ultimately the glycoprotein conformation. LDA involves 1) protein-level N-deglycosylation under native conditions, 2) trypsin digestion, 3) glycopeptide enrichment, 4) peptide-level N-deglycosylation and 5) quantitative MS-based analysis of formerly N-glycosylated peptides (FNGPs). LDA was initially developed and the experimental conditions optimized using bovine RNase B and fetuin. The method was then applied to glycoprotein extracts from LLC-MK2 epithelial cells upon treatment with dithiothreitol to induce endoplasmic reticulum stress and promote protein misfolding. Data from the LDA and 3D structure analysis showed that glycoproteins predominantly undergo structural changes in loops/turns upon ER stress as exemplified with detailed analysis of ephrin-A5, GALNT10, PVR and BCAM. These results show that LDA accurately reports on systems-wide conformational changes of glycoproteins induced under controlled treatment regimes. Thus, LDA opens avenues to study glycoprotein structural changes in a range of other physiological and pathophysiological conditions relevant to acute and chronic diseases. SignificanceWe describe a novel method termed limited deglycosylation assay (LDA), to probe conformational changes of glycoproteins on a systems-wide scale. This method improves the current toolbox of structural proteomics by combining site and conformational-specific PNGase F enzymatic activity with large scale quantitative proteomics. X-ray crystallography, nuclear magnetic resonance spectroscopy and cryoEM techniques are the major techniques applied to elucidate macromolecule structures. However, the size and heterogeneity of the oligosaccharide chains poses several challenges to the applications of these techniques to glycoproteins. The LDA method presented here, can be applied to a range of pathophysiological conditions and expanded to investigate PTMs-mediated structural changes in complex proteomes.

A novel knockout mouse for the small EDRK-rich factor 2 (Serf2) showing developmental and other deficits

The small EDRK-rich factor 2 (SERF2) is a highly conserved protein that modifies amyloid fibre assembly in vitro and promotes protein misfolding. However, the role of SERF2 in regulating age-related proteotoxicity remains largely unexplored due to a lack of in vivo models. Here, we report the generation of Serf2 knockout mice using an ES cell targeting approach, with Serf2 knockout alleles being bred onto different defined genetic backgrounds. We highlight phenotyping data from heterozygous Serf2+/− mice, including unexpected male-specific phenotypes in startle response and pre-pulse inhibition. We report embryonic lethality in Serf2−/− null animals when bred onto a C57BL/6 N background. However, homozygous null animals were viable on a mixed genetic background and, remarkably, developed without obvious abnormalities. The Serf2 knockout mice provide a powerful tool to further investigate the role of SERF2 protein in previously unexplored pathophysiological pathways in the context of a whole organism.

Inhibition of neuroinflammatory nitric oxide signaling suppresses glycation and prevents neuronal dysfunction in mouse prion disease

Several neurodegenerative diseases associated with protein misfolding (Alzheimer's and Parkinson's disease) exhibit oxidative and nitrergic stress following initiation of neuroinflammatory pathways. Associated nitric oxide (NO)-mediated posttranslational modifications impact upon protein functions that can exacerbate pathology. Nonenzymatic and irreversible glycation signaling has been implicated as an underlying pathway that promotes protein misfolding, but the direct interactions between both pathways are poorly understood. Here we investigated the therapeutic potential of pharmacologically suppressing neuroinflammatory NO signaling during early disease progression of prion-infected mice. Mice were injected daily with an NO synthase (NOS) inhibitor at early disease stages, hippocampal gene and protein expression levels of oxidative and nitrergic stress markers were analyzed, and electrophysiological characterization of pyramidal CA1 neurons was performed. Increased neuroinflammatory signaling was observed in mice between 6 and 10 wk postinoculation (w.p.i.) with scrapie prion protein. Their hippocampi were characterized by enhanced nitrergic stress associated with a decline in neuronal function by 9 w.p.i. Daily in vivo administration of the NOS inhibitor L-NAME between 6 and 9 w.p.i. at 20 mg/kg prevented the functional degeneration of hippocampal neurons in prion-diseased mice. We further found that this intervention in diseased mice reduced 3-nitrotyrosination of triose-phosphate isomerase, an enzyme involved in the formation of disease-associated glycation. Furthermore, L-NAME application led to a reduced expression of the receptor for advanced glycation end-products and the diminished accumulation of hippocampal prion misfolding. Our data suggest that suppressing neuroinflammatory NO signaling slows functional neurodegeneration and reduces nitrergic and glycation-associated cellular stress.

Extracellular vesicles - propagators of neuropathology and sources of potential biomarkers and therapeutics for neurodegenerative diseases.

Neurodegenerative diseases are characterised by the irreversible degeneration of neurons in the central or peripheral nervous systems. These include amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD) and prion diseases. Small extracellular vesicles (sEVs), a type of EV involved in cellular communication, have been well documented as propagating neurodegenerative diseases. These sEVs carry cargo, such as proteins and RNA, to recipient cells but are also capable of promoting protein misfolding, thus actively contributing to the progression of these diseases. sEV secretion is also a compensatory process for lysosomal dysfunction in the affected cells, despite inadvertently propagating disease to recipient cells. Despite this, sEV miRNAs have biomarker potential for the early diagnosis of these diseases, while stem cell-derived sEVs and those generated through exogenous assistance demonstrate the greatest therapeutic potential. This Review will highlight novel advancements in the involvement of sEVs as propagators of neuropathology, biomarkers and potential therapeutics in neurodegenerative diseases.

Inducible expression of a disease-associated ELANE mutation impairs granulocytic differentiation, without eliciting an unfolded protein response

Severe congenital neutropenia (SCN) is characterized by a near absence of neutrophils, rendering individuals with this disorder vulnerable to recurrent life-threatening infections. The majority of SCN cases arise because of germline mutations in the gene elastase, neutrophil-expressed (ELANE) encoding the neutrophil granule serine protease neutrophil elastase. Treatment with a high dose of granulocyte colony-stimulating factor increases neutrophil production and reduces infection risk. How ELANE mutations produce SCN remains unknown. The currently proposed mechanism is that ELANE mutations promote protein misfolding, resulting in endoplasmic reticulum stress and activation of the unfolded protein response (UPR), triggering death of neutrophil precursors and resulting in neutropenia. Here we studied the ELANE mutation p.G185R, often associated with greater clinical severity (e.g. decreased responsiveness to granulocyte colony-stimulating factor and increased leukemogenesis). Using an inducible expression system, we observed that this ELANE mutation diminishes enzymatic activity and granulocytic differentiation without significantly affecting cell proliferation, cell death, or UPR induction in murine myeloblast 32D and human promyelocytic NB4 cells. Impaired differentiation was associated with decreased expression of genes encoding critical hematopoietic transcription factors (Gfi1, Cebpd, Cebpe, and Spi1), cell surface proteins (Csf3r and Gr1), and neutrophil granule proteins (Mpo and Elane). Together, these findings challenge the currently prevailing model that SCN results from mutant ELANE, which triggers endoplasmic reticulum stress, UPR, and apoptosis.

β-Methylamino-L-alanine substitution of serine in SOD1 suggests a direct role in ALS etiology.

Exposure to the environmental toxin β-methylamino-L-alanine (BMAA) is linked to amyotrophic lateral sclerosis (ALS), but its disease-promoting mechanism remains unknown. We propose that incorporation of BMAA into the ALS-linked protein Cu,Zn superoxide dismutase (SOD1) upon translation promotes protein misfolding and aggregation, which has been linked to ALS onset and progression. Using molecular simulation and predictive energetic computation, we demonstrate that substituting any serine with BMAA in SOD1 results in structural destabilization and aberrant dynamics, promoting neurotoxic SOD1 aggregation. We propose that translational incorporation of BMAA into SOD1 is directly responsible for its toxicity in neurodegeneration, and BMAA modification of SOD1 may serve as a biomarker of ALS.

Mitochondrial-membrane association of α-synuclein: Pros and cons in consequence of Parkinson's disease pathophysiology

The mitochondrial association of α-synuclein has been known to play a crucial homeostatic role in the neuronal cells. The slightest of a tweak in this association cause for activating the neurodegenerative mechanism, ultimately leading to neuronal loss, the pathological feature of Parkinson's disease. Studies so far have highlighted several intrinsic and extrinsic factors that alter this association, promoting protein misfolding and mitochondrial dysfunction, both of which bring about cooperative cellular degeneracy. Despite the years of effort, the exact molecular association remains unspecified, forbidding the characterization of disease etiology. In this review, we summarize the accumulating evidence for this mitochondrial membrane association, sewing the scattered links to a clear understanding of this interaction.

Heat Shock-induced Phosphorylation of TAR DNA-binding Protein 43 (TDP-43) by MAPK/ERK Kinase Regulates TDP-43 Function

TAR DNA-binding protein (TDP-43) is a highly conserved and essential DNA- and RNA-binding protein that controls gene expression through RNA processing, in particular, regulation of splicing. Intracellular aggregation of TDP-43 is a hallmark of amyotrophic lateral sclerosis and ubiquitin-positive frontotemporal lobar degeneration. This TDP-43 pathology is also present in other types of neurodegeneration including Alzheimer's disease. We report here that TDP-43 is a substrate of MEK, a central kinase in the MAPK/ERK signaling pathway. TDP-43 dual phosphorylation by MEK, at threonine 153 and tyrosine 155 (p-T153/Y155), was dramatically increased by the heat shock response (HSR) in human cells. HSR promotes cell survival under proteotoxic conditions by maintaining protein homeostasis and preventing protein misfolding. MEK is activated by HSR and contributes to the regulation of proteome stability. Phosphorylated TDP-43 was not associated with TDP-43 aggregation, and p-T153/Y155 remained soluble under conditions that promote protein misfolding. We found that active MEK significantly alters TDP-43-regulated splicing and that phosphomimetic substitutions at these two residues reduce binding to GU-rich RNA. Cellular imaging using a phospho-specific p-T153/Y155 antibody showed that phosphorylated TDP-43 was specifically recruited to the nucleoli, suggesting that p-T153/Y155 regulates a previously unappreciated function of TDP-43 in the processing of nucleolar-associated RNA. These findings highlight a new mechanism that regulates TDP-43 function and homeostasis through phosphorylation and, therefore, may contribute to the development of strategies to prevent TDP-43 aggregation and to uncover previously unexplored roles of TDP-43 in cell metabolism.

CydDC-mediated reductant export in Escherichia coli controls the transcriptional wiring of energy metabolism and combats nitrosative stress.

The glutathione/cysteine exporter CydDC maintains redox balance in Escherichia coli. A cydD mutant strain was used to probe the influence of CydDC upon reduced thiol export, gene expression, metabolic perturbations, intracellular pH homoeostasis and tolerance to nitric oxide (NO). Loss of CydDC was found to decrease extracytoplasmic thiol levels, whereas overexpression diminished the cytoplasmic thiol content. Transcriptomic analysis revealed a dramatic up-regulation of protein chaperones, protein degradation (via phenylpropionate/phenylacetate catabolism), β-oxidation of fatty acids and genes involved in nitrate/nitrite reduction. (1)H NMR metabolomics revealed elevated methionine and betaine and diminished acetate and NAD(+) in cydD cells, which was consistent with the transcriptomics-based metabolic model. The growth rate and ΔpH, however, were unaffected, although the cydD strain did exhibit sensitivity to the NO-releasing compound NOC-12. These observations are consistent with the hypothesis that the loss of CydDC-mediated reductant export promotes protein misfolding, adaptations to energy metabolism and sensitivity to NO. The addition of both glutathione and cysteine to the medium was found to complement the loss of bd-type cytochrome synthesis in a cydD strain (a key component of the pleiotropic cydDC phenotype), providing the first direct evidence that CydDC substrates are able to restore the correct assembly of this respiratory oxidase. These data provide an insight into the metabolic flexibility of E. coli, highlight the importance of bacterial redox homoeostasis during nitrosative stress, and report for the first time the ability of periplasmic low molecular weight thiols to restore haem incorporation into a cytochrome complex.

Reactive γ-ketoaldehydes promote protein misfolding and preamyloid oligomer formation in rapidly-activated atrial cells

Rapid activation causes remodeling of atrial myocytes resembling that which occurs in experimental and human atrial fibrillation (AF). Using this cellular model, we previously observed transcriptional upregulation of proteins implicated in protein misfolding and amyloidosis. For organ-specific amyloidoses such as Alzheimer's disease, preamyloid oligomers (PAOs) are now recognized to be the primary cytotoxic species. In the setting of oxidative stress, highly-reactive lipid-derived mediators known as γ-ketoaldehydes (γ-KAs) have been identified that rapidly adduct proteins and cause PAO formation for amyloid β1–42 implicated in Alzheimer's. We hypothesized that rapid activation of atrial cells triggers oxidative stress with lipid peroxidation and formation of γ-KAs, which then rapidly crosslink proteins to generate PAOs. To investigate this hypothesis, rapidly-paced and control, spontaneously-beating atrial HL-1 cells were probed with a conformation-specific antibody recognizing PAOs. Rapid stimulation of atrial cells caused the generation of cytosolic PAOs along with a myocyte stress response (e.g., transcriptional upregulation of Nppa and Hspa1a), both of which were absent in control, unpaced cells. Rapid activation also caused the formation of superoxide and γ-KA adducts in atriomyocytes, while direct exposure of cells to γ-KAs resulted in PAO production. Increased cytosolic atrial natriuretic peptide (ANP), and the generation of ANP oligomers with exposure to γ-KAs and rapid atrial HL-1 cell stimulation, strongly suggest a role for ANP in PAO formation. Salicylamine (SA) is a small molecule scavenger of γ-KAs that can protect proteins from modification by these reactive compounds. PAO formation and transcriptional remodeling were inhibited when cells were stimulated in the presence of SA, but not with the antioxidant curcumin, which is incapable of scavenging γ-KAs. These results demonstrate that γ-KAs promote protein misfolding and PAO formation as a component of the atrial cell stress response to rapid activation, and they provide a potential mechanistic link between oxidative stress and atrial cell injury.

General introduction: recombinant protein production and purification of insoluble proteins.

Proteins are synthesized in heterologous systems because of the impossibility to obtain satisfactory yields from natural sources. The production of soluble and functional recombinant proteins is among the main goals in the biotechnological field. In this context, it is important to point out that under stress conditions, protein folding machinery is saturated and this promotes protein misfolding and, consequently, protein aggregation. Thus, the selection of the optimal expression organism and the most appropriate growth conditions to minimize the formation of insoluble proteins should be done according to the protein characteristics and downstream requirements. Escherichia coli is the most popular recombinant protein expression system despite the great development achieved so far by eukaryotic expression systems. Besides, other prokaryotic expression systems, such as lactic acid bacteria and psychrophilic bacteria, are gaining interest in this field. However, it is worth mentioning that prokaryotic expression system poses, in many cases, severe restrictions for a successful heterologous protein production. Thus, eukaryotic systems such as mammalian cells, insect cells, yeast, filamentous fungus, and microalgae are an interesting alternative for the production of these difficult-to-express proteins.

DSSylation, a novel guide for protein degradation?

DSSylation, a novel guide for protein degradation?

Impaired-UPS can be Compensated by Activation of Autophagy in Neurodegenerative Diseases

The ubiquitin-proteasome system (UPS) is a dynamic cellular pathway involved in the deaggregation of misfolded proteins through proteasome degradation. Impaired-UPS function is frequently observed in patients afflicted with neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. Increased oxidative stress has long been implicated with the pathogenesis of impaired-UPS function by promoting protein misfolding and the subsequent protein aggregate formation. Autophagy, a bulk lysosomal degradative process, mediates the clearance of toxic cellular constituents and protein aggregates via autophagosome formation and increasing evidence suggests an association between neurodegenerative disorders and defective autophagy. Therefore, it is crucial to understand the role of oxidative stress in impaired-UPS function and the sub-cellular source of oxidative stress. In addition, understanding the mechanism(s) by which autophaghy regulates UPS function will will allow us to develop novel therapeutics for neurodegenerative diseases. Here we demonstrated that rotenone activated nicotinamide adenine dinucleotide phosphatase (NADPH oxidase or Nox2) and Nox2-dependent oxidative stress resulted in impaired UPS machinery. Src kinase was persistently activated by Nox2-dependent superoxide production, which resulted in further Nox2 activation via p47phox phosphorylation and impaired autophagy by activating the autophagy repressor mTOR through PI3K/Akt phosphorylation. Inhibition of Nox2 or Src kinase mitigated excess oxidative stress, which induced autophagy and rescued UPS function. Our data highlight NADPH oxidase and Src kinase as possible autophagy modulators and potential therapeutic targets for common neurodegenerative diseases.

Nuclear Import Factor Srp1 and Its Associated Protein Sts1 Couple Ribosome-bound Nascent Polypeptides to Proteasomes for Cotranslational Degradation

Cotranslational protein degradation plays an important role in protein quality control and proteostasis. Although ubiquitylation has been suggested to signal cotranslational degradation of nascent polypeptides, cotranslational ubiquitylation occurs at a low level, suggesting the existence of an alternative route for delivery of nascent polypeptides to the proteasome. Here we report that the nuclear import factor Srp1 (also known as importin α or karyopherin α) is required for ubiquitin-independent cotranslational degradation of the transcription factor Rpn4. We further demonstrate that cotranslational protein degradation is generally impaired in the srp1-49 mutant. Srp1 binds nascent polypeptides emerging from the ribosome. The association of proteasomes with polysomes is weakened in srp1-49. The interaction between Srp1 and the proteasome is mediated by Sts1, a multicopy suppressor of srp1-49. The srp1-49 and sts1-2 mutants are hypersensitive to stressors that promote protein misfolding, underscoring the physiological function of Srp1 and Sts1 in degradation of misfolded nascent polypeptides. This study unveils a previously unknown role for Srp1 and Sts1 in cotranslational protein degradation and suggests a novel model whereby Srp1 and Sts1 cooperate to couple proteasomes to ribosome-bound nascent polypeptides.

Rotenone induces neurotoxicity through Rac1-dependent activation of NADPH oxidase in SHSY-5Y cells

Neurodegenerative diseases are attributed to impairment of the ubiquitin–proteasome system (UPS). Oxidative stress has been considered a contributing factor in the pathology of impaired UPS by promoting protein misfolding and subsequent protein aggregate formation. Increasing evidence suggests that NADPH oxidase is a likely source of excessive oxidative stress in neurodegenerative disorders. However, the mechanism of activation and its role in impaired UPS is not understood. We show that activation of NADPH oxidase in a neuroblastoma cell line (SHSY-5Y) resulted in increased oxidative and nitrosative stress, elevated cytosolic calcium, ER-stress, impaired UPS, and apoptosis. Rac1 inhibition mitigated the oxidative/nitrosative stress, prevented calcium-dependent ER-stress, and partially rescued UPS function. These findings demonstrate that Rac1 and NADPH oxidase play an important role in rotenone neurotoxicity.

GCK-MODY diabetes as a protein misfolding disease: The mutation R275C promotes protein misfolding, self-association and cellular degradation

GCK-MODY, dominantly inherited mild hyperglycemia, is associated with more than 600 mutations in the glucokinase gene. Different molecular mechanisms have been shown to explain GCK-MODY. Here, we report a Pakistani family harboring the glucokinase mutation c.823C>T (p.R275C). The recombinant and in cellulo expressed mutant pancreatic enzyme revealed slightly increased enzyme activity (kcat) and normal affinity for α-D-glucose, and resistance to limited proteolysis by trypsin comparable with wild-type. When stably expressed in HEK293 cells and MIN6 β-cells (at different levels), the mutant protein appeared misfolded and unstable with a propensity to form dimers and aggregates. Its degradation rate was increased, involving the lysosomal and proteasomal quality control systems. On mutation, a hydrogen bond between the R275 side-chain and the carbonyl oxygen of D267 is broken, destabilizing the F260-L271 loop structure and the protein. This promotes the formation of dimers/aggregates and suggests that an increased cellular degradation is the molecular mechanism by which R275C causes GCK-MODY.

Type II antithrombin deficiency caused by a large in‐frame insertion: structural, functional and pathological relevance

The metastable native conformation of serpins is required for their protease inhibition mechanism, but also renders them vulnerable to missense mutations that promote protein misfolding with pathological consequences. To characterize the first antithrombin deficiency caused by a large in-frame insertion. Functional, biochemical and molecular analysis of the proband and relatives was performed. Recombinant antithrombin was expressed in HEK-EBNA cells. Plasma and recombinant antithrombins were purified and sequenced by Edman degradation. The stability was evaluated by calorimetry. Reactive centre loop (RCL) exposure was determined by thrombin cleavage. Mutant antithrombin was crystallized as a dimer with latent plasma antithrombin. The patient, with a spontaneous pulmonary embolism, belongs to a family with significant thrombotic history. We identified a complex heterozygous in-frame insertion of 24 bp in SERPINC1, affecting strand 3 of β-sheet A, a region highly conserved in serpins. Surprisingly, the insertion resulted in a type II antithrombin deficiency with heparin binding defect. The mutant antithrombin, with a molecular weight of 59 kDa, had a proteolytic cleavage at W49 but maintained the N-terminal disulphide bonds, and was conformationally sensitive. The variant was non-inhibitory. Analysis of the crystal structure of the hyperstable recombinant protein showed that the inserted sequence annealed into β-sheet A as the fourth strand, and maintained a native RCL. This is the first case of a large in frame-insertion that allows correct folding, glycosylation, and secretion of a serpin, resulting in a conformationally sensitive non-inhibitory variant, which acquires a hyperstable conformation with a native RCL.

Arsenite interferes with protein folding and triggers formation of protein aggregates in yeast

Several metals and metalloids profoundly affect biological systems, but their impact on the proteome and mechanisms of toxicity are not fully understood. Here, we demonstrate that arsenite causes protein aggregation in Saccharomyces cerevisiae. Various molecular chaperones were found to be associated with arsenite-induced aggregates indicating that this metalloid promotes protein misfolding. Using in vivo and in vitro assays, we show that proteins in the process of synthesis/folding are particularly sensitive to arsenite-induced aggregation, that arsenite interferes with protein folding by acting on unfolded polypeptides, and that arsenite directly inhibits chaperone activity. Thus, folding inhibition contributes to arsenite toxicity in two ways: by aggregate formation and by chaperone inhibition. Importantly, arsenite-induced protein aggregates can act as seeds committing other, labile proteins to misfold and aggregate. Our findings describe a novel mechanism of toxicity that may explain the suggested role of this metalloid in the etiology and pathogenesis of protein folding disorders associated with arsenic poisoning.

Shock and awe: unleashing the heat shock response to treat Huntington disease

The heat shock response (HSR) is a highly conserved protective mechanism that enables cells to withstand diverse environmental stressors that disrupt protein homeostasis (proteostasis) and promote protein misfolding. It has been suggested that small-molecule drugs that elicit the HSR by activating the transcription factor heat shock factor 1 might help mitigate protein misfolding and aggregation in several devastating neurodegenerative disorders, including Huntington disease (HD). In this issue of the JCI, Labbadia et al. use a brain-penetrant Hsp90 inhibitor, HSP990, to induce the HSR in mouse models of HD. Unexpectedly, they observed that HSP990 confers only transient amelioration of a subset of HD-related phenotypes, because alterations in chromatin architecture impair the HSR upon disease progression. These findings suggest that synergistic combination therapies that simultaneously unleash the HSR and prevent its impairment are likely to be needed to restore proteostasis in HD.

Proteomics: a strategy to understand the novel targets in protein misfolding and cancer therapy

Proteins carry out important functions as they fold themselves. Protein misfolding occurs during different biochemical processes and may lead to the development of diseases such as cancer, which is characterized by genetic instability. The cancer microenvironment exposes malignant cells to a variety of stressful conditions that may further promote protein misfolding. Tumor development and progression often arises from mutations that interfere with the appropriate function of tumor-suppressor proteins and oncogenes. These may be due to alteration of catalytic activity of the protein, loss of binding sites for effector proteins or alterations of the native folded protein conformation. Src family kinases, p53, mTOR and C-terminus of HSC70 interacting protein (CHIPs) are some examples associated with protein misfolding and tumorigenesis. Molecular chaperones, such as heat-shock protein (HSP)70 and HSP90, assist protein folding and recognize target misfolded proteins for degradation. It is likely that this misfolding in cancer is linked by common principles, and may, therefore, present an exciting possibility to identify common targets for therapeutic intervention. Here we aim to review a number of examples that show how alterations in the folding of tumor-suppressor proteins or oncogenes lead to tumorigenesis. The possibility of targeting the targets to repair or degrade protein misfolding in cancer therapy is discussed.