Mutant p53 aggregates into prion-like amyloid oligomers and fibrils: implications for cancer

Liquid-liquid phase transitions and amyloid aggregation in proteins related to cancer and neurodegenerative diseases

Liquid-liquid phase separation (LLPS) and phase transition (LLPT) of proteins and nucleic acids have emerged as a new paradigm in cell biology. Here we will describe the recent findings about LLPS and LLPT, including the molecular and physical determinants leading to their formation, the resulting functions and their implications in cell physiology and disease. Amyloid aggregation is implicated in many neurodegenerative diseases and cancer, and LLPS of proteins involved in these diseases appear to be related to their function in different cell contexts. Amyloid formation would correspond to an irreversible liquid-to-solid transition, as clearly observed in the case of PrP, TDP43, FUS/TLS and tau protein in neurodegenerative pathologies as well as with the mutant tumor suppressor p53 in cancer. Nucleic acids play a modulatory effect on both LLPS and amyloid aggregation. Understanding the molecular events regulating how the demixing process advances to solid-like fibril materials is crucial for the development of novel therapeutic strategies against cancer and neurodegenerative maladies.

ISG15 Deficiency Enhances HIV-1 Infection by Accumulating Misfolded p53

HIV-1 has evolved many strategies to circumvent the host’s antiviral innate immune responses and establishes disseminated infection; the molecular mechanisms of these strategies are not entirely clear. We showed previously that USP18 contributes to HIV-1 replication by abrogating p21 antiviral function. Here, we demonstrate a mechanism by which USP18 mediates p21 downregulation in myeloid cells. USP18, by its protease activity, accumulates misfolded p53, which requires ISG15 for clearance. Depletion of ISG15 causes accumulation of misfolded dominant negative p53, which supports HIV-1 replication. This work clarifies the function and consequences of p53 modification by ISG15 and implicates USP18 in HIV-1 infection and potentially in carcinogenesis.

Macrophages and dendritic cells dominate early immune responses to lentiviruses. HIV-1 sensing by pathogen recognition receptors induces signaling cascades that culminate in type I alpha/beta interferon (IFN-α/β) induction. IFN-α/β signals back via the IFN-α/β receptors, inducing a plethora of IFN-stimulated gene (ISGs), including ISG15, p53, and p21^Cip1. p21 inhibits HIV-1 replication by inactivating the deoxynucleoside triphosphate (dNTP) biosynthesis pathway and activating the restriction factor SAMHD1. p21 is induced by functional p53. ISG15-specific isopeptidase USP18 negatively regulates IFN signaling. We showed previously that USP18 contributes to HIV-1 replication by abrogating p21 antiviral function. Here, we demonstrate a mechanism by which USP18 mediates p21 downregulation in myeloid cells. USP18, by its protease activity, accumulates misfolded p53, which requires ISG15 for its degradation. Depletion of ISG15 causes accumulation of misfolded dominant negative p53, which enhances HIV-1 replication. This work clarifies the function and consequences of p53 modification by ISG15 and implicates USP18 in HIV-1 infection and potentially in carcinogenesis.

An IRES-dependent translation of HYPK mRNA generates a truncated isoform of the protein that lacks the nuclear localization and functional ability

Different mechanisms of translation initiation process exist to start the protein synthesis from various viral and eukaryotic mRNA. The cap-independent and tertiary structure directed translation initiation of mRNAs forms the basis of internal ribosome entry site (IRES) mediated translation initiation that helps in cellular protein production in different conditions. HYPK protein sequesters different aggregation-prone proteins to help in the cellular proteostasis. HYPK mRNA is differentially translated from an internal start/initiation codon to generate an amino terminal-truncated isoform (HSPC136) of HYPK protein. In this study, we report that an IRES-dependent translation initiation of HYPK mRNA results in the formation of the HSPC136/HYPK-ΔN isoform of HYPK protein. The IRES-driven translation product, HYPK-ΔN, lacks the N-terminal tri-arginine motif that acts as the nuclear localization signal (NLS) in the full-length HYPK protein. While the full-length HYPK protein translocates to the nucleus and prevents the aggregation of the mutant p53 (p53-R248Q) protein, the HYPK-ΔN lacks this activity. The NLS of HYPK is not evolutionarily conserved and its exclusive presence in the HYPK of higher eukaryotic animals imparts additional advantage to the HYPK protein in tackling the cytosolic as well as nuclear protein aggregates. The presence of the NLS in full-length HYPK also allows this protein to modulate the cell cycle. These results provide a mechanistic detail of HYPK mRNA's translation initiation control by an IRES that dictates the formation of HYPC136/HYPK-ΔN which lacks the nuclear localization and functional ability.

Molecular basis of the scalp-ear-nipple syndrome unraveled by the characterization of disease-causing KCTD1 mutants

The scalp-ear-nipple (SEN) syndrome is an autosomal-dominant disorder characterized by cutis aplasia of the scalp and malformations of breast, external ears, digits, and nails. Genetic analyses have shown that the disease is caused by missense mutations of the KCTD1 protein, although the functional/structural basis of SEN insurgence is hitherto unknown. With the aim of unravelling the molecular basis of the SEN syndrome associated with KCTD1 mutations we here expressed and characterized several disease causing mutants. A preliminary dissection of the protein provides insights into the role that individual domains play in KCTD1 stability. The characterization of SEN-causing mutants indicates that, although the mutation sites are located in distant regions of the BTB domain or of the pre-BTB region, all of them are unable to interact with the transcription factor AP-2α, a well-known KCTD1 biological partner. Notably, all mutations, including the one located in the pre-BTB region, produce a significant destabilization of the protein. The structural role of the pre-BTB region in KCTD1 and other proteins of the family is corroborated by its sequence conservation in orthologs and paralogs. Interestingly, SEN-causing mutations also favor the tendency of KCTD1 to adopt structural states that are characterized by the ability to bind the β-amyloid fluorescent dye thioflavin T. The formation of aggregation-prone species may have important implications for the disease etiology. Collectively, these findings provide an intriguing picture of the functional and structural alterations induced by KCTD1 mutations that ultimately lead to disease.

Analyzing aggregation propensities of clinically relevant PTEN mutants: a new culprit in pathogenesis of cancer and other PTENopathies

While studies on pathological protein aggregation are largely limited to neurodegenerative disease, emerging evidence suggests that other diseases are also associated with pathogenic protein aggregation. For example, tumor suppressor protein p53, and its mutant conformers, undergo protein aggregation, exacerbating the cancer phenotype. These findings raise the possibility that inactivation of tumor suppressors via protein aggregation may participate in cancer and other disease pathologies. Since tumor suppressor protein PTEN has similar functions to p53, and is mutated in multiple diseases, we examined the aggregation propensity of PTEN wild-type and 1523 clinically relevant PTEN mutants. Applying computational tools to PTEN mutation databases revealed that PTEN wild-type protein can aggregate under physiological conditions, and 274 distinct PTEN mutants had increased aggregation propensity. To understand the mechanism underlying PTEN conformer aggregation, we analyzed the physicochemical properties of these 274 PTEN mutants and defined their aggregation potential. We conclude that increased aggregation propensity of select PTEN mutants may contribute to disease phenotypes. Our studies have built the foundation for interrogating the aggregation potential of these select mutants in cancers and in PTENopathies. Elucidating the pathogenic mechanisms associated with aggregation-prone PTEN conformers will aid in developing therapies that target PTEN-aggregates in multiple diseases.Communicated by Ramaswamy H. Sarma.

Rescue of degenerating neurons and cells by stem cell released molecules: using a physiological renormalization strategy

Evidence suggests that adult stem cell types and progenitor cells act collectively in a given tissue to maintain and heal organs, such as muscle, through a release of a multitude of molecules packaged into exosomes from the different cell types. Using this principle for the development of bioinspired therapeutics that induces homeostatic renormalization, here we show that the collection of molecules released from four cell types, including mesenchymal stem cells, fibroblast, neural stem cells, and astrocytes, rescues degenerating neurons and cells. Specifically, oxidative stress induced in a human recombinant TDP-43- or FUS-tGFP U2OS cell line by exposure to sodium arsenite was shown to be significantly reduced by our collection of molecules using in vitro imaging of FUS and TDP-43 stress granules. Furthermore, we also show that the collective secretome rescues cortical neurons from glutamate toxicity as evidenced by increased neurite outgrowth, reduced LDH release, and reduced caspase 3/7 activity. These data are the first in a series supporting the development of stem cell-based exosome systems therapeutics that uses a physiological renormalization strategy to treat neurodegenerative diseases.

Loss of the p53 transactivation domain results in high amyloid aggregation of the Δ40p53 isoform in endometrial carcinoma cells

Dysfunctional p53 formation and activity can result from aberrant expression and subcellular localization of distinct p53 isoforms or aggregates. Endometrial carcinoma (EC) is a cancer type in which p53 status is correlated with prognosis, and TP53 mutations are a frequent genetic modification. Here we aimed to evaluate the expression patterns of different p53 isoforms and their contributions to the formation and subcellular localization of p53 amyloid aggregates in both EC and endometrial nontumor cell lines. We found that full-length (fl) p53 and a truncated p53 isoform, Δ40p53, resulting from alternative splicing of exon 2 or alternative initiation of translation at ATG-40, are the predominantly expressed p53 variants in EC cells. However, Δ40p53 was the major p53 isoform in endometrial nontumor cells. Immunofluorescence assays revealed that Δ40p53 is mainly localized to cytoplasmic punctate structures of EC cells, resembling solid-phase structures similar to those found in neurodegenerative pathologies. Using light-scattering kinetics, CD, and transmission EM, we noted that the p53 N-terminal transactivation domain significantly reduces aggregation of the WT p53 DNA-binding domain, confirming the higher aggregation tendency of Δ40p53, which lacks this domain. This is the first report of cytoplasmic Δ40p53 in EC cells being a major component of amyloid aggregates. The differential aggregation properties of p53 isoforms in EC cells may open up new avenues in the development of therapeutic strategies that preferentially target specific p53 isoforms to prevent p53 amyloid aggregate formation.

Metabolic stress controls mutant p53 R248Q stability in acute myeloid leukemia cells

Eliminating mutant p53 (mt p53) protein could be a useful strategy to treat mt p53 tumors and potentially improve the prognosis of cancer patients. In this study, we unveil different mechanisms that eliminate p53-R248Q, one of the most frequent mutants found in human cancers. We show that the Hsp90 inhibitor 17-AAG eliminates R248Q by stimulating macroautophagy under normal growth conditions. Metabolic stress induced by the pyruvate dehydrogenase kinase-1 (PDK1) inhibitor dichloroacetate (DCA) inhibits the macroautophagy pathway. This induces the accumulation of R248Q, which in addition further inhibits macroautophagy. Combination of DCA and 17-AAG further decreases the autophagy flux compared to DCA alone. Despite this, this co-treatment strongly decreases R248Q levels. In this situation of metabolic stress, 17-AAG induces the binding of p53-R248Q to Hsc70 and the activation of Chaperone-Mediated Autophagy (CMA), leading to higher R248Q degradation than in non-stress conditions. Thus, different metabolic contexts induce diverse autophagy mechanisms that degrade p53-R248Q, and under metabolic stress, its degradation is CMA-mediated. Hence, we present different strategies to eliminate this mutant and provide new evidence of the crosstalk between macroautophagy and CMA and their potential use to target mutant p53.

A nuclear phosphoinositide kinase complex regulates p53

The tumour suppressor p53 (encoded by TP53) protects the genome against cellular stress and is frequently mutated in cancer. Mutant p53 acquires gain-of-function oncogenic activities that are dependent on its enhanced stability. However, the mechanisms by which nuclear p53 is stabilized are poorly understood. Here, we demonstrate that the stability of stress-induced wild-type and mutant p53 is regulated by the type I phosphatidylinositol phosphate kinase (PIPKI-α (also known as PIP5K1A)) and its product phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P₂). Nuclear PIPKI-α binds to p53 upon stress, resulting in the production and association of PtdIns(4,5)P₂ with p53. PtdIns(4,5)P₂ binding promotes the interaction between p53 and the small heat shock proteins HSP27 (also known as HSPB1) and αB-crystallin (also known as HSPB5), which stabilize nuclear p53. Moreover, inhibition of PIPKI-α or PtdIns(4,5)P₂ association results in p53 destabilization. Our results point to a previously unrecognized role of nuclear phosphoinositide signalling in regulating p53 stability and implicate this pathway as a promising therapeutic target in cancer.

Conformational stability and dynamics of the cancer-associated isoform Δ133p53β are modulated by p53 peptides and p53-specific DNA

p53 is a tumor suppressor protein that maintains genome stability, but its Δ133p53β and Δ160p53β isoforms promote breast cancer cell invasion. The sequence truncations in the p53 core domain raise key questions related to their physicochemical properties, including structural stabilities, interaction mechanisms, and DNA-binding abilities. Herein, we investigated the conformational dynamics of Δ133p53β and Δ160p53β with and without binding to p53-specific DNA by using molecular dynamics simulations. We observed that the core domains of the 2 truncated isoforms are much less stable than wild-type (wt) p53β, and the increased solvent exposure of their aggregation-triggering segment indicates their higher aggregation propensities than wt p53. We also found that Δ133p53β stability is modulable by peptide or DNA interactions. Adding a p53 peptide (derived from truncated p53 sequence 107-129) may help stabilize Δ133p53. Most importantly, our simulations of p53 isomer-DNA complexes indicate that Δ133p53β dimer, but not Δ160p53β dimer, could form a stable complex with p53-specific DNA, which is consistent with recent experiments. This study provides physicochemical insight into Δ133p53β, Δ133p53β-DNA complexes, Δ133p53β's pathologic mechanism, and peptide-based inhibitor design against p53-related cancers.-Lei, J., Qi, R., Tang, Y., Wang, W., Wei, G., Nussinov, R., Ma, B. Conformational stability and dynamics of the cancer-associated isoform Δ133p53β are modulated by p53 peptides and p53-specific DNA.

Fluorescent Biosensor for Detection of the R248Q Aggregation-Prone Mutant of p53

The p53 tumour suppressor and guardian of the genome undergoes missense mutations that lead to functional inactivation in 50 % of human cancers. These mutations occur mostly in the DNA-binding domain of the protein, and several of these result in conformational changes that lead to amyloid-like protein aggregation. Herein, we describe a fluorescent biosensor that reports on the R248Q mutant of p53 in vitro and in living cells, engineered through conjugation of an environmentally sensitive probe onto a peptide derived from the primary aggregation segment of p53. This biosensor was characterised both in vitro and by means of fluorescence microscopy following facilitated delivery into cultured cells. It is shown that this biosensor preferentially reports on the p53 R248Q mutant in the PC9 lung cancer cell line compared with other lung cancer cell lines harbouring either wild-type or no p53.

Anomalous Dense Liquid Condensates Host the Nucleation of Tumor Suppressor p53 Fibrils

About half of human cancers are associated with mutations of the tumor suppressor p53. Gained oncogenic functions of the mutants have been related to aggregation behaviors of wild-type and mutant p53. The thermodynamic and kinetic mechanisms of p53 aggregation are poorly understood. Here we find that wild-type p53 forms an anomalous liquid phase. The liquid condensates exhibit several behaviors beyond the scope of classical phase transition theories: their size, ca. 100 nm, is independent of the p53 concentration and decoupled from the protein mass held in the liquid phase. Furthermore, the liquid phase lacks constant solubility. The nucleation of p53 fibrils deviates from the accepted mechanism of sequential association of single solute molecules. We find that the liquid condensates serve as pre-assembled precursors of high p53 concentration that facilitate fibril assembly. Fibril nucleation hosted by precursors represents a novel biological pathway, which opens avenues to suppress protein fibrillation in aggregation diseases.

p53 reactivation with induction of massive apoptosis-1 (PRIMA-1) inhibits amyloid aggregation of mutant p53 in cancer cells

p53 mutants can form amyloid-like structures that accumulate in cells. p53 reactivation with induction of massive apoptosis-1 (PRIMA-1) and its primary active metabolite, 2-methylene-3-quinuclidinone (MQ), can restore unfolded p53 mutants to a native conformation that induces apoptosis and activates several p53 target genes. However, whether PRIMA-1 can clear p53 aggregates is unclear. In this study, we investigated whether PRIMA-1 can restore aggregated mutant p53 to a native form. We observed that the p53 mutant protein is more sensitive to both PRIMA-1 and MQ aggregation inhibition than WT p53. The results of anti-amyloid oligomer antibody assays revealed that PRIMA-1 reverses mutant p53 aggregate accumulation in cancer cells. Size-exclusion chromatography of the lysates from mutant p53-containing breast cancer and ovarian cell lines confirmed that PRIMA-1 substantially decreases p53 aggregates. We also show that MDA-MB-231 cell lysates can "seed" aggregation of the central core domain of recombinant WT p53, corroborating the prion-like behavior of mutant p53. We also noted that this aggregation effect was inhibited by MQ and PRIMA-1. This study provides the first demonstration that PRIMA-1 can rescue amyloid-state p53 mutants, a strategy that could be further explored as a cancer treatment.

Methods to Screen Compounds Against Mutant p53 Misfolding and Aggregation for Cancer Therapeutics

p53 is a critical tumor suppressor that functions as a transcription factor. Mutations in the TP53 gene are observed in more than 50% of cancer cases worldwide. Several of these mutations lead to a less stable, aggregation-prone protein that accumulates in cancer cells. These mutations are associated with a gain of oncogenic function, which leads to cancer progression. p53 amyloid aggregation is a common feature in most of these mutants; thus, it can be used as a druggable target to reactivate or induce the degradation of p53 and promote a retraction in the aggressive pattern of mutant p53-containing cells. We show here a series of experiments for the screening and validation of new p53 antiamyloid compounds.

p53 Isoforms and Their Implications in Cancer

In this review we focus on the major isoforms of the tumor-suppressor protein p53, dysfunction of which often leads to cancer. Mutations of the TP53 gene, particularly in the DNA binding domain, have been regarded as the main cause for p53 inactivation. However, recent reports demonstrating abundance of p53 isoforms, especially the N-terminally truncated ones, in the cancerous tissues suggest their involvement in carcinogenesis. These isoforms are ∆40p53, ∆133p53, and ∆160p53 (the names indicate their respective N-terminal truncation). Due to the lack of structural and functional characterizations the modes of action of the p53 isoforms are still unclear. Owing to the deletions in the functional domains, these isoforms can either be defective in DNA binding or more susceptive to altered ‘responsive elements’ than p53. Furthermore, they may exert a ‘dominant negative effect’ or induce more aggressive cancer by the ‘gain of function’. One possible mechanism of p53 inactivation can be through tetramerization with the ∆133p53 and ∆160p53 isoforms—both lacking part of the DNA binding domain. A recent report and unpublished data from our laboratory also suggest that these isoforms may inactivate p53 by fast aggregation—possibly due to ectopic overexpression. We further discuss the evolutionary significance of the p53 isoforms.

Mutations, protein homeostasis, and epigenetic control of genome integrity

From bacteria to humans, ancient stress responses enable organisms to contend with damage to both the genome and the proteome. These pathways have long been viewed as fundamentally separate responses. Yet recent discoveries from multiple fields have revealed surprising links between the two. Many DNA-damaging agents also target proteins, and mutagenesis induced by DNA damage produces variant proteins that are prone to misfolding, degradation, and aggregation. Likewise, recent studies have observed pervasive engagement of a p53-mediated response, and other factors linked to maintenance of genomic integrity, in response to misfolded protein stress. Perhaps most remarkably, protein aggregation and self-assembly has now been observed in multiple proteins that regulate the DNA damage response. The importance of these connections is highlighted by disease models of both cancer and neurodegeneration, in which compromised DNA repair machinery leads to profound defects in protein quality control, and vice versa.

Fibronectin amyloid-like aggregation alters its extracellular matrix incorporation and promotes a single and sparsed cell migration

Fibronectin (Fn) is an extracellular matrix (ECM) multifunctional glycoprotein essential for regulating cells behaviors. Within ECM, Fn is found as polymerized fibrils. Apart from fibrils, Fn could also form other kind of supramolecular assemblies such as aggregates. To gain insight into the impact of Fn aggregates on cell behavior, we generated several Fn oligomeric assemblies. These assemblies displayed various amyloid-like properties but were not cytotoxic. In presence of the more amyloid-like structured assemblies of Fn, the cell-ECM networks were altered and the cell shapes shifted toward extended mesenchymal morphologies. Additionnaly, the Fn amyloid-like aggregates promoted a single-cell and sparsed migration of SKOV3 cancer cells, which was associated with a relocalization of αv integrins from plasma membrane to perinuclear vesicles. These data pointed out that the features of supramolecular Fn assemblies could represent a higher level of fine-tuning cell phenotype, and especially migration of cancer cells.

CHIP promotes autophagy-mediated degradation of aggregating mutant p53 in hypoxic conditions

Tumor suppressor protein p53 aggregates in the hypoxic core of solid tumors. C terminus of Hsc70-interacting protein (CHIP) displays chaperone as well as E3 ligase activities in both stabilizing and degrading wild-type and mutant p53. In this study, we have discovered that CHIP selectively degrades aggregating mutant p53 under both normal and hypoxic conditions. Silencing of CHIP alleviates degradation of aggregating mutant p53 in both normoxia and hypoxia, but has no significant effect on the level of nonaggregating mutant p53. Although both U-box and TPR domains of CHIP are responsible for p53 degradation, the U-box domain selectively binds to aggregating mutant p53, whereas the TPR domain interacts with nonaggregating mutant p53. The degradation of mutant p53 by CHIP is shown to be via autophagy through K63-linked polyubiquitination. Both in normoxia and under physiological hypoxia, the level of aggregating mutant p53 in the presence of CHIP was reduced threefold, whereas under serum starvation, it was reduced fivefold. Interestingly, both wild-type and mutant p53 interact with and stabilize CHIP at the post-translational level, suggesting a chaperone synergy between p53 and CHIP. This finding may have strong therapeutic significance via selective degradation of oncogenic mutant p53 in regressing hypoxic tumors.

Aggregation-primed molten globule conformers of the p53 core domain provide potential tools for studying p53C aggregation in cancer

The functionality of the tumor suppressor p53 is altered in more than 50% of human cancers, and many individuals with cancer exhibit amyloid-like buildups of aggregated p53. An understanding of what triggers the pathogenic amyloid conversion of p53 is required for the further development of cancer therapies. Here, perturbation of the p53 core domain (p53C) with subdenaturing concentrations of guanidine hydrochloride and high hydrostatic pressure revealed native-like molten globule (MG) states, a subset of which were highly prone to amyloidogenic aggregation. We found that MG conformers of p53C, probably representing population-weighted averages of multiple states, have different volumetric properties, as determined by pressure perturbation and size-exclusion chromatography. We also found that they bind the fluorescent dye 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (bis-ANS) and have a native-like tertiary structure that occludes the single Trp residue in p53. Fluorescence experiments revealed conformational changes of the single Trp and Tyr residues before p53 unfolding and the presence of MG conformers, some of which were highly prone to aggregation. p53C exhibited marginal unfolding cooperativity, which could be modulated from unfolding to aggregation pathways with chemical or physical forces. We conclude that trapping amyloid precursor states in solution is a promising approach for understanding p53 aggregation in cancer. Our findings support the use of single-Trp fluorescence as a probe for evaluating p53 stability, effects of mutations, and the efficacy of therapeutics designed to stabilize p53.

Resveratrol prevents p53 aggregation in vitro and in breast cancer cells

One potential target for cancer therapeutics is the tumor suppressor p53, which is mutated in more than 50% of malignant tumors. Loss of function (LoF), dominant negative (DN) and gain of function (GoF) mutations in p53 are associated with amyloid aggregation. We tested the potential of resveratrol, a naturally occurring polyphenol, to interact and prevent the aggregation of wild-type and mutant p53 in vitro using fluorescence spectroscopy techniques and in human breast cancer cells (MDA-MB-231, HCC-70 and MCF-7) using immunofluorescence co-localization assays. Based on our data, an interaction occurs between resveratrol and the wild-type p53 core domain (p53C). In addition, resveratrol and its derivatives pterostilbene and piceatannol inhibit mutant p53C aggregation in vitro. Additionally, resveratrol reduces mutant p53 protein aggregation in MDA-MB-231 and HCC-70 cells but not in the wild-type p53 cell line MCF-7. To verify the effects of resveratrol on tumorigenicity, cell proliferation and cell migration assays were performed using MDA-MB-231 cells. Resveratrol significantly reduced the proliferative and migratory capabilities of these cells. Our study provides evidence that resveratrol directly modulates p53, enhancing our understanding of the mechanisms involved in p53 aggregation and its potential as a therapeutic strategy for cancer treatment.

Treating p53 Mutant Aggregation-Associated Cancer

p53 is a tumor suppressor protein. Under stressful conditions, p53 tightly regulates cell growth by promoting apoptosis and DNA repair. When p53 becomes mutated, it loses its function, resulting in abnormal cell proliferation and tumor progression. Depending on the p53 mutation, it has been shown to form aggregates leading to negative gain of function of the protein. p53 mutant associated aggregation has been observed in several cancer tissues and has been shown to promote tumor growth. Recent studies show correlation between p53 mutant aggregation, functional loss, and tumor growth. Moreover, p53 aggregation has been observed in biopsies, patient tissues, and in vivo studies. Given the fact that over fifty percent of cancers have p53 mutation and several of them are prone to aggregation, therapeutic strategies are needed for treating p53 mutant aggregation associated cancers. Recent studies using polyarginine analogues and designer peptides for inhibiting p53 aggregation and tumor growth gives further encouragement in treating cancer as a protein aggregation disease. In this review, we highlight the recent efforts in targeting p53 aggregation in cancer and propose the use of small stress molecules as potential p53-antiaggregation drugs.

A sticky situation: Aberrant protein-protein interactions in Parkinson's disease

The aberrant aggregation of normally soluble proteins into amyloid fibrils is the pathological hallmark of several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. Understanding this process will be key to developing both diagnostic and therapeutic approaches for neurodegenerative diseases. Recent advances in biophysical techniques, coupled with kinetic analyses have enabled a thorough description of the key molecular steps involved in protein aggregation. In this review, we discuss these advances and how they have been applied to study the ability of one such protein, α-Synuclein, to form neurotoxic oligomers.

Organizing biochemistry in space and time using prion-like self-assembly

Prion-like proteins have the capacity to adopt multiple stable conformations, at least one of which can recruit proteins from the native conformation into the alternative fold. Although classically associated with disease, prion-like assembly has recently been proposed to organize a range of normal biochemical processes in space and time. Organisms from bacteria to mammals use prion-like mechanisms to (re)organize their proteome in response to intracellular and extracellular stimuli. Prion-like behavior is an economical means to control biochemistry and gene regulation at the systems level, and prions can act as protein-based genes to facilitate quasi-Lamarckian inheritance of induced traits. These mechanisms allow individual cells to express distinct heritable traits using the same complement of polypeptides. Understanding and controlling prion-like behavior is therefore a promising strategy to combat diverse pathologies and organize engineered biological systems.

The dominant-negative interplay between p53, p63 and p73: A family affair

The tumor suppression activity of p53 is frequently impaired in cancers even when a wild-type copy of the gene is still present, suggesting that a dominant-negative effect is exerted by some of p53 mutants and isoforms. p63 and p73, which are related to p53, have also been reported to be subjected to a similar loss of function, suggesting that a dominant-negative interplay might happen between p53, p63 and p73. However, to which extent p53 hotspot mutants and isoforms of p53, p63 and p73 are able to interfere with the tumor suppressive activity of their siblings as well as the underlying mechanisms remain undeciphered. Using yeast, we showed that a dominant-negative effect is widely spread within the p53/p63/p73 family as all p53 loss-of-function hotspot mutants and several of the isoforms of p53 and p73 tested exhibit a dominant-negative potential. In addition, we found that this dominant-negative effect over p53 wild-type is based on tetramer poisoning through the formation of inactive hetero-tetramers and does not rely on a prion-like mechanism contrary to what has been previously suggested. We also showed that mutant p53-R175H gains the ability to inhibit p63 and p73 activity by a mechanism that is only partially based on tetramerization.

P. de Oliveira G. Targeting the Prion-like Aggregation of Mutant p53 to Combat Cancer

Prion-like behavior of several amyloidogenic proteins has been demonstrated in recent years. Despite having functional roles in some cases, irregular aggregation can have devastating consequences. The most commonly known amyloid diseases are Alzheimer's, Parkinson's, and Transmissible Spongiform Encephalopathies (TSEs). The pathophysiology of prion-like diseases involves the structural transformation of wild-type (wt) proteins to transmissible forms that can convert healthy proteins, generating aggregates. The mutant form of tumor suppressor protein, p53, has recently been shown to exhibit prion-like properties. Within the context of p53 aggregation and the search for ways to avert it, this review emphasizes discoveries, approaches, and research from our laboratory and others. Although its standard functions are strongly connected to tumor suppression, p53 mutants and aggregates are involved in cancer progression. p53 aggregates are heterogeneous assemblies composed of amorphous aggregates, oligomers, and amyloid-like fibrils. Evidence of these structures in tumor tissues, the in vitro capability for p53 mutants to coaggregate with wt protein, and the detection of cell-to-cell transmission indicate that cancer has the basic characteristics of prion and prion-like diseases. Various approaches aim to restore p53 functions in cancer. Methods include the use of small-molecule and peptide stabilizers of mutant p53, zinc administration, gene therapy, alkylating and DNA intercalators, and blockage of p53-MDM2 interaction. A primary challenge in developing small-molecule inhibitors of p53 aggregation is the large number of p53 mutations. Another issue is the inability to recover p53 function by dissociating mature fibrils. Consequently, efforts have emerged to target the intermediate species of the aggregation reaction. Φ-value analysis has been used to characterize the kinetics of the early phases of p53 aggregation. Our experiments using high hydrostatic pressure (HHP) and chemical denaturants have helped to clarify excited conformers of p53 that are prone to aggregation. Molecular dynamics (MD) and phasor analysis of single Trp fluorescence signals point toward the presence of preamyloidogenic conformations of p53, which are not observed for p63 or p73. Exploring the features of competent preamyloidogenic states of wt and different p53 mutants may provide a framework for designing personalized drugs for the restoration of p53 function. Protection of backbone hydrogen bonds (BHBs) has been shown to be an important factor for the stability of amyloidogenic proteins and was employed to identify and stabilize the structural defect resulting from the p53 Y220C mutation. Using MD simulations, we compared BHB protection factors between p53 family members to determine the donor-acceptor pairs in p53 that exhibit lower protection. The identification of structurally vulnerable sites in p53 should provide new insights into rational designs that can rapidly be screened using our experimental methodology. Through continued and combined efforts, the outlook is positive for the development of strategies for regulating p53 amyloid transformation.

Possible Role of the Polyglutamine Elongation in Evolution of Amyloid-Related Evolvability

The polyglutamine (polyQ) diseases, such as Huntington's disease and the spinocerebellar ataxias, are characterized by the accumulation of elongated polyQ sequences (epolyQ) and mostly occur during midlife. Considering that polyQ disorders have not been selected out in evolution, there might be important physiological functions of epolyQ during development and/or reproduction. In a similar context, the physiological functions of neurodegeneration-associated amyloidogenic proteins (APs), such as β-amyloid in Alzheimer's disease and α-synuclein in Parkinson's disease, remain elusive. In this regard, we recently proposed that evolvability for coping with diverse stressors in the brain, which is beneficial for offspring, might be relevant to the physiological functions of APs. Given analogous properties of APs and epolyQ in terms of neurotoxic amyloid-fibril formation, the objective of this paper is to determine whether evolvability could also be applied to the physiological functions of epolyQ. Indeed, APs and epolyQ are similar in many ways, including functional redundancy of non-amyloidogenic homologues, hormesis conferred by the heterogeneity of the stress-induced protein aggregates, the transgenerational prion-like transmission of the protein aggregates via germ cells, and the antagonistic pleiotropy relationship between evolvability and neurodegenerative disease. Given that epolyQ is widely expressed from microorganisms to human brain, whereas APs are only identified in vertebrates, evolvability of epolyQ is considered to be much more primitive compared to those of APs during evolution. Collectively, epolyQ may be not only be important in the pathophysiology of polyQ diseases, but also in the evolution of amyloid-related evolvability.

Role of Non-Coding RNAs in the Etiology of Bladder Cancer

According to data of the International Agency for Research on Cancer and the World Health Organization (Cancer Incidence in Five Continents, GLOBOCAN, and the World Health Organization Mortality), bladder is among the top ten body locations of cancer globally, with the highest incidence rates reported in Southern and Western Europe, North America, Northern Africa and Western Asia. Males (M) are more vulnerable to this disease than females (F), despite ample frequency variations in different countries, with a M:F ratio of 4.1:1 for incidence and 3.6:1 for mortality, worldwide. For a long time, bladder cancer was genetically classified through mutations of two genes, fibroblast growth factor receptor 3 (FGFR3, for low-grade, non-invasive papillary tumors) and tumor protein P53 (TP53, for high-grade, muscle-invasive tumors). However, more recently scientists have shown that this disease is far more complex, since genes directly involved are more than 150; so far, it has been described that altered gene expression (up- or down-regulation) may be present for up to 500 coding sequences in low-grade and up to 2300 in high-grade tumors. Non-coding RNAs are essential to explain, at least partially, this ample dysregulation. In this review, we summarize the present knowledge about long and short non-coding RNAs that have been linked to bladder cancer etiology.

Prions, amyloids, and RNA: Pieces of a puzzle

Amyloids are protein aggregates consisting of fibrils rich in β-sheets. Growth of amyloid fibrils occurs by the addition of protein molecules to the tip of an aggregate with a concurrent change of a conformation. Thus, amyloids are self-propagating protein conformations. In certain cases these conformations are transmissible / infectious; they are known as prions. Initially, amyloids were discovered as pathological extracellular deposits occurring in different tissues and organs. To date, amyloids and prions have been associated with over 30 incurable diseases in humans and animals. However, a number of recent studies demonstrate that amyloids are also functionally involved in a variety of biological processes, from biofilm formation by bacteria, to long-term memory in animals. Interestingly, amyloid-forming proteins are highly overrepresented among cellular factors engaged in all stages of mRNA life cycle: from transcription and translation, to storage and degradation. Here we review rapidly accumulating data on functional and pathogenic amyloids associated with mRNA processing, and discuss possible significance of prion and amyloid networks in the modulation of key cellular functions.

Protein aggregation, cardiovascular diseases, and exercise training: Where do we stand?

Cells ensure their protein quality control through the proteostasis network. Aging and age-related diseases, such as neurodegenerative and cardiovascular diseases, have been associated to the reduction of proteostasis network efficiency and, consequently, to the accumulation of protein misfolded aggregates. The decline in protein homeostasis has been associated with the development and progression of atherosclerotic cardiovascular disease, cardiac hypertrophy, cardiomyopathies, and heart failure. Exercise training is a key component of the management of patients with cardiovascular disease, consistently improving quality of life and prognosis. In this review, we give an overview on age-related protein aggregation, the role of the increase of misfolded protein aggregates on cardiovascular pathophysiology, and describe the beneficial or deleterious effects of the proteostasis network on the development of cardiovascular disease. We subsequently discuss how exercise training, a key lifestyle intervention in those with cardiovascular disease, could restore proteostasis and improve disease status.

Reduced Abundance and Subverted Functions of Proteins in Prion-Like Diseases: Gained Functions Fascinate but Lost Functions Affect Aetiology

Prions have served as pathfinders that reveal many aspects of proteostasis in neurons. The recent realization that several prominent neurodegenerative diseases spread via a prion-like mechanism illuminates new possibilities for diagnostics and therapeutics. Thus, key proteins in Alzheimer Disease and Amyotrophic lateral sclerosis (ALS), including amyloid-β precursor protein, Tau and superoxide dismutase 1 (SOD1), spread to adjacent cells in their misfolded aggregated forms and exhibit template-directed misfolding to induce further misfolding, disruptions to proteostasis and toxicity. Here we invert this comparison to ask what these prion-like diseases can teach us about the broad prion disease class, especially regarding the loss of these key proteins' function(s) as they misfold and aggregate. We also consider whether functional amyloids might reveal a role for subverted protein function in neurodegenerative disease. Our synthesis identifies SOD1 as an exemplar of protein functions being lost during prion-like protein misfolding, because SOD1 is inherently unstable and loses function in its misfolded disease-associated form. This has under-appreciated parallels amongst the canonical prion diseases, wherein the normally folded prion protein, PrPC, is reduced in abundance in fatal familial insomnia patients and during the preclinical phase in animal models, apparently via proteostatic mechanisms. Thus while template-directed misfolding and infectious properties represent gain-of-function that fascinates proteostasis researchers and defines (is required for) the prion(-like) diseases, loss and subversion of the functions attributed to hallmark proteins in neurodegenerative disease needs to be integrated into design towards effective therapeutics. We propose experiments to uniquely test these ideas.

p53 amyloid formation leading to its loss of function: implications in cancer pathogenesis

The transcriptional regulator p53 has an essential role in tumor suppression. Almost 50% of human cancers are associated with the loss of p53 functions, where p53 often accumulates in the nucleus as well as in cytoplasm. Although it has been previously suggested that amyloid formation could be a cause of p53 loss-of-function in subset of tumors, the characterization of these amyloids and its structure-function relationship is not yet established. In the current study, we provide several evidences for the presence of p53 amyloid formation (in human and animal cancer tissues); along with its isolation from human cancer tissues and the biophysical characterization of these tissue-derived fibrils. Using amyloid seed of p53 fragment (P8, p53(250-257)), we show that p53 amyloid formation in cells not only leads to its functional inactivation but also transforms it into an oncoprotein. The in vitro studies further show that cancer-associated mutation destabilizes the fold of p53 core domain and also accelerates the aggregation and amyloid formation by this protein. Furthermore, we also show evidence of prion-like cell-to-cell transmission of different p53 amyloid species including full-length p53, which is induced by internalized P8 fibrils. The present study suggests that p53 amyloid formation could be one of the possible cause of p53 loss of function and therefore, inhibiting p53 amyloidogenesis could restore p53 tumor suppressor functions.

Evidence of a Prion-Like Transmission of p53 Amyloid in Saccharomyces cerevisiae

Loss of p53 function is largely responsible for the occurrence of cancer in humans. Aggregation of mutant p53 has been found in multiple cancer cell types, suggesting a role of aggregation in loss of p53 function and cancer development. The p53 protein has recently been hypothesized to possess a prion-like conformation, although experimental evidence is lacking. Here, we report that human p53 can be inactivated upon exposure to preformed fibrils containing an aggregation-prone sequence-specific peptide, PILTIITL, derived from p53, and the inactive state was found to be stable for many generations. Importantly, we provide evidence of a prion-like transmission of these p53 aggregates. This study has significant implications for understanding cancer progression due to p53 malfunctioning without any loss-of-function mutation or occurrence of transcriptional inactivation. Our data might unlock new possibilities for understanding the disease and will lead to rational design of p53 aggregation inhibitors for the development of drugs against cancer.

Mutant p53 dictates the oncogenic activity of c-Abl in triple-negative breast cancers

We recently established c-Abl as a potent suppressor of triple-negative breast cancer (TNBC) progression through its reactivation of a p53:p21 signaling axis coupled to senescence. Moreover, we observed co-expression of p53 and c-Abl to be essential for normal mammary epithelial cell physiology, as this relationship is lost upon breast cancer progression. Cytoplasmic c-Abl activity is markedly increased in some TNBCs and contributes to disease progression; however, the mechanisms underlying these events remain largely unknown. In addressing this question, we show here that c-Abl is predominantly restricted to the cytoplasm of human MDA-MB-231 TNBC cells, and to the nucleus of human MCF-7 luminal A cells. TTK is a mitotic protein kinase that phosphorylates c-Abl on Thr735, thereby creating a recognition binding motif for 14-3-3 adaptor proteins in response to oxidative stress. By interrogating the METABRIC database, we observed a significant correlation between p53 expression and that of c-Abl and TTK in basal-like breast cancers. Moreover, heterologous expression of TTK in MCF-7 cells significantly stimulated their growth in part via a c-Abl-dependent mechanism. Conversely, depleting TTK expression in MDA-MB-231 cells not only inhibited their organoid growth in 3D-cultures, but also sensitized them to the tumor suppressing activities of c-Abl independent of its subcellular localization. Moreover, we show that mutant p53 forms cytoplasmic complexes with c-Abl, thereby dictating the subcellular localization of c-Abl and the sensitivity of MDA-MB-231 cells to Imatinib. In response to nutrient deprivation, c-Abl:p53 complexes readily accumulate in the nucleus, resulting in the hyperactivation of c-Abl and initiation of its anti-tumor activities. Collectively, we identified a novel mutant p53:c-Abl cytoplasmic signaling complex that promotes MDA-MB-231 cell growth and highlights the contextual cues that confer oncogenic activity to c-Abl in breast cancer.

Mechanisms and Functions of Spatial Protein Quality Control

A healthy proteome is essential for cell survival. Protein misfolding is linked to a rapidly expanding list of human diseases, ranging from neurodegenerative diseases to aging and cancer. Many of these diseases are characterized by the accumulation of misfolded proteins in intra- and extracellular inclusions, such as amyloid plaques. The clear link between protein misfolding and disease highlights the need to better understand the elaborate machinery that manages proteome homeostasis, or proteostasis, in the cell. Proteostasis depends on a network of molecular chaperones and clearance pathways involved in the recognition, refolding, and/or clearance of aberrant proteins. Recent studies reveal that an integral part of the cellular management of misfolded proteins is their spatial sequestration into several defined compartments. Here, we review the properties, function, and formation of these compartments. Spatial sequestration plays a central role in protein quality control and cellular fitness and represents a critical link to the pathogenesis of protein aggregation-linked diseases.

Cancer Chemoprevention by Resveratrol: The p53 Tumor Suppressor Protein as a Promising Molecular Target

Increasing epidemiological and experimental evidence has demonstrated an inverse relationship between the consumption of plant foods and the incidence of chronic diseases, including cancer. Microcomponents that are naturally present in such foods, especially polyphenols, are responsible for the benefits to human health. Resveratrol is a diet-derived cancer chemopreventive agent with high therapeutic potential, as demonstrated by different authors. The aim of this review is to collect and present recent evidence from the literature regarding resveratrol and its effects on cancer prevention, molecular signaling (especially regarding the involvement of p53 protein), and therapeutic perspectives with an emphasis on clinical trial results to date.

Nuclear Import and Export of the Thyroid Hormone Receptor

The thyroid hormone receptors, TRα1 and TRβ1, are members of the nuclear receptor superfamily that forms one of the most abundant classes of transcription factors in multicellular organisms. Although primarily localized to the nucleus, TRα1 and TRβ1 shuttle rapidly between the nucleus and cytoplasm. The fine balance between nuclear import and export of TRs has emerged as a critical control point for modulating thyroid hormone-responsive gene expression. Mutagenesis studies have defined two nuclear localization signal (NLS) motifs that direct nuclear import of TRα1: NLS-1 in the hinge domain and NLS-2 in the N-terminal A/B domain. Three nuclear export signal (NES) motifs reside in the ligand-binding domain. A combined approach of shRNA-mediated knockdown and coimmunoprecipitation assays revealed that nuclear entry of TRα1 is facilitated by importin 7, likely through interactions with NLS-2, and importin β1 and the adapter importin α1 interacting with both NLS-1 and NLS-2. Interestingly, TRβ1 lacks NLS-2 and nuclear import depends solely on the importin α1/β1 heterodimer. Heterokaryon and fluorescence recovery after photobleaching shuttling assays identified multiple exportins that play a role in nuclear export of TRα1, including CRM1 (exportin 1), and exportins 4, 5, and 7. Even single amino acid changes in TRs dramatically alter their intracellular distribution patterns. We conclude that mutations within NLS and NES motifs affect nuclear shuttling activity, and propose that TR mislocalization contributes to the development of some types of cancer and Resistance to Thyroid Hormone syndrome.

Polyarginine and its analogues inhibit p53 mutant aggregation and cancer cell proliferation in vitro

Arginine, a cationic amino acid is known to stabilize proteins under harsh conditions. It is widely used to stabilize protein aggregation, and to correct protein folding during protein production. Hence it would be a good therapeutic candidate for treating protein aggregation related diseases. Recent reports suggest, that the aggregation of tumor suppressor protein p53 is one of the leading causes of tumor progression. When mutated, p53 protein aggregates, loses its function leading to unwanted cell growth and ultimately results in tumor. Here in this study we focus on the inhibitory effects of polyarginine and its analogues polyornithine, canavanine, and citrulline on the inhibition of p53 mutant peptide aggregation, and p53 mutant cancer cell proliferation inhibition in vitro. Biochemical assays and cell toxicity studies were used to characterize the study. The results show that polyarginine, and polyornithine, in micromolar concentrations, significantly inhibits p53 conserved peptide aggregation, and the cell proliferation of p53 mutant cancer cells. Hence they could be promising candidates for treating p53 mutant/misfolded protein aggregation associated cancer.

Mutant p53 perturbs DNA replication checkpoint control through TopBP1 and Treslin

Accumulating evidence supports the gain-of-function of mutant forms of p53 (mutp53s). However, whether mutp53 directly perturbs the DNA replication checkpoint remains unclear. Previously, we have demonstrated that TopBP1 forms a complex with mutp53s and mediates their gain-of-function through NF-Y and p63/p73. Akt phosphorylates TopBP1 and induces its oligomerization, which inhibits its ATR-activating function. Here we show that various contact and conformational mutp53s bypass Akt to induce TopBP1 oligomerization and attenuate ATR checkpoint response during replication stress. The effect on ATR response caused by mutp53 can be exploited in a synthetic lethality strategy, as depletion of another ATR activator, DNA2, in mutp53-R273H-expressing cancer cells renders cells hypersensitive to cisplatin. Expression of mutp53-R273H also makes cancer cells more sensitive to DNA2 depletion or DNA2 inhibitors. In addition to ATR-activating function during replication stress, TopBP1 interacts with Treslin in a Cdk-dependent manner to initiate DNA replication during normal growth. We find that mutp53 also interferes with TopBP1 replication function. Several contact, but not conformational, mutp53s enhance the interaction between TopBP1 and Treslin and promote DNA replication despite the presence of a Cdk2 inhibitor. Together, these data uncover two distinct mechanisms by which mutp53 enhances DNA replication: (i) Both contact and conformational mutp53s can bind TopBP1 and attenuate the checkpoint response to replication stress, and (ii) during normal growth, contact (but not conformational) mutp53s can override the Cdk2 requirement to promote replication by facilitating the TopBP1/Treslin interaction.

Distinct modulatory role of RNA in the aggregation of the tumor suppressor protein p53 core domain

Inactivation of the tumor suppressor protein p53 by mutagenesis, chemical modification, protein-protein interaction, or aggregation has been associated with different human cancers. Although DNA is the typical substrate of p53, numerous studies have reported p53 interactions with RNA. Here, we have examined the effects of RNA of varied sequence, length, and origin on the mechanism of aggregation of the core domain of p53 (p53C) using light scattering, intrinsic fluorescence, transmission electron microscopy, thioflavin-T binding, seeding, and immunoblot assays. Our results are the first to demonstrate that RNA can modulate the aggregation of p53C and full-length p53. We found bimodal behavior of RNA in p53C aggregation. A low RNA:protein ratio (∼1:50) facilitates the accumulation of large amorphous aggregates of p53C. By contrast, at a high RNA:protein ratio (≥1:8), the amorphous aggregation of p53C is clearly suppressed. Instead, amyloid p53C oligomers are formed that can act as seeds nucleating de novo aggregation of p53C. We propose that structured RNAs prevent p53C aggregation through surface interaction and play a significant role in the regulation of the tumor suppressor protein.

Nuclear inclusion bodies of mutant and wild-type p53 in cancer: a hallmark of p53 inactivation and proteostasis remodelling by p53 aggregation

Although p53 protein aggregates have been observed in cancer cell lines and tumour tissue, their impact in cancer remains largely unknown. Here, we extensively screened for p53 aggregation phenotypes in tumour biopsies, and identified nuclear inclusion bodies (nIBs) of transcriptionally inactive mutant or wild-type p53 as the most frequent aggregation-like phenotype across six different cancer types. p53-positive nIBs co-stained with nuclear aggregation markers, and shared molecular hallmarks of nIBs commonly found in neurodegenerative disorders. In cell culture, tumour-associated stress was a strong inducer of p53 aggregation and nIB formation. This was most prominent for mutant p53, but could also be observed in wild-type p53 cell lines, for which nIB formation correlated with the loss of p53's transcriptional activity. Importantly, protein aggregation also fuelled the dysregulation of the proteostasis network in the tumour cell by inducing a hyperactivated, oncogenic heat-shock response, to which tumours are commonly addicted, and by overloading the proteasomal degradation system, an observation that was most pronounced for structurally destabilized mutant p53. Patients showing tumours with p53-positive nIBs suffered from a poor clinical outcome, similar to those with loss of p53 expression, and tumour biopsies showed a differential proteostatic expression profile associated with p53-positive nIBs. p53-positive nIBs therefore highlight a malignant state of the tumour that results from the interplay between (1) the functional inactivation of p53 through mutation and/or aggregation, and (2) microenvironmental stress, a combination that catalyses proteostatic dysregulation. This study highlights several unexpected clinical, biological and therapeutically unexplored parallels between cancer and neurodegeneration. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.