Potential roles for prions and protein-only inheritance in cancer

In Silico Bioinformatics Analysis on the Role of Long Non-Coding RNAs as Drivers and Gatekeepers of Androgen-Independent Prostate Cancer Using LNCaP and PC-3 Cells

Prostate cancer (PCa) is the leading cancer in men globally. The association between PCa and long non-coding RNAs (lncRNAs) has been reported. Aberrantly expressed lncRNAs have been documented in each of the cancer "hallmarks". Androgen signaling plays an important role in PCa progression. This study aimed to profile the aberrantly expressed lncRNAs in androgen-dependent (LNCaP) PCa compared to androgen-independent (PC-3) PCa cells. This was achieved by using a 384-well plate of PCa lncRNA gene panel. Differential expression of ±2 up or downregulation was determined using the CFX Maestro software v2.1. LncSEA and DIANA-miRPath were used to identify the enriched pathways. Telomerase RNA component (TERC) lncRNA was illustrated to participate in various tumourigenic classes by in silico bioinformatics analysis and was thus selected for validation using RT-qPCR. Further bioinformatics analysis revealed the involvement of differentially expressed lncRNAs in oncogenic pathways. Some lncRNAs undergo hypermethylation, others are encapsulated by exosomes, while others interact with several microRNAs (miRNAs), favouring tumourigenic pathways. Notably, TERC lncRNA was shown to interact with tumour-suppressor miRNAs hsa-miR-4429 and hsa-miR-320b. This interaction in turn activates TGF-β-signaling and ECM-receptor interaction pathways, favouring the progression of PCa. Understanding lncRNAs as competitive endogenous RNA molecules and their interactions with miRNAs may aid in the identification of novel prognostic PCa biomarkers and therapeutic targets.

Prion protein-dependent regulation of p53-MDM2 crosstalk during endoplasmic reticulum stress and doxorubicin treatments might be essential for cell fate in human breast cancer cell line, MCF-7

In this study, we investigated the effect of doxorubicin and tunicamycin treatment alone or in combination on MDM-, Cul9-and prion protein (PrP)-mediated subcellular regulation of p53 in the context of apoptosis and autophagy. MTT analysis was performed to determine the cytotoxic effect of the agents. Apoptosis was monitorized by ELISA, flow cytometry and JC-1 assay. Monodansylcadaverine assay was performed for autophagy. Western blotting and immunofluorescence were performed to determine p53, MDM2, CUL9 and PrP levels. Doxorubicin increased p53, MDM2 and CUL9 levels in a dose-dependent manner. Expression of p53 and MDM2 was higher at the 0.25 μM concentration of tunicamycin compared to the control, but it decreased at 0.5 μM and 1 μM concentrations. CUL9 expression was significantly decreased only after treatment of tunicamycin at 0.25 μM. According to its glycosylation status, the upper band of PrP increased only in combination treatment. In combination treatment, p53 expression was higher than control, whereas MDM2 and CUL9 expressions were decreased. Combination treatments may make MCF-7 cells more susceptible to apoptosis rather than autophagy. In conclusion, PrP may be important in determining the fate of cell death through crosstalk between proteins such as p53 and MDM2 under endoplasmic reticulum (ER) stress conditions. Further studies are needed to obtain in-depth information on these potential molecular networks.

Cellular Prion Protein Role in Cancer Biology: Is It A Potential Therapeutic Target?

Cancers are worldwide health concerns, whether they are sporadic or hereditary. The fundamental mechanism that causes somatic or oncogenic mutations and ultimately aids cancer development is still unknown. However, mammalian cells with protein-only somatic inheritance may also contribute to cancerous malignancies. Emerging data from a recent study show that prion-like proteins and prions (PrP^C) are crucial entities that have a functional role in developing neurological disorders and cancer. Furthermore, excessive PrP^C expression profiling has also been detected in non-neuronal tissues, such as the lymphoid cells, kidney, GIT, lung, muscle, and mammary glands. PrP^C expression is strongly linked with the proliferation and metastasis of pancreatic, prostate, colorectal, and breast malignancies. Similarly, experimental investigation presented that the PrP^C expression, including the prion protein-coding gene (PRNP) and p53 ag are directly associated with tumorigenicity and metastasis (tumor suppressor gene). The ERK2 (extracellular signal-regulated kinase) pathway also confers a robust metastatic capability for PrP^C-induced epithelial to mesenchymal transition. Additionally, prions could alter the epigenetic regulation of genes and overactive the mitogen-activated protein kinase (MAPK) signaling pathway, which promotes the development of cancer in humans. Protein overexpression or suppression caused by a prion and prion-like proteins has also been linked to oncogenesis and metastasis. Meanwhile, additional studies have discovered resistance to therapeutic targets, highlighting the significance of protein expression levels as potential diagnostic indicators and therapeutic targets.

Human RAD51 Protein Forms Amyloid-like Aggregates In Vitro

RAD51 is a central protein of homologous recombination and DNA repair processes that maintains genome stability and ensures the accurate repair of double-stranded breaks (DSBs). In this work, we assessed amyloid properties of RAD51 in vitro and in the bacterial curli-dependent amyloid generator (C-DAG) system. Resistance to ionic detergents, staining with amyloid-specific dyes, polarized microscopy, transmission electron microscopy (TEM), X-ray diffraction and other methods were used to evaluate the properties and structure of RAD51 aggregates. The purified human RAD51 protein formed detergent-resistant aggregates in vitro that had an unbranched cross-β fibrillar structure, which is typical for amyloids, and were stained with amyloid-specific dyes. Congo-red-stained RAD51 aggregates demonstrated birefringence under polarized light. RAD51 fibrils produced sharp circular X-ray reflections at 4.7 Å and 10 Å, demonstrating that they had a cross-β structure. Cytoplasmic aggregates of RAD51 were observed in cell cultures overexpressing RAD51. We demonstrated that a key protein that maintains genome stability, RAD51, has amyloid properties in vitro and in the C-DAG system and discussed the possible biological relevance of this observation.

Melatonin: Regulation of Prion Protein Phase Separation in Cancer Multidrug Resistance

The unique ability to adapt and thrive in inhospitable, stressful tumor microenvironments (TME) also renders cancer cells resistant to traditional chemotherapeutic treatments and/or novel pharmaceuticals. Cancer cells exhibit extensive metabolic alterations involving hypoxia, accelerated glycolysis, oxidative stress, and increased extracellular ATP that may activate ancient, conserved prion adaptive response strategies that exacerbate multidrug resistance (MDR) by exploiting cellular stress to increase cancer metastatic potential and stemness, balance proliferation and differentiation, and amplify resistance to apoptosis. The regulation of prions in MDR is further complicated by important, putative physiological functions of ligand-binding and signal transduction. Melatonin is capable of both enhancing physiological functions and inhibiting oncogenic properties of prion proteins. Through regulation of phase separation of the prion N-terminal domain which targets and interacts with lipid rafts, melatonin may prevent conformational changes that can result in aggregation and/or conversion to pathological, infectious isoforms. As a cancer therapy adjuvant, melatonin could modulate TME oxidative stress levels and hypoxia, reverse pH gradient changes, reduce lipid peroxidation, and protect lipid raft compositions to suppress prion-mediated, non-Mendelian, heritable, but often reversible epigenetic adaptations that facilitate cancer heterogeneity, stemness, metastasis, and drug resistance. This review examines some of the mechanisms that may balance physiological and pathological effects of prions and prion-like proteins achieved through the synergistic use of melatonin to ameliorate MDR, which remains a challenge in cancer treatment.

Neuroprotective effect and potential of cellular prion protein and its cleavage products for treatment of neurodegenerative disorders part II: strategies for therapeutics development

Introduction: The cellular prion protein (PrP^C), some of its derivatives (especially PrP N-terminal N1 peptide and shed PrP), and PrP^C-containing exosomes have strong neuroprotective activities, which have been reviewed in the companion article (Part I) and are briefly summarized here.Areas covered: We propose that elevating the extracellular levels of a protective PrP form using gene therapy and other approaches is a very promising novel avenue for prophylactic and therapeutic treatments against prion disease, Alzheimer's disease, and several other neurodegenerative diseases. We will dissect the pros and cons of various potential PrP-based treatment options and propose a few strategies that are more likely to succeed. The cited references were obtained from extensive PubMed searches of recent literature, including peer-reviewed original articles and review articles.Expert opinion: Concurrent knockdown of celllular PrP expression and elevation of the extracellular levels of a neuroprotective PrP N-terminal peptide via optimized gene therapy vectors is a highly promising broad-spectrum prophylactic and therapeutic strategy against several neurodegenerative diseases, including prion diseases, Alzheimer's disease and Parkinson's disease.

Neuroprotective effect and potential of cellular prion protein and its cleavage products for treatment of neurodegenerative disorders part I. a literature review

INTRODUCTION

The cellular prion protein (PrP^C) is well known for its pathogenic roles in prion diseases, several other neurodegenerative diseases (such as Alzheimer's disease), and multiple types of cancer, but the beneficial aspects of PrP^C and its cleavage products received much less attention.

AREAS COVERED

Here the authors will systematically review the literatures on the negative as well as protective aspects of PrP^C and its derivatives (especially PrP N-terminal N1 peptide and shed PrP). The authors will dissect the current findings on N1 and shed PrP, including evidence for their neuroprotective effects, the categories of PrP^C cleavage, and numerous cleavage enzymes involved. The authors will also discuss the protective effects and therapeutic potentials of PrP^C-rich exosomes. The cited articles were obtained from extensive PubMed searches of recent literature, including peer-reviewed original articles and review articles.

EXPERT OPINION

PrP and its N-terminal fragments have strong neuroprotective activities that should be explored for therapeutics and prophylactics development against prion disease, Alzheimer's disease and a few other neurodegenerative diseases. The strategies to develop PrP-based therapeutics and prophylactics for these neurodegenerative diseases will be discussed in a companion article (Part II).

Application of yeast to studying amyloid and prion diseases

Amyloids are fibrous cross-β protein aggregates that are capable of proliferation via nucleated polymerization. Amyloid conformation likely represents an ancient protein fold and is linked to various biological or pathological manifestations. Self-perpetuating amyloid-based protein conformers provide a molecular basis for transmissible (infectious or heritable) protein isoforms, termed prions. Amyloids and prions, as well as other types of misfolded aggregated proteins are associated with a variety of devastating mammalian and human diseases, such as Alzheimer's, Parkinson's and Huntington's diseases, transmissible spongiform encephalopathies (TSEs), amyotrophic lateral sclerosis (ALS) and transthyretinopathies. In yeast and fungi, amyloid-based prions control phenotypically detectable heritable traits. Simplicity of cultivation requirements and availability of powerful genetic approaches makes yeast Saccharomyces cerevisiae an excellent model system for studying molecular and cellular mechanisms governing amyloid formation and propagation. Genetic techniques allowing for the expression of mammalian or human amyloidogenic and prionogenic proteins in yeast enable researchers to capitalize on yeast advantages for characterization of the properties of disease-related proteins. Chimeric constructs employing mammalian and human aggregation-prone proteins or domains, fused to fluorophores or to endogenous yeast proteins allow for cytological or phenotypic detection of disease-related protein aggregation in yeast cells. Yeast systems are amenable to high-throughput screening for antagonists of amyloid formation, propagation and/or toxicity. This review summarizes up to date achievements of yeast assays in application to studying mammalian and human disease-related aggregating proteins, and discusses both limitations and further perspectives of yeast-based strategies.

Risk of Alzheimer's Disease in Cancer Patients: Analysis of Mortality Data from the US SEER Population-Based Registries

Previous studies have reported an inverse association between cancer and Alzheimer's disease (AD), which are leading causes of human morbidity and mortality. We analyzed the SEER (Surveillance, Epidemiology, and End Results) data to estimate the risk of AD death in (i) cancer patients relative to reference populations stratified on demographic and clinical variables, and (ii) female breast cancer (BC) patients treated with chemotherapy or radiotherapy, relative to those with no/unknown treatment status. Our results demonstrate the impact of race, cancer type, age and time since cancer diagnosis on the risk of AD death in cancer patients. While the risk of AD death was decreased in white patients diagnosed with various cancers at 45 or more years of age, it was increased in black patients diagnosed with cancers before 45 years of age (likely due to early onset AD). Chemotherapy decreased the risk of AD death in white women diagnosed with BC at the age of 65 or more, however radiotherapy displayed a more complex pattern with early decrease and late increase in the risk of AD death during a prolonged time interval after the treatment. Our data point to links between molecular mechanisms involved in cancer and AD, and to the potential applicability of some anti-cancer treatments against AD.

Anti-prion Butenolides and Diphenylpropanones from the Australian Ascidian Polycarpa procera

A library of 500 Australian marine invertebrate extracts was screened for anti-prion activity using a yeast-based assay, and this resulted in an extract from the ascidian Polycarpa procera showing potent activity. Purification of this extract led to the isolation of six new butenolide metabolites, the procerolides 1-4 and two related diphenylpropanones, the procerones 5 and 6, as the bioactive components. The structures of 1-6 were elucidated from the analysis of 1D/2D NMR and MS data, and their absolute configurations determined from comparison of experimental and computed ECD data. Compounds 1-6 were tested for anti-prion activity in a yeast-based assay, and 1 and 5 displayed potent bioactivity (EC₅₀ of 23 and 29 μM, respectively) comparable to the potently active anti-prion compound guanabenz. The procerolides and procerones are the first anti-prion compounds to be reported from ascidians, indicating that ascidians may be an untapped source of new lead anti-prion compounds.

Secreted cellular prion protein binds doxorubicin and correlates with anthracycline resistance in breast cancer

Anthracyclines are amongst the most effective chemotherapeutics ever developed, but they produce grueling side-effects, serious adverse events and resistance often develops over time. We found that these compounds can be sequestered by secreted cellular Prion protein (PrPC), blocking their cytotoxic activity. This effect was dose-dependent using either cell line-conditioned medium or human serum as a source of PrPC. Genetic depletion of PrPC or inhibition of binding via chelation of ionic copper prevented the interaction and restored cytotoxic activity. This was more pronounced for doxorubicin than its epimer, epirubicin. Investigating the relevance to breast cancer management, we found that the levels of PRNP transcript in pre-treatment tumor biopsies stratified relapse-free survival after neoadjuvant treatment with anthracyclines, particularly amongst doxorubicin-treated patients with residual disease at surgery (p=2.8E-08). These data suggest that local sequestration could mediate treatment resistance. Consistent with this, tumor cell expression of PrPC protein correlated with poorer response to doxorubicin but not epirubicin in an independent cohort analyzed by immunohistochemistry, particularly soluble isoforms released into the extracellular environment by shedding (p=0.015). These findings have important potential clinical implications for frontline regimen decision-making. We suggest there is warranted utility for prognostic PrPC/PRNP assays to guide chemo-sensitization strategies that exploit an understanding of PrPC-anthracycline-copper ion complexes.

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.

Biomolecular Assemblies: Moving from Observation to Predictive Design

Biomolecular assembly is a key driving force in nearly all life processes, providing structure, information storage, and communication within cells and at the whole organism level. These assembly processes rely on precise interactions between functional groups on nucleic acids, proteins, carbohydrates, and small molecules, and can be fine-tuned to span a range of time, length, and complexity scales. Recognizing the power of these motifs, researchers have sought to emulate and engineer biomolecular assemblies in the laboratory, with goals ranging from modulating cellular function to the creation of new polymeric materials. In most cases, engineering efforts are inspired or informed by understanding the structure and properties of naturally occurring assemblies, which has in turn fueled the development of predictive models that enable computational design of novel assemblies. This Review will focus on selected examples of protein assemblies, highlighting the story arc from initial discovery of an assembly, through initial engineering attempts, toward the ultimate goal of predictive design. The aim of this Review is to highlight areas where significant progress has been made, as well as to outline remaining challenges, as solving these challenges will be the key that unlocks the full power of biomolecules for advances in technology and medicine.

Yeast-based screening of natural product extracts results in the identification of prion inhibitors from a marine sponge

One of the major medical challenges of the twenty-first century is the treatment of incurable and fatal neurodegenerative disorders caused by misfolded prion proteins. Since the discovery of these diseases a number of studies have been conducted to identify small molecules for their treatment, however to date no curative treatment is available. These studies can be highly expensive and time consuming, but more recent experimental approaches indicate a significant application for yeast prions in these studies. We therefore used yeast prions to optimize previous high-throughput methods for the cheaper, easier and more rapid screening of natural extracts. Through this approach we aimed to identify natural yeast-prion inhibitors that could be useful in the development of novel treatment strategies for neurodegenerative disorders. We screened 500 marine invertebrate extracts from temperate waters in Australia allowing the identification of yeast-prion inhibiting extracts. Through the bioassay-driven chemical investigation of an active Suberites sponge extract, a group of bromotyrosine derivatives were identified as potent yeast-prion inhibitors. This study outlines the importance of natural products and yeast prions as a first-stage screen for the identification of new chemically diverse and bioactive compounds.

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.

Pathway-Based Kernel Boosting for the Analysis of Genome-Wide Association Studies

The analysis of genome-wide association studies (GWAS) benefits from the investigation of biologically meaningful gene sets, such as gene-interaction networks (pathways). We propose an extension to a successful kernel-based pathway analysis approach by integrating kernel functions into a powerful algorithmic framework for variable selection, to enable investigation of multiple pathways simultaneously. We employ genetic similarity kernels from the logistic kernel machine test (LKMT) as base-learners in a boosting algorithm. A model to explain case-control status is created iteratively by selecting pathways that improve its prediction ability. We evaluated our method in simulation studies adopting 50 pathways for different sample sizes and genetic effect strengths. Additionally, we included an exemplary application of kernel boosting to a rheumatoid arthritis and a lung cancer dataset. Simulations indicate that kernel boosting outperforms the LKMT in certain genetic scenarios. Applications to GWAS data on rheumatoid arthritis and lung cancer resulted in sparse models which were based on pathways interpretable in a clinical sense. Kernel boosting is highly flexible in terms of considered variables and overcomes the problem of multiple testing. Additionally, it enables the prediction of clinical outcomes. Thus, kernel boosting constitutes a new, powerful tool in the analysis of GWAS data and towards the understanding of biological processes involved in disease susceptibility.

The amyloid interactome: Exploring protein aggregation

Protein-protein interactions are the quintessence of physiological activities, but also participate in pathological conditions. Amyloid formation, an abnormal protein-protein interaction process, is a widespread phenomenon in divergent proteins and peptides, resulting in a variety of aggregation disorders. The complexity of the mechanisms underlying amyloid formation/amyloidogenicity is a matter of great scientific interest, since their revelation will provide important insight on principles governing protein misfolding, self-assembly and aggregation. The implication of more than one protein in the progression of different aggregation disorders, together with the cited synergistic occurrence between amyloidogenic proteins, highlights the necessity for a more universal approach, during the study of these proteins. In an attempt to address this pivotal need we constructed and analyzed the human amyloid interactome, a protein-protein interaction network of amyloidogenic proteins and their experimentally verified interactors. This network assembled known interconnections between well-characterized amyloidogenic proteins and proteins related to amyloid fibril formation. The consecutive extended computational analysis revealed significant topological characteristics and unraveled the functional roles of all constituent elements. This study introduces a detailed protein map of amyloidogenicity that will aid immensely towards separate intervention strategies, specifically targeting sub-networks of significant nodes, in an attempt to design possible novel therapeutics for aggregation disorders.

Cellular Prion Protein Mediates Pancreatic Cancer Cell Survival and Invasion through Association with and Enhanced Signaling of Notch1

Up-regulation of human prion protein (PrP) in patients with pancreatic ductal adenocarcinoma (PDAC) is associated with a poor prognosis. However, the underlying molecular mechanism of PrP-mediated tumorigenesis is not completely understood. In this study, we found that PDAC cell lines can be divided into either PrP high expresser or PrP low expresser. In addition to filamin A (FLNA), PrP interacts with Notch1, forming a PrP/FLNA/Notch1 complex. Silencing PrP in high-expresser cells decreases Notch1 expression and Notch1 signaling. These cells exhibited decreased proliferation, xenograft growth, and tumor invasion but show increased tumor apoptosis. These phenotypes were rescued by ectopically expressed and activated Notch1. By contrast, overexpression of PrP in low expressers increases Notch1 expression and signaling, enhances proliferation, and increases tumor invasion and xenograft growth that can be blocked by a Notch inhibitor. Our data further suggest that PrP increases Notch1 stability likely through suppression of Notch proteosome degradation. Additionally, we found that targeting PrP combined with anti-Notch is much more effective than singularly targeted therapy in retarding PDAC growth. Finally, we show that coexpression of PrP and Notch1 confers an even poorer prognosis than PrP expression alone. Taken together, our results have unraveled a novel molecular pathway driven by interactions between PrP and Notch1 in the progression of PDAC, supporting a critical tumor-promoting role of Notch1 in PrP-expressing PDAC tumors.

Cellular Prion Protein Mediates Pancreatic Cancer Cell Survival and Invasion through Association with and Enhanced Signaling of Notch1

Up-regulation of human prion protein (PrP) in patients with pancreatic ductal adenocarcinoma (PDAC) is associated with a poor prognosis. However, the underlying molecular mechanism of PrP-mediated tumorigenesis is not completely understood. In this study, we found that PDAC cell lines can be divided into either PrP high expresser or PrP low expresser. In addition to filamin A (FLNA), PrP interacts with Notch1, forming a PrP/FLNA/Notch1 complex. Silencing PrP in high-expresser cells decreases Notch1 expression and Notch1 signaling. These cells exhibited decreased proliferation, xenograft growth, and tumor invasion but show increased tumor apoptosis. These phenotypes were rescued by ectopically expressed and activated Notch1. By contrast, overexpression of PrP in low expressers increases Notch1 expression and signaling, enhances proliferation, and increases tumor invasion and xenograft growth that can be blocked by a Notch inhibitor. Our data further suggest that PrP increases Notch1 stability likely through suppression of Notch proteosome degradation. Additionally, we found that targeting PrP combined with anti-Notch is much more effective than singularly targeted therapy in retarding PDAC growth. Finally, we show that coexpression of PrP and Notch1 confers an even poorer prognosis than PrP expression alone. Taken together, our results have unraveled a novel molecular pathway driven by interactions between PrP and Notch1 in the progression of PDAC, supporting a critical tumor-promoting role of Notch1 in PrP-expressing PDAC tumors.

Expression of prion protein is closely associated with pathological and clinical progression and abnormalities of p53 in head and neck squamous cell carcinomas

Prion protein (PrP) is a glycosyl-phosphatidylinositol (GPI)-anchored membrane protein that functions as a unique pathogenic agent in transmissible spongiform encephalopathy (TSE). In the past decade, overexpression of PrP was observed in a number of human malignant tumors, such as gastric, breast and pancreatic cancer. However, the role of PrP expression in squamous cell carcinoma is rarely documented. To screen PrP expression in head and neck squamous cell carcinoma (HNSCCs), the paraffin-embedded specimens of 92 pathologically diagnosed HNSCCs were assessed by PrP-specific immunohistochemistry (IHC). A total of 55.43% (51/92) of the tested carcinoma tissues were PrP-positive. The rate of positivity and the staining intensity of PrP were closely related with the pathological degree of the HNSCCs; a higher rate of PrP expression was noted in the group of poorly differentiated cancers. PrP-positivity rates increased along with the progression of the clinical grade of the carcinomas. Further evaluation of the associations between PrP expression and the data concerning p53 abnormalities and human papillomavirus (HPV) infection in these samples as previously described, revealed that PrP-positive staining was more frequently detected in the tissues with p53-positive accumulation and the wild-type TP53 gene. The patients with a proline (Pro) polymorphism in SNP72 of TP53 showed significantly higher PrP-positive rates than those with arginine (Arg). No notable difference in PrP expression was identified between the HPV-positive and HPV-negative group. These data indicate a close association of PrP expression with clinical and histological differentiation of HNSCCs, as well as abnormalities of p53.

The cellular prion protein PrPc is a partner of the Wnt pathway in intestinal epithelial cells

We reported previously that the cellular prion protein (PrP(c)) is a component of desmosomes and contributes to the intestinal barrier function. We demonstrated also the presence of PrP(c) in the nucleus of proliferating intestinal epithelial cells. Here we sought to decipher the function of this nuclear pool. In human intestinal cancer cells Caco-2/TC7 and SW480 and normal crypt-like HIEC-6 cells, PrP(c) interacts, in cytoplasm and nucleus, with γ-catenin, one of its desmosomal partners, and with β-catenin and TCF7L2, effectors of the canonical Wnt pathway. PrP(c) up-regulates the transcriptional activity of the β-catenin/TCF7L2 complex, whereas γ-catenin down-regulates it. Silencing of PrP(c) results in the modulation of several Wnt target gene expressions in human cells, with different effects depending on their Wnt signaling status, and in mouse intestinal crypt cells in vivo. PrP(c) also interacts with the Hippo pathway effector YAP, suggesting that it may contribute to the regulation of gene transcription beyond the β-catenin/TCF7L2 complex. Finally, we demonstrate that PrP(c) is required for proper formation of intestinal organoids, indicating that it contributes to proliferation and survival of intestinal progenitors. In conclusion, PrP(c) must be considered as a new modulator of the Wnt signaling pathway in proliferating intestinal epithelial cells.

The aggregation of mutant p53 produces prion-like properties in cancer

The tumor suppressor protein p53 loses its function in more than 50% of human malignant tumors. Recent studies have suggested that mutant p53 can form aggregates that are related to loss-of-function effects, negative dominance and gain-of-function effects and cancers with a worsened prognosis. In recent years, several degenerative diseases have been shown to have prion-like properties similar to mammalian prion proteins (PrPs). However, whereas prion diseases are rare, the incidence of these neurodegenerative pathologies is high. Malignant tumors involving mutated forms of the tumor suppressor p53 protein seem to have similar substrata. The aggregation of the entire p53 protein and three functional domains of p53 into amyloid oligomers and fibrils has been demonstrated. Amyloid aggregates of mutant p53 have been detected in breast cancer and malignant skin tumors. Most p53 mutations related to cancer development are found in the DNA-binding domain (p53C), which has been experimentally shown to form amyloid oligomers and fibrils. Several computation programs have corroborated the predicted propensity of p53C to form aggregates, and some of these programs suggest that p53C is more likely to form aggregates than the globular domain of PrP. Overall, studies imply that mutant p53 exerts a dominant-negative regulatory effect on wild-type (WT) p53 and exerts gain-of-function effects when co-aggregating with other proteins such as p63, p73 and acetyltransferase p300. We review here the prion-like behavior of oncogenic p53 mutants that provides an explanation for their dominant-negative and gain-of-function properties and for the high metastatic potential of cancers bearing p53 mutations. The inhibition of the aggregation of p53 into oligomeric and fibrillar amyloids appears to be a promising target for therapeutic intervention in malignant tumor diseases.

Overexpression of PrPc, combined with MGr1-Ag/37LRP, is predictive of poor prognosis in gastric cancer

Prion protein (PrPc) has been previously reported to be involved in gastric cancer (GC) development and progression. However, the association between expression of PrPc and GC prognosis is yet poorly characterized. In the present study, the expressions of PrPc and MGr1-Ag/37LRP, a protein interacting with PrPc, were detected using the tissue microarray technique and immunohistochemical method to compare clinicopathological parameters of 238 GC patients. We found that the expressions of PrPc and MGr1-Ag/37LRP were upregulated in GC lesions compared with their expressions in adjacent noncancerous tissues (p<0.01). High expression of PrPc was detected in 37.39% (89/238) of GC patients and positively correlated with the expression of MGr1-Ag/37LRP (r=0.532, p<0.001). PrPc expression was associated with a number of clinicopathological parameters including depth of invasion and lymph node metastasis of the tumor (p<0.001). High expression of PrPc brought a poorer prognosis than low PrPc expression. Moreover, GC patients with high level of PrPc and high level of MGr1-Ag/37LRP had the poorest prognosis. Multivariate survival analysis suggested that, along with other parameters, combined expression of PrPc and MGr1-Ag/37LRP was independent prognostic factors for GC patients. These data indicates that overexpression of PrPc, combined with MGr1-Ag/37LRP, is predictive of poor prognosis in GC and thereby could be used to guide the clinical decision.

Expanding the prion concept to cancer biology: dominant-negative effect of aggregates of mutant p53 tumour suppressor

p53 is a key protein that participates in cell-cycle control, and its malfunction can lead to cancer. This tumour suppressor protein has three main domains; the N-terminal transactivation domain, the CTD (C-terminal domain) and the core domain (p53C) that constitutes the sequence-specific DBD (DNA-binding region). Most p53 mutations related to cancer development are found in the DBD. Aggregation of p53 into amyloid oligomers and fibrils has been shown. Moreover, amyloid aggregates of both the mutant and WT (wild-type) forms of p53 were detected in tumour tissues. We propose that if p53 aggregation occurred, it would be a crucial aspect of cancer development, as p53 would lose its WT functions in an aggregated state. Mutant p53 can also exert a dominant-negative regulatory effect on WT p53. Herein, we discuss the dominant-negative effect in light of p53 aggregation and the fact that amyloid-like mutant p53 can convert WT p53 into more aggregated species, leading into gain of function in addition to the loss of tumour suppressor function. In summary, the results obtained in the last decade indicate that cancer may have characteristics in common with amyloidogenic and prion diseases.

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

Over 50% of all human cancers lose p53 function. To evaluate the role of aggregation in cancer, we asked whether wild-type (WT) p53 and the hot-spot mutant R248Q could aggregate as amyloids under physiological conditions and whether the mutant could seed aggregation of the wild-type form. The central domains (p53C) of both constructs aggregated into a mixture of oligomers and fibrils. R248Q had a greater tendency to aggregate than WT p53. Full-length p53 aggregated into amyloid-like species that bound thioflavin T. The amyloid nature of the aggregates was demonstrated using x-ray diffraction, electron microscopy, FTIR, dynamic light scattering, cell viabilility assay, and anti-amyloid immunoassay. The x-ray diffraction pattern of the fibrillar aggregates was consistent with the typical conformation of cross β-sheet amyloid fibers with reflexions of 4.7 Å and 10 Å. A seed of R248Q p53C amyloid oligomers and fibrils accelerated the aggregation of WT p53C, a behavior typical of a prion. The R248Q mutant co-localized with amyloid-like species in a breast cancer sample, which further supported its prion-like effect. A tumor cell line containing mutant p53 also revealed massive aggregation of p53 in the nucleus. We conclude that aggregation of p53 into a mixture of oligomers and fibrils sequestrates the native protein into an inactive conformation that is typical of a prionoid. This prion-like behavior of oncogenic p53 mutants provides an explanation for the negative dominance effect and may serve as a potential target for cancer therapy.