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Alzheimer’s disease (AD) is the main cause of dementia, and β‐amyloid (Aβ) is a central factor in the initiation and progression of the disease. Different forms of Aβ have been identified as monomers, oligomers, and amyloid fibrils. Many proteins have been implicated as putative receptors of respective forms of Aβ. Distinct forms of Aβ oligomers are considered to be neurotoxic species that trigger the pathophysiology of AD. It was reported that cellular prion protein (PrPC) is one of the most selective and high‐affinity binding partners of Aβ oligomers. The interaction of Aβ oligomers with PrPC is important to synaptic dysfunction and loss. The binding of Aβ oligomers to PrPC has mostly been studied with synthetic peptides, cell culture, and murine models of AD by biochemical and biological methods. However, the molecular mechanisms underlying the relationship between Aβ oligomers and PrPC remain unclear, especially in the human brain. We immunohistochemically investigated the relationship between Aβ oligomers and PrPC in human brain tissue with and without amyloid pathology. We histologically demonstrate that PrPC accumulates with aging in human brain tissue even prior to AD mainly within diffuse‐type amyloid plaques, which are composed of more soluble Aβ oligomers without stacked β‐sheet fibril structures. Our results suggest that PrPC accumulating plaques are associated with more soluble Aβ oligomers, and appear even prior to AD. The investigation of PrPC accumulating plaques may provide new insights into AD., PrPC accumulates within a subset of diffuse‐type amyloid plaques (arrowheads). We propose this new subtype of amyloid plaque as the PrP (+) plaque, composed of more soluble and oligomeric Aβ. Antibodies: 6E10 (left), 3F4 (right); Insets: Higher magnification of the plaques (*).

Studies on the cellular prion protein (PrPC) have been actively conducted because misfolded PrPC is known to cause transmissible spongiform encephalopathies or prion disease. PrPC is a glycophosphatidylinositol-anchored cell surface glycoprotein that has been reported to affect several cellular functions such as stress protection, cellular differentiation, mitochondrial homeostasis, circadian rhythm, myelin homeostasis, and immune modulation. Recently, it has also been reported that PrPC mediates tumor progression by enhancing the proliferation, metastasis, and drug resistance of cancer cells. In addition, PrPC regulates cancer stem cell properties by interacting with cancer stem cell marker proteins. In this review, we summarize how PrPC promotes tumor progression in terms of proliferation, metastasis, drug resistance, and cancer stem cell properties. In addition, we discuss strategies to treat tumors by modulating the function and expression of PrPC via the regulation of HSPA1L/HIF-1α expression and using an anti-prion antibody.

The mobility of cellular prion protein (PrPC) in specific cell membrane domains and among distinct cell compartments dictates its molecular interactions and directs its cell function. PrPC works in concert with several partners to organize signaling platforms implicated in various cellular processes. The scaffold property of PrPC is able to gather a molecular repertoire to create heterogeneous membrane domains that favor endocytic events. Dynamic trafficking of PrPC through multiple pathways, in a well-orchestrated mechanism of intra and extracellular vesicular transport, defines its functional plasticity, and also assists the conversion and spreading of its infectious isoform associated with neurodegenerative diseases. In this review, we highlight how PrPC traffics across intra- and extracellular compartments and the consequences of this dynamic transport in governing cell functions and contributing to prion disease pathogenesis.

Cellular prion protein (PrP(C)) is a widely expressed glycosylphosphatidylinositol-anchored membrane protein. Scrapie prion protein is a misfolded and aggregated form of PrP(C) responsible for prion-induced neurodegenerative diseases. Understanding the function of the nonpathogenic PrP(C) monomer is an important objective. PrP(C) may be shed from the cell surface to generate soluble derivatives. Herein, we studied a recombinant derivative of PrP(C) (soluble cellular prion protein, S-PrP) that corresponds closely in sequence to a soluble form of PrP(C) shed from the cell surface by proteases in the A Disintegrin And Metalloprotease (ADAM) family. S-PrP activated cell-signaling in PC12 and N2a cells. TrkA was transactivated by Src family kinases and extracellular signal–regulated kinase 1/2 was activated downstream of Trk receptors. These cell-signaling events were dependent on the N-methyl-d-aspartate receptor (NMDA-R) and low-density lipoprotein receptor-related protein-1 (LRP1), which functioned as a cell-signaling receptor system in lipid rafts. Membrane-anchored PrP(C) and neural cell adhesion molecule were not required for S-PrP–initiated cell-signaling. S-PrP promoted PC12 cell neurite outgrowth. This response required the NMDA-R, LRP1, Src family kinases, and Trk receptors. In Schwann cells, S-PrP interacted with the LRP1/NMDA-R system to activate extracellular signal–regulated kinase 1/2 and promote cell migration. The effects of S-PrP on PC12 cell neurite outgrowth and Schwann cell migration were similar to those caused by other proteins that engage the LRP1/NMDA-R system, including activated α(2)-macroglobulin and tissue-type plasminogen activator. Collectively, these results demonstrate that shed forms of PrP(C) may exhibit important biological activities in the central nervous system and the peripheral nervous system by serving as ligands for the LRP1/NMDA-R system.

Cytoplasmic aggregation of the primarily nuclear TAR DNA-binding protein 43 (TDP-43) affects neurons in most amyotrophic lateral sclerosis (ALS) and approximately half of frontotemporal lobar degeneration (FTLD) cases. The cellular prion protein, PrPC, has been recognized as a common receptor and downstream effector of circulating neurotoxic species of several proteins involved in neurodegeneration. Here, capitalizing on our recently adapted TDP-43 real time quaking induced reaction, we set reproducible protocols to obtain standardized preparations of recombinant TDP-43 fibrils. We then exploited two different cellular systems (human SH-SY5Y and mouse N2a neuroblastoma cells) engineered to express low or high PrPC levels to investigate the link between PrPC expression on the cell surface and the internalization of TDP-43 fibrils. Fibril uptake was increased in cells overexpressing either human or mouse prion protein. Increased internalization was associated with detrimental consequences in all PrP-overexpressing cell lines but was milder in cells expressing the human form of the prion protein. As described for other amyloids, treatment with TDP-43 fibrils induced a reduction in the accumulation of the misfolded form of PrPC, PrPSc, in cells chronically infected with prions. Our results expand the list of misfolded proteins whose uptake and detrimental effects are mediated by PrPC, which encompass almost all pathological amyloids involved in neurodegeneration.

A cellular prion protein (PrPC) is a ubiquitous cell surface glycoprotein, and its physiological functions have been receiving increased attention. Endogenous PrPC is present in various kidney tissues and undergoes glomerular filtration. In prion diseases, abnormal prion proteins are found to accumulate in renal tissues and filtered into urine. Urinary prion protein could serve as a diagnostic biomarker. PrPC plays a role in cellular signaling pathways, reno-protective effects, and kidney iron uptake. PrPC signaling affects mitochondrial function via the ERK pathway and is affected by the regulatory influence of microRNAs, small molecules, and signaling proteins. Targeting PrPC in acute and chronic kidney disease could help improve iron homeostasis, ameliorate damage from ischemia/reperfusion injury, and enhance the efficacy of mesenchymal stem/stromal cell or extracellular vesicle-based therapeutic strategies. PrPC may also be under the influence of BMP/Smad signaling and affect the progression of TGF-β-related renal fibrosis. PrPC conveys TNF-α resistance in some renal cancers, and therefore, the coadministration of anti-PrPC antibodies improves chemotherapy. PrPC can be used to design antibody–drug conjugates, aptamer–drug conjugates, and customized tissue inhibitors of metalloproteinases to suppress cancer. With preclinical studies demonstrating promising results, further research on PrPC in the kidney may lead to innovative PrPC-based therapeutic strategies for renal disease.

// Jae-Kyo Jeong 1,2 and Sang-Youel Park 1,2 1 Biosafety Research Institute, College of Veterinary Medicine, Chonbuk National University, Jeonju, Korea 2 Department of Bioactive Material Sciences and Research Center of Bioactive Materials, Chonbuk National University, Jeonju, Korea Correspondence to: Sang-Youel Park, email: // Keywords : autophagy flux, alpha-7 nicotinic receptor, prpc, prion, Geotarget Received : April 03, 2015 Accepted : June 28, 2015 Published : July 22, 2015 Abstract Activation of the alpha7 nicotinic acetylcholine receptor (α7nAchR ) is regulated by prion protein (PrPC) expression and has a neuroprotective effect by modulating autophagic flux. In this study, we hypothesized that PrPC may regulate α7nAchR activation and that may prevent prion-related neurodegenerative diseases by regulating autophagic flux. PrP(106–126) treatment decreased α 7nAchR expression and activation of autophagic flux. In addition, the α7nAchR activator PNU-282987 enhanced autophagic flux and protected neuron cells against PrP(106–126)-induced apoptosis. However, activation of autophagy and the protective effects of PNU-282987 were inhibited in PrPC knockout hippocampal neuron cells. In addition, PrPC knockout hippocampal neuron cells showed decreased α7nAchR expression levels. Adenoviral overexpression of PrPC in PrPC knockout hippocampal neuron cells resulted in activation of autophagic flux and inhibition of prion peptide-mediated cell death via α7nAchR activation. This is the first report demonstrating that activation of α7nAchR -mediated autophagic flux is regulated by PrPC, and that activation of α7nAchR regulated by PrPC expression may play a pivotal role in protection of neuron cells against prion peptide-induced neuron cell death by autophagy. These results suggest that α7nAchR -mediated autophagic flux may be involved in the pathogenesis of prion-related diseases and may be a therapeutic target for prion-related neurodegenerative diseases.

// Jin-Young Park 1, * , Jae-Kyo Jeong 1, 2, * , Ju-Hee Lee 1, 2 , Ji-Hong Moon 1, 2 , Sung-Wook Kim 1 , You-Jin Lee 1, 2 , Sang-Youel Park 1, 2 1 Biosafety Research Institute, College of Veterinary Medicine, Chonbuk National University, Jeonju, Jeonbuk, South Korea 2 Department of Bioactive Material Sciences and Research Center of Bioactive Materials, Chonbuk National University, Jeonju, Jeonbuk, South Korea * These authors have contributed equally to this work Correspondence to: Sang-Youel Park, e-mail: sypark@chonbuk.ac.kr Keywords: PrPc, Hypoxia, TRAIL, HIF-1α, Colon cancer Received: October 01, 2014 Accepted: January 01, 2015 Published: January 20, 2015 ABSTRACT Hypoxia decreases cytotoxic responses to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein. Cellular prion protein (PrPc) is regulated by HIF-1α in neurons. We hypothesized that PrPc is involved in hypoxia-mediated resistance to TRAIL-induced apoptosis. We found that hypoxia induced PrPc protein and inhibited TRAIL-induced apoptosis. Thus silencing of PrPc increased TRAIL-induced apoptosis under hypoxia. Overexpression of PrPc protein using an adenoviral vector inhibited TRAIL-induced apoptosis. In xenograft model in vivo , shPrPc transfected cells were more sensitive to TRAIL-induced apoptosis than in shMock transfected cells. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia.

International audience; Extracellular vesicles (EVs) are composed of microvesicles and exosomes. Exosomes are small membrane vesicles (40-120 nm sized) of endosomal origin released in the extracellular medium from cells when multivesicular bodies fuse with the plasma membrane, whereas microvesicles (i.e., shedding vesicles, 100 nm to 1 μm sized) bud from the plasma membrane. Exosomes and microvesicles carry functional proteins and nucleic acids (especially mRNAs and microRNAs) that can be transferred to surrounding cells and tissues and can impact multiple dimensions of the cellular life. Most of the cells, if not all, from neuronal to immune cells, release exosomes and microvesicles in the extracellular medium, and all biological fluids including blood (serum/plasma), urine, cerebrospinal fluid, and saliva contain EVs.Prion-infected cultured cells are known to secrete infectivity into their environment. We characterized this cell-free form of prions and showed that infectivity was associated with exosomes. Since exosomes are produced by a variety of cells, including cells that actively accumulate prions, they could be a vehicle for infectivity in body fluids and could participate to the dissemination of prions in the organism. In addition, such infectious exosomes also represent a natural, simple, biological material to get key information on the abnormal PrP forms associated with infectivity.In this chapter, we describe first a method that allows exosomes and microvesicles isolation from prion-infected cell cultures and in a second time the strategies to characterize the prions containing exosomes and their ability to disseminate the prion agent.

Prion diseases are a family of transmissible, progressive, and uniformly fatal neurodegenerative disorders that affect humans and animals. Although cross-species transmissions of prions are usually limited by an apparent “species barrier”, the spread of a prion disease to humans by ingestion of contaminated food, or via other routes of exposure, indicates that animal prions can pose a significant public health risk. The infectious agent responsible for the transmission of prion diseases is a misfolded conformer of the prion protein, PrP Sc , a pathogenic isoform of the host-encoded, cellular prion protein, PrP C . The detailed mechanisms of prion conversion and replication, as well as the high-resolution structure of PrP Sc , are unknown. This review will discuss the general background related to prion biology and assess the structural models proposed to date, while highlighting the experimental challenges of elucidating the structure of PrP Sc . Keywords: prion; cellular prion protein; PrP

The cellular prion protein (PrPc) and hypoxia appear to be tightly intertwined. Beneficial effects of PrPc on neuronal survival under hypoxic conditions such as focal cerebral ischemia are strongly supported. Conversely, increasing evidence indicates detrimental effects of increased PrPc expression on cancer progression, another condition accompanied by low oxygen tensions. A switch between anaerobic and aerobic metabolism characterizes both conditions. A cellular process that might unite both is glycolysis. Putative role of PrPc in stimulation of glycolysis in times of need is indeed thought provoking. A significance of astrocytic PrPc expression for neuronal survival under hypoxic conditions and possible association of PrPc with the astrocyte-neuron lactate shuttle is considered. We posit PrPc-induced lactate production via transactivation of lactate dehydrogenase A by hypoxia inducible factor 1a as an important factor for survival of both neurons and tumor cells in hypoxic microenvironment. Concomitantly, we discuss a cross-talk between Wnt/b-catenin and PI3K/Akt signaling pathways in executing PrPc-induced activation of glycolysis. Finally, we would like to emphasize that we see a great potential in joining expertise from both fields, neuroscience and cancer research in revealing the mechanisms underlying hypoxia-related pathologies. PrPc may prove focal point for future research. Open-Access-Publikationsfonds 2016 peerReviewed

International audience; The cellular prion protein PrP(C)/CD230 is a GPI-anchor protein highly expressed in cells from the nervous and immune systems and well conserved among vertebrates. In the last decade, several studies suggested that PrP(C) displays antiviral properties by restricting the replication of different viruses, and in particular retroviruses such as murine leukemia virus (MuLV) and the human immunodeficiency virus type 1 (HIV-1). In this context, we previously showed that PrP(C) displays important similarities with the HIV-1 nucleocapsid protein and found that PrP(C) expression in a human cell line strongly reduced HIV-1 expression and virus production. Using different PrP(C) mutants, we report here that the anti-HIV-1 properties are mostly associated with the amino-terminal 24-KRPKP-28 basic domain. In agreement with its reported RNA chaperone activity, we found that PrP(C) binds to the viral genomic RNA of HIV-1 and negatively affects its translation. Using a combination of biochemical and cell imaging strategies, we found that PrP(C) colocalizes with the virus assembly machinery at the plasma membrane and at the virological synapse in infected T cells. Depletion of PrP(C) in infected T cells and microglial cells favors HIV-1 replication, confirming its negative impact on the HIV-1 life cycle.

A conformational conversion of the cellular prion protein (PrP(C)) is now recognized as the causal event of fatal neurodegenerative disorders, known as prion diseases. In spite of long-lasting efforts, however, the physiological role of PrP(C) remains unclear. It has been reported that PrP(C) is expressed in various areas of the olfactory system, including the olfactory epithelium, but its precise localization in olfactory sensory neurons (OSNs) is still debated. Here, using immunohistochemistry tools, we have reinvestigated the expression and localization of PrP(C) in the olfactory epithelium of adult congenic mice expressing different PrP(C) amounts, that is, wild-type, PrP-knockout, and transgenic PrP(C)-overexpressing animals. We found that PrP(C) was expressed in OSNs, in which, however, it was unevenly distributed, being detectable at low levels in cell bodies, dendrites and apical layer, and more abundantly in axons. We also studied the involvement of PrP(C) in the response of the olfactory epithelium to odorants, by comparing the electro-olfactograms of the 3 mouse lines subjected to different stimulation protocols. We found no significant difference between the 3 PrP genotypes, supporting previous reports that exclude a direct action of PrP(C) in the early signal transduction activity of the olfactory epithelium.

Conversion of the cellular isoform of the prion protein (PrPC) into the disease-associated isoform (PrPSc) plays a key role in the development of prion diseases. Within its cellular pathway, PrPCundergoes several posttranslational modifications, i.e., the attachment of two N-linked glycans and a glycosyl phosphatidyl inositol (GPI) anchor, by which it is linked to the plasma membrane on the exterior cell surface. To study the interaction of PrPCwith model membranes, we purified posttranslationally modified PrPCfrom transgenic Chinese hamster ovary (CHO) cells. The mono-, di- and oligomeric states of PrPCfree in solution were analyzed by analytical ultracentrifugation. The interaction of PrPCwith model membranes was studied using both lipid vesicles in solution and lipid bilayers bound to a chip surface. The equilibrium and mechanism of PrPCassociation with the model membranes were analyzed by surface plasmon resonance. Depending on the degree of saturation of binding sites, the concentration of PrPCreleased from the membrane into aqueous solution was estimated at between 10-9and 10-7 M. This corresponds to a free energy of the insertion reaction of -48 kJ/mol. Consequences for the conversion of PrPCto PrPScare discussed.

The cellular prion protein (PrP(C)) is an ubiquitously expressed glycoprotein that is most abundant in the central nervous system. It is thought to play a role in many cellular processes, including neuroprotection, but may also contribute to Alzheimer's disease and some cancers. However, it is best known for its central role in the prion diseases, such as Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE), and scrapie. These protein misfolding diseases can be sporadic, acquired, or genetic and are caused by refolding of endogenous PrP(C) into a beta sheet-rich, pathogenic form, PrP(Sc). Once prions are present in the central nervous system, they increase and spread during a long incubation period that is followed by a relatively short clinical disease phase, ending in death. PrP molecules can be broadly categorized as either 'good' (cellular) PrP(C) or 'bad' (scrapie prion-type) PrP(Sc), but both populations are heterogeneous and different forms of PrP(C) may influence various cellular activities. Both PrP(C) and PrP(Sc) are localized predominantly at the cell surface, with the C-terminus attached to the plasma membrane via a glycosyl-phosphatidylinositol (GPI) anchor and both can exist in cleaved forms. PrP(C) also has cytosolic and transmembrane forms, and PrP(Sc) is known to exist in a variety of conformations and aggregation states. Here, we discuss the roles of different PrP isoforms in sickness and in health, and show the subcellular distributions of several forms of PrP that are particularly relevant for PrP(C) to PrP(Sc) conversion and prion-induced pathology in the hippocampus. The Authors. Published by

The cellular prion protein (PrP(C)), a cell surface glycoprotein involved in prion disorders, has been shown to mediate the toxicity of several pathological aggregates, including its own misfolded state and some oligomeric assemblies of the amyloid β peptide, which are thought to be primarily responsible for the synaptic dysfunction characterizing Alzheimer's disease. Thus, elucidating the physiological function of PrP(C), and how it could be corrupted by the interaction with misfolded proteins, may provide important insights to understand the pathological processes of prion and Alzheimer's diseases, and possibly other neurodegenerative disorders. In this manuscript, we review the data supporting a role for PrP(C) at the intersection of different neurodegenerative diseases, discuss potential mechanisms by which this protein could mediate neurotoxic signals, and examine therapeutic approaches that may arise from the identification of PrP(C)-directed compounds.

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

International audience; Prions are infectious proteins responsible for a group of fatal neurodegenerative diseases called transmissible spongiform encephalopathies (TSEs), or prion diseases. In mammals, prions reproduce themselves by recruiting the normal cellular protein (PrPC) and inducing its conversion to the disease-causing isoform denominated PrPSc. Recently, anti-prion antibodies have been shown to permanently cure prion-infected cells. However, the inability of full-lenght antibodies and proteins to cross the blood-brain barrier (BBB) hampers their use in the therapy of TSEs in vivo. Alternatively, brain delivery of prion-specific scFv by adeno-associated virus (AAV) transfer delays the onset of the disease in infected mice, although protection is not complete. We investigated the anti-prion effects of a recombinant anti-PrP (D18) single-chain variable fragment (scFv) by direct addition to scrapie infected cell cultures or by infection with both lentivirus and adeno-associated virus (AAV) transducing vectors. We show that recombinant anti-PrP scFv is able to reduce proteinase K-resistant PrP content in infected cells. In addition, we demonstrate that lentiviruses are more efficient than AAV in gene transferring of the anti-PrP scFv gene and in reducing PrPSc content in infected neuronal cell lines. Finally, we have used a bioinformatic approach to construct a structural model of D18scFv-PrPC complex. Interestingly, according to the docking results, ArgPrP151 (Arg151 from prion protein) is the key residue for the interactions with D18scFv, anchoring the PrPC to the cavity of the antibody. Taken together, these results indicate that combined passive and active immunotherapy targeting PrP might be promising strategies for therapeutic intervention in prion diseases.

Tens of putative interacting partners of the cellular prion protein (PrP(C)) have been identified, yet the physiologic role of PrP(C) remains unclear. For the first time, however, a recent paper has demonstrated that the absence of PrP(C) produces a lethal phenotype. Starting from this evidence, here we discuss the validity of past and more recent literature supporting that, as part of protein platforms at the cell surface, PrP(C) may bridge extracellular matrix molecules and/or membrane proteins to intracellular signaling pathways.

While the prion protein (PrP) is clearly involved in neuropathology, its physiological roles remain elusive. Here, we demonstrate PrP functions in cell–substrate interaction in Drosophila S2, N2a and HeLa cells. PrP promotes cell spreading and/or filopodia formation when overexpressed, and lamellipodia when downregulated. Moreover, PrP normally accumulates in focal adhesions (FAs), and its downregulation leads to reduced FA numbers, increased FA length, along with Src and focal adhesion kinase (FAK) activation. Furthermore, its overexpression elicits the formation of novel FA-like structures, which require intact reggie/flotillin microdomains. Altogether, PrP modulates process formation and FA dynamics, possibly via signal transduction involving FAK and Src.

Inherited prion diseases are neurodegenerative pathologies related to genetic mutations in the prion protein (PrP) gene, which favour the conversion of PrPC into a conformationally altered pathogenic form, PrPSc. The molecular basis of PrPC/PrPSc conversion, the intracellular compartment where it occurs and how this process leads to neurological dysfunction are not yet known. We have studied the intracellular synthesis, degradation and localization of a PrP mutant associated with a genetic form of Creutzfeldt-Jakob disease (CJD), PrPT182A, in transfected FRT cells. PrPT182A is retained in the endoplasmic reticulum (ER), is mainly associated with detergent-resistant microdomains (DRMs) and is partially resistant to proteinase K digestion. Although an untranslocated form of this mutant is polyubiquitylated and undergoes ER-associated degradation, the proteasome is not responsible for the degradation of its misfolded form, suggesting that it does not have a role in the pathogenesis of inherited diseases. On the contrary, impairment of PrPT182A association with DRMs by cholesterol depletion leads to its accumulation in the ER and substantially increases its misfolding. These data support the previous hypothesis that DRMs are important for the correct folding of PrP and suggest that they might have a protective role in pathological scrapie-like conversion of PrP mutants.

RK13 cell lines generated to express bovine PrPC with a four extra octarepeat insertional mutation (Bo-10ORPrPC) show partially insoluble PrPC and lower rates of cell growth when compared to either the same cells expressing wild type Bo-6ORPrPC or the original RK13 cell line. The expression of Bo-10ORPrPC in cell cultures was also associated with changes in cell size and reorganization of the actin cytoskeleton. This last process was reversed by Clostridium difficile toxin-B, a specific inhibitor of small GTPase proteins. Further, in clones expressing Bo-10ORPrPC, increased proportions of cells at cell cycle stage G2/M were observed. Proteasome inhibitors caused a further expansion of G2/M-stage cells that was more marked in cell lines expressing Bo-10ORPrPC than those expressing Bo-6ORPrPC, while this effect was minimal or null in the original RK13 cell line. Hence, the presence of Bo-10ORPrPC in RK13 cells promotes cell cycle arrest at G2/M, and the effect is amplified by proteasome inhibition. These findings suggest a role for PrPC in cell morphology and cell cycle regulation, and open new avenues for understanding the mechanisms underlying PrP mutation-associated diseases. © 2006 Federation of European Biochemical Studies.

Prions have been extensively studied since they represent a new class of infectious agents in which a protein, PrPsc (prion scrapie), appears to be the sole component of the infectious particle. They are responsible for transmissible spongiform encephalopathies, which affect both humans and animals. The mechanism of disease propagation is well understood and involves the interaction of PrPsc with its cellular isoform (PrPc) and subsequently abnormal structural conversion of the latter. PrPc is a glycoprotein anchored on the cell surface by a glycosylphosphatidylinositol moiety and expressed in most cell types but mainly in neurons. Prion diseases have been associated with the accumulation of the abnormally folded protein and its neurotoxic effects; however, it is not known if PrPc loss of function is an important component. New efforts are addressing this question and trying to characterize the physiological function of PrPc. At least four different mouse strains in which the PrP gene was ablated were generated and the results regarding their phenotype are controversial. Localization of PrPc on the cell membrane makes it a potential candidate for a ligand uptake, cell adhesion and recognition molecule or a membrane signaling molecule. Recent data have shown a potential role for PrPc in the metabolism of copper and moreover that this metal stimulates PrPc endocytosis. Our group has recently demonstrated that PrPc is a high affinity laminin ligand and that this interaction mediates neuronal cell adhesion and neurite extension and maintenance. Moreover, PrPc-caveolin-1 dependent coupling seems to trigger the tyrosine kinase Fyn activation. These data provide the first evidence for PrPc involvement in signal transduction.

Purpose: the physiologic role of the cellular prion protein (PrPc) is unknown. Mice devoid of PrPc develop normally and show only minor deficits. However, electrophysiologic and histologic alterations found in these mice suggest a possible:role fur PrPc in seizure threshold and/or epilepsy.Methods: We tested the sensitivity of PrPc knockout mice to seizures induced by single convulsant or repeated subconvulsant (kindling) doses of pentylenetetrazol (PTZ), and to status epilepticus (SE) induced by kainic acid or pilocarpine.Results. in PTZ kindling, seizure severity progressed faster in the PrPc knockout group, in which 92.8% reached stage 5 or death after 4 days of stimulation, as opposed to 38.4% in wildtype animals: After 10 injections, mortality was 85.7% among knockouts and 15.3% among controls. After a single PTZ injection (60 mg/kg), overall mortality due to seizures was 91% in knockout mice, but only 33% among wild-type animals. Pilocarpine-induced SE (320 mg/kg) caused an 86.7% mortality in knockouts, as opposed to 40% in wild-type animals. Finally, after kainic acid injections (10 mg/kg), 70% of the knockouts developed at least one severe seizure, and 50% showed repetitive seizures, whereas no wild-type animal exhibited observable seizures.Conclusions: Animals lacking cellular prion protein expression are more susceptible to seizures induced by various convulsant agents. This is perhaps the most striking alteration yet found in PrPc-null mice, who at first analysis appeared to be completely normal. A possible role for PrPc in chronic and idiopathic (familial), secondary, or cryptogenic epilepsies in humans remains to be investigated. Univ Fed Rio Grande Sul, ICBS, Dept Bioquim, Ctr Memoria, BR-90035003 Porto Alegre, RS, Brazil UNIFESP, EPM, Dept Expt Neurol, São Paulo, Brazil Ludwig Inst Canc Res, São Paulo, Brazil UNIFESP, EPM, Dept Expt Neurol, São Paulo, Brazil Web of Science

Prions are an unconventional form of infectious agents composed only of protein and involved in transmissible spongiform encephalopathies in humans and animals. The infectious particle is composed by PrPsc which is an isoform of a normal cellular glycosyl-phosphatidylinositol (GPI) anchored protein, PrPc, of unknown function. The two proteins differ only in conformation, PrPc is composed of 40% a helix while PrPsc has 60% ß-sheet and 20% a helix structure. The infection mechanism is trigged by interaction of PrPsc with cellular prion protein causing conversion of the latter's conformation. Therefore, the infection spreads because new PrPsc molecules are generated exponentially from the normal PrPc. The accumulation of insoluble PrPsc is probably one of the events that lead to neuronal death. Conflicting data in the literature showed that PrPc internalization is mediated either by clathrin-coated pits or by caveolae-like membranous domains. However, both pathways seem to require a third protein (a receptor or a prion-binding protein) either to make the connection between the GPI-anchored molecule to clathrin or to convert PrPc into PrPsc. We have recently characterized a 66-kDa membrane receptor which binds PrPc in vitro and in vivo and mediates the neurotoxicity of a human prion peptide. Therefore, the receptor should have a role in the pathogenesis of prion-related diseases and in the normal cellular process. Further work is necessary to clarify the events triggered by the association of PrPc/PrPsc with the receptor.

We used a bovine brain cDNA library to perform a yeast two-hybrid assay with bovine mature PrP(C) as bait. The screening result showed that alphaB-crystalline interacted with PrP(C). The interaction was further evaluated both in vivo and in vitro with different methods, such as immunofluorescent colocalization, native polyacrylamide-gel electrophoresis, and IAsys biosensor assays. The results suggested that alphaB-crystalline may have the ability to refold denatured prion proteins, and provided first evidence that alphaB-crystalline is directly associated with prion protein.