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The cellular prion protein (PrPC) plays many roles in the developing and adult brain. In addition, PrPC binds to several amyloids in oligomeric and prefibrillar forms and may act as a putative receptor of abnormal misfolded protein species. The role of PrPC in tau seeding and spreading is not known. In the present study, we have inoculated well-characterized sarkosyl-insoluble fractions of sporadic Alzheimer's disease (sAD) into the brain of adult wild-type mice (Prnp+/+), Prnp0/0 (ZH3 strain) mice, and mice over-expressing the secreted form of PrPC lacking their GPI anchor (Tg44 strain). Phospho-tau (ptau) seeding and spreading involving neurons and oligodendrocytes were observed three and six months after inoculation. 3Rtau and 4Rtau deposits from the host tau, as revealed by inoculating Mapt0/0 mice and by using specific anti-mouse and anti-human tau antibodies suggest modulation of exon 10 splicing of the host mouse Mapt gene elicited by exogenous sAD-tau. However, no tau seeding and spreading differences were observed among Prnp genotypes. Our results show that PrPC does not affect tau seeding and spreading in vivo. [ABSTRACT FROM AUTHOR]

The properties of infectious prions and the pathology of the diseases they cause are dependent upon the unique conformation of each prion strain. How the pathology of prion disease correlates with different strains and genetic backgrounds has been investigated via in vivo assays, but how interactions between specific prion strains and cell types contribute to the pathology of prion disease has been dissected more effectively using in vitro cell lines. Observations made through in vivo and in vitro assays have informed each other with regard to not only how genetic variation influences prion properties, but also how infectious prions are taken up by cells, modified by cellular processes and propagated, and the cellular components they rely on for persistent infection. These studies suggest that persistent cellular infection results from a balance between prion propagation and degradation. This balance may be shifted depending upon how different cell lines process infectious prions, potentially altering prion stability, and how fast they can be transported to the lysosome. Thus, in vitro studies have given us a deeper understanding of the interactions between different prions and cell types and how they may influence prion disease phenotypes in vivo. [ABSTRACT FROM AUTHOR]

Cellular prion protein (PrPC) is a highly conserved glycoprotein, present both anchored in the cell membrane and soluble in the extracellular medium. It has a diversity of ligands and is variably expressed in numerous tissues and cell subtypes, most notably in the central nervous system (CNS). Its importance has been brought to light over the years both under physiological conditions, such as embryogenesis and immune system homeostasis, and in pathologies, such as cancer and neurodegenerative diseases. During development, PrPC plays an important role in CNS, participating in axonal growth and guidance and differentiation of glial cells, but also in other organs such as the heart, lung, and digestive system. In diseases, PrPC has been related to several types of tumors, modulating cancer stem cells, enhancing malignant properties, and inducing drug resistance. Also, in non-neoplastic diseases, such as Alzheimer's and Parkinson's diseases, PrPC seems to alter the dynamics of neurotoxic aggregate formation and, consequently, the progression of the disease. In this review, we explore in detail the multiple functions of this protein, which proved to be relevant for understanding the dynamics of organism homeostasis, as well as a promising target in the treatment of both neoplastic and degenerative diseases. [ABSTRACT FROM AUTHOR]

Diabetic retinopathy (DR), a major complication of diabetes caused by vascular damage and pathological proliferation of retinal vessels, often progresses to vision loss. Vascular endothelial growth factor (VEGF) signaling plays a pivotal role in the development of DR, but the exact underlying molecular mechanisms remain ill-defined. Cellular prion protein (PrPc) is a surface protein expressed by vascular endothelial cells, and the increased expression of PrPc is associated with physiological and pathological vascularization. Nevertheless, a role for PrPc in the development of DR has not been appreciated. Here, we addressed this question. We found that the development of streptozocin (STZ)-induced DR, but not the STZ-induced hyperglycemia/diabetes itself, was significantly attenuated in PrPc-KO mice, compared to control wildtype (WT) mice, evident by measurement of retinal vascular leakage, retinal neovascularization, a retinopathy score and visual acuity assessment. Moreover, the attenuation of DR severity seemingly resulted from attenuation of retinal neovascularization via VEGF/ras/rac signaling. Together, our study suggests a previously unappreciated role for PrPc in the development of DR. [ABSTRACT FROM AUTHOR]

Serine/threonine protein phosphatases have been described in many pathogenic bacteria as essential enzymes involved in phosphorylation-dependent signal transduction pathways and frequently associated with the virulence of these organisms. An inspection of Mycoplasma synoviae genome revealed the presence of a gene ( prpC) encoding a putative protein phosphatase of the protein phosphatase 2C (PP2C) subfamily. Here, we report a complete biochemical characterization of M. synoviae phosphatase (PrpC) and the particular role of metal ions in the structure-function relationship of this enzyme. PrpC amino acid sequence analysis revealed that all the residues involved in the dinuclear metal center and the putative third metal ion-coordinating residues, conserved in PP2C phosphatases, are present in PrpC. PrpC is a monomeric protein able to dephosphorylate phospho-substrates with Mn ions' dependence. Thermal stability analysis demonstrated the enzyme stability at mild temperatures and the influence of Mn ions in this property. Mass spectrometry analysis suggested that three metal ions bind to PrpC, two of which with an apparent high-affinity constant. Mutational analysis of the putative third metal-coordinating residues, Asp122 and Arg164, revealed that these variants exhibited a weaker binding of manganese ions, and that both mutations affected PrpC phosphatase activity. According to these results, PrpC is a metal-dependent protein phosphatase member with an improved stability in the holo form and with Asp122, possibly implicated in the third metal-binding site, essential to catalytic activity. [ABSTRACT FROM AUTHOR]

The cellular prion protein, encoded by Prnp gene, is involved in neuroprotection, neuroplasticity and neurodevelopment. The variant allele Valine at codon 129 of the Prnp was associated with decreased brain volume in healthy volunteers and schizophrenic patients. We investigate the association between the cerebellum volume and the presence of variant allele Valine at codon 129 of the Prnp gene in patients with mesial temporal lobe epilepsy related to hippocampal sclerosis (MTLE-HS). The Prnp coding sequence was determined in 41 refractory MTLE-HS patients. The cerebellum volume corrected by the intracranial volume of patients with the normal Prnp genotypes was compared with that of patients presenting the variant alleles at codon 129. Twenty patients showed the Met129Met genotype, 16 showed Met129Val, and 5 had Val129Val. There were no association among clinical, demographic, electrophysiological, antiepileptic drugs used, and the presence of the Prnp variant alleles. The presence of Prnp variant allele at codon 129 was not associated with the analyzed cerebellum volume. Prnp variant alleles at codon 129 are not associated with cerebellum volume in patients with refractory MTLE-HS. [ABSTRACT FROM AUTHOR]

Bacillus anthracis Ser/Thr protein kinase PrkC (BasPrkC) is important for virulence of the bacterium within the host. Homologs of PrkC and its cognate phosphatase PrpC (BasPrpC) are the most conserved mediators of signaling events in diverse bacteria. BasPrkC homolog in Bacillus subtilis regulates critical processes like spore germination and BasPrpC modulates the activity of BasPrkC by dephosphorylation. So far, biochemical and genetic studies have provided important insights into the roles of BasPrkC and BasPrpC; however, regulation of their activities is not known. We studied the regulation of BasPrkC/BasPrpC pair and observed that Zn metal ions can alter their activities. Zn promotes BasPrkC kinase activity while inhibits the BasPrpC phosphatase activity. Concentration of Zn in growing B. anthracis cells was found to vary with growth phase. Zn was found to be lowest in log phase cells while it was highest in spores. This variation in Zn concentration is significant for understanding the antagonistic activities of BasPrkC/BasPrpC pair. Our results also show that BasPrkC activity is modulated by temperature changes and kinase inhibitors. Additionally, we identified Elongation Factor Tu (BasEf-Tu) as a substrate of BasPrkC/BasPrpC pair and assessed the impact of their regulation on BasEf-Tu phosphorylation. Based on these results, we propose Zn as an important regulator of BasPrkC/BasPrpC mediated phosphorylation cascades. Thus, this study reveals additional means by which BasPrkC can be activated leading to autophosphorylation and substrate phosphorylation. [ABSTRACT FROM AUTHOR]

key event in the pathogenesis of prion diseases is the conversion of the normal cellular isoform of the prion protein into the disease-associated isoform, but the mechanisms operating in this critical event are not yet fully understood. A number of novel approaches have recently been developed to study factors influencing this process. One of these, the protein misfolding cyclical amplification (PMCA) technique, has been used to explore defined factors influencing the conversion of cellular prion protein in a cell-free model system. Although initially developed in animal models, this technique has been increasingly applied to human prion diseases. Recent studies have focused on the role of different isoforms of the disease-associated human prion protein and the effects of the naturally occurring polymorphism at codon 129 in the human prion protein gene on the conversion process, improving our understanding of the interaction between host and agent factors that influence the wide range of phenotypes in human prion diseases. This technique also allows a greatly enhanced sensitivity of detection of disease-associated prion protein in human tissues and fluids, which is potentially applicable to disease screening, particularly for variant Creutzfeldt-Jakob disease. The PMCA technique can also be used to model human susceptibility to a range of prions of non-human origin, which is likely to prove of considerable future interest as more novel and potentially pathogenic prion diseases are identified in animal species that form part of the human food chain. [ABSTRACT FROM AUTHOR]

We previously reported that treatment with P-glycoprotein (P-gp) substrates promotes in vitro invasion in multidrug-resistant (MDR) breast cancer cells. This effect is initiated by the P-gp pump function and mediated by interaction of P-gp with some unknown component(s). However, the underlying mechanism(s) remains poorly understood. Here we confirm a novel physical interaction between P-gp and cellular prion protein (PrPc). Blocking P-gp activity or depletion of PrPc inhibited paclitaxel (P-gp substrate)- induced invasion. Paclitaxel further facilitated the formation of P-gp/PrPc clusters residing in caveolar domains and promoted the association of P-gp with caveolin-1. Both caveolin-1 and the integrity of caveolae were required for the drug-induced invasion. In addition, the P-gp/PrPc complex also played an important role in anti-apoptotic activity of MCF7/Adr cells.These data provide new insights into the mode by which MDR breast cancers evade cytotoxic attacks from P-gp substrates and also suggest a role for P-gp/ PrPc interaction in this process. [ABSTRACT FROM AUTHOR]

Prion diseases are caused by an infectious agent constituted by a rogue protein called prion (PrPSc) of neuronal origin (PrPc) and are exemplified by Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cattle. Considerable efforts have been made to understand the cerebral damage caused by these diseases but a clear comprehensive view cannot be achieved without defining the neurophysiological function of PrPc. This lack of information is in part attributable to our ignorance of the precise localization of PrPc in the brain neuronal cell. One relevant option to explore this aspect is to undertake PrP immunohistochemistry at the electron-microscopy level, knowing that this challenge raises major technical constraints. In describing the attempts and restrictions of the various approaches used, we review here the efforts that have been invested in this particular field of prionology. The common result emerging from these contributions is that the synapse could be the site at which PrPc exerts its critical activity. This location suggests, in the perspective of synaptic regulation, that PrPc can be assigned multiple biological functions and supports the novel concept that prion-like changes are involved in long-term memory formation. The synaptic trait of PrPc and PrPSc suggests that synapse loss is the key event in neuronal death. Interestingly, synaptic alterations are also considered to be predominant in the pathophysiological mechanism in Alzheimer, Parkinson and Huntington diseases. All these brain disorders, characterized by the formation of a specific amyloid protein of synaptic origin, can be classified under the heading of amyloidogenic synaptopathies. [ABSTRACT FROM AUTHOR]

Exosomes are small membranous vesicles secreted by a number of cell types and can be isolated from conditioned cell media or bodily fluids such as urine and plasma. Exosome biogenesis involves the inward budding of multivesicular bodies (MVB) to form intraluminal vesicles (ILV). When fused with the plasma membrane, the MVB releases the vesicles into the extracellular environment as exosomes. Proposed functions of these vesicles include roles in cell–cell signalling, removal of unwanted proteins, and the transfer of pathogens between cells, such as HIV-1. Another such pathogen which exploits this pathway is the prion, the infectious particle responsible for the transmissible neurodegenerative diseases such as Creutzfeldt-Jakob disease (CJD) of humans or bovine spongiform encephalopathy (BSE) of cattle. Interestingly, this work is mirrored by studies on another protein involved in neurodegenerative disease, the amyloid precursor protein (APP) which is associated with Alzheimer’s disease (AD). Recent work has found APP proteolytic fragments in association with exosomes, suggesting a common pathway previously unknown for proteins associated with neurodegenerative diseases. This review will be discussing the current literature regarding the role of exosomes in secretion of the proteins, PrP and APP, and the subsequent implications for neurodegenerative disease. [ABSTRACT FROM AUTHOR]

Knowledge of the physiological function of cellular prion protein has been acquired from prion diseases such as Creutzfeldt–Jakob disease, as well as PRNP knock out and transgenic mice. Recent progress in neurobiology has further delineated the neuroprotective role played by cellular prion protein. In this paper, we review the role of cellular prion protein in cell survival including its antiapoptotic effect on Bax-mediated cell death and its responses to various environmental stresses including oxidative stress, and ischemia. Finally, we discuss the significance of cellular prion protein in different neurodegenerative diseases and the possible development of future therapies. [ABSTRACT FROM AUTHOR]

Transmissible spongiform encephalopathies (TSEs) in humans and animals are attributed to protein-only infectious agents, called prions. Prions have been proposed to arise from the conformational conversion of the cellular protein PrPC into a misfolded form (e.g., PrPSc for scrapie), which precipitates into aggregates and fibrils. It has been proposed that the conversion process is triggered by the interaction of the infectious form (PrPSc) with the cellular form (PrPC) or might result from a mutation in the gene for PrPC. However, until recently, all efforts to reproduce this process in vitro had failed, suggesting that host factors are necessary for prion replication. In this review we discuss recent findings such as the cellular factors that might be involved in the conformational conversion of prion proteins and the potential mechanisms by which they could operate. [ABSTRACT FROM AUTHOR]

Cellular prion protein (PrPC), a glycosylphosphatidylinositol-anchored membrane protein, was found in our lab to be widely expressed in gastric cancer cell lines. In order to evaluate its biological significance in human gastric cancer, we investigated its expression in a large series of gastric tissue samples (n = 124) by immuno histochemical staining with the monoclonal antibody 3F4. Compared with normal tissues, gastric adenocarcinoma showed increased PrPC expression, correlated with the histopathological differentiation (according to the WHO and Lauren classifications) and tumor progression (as documented by pTNM staging). To better understand the underlying mechanism, we introduced the PrPC and two pairs of RNAi into the poorly differentiated gastric cancer cell line AGS and found that PrPC suppressed ROS and slowed down apoptosis in transfected cells. Further study proved that the apoptosis-related protein Bcl-2 was upregulated whereas p53 and Bax were downregulated in the PrPC-transfected cells. A reverse effect was observed in PrPC siRNA-transfected cells. These results strongly suggested that PrPC might play a role as an effective antiapoptotic protein through Bcl-2-dependent apoptotic pathways in gastric cancer cells. Further study into the mechanism of these relationships might enrich the knowledge of PrP, better our understanding of the nature of gastric carcinoma, and further develop possible strategies to block or reverse the development of gastric carcinoma. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Prion diseases of humans and animals occur following infection with infectious agents containing PrPSc or in situations in which there is a mutation of the prior protein (PrP) gene. The cellular prion protein (PrPC) is a sialoglycoprotein that is expressed predominantly in neurons. PrPC is converted into a pathogenic form of PrP (PrPSc), which is distinguishable from PrPC by its relative resistance to protease digestion. A number of postulates have been advanced for the function of normal PrP (PrPC), but this issue has not been resolved. To investigate the function(s) of PrPC, we established clonal PC12 cell lines, which have elevated PrPC expression. The results show that there were alterations in dopamine metabolism and in monoamine oxidase (MAO) activity in transfected PC12 cells that overexpress PrPC. There was an increase in concentration of DOPAC, a metabolite of dopamine, and in MAO activity in cells overexpressing PrPC. MAO is involved in oxidative degradation of dopamine (DA). Our data suggest that PrPC plays a role in DA metabolism by regulating MAO activity. [ABSTRACT FROM AUTHOR]

1. Prion diseases include kuru, Creutzfeldt–Jakob disease (CJD), Gerstmann–Sträussler–Scheinker disease (GSS), and fatal familia insomnia (FFI) of humans, as well as scrapie and bovine spongiform encephalopathy (BSE) of animals. 2. All these disorders involve conversion of the normal, cellular prion protein (PrPC) into the corresponding scrapie isoform (PrPSc). PrPC adopts a structure rich in α-helices and devoid of β-sheet, in contrast to PrPSc, which has a high β-sheet content and is resistant to limited digestion by proteases. That a conformational transition features in the conversion of PrPC into PrPSc implies that prion diseases are disorders of protein conformation. 3. This concept has been extended by our studies with heat shock proteins (Hsp), many of which are thought to function as molecular chaperones. We found that the induction of some Hsps but not others was profoundly altered in scrapie-infected cells and that the distribution of Hsp73 is unusual in these cells. 4. Whether the conversion of PrPC into PrPSc is assisted by molecular chaperones, or if the accumulation of the abnormally folded PrPSc is complexed with Hsps remains to be established. [ABSTRACT FROM AUTHOR]