Dissecting the copper bioinorganic chemistry of the functional and pathological roles of the prion protein: Relevance in Alzheimer's disease and cancer

The cellular prion protein (PrP^C) is a metal-binding biomolecule that can interact with different protein partners involved in pivotal physiological processes, such as neurogenesis and neuronal plasticity. Recent studies profile copper and PrP^C as important players in the pathological mechanisms of Alzheimer's disease and cancer. Although the copper-PrP^C interaction has been characterized extensively, the role of the metal ion in the physiological and pathological roles of PrP^C has been barely explored. In this article, we discuss how copper binding and proteolytic processing may impact the ability of PrP^C to recruit protein partners for its functional roles. The importance to dissect the role of copper-PrP^C interactions in health and disease is also underscored.     

Identification of novel putative-binding proteins for cellular prion protein and a specific interaction with the STIP1 homology and U-Box-containing protein 1

ABSTRACT

Prion diseases involve the conversion of the endogenous cellular prion protein, PrP^C, into a misfolded infectious isoform, PrP^Sc. Several functions have been attributed to PrP^C, and its role has also been investigated in the olfactory system. PrP^C is expressed in both the olfactory bulb (OB) and olfactory epithelium (OE) and the nasal cavity is an important route of transmission of diseases caused by prions. Moreover, Prnp^?/? mice showed impaired behavior in olfactory tests. Given the high PrP^C expression in OE and its putative role in olfaction, we screened a mouse OE cDNA library to identify novel PrP^C-binding partners. Ten different putative PrP^C ligands were identified, which were involved in functions such as cellular proliferation and apoptosis, cytoskeleton and vesicle transport, ubiquitination of proteins, stress response, and other physiological processes. In vitro binding assays confirmed the interaction of PrP^C with STIP1 homology and U-Box containing protein 1 (Stub1) and are reported here for the first time. Stub1 is a co-chaperone with ubiquitin E3-ligase activity, which is associated with neurodegenerative diseases characterized by protein misfolding and aggregation. Physiological and pathological implications of PrP^C-Stub1 interaction are under investigation. The PrP^C-binding proteins identified here are not exclusive to the OE, suggesting that these interactions may occur in other tissues and play general biological roles. These data corroborate the proposal that PrP^C is part of a multiprotein complex that modulates several cellular functions and provide a platform for further studies on the physiological and pathological roles of prion protein.     

PrPC regulates epidermal growth factor receptor function and cell shape dynamics in Neuro2a cells

The prion protein (PrP) plays a key role in prion disease pathogenesis. Although the misfolded and pathologic variant of this protein (PrP^SC) has been studied in depth, the physiological role of PrP^C remains elusive and controversial. PrP^C is a cell‐surface glycoprotein involved in multiple cellular functions at the plasma membrane, where it interacts with a myriad of partners and regulates several intracellular signal transduction cascades. However, little is known about the gene expression changes modulated by PrP^C in animals and in cellular models. In this article, we present PrP^C‐dependent gene expression signature in N2a cells and its implication in the most overrepresented functions: cell cycle, cell growth and proliferation, and maintenance of cell shape. PrP^C over‐expression enhances cell proliferation and cell cycle re‐entrance after serum stimulation, while PrP^C silencing slows down cell cycle progression. In addition, MAP kinase and protein kinase B (AKT) pathway activation are under the regulation of PrP^C in asynchronous cells and following mitogenic stimulation. These effects are due in part to the modulation of epidermal growth factor receptor (EGFR) by PrP^C in the plasma membrane, where the two proteins interact in a multimeric complex. We also describe how PrP^C over‐expression modulates filopodia formation by Rho GTPase regulation mainly in an AKT‐Cdc42‐N‐WASP‐dependent pathway.

     

The nucleo-junctional interplay of the cellular prion protein: A new partner in cancer-related signaling pathways?

The cellular prion protein PrP^c plays important roles in proliferation, cell death and survival, differentiation and adhesion. The participation of PrP^c in tumor growth and metastasis was pointed out, but the underlying mechanisms were not deciphered completely. In the constantly renewing intestinal epithelium, our group demonstrated a dual localization of PrP^c, which is targeted to cell-cell junctions in interaction with Src kinase and desmosomal proteins in differentiated enterocytes, but is predominantly nuclear in dividing cells. While the role of PrP^c in the dynamics of intercellular junctions was confirmed in other biological systems, we unraveled its function in the nucleus only recently. We identified several nuclear PrP^c partners, which comprise γ-catenin, one of its desmosomal partners, β-catenin and TCF7L2, the main effectors of the canonical Wnt pathway, and YAP, one effector of the Hippo pathway. PrP^c up-regulates the activity of the β-catenin/TCF7L2 complex and its invalidation impairs the proliferation of intestinal progenitors. We discuss how PrP^c could participate to oncogenic processes through its interaction with Wnt and Hippo pathway effectors, which are controlled by cell-cell junctions and Src family kinases and dysregulated during tumorigenesis. This highlights new potential mechanisms that connect PrP^c expression and subcellular redistribution to cancer.     

The cellular prion protein (PrPC) as neuronal receptor for α-synuclein

The term ‘prion-like’ is used to define some misfolded protein species that propagate intercellularly, triggering protein aggregation in recipient cells. For cell binding, both direct plasma membrane interaction and membrane receptors have been described for particular amyloids. In this respect, emerging evidence demonstrates that several β-sheet enriched proteins can bind to the cellular prion protein (PrP^C). Among other interactions, the physiological relevance of the binding between β-amyloid and PrP^C has been a relevant focus of numerous studies. At the molecular level, published data point to the second charged cluster domain of the PrP^C molecule as the relevant binding domain of the β-amyloid/PrP^C interaction. In addition to β-amyloid, participation of PrP^C in binding α-synuclein, responsible for neurodegenerative synucleopathies, has been reported. Although results indicate relevant participation of PrP^C in the spreading of α-synuclein in living mice, the physiological relevance of the interaction remains elusive. In this comment, we focus our attention on summarizing current knowledge of PrP^C as a receptor for amyloid proteins and its physiological significance, with particular focus on α-synuclein.     

The cellular form of the prion protein is involved in controlling cell cycle dynamics,self‐renewal,and the fate of human embryonic stem cell differentiation

Prion protein (PrP^C), is a glycoprotein that is expressed on the cell surface. The current study examines the role of PrP^C in early human embryogenesis using human embryonic stem cells (hESCs) and tetracycline‐regulated lentiviral vectors that up‐regulate or suppresses PrP^C expression. Here, we show that expression of PrP^C in pluripotent hESCs cultured under self‐renewal conditions induced cell differentiation toward lineages of three germ layers. Silencing of PrP^C in hESCs undergoing spontaneous differentiation altered the dynamics of the cell cycle and changed the balance between the lineages of the three germ layers, where differentiation toward ectodermal lineages was suppressed. Moreover, over‐expression of PrP^C in hESCs undergoing spontaneous differentiation inhibited differentiation toward lineages of all three germ layers and helped to preserve high proliferation activity. These results illustrate that PrP^C is involved in key activities that dictate the status of hESCs including regulation of cell cycle dynamics, controlling the switch between self‐renewal and differentiation, and determining the fate of hESCs differentiation. This study suggests that PrP^C is at the crossroads of several signaling pathways that regulate the switch between preservation of or departure from the self‐renewal state, control cell proliferation activity, and define stem cell fate.     

The cellular form of the prion protein guides the differentiation of human embryonic stem cells into neuron-, oligodendrocyte-, and astrocyte-committed lineages

Prion protein, PrP^C, is a glycoprotein that is expressed on the cell surface beginning with the early stages of embryonic stem cell differentiation. Previously, we showed that ectopic expression of PrP^C in human embryonic stem cells (hESCs) triggered differentiation toward endodermal, mesodermal, and ectodermal lineages, whereas silencing of PrP^C suppressed differentiation toward ectodermal but not endodermal or mesodermal lineages. Considering that PrP^C might be involved in controlling the balance between cells of different lineages, the current study was designed to test whether PrP^C controls differentiation of hESCs into cells of neuron-, oligodendrocyte-, and astrocyte-committed lineages. PrP^C was silenced in hESCs cultured under three sets of conditions that were previously shown to induce hESCs differentiation into predominantly neuron-, oligodendrocyte-, and astrocyte-committed lineages. We found that silencing of PrP^C suppressed differentiation toward all three lineages. Similar results were observed in all three protocols, arguing that the effect of PrP^C was independent of differentiation conditions employed. Moreover, switching PrP^C expression during a differentiation time course revealed that silencing PrP^C expression during the very initial stage that corresponds to embryonic bodies has a more significant impact than silencing at later stages of differentiation. The current work illustrates that PrP^C controls differentiation of hESCs toward neuron-, oligodendrocyte-, and astrocyte-committed lineages and is likely involved at the stage of uncommitted neural progenitor cells rather than lineage-committed neural progenitors.     

The Cellular Prion Protein Interacts with the Tissue Non-Specific Alkaline Phosphatase in Membrane Microdomains of Bioaminergic Neuronal Cells

Background

The cellular prion protein, PrP^C, is GPI anchored and abundant in lipid rafts. The absolute requirement of PrP^C in neurodegeneration associated to prion diseases is well established. However, the function of this ubiquitous protein is still puzzling. Our previous work using the 1C11 neuronal model, provided evidence that PrP^C acts as a cell surface receptor. Besides a ubiquitous signaling function of PrP^C, we have described a neuronal specificity pointing to a role of PrP^C in neuronal homeostasis. 1C11 cells, upon appropriate induction, engage into neuronal differentiation programs, giving rise either to serotonergic (1C11^5-HT) or noradrenergic (1C11^NE) derivatives.

Methodology/Principal Findings

The neuronal specificity of PrP^C signaling prompted us to search for PrP^C partners in 1C11-derived bioaminergic neuronal cells. We show here by immunoprecipitation an association of PrP^C with an 80 kDa protein identified by mass spectrometry as the tissue non-specific alkaline phosphatase (TNAP). This interaction occurs in lipid rafts and is restricted to 1C11-derived neuronal progenies. Our data indicate that TNAP is implemented during the differentiation programs of 1C11^5-HT and 1C11^NE cells and is active at their cell surface. Noteworthy, TNAP may contribute to the regulation of serotonin or catecholamine synthesis in 1C11^5-HT and 1C11^NE bioaminergic cells by controlling pyridoxal phosphate levels. Finally, TNAP activity is shown to modulate the phosphorylation status of laminin and thereby its interaction with PrP.

Conclusion/Significance

The identification of a novel PrP^C partner in lipid rafts of neuronal cells favors the idea of a role of PrP in multiple functions. Because PrP^C and laminin functionally interact to support neuronal differentiation and memory consolidation, our findings introduce TNAP as a functional protagonist in the PrP^C-laminin interplay. The partnership between TNAP and PrP^C in neuronal cells may provide new clues as to the neurospecificity of PrP^C function.     

Is indeed the prion protein a Harlequin servant of "many" masters?

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 membrane proteins to intracellular signaling pathways.     

Anchorless 23–230 PrPC Interactomics for Elucidation of PrPC Protective Role

Accumulation of conformationally altered cellular proteins (i.e., prion protein) is the common feature of prions and other neurodegenerative diseases. Previous studies demonstrated that the lack of terminal sequence of cellular prion protein (PrP^C), necessary for the addition of glycosylphosphatidylinositol lipid anchor, leads to a protease-resistant conformation that resembles scrapie-associated isoform of prion protein. Moreover, mice overexpressing the truncated form of PrP^C showed late-onset, amyloid deposition, and the presence of a short protease-resistant PrP fragment in the brain similar to those found in Gerstmann–Sträussler–Scheinker disease patients. Therefore, the physiopathological function of truncated_/anchorless 23–230 PrP^C (Δ23–230 PrP^C) has come into focus of attention. The present study aims at revealing the physiopathological function of the anchorless PrP^C form by identifying its interacting proteins. The truncated_/anchorless Δ23–230 PrP^C along with its interacting proteins was affinity purified using STrEP-Tactin chromatography, in-gel digested, and identified by quadrupole time-of-flight tandem mass spectrometry analysis in prion protein-deficient murine hippocampus (HpL3-4) neuronal cell line. Twenty-three proteins appeared to interact with anchorless Δ23–230 PrP^C in HpL3-4 cells. Out of the 23 proteins, one novel protein, pyruvate kinase isozymes M1/M2 (PKM2), exhibited a potential interaction with the anchorless Δ23–230 form of PrP^C. Both reverse co-immunoprecipitation and confocal laser-scanning microscopic analysis confirmed an interaction of PKM2 with the anchorless Δ23–230 form of PrP^C. Furthermore, we provide the first evidence for co-localization of PKM2 and PrP^C as well as PrP^C-dependent PKM2 expression regulation. In addition, given the involvement of PrP^C in the regulation of apoptosis, we exposed HpL3-4 cells to staurosporine (STS)-mediated apoptotic stress. In response to STS-mediated apoptotic stress, HpL3-4 cells transiently expressing 23–230-truncated PrP^C were markedly less viable, were more prone to apoptosis and exhibited significantly higher PKM2 expressional regulation as compared with HpL3-4 cells transiently expressing full-length PrP^C (1–253 PrP^C). The enhanced STS-induced apoptosis was shown by increased caspase-3 cleavage. Together, our data suggest that the misbalance or over expression of anchorless Δ23–230 form of PrP^C in association with the expressional regulation of interacting proteins could render cells more prone to cellular insults-stress response, formation of aggregates and may ultimately be linked to the cell death.     

Interaction of Peptide Aptamers with Prion Protein Central Domain Promotes α-Cleavage of PrP<Superscript>C</Superscript>

Prion diseases are infectious and fatal neurodegenerative diseases affecting humans and animals. Transmission is possible within and between species with zoonotic potential. Currently, no prophylaxis or treatment exists. Prions are composed of the misfolded isoform PrP^Sc of the cellular prion protein PrP^C. Expression of PrP^C is a prerequisite for prion infection, and conformational conversion of PrP^C is induced upon its direct interaction with PrP^Sc. Inhibition of this interaction can abrogate prion propagation, and we have previously established peptide aptamers (PAs) binding to PrP^C as new anti-prion compounds. Here, we mapped the interaction site of PA8 in PrP and modeled the complex in silico to design targeted mutations in PA8 which presumably enhance binding properties. Using these PA8 variants, we could improve PA-mediated inhibition of PrP^Sc replication and de novo infection of neuronal cells. Furthermore, we demonstrate that binding of PA8 and its variants increases PrP^C α-cleavage and interferes with its internalization. This gives rise to high levels of the membrane-anchored PrP-C1 fragment, a transdominant negative inhibitor of prion replication. PA8 and its variants interact with PrP^C at its central and most highly conserved domain, a region which is crucial for prion conversion and facilitates toxic signaling of Aβ oligomers characteristic for Alzheimer’s disease. Our strategy allows for the first time to induce α-cleavage, which occurs within this central domain, independent of targeting the responsible protease. Therefore, interaction of PAs with PrP^C and enhancement of α-cleavage represent mechanisms that can be beneficial for the treatment of prion and other neurodegenerative diseases.     

Role of Lipid Rafts and GM1 in the Segregation and Processing of Prion Protein

The prion protein (PrP^C) is highly expressed within the nervous system. Similar to other GPI-anchored proteins, PrP^C is found in lipid rafts, membrane domains enriched in cholesterol and sphingolipids. PrP^C raft association, together with raft lipid composition, appears essential for the conversion of PrP^C into the scrapie isoform PrP^Sc, and the development of prion disease. Controversial findings were reported on the nature of PrP^C-containing rafts, as well as on the distribution of PrP^C between rafts and non-raft membranes. We investigated PrP^C/ganglioside relationships and their influence on PrP^C localization in a neuronal cellular model, cerebellar granule cells. Our findings argue that in these cells at least two PrP^C conformations coexist: in lipid rafts PrP^C is present in the native folding (α-helical), stabilized by chemico-physical condition, while it is mainly present in other membrane compartments in a PrP^Sc-like conformation. We verified, by means of antibody reactivity and circular dichroism spectroscopy, that changes in lipid raft-ganglioside content alters PrP^C conformation and interaction with lipid bilayers, without modifying PrP^C distribution or cleavage. Our data provide new insights into the cellular mechanism of prion conversion and suggest that GM1-prion protein interaction at the cell surface could play a significant role in the mechanism predisposing to pathology.     

The role of the prion protein in the internalization of α-synuclein amyloids

Synucleinopathies are a group of neurodegenerative diseases characterized by the accumulation of α-synuclein amyloids in several regions of the brain. α-Synuclein fibrils are able to spread via cell-to-cell transfer, and once inside the cells, they can template the misfolding and aggregation of the endogenous α-synuclein. Multiple mechanisms have been shown to participate in the process of propagation: endocytosis, tunneling nanotubes and macropinocytosis. Recently, we published a research showing that the cellular form of the prion protein (PrP^C) acts as a receptor for α-synuclein amyloid fibrils, facilitating their internalization through and endocytic pathway. This interaction occurs by a direct interaction between the fibrils and the N-terminal domain of PrP^C. In cell lines expressing the pathological form of PrP (PrP^Sc), the binding between PrP^C and α-synuclein fibrils prevents the formation and accumulation of PrP^Sc, since PrP^C is no longer available as a substrate for the pathological conversion templated by PrP^Sc. On the contrary, PrP^Sc deposits are cleared over passages, probably due to the increased processing of PrP^C into the neuroprotective fragments N1 and C1. Starting from these data, in this work we present new insights into the role of PrP^C in the internalization of protein amyloids and the possible therapeutic applications of these findings.     

Glypican-1 Mediates Both Prion Protein Lipid Raft Association and Disease Isoform Formation

In prion diseases, the cellular form of the prion protein, PrP^C, undergoes a conformational conversion to the infectious isoform, PrP^Sc. PrP^C associates with lipid rafts through its glycosyl-phosphatidylinositol (GPI) anchor and a region in its N-terminal domain which also binds to heparan sulfate proteoglycans (HSPGs). We show that heparin displaces PrP^C from rafts and promotes its endocytosis, suggesting that heparin competes with an endogenous raft-resident HSPG for binding to PrP^C. We then utilised a transmembrane-anchored form of PrP (PrP-TM), which is targeted to rafts solely by its N-terminal domain, to show that both heparin and phosphatidylinositol-specific phospholipase C can inhibit its association with detergent-resistant rafts, implying that a GPI-anchored HSPG targets PrP^C to rafts. Depletion of the major neuronal GPI-anchored HSPG, glypican-1, significantly reduced the raft association of PrP-TM and displaced PrP^C from rafts, promoting its endocytosis. Glypican-1 and PrP^C colocalised on the cell surface and both PrP^C and PrP^Sc co-immunoprecipitated with glypican-1. Critically, treatment of scrapie-infected N2a cells with glypican-1 siRNA significantly reduced PrP^Sc formation. In contrast, depletion of glypican-1 did not alter the inhibitory effect of PrP^C on the β-secretase cleavage of the Alzheimer''s amyloid precursor protein. These data indicate that glypican-1 is a novel cellular cofactor for prion conversion and we propose that it acts as a scaffold facilitating the interaction of PrP^C and PrP^Sc in lipid rafts.     

Loss of prion protein control of glucose metabolism promotes neurodegeneration in model of prion diseases

Corruption of cellular prion protein (PrP^C) function(s) at the plasma membrane of neurons is at the root of prion diseases, such as Creutzfeldt-Jakob disease and its variant in humans, and Bovine Spongiform Encephalopathies, better known as mad cow disease, in cattle. The roles exerted by PrP^C, however, remain poorly elucidated. With the perspective to grasp the molecular pathways of neurodegeneration occurring in prion diseases, and to identify therapeutic targets, achieving a better understanding of PrP^C roles is a priority. Based on global approaches that compare the proteome and metabolome of the PrP^C expressing 1C11 neuronal stem cell line to those of PrP^null-1C11 cells stably repressed for PrP^C expression, we here unravel that PrP^C contributes to the regulation of the energetic metabolism by orienting cells towards mitochondrial oxidative degradation of glucose. Through its coupling to cAMP/protein kinase A signaling, PrP^C tones down the expression of the pyruvate dehydrogenase kinase 4 (PDK4). Such an event favors the transfer of pyruvate into mitochondria and its conversion into acetyl-CoA by the pyruvate dehydrogenase complex and, thereby, limits fatty acids β-oxidation and subsequent onset of oxidative stress conditions. The corruption of PrP^C metabolic role by pathogenic prions PrP^Sc causes in the mouse hippocampus an imbalance between glucose oxidative degradation and fatty acids β-oxidation in a PDK4-dependent manner. The inhibition of PDK4 extends the survival of prion-infected mice, supporting that PrP^Sc-induced deregulation of PDK4 activity and subsequent metabolic derangements contribute to prion diseases. Our study posits PDK4 as a potential therapeutic target to fight against prion diseases.     

Poster Session PPo5: Basic Mechanisms of Neurodegeneration and Pathology

A large number of studies have analysed the putative functions of the prion protein (PrP^C) in mammals. Although its sequence conservation over a wide range of different animals may indicate that this protein could have a key role in prion diseases, an absolutely accepted involvement has not been found so far. We have recently reported that PrP^C regulates Nanog mRNA expression, the first non-redundant function of PrP^C in embryonic stem cells (ESC), which translates into control of pluripotency and early differentiation. Contrary to what it is believed, the other two members of the prion protein family, Doppel and Shadoo, cannot replace the absence of PrP^C, causing the appearance of a new embryoid body (EB) population in our in vitro culture. The similarities between EB and an early post-implantation embryo suggest that this might also occur in vivo, enhancing the importance of this finding. On the other hand, our data may support the hypothesis of a relationship between the loss of PrP^C function and neuronal degeneration in prion diseases. A reduction in brain stem cells pluripotency after PrP^C is misfolded into the pathological conformation (PrP^Sc) could lead to a delay or a disappearance of the normal brain damage recovery.     

A roadmap for investigating the role of the prion protein in depression associated with neurodegenerative disease

The physiological properties of the native, endogenous prion protein (PrP^C) is a matter of concern, due to its pleiotropic functions and links to neurodegenerative disorders and cancer. In line with our hypothesis that the basic function of PrP^C is to serve as a cell surface scaffold for the assembly of signaling modules, multiple interactions have been identified of PrP^C with signaling molecules, including neurotransmitter receptors. We recently reported evidence that PrP^C may modulate monoaminergic neurotransmission, as well as depressive-like behavior in mice. Here, we discuss how those results, together with a number of other studies, including our previous demonstration that both inflammatory and behavioral stress modulate PrP^C content in neutrophils, suggest a distributed role of PrP^C in clinical depression and inflammation associated with neurodegenerative diseases. An overarching understanding of the multiple interventions of PrP^C upon physiological events may both shed light on the pathogenesis of, as well as help the identification of novel therapeutic targets for clinical depression, Prion and Alzheimer's Diseases.     

��-Cleavage of cellular prion protein

The cellular prion protein (PrP^C) is subjected to various processing under physiological and pathological conditions, of which the α-cleavage within the central hydrophobic domain not only disrupts a region critical for both PrP toxicity and PrP^C to PrP^Sc conversion but also produces the N1 fragment that is neuroprotective and the C1 fragment that enhances the pro-apoptotic effect of staurosporine in one report and inhibits prion in another. The proteases responsible for the α-cleavage of PrP^C are controversial. The effect of ADAM10, ADAM17, and ADAM9 on N1 secretion clearly indicates their involvement in the α-cleavage of PrP^C, but there has been no report of direct PrP^C α-cleavage activity with any of the three ADAMs in a purified protein form. We demonstrated that, in muscle cells, ADAM8 is the primary protease for the α-cleavage of PrP^C, but another unidentified protease(s) must also play a minor role. We also found that PrP^C regulates ADAM8 expression, suggesting that a close examination on the relationships between PrP^C and its processing enzymes may reveal novel roles and underlying mechanisms for PrP^C in non-prion diseases such as asthma and cancer.     

Induction of ligand-specific PrPC signaling in human neuronal cells

Cellular prion protein (PrP^C) has attracted considerable attention for its role in transmissible spongiform encephalopathies (TSEs). In spite of being a point of intense research effort critical questions still remain regarding the physiological function of PrP^C and how these functions may change with the conversion of the protein into the infectious and pathological conformation (PrP^Sc). While emerging evidence suggests PrP^C/Sc are involved in signal transduction there is little consensus on the signaling pathways associated with the normal and diseased states. The purported involvement of PrP^C in signal transduction, and the association of TSEs with neural pathology, makes kinome analysis of human neurons an interesting and appropriate model to characterize patterns of signal transduction following activation of PrP^C by two commonly employed experimental ligands; antibody-induced dimerization by 6H4 and the amino acids 106-126 PrP peptide fragment (PrP 106–126). Analysis of the induced kinome responses reveals distinct patterns of signaling activity following each treatment. Specifically, stimulation of human neurons with the 6H4 antibody results in alterations in mitogen activated protein kinase (MAPK) signaling pathways while the 106-126 peptide activates growth factor related signaling pathways including vascular endothelial growth factor (VEGF) signaling and the phosphoinositide-3 kinase (PI3K) pathway. These pathways were validated through independent functional assays. Collectively these results indicate that stimulation of PrP^C with distinct ligands, even within the same cell type, results in unique patterns of signaling. While this investigation highlights the apparent functional versatility of PrP^C as a signaling molecule and may offer insight into cellular mechanisms of TSE pathology it also emphasizes the potential dangers associated with attributing activation of specific intracellular events to particular receptors through artificial models of receptor activation.     

Induction of ligand-specific PrPC signaling in human neuronal cells

Cellular prion protein (PrP^C) has attracted considerable attention for its role in transmissible spongiform encephalopathies (TSEs). In spite of being a point of intense research effort critical questions still remain regarding the physiological function of PrP^C and how these functions may change with the conversion of the protein into the infectious and pathological conformation (PrP^Sc). While emerging evidence suggests PrP^C/Sc are involved in signal transduction there is little consensus on the signaling pathways associated with the normal and diseased states. The purported involvement of PrP^C in signal transduction, and the association of TSEs with neural pathology, makes kinome analysis of human neurons an interesting and appropriate model to characterize patterns of signal transduction following activation of PrP^C by two commonly employed experimental ligands; antibody-induced dimerization by 6H4 and the amino acids 106-126 PrP peptide fragment (PrP 106–126). Analysis of the induced kinome responses reveals distinct patterns of signaling activity following each treatment. Specifically, stimulation of human neurons with the 6H4 antibody results in alterations in mitogen activated protein kinase (MAPK) signaling pathways while the 106-126 peptide activates growth factor related signaling pathways including vascular endothelial growth factor (VEGF) signaling and the phosphoinositide-3 kinase (PI3K) pathway. These pathways were validated through independent functional assays. Collectively these results indicate that stimulation of PrP^C with distinct ligands, even within the same cell type, results in unique patterns of signaling. While this investigation highlights the apparent functional versatility of PrP^C as a signaling molecule and may offer insight into cellular mechanisms of TSE pathology it also emphasizes the potential dangers associated with attributing activation of specific intracellular events to particular receptors through artificial models of receptor activation.