Identification of interaction domains of the prion protein with its 37-kDa/67-kDa laminin receptor

The structural line between prion and "prion-like": Insights from prion protein and tau

The concept of 'prion-like' behavior has emerged in the study of diseases involving protein misfolding where fibrillar structures, called amyloids, self-propagate and induce disease in a fashion similar to prions. From a biological standpoint, in order to be considered 'prion-like,' a protein must traverse cells and tissues and further propagate via a templated conformational change. Since 2017, cryo-electron microscopy structures from patient-derived 'prion-like' amyloids, in particular tau, have been presented and revealed structural similarities shared across amyloids. Since 2021, cryo-EM structures from prions of known infectivity have been added to the ex vivo amyloid structure family. In this review, we discuss current proposals for the 'prion-like' mechanisms of spread for tau and prion protein as well as discuss different influencers on structures of aggregates from tauopathies and prion diseases. Lastly, we discuss some of the current hypotheses for what may distinguish structures that are 'prion-like' from transmissible prion structures.

Resveratrol and its metabolites elicit neuroprotection via high-affinity binding to the laminin receptor at low nanomolar concentrations

Resveratrol prevents various neurodegenerative diseases in animal models despite reaching only low nanomolar concentrations in the brain after oral administration. In this study, based on the quenching of intrinsic tryptophan fluorescence and molecular docking, we found that trans-resveratrol, its conjugates (glucuronide and sulfate), and dihydro-resveratrol (intestinal microbial metabolite) bind with high affinities (Kd, 0.2-2 nm) to the peptide G palindromic sequence (near glycosaminoglycan-binding motif) of the 67-kDa laminin receptor (67LR). Preconditioning with low concentrations (0.01-10 nm) of these polyphenols, especially resveratrol-glucuronide, protected neuronal cells from death induced by serum withdrawal via activation of cAMP-mediated signaling pathways. This protection was prevented by a 67LR-blocking antibody, suggesting a role for this cell-surface receptor in neuroprotection by resveratrol metabolites.

Emerging roles of the cellular prion protein (PrPC) and 37/67 kDa laminin receptor (RPSA) interaction in cancer biology

The cellular prion protein (PrPC) is well-known for its involvement, under its pathogenic protease-resistant form (PrPSc), in a group of neurodegenerative diseases, known as prion diseases. PrPC is expressed in nervous system, as well as in other peripheral organs, and has been found overexpressed in several types of solid tumors. Notwithstanding, studies in recent years have disclosed an emerging role for PrPC in various cancer associated processes. PrPC has high binding affinity for 37/67 kDa laminin receptor (RPSA), a molecule that acts as a key player in tumorigenesis, affecting cell growth, adhesion, migration, invasion and cell death processes. Recently, we have characterized at cellular level, small molecules able to antagonize the direct PrPC binding to RPSA and their intracellular trafficking. These findings are very crucial considering that the main function of RPSA is to modulate key events in the metastasis cascade. Elucidation of the role played by PrPC/RPSA interaction in regulating tumor development, progression and response to treatment, represents a very promising challenge to gain pathogenetic information and discover novel specific biomarkers and/or therapeutic targets to be exploited in clinical settings. This review attempts to convey a detailed description of the complexity surrounding these multifaceted proteins from the perspective of cancer hallmarks, but with a specific focus on the role of their interaction in the control of proliferation, migration and invasion, genome instability and mutation, as well as resistance to cell death controlled by autophagic pathway.

Harnessing Human Papillomavirus’ Natural Tropism to Target Tumors

Human papillomaviruses (HPV) are small non-enveloped DNA tumor viruses established as the primary etiological agent for the development of cervical cancer. Decades of research have elucidated HPV’s primary attachment factor to be heparan sulfate proteoglycans (HSPG). Importantly, wounding and exposure of the epithelial basement membrane was found to be pivotal for efficient attachment and infection of HPV in vivo. Sulfation patterns on HSPG’s become modified at the site of wounds as they serve an important role promoting tissue healing, cell proliferation and neovascularization and it is these modifications recognized by HPV. Analogous HSPG modification patterns can be found on tumor cells as they too require the aforementioned processes to grow and metastasize. Although targeting tumor associated HSPG is not a novel concept, the use of HPV to target and treat tumors has only been realized in recent years. The work herein describes how decades of basic HPV research has culminated in the rational design of an HPV-based virus-like infrared light activated dye conjugate for the treatment of choroidal melanoma.

Cell biology of prion strains in vivo and in vitro

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.

Anchorless risk or released benefit? An updated view on the ADAM10-mediated shedding of the prion protein

The prion protein (PrP) is a broadly expressed glycoprotein linked with a multitude of (suggested) biological and pathological implications. Some of these roles seem to be due to constitutively generated proteolytic fragments of the protein. Among them is a soluble PrP form, which is released from the surface of neurons and other cell types by action of the metalloprotease ADAM10 in a process termed 'shedding'. The latter aspect is the focus of this review, which aims to provide a comprehensive overview on (i) the relevance of proteolytic processing in regulating cellular PrP functions, (ii) currently described involvement of shed PrP in neurodegenerative diseases (including prion diseases and Alzheimer's disease), (iii) shed PrP's expected roles in intercellular communication in many more (patho)physiological conditions (such as stroke, cancer or immune responses), (iv) and the need for improved research tools in respective (future) studies. Deeper mechanistic insight into roles played by PrP shedding and its resulting fragment may pave the way for improved diagnostics and future therapeutic approaches in diseases of the brain and beyond.

F1 ATP synthase β subunit is a putative receptor involved in white spot syndrome virus infection in shrimp by binding with viral envelope proteins VP51B and VP150

White spot syndrome virus (WSSV) is highly virulent toward shrimp, and F1 ATP synthase β subunit (ATPsyn-β) has been suggested to be involved in WSSV infection. Therefore, in this study, interactions between Penaeus monodon ATPsyn-β (PmATPsyn-β) and WSSV structural proteins were characterized. Based on the results of yeast two-hybrid, co-immunoprecipitation, and protein pull-down assays, WSSV VP51B and VP150 were identified as being able to interact with PmATPsyn-β. Membrane topology assay results indicated that VP51B and VP150 are envelope proteins with large portions exposed outside the WSSV virion. Cellular localization assay results demonstrated that VP51B and VP150 co-localize with PmATPsyn-β on the membranes of transfected cells. Enzyme-linked immunosorbent assay (ELISA) and competitive ELISA results demonstrated that VP51B and VP150 bound to PmATPsyn-β in a dose-dependent manner, which could be competitively inhibited by the addition of WSSV virions. In vivo neutralization assay results further showed that both recombinant VP51B and VP150 could delay mortality in shrimp challenged with WSSV.

Cellular Prion Protein (PrPc): Putative Interacting Partners and Consequences of the Interaction

Cellular prion protein (PrPc) is a small glycosylphosphatidylinositol (GPI) anchored protein most abundantly found in the outer leaflet of the plasma membrane (PM) in the central nervous system (CNS). PrPc misfolding causes neurodegenerative prion diseases in the CNS. PrPc interacts with a wide range of protein partners because of the intrinsically disordered nature of the protein’s N-terminus. Numerous studies have attempted to decipher the physiological role of the prion protein by searching for proteins which interact with PrPc. Biochemical characteristics and biological functions both appear to be affected by interacting protein partners. The key challenge in identifying a potential interacting partner is to demonstrate that binding to a specific ligand is necessary for cellular physiological function or malfunction. In this review, we have summarized the intracellular and extracellular interacting partners of PrPc and potential consequences of their binding. We also briefly describe prion disease-related mutations at the end of this review.

Novel regulators of PrPC expression as potential therapeutic targets in prion diseases

INTRODUCTION

Prion diseases are rare and fatal neurodegenerative disorders. The key molecular event in these disorders is the misfolding of the physiological form of the cellular prion protein, PrP^C, leading to the accumulation of a pathological isoform, PrP^Sc, with unique features. Both isoforms share the same primary sequence, lacking detectable differences in posttranslational modification, a major hurdle for their biochemical or biophysical independent characterization. The mechanism underlying the conversion of PrP^C to PrP^Sc is not completely understood, so finding an effective therapy to cure prion disorders is extremely challenging.

AREAS COVERED

This review discusses the strategies for decreasing prion replication and throws a spotlight on the relevance of PrP^C in the prion accumulation process.

EXPERT OPINION

PrP^C is the key substrate for prion pathology; hence, the most promising therapeutic approach appears to be the targeting of PrP^C to block the production of the infectious isoform. The use of RNA interference and antisense oligonucleotide technologies may offer opportunities for treatment because of their success in clinical trials for other neurodegenerative diseases.

Identification of the Neuroinvasive Pathogen Host Target, LamR, as an Endothelial Receptor for the Treponema pallidum Adhesin Tp0751

Treponema pallidum subsp. pallidum is the causative agent of syphilis, a human-specific sexually transmitted infection that causes a multistage disease with diverse clinical manifestations. Treponema pallidum undergoes rapid vascular dissemination to penetrate tissue, placental, and blood-brain barriers and gain access to distant tissue sites. The rapidity and extent of T. pallidum dissemination are well documented, but the molecular mechanisms have yet to be fully elucidated. One protein that has been shown to play a role in treponemal dissemination is Tp0751, a T. pallidum adhesin that interacts with host components found within the vasculature and mediates bacterial adherence to endothelial cells under shear flow conditions. In this study, we further explore the molecular interactions of Tp0751-mediated adhesion to the vascular endothelium. We demonstrate that recombinant Tp0751 adheres to human endothelial cells of macrovascular and microvascular origin, including a cerebral brain microvascular endothelial cell line. Adhesion assays using recombinant Tp0751 N-terminal truncations reveal that endothelial binding is localized to the lipocalin fold-containing domain of the protein. We also confirm this interaction using live T. pallidum and show that spirochete attachment to endothelial monolayers is disrupted by Tp0751-specific antiserum. Further, we identify the 67-kDa laminin receptor (LamR) as an endothelial receptor for Tp0751 using affinity chromatography, coimmunoprecipitation, and plate-based binding methodologies. Notably, LamR has been identified as a receptor for adhesion of other neurotropic invasive bacterial pathogens to brain endothelial cells, including Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae, suggesting the existence of a common mechanism for extravasation of invasive extracellular bacterial pathogens.IMPORTANCE Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subsp. pallidum. The continued incidence of syphilis demonstrates that screening and treatment strategies are not sufficient to curb this infectious disease, and there is currently no vaccine available. Herein we demonstrate that the T. pallidum adhesin Tp0751 interacts with endothelial cells that line the lumen of human blood vessels through the 67-kDa laminin receptor (LamR). Importantly, LamR is also a receptor for meningitis-causing neuroinvasive bacterial pathogens such as Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae Our findings enhance understanding of the Tp0751 adhesin and present the intriguing possibility that the molecular events of Tp0751-mediated treponemal dissemination may mimic the endothelial interaction strategies of other invasive pathogens.

RhoA/ROCK Regulates Prion Pathogenesis by Controlling Connexin 43 Activity

Scrapie infection, which converts cellular prion protein (PrP^C) into the pathological and infectious isoform (PrP^Sc), leads to neuronal cell death, glial cell activation and PrP^Sc accumulation. Previous studies reported that PrP^C regulates RhoA/Rho-associated kinase (ROCK) signaling and that connexin 43 (Cx43) expression is upregulated in in vitro and in vivo prion-infected models. However, whether there is a link between RhoA/ROCK and Cx43 in prion disease pathogenesis is uncertain. Here, we investigated the role of RhoA/ROCK signaling and Cx43 in prion diseases using in vitro and in vivo models. Scrapie infection induced RhoA activation, accompanied by increased phosphorylation of LIM kinase 1/2 (LIMK1/2) at Thr508/Thr505 and cofilin at Ser3 and reduced phosphorylation of RhoA at Ser188 in hippocampal neuronal cells and brains of mice. Scrapie infection-induced RhoA activation also resulted in PrP^Sc accumulation followed by a reduction in the interaction between RhoA and p190RhoGAP (a GTPase-activating protein). Interestingly, scrapie infection significantly enhanced the interaction between RhoA and Cx43. Moreover, RhoA and Cx43 colocalization was more visible in both the membrane and cytoplasm of scrapie-infected hippocampal neuronal cells than in controls. Finally, RhoA and ROCK inhibition reduced PrP^Sc accumulation and the RhoA/Cx43 interaction, leading to decreased Cx43 hemichannel activity in scrapie-infected hippocampal neuronal cells. These findings suggest that RhoA/ROCK regulates Cx43 activity, which may have an important role in the pathogenesis of prion disease.

Emerging Role of Cellular Prion Protein in the Maintenance and Expansion of Glioma Stem Cells

Cellular prion protein (PrP^C) is a membrane-anchored glycoprotein representing the physiological counterpart of PrP scrapie (PrP^Sc), which plays a pathogenetic role in prion diseases. Relatively little information is however available about physiological role of PrP^C. Although PrP^C ablation in mice does not induce lethal phenotypes, impairment of neuronal and bone marrow plasticity was reported in embryos and adult animals. In neurons, PrP^C stimulates neurite growth, prevents oxidative stress-dependent cell death, and favors antiapoptotic signaling. However, PrP^C activity is not restricted to post-mitotic neurons, but promotes cell proliferation and migration during embryogenesis and tissue regeneration in adult. PrP^C acts as scaffold to stabilize the binding between different membrane receptors, growth factors, and basement proteins, contributing to tumorigenesis. Indeed, ablation of PrP^C expression reduces cancer cell proliferation and migration and restores cell sensitivity to chemotherapy. Conversely, PrP^C overexpression in cancer stem cells (CSCs) from different tumors, including gliomas—the most malignant brain tumors—is predictive for poor prognosis, and correlates with relapses. The mechanisms of the PrP^C role in tumorigenesis and its molecular partners in this activity are the topic of the present review, with a particular focus on PrP^C contribution to glioma CSCs multipotency, invasiveness, and tumorigenicity.

In vitro Modeling of Prion Strain Tropism

Prions are atypical infectious agents lacking genetic material. Yet, various strains have been isolated from animals and humans using experimental models. They are distinguished by the resulting pattern of disease, including the localization of PrPsc deposits and the spongiform changes they induce in the brain of affected individuals. In this paper, we discuss the emerging use of cellular and acellular models to decipher the mechanisms involved in the strain-specific targeting of distinct brain regions. Recent studies suggest that neuronal cultures, protein misfolding cyclic amplification, and combination of both approaches may be useful to explore this under-investigated but central domain of the prion field.

Cell biology of prion infection

The development of multiple cell culture models of prion infection over the last two decades has led to a significant increase in our understanding of how prions infect cells. In particular, new techniques to distinguish exogenous from endogenous prions have allowed us for the first time to look in depth at the earliest stages of prion infection through to the establishment of persistent infection. These studies have shown that prions can infect multiple cell types, both neuronal and nonneuronal. Once in contact with the cell, they are rapidly taken up via multiple endocytic pathways. After uptake, the initial replication of prions occurs almost immediately on the plasma membrane and within multiple endocytic compartments. Following this acute stage of prion replication, persistent prion infection may or may not be established. Establishment of a persistent prion infection in cells appears to depend upon the achievement of a delicate balance between the rate of prion replication and degradation, the rate of cell division, and the efficiency of prion spread from cell to cell. Overall, cell culture models have shown that prion infection of the cell is a complex and variable process which can involve multiple cellular pathways and compartments even within a single cell.

LRP/LR specific antibody IgG1-iS18 impedes neurodegeneration in Alzheimer's disease mice

Alzheimer’s disease (AD) is a neurodegenerative disease caused by accumulation of amyloid beta (Aβ) plaque and neurofibrillary tangle formation. We have shown in vitro, that knock-down and blockade of the 37 kDa/67 kDa Laminin Receptor (LRP/LR) resulted in reduced Aβ induced cytotoxicity and Aβ accumulation. In order to test the effect of blocking LRP/LR on Aβ formation and AD associated symptoms, AD transgenic mice received the anti-LRP/LR specific antibody, IgG1-iS18 through intranasal administration. We show that this treatment resulted in an improvement in memory, and decreased Aβ plaque formation. Moreover, a significant decrease in Aβ₄₂ protein expression with a concomitant increase in amyloid precursor protein (APP) and telomerase reverse transcriptase (mTERT) levels was observed. These data recommend IgG1-iS18 as a potentially powerful therapeutic antibody for AD treatment.

Design and Applications of Cell-Selective Surfaces and Interfaces

Tissue regeneration involves versatile types of cells. The accumulation and disorganized behaviors of undesired cells impair the natural healing process, leading to uncontrolled immune response, restenosis, and/or fibrosis. Cell-selective surfaces and interfaces can have specific and positive effects on desired types of cells, allowing tissue regeneration with restored structures and functions. This review outlines the importance of surfaces and interfaces of biomaterials with cell-selective properties. The chemical and biological cues including peptides, antibodies, and other molecules, physical cues such as topography and elasticity, and physiological cues referring mainly to interactions between cells-cells and cell-chemokines or cytokines are effective modulators for achieving cell selectivity upon being applied into the design of biomaterials. Cell-selective biomaterials have also shown practical significance in tissue regeneration, in particular for endothelialization, nerve regeneration, capture of stem cells, and regeneration of tissues of multiple structures and functions.

Surface modification and endothelialization of polyurethane for vascular tissue engineering applications: a review

Cardiovascular implants, especially vascular grafts made of synthetic polymers, find wide clinical applications in the treatment of cardiovascular diseases. However, cases of failure still exist, notably caused by restenosis and thrombus formation. Aiming to solve these problems, various approaches to surface modification of synthetic vascular grafts have been used to improve both the hemocompatibility and long-term patency of artificial vascular grafts. Surface modification using hydrophilic molecules can enhance hemocompatibility, but this may limit the initial vascular endothelial cell adhesion. Therefore, the improvement of endothelialization on these grafts with specific peptides and biomolecules is now an exciting field of research. In this review, several techniques to improve surface modification and endothelialization on vascular grafts, mainly polyurethane (PU) grafts, are summarized, together with the recent development and evolution of the different strategies: from the use of PEG, zwitterions, and polysaccharides to peptides and other biomolecules and genes; from in vitro endothelialization to in vivo endothelialization; and from bio-inert and bio-active to bio-mimetic approaches.

A dock derived compound against laminin receptor (37 LR) exhibits anti-cancer properties in a prostate cancer cell line model

Laminin receptor (67 LR) is a 67 kDa protein derived from a 37 kDa precursor (37 LR). 37/67 LR is a strong clinical correlate for progression, aggression, and chemotherapeutic relapse of several cancers including breast, prostate, and colon. The ability of 37/67 LR to promote cancer cell aggressiveness is further increased by its ability to transduce physiochemical and mechanosensing signals in endothelial cells and modulate angiogenesis. Recently, it was demonstrated that 37/67 LR modulates the anti-angiogenic potential of the secreted glycoprotein pigment epithelium-derived factor (PEDF). Restoration of PEDF balance is a desirable therapeutic outcome, and we sought to identify a small molecule that could recapitulate known signaling properties of PEDF but without the additional complications of peptide formulation or gene delivery safety validation. We used an in silico drug discovery approach to target the interaction interface between PEDF and 37 LR. Following cell based counter screening and binding validation, we characterized a hit compound's anti-viability, activation of PEDF signaling-related genes, anti-wound healing, and anti-cancer signaling properties. This hit compound has potential for future development as a lead compound for treating tumor growth and inhibiting angiogenesis.

MGr1-Antigen/37 kDa laminin receptor precursor promotes cellular prion protein induced multi-drug-resistance of gastric cancer

Cellular prion protein (PrP^C), the infective agent of transmissible spongiform encephalopathies, is thought to be related to several cellular physiological and physiopathological processes. We have previously reported that PrP^C participates in multi-drug-resistance of gastric cancer. As the salient ligand molecule of PrP for participating in internalization and propagation of the scrapie form of prion protein (PrP^Sc), 37 kDa laminin receptor precursor protein (37LRP) shared the same gene coding sequence of MGr1-Ag, another protein previously found to be involved in multi-drug-resistance of gastric cancer in our lab. In the present study, we explored whether MGr1-Ag/37LRP contributed to PrP^C mediated multi-drug-resistance in gastric cancer. Immunohistochemical staining showed similar expression patterns of MGr1-Ag/37LRP and PrP^C in gastric cancer tissue serial sections. Western blot and immunohistochemistry also demonstrated correlative expression of MGr1-Ag/37LRP and PrP^C in gastric cancer cell lines. Interaction between MGr1-Ag/37LRP and PrP^C in gastric cancer cell lines and gastric cancer tissues were verified by immunofluorescence and co-immunoprecipitation. Furthermore, knockdown of MGr1-Ag/37LRP significantly attenuated PrP^C induced multi-drug-resistance by sensitizing drug-induced apoptosis through inhibition of AKT activation. In conclusion, MGr1-Ag/37LRP may interact with PrP^C and promote the PrP^C induced multi-drug-resistance in gastric cancer through PI3K/AKT pathway. The current study elucidates the mechanism of how PrP^C triggers intracellular signaling cascade resulting in multi-drug-resistance phenotype and provides a novel candidate molecular target against gastric cancer.

Physiological Functions of the Cellular Prion Protein

The prion protein, PrP^C, is a small, cell-surface glycoprotein notable primarily for its critical role in pathogenesis of the neurodegenerative disorders known as prion diseases. A hallmark of prion diseases is the conversion of PrP^C into an abnormally folded isoform, which provides a template for further pathogenic conversion of PrP^C, allowing disease to spread from cell to cell and, in some circumstances, to transfer to a new host. In addition to the putative neurotoxicity caused by the misfolded form(s), loss of normal PrP^C function could be an integral part of the neurodegenerative processes and, consequently, significant research efforts have been directed toward determining the physiological functions of PrP^C. In this review, we first summarise important aspects of the biochemistry of PrP^C before moving on to address the current understanding of the various proposed functions of the protein, including details of the underlying molecular mechanisms potentially involved in these functions. Over years of study, PrP^C has been associated with a wide array of different cellular processes and many interacting partners have been suggested. However, recent studies have cast doubt on the previously well-established links between PrP^C and processes such as stress-protection, copper homeostasis and neuronal excitability. Instead, the functions best-supported by the current literature include regulation of myelin maintenance and of processes linked to cellular differentiation, including proliferation, adhesion, and control of cell morphology. Intriguing connections have also been made between PrP^C and the modulation of circadian rhythm, glucose homeostasis, immune function and cellular iron uptake, all of which warrant further investigation.

The Biological Function of the Prion Protein: A Cell Surface Scaffold of Signaling Modules

The prion glycoprotein (PrP^C) is mostly located at the cell surface, tethered to the plasma membrane through a glycosyl-phosphatydil inositol (GPI) anchor. Misfolding of PrP^C is associated with the transmissible spongiform encephalopathies (TSEs), whereas its normal conformer serves as a receptor for oligomers of the β-amyloid peptide, which play a major role in the pathogenesis of Alzheimer’s Disease (AD). PrP^C is highly expressed in both the nervous and immune systems, as well as in other organs, but its functions are controversial. Extensive experimental work disclosed multiple physiological roles of PrP^C at the molecular, cellular and systemic levels, affecting the homeostasis of copper, neuroprotection, stem cell renewal and memory mechanisms, among others. Often each such process has been heralded as the bona fide function of PrP^C, despite restricted attention paid to a selected phenotypic trait, associated with either modulation of gene expression or to the engagement of PrP^C with a single ligand. In contrast, the GPI-anchored prion protein was shown to bind several extracellular and transmembrane ligands, which are required to endow that protein with the ability to play various roles in transmembrane signal transduction. In addition, differing sets of those ligands are available in cell type- and context-dependent scenarios. To account for such properties, we proposed that PrP^C serves as a dynamic platform for the assembly of signaling modules at the cell surface, with widespread consequences for both physiology and behavior. The current review advances the hypothesis that the biological function of the prion protein is that of a cell surface scaffold protein, based on the striking similarities of its functional properties with those of scaffold proteins involved in the organization of intracellular signal transduction pathways. Those properties are: the ability to recruit spatially restricted sets of binding molecules involved in specific signaling; mediation of the crosstalk of signaling pathways; reciprocal allosteric regulation with binding partners; compartmentalized responses; dependence of signaling properties upon posttranslational modification; and stoichiometric requirements and/or oligomerization-dependent impact on signaling. The scaffold concept may contribute to novel approaches to the development of effective treatments to hitherto incurable neurodegenerative diseases, through informed modulation of prion protein-ligand interactions.

Regulation of RhoA activity by the cellular prion protein

The cellular prion protein (PrP^C) is a highly conserved glycosylphosphatidylinositol (GPI)-anchored membrane protein that is involved in the signal transduction during the initial phase of neurite outgrowth. The Ras homolog gene family member A (RhoA) is a small GTPase that is known to have an essential role in regulating the development, differentiation, survival, and death of neurons in the central nervous system. Although recent studies have shown the dysregulation of RhoA in a variety of neurodegenerative diseases, the role of RhoA in prion pathogenesis remains unclear. Here, we investigated the regulation of RhoA-mediated signaling by PrP^C using both in vitro and in vivo models and found that overexpression of PrP^C significantly induced RhoA inactivation and RhoA phosphorylation in hippocampal neuronal cells and in the brains of transgenic mice. Using siRNA-mediated depletion of endogenous PrP^C and overexpression of disease-associated mutants of PrP^C, we confirmed that PrP^C induced RhoA inactivation, which accompanied RhoA phosphorylation but reduced the phosphorylation levels of LIM kinase (LIMK), leading to cofilin activation. In addition, PrP^C colocalized with RhoA, and the overexpression of PrP^C significantly increased neurite outgrowth in nerve growth factor-treated PC12 cells through RhoA inactivation. However, the disease-associated mutants of PrP^C decreased neurite outgrowth compared with wild-type PrP^C. Moreover, inhibition of Rho-associated kinase (ROCK) substantially facilitated neurite outgrowth in NGF-treated PC12 cells, similar to the effect induced by PrP^C. Interestingly, we found that the induction of RhoA inactivation occurred through the interaction of PrP^C with RhoA and that PrP^C enhanced the interaction between RhoA and p190RhoGAP (a GTPase-activating protein). These findings suggest that the interactions of PrP^C with RhoA and p190RhoGAP contribute to neurite outgrowth by controlling RhoA inactivation and RhoA-mediated signaling and that disease-associated mutations of PrP^C impair RhoA inactivation, which in turn leads to prion-related neurodegeneration.

PrP Knockout Cells Expressing Transmembrane PrP Resist Prion Infection

Glycosylphosphatidylinositol (GPI) anchoring of the prion protein (PrP^C) influences PrP^C misfolding into the disease-associated isoform, PrP^res, as well as prion propagation and infectivity. GPI proteins are found in cholesterol- and sphingolipid-rich membrane regions called rafts. Exchanging the GPI anchor for a nonraft transmembrane sequence redirects PrP^C away from rafts. Previous studies showed that nonraft transmembrane PrP^C variants resist conversion to PrP^res when transfected into scrapie-infected N2a neuroblastoma cells, likely due to segregation of transmembrane PrP^C and GPI-anchored PrP^res in distinct membrane environments. Thus, it remained unclear whether transmembrane PrP^C might convert to PrP^res if seeded by an exogenous source of PrP^res not associated with host cell rafts and without the potential influence of endogenous expression of GPI-anchored PrP^C To further explore these questions, constructs containing either a C-terminal wild-type GPI anchor signal sequence or a nonraft transmembrane sequence containing a flexible linker were expressed in a cell line derived from PrP knockout hippocampal neurons, NpL2. NpL2 cells have physiological similarities to primary neurons, representing a novel and advantageous model for studying transmissible spongiform encephalopathy (TSE) infection. Cells were infected with inocula from multiple prion strains and in different biochemical states (i.e., membrane bound as in brain microsomes from wild-type mice or purified GPI-anchorless amyloid fibrils). Only GPI-anchored PrP^C supported persistent PrP^res propagation. Our data provide strong evidence that in cell culture GPI anchor-directed membrane association of PrP^C is required for persistent PrP^res propagation, implicating raft microdomains as a location for conversion.

IMPORTANCE

Mechanisms of prion propagation, and what makes them transmissible, are poorly understood. Glycosylphosphatidylinositol (GPI) membrane anchoring of the prion protein (PrP^C) directs it to specific regions of cell membranes called rafts. In order to test the importance of the raft environment on prion propagation, we developed a novel model for prion infection where cells expressing either GPI-anchored PrP^C or transmembrane-anchored PrP^C, which partitions it to a different location, were treated with infectious, misfolded forms of the prion protein, PrP^res We show that only GPI-anchored PrP^C was able to convert to PrP^res and able to serially propagate. The results strongly suggest that GPI anchoring and the localization of PrP^C to rafts are crucial to the ability of PrP^C to propagate as a prion.

Anti-LRP/LR-specific antibody IgG1-iS18 impedes adhesion and invasion of pancreatic cancer and neuroblastoma cells

BACKGROUND

Cancer has become a global burden due to its high incidence and mortality rates, with an estimated 14.1 million cancer cases reported worldwide in 2012 particularly as a result of metastasis. Metastasis involves two crucial steps: adhesion and invasion, and the non-integrin receptor; the 37-kDa/67-kDa laminin receptor precursor/ high affinity laminin receptor (LRP/LR) has been shown to be overexpressed on the surface of tumorigenic cells, thus being implicated in the enhancement of these two crucial steps. The current study investigated the role of LRP/LR on the aggressiveness of pancreatic cancer (AsPC-1) and neuroblastoma (IMR-32) cells with respect to their adhesive and invasive potential.

METHODS

AsPC-1 and IMR-32 cells were utilized as the experimental cell lines for the study. Cell surface LRP/LR levels were visualised and quantified on the experimental and control (MCF-7) cell lines via confocal microscopy and flow cytometry, respectively. Total LRP/LR levels in the cell lines were assessed by Western blotting and the adhesive and invasive potential of the above-mentioned cell lines was determined before and after supplementation with the anti-LRP/LR specific antibody IgG1-iS18. Statistical significance of the data was confirmed via the use of the two-tailed student's t-test and Pearson's correlation coefficient.

RESULTS

Flow cytometry revealed that AsPC-1 and IMR-32 cells displayed significantly higher cell surface LRP/LR levels in comparison to the MCF-7 control cell line. However, Western blotting and subsequent densitometric analysis revealed that all three tumorigenic cell lines displayed no significant difference in total LRP/LR levels. The treatment of AsPC-1 and IMR-32 cells with IgG1-iS18 caused a significant reduction in the adhesive and invasive potential of the cells to laminin-1 and through the ECM-like Matrigel™, respectively. Pearson's correlation coefficients indicated a high correlation, thus suggesting a directly proportional relationship between cell surface LRP/LR levels and the adhesive and invasive potential of AsPC-1 and IMR-32 cells.

CONCLUSION

These findings suggest that through the interference of the LRP/LR-laminin-1 interaction, the anti-LRP/LR specific antibody IgG1-iS18 may act as an alternative therapeutic tool for the treatment of metastatic pancreatic cancer and neuroblastoma.

LRP/LR Antibody Mediated Rescuing of Amyloid-β-Induced Cytotoxicity is Dependent on PrPc in Alzheimer's Disease

The neuronal perturbations in Alzheimer's disease are attributed to the formation of extracellular amyloid-β (Aβ) neuritic plaques, composed predominantly of the neurotoxic Aβ42 isoform. Although the plaques have demonstrated a role in synaptic dysfunction, neuronal cytotoxicity has been attributed to soluble Aβ42 oligomers. The 37kDa/67kDa laminin receptor has been implicated in Aβ42 shedding and Aβ42-induced neuronal cytotoxicity, as well as internalization of this neurotoxic peptide. As the cellular prion protein binds to both LRP/LR and Aβ42, the mechanism underlying this cytotoxicity may be indirectly due to the PrPc-Aβ42 interaction with LRP/LR. The effects of this interaction were investigated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assays. PrPc overexpression significantly enhanced Aβ42 cytotoxicity in vitro, while PrP-/-  cells were more resistant to the cytotoxic effects of Aβ42 and exhibited significantly less cell death than PrPc expressing N2a cells. Although anti-LRP/LR specific antibody IgG1-iS18 significantly enhanced cell viability in both pSFV1-huPrP1-253 transfected and non-transfected cells treated with exogenous Aβ42, it failed to have any cell rescuing effect in PrP-/-  HpL3-4 cells. These results suggest that LRP/LR plays a significant role in Aβ42-PrPc mediated cytotoxicity and that anti-LRP/LR specific antibodies may serve as potential therapeutic tools for Alzheimer's disease.

Anti-LRP/LR specific antibody IgG1-iS18 significantly impedes adhesion and invasion in early and late stage colorectal carcinoma cells

Cancer is a highly complex disease that has become one of the leading causes of death globally. Metastasis, a major cause of cancer deaths, requires two crucial events known as adhesion and invasion. The 37kDa/67kDa laminin receptor [laminin receptor precursor/high-affinity laminin receptor (LRP/LR)] enhances these two steps, consequently aiding in cancer progression. In this study, the role of LRP/LR in adhesion and invasion of early (SW-480 & HT-29) and late (DLD-1) stage colorectal cancer cells has been investigated. Western blotting revealed that early and late stage colorectal cancer cells contained significantly higher total LRP/LR levels compared to poorly invasive MCF-7 breast cancer control cells. Flow cytometry revealed that all three stages of colorectal cancer displayed significantly higher cell surface LRP/LR levels. Furthermore, upon treatment of the colorectal cancer cells with the anti-LRP/LR specific antibody IgG1-iS18, adhesion to laminin-1 was significantly reduced in all three stages. Each stage's invasive potential was determined using the Matrigel™ invasion assay, which revealed that invasion is significantly impeded in all three colorectal cancer stages when the cells are incubated with IgG1-iS18. In addition, Pearson's correlation coefficients propose that both total and cell surface LRP/LR levels are directly proportional to the adhesive and invasive potential of all three stages of colorectal cancer. Hence, these findings indicate the potential for the use of the IgG1-iS18 antibody as a promising therapeutic tool for colorectal cancer patients of early and late stage.

Almost a century of prion protein(s): From pathology to physiology, and back to pathology

Prions are one of the few pathogens whose name is renowned at all population levels, after the dramatic years pervaded by the fear of eating prion-infected food. If now this, somehow irrational, scare of bovine meat inexorably transmitting devastating brain disorders is largely subdued, several prion-related issues are still unsolved, precluding the design of therapeutic approaches that could slow, if not halt, prion diseases. One unsolved issue is, for example, the role of the prion protein (PrP^C), whole conformational misfolding originates the prion but whose physiologic reason d'etre in neurons, and in cells at large, remains enigmatic. Preceded by a historical outline, the present review will discuss the functional pleiotropicity ascribed to PrP^C, and whether this aspect could fall, at least in part, into a more concise framework. It will also be devoted to radically different perspectives for PrP^C, which have been recently brought to the attention of the scientific world with unexpected force. Finally, it will discuss the possible reasons allowing an evolutionary conserved and benign protein, as PrP^C is, to turn into a high affinity receptor for pathologic misfolded oligomers, and to transmit their toxic message into neurons.

The Transition of the 37-Kda Laminin Receptor (Rpsa) to Higher Molecular Weight Species: Sumoylation or Artifact?

The 37-kDa laminin receptor (37LRP or RPSA) is a remarkable, multifaceted protein that functions in processes ranging from matrix adhesion to ribosome biogenesis. Its ability to engage extracellular laminin is further thought to contribute to cellular migration and invasion. Most commonly associated with metastatic cancer, RPSA is also increasingly found to be important in other pathologies, including microbial infection, neurodegenerative disease and developmental malformations. Importantly, it is thought to have higher molecular weight forms, including a 67-kDa species (67LR), the expression of which is linked to strong laminin binding and metastatic behavior. The composition of these larger forms has remained elusive and controversial. Homo- and heterodimerization have been proposed as events capable of building the larger species from the monomeric 37-kDa precursor, but solid evidence is lacking. Here, we present data suggesting that higher molecular weight species require SUMOylation to form. We also comment on the difficulty of isolating larger RPSA species for unambiguous identification and demonstrate that cell lines stably expressing tagged RPSA for long periods of time fail to produce tagged higher molecular weight RPSA. It is possible that higher molecular weight species like 67LR are not derived from RPSA.

Improvement of neuronal cell survival by astrocyte-derived exosomes under hypoxic and ischemic conditions depends on prion protein

Prion protein (PrP) protects neural cells against oxidative stress, hypoxia, ischemia, and hypoglycemia. In the present study we confirm that cultured PrP-deficient neurons are more sensitive to oxidative stress than wild-type neurons and present the novel findings that wild-type, but not PrP-deficient astrocytes protect wild-type cerebellar neurons against oxidative stress and that exosomes released from stressed wild-type, but not from stressed PrP-deficient astrocytes reduce neuronal cell death induced by oxidative stress. We show that neuroprotection by exosomes of stressed astrocytes depends on exosomal PrP but not on neuronal PrP and that astrocyte-derived exosomal PrP enters into neurons, suggesting neuronal uptake of astrocyte-derived exosomes. Upon exposure of wild-type astrocytes to hypoxic or ischemic conditions PrP levels in exosomes were increased. By mass spectrometry and Western blot analysis, we detected increased levels of 37/67 kDa laminin receptor, apolipoprotein E and the ribosomal proteins S3 and P0, and decreased levels of clusterin/apolipoprotein J in exosomes from wild-type astrocytes exposed to oxygen/glucose deprivation relative to exosomes from astrocytes maintained under normoxic conditions. The levels of these proteins were not altered in exosomes from stressed PrP-deficient astrocytes relative to unstressed PrP-deficient astrocytes. These results indicate that PrP in astrocytes is a sensor for oxidative stress and mediates beneficial cellular responses, e.g. release of exosomes carrying PrP and other molecules, resulting in improved survival of neurons under hypoxic and ischemic conditions.

The 37/67 kDa laminin receptor (LR) inhibitor, NSC47924, affects 37/67 kDa LR cell surface localization and interaction with the cellular prion protein

The 37/67 kDa laminin receptor (LR) is a non-integrin protein, which binds both laminin-1 of the extracellular matrix and prion proteins, that hold a central role in prion diseases. The 37/67 kDa LR has been identified as interactor for the prion protein (PrP(C)) and to be required for pathological PrP (PrP(Sc)) propagation in scrapie-infected neuronal cells, leading to the possibility that 37/67 kDa LR-PrP(C) interaction is related to the pathogenesis of prion diseases. A relationship between 37/67 kDa LR and PrP(C) in the presence of specific LR inhibitor compounds has not been investigated yet. We have characterized the trafficking of 37/67 kDa LR in both neuronal and non-neuronal cells, finding the receptor on the cell surface and nuclei, and identified the 67 kDa LR as the almost exclusive isoform interacting with PrP(C). Here, we show that the treatment with the 37/67 kDa LR inhibitor, NSC47924, affects both the direct 37/67 kDa LR-PrP(C) interaction in vitro and the formation of the immunocomplex in live cells, inducing a progressive internalization of 37/67 kDa LR and stabilization of PrP(C) on the cell surface. These data reveal NSC47924 as a useful tool to regulate PrP(C) and 37/67 kDa LR trafficking and degradation, representing a novel small molecule to be tested against prion diseases.

Proximity of SCG10 and prion protein in membrane rafts

The conversion of normal cellular prion protein (PrPC) into its pathogenic isoform (PrPSc) is an essential event in prion pathogenesis. In culture models, membrane rafts are suggested to play a critical role in PrPSc formation. To identify the candidate molecules capable of interacting with PrPC and facilitating PrPSc formation in membrane rafts, we applied a novel biochemical labeling method termed enzyme-mediated activation of radical sources. Enzyme-mediated activation of radical sources was applied to the Lubrol WX insoluble detergent-resistant membrane fractions from mouse neuroblastoma (N2a) cells in which the surface PrPC was labeled with HRP-conjugated anti-PrP antibody. Two-dimensional western blots of these preparations revealed biotinylated spots of approximately 20 kDa with an isoelectric point of 8.0-9.0. Liquid chromatography-tandem mass spectrometry analysis resulted in the identification of peptides containing SCG10, the neuron-specific microtubule regulator. Proximity of SCG10 and PrPC was confirmed using proximity ligation assay and co-immunoprecipitation assay. Transfection of persistently 22L prion-infected N2a cells with SCG10 small interfering RNA reduced SCG10 expression, but did not prevent PrPSc accumulation, indicating that SCG10 appears to be unrelated to PrPSc formation of 22L prion. Immunofluorescence and western blot analyses showed reduced levels of SCG10 in the hippocampus of prion-infected mice, suggesting a possible association between SCG10 levels and the prion neuropathogenesis. By applying a novel biochemical labeling method against detergent-resistant membrane fractions from mouse neuroblastoma cells, the neuron-specific microtubule-destabilization protein, SCG10 was identified as a novel candidate that is proximate to normal prion protein (PrP) in membrane rafts. SCG10 seemed unrelated to disease-related PrP formation under certain conditions, while there is a possible association between SCG10 levels and prion neuropathogenesis. Cover Image for this issue: doi: 10.1111/jnc.13310.

Knock-Down of the 37kDa/67kDa Laminin Receptor LRP/LR Impedes Telomerase Activity

Cancer has become a major problem worldwide due to its increasing incidence and mortality rates. Both the 37kDa/67kDa laminin receptor (LRP/LR) and telomerase are overexpressed in cancer cells. LRP/LR enhances the invasiveness of cancer cells thereby promoting metastasis, supporting angiogenesis and hampering apoptosis. An essential component of telomerase, hTERT is overexpressed in 85-90% of most cancers. hTERT expression and increased telomerase activity are associated with tumor progression. As LRP/LR and hTERT both play a role in cancer progression, we investigated a possible correlation between LRP/LR and telomerase. LRP/LR and hTERT co-localized in the perinuclear compartment of tumorigenic breast cancer (MDA_MB231) cells and non-tumorigenic human embryonic kidney (HEK293) cells. FLAG® Co-immunoprecipitation assays confirmed an interaction between LRP/LR and hTERT. In addition, flow cytometry revealed that both cell lines displayed high cell surface and intracellular LRP/LR and hTERT levels. Knock-down of LRP/LR by RNAi technology significantly reduced telomerase activity. These results suggest for the first time a novel function of LRP/LR in contributing to telomerase activity. siRNAs targeting LRP/LR may act as a potential alternative therapeutic tool for cancer treatment by (i) blocking metastasis (ii) promoting angiogenesis (iii) inducing apoptosis and (iv) impeding telomerase activity.

Ribosomal proteins as novel players in tumorigenesis

Ribosome biogenesis is the most demanding energetic and metabolic expenditure of the cell. The nucleolus, a nuclear compartment, coordinates rRNA transcription, maturation, and assembly into ribosome subunits. The transcription process is highly coordinated with ribosome biogenesis. In this context, ribosomal proteins (RPs) play a crucial role. In the last decade, an increasing number of studies have associated RPs with extraribosomal functions related to proliferation. Importantly, the expression of RPs appears to be deregulated in several human disorders due, at least in part, to genetic mutations. Although the deregulation of RPs in human malignancies is commonly observed, a more complex mechanism is believed to be involved, favoring the tumorigenic process, its progression and metastasis. This review explores the roles of the most frequently mutated oncogenes and tumor suppressor genes in human cancer that modulate ribosome biogenesis, including their interaction with RPs. In this regard, we propose a new focus for novel therapies.

MEK1 transduces the prion protein N2 fragment antioxidant effects

The prion protein (PrP(C)) when mis-folded is causally linked with a group of fatal neurodegenerative diseases called transmissible spongiform encephalopathies or prion diseases. PrP(C) normal function is still incompletely defined with such investigations complicated by PrP(C) post-translational modifications, such as internal cleavage, which feasibly could change, activate, or deactivate the function of this protein. Oxidative stress induces β-cleavage and the N-terminal product of this cleavage event, N2, demonstrates a cellular protective response against oxidative stress. The mechanisms by which N2 mediates cellular antioxidant protection were investigated within an in vitro cell model. N2 protection was regulated by copper binding to the octarepeat domain, directing the route of internalisation, which stimulated MEK1 signalling. Precise membrane interactions of N2, determined by copper saturation, and involving both the copper-co-ordinating octarepeat region and the structure conferred upon the N-terminal polybasic region by the proline motif, were essential for the correct engagement of this pathway. The phenomenon of PrP(C) post-translational modification, such as cleavage and copper co-ordination, as a molecular "switch" for activation or deactivation of certain functions provides new insight into the apparent multi-functionality of PrP(C).

Novel patented therapeutic approaches targeting the 37/67 kDa laminin receptor for treatment of cancer and Alzheimer's disease

INTRODUCTION

The 37/67 kDa high-affinity laminin receptor (laminin receptor precursor/laminin receptor, LRP/LR) is a multi-faceted cellular receptor. It plays a vital role in the malignancy of various cancer types where it is seen to contribute to invasion, adhesion, apoptosis evasion and angiogenesis. Furthermore, it has been found to play an important role in facilitating the processes leading to neurotoxicity in Alzheimer's disease (AD). Various therapeutic options targeting this receptor have been patented with the outlook on application for the treatment/prevention of these diseases.

AREAS COVERED

The various roles that LRP/LR plays in cancer, AD and infectious diseases caused by viruses and bacteria have been examined in detail and an overview of the current patented therapeutic strategies targeting this receptor is given.

EXPERT OPINION

Molecular tools directed against LRP/LR, such as antibodies and small interfering RNA, could prove to be effective in the prevention of metastasis and angiogenesis while inducing apoptosis in cancers. Moreover, these strategies could also be applied to AD where LRP/LR is seen to facilitate the production and internalization of the neurotoxic Aβ peptide. This review provides a comprehensive overview of the mechanisms by which LRP/LR is involved in eliciting pathogenic events, while showing how the use of patented approaches targeting this receptor could be used to treat them.

Looking into laminin receptor: critical discussion regarding the non-integrin 37/67-kDa laminin receptor/RPSA protein

The 37/67-kDa laminin receptor (LAMR/RPSA) was originally identified as a 67-kDa binding protein for laminin, an extracellular matrix glycoprotein that provides cellular adhesion to the basement membrane. LAMR has evolutionary origins, however, as a 37-kDa RPS2 family ribosomal component. Expressed in all domains of life, RPS2 proteins have been shown to have remarkably diverse physiological roles that vary across species. Contributing to laminin binding, ribosome biogenesis, cytoskeletal organization, and nuclear functions, this protein governs critical cellular processes including growth, survival, migration, protein synthesis, development, and differentiation. Unsurprisingly given its purview, LAMR has been associated with metastatic cancer, neurodegenerative disease and developmental abnormalities. Functioning in a receptor capacity, this protein also confers susceptibility to bacterial and viral infection. LAMR is clearly a molecule of consequence in human disease, directly mediating pathological events that make it a prime target for therapeutic interventions. Despite decades of research, there are still a large number of open questions regarding the cellular biology of LAMR, the nature of its ability to bind laminin, the function of its intrinsically disordered C-terminal region and its conversion from 37 to 67 kDa. This review attempts to convey an in-depth description of the complexity surrounding this multifaceted protein across functional, structural and pathological aspects.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.

MGr1-Ag/37LRP promotes growth and proliferation of gastric cancer in vitro and in vivo

Gastric carcinoma (GC) is an aggressive cancer with a poor prognosis. We previously reported that MGr1-Ag was involved in multidrug resistance and anti-apoptosis in GC. However, the exact function of MGr1-Ag in GC proliferation is not clear. In this study, we found that MGr1-Ag was highly expressed in GC tissues and four GC cell lines compared with nontumor gastric tissues or gastric epithelial mucosa cells. The high expression of MGr1-Ag/37LRP was also consistent with the decreased median survival time of GC patients. We employed lenti-mediated RNA interference technique to knock down MGr1-Ag expression in SGC7901 and MKN45 cells, respectively, and observed its effects on GC cells growth in vitro and in vivo. Further study showed that knockdown of MGr1-Ag could inhibit GC cell proliferation by inhibiting the cell cycle S-phase entry and induced apoptosis. Soft agar colony formation assay indicated that the colony formation ability of SGC7901 and MKN45 cells decreased after lenti-MGr1-Ag small interfering RNA (siRNA) infection. Western blot revealed that cyclin D1 and Bcl-2 expression were downregulated whereas p27 and Bax were upregulated in lenti-MGr-siRNA-infected GC cells. Further study demonstrated that the proliferation effect of MGr1-Ag in GC is dependent on its laminin-binding region. Taken together, these data revealed a novel function of MGr1-Ag that can possibly be used as an independent prognostic factor and a potential therapeutic target for GC.

High resolution imaging study of interactions between the 37 kDa/67 kDa laminin receptor and APP, beta-secretase and gamma-secretase in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia affecting the elderly. Neurodegeneration is caused by the amyloid beta (Aβ) peptide which is generated from the sequential proteolytic cleavage of the Amyloid Precursor Protein (APP) by the β– and γ- secretases. Previous reports revealed that the 37 kDa/67 kDa laminin receptor (LRP/LR) is involved in APP processing, however, the exact mechanism by which this occurs remains largely unclear. This study sought to assess whether LRP/LR interacted with APP, β- or γ-secretase. Detailed confocal microscopy revealed that LRP/LR showed a strong co-localisation with APP, β- and γ-secretase, respectively, at various sub-cellular locations. Superresolution Structured Illumination Microscopy (SR-SIM) showed that interactions were unlikely between LRP/LR and APP and β-secretase, respectively, while there was strong co-localisation between LRP/LR and γ-secretase at this 80 nm resolution. FRET was further employed to assess the possibility of protein-protein interactions and only an interaction between LRP/LR and γ-secretase was found. FLAG co-immunoprecipitation confirmed these findings as LRP/LR co-immunoprecipitated with γ-secretase, but failed to do so with APP. These findings indicate that LRP/LR exerts its influence on Aβ shedding via a direct interaction with the γ-secretase and possibly an indirect interaction with the β-secretase.

Roles of the cellular prion protein in the regulation of cell-cell junctions and barrier function

The cellular prion protein was historically characterized owing to its misfolding in prion disease. Although its physiological role remains incompletely understood, PrP(C) has emerged as an evolutionary conserved, multifaceted protein involved in a wide-range of biological processes. PrP(C) is a GPI-anchored protein targeted to the plasma membrane, in raft microdomains, where its interaction with a repertoire of binding partners, which differ depending on cell models, mediates its functions. Among identified PrP(C) partners are cell adhesion molecules. This review will focus on the multiple implications of PrP(C) in cell adhesion processes, mainly the regulation of cell-cell junctions in epithelial and endothelial cells and the consequences on barrier properties. We will show how recent findings argue for a role of PrP(C) in the recruitment of signaling molecules, which in turn control the targeting or the stability of adhesion complexes at the plasma membrane.

Anti-LRP/LR specific antibodies and shRNAs impede amyloid beta shedding in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia. The amyloid beta (Aβ) peptide is the predominant candidate aetiological agent and is generated through the sequential proteolytic cleavage of the Amyloid Precursor Protein (APP) by beta (β) and gamma (γ) secretases. Since the cellular prion protein (PrP^c) has been shown to regulate Aβ shedding, we investigated whether the cellular receptor for PrP^c, namely the 37 kDa/67 kDa Laminin Receptor (LRP/LR) played a role in Aβ shedding. Here we show that LRP/LR co-localises with the AD relevant proteins APP, β- and γ-secretase, respectively. Antibody blockage and shRNA knock-down of LRP/LR reduces Aβ shedding, due to impediment of β-secretase activity, rather than alteration of APP, β- and γ-secretase levels. These findings indicate that LRP/LR contributes to Aβ shedding and recommend anti-LRP/LR specific antibodies and shRNAs as novel therapeutic tools for AD treatment.

Anti-LRP/LR specific antibody IgG1-iS18 and knock-down of LRP/LR by shRNAs rescue cells from Aβ42 induced cytotoxicity

Alzheimer's disease (AD) is characterized by neurofibrillary tangles, senile plaques and neuronal loss. Amyloid beta (Aβ) is proposed to elicit neuronal loss through cell surface receptors. As Aβ shares common binding partners with the 37 kDa/67 kDa laminin receptor (LRP/LR), we investigated whether these proteins interact and the pathological significance of this association. An LRP/LR-Αβ₄₂ interaction was assessed by immunofluorescence microscopy and pull down assays. The cell biological effects were investigated by 3-(4,5-Dimethylthaizol-2-yl)-2,5-diphenyltetrazolium bromide and Bromodeoxyuridine assays. LRP/LR and Αβ₄₂ co-localised on the cell surface and formed immobilized complexes suggesting an interaction. Antibody blockade by IgG1-iS18 and shRNA mediated down regulation of LRP/LR significantly enhanced cell viability and proliferation in cells co-treated with Αβ₄₂ when compared to cells incubated with Αβ₄₂ only. Results suggest that LRP/LR is implicated in Αβ₄₂ mediated cytotoxicity and that anti-LRP/LR specific antibodies and shRNAs may serve as potential therapeutic tools for AD.

Infectious prion diseases in humans: cannibalism, iatrogenicity and zoonoses

In contrast with other neurodegenerative disorders associated to protein misfolding, human prion diseases include infectious forms (also called transmitted forms) such as kuru, iatrogenic Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease. The transmissible agent is thought to be solely composed of the abnormal isoform (PrP(Sc)) of the host-encoded prion protein that accumulated in the central nervous system of affected individuals. Compared to its normal counterpart, PrP(Sc) is β-sheet enriched and aggregated and its propagation is based on an autocatalytic conversion process. Increasing evidence supports the view that conformational variations of PrP(Sc) encoded the biological properties of the various prion strains that have been isolated by transmission studies in experimental models. Infectious forms of human prion diseases played a pivotal role in the emergence of the prion concept and in the characterization of the very unconventional properties of prions. They provide a unique model to understand how prion strains are selected and propagate in humans. Here, we review and discuss how genetic factors interplay with strain properties and route of transmission to influence disease susceptibility, incubation period and phenotypic expression in the light of the kuru epidemics due to ritual endocannibalism, the various series iatrogenic diseases secondary to extractive growth hormone treatment or dura mater graft and the epidemics of variant Creutzfeldt-Jakob disease linked to dietary exposure to the agent of bovine spongiform encephalopathy.

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.

Therapeutic approaches for prion disorders

Prion diseases are lethal for both humans and animals, and affected individuals die after several months following a rapid disease progression. Although researchers have attempted for decades to develop effective therapeutics for the therapy of human prion disorders, until now no efficient drug has been available on the market for transmissible spongiform encephalopathy (TSE) treatment or cure. Approximately 200 patients worldwide have died or suffer from variant Creutzfeldt-Jakob disease (CJD). Incidences for sporadic and familial CJD are approximately 1.5-2 per million per year and one per 10 million per year, respectively, in Europe. This review summarizes classical and modern trials for the development of effective anti-TSE drugs, introduces potential effective delivery systems, such as lentiviral and adeno-associated virus systems for antiprion components, including antibodies and siRNAs, and presents vaccination trials. Most of the antiprion drugs target prion protein PrP(c) and/or PrP(Sc). Alternative targets are receptors and coreceptors for PrP, that is, the 37/67-kDa laminin receptor and heparan sulfate proteoglycanes. We review clinical trials for the treatment of TSEs and describe hindrances and chances for a breakthrough in therapy of prion disorders.

The prion protein modulates A-type K+ currents mediated by Kv4.2 complexes through dipeptidyl aminopeptidase-like protein 6

Widely expressed in the adult central nervous system, the cellular prion protein (PrP(C)) is implicated in a variety of processes, including neuronal excitability. Dipeptidyl aminopeptidase-like protein 6 (DPP6) was first identified as a PrP(C) interactor using in vivo formaldehyde cross-linking of wild type (WT) mouse brain. This finding was confirmed in three cell lines and, because DPP6 directs the functional assembly of K(+) channels, we assessed the impact of WT and mutant PrP(C) upon Kv4.2-based cell surface macromolecular complexes. Whereas a Gerstmann-Sträussler-Scheinker disease version of PrP with eight extra octarepeats was a loss of function both for complex formation and for modulation of Kv4.2 channels, WT PrP(C), in a DPP6-dependent manner, modulated Kv4.2 channel properties, causing an increase in peak amplitude, a rightward shift of the voltage-dependent steady-state inactivation curve, a slower inactivation, and a faster recovery from steady-state inactivation. Thus, the net impact of wt PrP(C) was one of enhancement, which plays a critical role in the down-regulation of neuronal membrane excitability and is associated with a decreased susceptibility to seizures. Insofar as previous work has established a requirement for WT PrP(C) in the Aβ-dependent modulation of excitability in cholinergic basal forebrain neurons, our findings implicate PrP(C) regulation of Kv4.2 channels as a mechanism contributing to the effects of oligomeric Aβ upon neuronal excitability and viability.

The Soluble Form of the Cellular Prion Protein Enhances Phagocytic Activity and Cytokine Production by Human Monocytes Via Activation of ERK and NF-κB

The PrP(C) is expressed in many types of immune cells including monocytes and macrophages, however, its function in immune regulation remains to be elucidated. In the present study, we examined a role for PrP(C) in regulation of monocyte function. Specifically, the effect of a soluble form of PrP(C) was studied in human monocytes. A recombinant fusion protein of soluble human PrP(C) fused with the Fc portion of human IgG1 (designated as soluble PrP(C)-Fc) bound to the cell surface of monocytes, induced differentiation to macrophage-like cells, and enhanced adherence and phagocytic activity. In addition, soluble PrP(C)-Fc stimulated monocytes to produce pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Both ERK and NF-κB signaling pathways were activated in soluble PrP(C)-treated monocytes, and inhibitors of either pathway abrogated monocyte adherence and cytokine production. Taken together, we conclude that soluble PrP(C)-Fc enhanced adherence, phagocytosis, and cytokine production of monocytes via activation of the ERK and NF-κB signaling pathways.