Prion protein with an octapeptide insertion has impaired neuroprotective activity in transgenic mice

Indiana University-Purdue University Indianapolis, Indianapolis, Indiana, United States
The EMBO Journal (Impact Factor: 10.43). 07/2007; 26(11):2777-85. DOI: 10.1038/sj.emboj.7601726
Source: PubMed


Familial prion diseases are due to dominantly inherited, germline mutations in the PRNP gene that encodes the prion protein (PrP). The cellular mechanism underlying the pathogenic effect of these mutations remains uncertain. To investigate whether pathogenic mutations impair a normal, physiological activity of PrP, we have crossed Tg(PG14) mice, which express PrP with an octapeptide insertion associated with an inherited prion dementia, with Tg(PrPDelta32-134) mice. Tg(PrPDelta32-134) mice, which express an N-terminally truncated form of PrP, spontaneously develop a neurodegenerative phenotype that is stoichiometrically reversed by coexpression of wild-type PrP. We find that, at equivalent expression levels, PG14 PrP is significantly less efficient than wild-type PrP in suppressing the development of clinical symptoms and neuropathology in Tg(PrPDelta32-134) mice. Thus, our results suggest that some features of the neurological illness associated with inherited PrP mutations may be attributable to a loss of PrP neuroprotective function. This mechanism stands in contrast to the toxic gain-of-function mechanisms that are usually invoked to explain the pathogenesis of dominantly inherited neurodegenerative disorders.

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Available from: Bernardino Francesco Ghetti, Jun 06, 2014
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    • "Nevertheless, in uninfected transgenic mice, expression of N-terminally deleted PrPs triggers neurodegenerative phenotypes [63]–[65]. Other reports found that the octarepeats are dispensable when rescuing such toxic phenotypes with PrP constructs [26], [66]. Interestingly, one of these studies showed that octarepeat expansion impairs rescuing activity [66], whereas a later one concluded that the N-terminus is necessary and sufficient for PrP function [67]. "
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    ABSTRACT: Analyses of cultured cells and transgenic mice expressing prion protein (PrP) deletion mutants have revealed that some properties of PrP -such as its ability to misfold, aggregate and trigger neurotoxicity- are controlled by discrete molecular determinants within its protein domains. Although the contributions of these determinants to PrP biosynthesis and turnover are relatively well characterized, it is still unclear how they modulate cellular functions of PrP. To address this question, we used two defined activities of PrP as functional readouts: 1) the recruitment of PrP to cell-cell contacts in Drosophila S2 and human MCF-7 epithelial cells, and 2) the induction of PrP embryonic loss- and gain-of-function phenotypes in zebrafish. Our results show that homologous mutations in mouse and zebrafish PrPs similarly affect their subcellular localization patterns as well as their in vitro and in vivo activities. Among PrP's essential features, the N-terminal leader peptide was sufficient to drive targeting of our constructs to cell contact sites, whereas lack of GPI-anchoring and N-glycosylation rendered them inactive by blocking their cell surface expression. Importantly, our data suggest that the ability of PrP to homophilically trans-interact and elicit intracellular signaling is primarily encoded in its globular domain, and modulated by its repetitive domain. Thus, while the latter induces the local accumulation of PrPs at discrete punctae along cell contacts, the former counteracts this effect by promoting the continuous distribution of PrP. In early zebrafish embryos, deletion of either domain significantly impaired PrP's ability to modulate E-cadherin cell adhesion. Altogether, these experiments relate structural features of PrP to its subcellular distribution and in vivo activity. Furthermore, they show that despite their large evolutionary history, the roles of PrP domains and posttranslational modifications are conserved between mouse and zebrafish.
    Full-text · Article · Jul 2013 · PLoS ONE
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    • "The α-cleavage of PrPC, which takes place in the late secretory pathway [38], has been shown to be of utmost functional importance. Firstly, N-terminally truncated forms of PrPC lead to neurodegeneration in transgenic mice [39-41]. Secondly, the N1 fragment can counteract experimentally induced p53-dependent caspase-3 activation in vitro and in vivo, indicating a neuroprotective function [42]. "
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    ABSTRACT: The cellular prion protein (PrPC) fulfils several yet not completely understood physiological functions. Apart from these functions, it has the ability to misfold into a pathogenic scrapie form (PrPSc) leading to fatal transmissible spongiform encephalopathies. Proteolytic processing of PrPC generates N- and C-terminal fragments which play crucial roles both in the pathophysiology of prion diseases and in transducing physiological functions of PrPC. A-disintegrin-and-metalloproteinase 10 (ADAM10) has been proposed by cell culture experiments to be responsible for both shedding of PrPC and its α-cleavage. Here, we analyzed the role of ADAM10 in the proteolytic processing of PrPC in vivo. Using neuron-specific Adam10 knockout mice, we show that ADAM10 is the sheddase of PrPC and that its absence in vivo leads to increased amounts and accumulation of PrPC in the early secretory pathway by affecting its posttranslational processing. Elevated PrPC levels do not induce apoptotic signalling via p53. Furthermore, we show that ADAM10 is not responsible for the α-cleavage of PrPC. Our study elucidates the proteolytic processing of PrPC and proves a role of ADAM10 in shedding of PrPC in vivo. We suggest that ADAM10 is a mediator of PrPC homeostasis at the plasma membrane and, thus, might be a regulator of the multiple functions discussed for PrPC. Furthermore, identification of ADAM10 as the sheddase of PrPC opens the avenue to devising novel approaches for therapeutic interventions against prion diseases.
    Full-text · Article · May 2011 · Molecular Neurodegeneration
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    • "Although PrP C may not exist at the cell membrane as a constitutive dimer, dimeric forms of PrP C , the formation of which appears to be mediated by the well-conserved hydrophobic tract region, have been observed in cell culture and shown to be required for PrP to exert its protective role (Priola et al., 1995; Rambold et al., 2008). Consistent with this observation, PrP deletion mutants lacking the hydrophobic domain (and therefore possibly impaired in dimerization) are highly neurotoxic in vivo (Baumann et al., 2007; Li et al., 2007). Whereas hydrophobic tract-mediated dimerization may also explain the ability of PrP C to interact with Sho (Jiayu et al., 2009; Watts et al., 2009), additional elements within the prion-like domain may have an intrinsic ability to contribute to dimerization. "
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    ABSTRACT: Prion diseases are fatal neurodegenerative diseases of humans and animals which, in addition to sporadic and familial modes of manifestation, can be acquired via an infectious route of propagation. In disease, the prion protein (PrP(C)) undergoes a structural transition to its disease-causing form (PrP(Sc)) with profoundly different physicochemical properties. Surprisingly, despite intense interest in the prion protein, its function in the context of other cellular activities has largely remained elusive. We recently employed quantitative mass spectrometry to characterize the interactome of the prion protein in a murine neuroblastoma cell line (N2a), an established cell model for prion replication. Extensive bioinformatic analyses subsequently established an evolutionary link between the prion gene family and the family of ZIP (Zrt-, Irt-like protein) metal ion transporters. More specifically, sequence alignments, structural threading data and multiple additional pieces of evidence placed a ZIP5/ZIP6/ZIP10-like ancestor gene at the root of the PrP gene family. In this review we examine the biology of prion proteins and ZIP transporters from the viewpoint of a shared phylogenetic origin. We summarize and compare available data that shed light on genetics, function, expression, signaling, post-translational modifications and metal binding preferences of PrP and ZIP family members. Finally, we explore data indicative of retropositional origins of the prion gene founder and discuss a possible function for the prion-like (PL) domain within ZIP transporters. While throughout the article emphasis is placed on ZIP proteins, the intent is to highlight connections between PrP and ZIP transporters and uncover promising directions for future research.
    Full-text · Article · Dec 2010 · Progress in Neurobiology
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