Prion protein aggresomes are poly(A)+ ribonucleoprotein complexes that induce a PKR-mediated deficient cell stress response

Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, 3001 12(ème) Avenue Nord, Sherbrooke, Québec, Canada J1H 5N4.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 04/2008; 1783(3):479-91. DOI: 10.1016/j.bbamcr.2007.10.008
Source: PubMed


In mammalian cells, cytoplasmic protein aggregates generally coalesce to form aggresomal particles. Recent studies indicate that prion-infected cells produce prion protein (PrP) aggresomes, and that such aggregates may be present in the brain of infected mice. The molecular activity of PrP aggresomes has not been fully investigated. We report that PrP aggresomes initiate a cell stress response by activating the RNA-dependent protein kinase (PKR). Activated PKR phosphorylates the translation initiation factor eIF2alpha, resulting in protein synthesis shut-off. However, other components of the stress response, including the assembly of poly(A)+ RNA-containing stress granules and the synthesis of heat shock protein 70, are repressed. In situ hybridization experiments and affinity chromatography on oligo(dT)-cellulose showed that PrP aggresomes bind poly(A)+ RNA, and are therefore poly(A)+ ribonucleoprotein complexes. These findings support a model in which PrP aggresomes send neuronal cells into untimely demise by modifying the cell stress response, and by inducing the aggregation of poly(A)+ RNA.

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    • "An association of RNP aggregates with neurodegenerative diseases is well documented and mutations in RNA-binding proteins that promote self-assembly can be drivers of motor neuron diseases (Ash et al., 2014; King et al., 2012). Similarly, defective clearance of SGs leads to the pathological accumulation of RNP particles and underlies the pathology of amyotrophic lateral sclerosis, Huntington's disease, frontotemporal lobar degeneration and AD (Harris and Rubinsztein, 2011; Buchan et al., 2013; Koppers et al., 2012; King et al., 2012; Vanderweyde et al., 2012; Waelter et al., 2001; Goggin et al., 2008; Liu-Yesucevitz et al., 2010; Neumann et al., 2006; Menzies et al., 2015). Large scale proteomic screens from our laboratory have identified multiple SG-associated proteins as binding partners and substrates for SYK (Iliuk et al., 2010; Xue et al., 2012; Galan et al., 2011). "
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    ABSTRACT: Microglial cells in the brains of Alzheimer's patients are known to be recruited to amyloid-beta (Aβ) plaques where they exhibit an activated phenotype, but are defective for plaque removal by phagocytosis. In this study, we show that microglia stressed by exposure to sodium arsenite or Aβ(1–42) peptides or fibrils form extensive stress granules (SGs) to which the tyrosine kinase, SYK, is recruited. SYK enhances the formation of SGs, is active within the resulting SGs and stimulates the production of reactive oxygen and nitrogen species that are toxic to neuronal cells. This sequestration of SYK inhibits the ability of microglial cells to phagocytose Escherichia coli or Aβ fibrils. We find that aged microglial cells are more susceptible to the formation of SGs; and SGs containing SYK and phosphotyrosine are prevalent in the brains of patients with severe Alzheimer's disease. Phagocytic activity can be restored to stressed microglial cells by treatment with IgG, suggesting a mechanism to explain the therapeutic efficacy of intravenous IgG. These studies describe a mechanism by which stress, including exposure to Aβ, compromises the function of microglial cells in Alzheimer's disease and suggest approaches to restore activity to dysfunctional microglial cells.
    Full-text · Article · Oct 2015 · EBioMedicine
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    • "Biochemical studies of RNA binding protein associations in SGs require pretreatment with RNAse to determine whether SG proteins are directly associated or associated due to mutual binding to mRNA transcripts [16]. Biochemical studies of SGs also demonstrate that the RNA binding proteins present in SGs are triton or SDS insoluble (depending on the protein studied, and the conditions inducing the SG), which is analogous to the biochemistry of proteins aggregates in many neurodegenerative diseases [6,16,17,28,31,38-40]. "
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    ABSTRACT: The protein aggregation that occurs in neurodegenerative diseases is classically thought to occur as an undesirable, nonfunctional byproduct of protein misfolding. This model contrasts with the biology of RNA binding proteins, many of which are linked to neurodegenerative diseases. RNA binding proteins use protein aggregation as part of a normal regulated, physiological mechanism controlling protein synthesis. The process of regulated protein aggregation is most evident in formation of stress granules. Stress granules form when RNA binding proteins aggregate through their glycine rich domains. Stress granules function to sequester, silence and/or degrade RNA transcripts as part of a mechanism that adapts patterns of local RNA translation to facilitate the stress response. Aggregation of RNA binding proteins is reversible and is tightly regulated through pathways, such as phosphorylation of elongation initiation factor 2alpha. Microtubule associated protein tau also appears to regulate stress granule formation. Conversely, stress granule formation stimulates pathological changes associated with tau. In this review, I propose that the aggregation of many pathological, intracellular proteins, including TDP-43, FUS or tau, proceeds through the stress granule pathway. Mutations in genes coding for stress granule associated proteins or prolonged physiological stress, lead to enhanced stress granule formation, which accelerates the pathophysiology of protein aggregation in neurodegenerative diseases. Over-active stress granule formation could act to sequester functional RNA binding proteins and/or interfere with mRNA transport and translation, each of which might potentiate neurodegeneration. The reversibility of the stress granule pathway also offers novel opportunities to stimulate endogenous biochemical pathways to disaggregate these pathological stress granules, and perhaps delay the progression of disease.
    Full-text · Article · Nov 2012 · Molecular Neurodegeneration
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    • "Recombinant PrP also binds to total cellular RNA (Gomes et al. 2008b). Poly(A) + RNA pull-down experiments demonstrated an interaction between a cytoplasmic PrP C mutant and mRNAs (Goggin et al. 2008). NH 2 -PrP C is important for nucleic acid binding activity; binding sites for specific RNA aptamers mapped to residues 23–108 or 23–52 (Gabus et al. 2001a), and deletion of the OR (rPrPD51–90) abolished the binding of synthetic and cellular RNA to rPrP (Weiss et al. 1997; Sekiya et al. 2006; Gomes et al. 2008b). "
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    ABSTRACT: J. Neurochem. (2012) 120, 853–868. The physiological function of the prion protein (PrPC) and its conversion into its infectious form (PrPSc) are central issues to understanding the pathogenesis of prion diseases. The N-terminal moiety of PrPC (NH2-PrPC) is an unstructured region with the characteristic of interacting with a broad range of partners. These interactions endow PrPC with multifunctional and sometimes contrasting capabilities, including neuroprotection and neurotoxicity. Recently, binding of β-sheet rich conformers to NH2-PrPC demonstrated a probable neurotoxic function for PrPC in Alzheimer’s disease. NH2-PrPC also enhances the propagation of prions in vivo and is the target of the most potent antiprion compounds. Another level of complexity is provided by endoproteolysis and release of most of NH2-PrPC into the extracellular space. Further studies will be necessary to understand how NH2-PrPC regulates the physiological function of PrPC and how it is involved in the corruption of its normal function in diseases.
    Preview · Article · Dec 2011 · Journal of Neurochemistry
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