RESUMEN
The GPI-anchored prion protein (PrP(C)) is involved in neurodegeneration, either through misfolding in the Transmissible Spongiform Encephalopathies (TSE), or as a mediator of the neurotoxicity of peptide oligomers in Alzheimer's Disease. PrP(C) has been attributed pleiotropic functions, and appears to scaffold a variety of cell surface signaling modules, for example through its binding to several neurotransmitter receptors. Here we used transfected HEK293 cells to test for an interaction of PrP(C) with purinergic receptor P2X4R. The prion protein bound P2X4R in both overlay and co-immunoprecipitation assays, and co-localized mostly intracellularly, but occasionaly at the cell surface in confocal micrographs. Functional PrP(C):P2X4R interaction was tested by the uptake of a P2X4R-permeant compound, and by modulation of intracellular calcium. Unexpectedly, however, this interaction was traced to a selective effect of PrP(C) upon the content of co-transfected P2X4R. The results suggest a role of PrP(C) in proteostasis, dysfunctions of which may be involved in the pathogenesis of neurodegenerative diseases such as TSE and Alzheimer's Disease.
Asunto(s)
Cerebelo/química , Cerebelo/metabolismo , Proteínas PrPC/química , Proteínas PrPC/metabolismo , Receptores Purinérgicos P2X4/química , Receptores Purinérgicos P2X4/metabolismo , Animales , Sitios de Unión , Células HEK293 , Humanos , Unión Proteica , Ratas , Fracciones Subcelulares/química , Fracciones Subcelulares/metabolismoRESUMEN
We sought to examine interactions of the prion protein (PrP(C)) with monoaminergic systems due to: the role of PrP(C) in both Prion and Alzheimer diseases, which include clinical depression among their symptoms, the implication of monoamines in depression, and the hypothesis that PrP(C) serves as a scaffold for signaling systems. To that effect we compared both behavior and monoaminergic markers in wild type (WT) and PrP(C)-null (PrP(-/-)) mice. PrP(-/-) mice performed poorly when compared with WT in forced swimming, tail suspension, and novelty suppressed feeding tests, typical of depressive-like behavior, but not in the control open field nor rotarod motor tests; cyclic AMP responses to stimulation of D1 receptors by dopamine was selectively impaired in PrP(-/-) mice, and responses to serotonin, but not to norepinephrine, also differed between genotypes. Contents of dopamine, tyrosine hydroxylase, and the 5-HT5A serotonin receptor were increased in the cerebral cortex of PrP(-/-), as compared with WT mice. Microscopic colocalization, as well as binding in overlay assays were found of PrP(C) with both the 5HT5A and D1, but not D4 receptors. The data are consistent with the scaffolding of monoaminergic signaling modules by PrP(C), and may help understand the pathogenesis of clinical depression and neurodegenerative disorders.
Asunto(s)
Conducta Animal , Monoaminas Biogénicas/fisiología , Depresión/fisiopatología , Proteínas PrPC/fisiología , Animales , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteínas PrPC/genéticaRESUMEN
The prion protein (PrP(C)) is highly expressed in the nervous system, and its abnormal conformer is associated with prion diseases. PrP(C) is anchored to cell membranes by glycosylphosphatidylinositol, and transmembrane proteins are likely required for PrP(C)-mediated intracellular signaling. Binding of laminin (Ln) to PrP(C) modulates neuronal plasticity and memory. We addressed signaling pathways triggered by PrP(C)-Ln interaction in order to identify transmembrane proteins involved in the transduction of PrP(C)-Ln signals. The Ln γ1-chain peptide, which contains the Ln binding site for PrP(C), induced neuritogenesis through activation of phospholipase C (PLC), Ca(2+) mobilization from intracellular stores, and protein kinase C and extracellular signal-regulated kinase (ERK1/2) activation in primary cultures of neurons from wild-type, but not PrP(C)-null mice. Phage display, coimmunoprecipitation, and colocalization experiments showed that group I metabotropic glutamate receptors (mGluR1/5) associate with PrP(C). Expression of either mGluR1 or mGluR5 in HEK293 cells reconstituted the signaling pathways mediated by PrP(C)-Ln γ1 peptide interaction. Specific inhibitors of these receptors impaired PrP(C)-Ln γ1 peptide-induced signaling and neuritogenesis. These data show that group I mGluRs are involved in the transduction of cellular signals triggered by PrP(C)-Ln, and they support the notion that PrP(C) participates in the assembly of multiprotein complexes with physiological functions on neurons.
Asunto(s)
Laminina/metabolismo , Neuritas/fisiología , Proteínas PrPC/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Transducción de Señal/fisiología , Animales , Benzoatos/farmacología , Calcio/metabolismo , Células Cultivadas , Femenino , Glicina/análogos & derivados , Glicina/farmacología , Células HEK293 , Humanos , Immunoblotting , Laminina/genética , Laminina/farmacología , Masculino , Ratones , Ratones de la Cepa 129 , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína Quinasa 1 Activada por Mitógenos/metabolismo , Proteína Quinasa 3 Activada por Mitógenos/metabolismo , Neuritas/metabolismo , Neuronas/citología , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Proteínas PrPC/genética , Unión Proteica , Piridinas/farmacología , Receptor del Glutamato Metabotropico 5 , Receptores de Glutamato Metabotrópico/antagonistas & inhibidores , Receptores de Glutamato Metabotrópico/genética , Fosfolipasas de Tipo C/metabolismoRESUMEN
The secreted cochaperone STI1 triggers activation of protein kinase A (PKA) and ERK1/2 signaling by interacting with the cellular prion (PrP(C)) at the cell surface, resulting in neuroprotection and increased neuritogenesis. Here, we investigated whether STI1 triggers PrP(C) trafficking and tested whether this process controls PrP(C)-dependent signaling. We found that STI1, but not a STI1 mutant unable to bind PrP(C), induced PrP(C) endocytosis. STI1-induced signaling did not occur in cells devoid of endogenous PrP(C); however, heterologous expression of PrP(C) reconstituted both PKA and ERK1/2 activation. In contrast, a PrP(C) mutant lacking endocytic activity was unable to promote ERK1/2 activation induced by STI1, whereas it reconstituted PKA activity in the same condition, suggesting a key role of endocytosis in the former process. The activation of ERK1/2 by STI1 was transient and appeared to depend on the interaction of the two proteins at the cell surface or shortly after internalization. Moreover, inhibition of dynamin activity by expression of a dominant-negative mutant caused the accumulation and colocalization of these proteins at the plasma membrane, suggesting that both proteins use a dynamin-dependent internalization pathway. These results show that PrP(C) endocytosis is a necessary step to modulate STI1-dependent ERK1/2 signaling involved in neuritogenesis.
Asunto(s)
Encéfalo/metabolismo , Endocitosis/fisiología , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Proteínas de Choque Térmico/metabolismo , Neuronas/metabolismo , Proteínas PrPC/metabolismo , Animales , Células Cultivadas , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Dinaminas/metabolismo , Activación Enzimática/fisiología , Proteínas de Choque Térmico/genética , Sistema de Señalización de MAP Quinasas/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína Quinasa 1 Activada por Mitógenos/metabolismo , Proteína Quinasa 3 Activada por Mitógenos/metabolismo , Técnicas de Cultivo de Órganos , Proteínas PrPC/genética , Transporte de Proteínas/fisiologíaRESUMEN
The co-chaperone hop/STI-1 is a ligand of the cell surface prion protein (PrP(C)), and their interaction leads to signaling and biological effects. Among these, hop/STI-1 induces proliferation of A172 glioblastoma cells, dependent on both PrP(C) and activation of the Erk pathway. We tested whether clathrin-mediated endocytosis affects signaling induced by hop/STI-1. Both hyperosmolarity induced by sucrose and monodansyl-cadaverine blocked Erk activity induced by hop/STI-1, without affecting the high basal Akt activity typical of A172. The endocytosis inhibitors also affected the sub-cellular distribution of phosphorylated Erk, consistent with blockade of the latter's activity. The data indicate that signaling induced by hop/STI-1 depends on endocytosis. These findings are consistent with a role of sub-cellular trafficking in signal transduction following engagement by PrP(C) by ligands such as hop/STI-1, and may help help unravel both the functions of the prion protein, as well as possible loss-of-function components of prion diseases.