RESUMEN
Alterations in the functions of neuronal RNA-binding proteins (RBPs) can contribute to neurodegenerative diseases. However, neurons also express a set of widely distributed RBPs that may have developed specialized functions. Here, we show that the ubiquitous member of the otherwise neuronal Elavl/Hu family of RNA-binding proteins, Elavl1/HuR, has a neuroprotective role. Mice engineered to lack exclusively HuR in the hippocampal neurons of the central nervous system (CNS), maintain physiologic levels of neuronal Elavls and develop a partially diminished seizure response following strong glutamatergic excitation; however, they display an exacerbated neurodegenerative response subsequent to the initial excitotoxic event. This response was phenocopied in hippocampal cells devoid of ionotropic glutamate receptors in which the loss of HuR results in enhanced mitochondrial dysfunction, oxidative damage and programmed necrosis solely after glutamate challenge. The molecular dissection of HuR and nElavl mRNA targets revealed the existence of a HuR-restricted posttranscriptional regulon that failed in HuR-deficient neurons and is involved in cellular energetics and oxidation defense. Thus, HuR acts as a specialized controller of oxidative metabolism in neurons to confer protection from neurodegeneration.
Asunto(s)
Proteína 1 Similar a ELAV/metabolismo , Ácido Glutámico/metabolismo , Hipocampo/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Enfermedades Neurodegenerativas/metabolismo , Convulsiones/metabolismo , Animales , Proteína 1 Similar a ELAV/genética , Ácido Glutámico/genética , Hipocampo/patología , Ratones , Ratones Transgénicos , Proteínas del Tejido Nervioso/genética , Enfermedades Neurodegenerativas/genética , Enfermedades Neurodegenerativas/patología , Oxidación-Reducción , Estrés Oxidativo/genética , Convulsiones/genética , Convulsiones/patologíaRESUMEN
The shrA gene of Aspergillus nidulans codes for a structural and functional homologue of Shr3p, a yeast ER membrane protein, which plays a crucial role in the secretory pathway of yeast amino acid permeases. shrA is a single-copy gene, whose expression is early activated during germination of A. nidulans conidiospores. ShrA is localized in the ER of the fungal cells and partially complements the shr3delta phenotype. Differently from Saccharomyces cerevisiae, where SHr3p is necessary for membrane localization of the majority of amino acid permeases, deletion of the shrA locus in A. nidulans impairs a limited number of amino acid uptake activities, including those responsible for proline and aspartate transport. Strongly reduced membrane levels of a PrnB-sGFP fusion in a shrAdelta background clearly suggest a direct role of ShrA in the topogenesis of the proline specific transporter.
Asunto(s)
Sistemas de Transporte de Aminoácidos/metabolismo , Aspergillus nidulans/metabolismo , Proteínas Fúngicas/fisiología , Proteínas de Transporte de Membrana/fisiología , Secuencia de Aminoácidos , Sistemas de Transporte de Aminoácidos Neutros/genética , Fusión Artificial Génica , Ácido Aspártico/metabolismo , Retículo Endoplásmico/química , Proteínas Fúngicas/análisis , Eliminación de Gen , Regulación Fúngica de la Expresión Génica , Genes Reporteros , Prueba de Complementación Genética , Proteínas Fluorescentes Verdes/análisis , Proteínas Fluorescentes Verdes/genética , Proteínas de Transporte de Membrana/análisis , Datos de Secuencia Molecular , Filogenia , Prolina/metabolismo , ARN de Hongos/análisis , ARN Mensajero/análisis , Saccharomyces cerevisiae/genética , Homología de Secuencia de AminoácidoRESUMEN
Pre-mRNA processing in eukaryotes is thought to take place on a multitude of nuclear ribonucleoprotein (RNP) complexes, the most abundant of them being the heterogeneous nuclear (hn) RNP complexes. The identification in mammalian nuclear extracts of a novel, less-abundant 70-110 S heterogeneous RNP, named large heterogeneous nuclear RNP (LH-nRNP), has previously been reported by Aidinis, Sekeris and Guialis (1995) Nucleic Acids Res. 23, 2742-2753. The structural composition of the LH-nRNP complex has been determined following the production of polyclonal antibodies against the major protein constituents of the complex, the pair of the 72/74-kDa polypeptides. In the present study evidence is shown to prove that the 72/74-kDa proteins are members of the hnRNP M protein family, hereafter referred to as 72/74(M) polypeptides. The extensive application of two-dimensional gel electrophoresis, combined with specific immunoprecipitation and immunoblotting assays, has allowed the assignment of the 72/74(M) proteins to a subset of the hnRNP M family, characteristic of the presence of the LH-nRNP complex and distinct from the hnRNP-associated M1-M4 components. Moreover, the immunoselection of the LH-nRNP complex from [(32)P]orthophosphate-labelled HeLa cells, with the parallel application of UV irradiation, has permitted the identification of the 72/74(M) polypeptides as the sole protein constituents of the complex in direct contact with the RNA. It is proposed that LH-nRNP constitutes a discrete subset of hnRNP complexes, having a possible role in establishing specific interactions between hnRNP and nuclear-matrix protein components.
