RESUMO
Under conditions of endoplasmic reticulum (ER) stress, mammalian cells induce both translational repression and the unfolded protein response that transcriptionally activates genes encoding ER-resident molecular chaperones. To date, the only known pathway for translational repression in response to ER stress has been the phosphorylation of eIF-2alpha by the double-stranded RNA-activated protein kinase (PKR) or the transmembrane PKR-like ER kinase (PERK). Here we report another pathway in which the ER transmembrane kinase/ribonuclease IRE1beta induces translational repression through 28S ribosomal RNA cleavage in response to ER stress. The evidence suggests that both pathways are important for efficient translational repression during the ER stress response.
Assuntos
Retículo Endoplasmático/metabolismo , Proteínas de Membrana , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Sequência de Aminoácidos , Animais , Antibacterianos/farmacologia , Apoptose/fisiologia , Northern Blotting , Western Blotting , Células Cultivadas , Doxiciclina/farmacologia , Endorribonucleases , Humanos , Imuno-Histoquímica , Dados de Sequência Molecular , Fosforilação , Biossíntese de Proteínas , Proteínas Serina-Treonina Quinases/química , Estrutura Terciária de Proteína , RNA Ribossômico 28S/metabolismo , Alinhamento de Sequência , Transfecção , Tunicamicina/farmacologia , eIF-2 Quinase/genética , eIF-2 Quinase/metabolismoRESUMO
Several endoplasmic reticulum (ER)-resident proteins contain a unique C-terminal sequence (KDEL) which is required for the retention of these proteins in the ER. By searching a mouse EST database for records containing the nucleotide sequence encoding the KDEL motif, we extracted cDNAs encoding putative novel ER-resident proteins in addition to all of the known ER proteins bearing the KDEL motif. Using the sequence information obtained by this database search, we cloned the cDNA encoding a novel KDEL motif-bearing protein, ER protein 58 (EP58), sharing no significant homology to any of the known ER-resident proteins. Subcellular localization of EP58 in the ER was confirmed by cytoimmunofluorescence studies using epitope-tagged EP58. The EP58 gene was primarily expressed in embryo, placenta, and adult heart. Neither heat shock nor ER stress as tested here was sufficient to induce expression of the EP58 gene. A putative role of the N-terminal half of EP58 in protein-protein interaction is suggested by its similarity to the filamin rod domain. Similarity of the EP58 sequence with bacterial and fungus proteins suggests a possible role for EP58 in polysaccharide biosynthesis.
