Abstract
The unfolded protein response (UPR) is a signal transduction pathway that is activated by the accumulation of unfolded proteins in the endoplasmic reticulum (ER). In Saccharomyces cerevisiae the ER transmembrane receptor, Ire1p, transmits the signal to the nucleus culminating in the transcriptional activation of genes encoding an adaptive response. Yeast Ire1p requires both protein kinase and site-specific endoribonuclease (RNase) activities to signal the UPR. In mammalian cells, two homologs, Ire1 alpha and Ire1 beta, are implicated in signaling the UPR. To elucidate the RNase requirement for mammalian Ire1 function, we have identified five amino acid residues within IRE1 alpha that are essential for RNase activity but not kinase activity. These mutants were used to demonstrate that the RNase activity is required for UPR activation by IRE1 alpha and IRE1 beta. In addition, the data support that IRE1 RNase is activated by dimerization-induced trans-autophosphorylation and requires a homodimer of catalytically functional RNase domains. Finally, the RNase activity of wild-type IRE1 alpha down-regulates hIre1 alpha mRNA expression by a novel mechanism involving cis-mediated IRE1 alpha-dependent cleavage at three specific sites within the 5' end of Ire1 alpha mRNA.
MeSH terms
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Amino Acid Sequence
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Animals
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COS Cells
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Caenorhabditis elegans / genetics
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Chlorocebus aethiops
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Dimerization
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Endoplasmic Reticulum / metabolism
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Endoribonucleases
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Fungal Proteins / chemistry
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Fungal Proteins / genetics
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Fungal Proteins / physiology
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Gene Expression Regulation
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Helminth Proteins / chemistry
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Helminth Proteins / genetics
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Humans
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Membrane Glycoproteins / chemistry
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Membrane Glycoproteins / genetics
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Membrane Glycoproteins / physiology
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Membrane Proteins*
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Molecular Sequence Data
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Mutagenesis, Site-Directed
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Protein Folding
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Protein Serine-Threonine Kinases / chemistry
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / physiology*
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RNA Processing, Post-Transcriptional*
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RNA, Messenger / metabolism*
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Recombinant Fusion Proteins / biosynthesis
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Recombinant Fusion Proteins / genetics
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae / metabolism
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Saccharomyces cerevisiae Proteins*
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Sequence Alignment
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Sequence Homology, Amino Acid
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Signal Transduction / physiology*
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Transfection
Substances
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Fungal Proteins
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Helminth Proteins
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Membrane Glycoproteins
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Membrane Proteins
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RNA, Messenger
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Recombinant Fusion Proteins
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Saccharomyces cerevisiae Proteins
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ERN2 protein, human
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IRE1 protein, S cerevisiae
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Protein Serine-Threonine Kinases
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Endoribonucleases