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A Tale of Two Distinct Mechanisms for IRE1 RNase (752.9)
Author(s) -
Niwa Maho
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.28.1_supplement.752.9
Subject(s) - xbp1 , intron , rna ligase , rnase p , rna splicing , unfolded protein response , rna , rna silencing , endoribonuclease , microbiology and biotechnology , chemistry , biology , rna interference , gene , biochemistry
IRE1, an ER transmembrane receptor kinase, is a component of the Unfolded Protein Response (UPR) pathway, and acts as an endoribonuclease (RNase) to cleave the intron from XBP1/HAC1 mRNA coding an UPR‐specific transcription factor. Interestingly, recent reports have revealed that UPR also induces a decrease in levels of ER‐associated mRNAs, including INSULIN mRNA in an IRE1‐dependent manner 1 , which has been termed Regulated IRE1 Dependent Decay (RIDD). While XBP1/HAC1 splicing and RIDD are proposed to be carried out by IRE1, the mechanism by which IRE1 differentiates between XBP1 / HAC1 and RIDD substrate mRNAs has not been investigated. Major differences in the cleavage of the HAC1/XBP1 intron and of RIDD RNA include RNA sequences at the cleavage sites, and that HAC1/XBP1 mRNA cleavage occurs at the ends of the intron whereas certain RIDD substrate RNA are cleaved at multiple sites. In addition, HAC1/XBP1 exon cleavage must be coordinated with tRNA ligase activity while RIDD RNA fragments should be shielded from tRNA ligase to promote their degradation. Upon development of a robust in vitro RIDD RNase assay with purified recombinant IRE1 expressed in baculovirus or E. coli , we examined the molecular mechanisms by which IRE1 cleaves either HAC1/XBP1 or RIDD RNA substrates. We have found that IRE1 engaged in cleavage of HAC1/XBP1 RNA cannot be competed by addition of cold RIDD RNA, while HAC1/XBP1 RNA can be effectively competed by excess cold HAC1/XBP1. The converse was true for IRE1 engaged in RIDD cleavage. Further analyses revealed that IRE1 oligomer constitutes the site for RNA substrate binding and catalysis, while IRE1 that acts on RIDD RNA does not require oligomerization. Our study provides a molecular basis for designing strategies to differentially activate (inhibit) one of the Ire1 RNase activities without affecting the other which may lead to new strategies for treating diseases associated with IRE1 activation. #1: Hollien, J., Science 313 , 104 (2006), Han, D., Cell 138 , 562 (2009)