Specificity in endoplasmic reticulum-stress signaling in yeast entails a step-wise engagement of HAC1 mRNA to clusters of the stress sensor Ire1
Eelco van Anken,
David Pincus,
Scott Coyle,
Tomás Aragón,
Christof Osman,
Federica Lari,
Silvia Gómez Puerta,
Alexei V Korennykh,
Peter Walter
Affiliations
Eelco van Anken
Division of Genetics and Cell Biology, San Raffaele Scientific Institute, Milan, Italy; Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
David Pincus
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Scott Coyle
Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
Tomás Aragón
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States; Department of Gene Therapy and Gene Regulation, Center for Applied Medical Research, Pamplona, Spain
Christof Osman
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Federica Lari
Division of Genetics and Cell Biology, San Raffaele Scientific Institute, Milan, Italy
Silvia Gómez Puerta
Department of Gene Therapy and Gene Regulation, Center for Applied Medical Research, Pamplona, Spain
Alexei V Korennykh
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Peter Walter
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Insufficient protein-folding capacity in the endoplasmic reticulum (ER) induces the unfolded protein response (UPR). In the ER lumen, accumulation of unfolded proteins activates the transmembrane ER-stress sensor Ire1 and drives its oligomerization. In the cytosol, Ire1 recruits HAC1 mRNA, mediating its non-conventional splicing. The spliced mRNA is translated into Hac1, the key transcription activator of UPR target genes that mitigate ER-stress. In this study, we report that oligomeric assembly of the ER-lumenal domain is sufficient to drive Ire1 clustering. Clustering facilitates Ire1's cytosolic oligomeric assembly and HAC1 mRNA docking onto a positively charged motif in Ire1's cytosolic linker domain that tethers the kinase/RNase to the transmembrane domain. By the use of a synthetic bypass, we demonstrate that mRNA docking per se is a pre-requisite for initiating Ire1's RNase activity and, hence, splicing. We posit that such step-wise engagement between Ire1 and its mRNA substrate contributes to selectivity and efficiency in UPR signaling.
