The unfolded protein response (UPR) allows cells to adjust secretory pathway capacity according to need. Ire1, the endoplasmic reticulum (ER) stress sensor and central activator of the UPR is conserved from the budding yeast Saccharomyces cerevisiae to humans. Under ER stress conditions, Ire1 clusters into foci that enable optimal UPR activation. To discover factors that affect Ire1 clustering, we performed a high-content screen using a whole-genome yeast mutant library expressing Ire1-mCherry. We imaged the strains following UPR induction and found 154 strains that displayed alterations in Ire1 clustering. The hitswere enriched for iron and heme effectors and binding proteins. By performing pharmacological depletion and repletion, we confirmed that iron (Fe3+) affects UPR activation in both yeast and human cells. We suggest that Ire1 clustering propensity depends on membrane composition, which is governed by hemedependent biosynthesis of sterols. Our findings highlight the diverse cellular functions that feed into the UPR and emphasize the cross-talk between organelles required to concertedly maintain homeostasis.
Bibliographical noteFunding Information:
This work was performed through support of the Deutsche Forschungsgemeinschaft (DFG SFB1190 grant Compartmental Gates and Contact Sites to M.S.) and a Volkswagen Foundation (grant 93091 to M.S. and R.E.). M.B. was supported by a Junior Fellow award from the Simons Foundation. M.S. is an Incumbent of the Dr. Gilbert Omenn and Martha Darling Professorial Chair in Molecular Genetics. E.v.A acknowledges financial support by the Giovanni Armenise-Harvard Foundation, Associazione Italiana per la Ricerca sul Cancro (MFAG13584) and Ministero della Salute (RF-2011-02352852). T.A. acknowledges financial support from the Ministerio de Economıáy Competitividad (grants SAF2010-19239 and BFU2013-48703-P), a Ramon y Cajal contract from the Spanish Ministerio de Ciencia e Innovación, and from the I3 program of the Ministerio de Economıáy Competitividad. P.W. is an investigator of the Howard Hughes Medical Institute. Deposited in PMC for immediate release.
- Saccharomyces cerevisiae