Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
The Rockefeller University, New York, NY 10065, USA.
J Cell Sci. 2017 Oct 1;130(19):3222-3233. doi: 10.1242/jcs.201715. Epub 2017 Aug 9.
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 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 hits were enriched for iron and heme effectors and binding proteins. By performing pharmacological depletion and repletion, we confirmed that iron (Fe) affects UPR activation in both yeast and human cells. We suggest that Ire1 clustering propensity depends on membrane composition, which is governed by heme-dependent 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.
未折叠蛋白反应（UPR）使细胞能够根据需要调整分泌途径的能力。内质网（ER）应激传感器和 UPR 的核心激活剂 Ire1 从芽殖酵母到人类都保守。在 ER 应激条件下，Ire1 聚集成焦点，从而实现最佳的 UPR 激活。为了发现影响 Ire1 聚集的因素，我们使用表达 Ire1-mCherry 的全基因组酵母突变体文库进行了高内涵筛选。我们在 UPR 诱导后对菌株进行成像，发现 154 株菌株的 Ire1 聚集发生改变。这些命中富集了铁和血红素效应物和结合蛋白。通过进行药理学耗竭和补充，我们证实铁（Fe）在酵母和人类细胞中均影响 UPR 激活。我们认为 Ire1 聚集倾向取决于膜组成，而膜组成受固醇的血红素依赖性生物合成控制。我们的研究结果强调了 UPR 中涉及的多种细胞功能，并强调了为协调维持体内平衡而需要细胞器之间的串扰。
