Hydroxyurea induces an oxidative stress response that triggers ER expansion and cytoplasmic protein aggregation

The endoplasmic reticulum (ER) lumen provides the proper redox environment for disulfide bond formation, which is essential for the correct folding of proteins entering the secretory pathway and forming membranes. However, the precise mechanisms by which disruptions in protein folding within the ER activate proteostatic mechanisms remain to be fully elucidated. In this study, we demonstrate that in Schizosaccaromyces pombe the antineoplastic agent hydroxyurea (HU) induces a transient perinuclear ER expansion, Bip1 accumulation and the clustering of nuclear pore complexes in a specific region of the nuclear envelope. This striking phenotype is mimicked by diamide (DIA), a specific inducer of thiol stress, and can be prevented or rapidly reversed by dithiothreitol, a reducing agent, suggesting that ER expansion results from disulfide stress. Furthermore, HU or DIA treatments resulted in the accumulation of misfolded proteins in cytoplasmic foci containing Hsp104 disaggregase and Hsp70/Ssa1 chaperones. Our data show that HU impacts redox-dependent protein folding, impairs the secretory pathway and activates specific proteostatic mechanisms in both the ER and the cytoplasm. RNA-Seq profiling of wildtype S. pombe cells in control conditions, after incubation with 75 mM hydroxyurea for 60 minutes [HU60] and for 150 minutes [HU150]; and cultures treated with 3 mM diamide for 30 minutes [DIA30] and for 60 minutes [DIA60] or after incubation.