CRYPTOCHROMES promote daily protein homeostasis
David Wong, Estere Seinkmane, Aiwei Zeng, Alessandra Stangherlin, Nina M. Rzechorzek, Andrew D. Beale, Jason Day, Martin Reed, Sew‐Yeu Peak‐Chew, Christine T. Styles, Rachel S. Edgar, Marrit Putker, John S. O’Neill
Abstract
The daily organisation of most mammalian cellular functions is attributed to circadian regulation of clock‐controlled protein expression, driven by daily cycles of CRYPTOCHROME‐dependent transcriptional feedback repression. To test this, we used quantitative mass spectrometry to compare wild‐type and CRY‐deficient fibroblasts under constant conditions. In CRY‐deficient cells, we found that temporal variation in protein, phosphopeptide, and K+ abundance was at least as great as wild‐type controls. Most strikingly, the extent of temporal variation within either genotype was much smaller than overall differences in proteome composition between WT and CRY‐deficient cells. This proteome imbalance in CRY‐deficient cells and tissues was associated with increased susceptibility to proteotoxic stress, which impairs circadian robustness, and may contribute to the wide‐ranging phenotypes of CRY‐deficient mice. Rather than generating large‐scale daily variation in proteome composition, we suggest it is plausible that the various transcriptional and post‐translational functions of CRY proteins ultimately act to maintain protein and osmotic homeostasis against daily perturbation. CRYPTOCHROMES regulate proteome composition but are not required for its circadian organisation. Loss of these global transcriptional regulators leads to proteotoxic stress, which impairs the daily organisation of physiology in both cells and mice. CRYPTOCHROMES are not essential for circadian proteome oscillations but play a crucial role in the temporal regulation of protein and osmotic homeostasis.