A screenable in vivo assay to study proteostasis networks in Caenorhabditis elegans.

In eukaryotic cells, the ubiquitin/proteasome system (UPS) is a key determinant of proteostasis as it regulates the turnover of damaged proteins. However, it is still unclear how the UPS integrates intrinsic and environmental challenges to promote organismal development and survival. Here, we set up an in vivo degradation assay to facilitate the genetic identification of ubiquitin-dependent proteolysis pathways in the multicellular organism Caenorhabditis elegans. Using this assay, we found that mild induction of protein-folding stress, which is nontoxic for wild-type worms, strongly reduces ubiquitin-dependent protein turnover. Ubiquitin-mediated degradation is also reduced by metabolic stress, which correlates with life-span extension. Unlike other stress conditions, however, acute heat stress results in enhanced rather than reduced proteolysis. Intriguingly, our study provides the first evidence for the existence of tissue-specific degradation requirements because loss of key regulators of the UPS, such as proteasomal subunits, causes accumulation of the model substrate, depending on the tissue type. Thus, here we establish a screenable degradation assay that allows diverse genetic screening approaches for the identification of novel cell-type-specific proteostasis networks important for developmental processes, stress response, and aging, thereby substantially extending the work on recently described mechanistic UPS reporter studies.