ClpP Mediates Activation of a Mitochondrial Unfolded Protein Response in C. elegans

Summary The cellular response to unfolded and misfolded proteins in the mitochondrial matrix is poorly understood. Here, we report on a genome-wide RNAi-based screen for genes that signal the mitochondrial unfolded protein response (UPR mt ) in C. elegans . Unfolded protein stress in the mitochondria correlates with complex formation between a homeodomain-containing transcription factor DVE-1 and the small ubiquitin-like protein UBL-5, both of which are encoded by genes required for signaling the UPR mt . Activation of the UPR mt correlates temporally and spatially with nuclear redistribution of DVE-1 and with its enhanced binding to the promoters of mitochondrial chaperone genes. These events and the downstream UPR mt are attenuated in animals with reduced activity of clpp-1 , which encodes a mitochondrial matrix protease homologous to bacterial ClpP. As ClpP is known to function in the bacterial heat-shock response, our findings suggest that eukaryotes utilize component(s) from the protomitochondrial symbiont to signal the UPR mt .