Mitoprotein-induced stress launches a global transcriptional fail-safe program

Most mitochondrial proteins are synthesized as cytosolic precursor proteins before being imported into mitochondria. Cytosolic accumulation of mitochondrial precursors hazards cellular fitness and is associated with a growing number of diseases, but is not observed under physiological conditions. Individual mechanisms how cells avoid precursor accumulation outside mitochondria have recently been discovered, but their interplay and regulation have remained elusive. Here we show that cells rapidly launch a global transcriptional program to restore cellular proteostasis after induction of a “clogger” protein that reduces the number of available mitochondrial import sites. Cells upregulate the protein folding and proteolytic systems in the cytosol and downregulate both the cytosolic translation machinery and many mitochondrial metabolic enzymes, presumably to relieve the workload of the overstrained mitochondrial import system. We show that this transcriptional remodeling is a combination of a “wideband” core response regulated by the transcription factors Hsf1 and Rpn4 and a unique mitoprotein-induced downregulation of the OXPHOS components, the most abundant group of precursors. These findings not only depict the first comprehensive model of adaptations to mitochondrial import impairment, but also reveal their regulation, connecting so far isolated stress response mechanisms into a coordinated network of cellular reactions. Overall design: Examination of expression over time (timepoints 0, 10, 30, 90, 270 min after clogger induction) in 4 independent biological replicates, 2 strains expressing different clogger variants (b2-DHFR, b2delta-DHFR) and 2 reference strains expressing no clogger (empty vecgtor) or cytosolic DHFR

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Boos F, Krämer L, Groh C, Jung F, Haberkant P, Stein F, Wollweber F, Gackstatter A, Zöller E, van der Laan M, Savitski MM, Benes V, Herrmann JM