ABSTRACT
Stress response pathways detect and alleviate adverse conditions to safeguard cell and tissue homeostasis, yet their prolonged activation induces apoptosis and disrupts organismal health1-3. How stress responses are turned off at the right time and place remains poorly understood. Here we report a ubiquitin-dependent mechanism that silences the cellular response to mitochondrial protein import stress. Crucial to this process is the silencing factor of the integrated stress response (SIFI), a large E3 ligase complex mutated in ataxia and in early-onset dementia that degrades both unimported mitochondrial precursors and stress response components. By recognizing bifunctional substrate motifs that equally encode protein localization and stability, the SIFI complex turns off a general stress response after a specific stress event has been resolved. Pharmacological stress response silencing sustains cell survival even if stress resolution failed, which underscores the importance of signal termination and provides a roadmap for treating neurodegenerative diseases caused by mitochondrial import defects.
Subject(s)
Mitochondria , Mitochondrial Proteins , Mutation , Neurodegenerative Diseases , Stress, Physiological , Ubiquitin-Protein Ligases , Apoptosis/drug effects , Ataxia/genetics , Cell Survival/drug effects , Dementia/genetics , Mitochondria/genetics , Mitochondria/metabolism , Mitochondria/pathology , Mitochondrial Proteins/chemistry , Mitochondrial Proteins/metabolism , Multiprotein Complexes/antagonists & inhibitors , Multiprotein Complexes/genetics , Multiprotein Complexes/metabolism , Neurodegenerative Diseases/genetics , Neurodegenerative Diseases/metabolism , Neurodegenerative Diseases/pathology , Protein Stability/drug effects , Protein Transport/drug effects , Proteolysis/drug effects , Stress, Physiological/drug effects , Ubiquitin/metabolism , Ubiquitin-Protein Ligases/antagonists & inhibitors , Ubiquitin-Protein Ligases/genetics , Ubiquitin-Protein Ligases/metabolism , Ubiquitination/drug effectsABSTRACT
Cell-cell fusion is a frequent and essential event during development, and its dysregulation causes diseases ranging from infertility to muscle weakness. Fusing cells need to repeatedly remodel their plasma membrane through orchestrated formation and disassembly of actin filaments, but how the dynamic reorganization of the cortical actin cytoskeleton is controlled is still poorly understood. Here, we identified a ubiquitin-dependent toggle switch that establishes reversible actin bundling during mammalian cell fusion. We found that EPS8-IRSp53 complexes stabilize cortical actin bundles at sites of cell contact to promote close membrane alignment. EPS8 monoubiquitylation by CUL3KCTD10 displaces EPS8-IRSp53 from membranes and counteracts actin bundling, a dual activity that restricts actin bundling to allow paired cells to progress with fusion. We conclude that cytoskeletal rearrangements during development are precisely controlled by ubiquitylation, raising the possibility of modulating the efficiency of cell-cell fusion for therapeutic benefit.
