Abstract
FOXO (forkhead box O) transcription factors are tumor suppressors and increase the life spans of model organisms. Cellular stress, in particular oxidative stress caused by an increase in levels of reactive oxygen species (ROS), activates FOXOs through JNK-mediated phosphorylation. Importantly, JNK regulation of FOXO is evolutionarily conserved. Here we identified the pathway that mediates ROS-induced JNK-dependent FOXO regulation. Following increased ROS, RALA is activated by the exchange factor RLF (RalGDS-like factor), which is in complex with JIP1 (C-Jun-amino-terminal-interacting protein 1) and JNK. Active RALA consequently regulates assembly and activation of MLK3, MKK4, and JNK onto the JIP1 scaffold. Furthermore, regulation of FOXO by RALA and JIP1 is conserved in C. elegans, where both ral-1 and jip-1 depletion impairs heat shock-induced nuclear translocation of the FOXO orthologue DAF16.
Highlights
Forkhead box O (FOXO) transcription factors affect life span and age-related diseases
In the presence of growth factors, the insulin pathway through PI3K/PKB negatively regulates FOXOs, whereas FOXOs are activated by JNK following oxidative stress
We identified a role for the small GTPase RALA in JNK regulation of FOXO4
Summary
Forkhead box O (FOXO) transcription factors affect life span and age-related diseases. Results: Evolutionarily conserved role for RALA in stress-induced assembly of a JIP1 scaffold complex to ensure FOXO activity. Overexpression of a constitutive active RAL exchange factor or increased ROS levels result in JNK-dependent phosphorylation and activation of FOXO4 [5]. This suggests a pathway whereby RALA regulates JNK to modulate FOXO transcriptional activity. We show that activation of RALA results in the assembly of an active JIP1 scaffold complex consisting of MLK3, MKK4, and JNK Formation of this complex by RALA is necessary for proper JNK signaling toward FOXO4 and subsequent FOXO4 transcriptional activity. We show the conservation of RAL/JIP1-dependent FOXO regulation in C. elegans
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