Evolutionary conservation and characterization of the metazoan amino acid response

Abstract

Signaling pathways that respond to stress and sense nutrient availability are highly conserved throughout eukaryotes. In mammalian cells, these pathways have evolved to regulate immune responses, representing important therapeutic targets. Interestingly, components of these pathways can be found in plants, yeast and nematodes, where they also participate in response to abiotic and biotic stress. The Amino Acid Response (AAR) pathway, an ancient response to the cellular accumulation of uncharged tRNA, is part of the larger Integrated Stress Response (ISR) in mammals. The ISR consists of multiple branches, each one triggered by distinct stresses that produce phospho-eIF2α signal generation. Each ISR initiating stress results in a unique cellular response due to activation of both the ISR and additional parallel pathway(s) by the initiating stress, but, to date, no such alternate pathway has been identified for the AAR pathway. Despite its integral role in stress adaptation, the ISR has not been studied in early diverging animals. I have identified a highly conserved phosphorylation site in the protein eIF2α, the signature ISR effector, which allowed me to use a mammalian antibody to identify and characterize the ISR in the basal metazoan, Nematostella vectensis, revealing that the core components of the mammalian ISR were present over 550 million years ago in the common ancestor of cnidarians and bilaterians. Additionally, our lab has discovered a novel branch of the AAR pathway that regulates key tissue protective signals. Using evolutionary conservation of this pathway in model organisms, I have identified GCN1 as the branch point that links the signal generation components of the AAR pathway to downstream therapeutic effects. I then used transcriptomic and protein interaction analyses to begin to understand the scope of this pathway and identify key pathway regulators.