Impact of translation initiation factor eIF2-a phosphorylation during stress exposure. – STRESSOR

The dephosphorylation of eIF2-a though the induced expression of Ppp1r15a (GADD34), which forms a functional complex with protein phosphatase 1 (PP1) and thereby restore protein synthesis, will be at the center of this study. In particular the use of GADD34 specific inhibitors that competitively disrupt the interaction between PP1 and GADD34 will be tested in different experimental conditions and mouse disease models. Each of the teams of the consortium has developed a range of technical expertise and experimental tools, which will be of great importance for the study of the biochemical pathways structured around eIF2-a phosphorylation in vitro and in vivo.

The genetic of pharmacological incapacitation of producing functional GADD34 in splenic DCs exposed to LPS or dsRNA, caused abundant apoptotic cell death. Dephosphorylation of P-eIF2a during microbial activation is therefore an important part of a survival program allowing DC to perform their immune function after exposure to microbial stress. the study of GADD34 inhibition has also led to interesting finding on the reasons why only 5% of cells respond to viral stimulation and release type I IFNs. A chemical screen designed to identify novel inducers of autophagy has led to the discovery that signal transducer and activator of transcription 3 (STAT3) inhibitors can potently stimulate the autophagic flux. other projects on EIF2AK2-dependent autophagy inducers have revealed that several fatty acids including palmitate trigger autophagy via a pathway that involves the disruption of the STAT3-EIF2AK2 complex as well as its phosphorylation. Importantly , we have confirmed that ISR induction is triggering immuno-stimulatory cell death, which increases the efficacy of specific chemotherapeutic agents. Finally we have visualized in real time the eIF2a/ATF4 pathway induction in target tissues by different stressors, using novel ATF4-inducible luciferase mouse model.

All together much progress has been made and many synergies have arose from the results, Tt is however still early to define future prospect, but we anticipate that inhibitors of eIF2a Kinase and GADD34 will have interesting potential in setting up therapies agains neurodegenerative diseases as well as auto-immune diseases such as Lupus. While ISR triggering could potentiate existing chemio-therapies against cancer.

1. Nature Immunol. (12):1203-5. doi: 10.1038/ni.2759 : Comments on protein synthesis regulation for anti-microbial detection
2. Nature Neurosci. (9):1299-305: 10.1038/nn.3486. PMID: 23933749 : Importance of eif2a and associated kinases for Alzheimer's disease prevention.
3. Autophagy. 2013 Mar;9(3):415-7. role of eif2ak2 in the control of autophagy through transcription factor STAT3 .
4. Oncoimmunology. 2014 Mar 25;3:e28276=
5. Oncoimmunology. 2014 Jan 1;3(1):e27878 Demonstration of ISR induction to generate immunological cell death upon chimiotherapy and potentiate its effect.

One of the most prominent features of the cellular stress response, is the phosphorylation of the alpha subunit of the eukaryotic translation initiation factor 2 (eIF2-a). This phosphorylation impacts many functional compartments of the cell, in a response known as the integrated stress response (ISR). The research consortium assembled for this project has a great expertise in the stress pathways involved in eIF2-a phosphorylation. Each laboratory has demonstrated individually the importance of several branches of the ISR for the control of eIF2-a phosphorylation during studies as diverse as the impact of anticancer agents on the immunogenicity of tumors, the production of cytokines during the detection of pathogens by innate immune cells (Clavarino et al. in revision) or the ability of mammalian cells to respond to amino acids starvation. Although these results were obtained independently, they all intersect and raise important questions on the role of the ISR and the regulation of eIF2-a phosphorylation in the initiation of the immune response, as well as tumorogenesis. As a result, our collective aim is to define the molecular characteristics and specificities of the different ISR(s) induced in response to various chemotherapeutic agents,microbial stimuli or physiological disorders. In particular, we need to establish how autophagy, translation and the ISR are co-regulated in response to stress and how these important biochemical functions can be manipulated, through the identification of novel molecular targets. We will further explore the importance of the ISR both during inflammation and tumor development/treatment by studying the negative feed-back mechanism preventing cell death during stress. The dephosphorylation of eIF2-a though the induced expression of Ppp1r15a (GADD34), which forms a functional complex with protein phosphatase 1 (PP1) and thereby restore protein synthesis, will be at the center of this study. In particular the use of GADD34 specific inhibitors that competitively disrupt the interaction between PP1 and GADD34 will be tested in different experimental conditions and mouse disease models. Each of the teams of the consortium has developed a range of technical expertise and experimental tools, which will be of great importance for the study of the biochemical pathways structured around eIF2-a phosphorylation in vitro and in vivo.