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IEX-1: a new ERK substrate involved in both ERK survival activity and ERK activation
Josefina Garcia1, Yunbin Ye, Valérie Arranz
1Department of Hematology, Institut Cochin, INSERM U567, CNRS UMR 8104, Université René Descartes, 27 rue du Fg St Jacques, 75014 Paris, France.
Abstract:
IEX-1 is an early response and NF-kappaB target gene implicated in the regulation of cellular viability. We show here that IEX-1 is a substrate for ERKs and that IEX-1 and ERK regulate each other's activities. IEX-1 was isolated by phosphorylation screening with active ERK2 and found subsequently phosphorylated in vivo upon ERK activation. IEX-1 interacts with phosphorylated ERKs but not with c-jun N-terminal kinase (JNK) or p38. Upon phosphorylation by ERKs, IEX-1 acquires the ability to inhibit cell death induced by various stimuli. In turn, IEX-1 potentiates ERK activation in response to various growth factors. By using various IEX-1 mutants in which the ERK phosphoacceptor and/or ERK docking sites were mutated, we show that the IEX-1 pro-survival effect is dependent on its phosphorylation state but not on its ability to potentiate ERK activation. Conversely, IEX-1-induced modulation of ERK activation requires ERK-IEX-1 association but is independent of IEX-1 phosphorylation. Thus, IEX-1 is a new type of ERK substrate that has a dual role in ERK signaling by acting both as an ERK downstream effector mediating survival and as a regulator of ERK activation.
Insights
The study reveals that IEX-1, a gene regulating cell viability, is phosphorylated by Extracellular signal-Regulated Kinases (ERKs). This phosphorylation allows IEX-1 to inhibit cell death and also regulate ERK activation, highlighting a dual role in cell signaling.
Area of Science:
- Cellular Biology
- Molecular Signaling
- Signal Transduction
Background:
- IEX-1 is an early response gene and NF-kappaB target involved in cellular viability.
- Extracellular signal-Regulated Kinases (ERKs) are key regulators of cellular processes.
Purpose of the Study:
- To investigate the relationship between IEX-1 and ERKs.
- To elucidate the functional consequences of IEX-1 phosphorylation by ERKs.
Main Methods:
- Phosphorylation screening using active ERK2.
- In vivo phosphorylation analysis upon ERK activation.
- Co-immunoprecipitation to study protein interactions.
- Site-directed mutagenesis to analyze functional domains.
Main Results:
- IEX-1 is identified as a direct substrate for ERKs and is phosphorylated in vivo upon ERK activation.
- Phosphorylated IEX-1 inhibits apoptosis induced by various stimuli.
- IEX-1 potentiates ERK activation in response to growth factors.
- The pro-survival effect of IEX-1 depends on its phosphorylation, while its role in potentiating ERK activation requires ERK-IEX-1 association but not IEX-1 phosphorylation.
Conclusions:
- IEX-1 acts as a novel ERK substrate with a dual role in ERK signaling.
- IEX-1 functions as a downstream effector mediating cell survival.
- IEX-1 also acts as a regulator of ERK activation, influencing signal propagation.