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Arabidopsis eIF2alpha kinase GCN2 is essential for growth in stress conditions and is activated by wounding.

ABSTRACT: Phosphorylation of eIF2alpha provides a key mechanism for down-regulating protein synthesis in response to nutrient starvation or stresses in mammalian and yeast cells. However, this process has not been well characterized in plantsWe show here that in response to amino acid and purine starvations, UV, cold shock and wounding, the Arabidopsis GCN2 kinase (AtGCN2) is activated and phosphorylates eIF2alpha. We show that AtGCN2 is essential for plant growth in stress situations and that its activity results in a strong reduction in global protein synthesis.Our results suggest that a general amino acid control response is conserved between yeast and plants but that the plant enzyme evolved to fulfill a more general function as an upstream sensor and regulator of diverse stress-response pathways. The activation of AtGCN2 following wounding or exposure to methyl jasmonate, the ethylene precursor 1-Aminocyclopropane-1-carboxylic acid (ACC) and salicylic acid, further suggests that this enzyme could play a role in plant defense against insect herbivores.

SUBMITTER: Lageix S

PROVIDER: S-EPMC2639386 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature

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Arabidopsis eIF2alpha kinase GCN2 is essential for growth in stress conditions and is activated by wounding.

Lageix Sébastien S Lanet Elodie E Pouch-Pélissier Marie-Noëlle MN Espagnol Marie-Claude MC Robaglia Christophe C Deragon Jean-Marc JM Pélissier Thierry T

BMC plant biology 20081224

<h4>Background</h4>Phosphorylation of eIF2alpha provides a key mechanism for down-regulating protein synthesis in response to nutrient starvation or stresses in mammalian and yeast cells. However, this process has not been well characterized in plants<h4>Results</h4>We show here that in response to amino acid and purine starvations, UV, cold shock and wounding, the Arabidopsis GCN2 kinase (AtGCN2) is activated and phosphorylates eIF2alpha. We show that AtGCN2 is essential for plant growth in str ...[more]

PMID: 19108716

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Project description:Hepatic cytochromes P450 3A (P450s 3A) are endoplasmic reticulum (ER)-proteins, responsible for xenobiotic metabolism. They are degraded by the ubiquitin-dependent 26S proteasome. Consistent with this, we have shown that proteasomal inhibitors N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) and N-benzoyloxycarbonyl-Leu-Leu-Leu-B(OH)(2) (MG262) stabilize CYP3A proteins. However, MG132 has been reported to suppress P450s 3A as a result of impaired nuclear factor-kappaB activation and consequently reduced CYP3A protein stability. Because the MG132 concentration used in those studies was 10-fold higher than that required for CYP3A stabilization, we examined the effect of MG132 (0-300 microM) concentration-dependent proteasomal inhibition on CYP3A turnover in cultured primary rat hepatocytes. We found a biphasic MG132 concentration effect on CYP3A turnover: Stabilization at 5 to 10 muM with marked suppression at >100 microM. Proteasomal inhibitors reportedly induce ER stress, heat shock, and apoptotic response. At these high MG132 concentrations, such CYP3A suppression could be due to ER stress induction, so we monitored the activity of PERK [PKR (RNA-dependent protein kinase)-like ER kinase (EIF2AK3)], the ER stress-activated eukaryotic initiation factor 2alpha (eIF2alpha) kinase. Indeed, we found a marked (approximately 4-fold) MG132 concentration-dependent PERK autophosphorylation, along with an 8-fold increase in eIF2alpha-phosphorylation. In parallel, MG132 also activated GCN2 [general control nonderepressible-2 (EIF2AK4)] eIF2alpha kinase in a concentration-dependent manner, but not the heme-regulated inhibitor eIF2alpha kinase [(EIF2AK1)]. Pulse-chase, immunoprecipitation/immunoblotting analyses documented the consequently dramatic translational shutoff of total hepatic protein, including but not limited to CYP3A and tryptophan 2,3-dioxygenase protein syntheses. These findings reveal that at high concentrations, MG132 is indeed cytotoxic and can suppress CYP3A synthesis, a result confirmed by confocal immunofluorescence analyses of MG132-treated hepatocytes.

Dataset Information

Arabidopsis eIF2alpha kinase GCN2 is essential for growth in stress conditions and is activated by wounding.

Publications

Arabidopsis eIF2alpha kinase GCN2 is essential for growth in stress conditions and is activated by wounding.

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