Activation of Gcn2 in response to different stresses.

Silje Anda,Róbert Zach,Beáta Grallert,Juan Mata

doi:10.1371/journal.pone.0182143

Abstract

All organisms have evolved pathways to respond to different forms of cellular stress. The Gcn2 kinase is best known as a regulator of translation initiation in response to starvation for amino acids. Work in budding yeast has showed that the molecular mechanism of GCN2 activation involves the binding of uncharged tRNAs, which results in a conformational change and GCN2 activation. This pathway requires GCN1, which ensures delivery of the uncharged tRNA onto GCN2. However, Gcn2 is activated by a number of other stresses which do not obviously involve accumulation of uncharged tRNAs, raising the question how Gcn2 is activated under these conditions. Here we investigate the requirement for ongoing translation and tRNA binding for Gcn2 activation after different stresses in fission yeast. We find that mutating the tRNA-binding site on Gcn2 or deleting Gcn1 abolishes Gcn2 activation under all the investigated conditions. These results suggest that tRNA binding to Gcn2 is required for Gcn2 activation not only in response to starvation but also after UV irradiation and oxidative stress.

Highlights

All cells and organisms are surrounded by a changing and often stressful environment and have developed various signaling pathways to adapt to these changes
If Gcn2 activation occurs through a similar mechanism of tRNA accumulation after UV irradiation, one would expect that ongoing translation is required for activation
The phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) after UVC-irradiation was not affected by blocking translation by cycloheximide prior to UVC irradiation (Fig 1C and 1D), suggesting that ongoing translation is not required for Gcn2 activation after UVC irradiation

Summary

Introduction

All cells and organisms are surrounded by a changing and often stressful environment and have developed various signaling pathways to adapt to these changes. Translational regulation in response to different types of stress involves phosphorylation of serine (Ser 52 in S. pombe) of the eukaryotic translation initiation factor 2α (eIF2α) [1]. This phosphorylation is thought to lead to a general downregulation of translation, accompanied by an enhanced translation of specific stress-response mRNAs [2,3,4]. Gcn was first described in budding yeast as a regulator of eIF2α phosphorylation in response to amino-acid starvation. This role is conserved from yeast to human cells and the extent of conservation is such that the human Gcn can functionally replace the budding yeast Gcn2 [5]. Fission yeast has several eIF2α kinases and it is GCN2 that is activated in response to nutrient deprivation [6,7,8,9]

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