Impact of Hydrogen Peroxide on Protein Synthesis in Yeast

Abstract

Cells must be able to respond and adapt to different stress conditions to maintain normal function. A common response to stress is the global inhibition of protein synthesis. Protein synthesis is an expensive process consuming much of the cell's energy. Consequently, it must be tightly regulated to conserve resources. One of these stress conditions is oxidative stress, resulting from the accumulation of reactive oxygen species (ROS) mainly produced by the mitochondria but also by other intracellular sources. Cells utilize a variety of antioxidant systems to protect against ROS, directing signaling and adaptation responses at lower levels and/or detoxification as levels increase to preclude the accumulation of damage. In this review, we focus on the role of hydrogen peroxide, H₂O₂, as a signaling molecule regulating protein synthesis at different levels, including transcription and various parts of the translation process, e.g., initiation, elongation, termination and ribosome recycling.

Keywords: cysteine thiols; hydrogen peroxide; protein synthesis; signaling.

Figure 1

Impact of H₂O₂ on transcription in yeast. Five different transcription factors respond to H₂O₂ in yeast. Upon H₂O₂ addition, Yap1 is retained in the nucleus where it stimulates the expression of target genes. Gpx3 is the H₂O₂ sensor of Yap1 that uses its cysteine 36 to form a disulfide bond with the cysteine C598 of Yap1, eventually resolved into a Yap1 intramolecular disulfide bond (between C598 and C303) inhibiting nuclear export. Yap1 controls the expression of different genes most of which require the presence of Skn7 as well. Upon the addition of t-butyl hydrogen peroxide (t-BOOH), Hsf1 interacts with Skn7 to achieve maximal induction of several HSP genes. Msn2/4 sensing of H₂O₂ is accomplished through PKA-dependent phosphorylation. Maf1 controls the availability of tRNAs under H₂O₂ through binding to PolIII. Under H₂O₂ conditions, Sfp1 is localized in the cytosol and RP gene expression is inhibited.

Figure 2

Impact of H₂O₂ on translation initiation. Integrative stress response. Under H₂O₂, eIf2α is phosphorylated by Gcn2, ternary complex levels decrease and translation is inhibited. Moreover, the translation of GCN4, a transcription factor that activates gene expression in response to stress, may be activated, at least in the divergent w303 yeast strain background [63]. In addition, upon Gcn2 activation, sulfiredoxin, Srx1, is more efficiently translated upon addition of H₂O₂ to cells grown under caloric restriction [63].

Figure 3

Impact of H₂O₂ function on translation initiation. The TOR pathway. In mammalian cells, H₂O₂ and hypoxia inhibit protein synthesis through inhibition of 4E-BP (A). There is a partial overlap in target genes of both pathways for translation inhibition under H₂O₂ conditions (B).

Figure 4

Effects of H₂O₂ on translation elongation. In yeast, eIE1A and eIE1B can be modified by protein S-thiolation in response to high concentrations of H₂O₂. Increase in the methylation in the wobble base 5-methyl-C (m⁵c) at position C34 of tRNA ^LEU(CAA) in response to H₂O₂ enhances the efficiency of translation of genes enriched in the UUG codon (as RPL22A and RPL22B) and causes a change in ribosome composition.

Figure 5

Effect of H₂O₂ on translation termination. Eukaryotic release factor 3, eRF3, forms prion aggregates known as [PSI⁺] under H₂O₂ conditions and can no longer perform its normal function in translation termination, leading to an elevated readthrough of termination codons.