The Gcn4 transcription factor reduces protein synthesis capacity and extends yeast lifespan

Abstract

In Saccharomyces cerevisiae, deletion of large ribosomal subunit protein-encoding genes increases the replicative lifespan in a Gcn4-dependent manner. However, how Gcn4, a key transcriptional activator of amino acid biosynthesis genes, increases lifespan, is unknown. Here we show that Gcn4 acts as a repressor of protein synthesis. By analyzing the messenger RNA and protein abundance, ribosome occupancy and protein synthesis rate in various yeast strains, we demonstrate that Gcn4 is sufficient to reduce protein synthesis and increase yeast lifespan. Chromatin immunoprecipitation reveals Gcn4 binding not only at genes that are activated, but also at genes, some encoding ribosomal proteins, that are repressed upon Gcn4 overexpression. The promoters of repressed genes contain Rap1 binding motifs. Our data suggest that Gcn4 is a central regulator of protein synthesis under multiple perturbations, including ribosomal protein gene deletions, calorie restriction, and rapamycin treatment, and provide an explanation for its role in longevity and stress response.

Genome-scale reconstruction of Gcn4/ATF4 networks driving a growth program

“…Here, there is a somewhat contradictory observation, as follows. Several earlier studies have reported, repression of ribosomal gene by the elevated Gcn4 level in cells (Bose et al, 2012;Joo et al, 2010;Mittal et al, 2017). In contrast, here, despite high Gcn4 levels in cells, methionine strongly induces ribosomal and translation related genes.…”

“…Gcn4 is a transcriptional master--regulator, conventionally studied in the context of starvation and other stress conditions, as part of the integrated stress response (Hinnebusch, 2005;Hinnebusch and Natarajan, 2002;Mascarenhas et al, 2008;Natarajan et al, 2001;Pakos--Zebrucka et al, 2016). Therefore, nearly all existing studies of Gcn4 have used pharmacological inhibitors of amino acid biosynthesis, such as 3--amino triazole (3--AT) or sulfo meturon (SM) to induce Gcn4 (Akhter and Rosonina, 2016;Albrecht et al, 1998;Mittal et al, 2017;Natarajan et al, 2001;Rawal et al, 2018). Indeed, our current understanding of Gcn4 function comes primarily from contexts of nutrient--stress and starvation conditions.…”

“…During severe amino acid starvation, the translation of Gcn4 mRNA increases, through the activation of the Gcn2 kinase, and subsequent eIF2--alpha phosphorylation (Hinnebusch, 1994(Hinnebusch, , 2005Hinnebusch et al, 2004). This resultant increase in Gcn4 protein allows it to function as a transcriptional activator, where it induces transcripts primarily involved in amino acid biosynthesis, thereby allowing cells to restore amino acid levels and survive severe starvation (Hinnebusch, 2005;Mittal et al, 2017;Natarajan et al, 2001;Rawal et al, 2018). Almost our entire current knowledge of Gcn4 function comes from studying its roles during starvation.…”

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

“…Some are listed below: (i) GH-deficient mouse models have shown improved proteostasis with reduced protein as well as DNA synthesis with sex-and tissue-specific differences (237,238). Most recent ageing research in yeast (239,240) and C. elegans (241) are provocative towards inquiring with the GHRKO model into the status of transcription factors like Gcn4 or Atf4 and proteostasis status. (ii) Bartke and colleagues, have dealt intensively into various conditions of GH deficit and ageing (198,242) and recently reported that a short (6 weeks) phase of early exposure to GH (starting at 2 weeks age) reduced lifespan and cellular stress resistance in Ames dwarf mice (243).…”

Gene regulatory network reconstruction using single-cell RNA sequencing of barcoded genotypes in diverse environments

“…Construction of GRNs based on the transcription factors in these pathways has had mixed success; the high redundancy of the NCR pathway has proven challenging to deconvolute (Milias-Argeitis et al, 2016) . The GAAC pathway is more straightforward, although separating direct and indirect regulation remains difficult, even with high-quality experimental data (Mittal et al, 2017) . As a result, a comprehensive GRN for nitrogen metabolism has remained elusive, despite successes in identifying genes that respond to changes in environmental nitrogen (Airoldi et al, 2016) and identification of post-transcriptional control mechanisms that underlie these changes (Miller et al, 2018) .…”