Abstract
The AMPK/Snf1 kinase has a central role in carbon metabolism homeostasis in Saccharomyces cerevisiae. In this study, we show that Snf1 activity, which requires phosphorylation of the Thr210 residue, is needed for protection against selenite toxicity. Such protection involves the Elm1 kinase, which acts upstream of Snf1 to activate it. Basal Snf1 activity is sufficient for the defense against selenite, although Snf1 Thr210 phosphorylation levels become increased at advanced treatment times, probably by inhibition of the Snf1 dephosphorylation function of the Reg1 phosphatase. Contrary to glucose deprivation, Snf1 remains cytosolic during selenite treatment, and the protective function of the kinase does not require its known nuclear effectors. Upon selenite treatment, a null snf1 mutant displays higher levels of oxidized versus reduced glutathione compared to wild type cells, and its hypersensitivity to the agent is rescued by overexpression of the glutathione reductase gene GLR1. In the presence of agents such as diethyl maleate or diamide, which cause alterations in glutathione redox homeostasis by increasing the levels of oxidized glutathione, yeast cells also require Snf1 in an Elm1-dependent manner for growth. These observations demonstrate a role of Snf1 to protect yeast cells in situations where glutathione-dependent redox homeostasis is altered to a more oxidant intracellular environment and associates AMPK to responses against oxidative stress.
Highlights
The AMP-activated protein kinase (AMPK) family is constituted by protein complexes that participate in metabolic stress responses addressed to maintain cellular ATP levels in eukaryotes [1]
AMPK/Snf1 responds to metabolic stress in yeast cells, its kinase activity being required for adaptation to glucose limitation and growth in alternative carbon sources [3]
In the present study we have shown that Snf1 activity is required for defense of S. cerevisiae cells upon selenite treatment
Summary
The AMP-activated protein kinase (AMPK) family is constituted by protein complexes that participate in metabolic stress responses addressed to maintain cellular ATP levels in eukaryotes [1]. Full activity of the catalytic a subunit of the AMPK complex requires phosphorylation of a T-loop threonine residue, as well as binding of the b and c subunits. Activation of Snf needs phosphorylation of the T-loop Thr210 residue. This is carried out by one of the three redundant kinases Sak, Elm or Tos3 [4,5]. The phosphorylation state of Thr210 is negatively regulated by the protein phosphatase 1 (PP1) complex. This is composed by the Glc catalytic subunit and the Reg regulatory subunit [6]. Among the best-characterized nuclear protein targets of Snf are the Mig repressor and the Cat, Sip and Adr transcriptional activators [3]
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