Convergence of the Target of Rapamycin and the Snf1 Protein Kinase Pathways in the Regulation of the Subcellular Localization of Msn2, a Transcriptional Activator of STRE (Stress Response Element)-regulated Genes

Isabel Mayordomo,Francisco Estruch,Pascual Sanz

doi:10.1074/jbc.m204198200

Abstract

The subcellular localization of Msn2, a transcriptional activator of STRE (stress response element)-regulated genes, is modulated by carbon source availability. In cells growing in glucose, Msn2 is located mainly in the cytosol, whereas in carbon source-starved cells, Msn2 is located largely inside the nucleus. However, in cells lacking Reg1 (the regulatory subunit of the Reg1/Glc7 protein phosphatase complex), the regulation of subcellular distribution is absent, Msn2 being constitutively present in the cytosol. The localization defect in these mutants is specific for carbon starvation stress, and it is because of the presence of an abnormally active Snf1 protein kinase that inhibits the nuclear localization of Msn2 upon carbon starvation. Active Snf1 kinase is also able to avoid the effects of rapamycin, a drug that by inhibiting the TOR kinase pathway leads to a nuclear localization of Msn2 in wild type cells. Therefore, active Snf1 and the TOR kinase pathway may affect similar cytosolic steps in the regulation of the subcellular localization of Msn2.

Highlights

The yeast Saccharomyces cerevisiae regulates metabolism, gene expression, and growth in response to carbon source availability
Because the Snf1 protein kinase pathway is one of the main regulators of glucose signaling, we decided to determine whether components involved in the Snf1 pathway were involved in the regulation of the subcellular localization of Msn2 in response to glucose
Stress factors influence cellular metabolism, gene expression, and growth rate by a “general stress response” system that regulates the coordinated induction of many stress genes through a common cis element in their promoter, the stress response element STRE [38]

Summary

EXPERIMENTAL PROCEDURES

To construct strains reg1⌬ snf1⌬ and reg1⌬ gal83⌬, a BamHI fragment of pUC-snf1⌬::KanMX4 (see below) and a XhoI/SpeI fragment from plasmid pOV1 [28] were used to introduce, respectively, snf1⌬::KanMX4 and gal83⌬::TRP1 mutated alleles by gene disruption.

TABLE I Strains used in this study

RESULTS

Cytosolic Cytosolic Cytosolic Cytosolic

DISCUSSION