Eukaryotic Cell
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Eukaryotic Cell, October 2004, p. 1261-1271, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1261-1271.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

PP2A Phosphatase Activity Is Required for Stress and Tor Kinase Regulation of Yeast Stress Response Factor Msn2p

Arti Santhanam,1,2 Alan Hartley,3 Katrin Düvel,4 James R. Broach,4 and Stephen Garrett1,2*

Graduate School of Biomedical Sciences,1 Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark,2 Department of Molecular Biology, Princeton University, Princeton, New Jersey,4 Lake Wylie Family Chiropractic, Lake Wylie, South Carolina3

Received 4 March 2004/ Accepted 16 June 2004

In response to stress and nutrient starvation, the Saccharomyces cerevisiae transcription factor Msn2p accumulates in the nucleus and activates expression of a broad array of genes. Here, we analyze the role of the Tor (target of rapamycin) signaling pathway in mediating these responses. Inactivation of the Tor pathway component Tap42p using tap42(Ts) alleles causes a sustained nuclear localization similar to that after the addition of the Tor kinase inhibitor rapamycin. Effects of Tap42p inactivation and rapamycin addition could be suppressed by deletion of TIP41, which encodes a Tap42p-interacting protein. These results support the notion that rapamycin affects Msn2p by inactivating Tap42p function. Tap42p interacts with the catalytic subunit of PP2A (protein phosphatase 2A) and PP2A-like phosphatases. Deletion of either the catalytic or regulatory subunit that forms the PP2A phosphatase complex prevents nuclear accumulation of Msn2p in the tap42(Ts) strain and in wild-type strains treated with rapamycin. These results suggest that Tap42p is an inhibitor of PP2A phosphatase, which in turn inhibits nuclear export of Msn2p. Interestingly, PP2A function is also required for nuclear accumulation of Msn2p in response to stresses, such as heat and osmotic shock, as well as nitrogen (but not glucose) starvation. Thus, PP2A and the Tor kinase pathway transduce stress and nitrogen starvation signals to Msn2p. Finally, Msn2p localization is unaffected by conditional loss of 14-3-3 protein function, ruling out the possibility that 14-3-3 proteins act as a scaffold to sequester Msn2p in the cytoplasm.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, Newark, NJ 07101. Phone: (973) 972-4483, ext. 20698. Fax: (973) 972-8982. E-mail: garretst{at}umdnj.edu.

Eukaryotic Cell, October 2004, p. 1261-1271, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1261-1271.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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Copyright © 2004 by the American Society for Microbiology.