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Reference: Tate JJ, et al. (2009) Rapamycin-induced Gln3 Dephosphorylation Is Insufficient for Nuclear Localization: Sit4 AND PP2A PHOSPHATASES ARE REGULATED AND FUNCTION DIFFERENTLY. J Biol Chem 284(4):2522-34

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Abstract

Gln3, the major activator of nitrogen catabolite repression- (NCR-) sensitive transcription, is often used as an assay of Tor pathway regulation in S. cerevisiae. Gln3 is cytoplasmic in cells cultured with repressive nitrogen sources (Gln) and nuclear with depressive ones (Pro) or after treating Gln-grown cells with the Tor inhibitor, rapamycin (Rap). In Rap-treated or Pro-grown cells, Sit4 is posited to dephosphorylate Gln3 which then dissociates from a Gln3-Ure2 complex and enters the nucleus. However, in contrast with this view, Sit4-dependent Gln3 dephosphorylation is greater in Gln than Pro. Investigating this paradox, we show that PP2A- (another Tor pathway phosphatase) dependent Gln3 dephosphorylation is regulated oppositely to that of Sit4, being greatest in Pro- and least in Gln-grown cells. It thus parallels nuclear Gln3 localization and NCR-sensitive transcription. However, since PP2A isn't required for nuclear Gln3 localization in Pro, PP2A-dependent Gln3 dephosphorylation and nuclear localization are likely parallel responses to derepressive nitrogen sources. In contrast, Rap-induced nuclear Gln3 localization absolutely requires all four PP2A components (Pph21/22, Tpd3, Cdc55 and Rts1). In pph21Delta22Delta, tpd3Delta, or cdc55{DELAT} cells, however, Gln3 is dephosphorylated to the same level as in Rap-treated wild type cells, indicating Rap-induced Gln3 dephosphorylation is insufficient to achieve nuclear localization. Finally, PP2A-dependent Gln3 dephosphorylation parallels conditions where Gln3 is most nuclear, while Sit4-dependent and Rap-induced dephosphorylation parallels those where Gln3 is most cytoplasmic, suggesting the effects of these phosphatases on Gln3 may occur in different cellular compartments.

Reference Type
Journal Article
Authors
Tate JJ, Georis I, Feller A, Dubois E, Cooper TG
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