Intranuclear Function for Protein Phosphatase 2A: Pph21 and Pph22 Are Required for Rapamycin-Induced GATA Factor Binding to the DAL5 Promoter in Yeast

Institut de Recherches Microbiologiques J.-M. Wiame, Laboratoire de Microbiologie, Université Libre de Bruxelles, B1070 Brussels, Belgium.
Molecular and Cellular Biology (Impact Factor: 4.78). 10/2010; 31(1):92-104. DOI: 10.1128/MCB.00482-10
Source: PubMed


Protein phosphatase 2A (PP2A), a central Tor pathway phosphatase consisting of a catalytic subunit (Pph21 or Pph22), a scaffold
subunit (Tpd3), and one of two regulatory subunits (Cdc55 or Rts1), has been repeatedly shown to play important roles in cytoplasmically
localized signal transduction activities. In contrast, its involvement in intranuclear control of mRNA production has heretofore
not been reported. Here, we demonstrate for the first time that binding of the nitrogen catabolite repression-responsive GATA
transcription activators (Gln3 and Gat1) to the DAL5 promoter and DAL5 expression require Pph21/22-Tpd3-Cdc55/Rts1 in rapamycin-treated glutamine-grown cells. This conclusion is supported by the
following observations. (i) Rapamycin-induced DAL5 expression along with Gln3 and Gat1 binding to the DAL5 promoter fails to occur in pph21Δ pph22Δ, tpd3Δ, and cdc55Δ rts1Δ mutants. (ii) The Pph21/22 requirement persists even when Gat1 and Gln3 are rendered constitutively nuclear, thus dissociating
the intranuclear requirement of PP2A from its partial requirement for rapamycin-induced nuclear Gat1 localization. (iii) Pph21-Myc13 (Ppp21 tagged at the C terminus with 13 copies of the Myc epitope) weakly associates with the DAL5 promoter in a Gat1-dependent manner, whereas a similar Pph22-Myc13 association requires both Gln3 and Gat1. Finally, we demonstrate that a pph21Δ pph22Δ double mutant is epistatic to ure2Δ for nuclear Gat1 localization in untreated glutamine-grown cells, whereas for Gln3, just the opposite occurs: i.e., ure2Δ is epistatic to pph21Δ pph22Δ. This final observation adds additional support to our previous conclusion that the Gln3 and Gat1 GATA factor localizations
are predominantly controlled by different regulatory pathways.

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    • "(2) In contrast to Gln3, Gat1 nuclear localization is largely Ure2-independent (Georis et al. 2008). (3) Nuclear localization of Gln3 and Gat1 exhibits distinct requirements for the TORC1-regulated phosphatases (Tate et al. 2010; Georis et al. 2011b). Early investigations of Gln3 regulation established that under steady state, nitrogen-rich conditions, cytoplasmic Gln3 was situated within or tightly associated with a cytoplasmic membrane system (Cox et al. 2002). "
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