Yeast Endosulfines Control Entry into Quiescence and Chronological Life Span by
Inhibiting Protein Phosphatase 2A
Se´ verine Bontron,1 Malika Jaquenoud,1 Stefania Vaga,2 Nicolas Talarek,1 Bernd Bodenmiller,2 Ruedi Aebersold,2
and Claudio De Virgilio
Cell Rep. 2013 Jan 31;3(1):16-22. doi: 10.1016/j.celrep.2012.11.025. Epub 2012 Dec 27.
Presenter :Shih-Kang Kao
Commentator : Chi-Wu Chiang, Ph.D
Date/Time : 2013/05/02 17:10-18:00
Location : Room 602, Med College Building
Background:
Initiation of the quiescence program in eukaryotic cells is a highly coordinated process. In yeast, quiescence
is primarily induced by limitation for essential nutrients in which cells cease growing, arrest cell division in the
G1 phase of the cell cycle, and ensure normal chronological life span (CLS) of cells during long periods of
starvation. Target of Rapamycin Complex 1 (TORC1) pathway and protein kinase A (PKA) pathway are two
major nutrient signaling pathways which regulate yeast cells to initiate the quiescence program. Limitation of the
nitrogen and/or carbon attenuates TORC1and PKA, respectively, and activates the protein kinase Rim15, which
induces numerous important aspects of the quiescence program. Rim15-dependent phosphorylation of the
endosulfines Igo1/2 is essential for mRNAs, which are transcriptionally controlled by the stress response (STRE)
and postdiauxic shift (PDS) transcription factors Msn2/4 and Gis1, respectively, to be sheltered from degradation
via the 5`-3` mRNA decay pathway. However, the molecular elements linking Rim15 to distal readouts are only
partially characterized.
Objective:
To identify the element linking Rim15 to downstream effectors in TORC1-/PKA- mediated regulation of
quiescence and chronological life span.
Results:
The authors used a genome-wide screen for mutations that are able to show that loss of PP2ACdc55 enables
rim15Δ and igo1Δigo2Δcells to properly enter quiescence and proper setup of CLS. Then authors use yeast
two-hybrid assay and co-immunoprecipiation to investigate the interaction between Igo1 , Cdc55 and Pph21. To
decode the molecular events that critically affect the quiescence program, the authors use label-free quantitative
phosphoproteomics screening to identify PP2ACdc55 target proteins. Intriguingly, Vts1 and Gis1, which have
previously been implicated in regulating gene expression of nutrient controlled genes, two are candidate targets
of PP2ACdc55. To validate the results of phosphoproteome studies, the authors validated Gis1 as a PP2ACdc55
target by phosphate affinity gel electrophoresis co-immunoprecipitation and in vitro phosphatase assay. The data
show that Rim15-activated Igo1/2 specifically antagonize PP2ACdc55-mediated dephosphorylation of Gis1 at
Ser425 in rapamycin-treated cells then authors used reporter assay and chromatin IP(ChIP) to show that
PP2ACdc55 regulates Gis1 promoter recruitment in part independently of Ser425.
Conclusion:
Rim15 controls transcription of a specific set of nutrient-controlled genes by regulating the phosphorylation
status, and hence promoter recruitment of Gis1 indirectly via the activation of Igo1 and subsequent inhibition of
PP2ACdc55.