Yeast 3-Phosphoinositide-dependent Protein Kinase-1 (PDK1) Orthologs Pkh1-3 Differentially Regulate Phosphorylation of Protein Kinase A (PKA) and the Protein Kinase B (PKB)/S6K Ortholog Sch9

Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Department of Molecular Microbiology, VIB, B-3001 Leuven-Heverlee, Flanders, Belgium.
Journal of Biological Chemistry (Impact Factor: 4.57). 06/2011; 286(25):22017-27. DOI: 10.1074/jbc.M110.200071
Source: PubMed


Pkh1, -2, and -3 are the yeast orthologs of mammalian 3-phosphoinositide-dependent protein kinase-1 (PDK1). Although essential for viability, their functioning remains poorly understood. Sch9, the yeast protein kinase B and/or S6K ortholog, has been identified as one of their targets. We now have shown that in vitro interaction of Pkh1 and Sch9 depends on the hydrophobic PDK1-interacting fragment pocket in Pkh1 and requires the complementary hydrophobic motif in Sch9. We demonstrated that Pkh1 phosphorylates Sch9 both in vitro and in vivo on its PDK1 site and that this phosphorylation is essential for a wild type cell size. In vivo phosphorylation on this site disappeared during nitrogen deprivation and rapidly increased again upon nitrogen resupplementation. In addition, we have shown here for the first time that the PDK1 site in protein kinase A is phosphorylated by Pkh1 in vitro, that this phosphorylation is Pkh-dependent in vivo and occurs during or shortly after synthesis of the protein kinase A catalytic subunits. Mutagenesis of the PDK1 site in Tpk1 abolished binding of the regulatory subunit and cAMP dependence. As opposed to PDK1 site phosphorylation of Sch9, phosphorylation of the PDK1 site in Tpk1 was not regulated by nitrogen availability. These results bring new insight into the control and prevalence of PDK1 site phosphorylation in yeast by Pkh protein kinases.

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    • "All rights reserved. catalytic Tpk1 subunit interferes with binding to the regulatory Bcy1 subunit and thus with cAMP-dependency (Voordeckers, et al., 2011, Haesendonckx, et al., 2012). This regulation establishes a link between sphingolipid signaling pathways and PKA. "
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    • "TORC1 then signals to downstream effectors to regulate transcriptional and translational processes controlling cell growth and proliferation [9]. The best-characterized TORC1 target in yeast is the AGC kinase family member Sch9, which is a functional ortholog to the Akt/PKB and ribosomal S6 kinases [10]. Sch9 is phosphorylated on multiple serine and threonine residues by TORC1, resulting in Sch9 activation [11]. "
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    • "This is accompanied by a reduction of the REV1 DNA repair protein expression and of translesional synthesis. The phosphorylation of Sch9 is essential for a wild type cell size [53]. The Sir2 deacetylase is a highly conserved gene, that modulates lifespan in yeast, worms, and flies and stress response in mammals. "
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