Phosphorylation of the Saccharomyces cerevisiae Grx4p glutaredoxin by the Bud32p kinase unveils a novel signaling pathway involving Sch9p, a yeast member of the Akt / PKB subfamily.
The Saccharomyces cerevisiae atypical protein kinase Bud32p is a member of the nuclear endopeptidase-like, kinase, chromatin-associated/kinase, endopeptidase-like and other protein of small size (EKC/KEOPS) complex, known to be involved in the control of transcription and telomere homeostasis. Complex subunits (Pcc1p, Pcc2p, Cgi121p, Kae1p) represent, however, a small subset of the proteins able to interact with Bud32p, suggesting that this protein may be endowed with additional roles unrelated to its participation in the EKC/KEOPS complex. In this context, we investigated the relationships between Bud32p and the nuclear glutaredoxin Grx4p, showing that it is actually a physiological substrate of the kinase and that Bud32p contributes to the full functionality of Grx4p in vivo. We also show that this regulatory system is influenced by the phosphorylation of Bud32p at Ser258, which is specifically mediated by the Sch9p kinase [yeast homolog of mammalian protein kinase B (Akt/PKB)]. Notably, Ser258 phosphorylation of Bud32p does not alter the catalytic activity of the protein kinase per se, but positively regulates its ability to interact with Grx4p and thus to phosphorylate it. Interestingly, this novel signaling pathway represents a function of Bud32p that is independent from its role in the EKC/KEOPS complex, as the known functions of the complex in the regulation of transcription and telomere homeostasis are unaffected when the cascade is impaired. A similar relationship has already been observed in humans between Akt/PKB and p53-related protein kinase (Bud32p homolog), and could indicate that this pathway is conserved throughout evolution.
Peggion
Caterina
C
Dipartimento di Chimica Biologica dell'Università di Padova, Italy.
Lopreiato
Raffaele
R
Casanova
Elena
E
Ruzzene
Maria
M
Facchin
Sonia
S
Pinna
Lorenzo A
LA
Carignani
Giovanna
G
Sartori
Geppo
G
D005686:Galactokinase / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D054477:Glutaredoxins / Q000235:genetics / Q000378:metabolism*; D047468:Immunoprecipitation; D009154:Mutation; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D016615:Telomere / Q000378:metabolism; D015533:Transcriptional Activation; D014170:Transformation, Genetic
D054477:Glutaredoxins; C516012:Grx4 protein, S cerevisiae; C509947:KEOPS complex, S cerevisiae; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D010768:Phosphoserine; D012694:Serine; C108301:BUD32 protein, S cerevisiae; C524219:GAL1 protein, S cerevisiae; D005686:Galactokinase; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C530964:SCH9 protein, S cerevisiae