title: C. elegans SUR-6/PR55 cooperates with LET-92/protein phosphatase 2A and promotes Raf activity independently of inhibitory Akt phosphorylation sites.
abstract: Protein phosphatase 2A (PP2A) can both positively and negatively influence the Ras/Raf/MEK/ERK signaling pathway, but its relevant substrates are largely unknown. In C. elegans, the PR55/B regulatory subunit of PP2A, which is encoded by sur-6, positively regulates Ras-mediated vulval induction and acts at a step between Ras and Raf. We show that the catalytic subunit (C) of PP2A, which is encoded by let-92, also positively regulates vulval induction. Therefore SUR-6/PR55 and LET-92/PP2A-C probably act together to dephosphorylate a Ras pathway substrate. PP2A has been proposed to activate the Raf kinase by removing inhibitory phosphates from Ser259 from Raf-1 or from equivalent Akt phosphorylation sites in other Raf family members. However, we find that mutant forms of C. elegans LIN-45 RAF that lack these sites still require sur-6. Therefore, SUR-6 must influence Raf activity via a different mechanism. SUR-6 and KSR (kinase suppressor of Ras) function at a similar step in Raf activation but our genetic analysis suggests that KSR activity is intact in sur-6 mutants. We identify the kinase PAR-1 as a negative regulator of vulval induction and show that it acts in opposition to SUR-6 and KSR-1. In addition to their roles in Ras signaling, SUR-6/PR55 and LET-92/PP2A-C cooperate to control mitotic progression during early embryogenesis.
authors.affiliation: Department of Genetics, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Gautam
authors.initials: G
authors.lastname: Kao
authors.forename: Simon
authors.initials: S
authors.lastname: Tuck
authors.forename: David
authors.initials: D
authors.lastname: Baillie
authors.forename: Meera V
authors.initials: MV
authors.lastname: Sundaram
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000196:embryology / Q000201:enzymology* / Q000235:genetics; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D029721:Drosophila Proteins; D005260:Female; D019950:Mitogen-Activated Protein Kinase 1; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D014844:Vulva / Q000196:embryology
chemical_list: D029742:Caenorhabditis elegans Proteins; D029721:Drosophila Proteins; D011518:Proto-Oncogene Proteins; C409406:PAR-1 protein, C elegans; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; C085697:mpk-1 protein, C elegans; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C489811:SUR-6 protein, C elegans; C490690:PTP-ER protein, Drosophila; D017027:Protein Tyrosine Phosphatases