title: RasGAP Shields Akt from Deactivating Phosphatases in Fibroblast Growth Factor Signaling but Loses This Ability Once Cleaved by Caspase-3.
abstract: Fibroblast growth factor receptors (FGFRs) are involved in proliferative and differentiation physiological responses. Deregulation of FGFR-mediated signaling involving the Ras/PI3K/Akt and the Ras/Raf/ERK MAPK pathways is causally involved in the development of several cancers. The caspase-3/p120 RasGAP module is a stress sensor switch. Under mild stress conditions, RasGAP is cleaved by caspase-3 at position 455. The resulting N-terminal fragment, called fragment N, stimulates anti-death signaling. When caspase-3 activity further increases, fragment N is cleaved at position 157. This generates a fragment, called N2, that no longer protects cells. Here, we investigated in Xenopus oocytes the impact of RasGAP and its fragments on FGF1-mediated signaling during G2/M cell cycle transition. RasGAP used its N-terminal Src homology 2 domain to bind FGFR once stimulated by FGF1, and this was necessary for the recruitment of Akt to the FGFR complex. Fragment N, which did not associate with the FGFR complex, favored FGF1-induced ERK stimulation, leading to accelerated G2/M transition. In contrast, fragment N2 bound the FGFR, and this inhibited mTORC2-dependent Akt Ser-473 phosphorylation and ERK2 phosphorylation but not phosphorylation of Akt on Thr-308. This also blocked cell cycle progression. Inhibition of Akt Ser-473 phosphorylation and entry into G2/M was relieved by PHLPP phosphatase inhibition. Hence, full-length RasGAP favors Akt activity by shielding it from deactivating phosphatases. This shielding was abrogated by fragment N2. These results highlight the role played by RasGAP in FGFR signaling and how graded stress intensities, by generating different RasGAP fragments, can positively or negatively impact this signaling.
authors.affiliation: From the Université de Lille 1, Sciences et Technologies, Team Signal Division Regulation, CNRS UMR 8576, SN3, 59655 Villeneuve d'Ascq Cedex, France, katia.maggio@univ-lille1.fr.
authors.forename: Katia
authors.initials: K
authors.lastname: Cailliau
authors.affiliation: From the Université de Lille 1, Sciences et Technologies, Team Signal Division Regulation, CNRS UMR 8576, SN3, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Arlette
authors.initials: A
authors.lastname: Lescuyer
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS UMR8104, Institut Cochin, 22 rue Méchain, 75014 Paris, France, the Université Paris Descartes, Sorbonne Paris Cité, 24 Rue du Faubourg Saint Jacques, 75014 Paris, France, and.
authors.forename: Anne-Françoise
authors.initials: AF
authors.lastname: Burnol
authors.affiliation: the Department of Physiology, Université de Lausanne, Rue du Bugnon 7, 1005 Lausanne, Switzerland.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Cuesta-Marbán
authors.affiliation: the Department of Physiology, Université de Lausanne, Rue du Bugnon 7, 1005 Lausanne, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Widmann
authors.affiliation: From the Université de Lille 1, Sciences et Technologies, Team Signal Division Regulation, CNRS UMR 8576, SN3, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Edith
authors.initials: E
authors.lastname: Browaeys-Poly
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D016220:Fibroblast Growth Factor 1 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D005786:Gene Expression Regulation; D006801:Humans; D000076225:Mechanistic Target of Rapamycin Complex 2; D008845:Microinjections; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010053:Ovary / Q000166:cytology / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D061251:Primary Cell Culture; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis; D020729:p120 GTPase Activating Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D020729:p120 GTPase Activating Protein; D016220:Fibroblast Growth Factor 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; C400601:PHLPP1 protein, human; D010749:Phosphoprotein Phosphatases; D053148:Caspase 3
keywords: Akt PKB; GTPase-activating protein (GAP); Xenopus; caspase; cell signaling; fibroblast growth factor receptor (FGFR); mitogen-activated protein kinase (MAPK); oocyte; phosphatase; receptor tyrosine kinase