title: The molecular scaffold kinase suppressor of Ras 1 is a modifier of RasV12-induced and replicative senescence.
abstract: In primary mouse embryo fibroblasts (MEFs), oncogenic Ras induces growth arrest via Raf/MEK/extracellular signal-regulated kinase (ERK)-mediated activation of the p19ARF/p53 and INK4/Rb tumor suppressor pathways. Ablation of these same pathways causes spontaneous immortalization in MEFs, and oncogenic transformation by Ras requires ablation of one or both of these pathways. We show that Kinase Suppressor of Ras 1 (KSR1), a molecular scaffold for the Raf/MEK/ERK cascade, is necessary for RasV12-induced senescence, and its disruption enhances primary MEF immortalization. RasV12 failed to induce p53, p19ARF, p16INK4a, and p15INK4b expression in KSR1-/- MEFs and increased proliferation instead of causing growth arrest. Reintroduction of wild-type KSR1, but not a mutated KSR1 construct unable to bind activated ERK, rescued RasV12-induced senescence. On continuous culture, deletion of KSR1 accelerated the establishment of spontaneously immortalized cultures and increased the proportion of cultures escaping replicative crisis. Despite enhancing escape from both RasV12-induced and replicative senescence, however, both primary and immortalized KSR1-/- MEFs are completely resistant to RasV12-induced transformation. These data show that escape from senescence is not necessarily a precursor for oncogenic transformation. Furthermore, these data indicate that KSR1 is a member of a unique class of proteins whose deletion blocks both senescence and transformation.
authors.affiliation: University of Nebraska Medical Center, Eppley Institute for Research in Cancer and Allied Diseases, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Kortum
authors.forename: Heidi J
authors.initials: HJ
authors.lastname: Johnson
authors.forename: Diane L
authors.initials: DL
authors.lastname: Costanzo
authors.forename: Deanna J
authors.initials: DJ
authors.lastname: Volle
authors.forename: Gina L
authors.initials: GL
authors.lastname: Razidlo
authors.forename: Angela M
authors.initials: AM
authors.lastname: Fusello
authors.forename: Andrey S
authors.initials: AS
authors.lastname: Shaw
authors.forename: Robert E
authors.initials: RE
authors.lastname: Lewis
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000235:genetics / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D051379:Mice; D009154:Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D025803:Tumor Suppressor Protein p14ARF / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C417743:Cdkn2a protein, mouse; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D018631:ras Proteins