title: Dissection of RAS downstream pathways in melanomagenesis: a role for Ral in transformation.
abstract: Cutaneous malignant melanoma is considered one of the most deadly human cancers, based on both its penchant for metastatic spread and its typical resistance to currently available therapy. Long known to harbor oncogenic NRAS mutations, melanomas were more recently reported to be frequent bearers of activating mutations in BRAF, one of the effectors situated downstream of wild-type NRAS. NRAS and BRAF mutations are rarely found in the same melanoma, suggesting that they may possess important overlapping oncogenic activities. Here, we compare and contrast the oncogenic roles of the three major NRas downstream effectors, Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine exchange factor (RalGEF), using genetically engineered Arf-deficient immortalized mouse melanocytes as a model system. Although no single downstream pathway could recapitulate all of the consequences of oncogenic NRas expression, our data indicate a prominent role for BRaf and PI3K in melanocyte senescence and invasiveness, respectively. More surprisingly, we discovered that constitutive RalGEF activation had a major impact on several malignant phenotypes, particularly anchorage-independent growth, indicating that this often overlooked pathway should be more carefully evaluated as a possible therapeutic target.
authors.affiliation: Laboratory of Cancer Biology and Genetics, National Cancer Institute, NIH, Bethesda, MD 20892-4264, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Mishra
authors.forename: L
authors.initials: L
authors.lastname: Ha
authors.forename: J
authors.initials: J
authors.lastname: Rieker
authors.forename: E V
authors.initials: EV
authors.lastname: Sviderskaya
authors.forename: D C
authors.initials: DC
authors.lastname: Bennett
authors.forename: M D
authors.initials: MD
authors.lastname: Oberst
authors.forename: K
authors.initials: K
authors.lastname: Kelly
authors.forename: G
authors.initials: G
authors.lastname: Merlino
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000502:physiology; D011905:Genes, ras / Q000502:physiology*; D008545:Melanoma / Q000209:etiology*; D051379:Mice; D051059:PTEN Phosphohydrolase / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D048493:Proto-Oncogene Proteins B-raf / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology; D015398:Signal Transduction; D020726:ral Guanine Nucleotide Exchange Factor / Q000502:physiology*
chemical_list: C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D020726:ral Guanine Nucleotide Exchange Factor; D019869:Phosphatidylinositol 3-Kinases; C482119:BRAF protein, human; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D051059:PTEN Phosphohydrolase