title: Oncogenic and wild-type Ras play divergent roles in the regulation of mitogen-activated protein kinase signaling.
abstract: H-Ras, K-Ras, and N-Ras regulate cellular growth and survival and are often activated by somatic mutation in human tumors. Although oncogenic lesions occur in a single Ras isoform within individual tumors, it is unclear whether the remaining wild-type isoforms play supporting roles in tumor growth. Here, we show that oncogenic and wild-type Ras isoforms play independent and nonredundant roles within the cell. Oncogenic Ras regulates basal effector pathway signaling, whereas wild-type Ras mediates signaling downstream of activated receptor tyrosine kinases (RTK). We show that both are necessary for exponential growth of Ras-mutant cell lines. Furthermore, we show that oncogenic Ras desensitizes signaling from EGF receptor (EGFR). Depletion of oncogenic Ras with siRNA oligonucleotides relieves this negative feedback, leading to the hyperactivation of EGFR and wild-type Ras signaling. Consistent with this model, combining oncogenic Ras depletion with EGFR inhibition potently increases cell death.
  
  
  CONCLUSIONS
  The results of this study highlight a novel role for wild-type Ras signaling in cancer cells harboring oncogenic RAS mutations. Furthermore, these findings reveal that therapeutically targeting oncogenic Ras signaling alone may be ineffective owing to feedback activation of RTKs, and suggest that blocking upstream RTKs in combination with downstream effector pathways may be beneficial in the treatment of Ras-mutant tumors.
authors.affiliation: Helen Diller Family Comprehensive Cancer Center, Department of Medicine, University of California San Francisco, San Francisco, California 94143, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Young
authors.forename: David
authors.initials: D
authors.lastname: Lou
authors.forename: Frank
authors.initials: F
authors.lastname: McCormick
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000378:metabolism; D000069347:Erlotinib Hydrochloride; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D000069347:Erlotinib Hydrochloride; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases