Ras effector pathways modulate scatter factor-stimulated NF-kappaB signaling and protection against DNA damage

Oncogene. 2007 Jul 19;26(33):4774-96. doi: 10.1038/sj.onc.1210271. Epub 2007 Feb 12.


Scatter factor (SF) (hepatocyte growth factor) is a pleiotrophic cytokine that accumulates within tumors in vivo and protects tumor cells against cytotoxicity and apoptosis due to DNA damaging agents in vitro. Previous studies have established that SF-mediated cell protection involves antiapoptotic signaling from its receptor (c-Met) to PI3 kinase --> c-Akt --> Pak1 (p21-activated kinase -1) --> NF-kappaB (nuclear factor-kappa B). Here, we found that Ras proteins (H-Ras and R-Ras) enhance SF-mediated activation of NF-kappaB and protection of DU-145 and MDCK (Madin-Darby canine kidney) cells against the topoisomerase IIalpha inhibitor adriamycin. Studies of Ras effector loop mutants and their downstream effectors suggest that Ras/PI3 kinase and Ras/Raf1 pathways contribute to SF stimulation of NF-kappaB signaling and cell protection. Further studies revealed that Raf1 positively regulates the ability of SF to stimulate NF-kappaB activity and cell protection. The ability of Raf1 to stimulate NF-kappaB activity was not due to the classical Raf1 --> MEK1/2 --> ERK1/2 pathway. However, we found that a MEK3/6 --> p38 pathway contributes to SF-mediated activation of NF-kappaB. In contrast, RalA, a target of the Ras/RalGDS pathway negatively regulated the ability of SF to stimulate NF-kappaB activity and cell protection. Ras, Raf1 and RalA modulate SF stimulation of NF-kappaB activity, in part, by regulating IkappaB kinase (IKK)-beta kinase activity. These findings suggest that Ras/Raf1/RalA pathways may converge to modulate NF-kappaB activation and SF-mediated survival signaling at the IKK complex and/or a kinase upstream of this complex.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / pharmacology
  • Cell Line
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • DNA Damage*
  • Dose-Response Relationship, Drug
  • Doxorubicin / pharmacology
  • Genetic Vectors / genetics
  • Hepatocyte Growth Factor / genetics
  • Hepatocyte Growth Factor / metabolism*
  • Humans
  • I-kappa B Kinase / genetics
  • I-kappa B Kinase / metabolism
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / metabolism
  • Mutation
  • NF-kappa B / genetics
  • NF-kappa B / metabolism*
  • Phosphorylation
  • Protein Binding
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism
  • RNA Interference
  • Signal Transduction / genetics
  • Signal Transduction / physiology*
  • Transfection
  • ral GTP-Binding Proteins / genetics
  • ral GTP-Binding Proteins / metabolism
  • ras Proteins / genetics
  • ras Proteins / metabolism*


  • Antibiotics, Antineoplastic
  • NF-kappa B
  • Hepatocyte Growth Factor
  • Doxorubicin
  • Proto-Oncogene Proteins c-raf
  • I-kappa B Kinase
  • Mitogen-Activated Protein Kinases
  • RALA protein, human
  • ral GTP-Binding Proteins
  • ras Proteins