Activation of Rac1, RhoA, and mitogen-activated protein kinases is required for Ras transformation.
Although substantial evidence supports a critical role for the activation of Raf-1 and mitogen-activated protein kinases (MAPKs) in oncogenic Ras-mediated transformation, recent evidence suggests that Ras may activate a second signaling pathway which involves the Ras-related proteins Rac1 and RhoA. Consequently, we used three complementary approaches to determine the contribution of Rac1 and RhoA function to oncogenic Ras-mediated transformation. First, whereas constitutively activated mutants of Rac1 and RhoA showed very weak transforming activity when transfected alone, their coexpression with a weakly transforming Raf-1 mutant caused a greater than 35-fold enhancement of transforming activity. Second, we observed that coexpression of dominant negative mutants of Rac1 and RhoA reduced oncogenic Ras transforming activity. Third, activated Rac1 and RhoA further enhanced oncogenic Ras-triggered morphologic transformation, as well as growth in soft agar and cell motility. Finally, we also observed that kinase-deficient MAPKs inhibited Ras transformation. Taken together, these data support the possibility that oncogenic Ras activation of Rac1 and RhoA, coupled with activation of the Raf/MAPK pathway, is required to trigger the full morphogenic and mitogenic consequences of oncogenic Ras transformation.
Khosravi-Far
R
R
Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill 27599, USA.
Solski
P A
PA
Clark
G J
GJ
Kinch
M S
MS
Der
C J
CJ
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D002465:Cell Movement; D002471:Cell Transformation, Neoplastic; D003599:Cytoskeleton / Q000648:ultrastructure; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D005799:Genes, Dominant; D006801:Humans; D051379:Mice; D017354:Point Mutation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D015398:Signal Transduction; D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein
D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein