Dbl and Vav mediate transformation via mitogen-activated protein kinase pathways that are distinct from those activated by oncogenic Ras.
Vav and Dbl are members of a novel class of oncogene proteins that share significant sequence identity in a approximately 250-amino-acid domain, designated the Dbl homology domain. Although Dbl functions as a guanine nucleotide exchange factor (GEF) and activator of Rho family proteins, recent evidence has demonstrated that Vav functions as a GEF for Ras proteins. Thus, transformation by Vav and Dbl may be a consequence of constitutive activation of Ras and Rho proteins, respectively. To address this possibility, we have compared the transforming activities of Vav and Dbl with that of the Ras GEF, GRF/CDC25. As expected, GRF-transformed cells exhibited the same reduction in actin stress fibers and focal adhesions as Ras-transformed cells. In contrast, Vav- and Dbl-transformed cells showed the same well-developed stress fibers and focal adhesions observed in normal or RhoA(63L)-transformed NIH 3T3 cells. Furthermore, neither Vav- or Dbl-transformed cells exhibited the elevated levels of Ras-GTP (60%) observed with GRF-transformed cells. Finally, GRF, but not Vav or Dbl, induced transcriptional activation from Ras-responsive DNA elements (ets/AP-1, fos promoter, and kappa B). However, like Ras- and GRF-transformed cells, both Vav- and Dbl-transformed cells exhibited constitutively activated mitogen-activated protein kinases (MAPKs) (primarily p42MAPK/ERK2). Since kinase-deficient forms of p42MAPK/ERK2 and p44MAPK/ERK1 inhibited Dbl transformation, MAPK activation may be an important component of its transforming activity. Taken together, our observations indicate that Vav and Dbl transformation is not a consequence of Ras activation and instead may involve the constitutive activation of MAPKs.
Khosravi-Far
R
R
Department of Cellular Biology, University of North Carolina at Chapel Hill 27599.
Chrzanowska-Wodnicka
M
M
Solski
P A
PA
Eva
A
A
Burridge
K
K
Der
C J
CJ
D016475:3T3 Cells; D000199:Actins / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002448:Cell Adhesion; D002471:Cell Transformation, Neoplastic; D029721:Drosophila Proteins; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1
D000199:Actins; D029721:Drosophila Proteins; D020662:Guanine Nucleotide Exchange Factors; C512843:Mcf2 protein, mouse; D008565:Membrane Proteins; D015513:Oncogene Proteins; D011506:Proteins; D051567:Proto-Oncogene Proteins c-vav; D015682:Retroviridae Proteins, Oncogenic; C081481:Rho protein, Drosophila; C472498:Stet protein, Drosophila; C496619:Vav1 protein, mouse; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1; D006160:Guanosine Triphosphate; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)