Dependence of Dbl and Dbs transformation on MEK and NF-kappaB activation.
Dbs was identified initially as a transforming protein and is a member of the Dbl family of proteins (>20 mammalian members). Here we show that Dbs, like its rat homolog Ost and the closely related Dbl, exhibited guanine nucleotide exchange activity for the Rho family members RhoA and Cdc42, but not Rac1, in vitro. Dbs transforming activity was blocked by specific inhibitors of RhoA and Cdc42 function, demonstrating the importance of these small GTPases in Dbs-mediated growth deregulation. Although Dbs transformation was dependent upon the structural integrity of its pleckstrin homology (PH) domain, replacement of the PH domain with a membrane localization signal restored transforming activity. Thus, the PH domain of Dbs (but not Dbl) may be important in modulating association with the plasma membrane, where its GTPase substrates reside. Both Dbs and Dbl activate multiple signaling pathways that include activation of the Elk-1, Jun, and NF-kappaB transcription factors and stimulation of transcription from the cyclin D1 promoter. We found that Elk-1 and NF-kappaB, but not Jun, activation was necessary for Dbl and Dbs transformation. Finally, we have observed that Dbl and Dbs regulated transcription from the cyclin D1 promoter in a NF-kappaB-dependent manner. Previous studies have dissociated actin cytoskeletal activity from the transforming potential of RhoA and Cdc42. These observations, when taken together with those of the present study, suggest that altered gene expression, and not actin reorganization, is the critical mediator of Dbl and Rho family protein transformation.
Whitehead
I P
IP
Department of Microbiology, UMDNJ-New Jersey Medical School, Newark, New Jersey 07103, USA.
Lambert
Q T
QT
Glaven
J A
JA
Abe
K
K
Rossman
K L
KL
Mahon
G M
GM
Trzaskos
J M
JM
Kay
R
R
Campbell
S L
SL
Der
C J
CJ
D016475:3T3 Cells; D000818:Animals; D002471:Cell Transformation, Neoplastic; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; D008565:Membrane Proteins; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D020662:Guanine Nucleotide Exchange Factors; C512843:Mcf2 protein, mouse; C092132:Mcf2l protein, mouse; D008565:Membrane Proteins; D016328:NF-kappa B; D015682:Retroviridae Proteins, Oncogenic; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; C482127:Map2k1 protein, mouse; C482562:Map2k4 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D020764:cdc42 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein