Activation of G1 progression, JNK mitogen-activated protein kinase, and actin filament assembly by the exchange factor FGD1.
Cdc42 has been shown to control bifurcating pathways leading to filopodia formation/G1 cell cycle progression and to JNK mitogen-activated protein kinase activation. To dissect these pathways further, the cellular effects induced by a Cdc42 guanine nucleotide exchange factor, FGD1, have been examined. All exchange factors acting on the Rho GTPase family have juxtaposed Dbl homology (DH) and pleckstrin homology (PH) domains. We report here that FGD1 triggers G1 cell cycle progression and filopodia formation in Swiss 3T3 fibroblasts as well as JNK mitogen-activated protein kinase activation in COS cell transfection assays. FGD1-induced filopodia formation is Cdc42-dependent, and both the DH and PH domains are essential. Although expression of the FGD1 DH domain alone does not activate Cdc42 and induce filopodia, it does trigger both the JNK cascade in COS cells and G1 progression in quiescent Swiss 3T3 cells. We conclude that FGD1 can trigger G1 progression independently of actin polymerization or integrin adhesion complex assembly. Furthermore, since FGD1 activates JNK and G1 progression in a Cdc42-independent manner, it must have additional, as yet unidentified, targets.
Nagata
K
K
Medical Research Council Laboratory for Molecular Cell Biology, Cancer Research Campaign Oncogene and Signal Transduction Group, University College London, Gower Street, London WC1E 6BT, United Kingdom.
Driessens
M
M
Lamarche
N
N
Gorski
J L
JL
Hall
A
A
D016475:3T3 Cells; D000199:Actins / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000378:metabolism; D004789:Enzyme Activation; D016193:G1 Phase; D019204:GTP-Binding Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D020764:cdc42 GTP-Binding Protein; D054462:p21-Activated Kinases
D000199:Actins; D018797:Cell Cycle Proteins; C097489:Fgd1 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein