B-RAF regulation of Rnd3 participates in actin cytoskeletal and focal adhesion organization.
The actin cytoskeleton controls multiple cellular functions, including cell morphology, movement, and growth. Accumulating evidence indicates that oncogenic activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 (MEK/ERK1/2) pathway is accompanied by actin cytoskeletal reorganization. However, the signaling events contributing to actin cytoskeleton remodeling mediated by aberrant ERK1/2 activation are largely unknown. Mutant B-RAF is found in a variety of cancers, including melanoma, and it enhances activation of the MEK/ERK1/2 pathway. We show that targeted knockdown of B-RAF with small interfering RNA or pharmacological inhibition of MEK increased actin stress fiber formation and stabilized focal adhesion dynamics in human melanoma cells. These effects were due to stimulation of the Rho/Rho kinase (ROCK)/LIM kinase-2 signaling pathway, cumulating in the inactivation of the actin depolymerizing/severing protein cofilin. The expression of Rnd3, a Rho antagonist, was attenuated after B-RAF knockdown or MEK inhibition, but it was enhanced in melanocytes expressing active B-RAF. Constitutive expression of Rnd3 suppressed the actin cytoskeletal and focal adhesion effects mediated by B-RAF knockdown. Depletion of Rnd3 elevated cofilin phosphorylation and stress fiber formation and reduced cell invasion. Together, our results identify Rnd3 as a regulator of cross talk between the RAF/MEK/ERK and Rho/ROCK signaling pathways, and a key contributor to oncogene-mediated reorganization of the actin cytoskeleton and focal adhesions.
Center for Cell Biology and Cancer Research, Albany Medical College, Albany, NY 12208, USA.
R Matthew
RM
Klein
Laurie S
LS
Spofford
Ethan V
EV
Abel
Arisa
A
Ortiz
Andrew E
AE
Aplin
D051339:Actin Depolymerizing Factors / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D045744:Cell Line, Tumor; D003599:Cytoskeleton / Q000201:enzymology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D022001:Focal Adhesions / Q000201:enzymology*; D006801:Humans; D054461:Lim Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008545:Melanoma / Q000378:metabolism / Q000473:pathology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D009361:Neoplasm Invasiveness; D010766:Phosphorylation; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism*; D022502:Stress Fibers / Q000201:enzymology; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000378:metabolism
D051339:Actin Depolymerizing Factors; D000199:Actins; D050505:Mutant Proteins; D054461:Lim Kinases; D048493:Proto-Oncogene Proteins B-raf; D054460:rho-Associated Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C508705:RND3 protein, human; D020741:rho GTP-Binding Proteins