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J. Cell Biol.,
Volume 143, Number 1, October 5, 1998 267-276
Cancer Research Center, The Burnham Institute, La Jolla, California 92037
Adherent cells assemble fibronectin into a
fibrillar matrix on their apical surface. The fibril formation is initiated by fibronectin binding to the integrins
5
1 and
v
3, and is completed by a process that includes fibronectin self-assembly. We found that a 76-
amino acid fragment of fibronectin (III1-C) that forms one of the self-assembly sites caused disassembly of
preformed fibronectin matrix without affecting cell adhesion. Treating attached fibroblasts or endothelial
cells with III1-C inhibited cell migration and proliferation. Rho-dependent stress fiber formation and Rho-dependent focal contact protein phosphorylation were
also inhibited, whereas Cdc42 was activated, leading to
actin polymerization into filopodia. ACK (activated
Cdc42-binding kinase) and p38 MAPK (mitogen-activated protein kinase), two downstream effectors of
Cdc42, were activated, whereas PAK (p21-activated kinase) and JNK/SAPK (c-Jun NH2-terminal kinase/
stress-activated protein kinase) were inhibited. III1-C treatment also modulated activation of JNK and ERK
(extracellular signal-regulated kinases) in response to
growth factors, and reduced the activity of the cyclin
E-cdk2 complex. These results indicate that the absence of fibronectin matrix causes activation of Cdc42, and that fibronectin matrix is required for Rho activation and cell cycle progression.
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