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Vol. 18, Issue 1, 66-75, January 2007
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Division of Biomedical Sciences, Imperial College London, London SW7 2AZ, United Kingdom
Submitted August 7, 2006;
Revised October 2, 2006;
Accepted October 13, 2006
Monitoring Editor: Richard Assoian
Extracellular matrix is integral to tissue architecture and regulates many aspects of cell behavior. Fibronectin matrix assembly involves the actin cytoskeleton and the small GTPase RhoA, but downstream signaling is not understood. Here, down-regulation of either rho kinase isoform (ROCK I or -II) by small interfering RNA treatment blocked fibronectin matrix assembly, although the phenotypes were distinct and despite persistence of the alternate kinase. Remnant fibronectin on ROCK-deficient fibroblasts was mostly punctate and more deoxycholate soluble compared with controls. Fibronectin matrix assembly defects in ROCK-deficient cells did not result from decreased synthesis/secretion, altered fibronectin mRNA splicing, metalloproteinase activity, or
5
1 integrin dysfunction. Rescue could be effected by ROCK protein restoration or phosphomimetic myosin light chain expression. However, the effect of ROCK I deficiency on fibronectin matrix assembly was secondary to altered cell surface morphology, rich in filopodia, resulting from high GTPCdc42 levels. Total internal reflection microscopy revealed that a submembranous pool of myosin light chain in control cells was missing in ROCK II-deficient cells and replaced by stress fibers. Together, two rho kinases contribute to fibronectin matrix assembly in a different manner and cortical myosin II-driven contractility, but not stress fibers, may be critical in this activity.
This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E06-08-0684) on October 25, 2006.
Address correspondence to: John R. Couchman (j.couchman{at}imperial.ac.uk)
Abbreviations used: DOC, deoxycholate; ERM, ezrin/radixin/moesin; FN, fibronectin; MLC, myosin light chain; REF, rat embryo fibroblasts; TIRF, total internal reflection microscopy.
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