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Published online 25 July 2005. doi:10.1083/jcb.200412043
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 170, Number 3, 443-453
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Article

 The Rho kinases I and II regulate different aspects of myosin II activity

Atsuko Yoneda, Hinke A.B. Multhaupt, and John R. Couchman

Division of Biomedical Sciences, Faculty of Medicine, Imperial College London, London SW7 2AZ, England, UK

Correspondence to John R. Couchman: j.couchman{at}imperial.ac.uk

The homologous mammalian rho kinases (ROCK I and II) are assumed to be functionally redundant, based largely on kinase construct overexpression. As downstream effectors of Rho GTPases, their major substrates are myosin light chain and myosin phosphatase. Both kinases are implicated in microfilament bundle assembly and smooth muscle contractility. Here, analysis of fibroblast adhesion to fibronectin revealed that although ROCK II was more abundant, its activity was always lower than ROCK I. Specific reduction of ROCK I by siRNA resulted in loss of stress fibers and focal adhesions, despite persistent ROCK II and guanine triphosphate–bound RhoA. In contrast, the microfilament cytoskeleton was enhanced by ROCK II down-regulation. Phagocytic uptake of fibronectin-coated beads was strongly down-regulated in ROCK II–depleted cells but not those lacking ROCK I. These effects originated in part from distinct lipid-binding preferences of ROCK pleckstrin homology domains. ROCK II bound phosphatidylinositol 3,4,5P3 and was sensitive to its levels, properties not shared by ROCK I. Therefore, endogenous ROCKs are distinctly regulated and in turn are involved with different myosin compartments.

Abbreviations used in this paper: FN, fibronectin; GRP1, general receptor for phosphoinositides-1; LPA, lysophosphatidic acid; MLC, myosin light chain; MYPT, myosin-binding subunit of myosin phosphatase; PH, pleckstrin homology; PI, phosphoinositide; PtdIns, phosphatidylinositol; REF, rat embryo fibroblast.


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