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J. Cell Biol.,
Volume 141, Number 7, June 29, 1998 1625-1636


* Department of Pharmacology, Kyoto University Faculty of Medicine, Sakyo, Kyoto 606-8315, Japan; A critical role for the small GTPase Rho
and one of its targets, p160ROCK (a Rho-associated
coiled coil-forming protein kinase), in neurite remodeling was examined in neuroblastoma N1E-115 cells. Using wild-type and a dominant-negative form of
p160ROCK and a p160ROCK-specific inhibitor, Y-27632,
we show here that p160ROCK activation is necessary
and sufficient for the agonist-induced neurite retraction
and cell rounding. The neurite retraction was accompanied by elevated phosphorylation of myosin light chain and the disassembly of the intermediate filaments and
microtubules. Y-27632 blocked both neurite retraction
and the elevation of myosin light chain phosphorylation
in a similar concentration-dependent manner. On the
other hand, suppression of p160ROCK activity by expression of a dominant-negative form of p160ROCK
induced neurites in the presence of serum by inducing
the reassembly of the intermediate filaments and microtubules. The neurite outgrowth by the p160ROCK inhibition was blocked by coexpression of dominant-negative forms of Cdc42 and Rac, indicating that
p160ROCK constitutively and negatively regulates
neurite formation at least in part by inhibiting activation of Cdc42 and Rac. The assembly of microtubules
and intermediate filaments to form extended processes
by inhibitors of the Rho-ROCK pathway was also observed in Swiss 3T3 cells. These results indicate that
Rho/ROCK-dependent tonic inhibition of cell process
extension is exerted via activation of the actomysin-based contractility, in conjunction with a suppression of
assembly of intermediate filaments and microtubules in
many cell types including, but not exclusive to, neuronal cells.
Discovery Research,
Yoshitomi Pharmaceutical Industries, Iruma, Saitama 358-0026, Japan; § Division of Cellular Biochemistry, The Netherlands
Cancer Institute, 1066 CX, Amsterdam, The Netherlands; and
Department of Molecular Biology and Biochemistry, Rutgers
University, Piscataway, New Jersey 08855-1059
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