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J. Cell Biol.,
Volume 145, Number 2, April 19, 1999 347-361


* Division of Signal Transduction, Nara Institute of Science and Technology, Ikoma 630-0101, Japan; Adducin is a membrane skeletal protein that
binds to actin filaments (F-actin) and thereby promotes
the association of spectrin with F-actin to form a spectrin-actin meshwork beneath plasma membranes such
as ruffling membranes. Rho-associated kinase (Rho- kinase), which is activated by the small guanosine triphosphatase Rho, phosphorylates
Howard Hughes Medical
Institute and Departments of Cell Biology and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710;
and § Department of Virology II, National Institute of Infectious Diseases, Tokyo 162-8640, Japan
-adducin and thereby
enhances the F-actin-binding activity of
-adducin in
vitro. Here we identified the sites of phosphorylation of
-adducin by Rho-kinase as Thr445 and Thr480. We
prepared antibody that specifically recognized
-adducin phosphorylated at Thr445, and found by use of this
antibody that Rho-kinase phosphorylated
-adducin at
Thr445 in COS7 cells in a Rho-dependent manner.
Phosphorylated
-adducin accumulated in the membrane ruffling area of Madin-Darby canine kidney
(MDCK) epithelial cells and the leading edge of scattering cells during the action of tetradecanoylphorbol-13-acetate (TPA) or hepatocyte growth factor (HGF).
The microinjection of Botulinum C3 ADP-ribosyl-transferase, dominant negative Rho-kinase, or
-adducinT445A,T480A (substitution of Thr445 and
Thr480 by Ala) inhibited the TPA-induced membrane
ruffling in MDCK cells and wound-induced migra-
tion in NRK49F cells.
-AdducinT445D,T480D (substi-
tution of Thr445 and Thr480 by Asp), but not
-adducinT445A,T480A, counteracted the inhibitory
effect of the dominant negative Rho-kinase on the
TPA-induced membrane ruffling in MDCK cells. Taken
together, these results indicate that Rho-kinase phosphorylates
-adducin downstream of Rho in vivo, and
that the phosphorylation of adducin by Rho-kinase
plays a crucial role in the regulation of membrane ruffling and cell motility.
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