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J. Cell Biol.,
Volume 140, Number 6, March 23, 1998 1383-1393



* Pathology Division, National Cancer Center Research Institute, Tokyo 104, Japan; Regulation of the actin cytoskeleton may
play a crucial role in cell motility and cancer invasion.
We have produced a monoclonal antibody (NCC-
Lu-632, IgM, k) reactive with an antigenic protein that
is upregulated upon enhanced cell movement. The cDNA
for the antigen molecule was found to encode a novel
isoform of nonmuscle
Department of Oral and Maxillofacial
Surgery, Tokyo Medical College, Tokyo 160, Japan; and § Hirohashi Cell Configuration Project, ERATO, Japan Scientific and
Technology Corporation (JST), Tsukuba 300-26, Japan
-actinin. This isoform (designated actinin-4) was concentrated in the cytoplasm
where cells were sharply extended and in cells migrating and located at the edge of cell clusters, but was absent from focal adhesion plaques or adherens junctions,
where the classic isoform (actinin-1) was concentrated.
Actinin-4 shifted steadily from the cytoplasm to the nucleus upon inhibition of phosphatidylinositol 3 kinase
or actin depolymerization. The cytoplasmic localization of actinin-4 was closely associated with an infiltrative
histological phenotype and correlated significantly with
a poorer prognosis in 61 cases of breast cancer. These
findings suggest that cytoplasmic actinin-4 regulates the
actin cytoskeleton and increases cellular motility and
that its inactivation by transfer to the nucleus abolishes
the metastatic potential of human cancers.
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