Biology Reference
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immunoprecipitation experiments revealed that endogenous N-WASp forms
complexes with cortactin (Mizutani et al., 2002; Weaver et al., 2000). During
tumour metastasis, degradation of the extracellular matrix (ECM) is
considered a key process for malignant cells to escape the primary tumour
and to invade other tissues. It was shown that matrix metalloproteases
(MMPs), which degrade ECM, are localized at the leading edges of migrating
cells. MMPs were also found to be concentrated at podosomes. Interestingly,
MMP localization at podosomes was dependent on N-WASp. Wild-type N-
WASp expression in 3Y1-src cells induced formation of larger podosomes in
comparison with controls and localization of high levels of MMPs in
podosomes. In contrast, expression of a dominant-negative N-WASp
inhibited formation of podosomes and concentration of MMP in podosomes
(Mizutani et al., 2002). These results suggest the importance of N-WASp in
podosome formation and MMP localization, which are processes underlying
the invasive phenotype of 3Y1-src cells.
In multicellular organisms, movement of cells is essential in the normal
development of many organs and tissues. Epithelial tubulogenesis, which is
necessary for proper development of organs, including the kidneys, lungs, and
mammary glands, requires complex cell rearrangements involving cell-cell
adhesion, cell polarity, migration and invasion. The organization of the actin
cytoskeleton is fundamental to these processes. When cultured in collagen
gels, MDCK cells form spherical cysts with fluid-filled lumens. In the presence
of hepatocyte growth factor (HGF), MDCK cysts form branching tubules,
and branching tube formation is suppressed in MDCK cells expressing a
dominant-negative N-WASp (Yamaguchi et al., 2002). During cyst formation,
cells in the cyst wall produce small extensions containing actin filaments into
the surrounding gel matrix. N-WASp accumulates in these extensions of the
cyst walls and in the tips of the extending tubules (Yamaguchi et al., 2002).
However, inhibition of N-WASp function by expression of a dominant-
negative N-WASp did not affect cell-cell adhesion, cell polarity, or scattering
in response to HGF. In contrast, directed migration toward HGF through
membrane filters was inhibited, though the inhibitory effect of the dominant-
negative N-WASp was relatively small compared with its effect on
tubulogenesis. When cultured on collagen gel, MDCK cells grow as a
monolayer confined to the surface of the gel. In the presence of HGF, MDCK
cells invade the underlying collagen gel and form foci in the gel. MDCK cells
expressing a dominant-negative N-WASp showed impairment of the invasive
phenotype. In this case, N-WASp was also concentrated at the cell projections
that extended into the collagen gel. Strong F-actin signals were also observed
at these projections and were clearly co-localized with those of N-WASp
(Yamaguchi et al., 2002). These data indicate that N-WASp regulates HGF-
induced cell migration and invasion, which are required for epithelial
tubulogenesis.
