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and
*Department of Microbiology and Immunology and
§The
Feist-Weiller Cancer Center, Louisiana State University Medical Center,
Shreveport, Louisiana 71130;
Rho family proteins have been implicated in regulating various
cellular processes, including actin cytoskeleton organization, endocytosis, cell cycle, and gene expression. In this study, we analyzed the function of a novel Dictyostelium
discoideum Rho family protein (RacC). A cell line was generated
that conditionally overexpressed wild-type RacC three- to fourfold
relative to endogenous RacC. Light and scanning electron microscopy
indicated that the morphology of the RacC-overexpressing cells [RacC
WT(+) cells] was significantly altered compared with control cells. In
contrast to the cortical F-actin distribution normally observed, RacC
WT(+) cells displayed unusual dorsal and peripheral F-actin-rich
surface blebs (petalopodia, for flower-like). Furthermore, phagocytosis in the RacC WT(+) cells was induced threefold relative to control Ax2
cells, whereas fluid-phase pinocytosis was reduced threefold, primarily
as the result of an inhibition of macropinocytosis. Efflux of
fluid-phase markers was also reduced in the RacC WT(+) cells,
suggesting that RacC may regulate postinternalization steps along
the endolysosomal pathway. Treatment of cells with Wortmannin and
LY294002 (phosphatidylinositol 3-kinase inhibitors)
prevented the RacC-induced morphological changes but did not affect
phagocytosis, suggesting that petalopodia are probably not required for
RacC-induced phagocytosis. In contrast, inactivating
diacylglycerol-binding motif-containing proteins by treating cells
with the drug calphostin C completely inhibited phagocytosis in control
and RacC WT(+) cells. These results suggest that RacC plays a role in
actin cytoskeleton organization and phagocytosis in
Dictyostelium.
Department of Molecular and
Cell Biology, University of Connecticut, Storrs, Connecticut 06269; and
Department of Biology, University of Arkansas, Little
Rock, Little Rock, Arkansas 72204
Corresponding author. E-mail
address: jcarde{at}nomvs.lsumc.edu.
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