G Protein β Subunit–null Mutants Are Impaired in Phagocytosis and Chemotaxis Due to Inappropriate Regulation of the Actin Cytoskeleton |
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Authors: | Barbara Peracino Jane Borleis Tian Jin Monika Westphal Jean-Marc Schwartz Lijun Wu Enrico Bracco Günther Gerisch Peter Devreotes and Salvatore Bozzaro |
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Institution: | Barbara Peracino, Jane Borleis, Tian Jin, Monika Westphal, Jean-Marc Schwartz, Lijun Wu, Enrico Bracco, Günther Gerisch, Peter Devreotes, and Salvatore Bozzaro |
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Abstract: | Chemotaxis and phagocytosis are basically similar in cells of the immune system and in Dictyostelium amebae. Deletion of the unique G protein β subunit in D. discoideum impaired phagocytosis but had little effect on fluid-phase endocytosis, cytokinesis, or random motility. Constitutive expression of wild-type β subunit restored phagocytosis and normal development. Chemoattractants released by cells or bacteria trigger typical transient actin polymerization responses in wild-type cells. In β subunit–null cells, and in a series of β subunit point mutants, these responses were impaired to a degree that correlated with the defect in phagocytosis. Image analysis of green fluorescent protein–actin transfected cells showed that β subunit– null cells were defective in reshaping the actin network into a phagocytic cup, and eventually a phagosome, in response to particle attachment. Our results indicate that signaling through heterotrimeric G proteins is required for regulating the actin cytoskeleton during phagocytic uptake, as previously shown for chemotaxis. Inhibitors of phospholipase C and intracellular Ca2+ mobilization inhibited phagocytosis, suggesting the possible involvement of these effectors in the process. |
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