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12 Bacterial Manipulation of the Host Cell Cytoskeleton
This chapter illustrates several modes of bacterial manipulation of the host cell cytoskeleton using a few well-studied examples and explores interactions of various pathogenic bacteria with the actin cytoskeleton of both phagocytic and nonphagocytic host cells. These interactions are generally mediated by specific bacterial gene products, virulence factors, whose sole function is to mimic or interfere with normal host cell signals, in this case, those that regulate actin filament dynamics. A section focuses on the ability of Shigella to invade epithelial cells by a process that triggers global changes in the cellular actin cytoskeleton that result in membrane ruffles and macropinocytosis. Importantly, both zipper and trigger uptake mechanisms proceed using energy derived from the host cell. The cytoskeletal and membrane rearrangements that are responsible for bacterial invasion require no energetic input from the bacterium once the type III secretion apparatus is made (for the trigger mechanism of uptake); they invade by persuasion rather than by force. The chapter further focuses on four well-characterized cytoskeletal manipulators: YopE, YopH, YopT, and YpkA/YopO. Intracellular motility allows pathogens to spread directly from the cytoplasm of one cell into the cytoplasm of an adjacent cell. The many processes used by bacterial pathogens of cellular invasion, inhibition of internalization, cellular adhesion, and intercellular spread may appear diverse, but they are linked by common molecules: the components of the host cell cytoskeleton. In becoming better pathogens, these bacteria have come to a highly evolved appreciation of the subtlety required to regulate it.