IpaA targets beta1 integrins and rho to promote actin cytoskeleton rearrangements necessary for Shigella entry.
Shigella invasion into the colonic epithelium involves many steps including the formation of large membrane protrusions by the epithelial cells that facilitate bacterial engulfment. IpaA, a Shigella protein secreted into target cells upon cell contact induces a loss of actin stress fibers in cells and promotes the reorganization of actin at the site of entry. The mechanism for this is not known but is thought to involve recruitment of the focal adhesion protein vinculin to IpaA. Here we have examined the mechanism for the effects of IpaA on the actin cytoskeleton. We show that IpaA-induced loss of actin stress fibers and cell rounding do not require vinculin expression or an intact vinculin binding site on IpaA. Rather, we find that cells expressing IpaA exhibited elevated Rho activity and increased myosin light chain phosphorylation. In addition, IpaA decreases integrin affinity for extracellular matrix ligands by interfering with talin recruitment to the integrin cytoplasmic tail. The combination of these two effects, namely weakened adhesion and increased contractility, account for the loss of actin stress fibers and cell rounding observed in cells exposed to IpaA.
Demali
Kris A
KA
Department of Cell and Developmental Biology and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA. kris-demail@uiowa.edu
Jue
April L
AL
Burridge
Keith
K
D000199:Actins / Q000737:chemistry*; D000818:Animals; D000942:Antigens, Bacterial / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D018994:Myosin Light Chains / Q000737:chemistry; D010766:Phosphorylation; D016596:Vinculin / Q000737:chemistry; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
D000199:Actins; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D019012:Integrin beta1; C063664:IpaA protein, Shigella flexneri; D018994:Myosin Light Chains; D016596:Vinculin; D049452:Green Fluorescent Proteins; D020741:rho GTP-Binding Proteins