Efficient uptake of Yersinia pseudotuberculosis via integrin receptors involves a Rac1–Arp 2/3 pathway that bypasses N‐WASP function

Abstract

Efficient uptake of Yersinia pseudotuberculosis into cultured mammalian cells is the result of high‐affinity binding of invasin to β1 chain integrins. We demonstrate here that uptake requires Rac1 and Arp 2/3 function. Bacterial uptake was stimulated by GTPγS, but was inhibited in mammalian cells transfected with the interfering Rac1‐N17 derivative. Rac1 was found to be activated in response to integrin engagement by invasin, whereas Rac1 and Arp 2/3 were found to be intensely localized around phagosomes bearing bacteria, indicating a specific role for Rac1 signalling from the nascent phagosome to downstream effectors. To determine whether the Arp 2/3 complex was a component of this proposed pathway, cells overproducing various derivatives of Scar1/WAVE1, an Arp 2/3‐binding protein, were analysed. Sequestration of Arp 2/3 away from the phagocytic cup as a result of Scar1/WAVE1 overproduction dramatically inhibited uptake. To determine whether signalling from Rac1 to Arp 2/3 occurred via N‐WASP, uptake was analysed in a cell line lacking expression of WASP and N‐WASP. Uptake was unaffected by the absence of these proteins, indicating that β1 integrin signalling from Rac1 to Arp 2/3 can occur in the absence of N‐WASP function.

Sequestering of Rac by the Yersinia Effector YopO Blocks Fcγ Receptor-mediated Phagocytosis

“…Nevertheless, they provide an explanation for why YopO has an effect on NADPH oxidase activation, a process that is Rac2-dependent (35). Furthermore, our work supports the data that suggest Yersinia target ␤ 1 -integrin-mediated uptake by phagocytes, a process shown to require Rac and not Rho (36).…”

TheYersinia pestisAil Protein Mediates Binding and Yop Delivery to Host Cells Required for Plague Virulence

“…In Y. pseudotuberculosis, it has been demonstrated that the nature of the adhesin and the specific signaling cascade that it triggers in host cells are critical in determining the efficiency of Yop delivery (38). It has been proposed that integrin-mediated signaling in host cells following Y. pseudotuberculosis invasin-integrin interaction re-sults in a series of events leading to efficient YopB/YopD pore formation in host cells and subsequent T3SS-mediated Yop delivery (1,2,38,62,66). We hypothesize that since Y. pestis lacks invasin, Ail may mediate a receptor interaction that initiates a similar series of events leading to pore formation and Yop delivery.…”

Adhesion signaling – crosstalk between integrins, Src and Rho

“…Invasin tightly binds to, and causes clustering of, β1 integrins on the cell surface, thereby leading to rapid activation of Rac1 and the induction of membrane protrusions in host cells. Rac1 activity is required for membrane ruffling initiated by integrin-invasin interactions and for uptake of Yersinia bacteria by host cells (Alrutz et al, 2001). The FAK-Src complex might transmit signaling from β1 integrins to Rac1 GTP loading; this is supported by the findings that invasin-mediated bacterial uptake is impaired in FAK -/-cells, and that the expression of a FAK Y397F mutant that cannot bind to SFKs does not restore this defect (Alrutz and Isberg, 1998;Bruce-Staskal et al, 2002).…”