Yersinia pseudotuberculosis Spatially Controls Activation and Misregulation of Host Cell Rac1

Abstract

Yersinia pseudotuberculosis binds host cells and modulates the mammalian Rac1 guanosine triphosphatase (GTPase) at two levels. Activation of Rac1 results from integrin receptor engagement, while misregulation is promoted by translocation of YopE and YopT proteins into target cells. Little is known regarding how these various factors interplay to control Rac1 dynamics. To investigate these competing processes, the localization of Rac1 activation was imaged microscopically using fluorescence resonance energy transfer. In the absence of translocated effectors, bacteria induced activation of the GTPase at the site of bacterial binding. In contrast, the entire cellular pool of Rac1 was inactivated shortly after translocation of YopE RhoGAP. Inactivation required membrane localization of Rac1. The translocated protease YopT had very different effects on Rac1. This protein, which removes the membrane localization site of Rac1, did not inactivate Rac1, but promoted entry of cleaved activated Rac1 molecules into the host cell nucleus, allowing Rac1 to localize with nuclear guanosine nucleotide exchange factors. As was true for YopE, membrane-associated Rac1 was the target for YopT, indicating that the two translocated effectors may compete for the same pool of target protein. Consistent with the observation that YopE inactivation requires membrane localization of Rac1, the presence of YopT in the cell interfered with the action of the YopE RhoGAP. As a result, interaction of target cells with a strain that produces both YopT and YopE resulted in two spatially distinct pools of Rac1: an inactive cytoplasmic pool and an activated nuclear pool. These studies demonstrate that competition between bacterial virulence factors for access to host substrates is controlled by the spatial arrangement of a target protein. In turn, the combined effects of translocated bacterial proteins are to generate pools of a single signaling molecule with distinct localization and activation states in a single cell.

Yersinia enterocolitica differentially modulates RhoG activity in host cells

“…some signalling pathways to Rac are not blocked by YopE; (2) cooperation of Yersinia YopE and YopT can lead to differentially activated and localised pools of Rac in cells; and (3) YopE of some Yersinia serotypes is degraded in host cells leading to reactivation of Rac1, a highly sophisticated strategy evolves by which Yersinia manipulates the Rac1 signalling network (Andor et al, 2001;Hentschke et al, 2007;Ruckdeschel et al, 2006;Wong and Isberg, 2005b).…”

“…We have reported previously that the ability of YopE to inhibit Rac regulated actin structures depends on the signal pathway by which Rac is activated (Andor et al, 2001). Recent work shows that the combined action of YopT and YopE produces two distinct pools of Rac1: an active nuclear pool and an inactive cytosolic pool (Wong and Isberg, 2005b). Notably, YopE of some Yersinia serotypes can also be degraded by the host cell proteasome, which causes reactivation of Rac1 (Ruckdeschel et al, 2006).…”

PDGF-induced human airway smooth muscle cell proliferation requires STAT3 and the small GTPase Rac1

“…Interestingly, work by others has identified a nuclear localization signal in Rac1 (51) and has shown by fluorescence resonance energy transfer that activated Rac1 can localize to the nucleus (52). The function of the nuclear Rac1, however, is still not understood.…”

The Proteasome Pathway Destabilizes Yersinia Outer Protein E and Represses Its Antihost Cell Activities

“…Thus, it could be possible that the termination of the YopE effects regulates the accessibility of YopT or YopO/YpkA to the Rho-GTPases. In fact, it has been shown that YopE and YopT can compete for the same reservoir of Rac1 and generate two spatially distinct, differentially activated pools of Rac (54). This effect of sequential Yop action may be important for the infection process.…”