Differential activation and function of Rho GTPases during Salmonella-host cell interactions.

Salmonella enterica, the cause of food poisoning and typhoid fever, has evolved sophisticated mechanisms to modulate Rho family guanosine triphosphatases (GTPases) to mediate specific cellular responses such as actin remodeling, macropinocytosis, and nuclear responses. These responses are largely the result of the activity of a set of bacterial proteins (SopE, SopE2, and SopB) that, upon delivery into host cells via a type III secretion system, activate specific Rho family GTPases either directly (SopE and SopE2) or indirectly (SopB) through the stimulation of an endogenous exchange factor. We show that different Rho family GTPases play a distinct role in Salmonella-induced cellular responses. In addition, we report that SopB stimulates cellular responses by activating SH3-containing guanine nucleotide exchange factor (SGEF), an exchange factor for RhoG, which we found plays a central role in the actin cytoskeleton remodeling stimulated by Salmonella. These results reveal a remarkable level of complexity in the manipulation of Rho family GTPases by a bacterial pathogen.