Regulation of Actin Dynamics during Salmonella Invasion

Salmonella enterica serovar Typhimurium (S. Typhimurium) invasion begins with the translocation of bacterial virulence proteins (called effectors) into host cells via a type 3 secretion system (T3SS). These effectors serve to manipulate host cell machinery leading to the formation of a cell surface structure called an invasion ruffle that subsequently mediates bacterial internalization into the host cell. Following entry, the bacteria continues to manipulate host signalling factors to establish a replicative niche. There is still much to be learned about the host machinery that is exploited by S. Typhimurium during infection. In my thesis, I show that the formin, FHOD1 plays an important role in S.Typhimurium invasion. FHOD1 is phosphorylated during S. Typhimurium invasion, a process that requires the bacterial T3SS effectors SopB and SopE/E2, as well as host proteins RhoA and ROCKII. FHOD1 and Arp2/3 are both recruited to the same invasion ruffle, but contribute differently to its formation and also display different kinetics of recruitment. The Rho GTPase family of proteins is comprised of 20 members. In the context of S. Typhimurium invasion, only Rac1, Cdc42, and RhoG have been extensively studied. A screen was conducted and revealed recruitment of RhoB, RhoD, RhoH, and RhoJ to the S. Typhimurium invasion site in a SopB-dependent manner. Regulation of Rho GTPases is achieved via post-translational modifications such as palmitoylation. To this end, I demonstrated that palmitoylation of host proteins promotes S. Typhimurium invasion and PI(3,4,5)P3 production at the invasion ruffle. Furthermore, the ability of SopB to recruit lipid rafts to the S. Typhimurium invasion site may allow for specific recruitment of palmitoylated Rho GTPases. Collectively, this data provides new insight on formation of the invasion ruffle and identifies new host factors that are exploited by S. Typhimurium to invade host cells.Ph.D.2018-02-19 00:00:0