Rickettsia conorii, a member of the spotted fever group (SFG) Rickettsia, is an obligate intracellular, tick borne pathogen and is the causative agent of Mediterranean spotted fever. Aerosol transmission of rickettsia can occur and therefore, represents a bioterrorist threat for the United States. The pathogenesis of R. conorii, upon transmission into the host, depends on the pathogen's ability to bind to and invade target host cells. SFG rickettsia express several outer membrane proteins termed Sca (Surface Cell Antigens) that exhibit high homology to autotransporter families in Gram-negative bacteria. Two members of this family, rOmpA (Sca0) and rOmpB (Sca5) are both thought to be involved in rickettsial adherence and invasion on normally non-phagocytic mammalian cells. We have previously demonstrated that R. conorii infection of host cells results in the induction of distinct host cell signaling pathways ultimately leading to Arp2/3-dependent bacterial uptake. However, the bacterial ligand(s) and host cell receptor(s) involved in this process were not known. We recently identified a mammalian host protein, Ku70, as a receptor involved in R. conorii invasion. We have also demonstrated that R. conorii recruits the ubiquitin ligase c-Cbl to sites of infection and that reduction of endogenous c-Cbl expression by siRNA inhibits R. conorii entry in vitro. We have also shown that R. conorii induces the c-Cbl mediated ubiquitination of Ku70, suggesting that the host cell endocytic machinery may also be involved in the R. conorii entry process. Interestingly, we have shown that rOmpB binds to Ku70, suggesting that this adhesin-host cell receptor pair interaction may be critical to the entry process. In addition, our data suggests that other Rickettsial virulence factors likely contribute to pathogenesis. The goals of our research are several fold:
Further elucidate the molecular mechanisms of SFG rickettsial invasion of non-phagocytic cells.
Understand the contribution of rickettsial surface adhesins and host cell receptors to the initiation and progression of SFG rickettsial pathogenesis.
Understand the contribution of surface proteins to the generation of protective humoral immunity.
Identify putative targets that can be exploited for the development of novel anti-microbial therapies.
Rickettsia conorii, a member of the spotted fever group (SFG) Rickettsia, is an obligate intracellular, tick borne pathogen and is the causative agent of Mediterranean spotted fever. Aerosol transmission of rickettsia can occur and therefore, represents a bioterrorist threat for the United States. The pathogenesis of R. conorii, upon transmission into the host, depends on the pathogen's ability to bind to and invade target host cells. SFG rickettsia express several outer membrane proteins termed Sca (Surface Cell Antigens) that exhibit high homology to autotransporter families in Gram-negative bacteria. Two members of this family, rOmpA (Sca0) and rOmpB (Sca5) are both thought to be involved in rickettsial adherence and invasion on normally non-phagocytic mammalian cells. We have previously demonstrated that R. conorii infection of host cells results in the induction of distinct host cell signaling pathways ultimately leading to Arp2/3-dependent bacterial uptake. However, the bacterial ligand(s) and host cell receptor(s) involved in this process were not known. We recently identified a mammalian host protein, Ku70, as a receptor involved in R. conorii invasion. We have also demonstrated that R. conorii recruits the ubiquitin ligase c-Cbl to sites of infection and that reduction of endogenous c-Cbl expression by siRNA inhibits R. conorii entry in vitro. We have also shown that R. conorii induces the c-Cbl mediated ubiquitination of Ku70, suggesting that the host cell endocytic machinery may also be involved in the R. conorii entry process. Interestingly, we have shown that rOmpB binds to Ku70, suggesting that this adhesin-host cell receptor pair interaction may be critical to the entry process. In addition, our data suggests that other Rickettsial virulence factors likely contribute to pathogenesis. The goals of our research are several fold: