Bacterial Virulence Factor and Host Stress-Response Kinase

of a dissertation at the University of Miami. Dissertation supervised by Associate Professor Kurt Schesser. No. of pages in text. (88) Animals possess several different defense mechanisms to resist microbial infection. These defense mechanisms have different signaling pathway and receptors. Pathogens have also evolved different mechanisms to act against such defense mechanisms of the host. Previously we observed that in a yeast-based model, the activities of the Yersinia protein-kinase A (YpkA) and outerprotein J (YopJ) virulence factors converge on the eIF2α kinase Hri2. This pathway, eIF2α signaling, has been well characterized for regulation of global protein synthesis and to facilitate this function, in case of stress, four kinases are present in mammalian cells (GCN2, PERK, PKR and HRI). Out of these four, eIF2α kinase PKR has been well-studied for its role in viral infection but so far none of these studies have linked eIF2α signaling to bacterial infection. In this report we observed that eIF2α signaling plays a modulatory role during bacterial infection (Yersinia, Listeria and Chlamydia) as well as in Plasmodium infection which causes malaria. Induction of pro-inflammatory cytokines and bacterial invasion are the two major activities affected by the eIF2α signaling pathway. We demonstrated that in mammalian cells activation of the eIF2α signaling pathway by different stress-inducers is reduced by YopJ. We showed that the one of the well documented activity of YopJ, which is inhibiting NF-κB pathway, is also dependent upon the eIF2α signaling pathway. Further in an infection based system, we observed that bacterial infection activates this signaling pathway. Specifically, the eIF2α kinase HRI regulates bacterial trafficking and translocation of virulence factors inside the host cells. For Listeria, the absence of HRI delayed the trafficking of bacteria to the cytosol. For Chlamydia, the absence of HRI negatively affected intracellular growth. Surprisingly, in Plasmodium infection, HRI-/mice resist the proliferation of blood stage parasites compared to HRI+/+ mice. We also observed defects in translocation of virulence factors by Yersinia. Induction of proinflammatory cytokines as well as antigen presentation by MHC class-I, during Listeria infection was also dependent upon HRI. We suggest that microbial pathogens take advantage of the host factor HRI during infection which probably has consequences in disease progression. Collectively, our data suggest that eIF2α signaling which is important for anti-viral responses are also important during bacterial infection.