Publication Date

2012-08-03

Availability

Open access

Embargo Period

2012-08-03

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Microbiology and Immunology (Medicine)

Date of Defense

2012-06-07

First Committee Member

Kurt Schesser

Second Committee Member

Gregory Plano

Third Committee Member

Kenneth Fields

Fourth Committee Member

Ed harhaj

Fifth Committee Member

Richard Rotundo

Sixth Committee Member

James B Bliska

Abstract

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 outer- protein J (YopJ) virulence factors converge on the eIF2 kinase Hri2. This pathway, eIF2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, eIF2 kinase PKR has been well-studied for its role in viral infection but so far none of these studies have linked eIF2signaling to bacterial infection. In this report we observed that eIF2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 eIF2 signaling pathway. We demonstrated that in mammalian cells activation of the eIF2 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-B pathway, is also dependent upon the eIF2 signaling pathway. Further in an infection based system, we observed that bacterial infection activates this signaling pathway. Specifically, the eIF2 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 pro-inflammatory 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 eIF2signaling which is important for anti-viral responses are also important during bacterial infection.

Keywords

Heme Regulated Kinase(HRI); Yersinia protein-kinaseA(YpkA):Yersinia outer- proteinJ(YopJ); Eukaryotic initiation factor(eIF)

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