Molecular mechanisms mediating activation of cytomegalovirus major immediate early enhancer in allogeneic transplantation

Soo Jung Kim

doi:https://doi.org/10.21985/N2P102

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Molecular mechanisms mediating activation of cytomegalovirus major immediate early enhancer in allogeneic transplantation

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Reactivation of latent human cytomegalovirus is of significant concern in immunocompromised transplant patients. However, the mechanisms controlling reactivation of latent CMV have not been understood. It is likely that reactivation is initiated by induction of IE gene expression. In this thesis, I studied molecular mechanisms leading to transcriptional activation of IE gene expression in vivo. Using transgenic mice carrying a beta-galactosidase reporter gene under the control of the HCMV major immediate early enhancer and deficient in the TNF receptors, I demonstrated that signaling through TNF receptors plays a critical role in activation of the HCMV enhancer in allogeneic kidney transplantation. This occurred primarily through TNFR2. Furthermore, I demonstrated that signaling through the TNF receptors is required for activation of NF-kB in allogeneic transplantation. The JunD component of AP-1 was also activated very strongly in allogeneic transplants, but this activation occurred independently of signaling through the TNF receptors. In addition, I studied the role of oxidative stress induced by renal ischemia/reperfusion injury (I/R) in activation of the enhancer. Allogeneic transplantation induces nonspecific injury due to deprivation of oxygen resulting from interruption of blood flow (ischemia) and subsequent restoration of blood flow (reperfusion injury) as well as injury due to immune recognition of foreign antigens. I demonstrated that renal ischemia/reperfusion injury (I/R) activates the HCMV enhancer independently of TNF. Induction of MIEP-lacZ expression was preceded by weak and transient activation of NF-kB and strong and sustained activation of AP-1, especially JunD. Activation of transcription factors was preceded by TNFR-independent formation of reactive oxygen species (ROS). These results are consistent with the hypothesis that TNF-independent signaling due to oxidative stress induced by I/R injury can activate the HCMV enhancer through ROS-mediated activation of AP-1. My results suggest that activation of either the TNF signaling pathway or the MAP kinase signaling pathway can activate the enhancer, and targeting these pathways may have therapeutic value in patients with CMV infection.

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