Mechanism of interleukin-8 induction by human cytomegalovirus UL76 protein

Dissertation presented to obtain the Ph.D degree in Biology

Human cytomegalovirus (HCMV) is a -herpesvirus that infects healthy individuals, usually asymptomatically, but can cause severe or fatal disease in immunocompromised individuals such as transplant recipients or AIDS patients. Primary HCMV infection, as with other herpesviruses, is followed by establishment of lifelong latency and periodic reactivation. To ensure its survival and propagation within the host, HCMV has evolved many strategies to subvert both innate and adaptive host immunity. It is known that HCMV infection induces production of interleukin-8 (IL-8), a proinflammatory chemokine with neutrophil chemotatic activity. Significantly, neutrophils are a major carrier of HCMV during viremia and they are able to transmit infectious virus to other cells, playing a key role in virus dissemination through their contact with endothelial cells. In addition, IL-8 enhances HCMV virion production. This work has identified an HCMV gene (UL76), with the relevant property of inducing IL-8 expression at both transcriptional and protein levels. Interestingly, the murine homologue, MHV-68 ORF20, has no significant effect in the expression of IL-8. The main objective of this work was to characterize the mechanism of IL-8 induction by UL76 and the impact of its expression during the viral infection. The UL76-mediated enhancement of luciferase activity was abolished when the NF-kB binding element was mutated in the IL-8 promoter luciferase reporter, thereby demonstrating that activation of NF-kB is essential for the UL76-mediated induction of IL-8. Consistent with the requirement for NF-kB pathway activation, IKK- and degradation of Ik were essential for IL-8 induction by UL76. In addition, and as might be predicted, expression of UL76 resulted in the translocation of p65 to the nucleus.(...)