NF-κB A Potential Therapeutic Target for Inhibition of Human Cytomegalovirus (Re)activation?

Abstract

From clinical studies the proinflammatory cytokine TNFα was proposed to play a key role in human cytomegalovirus (HCMV) reactivation from latency. In vitro experiments confirmed that TNFα stimulates the activity of the HCMV IE1/2 enhancer/promoter, which controls immediate early protein IE1 and IE2 gene expression via activation of the transcription factor NFκB and its binding to putative binding sites in the IE1/2 enhancer. NFκB was also proposed to be involved in IE1-mediated autostimulation of this promoter. The IE1/2 enhancer of HCMV contains four putative NFκB binding sites which differ in their distance to the transcription start site as well as in their sequence. Construction and testing of a series of promoter mutants demonstrated that NFκB is essential for both TNFα and IE1 stimulation. Furthermore, we were able to show that although all four NFκB sites bind NFκB with similar affinity in vitro, the contribution to TNFα and IE1 stimulation differs in correlation with the distance to the transcription start site and the sequence. Site 1 and 3 play the most dominant role and site 2 an intermediate, while site 4, which is conserved in sequence but far distant from the transcription start site, had no influence on NFκBmediated regulation of the IE1/2 promoter. Specific inhibition of NFκB signalling by coexpression of a dominantnegative IκB variant reduced TNFα stimulation of the IE1/2 enhancer/promoter by up to 80%. From this data, inhibitors of NFκB activation are suggested to be an alternative therapeutical strategy to interfere with HCMV (re)activation in undifferentiated monocyte/granulocyte progenitor cells in patients with a high risk of inflammationrelated HCMV (re)activation.