Modulation of human cytomegalovirus immediate-early gene enhancer by mitogen-activated protein kinase kinase kinase-1

The immediate-early (IE) promoter of human cytomegalovirus (HCMV) constitut es a primary genetic switch, which determines the progression of viral infe ction. Earlier reports by others have shown mitogen-activated protein kinas e kinase kinase-1 (MEKK1) to be able to up-regulate HCMV-IE promoter throug h downstream mitogen-activated protein kinase (MAPK) pathways. However, we noticed that the activation of the HCMV-IE promoter by constitutively activ e MEKK1 (MEKK1-TRU) might not be through the MAPK pathways. Using a HCMV-IE enhancer/promoter (-522 to +72) driving a luciferase reporter, we demonstr ated that the downstream MAPK activation actually repressed the up-regulati on of the promoter by MEKK1 in CHO-KI and human 293 cells. We further found that the upregulation of HCMV-IE promoter by MEKK1 could be in great exten t suppressed by over-expression of I kappaB alpha. Deletion of the NF kappa B/rel sites in the HCMV-IE enhancer region by mutagenesis proportionally re duced the transcriptional activation by MEKK1-TRU, whereas deletion of the ATF/CREB binding sites or cyclic AMP response elements (CRE) had no effects . Furthermore, the NF kappaB/rel deletion mutant also showed repression on the basic transcription activity of the HCMV-IE promoter. Our results indic ate that the NF kappaB/rel sites are not only responsible for the modulatio n of HCMV-IE enhancer activity by MEKK1 but also control the basic transcri ption activity of the HCMV-IE promoter. On the other hand, the four consens us CRE sites were found to have no function in the activation of the promot er by MEKK1. (C) 2001 Wiley-Liss, Inc.