We previously demonstrated that human cytomegalovirus (HCMV)
infection induced the activation of the cellular
transcription factor NF-kappaB. Here, we investigate the mechanism for the HCMV-induced
NF-kappaB activation and the role that the induced
NF-kappaB plays in transactivation of the major immediate-early promoter (MIEP) and production of immediate-early (IE)
proteins. Using a dominant-negative inhibitor of
NF-kappaB, the IkappaB-superrepressor, we demonstrated that active
NF-kappaB is critical for transactivation of the HCMV MIEP. Investigation of the mechanisms of
NF-kappaB activation following HCMV
infection showed a rapid and sustained decrease in the inhibitors of
NF-kappaB,
IkappaBalpha and
IkappaBbeta. Because the IkappaB
kinases (IKKs) regulate the degradation of the IkappaBs, virus-mediated changes in the IKKs were examined next. Using dominant-negative forms of the IKKs, we showed significant decreases in transactivation of the MIEP in the presence of these mutants. In addition,
protein levels of members of the IKK complex and IKK
kinase activity were upregulated throughout the time course of
infection. Lastly, the role
NF-kappaB plays in HCMV IE
mRNA and
protein production during
infection was examined. Using
aspirin and
MG-132, we demonstrated that production of IE
protein and
mRNA was significantly decreased and delayed in infected cells treated with these drugs. Together, the results of these studies suggest that virus-mediated
NF-kappaB activation, through the dysregulation of the IKK complex, plays a primary role in the initiation of the HCMV gene cascade in fibroblasts and may provide new targets for therapeutic intervention.