We previously observed that human cytomegalovirus (CMV) infection induced a massive production of a chemokine with potent neutrophil chemotactic activity, interleukin-8 (IL-8). Hence, we examined the effect of CMV immediate early (IE) gene products on IL-8 production by the human astrocytoma cell line, U373MG. Transient or stable transfection with a CMV IE1 gene expression vector, but not with a IE2 gene expression vector, significantly augmented IL-8 protein secretion and IL-8 mRNA expression. Luciferase activity was enhanced in U373MG cells when the cells were cotransfected with CMV IE1 and chimeric firefly luciferase reporter genes driven by the transcriptional regulatory region of the human IL-8 gene. Moreover, IE1 gene-mediated enhancement of luciferase activity was abolished by the introduction of mutations into the AP-1 or NF-kappaB factor binding elements in the regulatory region of the IL-8 promoter. Furthermore, electrophoretic mobility shift assays demonstrated that CMV IE1 gene products induced the formation of NF-kappaB or AP-1 complexes. Finally, Western blotting analysis demonstrated that the CMV IE1 gene product increased the amount of NF-kappaB complexes translocated into the nucleus. Collectively, CMV Hi gene expression may be sufficient to activate AP-1 and NF-kappaB, resulting in IL-8 gene expression.