Human immunodeficiency virus infection is associated with inflammation and endothelial cell activation that cannot be ascribed to direct infection by the virus or to the presence of opportunistic infections. Factors related to the virus itself, to the host and/or to environmental exposures probably account for these observations. The HIV protein Tat, a viral regulator required for efficient transcription of the viral genome in host cells is secreted from infected cells and taken up by uninfected by-stander cells. Tat can also act as a general transcriptional activator of key inflammatory molecules. We have examined whether Tat contributes to this endothelial cell activation by activating NF-kappaB. Human endothelial cells exposed to Tat in the culture medium activated E-selectin expression with delayed kinetics compared with tumor necrosis factor (TNF). Tat-mediated E-selectin up-regulation required the basic domain of Tat and was inhibited by a Tat antibody. Transfection of human E-selectin promoter-luciferase reporter constructs into Tat-bearing cells or into endothelial cells co-transfected with a Tat expression vector resulted in induction of luciferase expression. Either Tat or TNF activated p65 translocation and binding to an oligonucleotide containing the E-selectin kappaB site 3 sequence. Tat-mediated p65 translocation was also delayed compared with TNF. Neither agent induced new synthesis of p65. A super-repressor adenovirus (AdIkappaBalphaSR) that constitutively sequesters IkappaB in the cytoplasm as well as cycloheximide or actinomycin D inhibited Tat- or TNF-mediated kappaB translocation and E-selectin up-regulation.