Recent studies have reported that lymphocytes produce, transport and bind dopamine present in plasma. However, the action of dopamine on HIV-1 gene expression in cells of the immune system has not yet been examined. Here, we have investigated the regulation of HIV-1 expression by dopamine in Jurkat T cells and in primary blood mononuclear cells (PBMC). HIV-1 replication was increased by dopamine, which correlated with the increased levels of HIV-1 transactivation. Our transient expression data revealed that dopamine stimulated transcription through the NF-kappaB element present in the long terminal repeat. The importance of NF-kappaB sites was confirmed by using vectors containing wild-type or mutant kappaB sites in a heterologous promoter. Consistent with the role of NF-kappaB in mediating dopamine responsiveness, the proteasome inhibitor MG132 abolished dopamine-induced transcriptional activation. We further explored the effect of dopamine in the presence of phorbol esters or tumor necrosis factor-alpha (TNF-alpha) known to activate NF-kappaB. The combination of dopamine and TNF-alpha led to a stimulation of HIV-1 transcription and replication. However, in contrast with TNF-alpha, dopamine treatment did not affect NF-kappaB DNA binding activity nor the concentrations of p50, p65 and IkappaB-alpha proteins, which suggests a distinct NF-kappaB activation mechanism. These results reveal a new link between the dopamine system, cytokine signaling pathway and regulation of gene expression via the involvement of NF-kappaB in T cells and PBMC.