In vitro study of functional involvement of Sp1, NF-kappa B/Rel, and AP1 in phorbol 12-myristate 13-acetate-mediated HIV-1 long terminal repeat activation.

We examined the cooperative activity between the Sp1 and NF-kappa B/Rel sites of the human immunodeficiency virus type 1 long terminal repeat in response to phorbol 12-myristate 13-acetate (PMA) stimulation in an in vitro transcription assay. Sp1 sites alone do not account for the activation induced by PMA. When mutations in Sp1 sites were combined with mutations in the NF-kappa B/Rel sites, a dramatic reduction in PMA-induced transcriptional activity was observed. This reduction was much greater than the reduction associated with mutations involving only the NF-kappa B/Rel sites. This finding suggests that there is functional cooperation between Sp1 and NF-kappa B/Rel and that this is one possible mechanism for transcription activation by NF-kappa B/Rel. The three AP1 sites in the negative regulatory region of the long terminal repeat, however, seem to be uninvolved in the earliest moments of transcriptional activation by PMA.