An NF-kappa B site in the 5'-untranslated leader region of the human immunodeficiency virus type 1 enhances the viral expression in response to NF-kappa B-activating stimuli

The 5'-untranslated leader region of human immunodeficiency virus, type 1 (HIV-1), includes a complex array of putative regulatory elements whose role in the viral expression is not completely understood. Here we demonstrate the presence of an NF-kappa B-responsive element in the trans-activation response (TAR) region of HIV-1 that confers the full induction of HIV-1 long terminal repeat (LTR) in response to NF-kappa B-activating stimuli, such as DNA alkylating agents, phorbol 12-myristate 13-acetate, and tumor necrosis factor-alpha. The TAR NF-kappa B site GGGAGCTCTC spans from positions +31 to +40 and cooperates with the NF-kappa B enhancer upstream of the TATA box in the NF-kappa B-mediated induction of HIV-1 LTR. The conclusion stems from the following observations: (i) deletion of the two NF-kappa B sites upstream of the TATA box reduces, but does not abolish, the HIV-1 LTR activation by NF-kappa B inducers; (ii) deletion or base pair substitutions of the TAR NF-kappa B site significantly reduce the HIV-1 LTR activation by NF-kappa B inducers; (iii) deletions of both the NF-kappa B sites upstream of the TATA box and the TAR NF-kappa B site abolish the activation of HIV-1 LTR in response to NF-kappa B inducers. Moreover, the p50 . p65 NF-kappa B complex binds to the TAR NF-kappa B sequence and trans-activates the TAR NF-kappa B-directed expression. The identification of an additional NF-kappa B site in the HIV-1 LTR points to the relevance of NF-kappa B factors in the HIV-1 Life cycle.