Lack of responsiveness of a nuclear factor-kappaB-regulated promoter to transactivation by human immunodeficiency virus 1 Tat in HeLa cells.

Transcriptional activation by Tat protein is in large part dependent on interactions with the TAR RNA element located in the 5'-untranslated region of all human immunodeficiency virus type 1 (HIV-1) transcripts. In addition, Tat has been shown to induce nuclear translocation of nuclear factor-kappaB (NF-kappaB), potentially contributing to gene induction. The NF-kappaB responsive reporter construct, (PRDII)(4)-CAT, was used to explore transcription resulting from NF-kappaB activated by Tat. Tat did not activate (PRDII)(4)-CAT, whereas (PRDII)(4)-CAT was highly responsive to either transfected Rel A or to tumor necrosis factor-alpha (TNF-alpha). Despite its inability to directly induce, Tat enhanced the responsiveness of (PRDII)(4)-CAT to either transfected Rel A or to TNF-alpha by approximately 2.5-fold. High levels of CAT activity were seen with HIV-LTR-derived reporters that contained kappaB and TAR elements in response to transfected Tat in the absence of either transfected Rel A or exogenous TNF-alpha, and overexpression of IkappaBalpha with Tat inhibited CAT activity by 60% to 80%, suggesting that some activation of NF-kappaB by Tat was occurring. HIV-LTR reporter activities were enhanced three fold to sixfold compared with Tat alone when additional NF-kappaB was provided by transfection or by activation with TNF-alpha. These data indicate that Tat is unable to activate some NF-kappaB-responsive promoters but is able to synergize with NF-kappaB in the activation of both HIV-derived and non-HIV-derived promoters.