Role of acetylases and deacetylase inhibitors in IRF-1-mediated HIV-1 long terminal repeat transcription.

There is strong evidence that both transcriptional activation and silencing are mediated through the recruitment of enzymes that control reversible protein acetylation: histone acetylase (HAT) and histone deacetylase proteins. Acetylation is also a critical post-translational modification of general and tissue-specific transcription factors. In HIV-1-infected cells, the long terminal repeat (LTR) promoter, once organized into chromatin, is transcriptionally inactive in the absence of stimulation. LTR transcription is regulated by protein acetylation, since treatment with deacetylase inhibitors markedly induces transcriptional activity of the LTR. Besides cellular transcription factors involved in LTR activation, early in infection, and during reactivation from latency, we have previously shown that proteins of the IRF family play an important role. In particular, IRF-1 is able per se to stimulate HIV-1 LTR transcription even in the absence of Tat. IRF-1 is also acetylated and associates with HATs such as p300/CBP and PCAF to form a multiprotein complex that assembles on the promoter of target genes. Here we show that CBP can be recruited by IRF-1 to the HIV-1 LTR promoter even in the absence of Tat and that treatment with deacetylase inhibitors, such as trichostatin A (TSA), increases LTR transactivation in response to both IRF-1 and Tat. These results help to define the architecture of interactions between transcription factors binding HIV-1 LTR and confirm the possibility that deacetylase inhibitors, such as TSA, combined with antiviral therapy may represent a valuable approach to control HIV-1 infection.