Transcriptional activation and chromatin remodeling of the HIV‐1 promoter in response to histone acetylation.

After integration in the host cell genome, the HIV‐1 provirus is packaged into chromatin. A specific chromatin disruption occurs in the HIV‐1 promoter during transcriptional activation in response to TNF‐alpha, suggesting that chromatin plays a repressive role in HIV‐1 transcription and that chromatin modification(s) might result in transcriptional activation. We have treated several cell lines latently infected with HIV‐1 with two new specific inhibitors of histone deacetylase, trapoxin (TPX) and trichostatin A (TSA), to cause a global hyperacetylation of cellular histones. Treatment with both drugs results in the transcriptional activation of the HIV‐1 promoter and in a marked increase in virus production. Dose‐response curves and kinetic analysis show a close correlation between the level of histone acetylation and HIV‐1 gene expression. In contrast, both TPX and TSA have little or no effect on HIV‐1 promoter activity following transient transfection of an HIV‐1 promoter‐reporter plasmid. Activation of HIV‐1 transcription by TSA and TPX treatment occurs in the absence of NF‐kappa B induction. Chromatin analysis of the HIV‐1 genome shows that a single nucleosome (nuc‐1) located at the transcription start and known to be disrupted following TNF‐alpha treatment, is also disrupted following TPX or TSA treatment. This disruption is independent of transcription as it is resistant to alpha‐amanitin. These observations further support the crucial role played by nuc‐1 in the suppression of HIV‐1 transcription during latency and demonstrate that transcriptional activation of HIV‐1 can proceed through a chromatin modification.