Requirement for SWI/SNF chromatin-remodeling complex in Tat-mediated activation of the HIV-1 promoter

Activation of the human immunodeficiency virus type-1 (HIV-1) promoter in infected cells requires the sequential recruitment of several cellular factors to facilitate the formation of a processive elongation complex. The nucleosomal reorganization of the HIV-1 long terminal repeat (LTR) observed upon Tat stimulation suggests that chromatin-remodeling complexes could play a role during this process. Here, we reported that Tat interacts directly with Brm, a DNA-dependent ATPase subunit of the SWI/SNF chromatin-remodeling complex, to activate the HIV-1 LTR. Inhibition of Brm via small interfering RNAs impaired Tat-mediated transactivation of an integrated HIV-1 promoter. Furthermore, Brm is recruited in vivo to the HIV-1 LTR in a Tat-dependent manner. Interestingly, we found that Tat/Brm interaction is regulated by Tat lysine 50 acetylation. These data show the requirement of Tat-mediated recruitment of SWI/SNF chromatin-remodeling complex to HIV-1 promoter in the activation of the LTR

Suv39H1 and HP1γ are responsible for chromatin-mediated HIV-1 transcriptional silencing and post-integration latency

HIV-1 gene expression is the major determinant regulating the rate of virus replication and, consequently, AIDS progression. Following primary infection, most infected cells produce virus. However, a small population becomes latently infected and constitutes the viral reservoir. This stable viral reservoir seriously challenges the hope of complete viral eradication. Viewed in this context, it is critical to define the molecular mechanisms involved in the establishment of transcriptional latency and the reactivation of viral expression. We show that Suv39H1, HP1γ and histone H3Lys9 trimethylation play a major role in chromatin-mediated repression of integrated HIV-1 gene expression. Suv39H1, HP1γ and histone H3Lys9 trimethylation are reversibly associated with HIV-1 in a transcription-dependent manner. Finally, we show in different cellular models, including PBMCs from HIV-1-infected donors, that HIV-1 reactivation could be achieved after HP1γ RNA interference