HIV-1 Tat Superinduces NF-kB Responsive Gene Expression through Inhibition of the SIRT1 Deacetylase

Hye-Sook Kwon, J. David Gladstone Institutes
Biomedical and Clinical Sciences

The viral Tat protein transactivates the HIV-1 promoter through binding to the TAR RNA element. Tat also modulates the expression of cellular genes in a TAR-independent manner. Here, we report that Tat increases the activity of the transcription factor NF-kappa B by interfering with the nicotinamide adenine dinucleotide-dependent deacetylase SIRT1. Tat directly interacts with the deacetylase domain of SIRT1 and blocks the ability of SIRT1 to deacetylate lysine 310 (K310) in recombinant NF-kappa B/p65. Consistent with these findings, we show that Tat expression induces hyperacetylation of cellular p65 in the presence of SIRT1 using antibodies specific for acetylated K310 in p65. In cotransfection experiments using NF-kappa B reporter genes, Tat neutralizes the negative effect of SIRT1 on the transcriptional activity of wildtype p65, but not of mutant p65 in which lysine 310 was changed to arginine (K310R).This neutralizing effect is lost on a mutant SIRT1 protein that no longer binds to Tat. Tat expressed in mouse embryonic fibroblasts (MEFs) isolated from SIRT1-/- mice has no effect on the activity of endogenous NF-kappa B responsive genes as determined by real-time PCR. In contrast, Tat expressed in MEF cells in which SIRT1 expression has been reconstituted after retroviral infection superinduces transcriptional activities of endogenous I kappa B alpha and E-selectin genes in response to TNF alpha. These experiments collectively show that Tat activates NF-kappa B responsive gene expression through SIRT1, a TAR-independent mechanism that can contribute to Tat-mediated superinduction of the HIV promoter as well as cellular promoters in activated CD4+ T cells.