HIV-1 Tat transcriptional activity is regulated by acetylation

Abstract

The human immunodeficiency virus (HIV) trans- activator protein, Tat, stimulates transcription from the viral long-terminal repeats (LTR) through an RNA hairpin element, trans-activation responsive region (TAR). We and others have shown that trans-activator protein (Tat)-associated histone acetyltransferases (TAHs), p300 and p300/CBP-associating factor (PCAF), assist functionally in the activation of chromosomally integrated HIV-1 LTR. Here, we show that p300 and PCAF also directly acetylate Tat. We defined two sites of acetylation located in different functional domains of Tat. p300 acetylated Lys50 in the TAR RNA binding domain, while PCAF acetylated Lys28 in the activation domain of Tat. In support of a functional role for acetylation in vivo, histone deacetylase inhibitor (trichostatin A) synergized with Tat in transcriptional activation of the HIV-1 LTR. Synergism was TAR-dependent and required the intact presence of both Lys28 and Lys50. Mechanistically, acetylation at Lys28 by PCAF enhanced Tat binding to the Tat-associated kinase, CDK9/P-TEFb, while acetylation by p300 at Lys50 of Tat promoted the dissociation of Tat from TAR RNA that occurs during early transcription elongation. These data suggest that acetylation of Tat regulates two discrete and functionally critical steps in transcription, binding to an RNAP II CTD-kinase and release of Tat from TAR RNA.

The RNA binding protein Sam68 is acetylated in tumor cell lines, and its acetylation correlates with enhanced RNA binding activity

“…RNA binding proteins represent a new class of substrates for acetyltransferases. The HIV-1 viral RNA binding trans-activator protein, Tat, was shown to be a substrate for the acetyltransferases p300 and PCAF (Kiernan et al, 1999). Acetylation within the RNA binding domain of Tat by p300 inhibits Tat binding to the trans-activation responsive region (TAR) RNA, which promotes the transcription of viral messages (Kiernan et al, 1999).…”

“…The HIV-1 viral RNA binding trans-activator protein, Tat, was shown to be a substrate for the acetyltransferases p300 and PCAF (Kiernan et al, 1999). Acetylation within the RNA binding domain of Tat by p300 inhibits Tat binding to the trans-activation responsive region (TAR) RNA, which promotes the transcription of viral messages (Kiernan et al, 1999). In contrast, acetylation of Sam68 by CBP in vitro appears to occur within the amino terminal region flanking the RNA binding domain ( Figure 5).…”

Stable gene expression occurs from a minority of integrated HIV-1-based vectors: transcriptional silencing is present in the majority

“…TSA is reported to act by allowing the acetylation of Tat, allowing dissociation from the Tat responsive element TAR after phosphorylation of the C-terminal domain of the RNA polymerase recycling Tat to act on another TAR. 38 If the Tat level of the cell is very low, then TSA would have limited substrate on which to inhibit the effect of histone deacetylases to affect transcription. Consistent with this, some preliminary data showed that applying TSA to cells with active integrated construct seemed to enhance their expression level (unpublished data).…”

Implication de la voie des microARN dans la réplication du VIH-1

“…Le travail de Dennis Lo et al [4] ( Figure 1) utilise le génotypage par SNP (single nucleotide polymorphism) et la quantification des transcrits du gène PLAC4 (placenta specific protein 4) situé sur le chromosome 21, exprimés de façon prévalente au niveau du placenta et dont une proportion passe dans la circulation [5]. La méthode implique l'extraction des ARN du plasma, l'amplification par RT-PCR d'un locus SNP (rs8130833) sur le chromosome 21 (locus qui n'est informatif que dans 45 % de la population) et l'analyse quantitative par spectrométrie de masse des produits d'amplification.…”