Activation of Human Immunodeficiency Virus Transcription in T Cells Revisited: NF-κB p65 Stimulates Transcriptional Elongation

Abstract

Human immunodeficiency virus type 1 (HIV-1) is able to establish a persistent latent infection during which the integrated provirus remains transcriptionally silent. Viral transcription is stimulated by NF-B, which is activated following the exposure of infected T cells to antigens or mitogens. Although it is commonly assumed that NF-B stimulates transcriptional initiation alone, we have found using RNase protection assays that, in addition to stimulating initiation, it can also stimulate elongation from the HIV-1 long terminal repeat. When either Jurkat or CCRF/CEM cells were activated by the mitogens phorbol myristate acetate and phytohemagglutinin, elongation, as measured by the proportion of full-length transcripts, increased two-to fourfold, even in the absence of Tat. Transfection of T cells with plasmids carrying the different subunits of NF-B demonstrated that the activation of transcriptional elongation is mediated specifically by the p65 subunit. It seems likely that initiation is activated because of NF-B's ability to disrupt chromatin structures through the recruitment of histone acetyltransferases. To test whether p65 could stimulate elongation under conditions where it did not affect histone acetylation, cells were treated with the histone deacetylase inhibitor trichostatin A. Remarkably, addition of p65 to the trichostatin A-treated cell lines resulted in a dramatic increase in transcription elongation, reaching levels equivalent to those observed in the presence of Tat. We suggest that the activation of elongation by NF-B p65 involves a distinct biochemical mechanism, probably the activation of carboxyl-terminal domain kinases at the promoter.

Transcriptional burst frequency and burst size are equally modulated across the human genome

“…This observed decrease in k off with TNF induction leads to extended duration of bursts and is consistent with the reported inhibition of p50-HDAC1 repressivecomplex formation at LTR NFκB sites by p50/RelA heterodimers (33)-the successful formation of HDAC1 leads to weakened recruitment of RNA polymerase II and weakened transcriptional initiation (34). The observed increases in k on are also consistent with increased recruitment of RNA polymerase II to the LTR promoter NFκB sites induced by TNF (35,36). Fitted parameter estimates of LTR residency time in the presence of TNF were used to represent an average over the first 12 h of stimulation given the dynamic nonlinear nature of the NFκB response (37,38).…”

CD28 ligation in the absence of TCR promotes RelA/NF‐κB recruitment and trans‐activation of the HIV‐1 LTR

“…Among the NF-jB subunits, RelA has been shown to strongly trans-activate the HIV-1 LTR, by stimulating the transcriptional elongation by RNA polymerase II [9,11]. Consistently, we found that the over-expression of RelA in J1G5 cells strongly induced LTR-luciferase activity within 4-6 h (Fig.…”

Mechanisms of HIV-1 Inhibition by the Lipid Mediator N-Arachidonoyldopamine

“…In contrast, it has been shown that p65 can also stimulate elongation from the HIV-1-LTR (70), and it is possible that NADA inhibits both the transcriptional and elongation activities of the p65 NF-B subunit; this could explain the fact that NADA is a more potent inhibitor of NF-B in the context of the full HIV-1-LTR promoter.…”