Activation of human immunodeficiency virus transcription in T cells revisited: NF-kappa B p65 stimulates transcriptional elongation

Human immunodeficiency virus type 1 (HIV-1) is able to establish a persiste nt latent infection during which the integrated provirus remains transcript ionally silent. Viral transcription is stimulated by NF-kappaB, which is ac tivated following the exposure of infected T cells to antigens or mitogens. Although it is commonly assumed that NF-kappaB stimulates transcriptional initiation alone, we have found using RNase protection assays that, in addi tion to stimulating initiation, it can also stimulate elongation from the H IV-1 long terminal repeat. When either Jurkat or CCRF/CEM cells were activa ted by the mitogens phorbol myristate acetate and phytohemagglutinin, elong ation, 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-kappaB demonstrated that the activation of transcriptional elongation is mediated specifically by the p 65 subunit. It seems likely that initiation is activated because of NF-kapp aB's ability to disrupt chromatin structures through the recruitment of his tone acetyltransferases. To test whether p65 could stimulate elongation und er conditions where it did not affect histone acetylation, cells were treat ed with the histone deacetylase inhibitor trichostatin A. Remarkably, addit ion of p65 to the trichostatin A-treated cell lines resulted in a dramatic increase in transcription elongation, reaching levels equivalent to those o bserved in the presence of Tat. We suggest that the activation of elongatio n by NF-kappaB p65 involves a distinct biochemical mechanism, probably the activation of carboxyl-terminal domain kinases at the promoter.