Transcriptional activation of the tat-defective human immunodeficiency virus type-1 provirus: effect of interferon.

The effect of human interferon-alpha 2 (HuIFN-alpha 2) on the activation of HIV-1 provirus was studied in cell lines containing either an integrated tat-defective HIV-1 provirus (HIV-1 (-tat)) (HNHIVdt4 cells) or the HIV-1 (-tat) provirus and a plasmid in which the expression of HuIFN-alpha 2 was under the control of HIV LTR (HNHIV alpha 1 cells). In both cell lines, the expression of HIV-1 RNA was below the limit of detection, but transcription of the HIV-1 (-tat) provirus could be induced either by transfection with Tat-expressing plasmid or by treatment with TPA and cycloheximide (CHX). By contrast, stimulation with TPA alone induced HIV-1 transcription only in HNHIVdt4 cells, but not in HNHIV alpha 1 cells that produced low levels of IFN-alpha constitutively. Similarly in a transient expression assay, TPA upregulated transcription of the transfected HIV-1 CAT plasmid only in HNHIVdt4 cells, but not in HNHIV alpha 1 cells. UV-crosslinking analysis of NF-kappa B-specific proteins induced in TPA-treated cells showed the presence of 45 and 55 kDa NF-kappa B-binding protein in TPA-induced HNHIVdt4 cells while, in HNHIV alpha 1 cells, we detected only 55-, 110-, and 200-kDa proteins, but no 45-kDa protein. The transcriptional effects of IFN could not, however, be seen in the presence of Tat protein, suggesting that the virus developed a mechanism to overcome the IFN-mediated restrictions.