The kappa B sites in the human immunodeficiency virus type 1 long terminal repeat enhance virus replication yet are not absolutely required for viral growth

The dependence of human immunodeficiency virus type 1 (HIV-1) on its NF-kappa B binding sites (kappa B sites) for replication in transformed and primary T-cell targets was examined by infecting cells with HIV-1 reporter viruses containing kappa B Site enhancer mutations, Viral transcription was measured either with luciferase-expressing HIV-1 that infects for a single round off by flow cytometric analyses with HIV-1 expressing placental alkaline phosphatase (FLAP) or green-fluorescent]protein (GFP). Both PLAP- and GFP-expressing viruses spread from cell to cell and allowed analysis of viral gene expression patterns in single cells, Infection of a panel of T-cell lines with different basal levels of NF-kappa B demonstrated a direct correlation between the amount of constitutive nuclear NF-kappa B and the degree to which a wild-type virus outperformed kappa B Site mutants, One T-cell line with a constitutively high level of nuclear NF-kappa B, PM1, showed a 20-fold decrease in transcription when its kappa B sites were mutated, In contrast, in a T-cell line with a low basal level of NF-kappa B, SupT1, mutation of the kappa B Site in the enhancer had no effect on viral transcription or growth rate, Phytohemagglutinin-activated peripheral blood mononuclear cells showed a large dependence on the kappa B sites for optimal virus growth. Viruses without marker genes corroborated the finding that mutations to the kappa B sites impair virus production in cells with a high basal level of NF-kappa B, These data show that in T cells, HIV-1 can use NF-kappa B to enhance its growth but the virus is clearly able to grow in its absence.