Analysis of the HIV-1 LTR NF-kappa B-proximal Sp site III: Evidence for cell type-specific gene regulation and viral replication

It has been widely demonstrated that the human immunodeficiency virus type 1 (HIV-1) envelope, specifically the V3 loop of the gp120 spike, evolves to facilitate adaptation to different cellular populations within an infected host Less energy has been directed at determining whether the viral promot er, designated the long terminal repeat (LTR), also exhibits this adaptive quality. Because of the unique nature of the cell populations infected duri ng the course of HIV-1 infection, one might expect the opportunity for such adaptation to exist. This would permit select viral species to take advant age of the different array of conditions and factors influencing transcript ion within a given cell type. To investigate this hypothesis, the function of natural variants of the NF-kappa B-proximal Sp element (Sp site III) was examined in human cell line models of the two major cell types infected du ring the natural course of HIV-1 infection, T cells and monocytes. Utilizin g the HIV-1 LAI molecular clone, which naturally contains a high-affinity S p site III, substitution of low-affinity Sp sites in place of the natural s ite III element markedly decreased viral replication in Jurkat T cells. How ever, these substitutions had relatively small effects on viral replication in U-937 monocytic cells. Transient transfections of HIV-1 LAI-based LTR-l uciferase constructs into these cell lines suggest that the large reduction in viral replication in Jurkat T cells, caused by low-affinity Sp site III variants, may result from reduced basal as well as Vpr- and Tar-activated LTR activities in Jurkat T cells compared to those in U-937 monocytic cells . When the function of Sp site III was examined in the context of HIV-1 YU- 2-based LTR-luciferase constructs, substitution of a high-affinity element in place of the natural low-affinity element resulted in increased basal YU -2 LTR activity in Jurkat T cells and reduced activity in U-937 monocytic c ells. These observations suggest that recruitment of Sp family members to S p site III is of greater importance to the function of the viral promoter i n the Jurkat T cell line as compared to the U-937 monocytic cell line. Thes e observations also suggest that other regions of the LTR may compensate fo r Sp recruitment defects in specific cell populations. (C) 2000 Academic Pr ess.