Inhibition of HIV-1 transmission by interferon and 3'-azido-3'-deoxythymidine during de novo infection of promonocytic cells.

HIV-1 infection of promonocytic U937 cells was used to examined induction of IFN-alpha/beta gene expression and to determine the inhibitory effects of IFN-alpha 2 and/or AZT on de novo HIV-1 infection, initiated either by coculture of virus-shedding U9-IIIB cells with uninfected cells or by incubation of U937 cells with virus-containing supernatants. Usually 21-28 days were required to transmit virus to greater than 90% of the cell culture. HIV-1 infection did not stimulate constitutive production of endogenous IFN-alpha 1/alpha 2 or IFN-beta genes, although induction of IFN RNA was observed following coinfection with the paramyxovirus Sendai. Exogenous rIFN-alpha 2 treatment decreased the intracellular accumulation of viral RNA 5- to 20-fold as determined by Northern blot analysis and the extracellular levels of HIV-1 as measured by p24 ELISA antigen capture. The effect was most dramatic at a time coincident with the rapid increase in virus spread through the cell culture (Days 10-18). During the fourth week of infection, HIV-1 multiplication was able to overcome the IFN-induced block in virus spread. AZT was not effective in limiting virus spread in the cocultivation experiments. When U937 cells were infected with virus-containing supernatants from U9-IIIB cells, IFN and AZT acted in combination to limit the number of infected cells and to inhibit intracellular accumulation of viral RNA. These experiments suggest that subtle differences in the mode of virus transmission in monocytic cells may alter the efficacy of combination antiretroviral therapy.

Induction of human interferon gene expression is associated with a nuclear factor that interacts with the NF-kappa B site of the human immunodeficiency virus enhancer.

The relationship between transcription of alpha and beta interferon (IFN-alpha and IFN-beta) genes and the interaction of IFN promoter-binding transcription factors has been examined in monoblastoid U937 cells following priming with recombinant IFN-alpha 2 (rIFN-alpha 2) and Sendai virus induction. Pretreatment of U937 cells with rIFN-alpha 2 prior to Sendai virus infection increased the mRNA levels of IFN-alpha 1, IFN-alpha 2, and IFN-beta as well as the final yield of biologically active IFN. Analysis of nuclear protein-IFN promoter DNA interactions by electrophoretic mobility-shift assays demonstrated increased factor binding to IFN-alpha 1 and IFN-beta regulatory domains, although no new induction-specific complexes were identified. On the basis of competition electrophoretic mobility-shift assay results, factors interacting with the IFN-alpha 1 and IFN-beta promoters appear to be distinct DNA-binding proteins. U937 factor binding was localized to the P2 domain (-64 to -55) of the IFN-beta regulatory element, a sequence motif with 80% homology to the recognition site of transcription factor NF-kappa B. Protein-DNA interactions within the IFN-beta P2 domain were, in fact, specifically competed by either excess homologous P2 fragment or the human immunodeficiency virus enhancer element which contains two duplicated NF-kappa B recognition sites. Hybrid promoter-chloramphenicol acetyltransferase fusion plasmids, containing either the IFN-beta regulatory element or the human immunodeficiency virus enhancer element linked to the simian virus 40 promoter, were analyzed for virus and phorbol ester inducibility in epithelial and lymphoid cells, respectively. In the 293 cell line, both plasmids were constitutively expressed but not virus inducible, while in Jurkat cells, chloramphenicol acetyltransferase activity from these plasmids was induced by tumor-promoting agent treatment. These experiments suggest that induction of IFN gene expression may be controlled in part by transcription regulatory proteins binding to an NF-kappa B-like site within the IFN-beta promoter.