Regulation of HIV-1 Preintegration Transcription by Tat and Cellular Transcription Factors NF-kappa B and Sp1




Meltzer, Beatrix Wilhelmina

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For a productive life cycle, HIV-1 needs to integrate its genome into the human cellular chromatin. Studies have shown, however, that prior to integration, the unintegrated viral genome is transcriptional active. The role of cellular transcription factors, such as Sp1 and NF-κB, and the viral protein Tat with respect to regulation of preintegration transcription is not yet understood. This early transcriptional activity also generates three regulatory proteins: Tat, Nef and Rev. Nef from unintegrated viral DNA has been shown to downregulate the cell surface expression of CD4, CXCR4, CCR5, and MHC class I. However, the functional importance of Tat produced from preintegration transcription in the viral life cycle is unclear. In this dissertation, I demonstrate that either deleting Tat or TAR from the HIV-1 viral genome causes a decrease in the packaging of the virion genomes, resulting in a decrease in the subsequent viral reverse transcription and preintegration transcription in target cells. The Tat defect can be complemented by providing the Tat in trans in the virion producer cells. I also demonstrate that the basal transcription from nonintegrated viral DNA is regulated by Sp1 and NF-κB; mutations in the Sp1 and NF-κB binding sites decrease preintegration transcription, and mutations in all three Sp1 binding sites cause the greatest impairment in preintegration transcription. I further demonstrate that Tat produced from unintegrated viral DNA is functional in stimulating HIV-1 LTR. Nevertheless, the nonintegrated viral DNA is less receptive to Tat transactivation than integrated provirus. I also confirm that nonintegrated viral DNA is assembled into a minichromatin which may inhibit preintegration transcription in the absence of Tat. Thus, the early Tat produced from nonintegrated viral DNA is functionally important in maintaining an open chromatin for persistent low-level transcription, which can modulate cellular activity to promote infection.