Human immunodeficiency virus (HIV) causes significant morbidity and mortality worldwide, yet several HIV proteins have not been fully characterized. The development of cell culture models to study retroviruses has accelerated discovery of basic steps in the HIV lifecycle. Examination of the HIV proteins reverse transcriptase, integrase, protease, Gag and Env in cell lines has led to life-saving pharmacological therapies. In contrast, lentiviral accessory proteins such as viral infectivity factor (Vif) and viral protein R (Vpr) are not yet targeted therapeutically, and are not required for replication in many cell lines. However, accessory proteins are required for HIV to counteract the innate immune system in vivo. Vpr is conserved among lentiviruses, but its function is unknown. In this dissertation, we examine the role of Vpr during HIV-1 infection of primary macrophages, primary CD4+ T cells and cell lines.
We report that uracilation of HIV DNA by the host cytidine deaminase APOBEC3G (A3G) leads to upregulation of natural killer (NK) cell-activating ligands in CD4+ T cells. HIV limits NK cell-activating ligand upregulation by targeting A3G for degradation through Vif. Additionally, we propose that Vpr counteracts uracilation of HIV DNA by recruiting the host uracil DNA glycosylase UNG2. We also explore the ability of Vpr to suppress the antiviral response to HIV, and identify novel restrictions to HIV infection in primary macrophages counteracted by Vpr. Vpr enhances the spread of HIV-1 in macrophages by increasing virus production per infected cell. Surprisingly, Vpr also increases the intracellular level and virion incorporation of Env by preventing Env lysosomal degradation. Importantly, these novel Vpr activities are dependent on the DCAF1-DDB1-Cul4 E3 ubiquitin ligase complex. We also identify novel cell culture conditions that increase the requirement for Vpr to infect macrophages with HIV. Mechanisms of action of eight of the nine HIV-1 genes have been determined. However, vpr is unique because its function has not yet been characterized. This dissertation describes a systematic study of the mechanism through which Vpr enhances HIV replication in primary macrophages. Mechanistic insight into the function of Vpr in HIV-infected macrophages may lead to novel strategies to cure HIV.PHDImmunologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120706/1/mmashiba_1.pd
