SMC1A/3 cohesin complex-mediated silencing of unintegrated HIV-1 DNA and the antagonism by Vpr - ABSTRACT Human immunodeficiency virus (HIV-1) infection can lead to the deadly disease acquired immunodeficiency syndrome (AIDS). During the natural infection of HIV-1, some viral DNAs are integrated into host genome, but the vast majority of viral DNAs exist in an unintegrated state. Transcriptional regulation of unintegrated HIV-1 DNA plays important roles in HIV-1 infection and pathogenesis. In contrast to the robust viral gene expression from integrated viral DNA, the extrachromosomal, unintegrated viral DNAs are very poorly transcribed. The exact mechanisms for the silencing of unintegrated HIV-1 DNA are not well understood, which constitutes a major knowledge gap in HIV-1 research. HIV-1 accessory protein Vpr enhances viral gene expression from unintegrated HIV-1 DNA by targeting host proteins for degradation. In search for Vpr target host factor(s) that can silence unintegrated HIV-1 DNA, we have performed a CRISPR-Cas9 knockout screening of Vpr target genes and identified NS1BP. We also found that NS1BP-interacting partner, the SMC1A/3 cohesin complex, is required for the silencing of unintegrated HIV-1 DNA. We hypothesize that NS1BP acts as a cofactor to facilitate the loading of the SMC1A/3 cohesin complex on viral DNA, which results in viral chromatin compaction and gene suppression, and Vpr-mediated degradation of NS1BP results in the dissociation of the cohesin complex from viral DNA, which consequently depresses the silencing of unintegrated HIV-1 DNA. In this project, we will determine the mechanism by which NS1BP and the SMC1A/3 cohesin complex mediate the silencing of unintegrated HIV-1 DNA (Aim 1), and elucidate the mechanism by which Vpr antagonizes the silencing mediated by NS1BP and the cohesin complex (Aim 2). Our proposed studies will significantly extend our understanding of the molecular mechanism for the transcriptional regulation of unintegrated HIV-1 DNA and provide new information regarding the epigenetic silencing of HIV-1 DNA. In the long term, these studies will provide new targets and strategies for the cure of HIV-1 infection.
