The role of unintegrated DNA in HIV infection

Abstract

Integration of the reverse transcribed viral genome into host chromatin is the hallmark of retroviral replication. Yet, during natural HIV infection, various unintegrated viral DNA forms exist in abundance. Though linear viral cDNA is the precursor to an integrated provirus, increasing evidence suggests that transcription and translation of unintegrated DNAs prior to integration may aid productive infection through the expression of early viral genes. Additionally, unintegrated DNA has the capacity to result in preintegration latency, or to be rescued and yield productive infection and so unintegrated DNA, in some circumstances, may be considered to be a viral reservoir. Recently, there has been interest in further defining the role and function of unintegrated viral DNAs, in part because the use of anti-HIV integrase inhibitors leads to an abundance of unintegrated DNA, but also because of the potential use of non-integrating lentiviral vectors in gene therapy and vaccines. There is now increased understanding that unintegrated viral DNA can either arise from, or be degraded through, interactions with host DNA repair enzymes that may represent a form of host antiviral defence. This review focuses on the role of unintegrated DNA in HIV infection and additionally considers the potential implications for antiviral therapy.

Post-transcriptional gene silencing, transcriptional gene silencing and human immunodeficiency virus

“…In addition, the 1-LTR and 2-LTR circle intermediates of abortive HIV integration, which reside within the nucleus, may be targeted as well. While transcription and translation of viral genes from these unintegrated DNA forms has been observed, the contribution of these to actual infection is not clear [207] . And lastly, the linear DNA intermediate, that is synthesized in the cytoplasm by the RT enzyme and will become integrated as provirus, also contains the two viral LTRs, and several host proteins are known to interact with it [207] .…”

“…While transcription and translation of viral genes from these unintegrated DNA forms has been observed, the contribution of these to actual infection is not clear [207] . And lastly, the linear DNA intermediate, that is synthesized in the cytoplasm by the RT enzyme and will become integrated as provirus, also contains the two viral LTRs, and several host proteins are known to interact with it [207] . While PTGS acts only post-HIV integration on viral mRNAs, rather than on incoming viral RNA genomes [208] , the effect of promotertargeted siRNAs in the incoming reverse-transcribed HIV genome and other unintegrated DNA forms has not been investigated.…”

Cellular and viral determinants of retroviral nuclear entry

“…c. Formation of 2 daughter nuclei containing integrated viral DNA. from the processed 3= end and any site within the reverse-transcribed transcripts (Sloan and Wainberg 2011). Interestingly, MLV and prototype foamy virus (PFV) produce circular 2-LTRs in the cytoplasm at the early stage of infection (Delelis et al 2003;Serhan et al 2004).…”

“…HIV-1 enters the nucleus through the NPC (Cullen 2006;Huthoff and Towers 2008;Biswas et al 2012;Chan et al 2014). If the viral cDNA is arrested in the cytoplasm or is unable to undergo integration in either dividing or nondividing cells, then different types of unintegrated DNA species (dead-end products of reverse transcription) are formed, such as 1-LTR, 2-LTR, and autointegrants (Delelis et al 2003;Sloan and Wainberg 2011). Among them, 2-LTR circles result from nonhomologous end joining and are a nuclear import marker, while 1-LTR results from homologous recombination of one copy of the viral LTR.…”

Establishment and Reversal of HIV-1 Latency in Naive and Central Memory CD4+T CellsIn Vitro

“…ϩ T cells (58)(59)(60)(61). To exclude the possibility that some forms of this unintegrated HIV-1 DNA become integrated upon T cell activation, resulting in productive infection and virus particle production, we next assessed the contribution of unintegrated HIV-1 LAI DNA to extracellular vRNA production from both T N and T CM cells by including the integrase inhibitor raltegravir (RAL) at the same time as anti-CD3/CD28 (Fig.…”