Vpr expression abolishes the capacity of HIV-1 infected cells to repair uracilated DNA

Abstract

The human immunodeficiency virus type 1 (HIV-1) Vpr protein binds to the cellular uracil–DNA glycosylase UNG2 and induces its degradation through the assembly with the DDB1-CUL4 ubiquitin ligase complex. This interaction counteracts the antiviral activity exerted by UNG2 on HIV-1 gene transcription, as previously reported by us. In this work, we show that Vpr expression in the context of HIV-1 infection markedly decreases UNG2 expression in transformed or primary CD4+ T lymphocytes. We demonstrate for the first time that Vpr-UNG2 interaction significantly impairs the uracil excision activity of infected cells. The loss of uracil excision activity coincides with a significant accumulation of uracilated bases in the genome of infected cells without changes in cell division. Although UNG2 expression and uracil–DNA glycosylase activity are recovered after the peak of retroviral replication, the mutagenic effect of transient DNA uracilation in cycling cells should be taken into account. Therefore, the possible consequences of Vpr-mediated temporary depletion of endogenous nuclear UNG2 and subsequent alteration of the genomic integrity of infected cells need to be evaluated in the physiopathogenesis of HIV infection.

HIV-1 and HIV-2 exhibit divergent interactions with HLTF and UNG2 DNA repair proteins

“…Indeed, the key role for a dUTP-mediated antiretroviral host defense pathway is evident from the fact that many retrovirus families captured a host dUTPase gene during viral evolution (51,52). Although HIV-1 does not encode dUTPase, its Vpr protein effectively prevents UNG2-initiated uracil excision repair (31). This alternative mechanism may allow HIV-1 to alleviative negative consequences of UNG2-mediated uracil excision and downstream pathways for the integrity of HIV-1 cDNA (19).…”

“…Separately, HIV-1 and HIV-2 Vpr were reported to bind a base excision repair enzyme, uracil DNA glycosylase (UNG2), which can restrict HIV-1 infection in cells with high concentrations of dUTP (19,(27)(28)(29). HIV-1 Vpr was shown to target UNG2 to the ubiquitin proteasome pathway via the CRL4 DCAF1 E3 complex and thereby disrupt UNG2-initiated base excision repair in HIV-1-infected cells (30)(31)(32).…”

The DDB1–DCAF1–Vpr–UNG2 crystal structure reveals how HIV-1 Vpr steers human UNG2 toward destruction

“…HIV-1 Vpr loads UNG2 onto CRL4-DCAF1 E3 for polyubiquitynation and subsequent proteasome-mediated degradation 29 . As a result, UNG2 levels are depleted and uracil BER compromised in HIV-1 infected primary target cells 34,35 . Whereas the above findings are strong evidence for a role of UNG2 in HIV-1 infection, deciphering UNG2’s detailed effects so far have remained elusive.…”

Retroviral Factors Promoting Infectivity

“…For example, it remains unclear whether the interaction with Vpr results in degradation or promotion of UNG2 activity. [52][53][54][55][56] So, how can association of Vpr with UNG2 promote infectivity? According to one view, if uracil deglycosylation activity has a detrimental effect on HIV-1 infection, because it promotes degradation of the retroviral genome, 54,57 the positive effect of Vpr on virion infectivity toward macrophages derives from the ability of Vpr to protect the retroviral genome by targeting UNG2 to proteasomal degradation.…”

“…According to one view, if uracil deglycosylation activity has a detrimental effect on HIV-1 infection, because it promotes degradation of the retroviral genome, 54,57 the positive effect of Vpr on virion infectivity toward macrophages derives from the ability of Vpr to protect the retroviral genome by targeting UNG2 to proteasomal degradation. 55,58,59 According to another line of research, UNG2 recruited by Vpr would rather repair the uracilated retroviral DNA, preventing its downstream degradation. 52,60 However, the studies supporting the latter hypothesis indicate that retroviral IN, rather than Vpr, is the main determinant which directs UNG2 incorporation into retroviral particles.…”