Abstract
BackgroundDuring the early stage of HIV-1 replication, integrase (IN) plays important roles at several steps, including reverse transcription, viral DNA nuclear import, targeting viral DNA to host chromatin and integration. Previous studies have demonstrated that HIV-1 IN interacts with a cellular Lens epithelium-derived growth factor (LEDGF/p75) and that this viral/cellular interaction plays an important role for tethering HIV-1 preintegration complexes (PICs) to transcriptionally active units of host chromatin. Meanwhile, other studies have revealed that the efficient knockdown and/or knockout of LEDGF/p75 could not abolish HIV infection, suggesting a LEDGF/p75-independent action of IN for viral DNA chromatin targeting and integration, even though the underlying mechanism(s) is not fully understood.ResultsIn this study, we performed site-directed mutagenic analysis at the C-terminal region of the IN catalytic core domain responsible for IN/chromatin binding and IN/LEDGF/p75 interaction. The results showed that the IN mutations H171A, L172A and EH170,1AA, located in the loop region 170EHLK173 between the α4 and α5 helices of IN, severely impaired the interaction with LEDGF/p75 but were still able to bind chromatin. In addition, our combined knockdown approach for LEDGF/p75 also failed to dissociate IN from chromatin. This suggests that IN has a LEDGF/p75-independent determinant for host chromatin binding. Furthermore, a single-round HIV-1 replication assay showed that the viruses harboring IN mutants capable of LEDGF/p75-independent chromatin binding still sustained a low level of infection, while the chromatin-binding defective mutant was non-infectious.ConclusionsAll of these data indicate that, even though the presence of LEDGF/p75 is important for a productive HIV-1 replication, IN has the ability to bind chromatin in a LEDGF/p75-independent manner and sustains a low level of HIV-1 infection. Hence, it is interesting to define the mechanism(s) underlying IN-mediated LEDGF/p75-independent chromatin targeting, and further studies in this regard will help for a better understanding of the molecular mechanism of chromatin targeting by IN during HIV-1 infection.
Highlights
During the early stage of human immunodeficiency virus type 1 (HIV-1) replication, integrase (IN) plays important roles at several steps, including reverse transcription, viral DNA nuclear import, targeting viral DNA to host chromatin and integration
Viruses bearing IN mutants with chromatin-binding ability still sustained low levels of viral infection. All of these results clearly indicated that while the LEDGF/p75-binding ability of IN is important for productive HIV-1 replication, the IN has the ability to bind chromatin in a LEDGF/p75-independent manner and is sufficient to sustain a low level of HIV-1 infection
Analysis of different HIV-1 IN mutants for their chromatin- and LEDGF/p75-binding Our previous study showed that three IN catalytic core domain (CCD) mutants V165A, A179P, KR186,7AA, which cannot bind LEDGF/ p75, lack the ability to bind to host chromatin [24]
Summary
During the early stage of HIV-1 replication, integrase (IN) plays important roles at several steps, including reverse transcription, viral DNA nuclear import, targeting viral DNA to host chromatin and integration. The integration of proviral DNA is a two-step process involving 3’ processing and 5’ strand transfer, which has been well characterized et al.) [3] These cellular proteins include Lens epithelium-derived growth factor (LEDGF), Integrase interactor 1 (INi1), high-mobility group protein 1 (HMGA1), barrier to auto-integration factor (BAF), Heat shock protein 60 (HSP60), Polycomb group embryonic ectoderm development (EED) protein, etc. The LEDGF/p75 plays multiple roles during HIV-1 infection through interaction with IN, such as protecting IN from proteasomal degradation [5], potentially affecting the nuclear transport of IN [5,14], stabilizing IN as a tetramer [15], enhancing IN enzymatic activities [16,17] and, most strikingly, serving as the IN-to-chromatin tethering factor driving PICs to transcriptionally active regions of host chromosomes [5,14]
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