HIV-1 requires capsid remodelling at the nuclear pore for nuclear entry and integration

The capsid (CA) lattice of the HIV-1 core plays a key role during infection. From the moment the core is released into the cytoplasm, it interacts with a range of cellular factors that, ultimately, direct the pre-integration complex to the integration site. For integration to occur, the CA lattice must disassemble. Early uncoating or a failure to do so has detrimental effects on virus infectivity, indicating that an optimal stability of the viral core is crucial for infection. Here, we introduced cysteine residues into HIV-1 CA in order to induce disulphide bond formation and engineer hyper-stable mutants that are slower or unable to uncoat, and then followed their replication. From a panel of mutants, we identified three with increased capsid stability in cells and found that, whilst the M68C/E212C mutant had a 5-fold reduction in reverse transcription, two mutants, A14C/E45C and E180C, were able to reverse transcribe to approximately WT levels in cycling cells. Moreover, these mutants only had a 5-fold reduction in 2-LTR circle production, suggesting that not only could reverse transcription complete in hyper-stable cores, but that the nascent viral cDNA could enter the nuclear compartment. Furthermore, we observed A14C/E45C mutant capsid in nuclear and chromatin-associated fractions implying that the hyper-stable cores themselves entered the nucleus. Immunofluorescence studies revealed that although the A14C/E45C mutant capsid reached the nuclear pore with the same kinetics as wild type capsid, it was then retained at the pore in association with Nup153. Crucially, infection with the hyper-stable mutants did not promote CPSF6 re-localisation to nuclear speckles, despite the mutant capsids being competent for CPSF6 binding. These observations suggest that hyper-stable cores are not able to uncoat, or remodel, enough to pass through or dissociate from the nuclear pore and integrate successfully. This, is turn, highlights the importance of capsid lattice flexibility for nuclear entry. In conclusion, we hypothesise that during a productive infection, a capsid remodelling step takes place at the nuclear pore that releases the core complex from Nup153, and relays it to CPSF6, which then localises it to chromatin ready for integration.

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HIV-1 requires capsid remodelling at the nuclear pore for nuclear entry and integration

10.1101/2021.03.18.436028 ◽

2021 ◽

Author(s):

Anabel Guedán ◽

Callum D Donaldson ◽

Ophélie Cosnefroy ◽

Ian A Taylor ◽

Kate N. Bishop

Keyword(s):

Reverse Transcription ◽

Integration Site ◽

Productive Infection ◽

Nuclear Pore ◽

Virus Infectivity ◽

Nuclear Speckles ◽

Nuclear Entry ◽

The Core ◽

Fold Reduction ◽

Hiv 1

The capsid (CA) lattice of the HIV-1 core plays a key role during infection. From the moment the core is released into the cytoplasm, it interacts with a range of cellular factors that, ultimately, direct the pre-integration complex to the integration site. For integration to occur, the CA lattice must disassemble. Early uncoating or a failure to do so has detrimental effects on virus infectivity, indicating that an optimal stability of the viral core is crucial for infection. Here, we introduced cysteine residues into HIV-1 CA in order to induce disulphide bond formation and engineer hyper-stable mutants that are slower or unable to uncoat, and then followed their replication. From a panel of mutants, we identified three with increased capsid stability in cells and found that, whilst the M68C/E212C mutant had a 5-fold reduction in reverse transcription, two mutants, A14C/E45C and E180C, were able to reverse transcribe to approximately WT levels. Moreover, these mutants only had a 5-fold reduction in 2-LTR circle production, suggesting that not only could reverse transcription complete in hyper-stable cores, but that the nascent viral cDNA could enter the nuclear compartment. Furthermore, we observed significant levels of A14C/E45C mutant capsid in nuclear and chromatin-associated fractions implying that the hyper-stable cores themselves entered the nucleus. Immunofluorescence studies revealed that although the A14C/E45C mutant capsid reached the nuclear pore with the same kinetics as wild type capsid, it was then retained at the pore in association with Nup153. Crucially, infection with the hyper-stable mutants did not promote CPSF6 re-localisation to nuclear speckles, despite the mutant capsids being competent for CPSF6 binding. These observations suggest that hyper-stable cores are not able to uncoat, or remodel, enough to pass through or dissociate from the nuclear pore and integrate successfully. This, is turn, highlights the importance of capsid lattice flexibility for nuclear entry. In conclusion, we hypothesise that during a productive infection, a capsid remodelling step takes place at the nuclear pore that releases the core complex from Nup153, and relays it to CPSF6, which then localises it to chromatin ready for integration.

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HIV-1 replication complexes accumulate in nuclear speckles and integrate into speckle-associated genomic domains

Nature Communications ◽

10.1038/s41467-020-17256-8 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 8

Author(s):

Ashwanth C. Francis ◽

Mariana Marin ◽

Parmit K. Singh ◽

Vasudevan Achuthan ◽

Mathew J. Prellberg ◽

...

Keyword(s):

Viral Replication ◽

Nuclear Import ◽

Integration Site ◽

Nuclear Speckles ◽

Nuclear Entry ◽

Primary Monocyte ◽

Integration Sites ◽

Cleavage And Polyadenylation ◽

Specificity Factor ◽

Hiv 1

AbstractThe early steps of HIV-1 infection, such as uncoating, reverse transcription, nuclear import, and transport to integration sites are incompletely understood. Here, we imaged nuclear entry and transport of HIV-1 replication complexes in cell lines, primary monocyte-derived macrophages (MDMs) and CD4+ T cells. We show that viral replication complexes traffic to and accumulate within nuclear speckles and that these steps precede the completion of viral DNA synthesis. HIV-1 transport to nuclear speckles is dependent on the interaction of the capsid proteins with host cleavage and polyadenylation specificity factor 6 (CPSF6), which is also required to stabilize the association of the viral replication complexes with nuclear speckles. Importantly, integration site analyses reveal a strong preference for HIV-1 to integrate into speckle-associated genomic domains. Collectively, our results demonstrate that nuclear speckles provide an architectural basis for nuclear homing of HIV-1 replication complexes and subsequent integration into associated genomic loci.

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Nuclear Import of HIV-1

Viruses ◽

10.3390/v13112242 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2242

Author(s):

Qi Shen ◽

Chunxiang Wu ◽

Christian Freniere ◽

Therese N. Tripler ◽

Yong Xiong

Keyword(s):

Reverse Transcription ◽

Nuclear Import ◽

Integration Site ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

New Paradigm ◽

Retroviral Infection ◽

Dividing Cells ◽

Pore Complexes ◽

Hiv 1

The delivery of the HIV-1 genome into the nucleus is an indispensable step in retroviral infection of non-dividing cells, but the mechanism of HIV-1 nuclear import has been a longstanding debate due to controversial experimental evidence. It was commonly believed that the HIV-1 capsid would need to disassemble (uncoat) in the cytosol before nuclear import because the capsid is larger than the central channel of nuclear pore complexes (NPCs); however, increasing evidence demonstrates that intact, or nearly intact, HIV-1 capsid passes through the NPC to enter the nucleus. With the protection of the capsid, the HIV-1 core completes reverse transcription in the nucleus and is translocated to the integration site. Uncoating occurs while, or after, the viral genome is released near the integration site. These independent discoveries reveal a compelling new paradigm of this important step of the HIV-1 life cycle. In this review, we summarize the recent studies related to HIV-1 nuclear import, highlighting the spatial–temporal relationship between the nuclear entry of the virus core, reverse transcription, and capsid uncoating.

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The Role of Capsid in HIV-1 Nuclear Entry

Viruses ◽

10.3390/v13081425 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1425

Author(s):

Anabel Guedán ◽

Eve R. Caroe ◽

Genevieve C. R. Barr ◽

Kate N. Bishop

Keyword(s):

Nuclear Pore ◽

Outer Face ◽

Nuclear Entry ◽

Nuclear Compartment ◽

Critical Step ◽

Technological Advances ◽

Dividing Cells ◽

Hiv 1 ◽

Gain Access

HIV-1 can infect non-dividing cells. The nuclear envelope therefore represents a barrier that HIV-1 must traverse in order to gain access to the host cell chromatin for integration. Hence, nuclear entry is a critical step in the early stages of HIV-1 replication. Following membrane fusion, the viral capsid (CA) lattice, which forms the outer face of the retroviral core, makes numerous interactions with cellular proteins that orchestrate the progress of HIV-1 through the replication cycle. The ability of CA to interact with nuclear pore proteins and other host factors around the nuclear pore determines whether nuclear entry occurs. Uncoating, the process by which the CA lattice opens and/or disassembles, is another critical step that must occur prior to integration. Both early and delayed uncoating have detrimental effects on viral infectivity. How uncoating relates to nuclear entry is currently hotly debated. Recent technological advances have led to intense discussions about the timing, location, and requirements for uncoating and have prompted the field to consider alternative uncoating scenarios that presently focus on uncoating at the nuclear pore and within the nuclear compartment. This review describes recent advances in the study of HIV-1 nuclear entry, outlines the interactions of the retroviral CA protein, and discusses the challenges of investigating HIV-1 uncoating.

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PF74 Inhibits HIV-1 Integration by Altering the Composition of the Preintegration Complex

Journal of Virology ◽

10.1128/jvi.01741-18 ◽

2018 ◽

Vol 93 (6) ◽

Cited By ~ 11

Author(s):

Muthukumar Balasubramaniam ◽

Jing Zhou ◽

Amma Addai ◽

Phillip Martinez ◽

Jui Pandhare ◽

...

Keyword(s):

Reverse Transcription ◽

Integrase Inhibitor ◽

Antiviral Effect ◽

Inhibitory Effect ◽

Clear Understanding ◽

Nuclear Entry ◽

Preintegration Complex ◽

Gradient Based ◽

Hiv 1

ABSTRACTThe HIV-1 capsid protein (CA) facilitates reverse transcription and nuclear entry of the virus. However, CA’s role in post-nuclear entry steps remains speculative. We describe a direct link between CA and integration by employing the capsid inhibitor PF74 as a probe coupled with the biochemical analysis of HIV-1 preintegration complexes (PICs) isolated from acutely infected cells. At a low micromolar concentration, PF74 potently inhibited HIV-1 infection without affecting reverse transcription. Surprisingly, PF74 markedly reduced proviral integration owing to inhibition of nuclear entry and/or integration. However, a 2-fold reduction in nuclear entry by PF74 did not quantitatively correlate with the level of antiviral activity. Titration of PF74 against the integrase inhibitor raltegravir showed an additive antiviral effect that is dependent on a block at the post-nuclear entry step. PF74’s inhibitory effect was not due to the formation of defective viral DNA ends or a delay in integration, suggesting that the compound inhibits PIC-associated integration activity. Unexpectedly, PICs recovered from cells infected in the presence of PF74 exhibited elevated integration activity. PF74’s effect on PIC activity is CA specific since the compound did not increase the integration activity of PICs of a PF74-resistant HIV-1 CA mutant. Sucrose gradient-based fractionation studies revealed that PICs assembled in the presence of PF74 contained lower levels of CA, suggesting a negative association between CA and PIC-associated integration activity. Finally, the addition of a CA-specific antibody or PF74 inhibited PIC-associated integration activity. Collectively, our results demonstrate that PF74’s targeting of PIC-associated CA results in impaired HIV-1 integration.IMPORTANCEAntiretroviral therapy (ART) that uses various combinations of small molecule inhibitors has been highly effective in controlling HIV. However, the drugs used in the ART regimen are expensive, cause side effects, and face viral resistance. The HIV-1 CA plays critical roles in the virus life cycle and is an attractive therapeutic target. While currently there is no CA-based therapy, highly potent CA-specific inhibitors are being developed as a new class of antivirals. Efforts to develop a CA-targeted therapy can be aided through a clear understanding of the role of CA in HIV-1 infection. CA is well established to coordinate reverse transcription and nuclear entry of the virus. However, the role of CA in post-nuclear entry steps of HIV-1 infection is poorly understood. We show that a CA-specific drug PF74 inhibits HIV-1 integration revealing a novel role of this multifunctional viral protein in a post-nuclear entry step of HIV-1 infection.

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PF74 Reinforces the HIV-1 Capsid To Impair Reverse Transcription-Induced Uncoating

Journal of Virology ◽

10.1128/jvi.00845-18 ◽

2018 ◽

Vol 92 (20) ◽

Cited By ~ 21

Author(s):

Sanela Rankovic ◽

Ruben Ramalho ◽

Christopher Aiken ◽

Itay Rousso

Keyword(s):

Atomic Force Microscopy ◽

Small Molecule ◽

Reverse Transcription ◽

Direct Evidence ◽

Main Body ◽

Force Microscopy ◽

The Core ◽

Atomic Force ◽

Capsid Stability ◽

Hiv 1

ABSTRACTThe RNA genome of human immunodeficiency virus type 1 (HIV-1) is enclosed in a cone-shaped capsid shell that disassembles following cell entry via a process known as uncoating. During HIV-1 infection, the capsid is important for reverse transcription and entry of the virus into the target cell nucleus. The small molecule PF74 inhibits HIV-1 infection at early stages by binding to the capsid and perturbing uncoating. However, the mechanism by which PF74 alters capsid stability and reduces viral infection is presently unknown. Here, we show, using atomic force microscopy (AFM), that binding of PF74 to recombinant capsid-like assemblies and to HIV-1 isolated cores stabilizes the capsid in a concentration-dependent manner. At a PF74 concentration of 10 μM, the mechanical stability of the core is increased to a level similar to that of the intrinsically hyperstable capsid mutant E45A. PF74 also prevented the complete disassembly of HIV-1 cores normally observed during 24 h of reverse transcription. Specifically, cores treated with PF74 only partially disassembled: the main body of the capsid remained intact and stiff, and a cap-like structure dissociated from the narrow end of the core. Moreover, the internal coiled structure that was observed to form during reverse transcriptionin vitropersisted throughout the duration of the measurement (∼24 h). Our results provide direct evidence that PF74 directly stabilizes the HIV-1 capsid lattice, thereby permitting reverse transcription while interfering with a late step in uncoating.IMPORTANCEThe capsid-binding small molecule PF74 inhibits HIV-1 infection at early stages and perturbs uncoating. However, the mechanism by which PF74 alters capsid stability and reduces viral infection is presently unknown. We recently introduced time-lapse atomic force microscopy to study the morphology and physical properties of HIV-1 cores during the course of reverse transcription. Here, we apply this AFM methodology to show that PF74 prevented the complete disassembly of HIV-1 cores normally observed during 24 h of reverse transcription. Specifically, cores with PF74 only partially disassembled: the main body of the capsid remained intact and stiff, but a cap-like structure dissociated from the narrow end of the core HIV-1. Our result provides direct evidence that PF74 directly stabilizes the HIV-1 capsid lattice.

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HIV-1 uncoats in the nucleus near sites of integration

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1920631117 ◽

2020 ◽

Vol 117 (10) ◽

pp. 5486-5493 ◽

Cited By ~ 38

Author(s):

Ryan C. Burdick ◽

Chenglei Li ◽

MohamedHusen Munshi ◽

Jonathan M. O. Rawson ◽

Kunio Nagashima ◽

...

Keyword(s):

Reverse Transcription ◽

Nuclear Import ◽

Host Protein ◽

Productive Infection ◽

Protein Cleavage ◽

Integration Sites ◽

Specificity Factor ◽

Infected Cells ◽

Viral Dna Integration ◽

Hiv 1

HIV-1 capsid core disassembly (uncoating) must occur before integration of viral genomic DNA into the host chromosomes, yet remarkably, the timing and cellular location of uncoating is unknown. Previous studies have proposed that intact viral cores are too large to fit through nuclear pores and uncoating occurs in the cytoplasm in coordination with reverse transcription or at the nuclear envelope during nuclear import. The capsid protein (CA) content of the infectious viral cores is not well defined because methods for directly labeling and quantifying the CA in viral cores have been unavailable. In addition, it has been difficult to identify the infectious virions because only one of ∼50 virions in infected cells leads to productive infection. Here, we developed methods to analyze HIV-1 uncoating by direct labeling of CA with GFP and to identify infectious virions by tracking viral cores in living infected cells through viral DNA integration and proviral DNA transcription. Astonishingly, our results show that intact (or nearly intact) viral cores enter the nucleus through a mechanism involving interactions with host protein cleavage and polyadenylation specificity factor 6 (CPSF6), complete reverse transcription in the nucleus before uncoating, and uncoat <1.5 h before integration near (<1.5 μm) their genomic integration sites. These results fundamentally change our current understanding of HIV-1 postentry replication events including mechanisms of nuclear import, uncoating, reverse transcription, integration, and evasion of innate immunity.

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Mutations altering acetylated residues in the CTD of HIV-1 integrase cause defects in proviral transcription at early times after integration of viral DNA

PLoS Pathogens ◽

10.1371/journal.ppat.1009147 ◽

2020 ◽

Vol 16 (12) ◽

pp. e1009147

Author(s):

Shelby Winans ◽

Stephen P. Goff

Keyword(s):

Life Cycle ◽

Histone Modifications ◽

Reverse Transcription ◽

Integration Site ◽

Viral Dna ◽

Large Defect ◽

Central Function ◽

Site Distribution ◽

Hiv 1

The central function of the retroviral integrase protein (IN) is to catalyze the integration of viral DNA into the host genome to form the provirus. The IN protein has also been reported to play a role in a number of other processes throughout the retroviral life cycle such as reverse transcription, nuclear import and particle morphogenesis. Studies have shown that HIV-1 IN is subject to multiple post-translational modifications (PTMs) including acetylation, phosphorylation and SUMOylation. However, the importance of these modifications during infection has been contentious. In this study we attempt to clarify the role of acetylation of HIV-1 IN during the retroviral life cycle. We show that conservative mutation of the known acetylated lysine residues has only a modest effect on reverse transcription and proviral integration efficiency in vivo. However, we observe a large defect in successful expression of proviral genes at early times after infection by an acetylation-deficient IN mutant that cannot be explained by delayed integration dynamics. We demonstrate that the difference between the expression of proviruses integrated by an acetylation mutant and WT IN is likely not due to altered integration site distribution but rather directly due to a lower rate of transcription. Further, the effect of the IN mutation on proviral gene expression is independent of the Tat protein or the LTR promoter. At early times after integration when the transcription defect is observed, the LTRs of proviruses integrated by the mutant IN have altered histone modifications as well as reduced IN protein occupancy. Over time as the transcription defect in the mutant virus diminishes, histone modifications on the WT and mutant proviral LTRs reach comparable levels. These results highlight an unexpected role for the IN protein in regulating proviral transcription at early times post-integration.

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Cone-shaped HIV-1 capsids are transported through intact nuclear pores

10.1101/2020.07.30.193524 ◽

2020 ◽

Cited By ~ 3

Author(s):

Vojtech Zila ◽

Erica Margiotta ◽

Beata Turonova ◽

Thorsten G. Müller ◽

Christian E. Zimmerli ◽

...

Keyword(s):

Nuclear Import ◽

Light And Electron Microscopy ◽

Productive Infection ◽

Nuclear Pore ◽

Major Health ◽

Replication Complex ◽

Empty Capsid ◽

Immunodeficiency Virus ◽

Subtomogram Averaging ◽

Hiv 1

AbstractHuman immunodeficiency virus (HIV-1) remains a major health threat. Viral capsid uncoating and nuclear import of the viral genome are critical for productive infection. The size of the HIV-1 capsid is generally believed to exceed the diameter of the nuclear pore complex (NPC), indicating that capsid uncoating has to occur prior to nuclear import. Here, we combined correlative light and electron microscopy with subtomogram averaging to capture the structural status of reverse transcription-competent HIV-1 complexes in infected T cells. We demonstrate that the diameter of the NPC in cellulo is sufficient for the import of apparently intact, coneshaped capsids. Subsequent to nuclear import, we detected disrupted and empty capsid fragments, indicating that uncoating of the replication complex occurs by breaking the capsid open, and not by disassembly into individual subunits. Our data directly visualize a key step in HIV-1 replication and enhance our mechanistic understanding of the viral life cycle.

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The HIV-1 capsid core is an opportunistic nuclear import receptor

10.1101/2021.12.02.470925 ◽

2021 ◽

Author(s):

Guangai Xue ◽

Hyun Jae Yu ◽

Shih Lin Goh ◽

Anna T. Gres ◽

Mehmet Hakan Guney ◽

...

Keyword(s):

Nuclear Transport ◽

Host Factors ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

Nuclear Entry ◽

Critical Determinant ◽

Subsequent Work ◽

Biological Assays ◽

Pore Complexes ◽

Hiv 1

The movement of viruses and other large macromolecular cargo through nuclear pore complexes (NPCs) is poorly understood. The human immunodeficiency virus type 1 (HIV-1) provides an attractive model to interrogate this process due to the genetic and cell biological assays to score virus nuclear entry in living cells. Although initial studies of HIV-1 infection of nondividing cells focused on karyophilic virion proteins, subsequent work revealed the viral capsid (CA), the chief structural component of the pre-integration complex (PIC), to be a critical determinant in nuclear transport1. In support of this model, HIV-1 interactions with NPCs can be altered through CA mutation2, which makes direct contact with nucleoporins (Nups)3–5. Here we identify Nup35, Nup153, and POM121 to coordinately support HIV-1 nuclear entry. For Nup35 and POM121, this dependence was strongly dependent cyclophilin A (CypA) interaction with CA. Mutation of CA or removal of soluble host factors changed the interaction with the NPC. Collectively, these findings implicate the HIV-1 CA hexameric lattice that encapsulates the viral genome as a macromolecular nuclear transport receptor (NTR) that exploits soluble host factors to modulate NPC requirements during nuclear invasion.

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