During uncoating, the conical capsid of HIV disassembles by dissociation of the p24 capsid protein (CA). Uncoating is known to be required for HIV replication, but the mechanism is poorly defined. Here, we examined the timing and effect of two capsid binding drugs (PF74 and BI2) on infectivity and capsid integrity in HIV-1-infected cells. The virus remained susceptible to the action of PF74 and BI2 for hours after uncoating as defined in parallel drug addition and cyclosporine (CsA) washout assays to detect the kinetics of drug susceptibility and uncoating, respectively. Resistance mutations in CA decreased the potency of these compounds, demonstrating that CA is the target of drug action. However, neither drug altered capsid integrity in a fluorescence microscopy-based assay. These data suggest that PF74 and BI2 do not alter HIV-1 uncoating but rather affect a later step in viral replication. Because both drugs bind CA, we hypothesized that a residual amount of CA associates with the viral complex after the loss of the conical capsid to serve as a target for these drugs. Superresolution structured illumination microscopy (SIM) revealed that CA localized to viral complexes in the nuclei of infected cells. Using image quantification, we determined that viral complexes localized in the nucleus displayed a smaller amount of CA than complexes at the nuclear membrane, in the cytoplasm, or in controls. Collectively, these data suggest that a subset of CA remains associated with the viral complex after uncoating and that this residual CA is the target of PF74 and BI2. IMPORTANCEThe HIV-1 capsid is a target of interest for new antiviral therapies. This conical capsid is composed of monomers of the viral CA protein. During HIV-1 replication, the capsid must disassemble by a poorly defined process called uncoating. CA has also been implicated in later steps of replication, including nuclear import and integration. In this study, we used cell-based assays to examine the effect of two CA binding drugs (PF74 and BI2) on viral replication in infected cells. HIV-1 was susceptible to both drugs for hours after uncoating, suggesting that these drugs affect later steps of viral replication. High-resolution structured illumination microscopy (SIM) revealed that a subset of CA localized to viral complexes in the nuclei of cells. Collectively, these data suggest that a subset of CA remains associated with the viral complex after uncoating, which may facilitate later steps of viral replication and serve as a drug target. Monomers of the viral capsid protein (CA) are arranged in a hexameric lattice to form the conical capsid of HIV-1. This structure contains the viral RNAs and associated viral proteins and is released into the cytoplasm of the cell after viral fusion. For the viral genome to ultimately integrate, the conical capsid must disassemble by a process called uncoating. During this time, in the reverse transcription complex (RTC) the viral RNA genome is reverse transcribed into double-stranded DNA. Once reverse transc...

The majority of new HIV infections occur in women as a result of heterosexual intercourse, overcoming multiple innate barriers to infection within the mucosa. However, the avenues through which infection is established, and the nature of bottlenecks to transmission, have been the source of considerable investigation and contention. Using a high dose of a single round non-replicating SIV-based vector containing a novel dual reporter system, we determined the sites of infection by the inoculum using the rhesus macaque vaginal transmission model. Here we show that the entire female reproductive tract (FRT), including the vagina, ecto- and endocervix, along with ovaries and local draining lymph nodes can contain transduced cells only 48 hours after inoculation. The distribution of infection shows that virions quickly disseminate after exposure and can access target cells throughout the FRT, with an apparent preference for infection in squamous vaginal and ectocervical mucosa. JRFL enveloped virions infect diverse CD4 expressing cell types, with T cells resident throughout the FRT representing the primary target. These findings establish a new perspective that the entire FRT is susceptible and virus can reach as far as the ovary and local draining lymph nodes. Based on these findings, it is essential that protective mechanisms for prevention of HIV acquisition must be present at protective levels throughout the entire FRT to provide complete protection.

After viral fusion with the cell membrane, the conical capsid of HIV-1 disassembles by a process called uncoating. We recently utilized the cyclosporine (CsA) washout assay, in which TRIM-CypA-mediated restriction of viral replication is used to detect the state of the viral capsid, to study the kinetics of uncoating in HIV-1-infected cells. Here we have extended this analysis to examine the effects of p24 capsid protein (p24 CA ) mutations and cellular environment on the kinetics of uncoating in infected cells. We found that p24 CA mutations can significantly increase (A92E), delay (E45A and N74D), or have no effect (G94D) on the rate of uncoating and that these alterations are not due to changes in reverse transcription. Inhibition of reverse transcription delayed uncoating kinetics to an extent similar to that of the wild-type virus with all the p24 CA mutant viruses tested. In addition, we observed differences in uncoating in two cell lines, which suggests that the cellular environment can differentially impact the disassembly of wild-type and mutant capsids. Collectively, these experiments suggest that viral and cellular factors are important for the process of uncoating. Finally, these data support the model whereby early steps in reverse transcription facilitate HIV-1 uncoating. IMPORTANCEThe HIV-1 capsid is a cone-shaped structure, composed of the HIV-1-encoded protein p24 CA , which contains the viral RNA and other proteins needed for infection. After the virus enters a target cell, this capsid must disassemble by a process called uncoating. Uncoating is required for HIV-1 infection to progress, but the details of how this process occurs is not known. In this study, we used an in vivo assay to examine the uncoating process in HIV-1-infected cells. We determined that p24 CA mutations could increase or decrease the rate of uncoating and that this rate varied in different cell lines. We also found that reverse transcription of the viral RNA altered the process of uncoating before the p24 CA mutations. Collectively, these experiments provide a better understanding of how viral and cellular factors are involved with a poorly understood step in HIV-1 infection.

To gain insight into female-to-male HIV sexual transmission and how male circumcision protects against this mode of transmission, we visualized HIV-1 interactions with foreskin and penile tissues in ex vivo tissue culture and in vivo rhesus macaque models utilizing epifluorescent microscopy. 12 foreskin and 14 cadaveric penile specimens were cultured with R5-tropic photoactivatable (PA)-GFP HIV-1 for 4 or 24 hours. Tissue cryosections were immunofluorescently imaged for epithelial and immune cell markers. Images were analyzed for total virions, proportion of penetrators, depth of virion penetration, as well as immune cell counts and depths in the tissue. We visualized individual PA virions breaching penile epithelial surfaces in the explant and macaque model. Using kernel density estimated probabilities of localizing a virion or immune cell at certain tissue depths revealed that interactions between virions and cells were more likely to occur in the inner foreskin or glans penis (from local or cadaveric donors, respectively). Using statistical models to account for repeated measures and zero-inflated datasets, we found no difference in total virions visualized at 4 hours between inner and outer foreskins from local donors. At 24 hours, there were more virions in inner as compared to outer foreskin (0.0495 +/− 0.0154 and 0.0171 +/− 0.0038 virions/image, p = 0.001). In the cadaveric specimens, we observed more virions in inner foreskin (0.0507 +/− 0.0079 virions/image) than glans tissue (0.0167 +/− 0.0033 virions/image, p<0.001), but a greater proportion was seen penetrating uncircumcised glans tissue (0.0458 +/− 0.0188 vs. 0.0151 +/− 0.0100 virions/image, p = 0.099) and to significantly greater mean depths (29.162 +/− 3.908 vs. 12.466 +/− 2.985 μm). Our in vivo macaque model confirmed that virions can breach penile squamous epithelia in a living model. In summary, these results suggest that the inner foreskin and glans epithelia may be important sites for HIV transmission in uncircumcised men.

Influenza A virus (IAV) replicates in the upper respiratory tract of humans at 33 °C and in the intestinal tract of birds at close to 41 °C. The viral RNA polymerase complex comprises three subunits (PA, PB1 and PB2) and plays an important role in host adaptation. We therefore developed an in vitro system to examine the temperature sensitivity of IAV RNA polymerase complexes from different origins. Complexes were prepared from human lung epithelial cells (A549) using a novel adenoviral expression system. Affinity-purified complexes were generated that contained either all three subunits (PA/PB1/PB2) from the A/Viet/1203/04 H5N1 virus (H/H/H) or the A/WSN/33 H1N1 strain (W/W/W). We also prepared chimeric complexes in which the PB2 subunit was exchanged (H/H/W, W/W/H) or substituted with an avian PB2 from the A/chicken/Nanchang/3-120/01 H3N2 strain (W/W/N). All complexes were functional in transcription, cap-binding and endonucleolytic activity. Complexes containing the H5N1 or Nanchang PB2 protein retained transcriptional activity over a broad temperature range (30–42 °C). In contrast, complexes containing the WSN PB2 protein lost activity at elevated temperatures (39 °C or higher). The E627K mutation in the avian PB2 was not required for this effect. Finally, the avian PB2 subunit was shown to confer enhanced stability to the WSN 3P complex. These results show that PB2 plays an important role in regulating the temperature optimum for IAV RNA polymerase activity, possibly due to effects on the functional stability of the 3P complex.