LuSIV Cells: A Reporter Cell Line for the Detection and Quantitation of a Single Cycle of HIV and SIV Replication

AbstractA single cycle of viral replication is the time required for a virus to enter the host cell, replicate its genome, and produce infectious progeny virions. The primate lentiviruses, human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), require on average 24 h to complete one cycle of replication. We have now developed and characterized a reporter assay system in CEMx174 cells for the quantitative measurement of HIV/SIV infection within a single replication cycle. The SIVmac239 LTR (−225 → +149) was cloned upstream of the firefly luciferase reporter gene and this reporter plasmid is maintained in CEMx174 cells under stable selection. This cell line, designated LuSIV, is highly sensitive to infection by primary and laboratory strains of HIV/SIV, resulting in Tat-mediated expression of luciferase, which correlates with viral infectivity. Furthermore, manipulation of LuSIV cells for the detection of luciferase activity is easy to perform and requires a minimal amount of time as compared to current HIV/SIV detection systems. The LuSIV system is a powerful tool for the analysis of HIV/SIV infection that provides a unique assay system that can detect virus replication prior to 24 h and does not require virus to spread from cell to cell. Thus these cells can be used for the study of replication-deficient viruses and the high throughput screening of antivirals, or other inhibitors of infection

Exosomes and HIV Gag bud from endosome-like domains of the T cell plasma membrane

Exosomes are secreted, single membrane organelles of ∼100 nm diameter. Their biogenesis is typically thought to occur in a two-step process involving (1) outward vesicle budding at limiting membranes of endosomes (outward = away from the cytoplasm), which generates intralumenal vesicles, followed by (2) endosome–plasma membrane fusion, which releases these internal vesicles into the extracellular milieu as exosomes. In this study, we present evidence that certain cells, including Jurkat T cells, possess discrete domains of plasma membrane that are enriched for exosomal and endosomal proteins, retain the endosomal property of outward vesicle budding, and serve as sites of immediate exosome biogenesis. It has been hypothesized that retroviruses utilize the exosome biogenesis pathway for the formation of infectious particles. In support of this, we find that Jurkat T cells direct the key budding factor of HIV, HIV Gag, to these endosome-like domains of plasma membrane and secrete HIV Gag from the cell in exosomes

Caveolin-1 suppresses Human Immunodeficiency virus-1 replication by inhibiting acetylation of NF-κB

AbstractCaveolin-1 is an integral membrane protein primarily responsible for the formation of membrane structures known as caveolae. Caveolae are specialized lipid rafts involved in protein trafficking, cholesterol homeostasis, and a number of signaling functions. It has been demonstrated that caveolin-1 suppresses HIV-1 protein expression. We found that co-transfecting cells with HIV-1 and caveolin-1 constructs, results in a marked decrease in the level of HIV-1 transcription relative to cells transfected with HIV-1 DNA alone. Correspondingly, reduction of endogenous caveolin-1 expression by siRNA-mediated silencing resulted in an enhancement of HIV-1 replication. Further, we observed a loss of caveolin-mediated suppression of HIV-1 transcription in promoter studies with reporters containing mutations in the NF-κB binding site. Our analysis of the posttranslational modification status of the p65 subunit of NF-κB demonstrates hypoacetylation of p65 in the presence of caveolin-1. Since hypoacetylated p65 has been shown to inhibit transcription, we conclude that caveolin-1 inhibits HIV-1 transcription through a NF-κB-dependent mechanism

Vaginal transmission of cell-associated HIV-1 in the mouse is blocked by a topical, membrane-modifying agent

Because both HIV-1 virions and HIV-infected cells are present in the semen and cervical mucus of infected individuals, HIV-1 prevention strategies must consider both cell-free and cell-associated virus. Antibodies that target HIV-1 virions have been shown to prevent vaginal transmission of cell-free virus in macaques, but since cell-associated transmission has not been reliably demonstrated in this model system, no strategies to prevent such transmission have been tested. We have employed a mouse model in which SCID mice carry human peripheral blood leukocytes (HuPBLs). In these mice, vaginal transmission of cell-associated, but not cell-free, HIV-1 transmission occurs, mediated by transepithelial migration of HIV-infected cells. Topical application of β-cyclodextrin (β-CD), a cholesterol-sequestering agent that interferes with cell migration and budding of virus from lipid rafts, blocks transmission of cell-associated HIV-1. The HuPBL-SCID model of vaginal HIV-1 transmission should prove useful for investigating cell-associated HIV-1 transmucosal HIV-1 transmission, as well as for screening reagents for their potential efficacy in preventing sexual HIV-1 transmission

The Conserved Set of Host Proteins Incorporated into HIV‑1 Virions Suggests a Common Egress Pathway in Multiple Cell Types

HIV-1 incorporates a large array of host proteins into virions. Determining the host protein composition in HIV virions has technical difficulties, including copurification of microvesicles. We developed an alternative purification technique using cholesterol that differentially modulates the density of virions and microvesicles (density modification, DM) allowing for high-yield virion purification that is essential for tandem mass spectrometric and quantitative proteomic (iTRAQ) analysis. DM purified virions were analyzed using iTRAQ and validated against Optiprep (60% iodixanol) purified virions. We were able to characterize host protein incorporation in DM-purified HIV particles derived from CD4+ T-cell lines; we compared this data set to a reprocessed data set of monocyte-derived macrophages (MDM) derived HIV-1 using the same bioinformatics pipeline. Seventy-nine clustered proteins were shared between the MDM derived and T-cell derived data set. These clusters included an extensive collection of actin isoforms, HLA proteins, chaperones, and a handful of other proteins, many of which have previously been documented to interact with viral proteins. Other proteins of note were ERM proteins, the dynamin domain containing protein EH4, a phosphodiesterase, and cyclophilin A. As these proteins are incorporated in virions produced in both cell types, we hypothesize that these proteins may have direct interactions with viral proteins or may be important in the viral life cycle. Additionally, identified common set proteins are predicted to interact with >1000 related human proteins. Many of these secondary interacting proteins are reported to be incorporated into virions, including ERM proteins and adhesion molecules. Thus, only a few direct interactions between host and viral proteins may dictate the host protein composition in virions. Ultimately, interaction and expression differences in host proteins between cell types may drive virion phenotypic diversity, despite conserved viral protein–host protein interactions between cell types