Browsing by Subject "HTLV-1"

Now showing 1 - 3 of 3
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    Establishment of Human Retrovirus Particle Assembly Sites
    (2022-12) Schilling, Daniel
    Human immunodeficiency virus (HIV) currently infects about 37 million people globally and has led to over 35 million deaths since its emergence in the human population by causing acquired immunodeficiency syndrome (AIDS). HIV type 1 (HIV-1) is responsible for the AIDS pandemic). HIV-1 spreads by intravenous drug use, sexual contact, blood transfusions, breastfeeding). Virus particle assembly is a foundationally important aspect in all modes of infectious spread and virus transmission. Comparative analyses with closely related human retroviruses can be particularly informative when studying areas including virus particle assembly and host-cell interactions that influence this process – which represents an important knowledge gap in the field. In preliminary studies, our collaborative research team has observed that the actin cortex can act as physical barrier for HIV-1 Gag recruitment to the plasma membrane (PM), particularly retroviral Gag-genomic RNA (gRNA) complexes. The actin cortex is functioning as a non-specific barrier that limits potential virus assembly sites on the PM. Here, in this fellowship application, experiments are proposed to gain further insights into the fundamental aspects of how virus-host cell interactions establish virus particle assembly sites. First, studies are proposed to investigate virus assembly sites in the context of the actin cortex. Multiple experimental approaches with be used to test the hypothesis that the actin cortex acts as a physical barrier for Gag-gRNA complexes, including comparative analyses in the context of cell-cell contact and using closely related human retroviruses. Second, I propose to investigate the role of the tumor suppressor adenomatous polyposis coli (APC) protein enrichment at virus particle assembly sites, testing the hypothesis that APCs interaction with the Gag protein helps to stabilize the Gag lattice and enhance the efficiency of Gag puncta biogenesis and gRNA recruitment. Comparative analyses will be leveraged to understand how APC may rely on interactions with actin filaments and play a more significant role during virus particle assembly at cell-cell contacts. Together, these studies will provide new insights into HIV-1 particle assembly, and advance knowledge in this crucial aspect of virus replication.
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    Studies on the Assembly and Morphology of Human T-Cell Leukemia Virus Type 1
    (2019-08) Maldonado-Ortiz, José
    The group-specific antigen (Gag) polyprotein is an essential retrovirus structural protein required for the assembly and release of virus particles. Present knowledge of Gag biology has been limited to a few retroviruses. Furthermore, current understanding of the diversity in the nature of Gag structure and function in virus particle assembly is limited. Human T-cell leukemia virus type 1 (HTLV-1) is a deltaretrovirus that causes an adult T-cell leukemia/lymphoma (ATLL), HTLV-1-associated-myelopathy/tropical spastic paraparesis (HAM/TSP), and other neurotropic conditions. HTLV-1 has infected approximately 15 million individuals worldwide. A general knowledge gap exists regarding the details of HTLV-1 replication, including particle assembly. To address this, and to test the overarching hypothesis that HTLV-1 particle assembly is distinct from that of other retroviruses, this dissertation focused on investigating three key aspects of HTLV-1 immature and mature particle morphology. First, an analysis of the morphology and Gag stoichiometry of HTLV-1-like particles and authentic, mature HTLV-1 particles by using cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission electron microscopy (STEM) was conducted. HTLV-1-like particles mimicked the morphology of immature authentic HTLV-1 virions. Importantly, it was observed for the first time that the morphology of these virus-like particles (VLPs) has the unique local feature of a flat Gag lattice that does not follow the curvature of the viral membrane, resulting in an enlarged distance between the Gag lattice and the viral membrane. Measurement of the average size and mass of VLPs and authentic HTLV-1 particles suggested a consistent range of size and Gag copy numbers in these two groups of particles. The unique local flat Gag lattice morphological feature observed suggests that HTLV-1 Gag could be arranged in a lattice structure that is distinct from that of other retroviruses characterized to date. Second, the effects of Gag proteins labeled at the carboxy terminus with a fluorophore protein were analyzed for their influence on particle morphology. In particular, a HTLV-1 Gag expression construct with the yellow fluorescence protein (YFP) fused to the carboxy-terminus was used as a surrogate for the HTLV-1 Gag-Pro to assess the effects of co-packaging of Gag and a Gag-YFP on virus-like particle morphology and particles were analyzed by cryo-TEM. STEM and fluorescence fluctuation spectroscopy (FFS) were also used to determine the Gag stoichiometry. Ratios of 3:1 (Gag:Gag-YFP) or greater were found to result in a particle morphology indistinguishable from that of VLPs produced with the untagged HTLV-1 Gag, i.e., a mean diameter of ~113 nm and a mass of 220 MDa as determined by cryo-TEM and STEM, respectively. This information is useful for the quantitative analysis of Gag-Gag interactions that occur during virus particle assembly and in released immature particles. Third, cryo-electron tomography (cryo-ET) was used to analyze mature HTLV-1 particle morphology. Particles produced from MT-2 cells were polymorphic, roughly spherical, and varied in size. Capsid cores, when present, were typically poorly defined polyhedral structures with at least one curved region contacting the inner face of the viral membrane. Most of the particles observed lacked a defined capsid core, which likely impacts HTLV-1 particle infectivity. Taken together, the findings of this dissertation provide new insights into the nature of immature and mature HTLV-1 assembly and morphology and provide foundational knowledge towards an advanced understanding of the HTLV particle assembly pathway.
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    Studies on the Molecular Determinants of Human Retrovirus Diversity
    (2021-09) Meissner, Morgan
    The human immunodeficiency viruses (HIVs) are two species (HIV type 1, HIV-1; HIV type 2, HIV-2) in the Lentivirus genus of the Retroviridae family of viruses and are the etiological agents of acquired immunodeficiency syndrome (AIDS). Nearly 75 million people have been infected with HIV-1 and HIV-2 since their emergence in the human population and they are responsible for the deaths of almost 32 million individuals to date. One of the key drivers of the HIV-1 pandemic is the extreme genetic diversity of the virus, which drives the development of antiviral drug resistance and frustrates vaccine development. Retroviruses also exhibit considerable structural diversity, which may have important implications for infectivity and replication. Human T-cell leukemia virus type 1 (HTLV-1), within the Deltaretrovirus genus, is also a major pathogenic human retrovirus. HIV-2 and HTLV-1 exhibit markedly reduced rates of transmissibility and potentially evolution compared with HIV-1 and are therefore understudied relative to their pandemic counterpart. The overarching goal of this thesis was to characterize the viral and cellular determinants of the molecular diversity of human retroviruses, with an emphasis on HTLV-1 and HIV-2. To this end, experiments were conducted which 1) characterized the structural diversity of authentic HTLV-1 particles derived from the chronically infected SP cell line, demonstrating that intact capsid cores are relatively rare among HTLV-1 particles; and 2) examined the contribution of host apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) proteins to HIV-2 mutagenesis, which revealed that despite their role as potent mutagens of HIV-1, APOBEC3-mediated mutagenesis of HIV-2 is limited. Additionally, a user-friendly sequence analysis workflow was developed that enables the ultra-accurate detection of mutations within HIV-1 and HIV-2, which reduces the background error rate of traditional Illumina next-generation sequencing by approximately 100-fold. This workflow is already being employed to characterize the contributions of additional cellular proteins to retroviral mutagenesis, including the host protein SAM domain and HD domain- containing protein 1 (SAMHD1). Taken together, these studies provide new insights into the structural and genetic diversity of human retroviruses, particularly those which have historically been poorly characterized and underappreciated.