Showing papers by "Bryan R. Cullen published in 2001"
TL;DR: It is demonstrated that NXF3, a human RNA binding protein related to TAP, lacks a carboxy-terminal domain yet retains the ability to export tethered RNA transcripts and to shuttle between the nucleus and the cytoplasm.
112 citations
TL;DR: This brief overview of the strategies used by viruses to transport their genomes into the nuclei of target cells reveals that there are considerable differences in detail, but it appears clear that drugs that could stabilize the virion structure and interfere with nuclear entry of the viral genome, would potentially be effective inhibitors of viral replication.
94 citations
TL;DR: It is concluded that the laboratory C XCR4-tropic HIV-1 isolate exhibits a significantly higher CXCR4 requirement for efficient infection than do the primary CX CR4- tropic isolates and that this difference can explain the poor ability of the laboratory HIV- 1 isolate to replicate in primary macrophages.
Abstract: Laboratory isolates of human immunodeficiency virus type 1 (HIV-1) that utilize CXCR4 as a coreceptor infect primary human macrophages inefficiently even though these express a low but detectable level of cell surface CXCR4. In contrast, infection of primary macrophages by primary CXCR4-tropic HIV-1 isolates is readily detectable. Here, we provide evidence suggesting that this difference in cell tropism results from a higher requirement for cell surface CXCR4 for infection by laboratory HIV-1 isolates. Transfected COS7 cells that express a high level of CD4 but a low level of CXCR4 were infected significantly more efficiently by two primary CXCR4-tropic HIV-1 isolates compared to the prototypic laboratory HIV-1 isolate IIIB. More importantly, overexpression of either wild-type or signaling-defective CXCR4 on primary macrophages dramatically enhanced the efficiency of infection by the laboratory HIV-1 isolate yet only modestly enhanced infection by either primary CXCR4-tropic virus. Overexpression of CD4 had, in contrast, only a limited effect on macrophage infection by the laboratory HIV-1, although infection by the primary isolates was markedly enhanced. We therefore conclude that the laboratory CXCR4-tropic HIV-1 isolate exhibits a significantly higher CXCR4 requirement for efficient infection than do the primary CXCR4-tropic isolates and that this difference can explain the poor ability of the laboratory HIV-1 isolate to replicate in primary macrophages. More generally, we propose that the cell tropisms displayed by different strains of HIV-1 in culture can largely be explained on the basis of differential requirements for cell surface CD4 and/or coreceptor expression levels.
93 citations
TL;DR: It is shown that deletion of the R region has little effect on gag mRNA levels but that R deletions that would be predicted to leave thepol 5′ splice site intact nevertheless inhibit the production of the spliced pol mRNA, implying that the HFV R region acts in the nucleus to modify the cytoplasmic fate of target HFV mRNA.
Abstract: It has been suggested that sequences located within the 5′ noncoding region of human foamy virus (HFV) are critical for expression of the viral Gag and Pol structural proteins. Here, we identify a discrete ∼151-nucleotide sequence, located within the R region of the HFV long terminal repeat, that activates HFV Gag and Pol expression when present in the 5′ noncoding region but that is inactive when inverted or when placed in the 3′ noncoding region. Sequences that are critical for the expression of both Gag and Pol include not only the 5′ splice site positioned at +51 in the R region, which is used to generate the spliced pol mRNA, but also intronic R sequences located well 3′ to this splice site. Analysis of total cellular gag and pol mRNA expression demonstrates that deletion of the R region has little effect on gag mRNA levels but that R deletions that would be predicted to leave the pol 5′ splice site intact nevertheless inhibit the production of the spliced pol mRNA. Gag expression can be largely rescued by the introduction of an intron into the 5′ noncoding sequence in place of the R region but not by an intron or any one of several distinct retroviral nuclear RNA export sequences inserted into the mRNA 3′ noncoding sequence. Neither the R element nor the introduced 5′ intron markedly affects the cytoplasmic level of HFV gag mRNA. The poor translational utilization of these cytoplasmic mRNAs when the R region is not present in cis also extended to a cat indicator gene linked to an internal ribosome entry site introduced into the 3′ noncoding region. Together these data imply that the HFV R region acts in the nucleus to modify the cytoplasmic fate of target HFV mRNA. The close similarity between the role of the HFV R region revealed in this study and previous data (M. Butsch, S. Hull, Y. Wang, T. M. Roberts, and K. Boris-Lawrie, J. Virol. 73:4847–4855, 1999) demonstrating a critical role for the R region in activating gene expression in the unrelated retrovirus spleen necrosis virus suggests that several distinct retrovirus families may utilize a common yet novel mechanism for the posttranscriptional activation of viral structural protein expression.
28 citations
TL;DR: Changing a single residue in quail Tap, glutamine 246, to arginine, the residue found in human Tap, rescues both CTE function and CTE binding, emphasize the potential importance of cross-species genetic complementation in the identification and characterization of cellular factors that are critical for different aspects of viral replication.
Abstract: The Tap protein mediates the sequence-specific nuclear export of mRNAs bearing the retroviral constitutive transport element (CTE) and also plays a critical role in the sequence nonspecific export of cellular mRNAs. Previously, we have demonstrated that CTE function displays species specificity, that is, the CTE functions in human but not quail cells. Here, we demonstrate that quail Tap fails to support CTE function because it cannot bind the CTE. However, changing a single residue in quail Tap, glutamine 246, to arginine, the residue found in human Tap, rescues both CTE function and CTE binding. This residue, which is located on the exterior of a recently reported molecular structure of Tap, defines a surface on Tap that is critical for CTE binding. These data emphasize the potential importance of cross-species genetic complementation in the identification and characterization of cellular factors that are critical for different aspects of viral replication.
26 citations
TL;DR: Identification of HIV-1 variants capable of entering T cells via the CD8 receptor suggests a new mode of viral pathogenesis, but are these variants rare, aberrant viruses or a real problem?
Abstract: Identification of HIV-1 variants capable of entering T cells via the CD8 receptor suggests a new mode of viral pathogenesis. But are these variants rare, aberrant viruses or a real problem?
11 citations