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L Ratner

Publications and source records attributed to L Ratner.

At least 37 records · Page 2Linked to original sources
PubMed1996

Sequence heterogeneity of Nef transcripts in HIV-1-infected subjects at different stages of disease.

Nef transcripts were analyzed from peripheral blood mononuclear cells of 10 HIV-1-infected subjects with 9-822 CD4+ lymphocytes/cu mm, including 4 individuals with a probable common source infection. There was no relationship between the phylogenetic position of the various nef sequences and the disease state of the person from whom they were derived. The nef open reading frame was disrupted in all three clones from only 1 subject. Functional analyses of a representative clone from each of the remaining 9 subjects showed that all nef alleles were capable of CD4 cell surface down-regulation, but only three nef alleles suppressed the induction of IL-2 transcription.

Amino Acid Sequence↗
PubMed1996

c-sis/PDGF-B promoter transactivation by the Yax protein of human T-cell leukemia virus type 1.

The human c-sis proto-oncogene promoter is transactivated by the human T-cell leukemia virus type 1 Tax protein in human Jurkat T-cells. Transactivation was >7-fold in Jurkat cells stably expressing the Tax protein (Jurkat-Tax) than in Jurkat E6.1 cells and was further enhanced in Jurkat-Tax cells stimulated with 12-O-tetradecanoylphorbol-13-acetate and the calcium ionophore, ionomycin. Deletion analysis showed that a 167-base pair promoter fragment retained full Tax responsiveness. Insertion of this minimal Tax-responsive region into a heterologous, minimal promoter resulted in approximately a 7-fold increase of transcriptional activation in the presence of Tax. Linker-scanning insertion analysis of this region identified Tax-responsive elements at nucleotides -64 to -45 (TRE1) and -34 to -15 (TATA box region). TRE1 contains a consensus binding site for the Sp family of transcription factors. The TATA box region corresponds to the TATA box and its 3'-neighboring sequence. Gel-shift and antibody supershift analysis of TRE1-binding proteins in unstimulated Jurkat E6.1 and Jurkat-Tax nuclear extracts identified Sp1 and Sp3 as the main TRE1 binding factors. Nuclear extracts from stimulated Jurkat E6.1 and Jurkat-Tax cells identified an additional TRE1 binding factor, Egr-1. These studies define a novel mechanism whereby Tax transactivates the c-sis promoter.

Base Sequence↗
PubMed1996

Virology.

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Animals↗
PubMed1996

Transgenic mouse models for HTLV-I infection.

Human T-cell leukemia virus type I (HTLV-I) was the first human retrovirus isolated and is responsible for at least one form of human leukemia. The pathogenic mechanism(s) whereby HTLV transforms T lymphocytes in vivo is(are) obscure due to its long-term latency and the lack of practical representative animal models. The tax gene of HTLV-I has been implicated in this transformation process because of its ability to transactivate several cellular genes associated with T-cell replication and activation. Here, transgenic mouse models are discussed that express the Tax protein of HTLV-I and provide insights into its role in the cellular transformation process.

Animals↗
PubMed1996

In vitro CD4+ lymphocyte transformation and infection in a rabbit model with a molecular clone of human T-cell lymphotrophic virus type 1.

We transfected human and rabbit peripheral blood mononuclear cells (PBMC) with the ACH molecular clone of human T-cell lymphotropic virus type 1 (HTLV-1) to study its in vitro and in vivo properties. PBMC transfected with ACH were shown to transfer infection to naive PBMC. ACH transformed rabbit PBMC, as indicated by interleukin-2-independent proliferation of a transfectant culture. This transformant culture was shown by flow cytometric analysis to be a CD4+ CD25+ T-lymphocyte population containing, as determined by Southern blot analysis, at least three integrated HTLV-1 proviral copies. HTLV-1 infection was produced in rabbits inoculated with ACH-transfected, irradiated PBMC. Inoculated rabbits seroconverted to positivity for antibodies against HTLV-1 and had steady or rising HTLV-1 enzyme-linked immunosorbent assay antibody titers. Western blot (immunoblot) analysis revealed sustained seroconversion of rabbits to positivity for antibodies against all major viral antigenic determinants. Infection of rabbits was further demonstrated by antigen capture assay of p24 in PBMC and lymph node cultures and PCR amplification of proviral sequences from PBMC. These data suggest that ACH, like wild-type HTLV-1, infects and transforms primary CD4+ T lymphocytes and is infectious in vivo. This clone will facilitate investigations into the role of viral genes on biological properties of HTLV-1 in vitro and in vivo.

Animals↗
PubMed1996

Human immunodeficiency virus type 1 capsid formation in reticulocyte lysates.

The Gag polyprotein of human immunodeficiency virus (HIV) (Pr55Gag) contains sufficient information to direct particle assembly events when expressed within tissue culture cells. HIV Gag proteins normally form particles at a plasma membrane assembly site, in a manner analogous to that of the type C avian and mammalian leukemia/sarcoma viruses. It has not previously been demonstrated that immature HIV capsids can form without budding through an intact cellular membrane. In this study, a rabbit reticulocyte lysate translation reaction was used to recreate HIV capsid formation in vitro. Production of HIV-1 Pr55Gag and of a matrix-deleted Gag construct resulted in the formation of a subset of Gag protein structures with an equilibrium density of 1.15 g/ml. Gel filtration chromatography revealed these Gag protein structures to be larger than 2 x 10(6) Da, consistent with the formation of large multimers or capsids. These Gag protein structures were protease sensitive in the absence of detergent, indicating that they did not contain a complete lipid envelope. Spherical structures were detected by electron microscopy within the reticulocyte lysate reaction mixtures and appeared essentially identical to immature HIV capsids or retrovirus-like particles. These results demonstrate that the HIV Gag protein is capable of producing immature capsids in a cell-free reaction and that such capsids lack a complete lipid envelope.

Animals↗
PubMed1996

Cooperative effects of the human immunodeficiency virus type 1 envelope variable loops V1 and V3 in mediating infectivity for T cells.

Insertion of T-cell line-tropic V3 and V4 loops from the HXB2 strain into the macrophage-tropic YU-2 envelope resulted in a virus with delayed infectivity for HUT78 and Jurkat cells compared with HXB2. Sequence analysis of viral DNA derived from long-term cultures of Jurkat cells revealed a specific mutation that changed a highly conserved Asn residue in the V1 loop of Env to an Asp residue (N-136-->D). Introduction of this mutation into clones containing a T-cell line-tropic V3 loop, either with or without a T-cell line-tropic V4 loop, resulted in viruses that replicated to high levels in Jurkat cells and peripheral blood lymphocytes. The Env proteins from these constructs were expressed with the vaccinia virus/T7 hybrid system and were found to be translated, processed, and cleaved and to bind to soluble CD4 similar to the wild-type HXB2 and YU-2 Env proteins. Env-mediated fusion with HeLa T4+ cells, however, was regulated by both the altered V1 loop and T-cell line-tropic V3 loop. These results suggest that subsequent to the initial gp120-CD4 binding event, a functional interaction can occur between the altered V1 loop and T-cell line-tropic V3 loop that results in infection of Jurkat cells and peripheral blood lymphocytes.

Amino Acid Sequence↗
PubMed1995

Weekly oral etoposide in patients with Kaposi's sarcoma associated with human immunodeficiency virus infection: a phase I multicenter trial of the AIDS Clinical Trials Group.

We conducted a Phase I trial to evaluate the safety, maximally tolerated dose (MTD), antitumor activity, and pharmacology of once-weekly oral etoposide in patients with Kaposi's sarcoma (KS) and AIDS. From September 1990 to October 1991, 27 eligible patients with biopsy-confirmed KS were treated at six etoposide dose levels, ranging from 150 to 400 mg weekly. Patients were treated until their tumor progressed or until unacceptable toxicity developed. On the first day of therapy, etoposide plasma concentrations were measured by high-performance liquid chromatography. The MTD was defined as the etoposide dose that induced reversible grade 3 toxicity in three of six patients during the first 4 weeks. Although dose-limiting toxicity was uncommon during the first 4 weeks of treatment (three of 27 patients), and the MTD was not reached, with longer treatment > 50% of patients developed dose-limiting toxicities, most commonly neutropenia. Responses were observed at all dosage levels (except 350 mg weekly), with partial tumor regression documented in nine (36%) of 25 evaluable patients. There was marked variability in etoposide area under the plasma concentration versus time curve, elimination half-time (t1/2), and urinary excretion. These pharmacokinetic features were not, however, associated with the presence of gastrointestinal symptoms, the severity of side effects, or tumor response. We conclude that weekly oral etoposide can be safely administered to patients with AIDS and KS. The observed antitumor effects over a wide range of doses support further studies with very low and minimally toxic etoposide doses, alone or in combination with other agents.

Acquired Immunodeficiency Syndrome↗
PubMed1995

HIV-1 Nef protein downregulation of CD4 surface expression: relevance of the lck binding domain of CD4.

HIV Nef protein downregulates the surface expression of CD4 on T-cells but its mechanism of activity is unknown. We have analyzed the relevance of different portions of the CD4 molecule with respect to the activity of Nef. Upon transfection of Jurkat T-cells that express Nef or do not express Nef with constructs that include different domains of the CD4 molecule, we demonstrated that Nef downregulation of CD4 requires the first 30 amino acids of the CD4 cytoplasmic tail and that the lck-binding domain of CD4 was at least partially responsible for this effect. Furthermore, upon transfection of U-937 cells with an lck-expressing plasmid we showed that CD4 downregulation by Nef is significantly more efficient when lck is present. Finally, by measuring the rate of CD4 endocytosis by a novel flow cytometric method we showed that the effect of Nef on CD4 surface expression resulted from accelerated CD4 internalization.

Amino Acid Sequence↗
PubMed1995

Development of leukemia in mice transgenic for the tax gene of human T-cell leukemia virus type I.

The human T-cell leukemia virus type I Tax protein trans-activates several cellular genes implicated in T-cell replication and activation. To investigate its leukemogenic potential, Tax was targeted to the mature T-lymphocyte compartment in transgenic mice by using the human granzyme B promoter. These mice developed large granular lymphocytic leukemia, demonstrating that expression of Tax in the lymphocyte compartment is sufficient for the development of leukemia. Furthermore, these observations suggest that human T-cell leukemia virus infection may be involved in the development of large granular lymphocytic leukemia.

Animals↗
PubMed1995

Nef.

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Amino Acid Sequence↗
PubMed1995

Sera from HIV-1 infected individuals in all stages of disease preferentially recognize the V3 loop of the prototypic macrophage-tropic glycoprotein gp120 ADA.

The outer membrane glycoprotein gp120 and the transmembrane glycoprotein gp41 are predominant targets of the humoral immune response to infection by human immunodeficiency virus type 1. The third hypervariable region (V3 loop) is the principal neutralizing domain and is the primary target of neutralizing antibodies directed against the envelope proteins of HIV-1. The V3 loop is also the major determinant for HIV-1 cell-specific tropism. To further characterize the humoral immune response directed against the gp120 envelope proteins, we expressed two prototypic gp120 envelope proteins (LAI/HXB2 and ADA) and chimeric gp120 envelope proteins in stable transfected Drosophila melanogaster Schneider 2 cells. Sera from four infected adults over the course of infection [McNearney et al. (1992) Proc. natn. Acad. Sci. U.S.A. 89, p. 10,242] were assayed for reactivity with the respective envelope proteins. Sera obtained at early stages preferentially recognized the gp120 envelope protein ADA, whereas in later stages of infection the sera showed diminished reactivity with both gp120 LAI/HXB2 and gp120 ADA. Chimeric envelope proteins revealed that the humoral response was directed primarily against the V3 loop of gp120 ADA. Furthermore, 22 sera from HIV-1 infected individuals in different stages of the disease were tested. Reactivity of sera with the gp120 envelope protein ADA was seven-fold higher than with the gp120 envelope protein LAI/HXB2. Our results suggest that the humoral immune response is preferentially elicited against the V3 loop of the prototypic macrophage-tropic gp120 envelope protein ADA.

Adult↗
PubMed1995

A leucine triplet repeat sequence (LXX)4 in p6gag is important for Vpr incorporation into human immunodeficiency virus type 1 particles.

Incorporation of Vpr into human immunodeficiency virus type 1 (HIV-1) virions is mediated by the Gag protein, independently of other viral components. We have coexpressed Vpr and Gag constructs in a vaccinia virus expression system in order to map the region of Gag involved in Vpr packaging. Deletion of the carboxyl-terminal p6 region of Gag impaired the ability of Gag to package Vpr. To confirm the role of p6 in Vpr packaging, Rous sarcoma virus (RSV)-HIV chimeras containing HIV-1 p6 were constructed. Although RSV Gag does not package Vpr into virus particles, a chimera containing HIV-1 p6 is sufficient for Vpr incorporation. To map the region of p6 involved in Vpr packaging, a series of p6 point mutations and deletion mutations was analyzed. Mutations in the N-terminal p6 proline-rich domain, for which preliminary evidence shows a marked decrease in virion incorporated RNA, did not affect Vpr incorporation. Deletion of residues 1 to 31 of HIV-1 p6 did not affect Vpr packaging, but residues 35 to 47, including an (LXX)4 domain, were required for Vpr incorporation into virus particles.

Amino Acid Sequence↗
PubMed1994

Construction and characterization of infectious human T-cell leukemia virus type 1 molecular clones.

Molecular clones of human T-cell leukemia virus type 1 (HTLV-1) have been constructed and stably propagated in plasmids in Escherichia coli. Expression of Tax could be demonstrated from these clones in fibroblast and epithelial cell lines. HOS cells stably transfected with HTLV-1 clone ACH produced all three classes of viral transcripts and Gag proteins. Virus-like particles were also produced from ACH transfected HOS cells as demonstrated by sucrose gradient and electron microscopic analyses. Transfection of peripheral blood mononuclear cells with ACH resulted in production of infectious virus particles which induced lymphocyte proliferation. This study describes useful reagents for further examination of the biological properties of HTLV-1.

Base Sequence↗
PubMed1994

Killing of primary CD4+ T cells by non-syncytium-inducing macrophage-tropic human immunodeficiency virus type 1.

Understanding the mechanism by which human immunodeficiency virus type 1 (HIV-1) kills CD4+ T lymphocytes is important to the development of therapeutic and prophylactic strategies. Recent studies have indicated that, in some cases, progression to AIDS is associated with the appearance of syncytium-inducing, T cell line-tropic HIV-1 variants. Nevertheless, approximately 50% of subjects with AIDS harbor only non-syncytium-inducing, macrophage-tropic (NSI-M) variants of HIV-1. In most asymptomatic patients, NSI-M HIV-1 isolates are the predominant virus type found. We report here that cytopathicity of NSI-M HIV-1 for primary CD4+ T lymphocytes can be directly detected in vitro. The extent of CD4+ T-cell killing was not completely correlated with the rate of viral replication, suggesting that other characteristics of HIV-1 contribute to its cytopathicity. Our findings suggest that: (i) direct killing by NSI-M HIV-1 may contribute to CD4+ T-lymphocyte depletion in vivo, and (ii) the determinants of HIV-1 cytopathicity for CD4+ T lymphocytes and cell tropism or syncytia-forming ability are not necessarily tightly linked.

Acquired Immunodeficiency Syndrome↗