Mesenchymal stem cells as vehicles for gene delivery

Mesenchymal stem cells contribute to the regeneration of mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon, adipose, and marrow stroma. Transduction of mesenchymal stem cells from species other than humans is required for the development of disease models in which mesenchymal stem cells-based gene delivery is evaluated. Attempts to transduce mesenchymal stem cells from some species with amphotropic retroviral vectors were unsuccessful, leading to comparative mesenchymal stem cells transductions with xenotropic and gibbon-ape leukemia virus envelope-pseudotyped retroviral vectors. Human, baboon, canine, and rat mesenchymal stem cells were transduced optimally with amphotropic vector supernatants. In contrast, sheep, goat, and pig mesenchymal stem cells showed highest transduction levels with xenotropic retroviral vector supernatant, and rabbit mesenchymal stem cells were transduced optimally with gibbon-ape-enveloped vectors. Using a myeloablative canine transplantation model and gene-marked canine mesenchymal stem cells, the biodistribution of infused and ex vivo expanded mesenchymal stem cells were examined. The majority of transduced canine mesenchymal stem cells were found in the bone marrow samples. The current study shows the use of mesenchymal stem cells as a delivery vehicle for gene transfer studies, and validates the feasibility of delivering mesenchymal stem cells to the marrow compartment for stromal regeneration after cancer-associated cytotoxic therapies.

Human immunodeficiency virus type 1 vectors efficiently transduce human hematopoietic stem cells

Lentiviruses are potentially advantageous compared to oncoretroviruses as gene transfer agents because they can infect nondividing cells. We demonstrate here that human immunodeficiency virus type 1 (HIV-1)-based vectors were highly efficient in transducing purified human hematopoietic stem cells. Transduction rates, measured by marker gene expression or by PCR of the integrated provirus, exceeded 50%, and transduction appeared to be independent of mitosis. Derivatives of HIV-1 were constructed to optimize the vector, and a deletion of most of Vif and Vpr was required to ensure the long-term persistence of transduced cells with relatively stable expression of the marker gene product. These results extend the utility of this lentivirus vector system.

Scaffold attachment region-mediated enhancement of retroviral vector expression in primary T cells

We have studied retroviral transgene expression in primary human lymphocytes. Our data demonstrate that transgene expression is high in activated primary CD4+ T cells but significantly decreased in mitotically quiescent cells. Incorporation of a DNA fragment from the scaffold attachment region (SAR) of the human beta interferon gene into the vector improved transgene expression, particularly in quiescent cells. The SAR element functioned in an orientation-dependent manner and enhanced expression of Moloney murine leukemia virus- and murine embryonic stem cell-based vectors. Clonal analysis of transduced T cells showed that the SAR sequence did not confer position-independent expression on a transgene but rather prevented the decrease of expression when cells became quiescent. The SAR sequence also enhanced transgene expression in T cells generated from retrovirally transduced CD34-enriched hematopoietic progenitor-stem cells in a SCID-hu thymus-liver mouse model. We have used the SAR-containing retroviral vector to express the RevM10 gene, a trans-dominant mutant of the human immunodeficiency virus type 1 (HIV-1) Rev gene. Compared to a standard retroviral vector, the SAR-containing vector was up to 2 orders of magnitude more efficient in inhibiting replication of the HIV-1 virus in infected CD4+ peripheral blood lymphocyte populations in vitro. This is the first demonstration that SAR elements can be used to improve retroviral vector expression in human primary T cells.

Comparative analyses of intracellularly expressed antisense RNAs as inhibitors of human immunodeficiency virus type 1 replication

The antiviral activities of intracellularly expressed antisense RNAs complementary to the human immunodeficiency virus type 1 (HIV-1) pol, vif, and env genes and the 3' long terminal repeat (LTR) sequence were evaluated in this comparative study. Retroviral vectors expressing the antisense RNAs as part of the Moloney murine leukemia virus LTR promoter-directed retroviral transcript were constructed. The CD4+ T-cell line CEM-SS was transduced with retroviral constructs, and Northern blot analyses showed high steady-state antisense RNA expression levels. The most efficient inhibition of HIV-1 replication was observed with the env antisense RNA, followed by the pol complementary sequence, leading to 2- to 3-log10 reductions in p24 antigen production even at high inoculation doses (4 x 10(4) 50% tissue culture infective doses) of the HIV-1 strain HXB3. The strong antiviral effect correlated with a reduction of HIV-1 steady-state RNA levels, and with intracellular Tat protein production, suggesting that antisense transcripts act at an early step of HIV-1 replication. A lower steady-state antisense RNA level was detected in transduced primary CD4+ lymphocytes than in CEM-SS cells. Nevertheless, replication of the HIV-1 JR-CSF isolate was reduced with both the pol and env antisense RNA. Intracellularly expressed antisense sequences demonstrated more pronounced antiviral efficacy than the transdominant RevM10 protein, making these antisense RNAs a promising gene therapy strategy for HIV-1.

Inhibition of human immunodeficiency virus type 1 replication in myelomonocytic cells derived from retroviral vector-transduced peripheral blood progenitor cells

Monocytes and macrophages (Mo/Mphi) contribute to the pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. A successful hematopoietic stem/progenitor cell (HSPC)-based gene therapy strategy for HIV-1 disease must protect Mo/Mphi as well as T cells from HIV-1-related pathology. In this report, we demonstrate that RevM10-transduced HSPCs isolated from cytokine-mobilized peripheral blood give rise to Mo/Mphi suppressing replication of Mphi-tropic HIV-1 isolates. A Moloney murine leukemia virus (MoMLV)-based retroviral vector encoding a bicistronic mRNA co-expressing RevM10 and the murine CD8alpha' chain (Lyt2) was used to transduce HSPCs. Following transduction, these cells were expanded and differentiated by short-term culture in methylcellulose containing various cytokines. In vitro differentiated Mo/Mphi were enriched by fluorescence activated cell sorting (FACS) for the co-expressed transgene (Lyt2) and myelomonocytic (CD33, CD14) surface markers. HIV-1 replication of two Mphi-tropic isolates (JR-FL, BaL) was inhibited in Mo/Mphi expressing RevM10 and Lyt2 relative to control cells expressing only Lyt2 but no functional RevM10 gene product. Cell proliferation and expression of lineage-specific surface markers was not altered in transduced, in vitro differentiated Mo/Mphi cells. This study supports the feasibility of HSPC-based gene therapy as a future treatment for HIV-1 disease.

Antiviral potency of drug-gene therapy combinations against human immunodeficiency virus type 1

Gene therapy for the treatment of human immunodeficiency virus type 1 (HIV-1) infection using intracellular immunization strategies is currently being tested in clinical trials. With the continuing development of potent antiretroviral drugs (e.g., reverse transcriptase [RT] and protease [PR] inhibitors), it is likely that HIV-1 gene therapy will be applied to humans concurrently receiving such antiretroviral medication. In this study, we assessed the in vitro antiviral efficacy of two gene therapy strategies (trans-dominant RevM10, Gag antisense RNA) in combination with clinically relevant RT (AZT, ddC) or PR (indinavir) inhibitors. Retrovirally transduced, human T cell lines expressing antiviral gene constructs were inoculated with high doses of HIV-1HXB3 in the presence or absence of inhibitors. The combination of RevM10 or Gag antisense RNA with antiviral drugs inhibited HIV-1 replication 10-fold more effectively than the single antiviral drug regimen alone. More importantly, we also addressed whether gene therapy strategies are effective against drug-resistant HIV-1 isolates. Both the RevM10 and Gag antisense RNA strategies showed antiviral efficacy against several RT inhibitor-resistant HIV-1 isolates equivalent to their inhibition of HIV-1HXB3 replication. In summary, our data demonstrate the greater than additive antiviral efficacy of gene therapy strategies and RT or PR inhibitors, and that gene therapy approaches are effective against drug-resistant HIV-1 viral isolates.

Hematopoietic potential and retroviral transduction of CD34+ Thy-1+ peripheral blood stem cells from asymptomatic human immunodeficiency virus type-1-infected individuals mobilized with granulocyte colony-stimulating factor

The potential of hematopoietic stem cells (HSCs) from human immunodeficiency virus type-1 (HIV-1)-infected individuals, eg, self-renewal and multilineage differentiative capacity, might be perturbed due to the underlying disease. In this study, we assessed the HSC activity in the CD34+ Thy-1+ cell population of peripheral blood stem cells (PBSCs) of three asymptomatic HIV-1-infected individuals after granulocyte colony-stimulating factor (G-CSF; 10 microg/kg/d) mobilization. On day 4 of G-CSF treatment, 0.8% to 1% of the total blood mononuclear cells were CD34+. Leukapheresis followed by a two-step cell isolation process yielded a CD34+ Thy-1+ cell population of high purity (76% to 92% CD34+ Thy-1+ cells). This cell population showed no evidence of HIV-1-containing cells based on a semiquantitative HIV-1 DNA polymerase chain reaction. Furthermore, the purified cells showed normal hematopoietic potential in in vitro clonogenic assays. Successful gene transfer into committed progenitor cells (colony-forming units-cells) and more primitive stem/progenitor cells (long-term culture colony-forming cells) could be shown after amphotropic retroviral transduction. These data provide evidence that the CD34+ Thy-1+ stem cell compartment can be mobilized and enriched in early stage HIV-1-infected patients. Furthermore, successful transduction of this cell population as a prerequisite for stem cell-based clinical gene therapy protocols was demonstrated.

Novel retroviral packaging cell lines: complementary tropisms and improved vector production for efficient gene transfer

We report increased transduction of human hematopoietic progenitor cells through a combination of novel retroviral vector packaging cell lines, and improved vector supernatant production. The new ProPak packaging cell lines produce either murine leukemia virus (MLV) xenotropic (ProPak-X cells) or amphotropic particles (ProPak-A cells), and ProPak-based producer cells were demonstrated to be free of replication-competent retrovirus (RCR) by stringent testing. Vector supernatants from ProPak or existing packaging cell lines producing different pseudotyped particles (amphotropic MLV, xenotropic MLV or gibbon ape leukemia virus) were compared for the ability to transduce clinically relevant human hematopoietic cells. All vector types transduced primary human CD34-positive or CD4-positive cells, regardless of tropism. However, consistently higher transduction of target cells was achieved with ProPak-derived amphotropic vector than with PA317-packaged amphotropic vector. The highest transduction of human hematopoietic progenitor cells was achieved with vector supernatant generated from a coculture of the ProPak-X and ProPak-A cell lines. This ping-pong amplification yielded supernatant containing vector targeted to two distinct receptors present on human cells, and did not result in detectable RCR formation. In addition, we describe conditions for improved vector supernatant production in a packed-bed bioreactor.

RevM10-expressing T cells derived in vivo from transduced human hematopoietic stem-progenitor cells inhibit human immunodeficiency virus replication

A key feature of the pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection is the gradual loss of CD4-positive T cells. A number of gene therapy strategies have been designed with the intent of inhibiting HIV replication in mature T cells. As T cells are products of hematolymphoid differentiation, insertion of antiviral genes into hematopoietic stem cells could serve as a vehicle to confer long-term protection in progeny T cells derived from transduced stem cells. One such "cellular immunization" strategy utilizes the gene coding for the HIV-1 rev trans-dominant mutant protein RevM10 which has been demonstrated to inhibit HIV-1 replication in T-cell lines and in primary T cells. In this study, we used a Moloney murine leukemia virus-based retrovirus encoding a bicistronic message coexpressing RevM10 and the murine CD8-alpha' chain (Lyt2). This vector allows rapid selection of transgene-expressing cells as well as quantitation of transgene expression. We demonstrate that RevM10-transduced CD34-enriched hematopoietic progenitor-stem cells (HPSC) isolated from human umbilical cord blood or from granulocyte colony-stimulating factor-mobilized peripheral blood can give rise to mature thymocytes in the SCID-hu thymus/liver mouse model. The phenotypic distribution of HPSC-derived thymocytes is normal, and expression of the transgene can be detected by flow cytometric analysis. Moreover, we demonstrate that RevM10 can inhibit HIV replication in T cells derived from transduced HPSC after expansion in vitro. This is the first demonstration of anti-HIV efficacy in T cells derived from transduced human HPSC.

Hematopoietic stem cell-based gene therapy for acquired immunodeficiency syndrome: efficient transduction and expression of RevM10 in myeloid cells in vivo and in vitro

Gene delivery via the hematopoietic stem cell (HSC) offers an attractive means to introduce antiviral genes into both T cells and macrophages for acquired immunodeficiency syndrome (AIDS) gene therapy. An amphotropic retroviral vector encoding a bicistronic gene coexpressing RevM10 and the murine CD8alpha' chain (lyt2) was developed to transduce HSC/progenitor cells. After transduction of CD34+ cells isolated from human umbilical cord blood, the lyt2 molecule detected by flow cytometry was used to monitor the level of gene transduction and expression and to enrich RevM10-expressing cells by cell sorting without drug selection. Using this quantitative method, high levels of gene transduction and expression (around 20%) were achieved by high-speed centrifugation of CD34+ cells with the retroviral supernatant (spinoculation). After reconstitution of human bone marrow implanted in SCID mice (SCID-hu bone) with the transduced HSC/progenitor cells, a significant number of donor-derived CD14+ bone marrow cells were found to express the RevM10/lyt2 gene. Finally, replication of a macrophage-tropic human immunodeficiency virus-type 1 (HIV-1) isolate was greatly inhibited in the lyt2+/CD14+ cells differentiated from transduced CD34+ cells after the enrichment of lyt2+ population. Thus, the RevM10 gene did not appear to inhibit the differentiation of HSC/progneitor cells into monocytes/macrophages. The level of retrovirus-mediated RevM10 expression in monocytes/macrophages derived from transduced HSCs is sufficient to suppress HIV-1 replication.

High transdominant RevM10 protein levels are required to inhibit HIV-1 replication in cell lines and primary T cells: implication for gene therapy of AIDS

Expression of antiviral genes in CD4+ T cells has been proposed as a strategy for gene therapy of AIDS. Over the past years, we and others have developed retroviral vectors encoding the RevM10 protein, a dominant-negative mutant of the HIV-1 Rev trans-activator protein. We could demonstrate gene transfer and inhibition of HIV-1 replication in cultured T cell lines and primary T cells. However, little is known about the levels of the antiviral protein required to achieve a therapeutic effect, particularly in primary cells. In this report, we compare different vector designs with regard to expression of the antiviral gene to develop an optimal vector for clinical applications. Our results demonstrate that intracellular steady-state RevM10 protein levels expressed from the Moloney murine leukemia virus (MoMLV), myeloproliferative sarcoma virus (MPSV) or mouse embryonic stem cell virus (MESV) promoters located in the long terminal repeat (LTR) were uniformly higher than from internal promoters (eg CMV, PGK). Analysis of selected vectors in acutely and chronically HIV-infected cell lines suggested that threshold levels of RevM10 expression are required to achieve inhibition of HIV replication. LTR-driven RevM10 expression also yielded high steady-state protein levels in activated primary T cells resulting in inhibition of HIV replication, and there was no apparent difference between the MoMLV, MPSV and MESV-LTR vectors. However, RevM10 expression was down-regulated in resting primary cells and consequently anti-HIV efficacy was significantly reduced. Taken together, the data suggest that relatively high steady-state levels of RevM10 protein are required to achieve inhibition of HIV replication and that the MPSV- and MESV-derived retroviral vectors show no advantage over the MoMLV-based vectors for expression of anti-HIV genes in human T cells.

Intracellular expression of RNA transcripts complementary to the human immunodeficiency virus type 1 gag gene inhibits viral replication in human CD4+ lymphocytes

Intracellular expression of antisense transcripts was evaluated for its potential to interfere with human immunodeficiency virus type 1 (HIV-1) replication. Retroviral vectors encoding HIV-1 psi-gag complementary sequences downstream of a selectable gene (neo, puromycin gene, or Lyt2 gene) were stable and yielded high titers. Human CEMSS T cells were transduced with amphotropic retroviral vectors to express RNA complementary to the psi-gag sequence of HIV-1. Replication of laboratory-adapted HIV-1 strains was inhibited by more than 1 order of magnitude (log10) in these transduced cells even at high inoculation doses (4 x 10(4) 50% tissue culture infective doses). Antisense-mediated anti-HIV efficacy was further demonstrated by survival of CD4+ cells in these cultures relative to controls. The level of anti-HIV-1 activity of the psi-gag antisense sequence correlated with the length of the antisense transcript. Maximal anti-HIV efficacy was observed with complementary sequence more than 1,000 nucleotides long, whereas transcripts less than 400 nucleotides long failed to inhibit HIV-1 replication. Expression of psi-gag antisense RNA also reduced HIV-1 JR-CSF replication 10-fold in primary CD4+ lymphocytes. These results obtained with a T-cell line and primary peripheral blood lymphocytes indicate the potential of long antisense RNAs as an efficient anti-HIV-1 therapeutic agent for gene therapy.

Intracellular expression of human immunodeficiency virus type 1 (HIV-1) protease variants inhibits replication of wild-type and protease inhibitor-resistant HIV-1 strains in human T-cell lines

The enzymatic activity of the human immunodeficiency type 1 (HIV-1) protease (PR) is crucial to render HIV-1 virions mature and infectious. Hence, genetic intervention strategies based on trans-dominant (td) variants of the HIV-1 PR might be an alternative to current pharmacological and gene therapy regimens for AIDS. CD4-positive human CEM-SS T-cell lines were generated which constitutively expressed HIV-1 td PR variants. HIV-1 infection experiments demonstrated severely reduced HIV-1 replication in these td PR CEM-SS cell lines compared with control T cells expressing wild-type PR. Furthermore, replication of an HIV-1 isolate bearing a PR inhibitor-resistant PR was blocked, showing that genetic intervention strategies based on td PRs can be effective against HIV-1 isolates containing PR inhibitor-resistant mutants.

Intracellular expression of cellular eIF-5A mutants inhibits HIV-1 replication in human T cells: a feasibility study

Previously, we described two mutants of the cellular Rev co-factor, eukaryotic initiation factor 5A (eIF-5A M13 and M14), which suppress human immunodeficiency virus type 1 (HIV-1) SF2 replication in clonal T cell lines. This study introduced the notion that it is possible to develop gene therapies against infectious agents on the basis of mutant host factors required for viral replication. In this report, we provide further evidence to support this new paradigm and describe murine leukemia virus (MLV)-based retroviral vectors expressing three different eIF-5A mutants from the viral long terminal repeat (LTR). HIV-1 replication (SF2, HXB-3) was reduced up to 2 orders of magnitude in transduced, polyclonal T cell populations. All eIF-5A mutants also showed antiviral activity (approximately seven-fold reduction) in a chronic HIV-1 infection model. Expression of eIF-5A mutant M13 delta in peripheral blood lymphocytes (PBLs) showed no difference in proliferation and metabolic activity as determined in a 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT)-assay, suggesting that expression of this type of mutant protein is not associated with cellular toxicity. In summary, these data suggest that gene therapy for HIV-1 infection can be developed on the basis of mutants of the Rev co-factor eIF-5A.

Sustained retroviral gene marking and expression in lymphoid and myeloid cells derived from transduced hematopoietic progenitor cells

The expression of antiviral genes in human hematopoietic stem or progenitor cells has been proposed as a strategy for gene therapy of AIDS. To be successful, this strategy requires safe and efficient transfer of the therapeutic gene into hematopoietic cells and gene expression has to be maintained in HIV susceptible cells following differentiation. We have used retroviral vectors to transfer the gene for a transdominant inhibitor of HIV replication (RevM10) into CD34+ stem/progenitor cells isolated from human umbilical cord blood (UCB). Following transduction, cells were allowed to differentiate either in vitro in clonogenic assays and long-term stromal cell cultures or in human thymus implanted in immunodeficient scid/scid mice in vivo (SCID-hu). Following differentiation and expansion, multiple lineages of cells were shown to carry the transgene. A higher percentage of gene-marked progenitor cells (10-30% in most cases) were detected in methylcellulose colony assays and in long-term stromal cell cultures (1-5%). In contrast, gene-marked T cells derived from transduced CD34+ cells in a SCID-hu model were detected at an even lower frequency (0.01-1%). RevM10 RNA expression was detected in CD34+ cells immediately after transduction and was maintained after in vitro differentiation of those cells into CD14+ myeloid cells. In T cells, the RevM10-specific RNA was detectable by RT-PCR and also by semiquantitative RNase protection. These findings demonstrate that LTR-driven gene expression is sustained in relevant cells derived from retrovirus-transduced hematopoietic progenitor cells after extensive differentiation in vitro and in vivo and suggest that stringent in vivo, rather than in vitro assays, may be a better preclinical system to improve gene marking and expression in hematopoietic cells.

Improved detection of replication-competent retrovirus

Recombinant retroviral vectors are the predominant delivery system in human gene therapy protocols. Since contaminating replication-competent retrovirus (RCR) can arise during the production of retroviral vector supernatants, sensitive assays for the screening of supernatants are necessary. In this study, we present a marker rescue assay based upon a Mus dunni cell line stably transduced with a lacZ gene. We show that detection of RCR in vector supernatants by the M. dunni lacZ marker rescue assay or PG-4 S+ L- focus-forming assay is equally sensitive. By inoculating test supernatants under centrifugation (which we term spinoculation), we increased the sensitivity of detection of RCR 10 to 100-fold with the PG-4 S+ L- and lacZ marker rescue assays. While the spinoculation protocol had no adverse effects on cells, spinoculation of high titer vector supernatants onto PG-4 cells resulted in some cytotoxicity, making identification of RCR positive cultures difficult. However, spinoculation of vector supernatants onto M. dunni lacZ cells resulted in no cytotoxicity, and also partially overcame inhibition of detection of low levels of RCR due to the presence of high titer replication-incompetent vector.

Retroviral vectors designed for targeted expression of RNA polymerase III-driven transcripts: a comparative study

Retroviral gene delivery systems for RNA polymerase II (RNA pol II)-based promoters have been developed and are widely used in gene transfer studies. In contrast, gene delivery systems with RNA pol III-based expression cassettes have not been studied comprehensively, although therapeutic applications (e.g., ribozymes, antisense, triplex RNA and RNA decoys) have been proposed. In this report, we describe retroviral vectors designed to optimize expression of short chimeric RNAs transcribed from a number of RNA pol III promoters. Our results show that all analysed RNA pol III expression cassettes (tRNA, U6, Ad VA1), regardless of orientation, do not transcribe efficiently when located between the retroviral long terminal repeats (LTRs). In contrast, high steady-state expression levels can be achieved by inserting the RNA pol III expression cassette into the U3 region of the LTR (double-copy design). Compared to human tRNA gene promoters (tRNA(Met), tRNA(Val)), the human small nuclear RNA U6 gene (U6) and the adenovirus virus-associated RNA 1 (Ad VA1) gene promoters yielded higher expression levels. The majority of the chimeric U6-derived transcripts were detected in the nuclear RNA fraction, and the VA1 and tRNA-driven transcripts were predominantly detected in the cytoplasmic compartments. This report is the first comparative study of RNA pol III-driven promoters expressing short chimeric transcripts leading to an optimized retroviral-vector design.

A novel human amphotropic packaging cell line: high titer, complement resistance, and improved safety

Successful retroviral-mediated gene therapy will depend on safe, efficient packaging cell lines for vector particle production. Existing packaging lines for murine leukemia virus (MLV)-based vectors are predominantly derived from NIH/3T3 cells which carry endogenous MLV sequences that could participate in recombination to form replication-competent retrovirus (RCR). To identify cells devoid of such sequences, we screened genomic DNA from eight cell lines. DNA from the human 293 cell line did not cross-hybridize with MLV sequences, and these cells were able to secrete Gag particles after transfection. We derived a stable amphotropic packaging cell line (called ProPak-A) in 293 cells in which the Gag-Pol and Env (packaging) functions are expressed separately from a heterologous (non-MLV) promoter, to maximally reduce homology between packaging and vector sequences. ProPak-A-based producer cells are efficient, yielding higher stable titers than PA317-based producers. In addition, a vector that consistently gave rise to RCR in PA317 cells never resulted in detectable RCR in ProPak-A-based producer cultures. We have also shown that ProPak-A-packaged particles are not inactivated by human serum. Thus, the packaging cells we describe are as efficient and safer than the amphotropic packaging cells most commonly used in clinical gene therapy work and are also more appropriate for in vivo gene delivery.

Detection of intracellular HIV-1 Rev protein by flow cytometry

The Rev trans-activator protein plays a pivotal role in human immunodeficiency virus type 1 (HIV-1) replication by allowing expression of the viral structural proteins. We have developed a protocol to quantitatively assay intracellular steady state levels of Rev Ag (Rev wild type and RevM10 proteins) by flow cytometry. Three fixation and permeabilization techniques were compared. These protocols varied in the magnitude of the signal which could be detected, and in the ability to distinguish between Rev Ag positive and negative populations. This technology is applicable to a variety transduced or transfected cell types (species, lineage), and for cell lines and primary cells acutely infected with HIV-1. The assay is therefore a valuable tool both to analyze Rev protein expression levels in HIV-infected cells and to optimize delivery of the dominant-negative RevM10 gene for clinical gene therapy applications. In addition, a second, independent intracellular protein (HIV-Tat) has been detected using the same approach.

Retroviral end-point titer is not predictive of gene transfer efficiency: implications for vector production

Efforts to improve gene transfer (transduction) efficiency achieved with retroviral vectors often focus on increasing the end-point titer. In this study, we assayed more than 70 retroviral vector supernatants for end-point titer and for the ability to transfer reporter genes into cell populations (referred to as transduction efficiency). We found no correlation between end-point titer and transduction efficiency. We also show that increasing end-point titer by ultrafiltration does not necessarily increase transduction efficiency. Evidence presented shows that nontransducing retroviral particles interfere with transducing virions and reduce transduction efficiency without reducing end-point titer. We have investigated production parameters and stability of retroviral vector particles using transduction efficiency as a measure of supernatant potency. Analysis of the production kinetics showed that the rate of virus production was marginally higher at 37 degrees C than at 32 degrees C. However, recombinant amphotropic retrovirus particles are significantly more stable at 32 degrees C than at 37 degrees C. In addition, we show that short incubation periods are sufficient to yield supernatants with high transduction efficiencies. We have implemented improved culture conditions, including short incubation periods, by continually perfusing medium over producer cells in a packed-bed bioreactor incubated at 32 degrees C. By operating the packed-bed bioreactor in perfusion mode, retroviral vector supernatants with a high transduction efficiency can be routinely produced in large quantities.

Genetic instability of a MoMLV-based antisense double-copy retroviral vector designed for HIV-1 gene therapy

We constructed a retroviral vector encoding a mutant tRNA(imet) gene followed by a HIV-1 rev-specific antisense sequence in the U3 region of the 3' long terminal repeat (LTR). This Moloney murine leukemia virus (MoMLV)-based double-copy retroviral vector was used to transduce human lymphoblastoid T-cell lines (CEM, Jurkat). In some clonal cell lines the expected short transcript initiated either from the 5' or 3' LTR tRNA-alpha rev gene was not detectable by Northern blot analyses of transduced, G418-resistant cells with an alpha rev-specific oligonucleotide probe. In other clonal cells, neither the short polymerase III transcript nor the full-length genomic polymerase II transcript (containing the 3' LTR tRNA-alpha rev gene) was detectable when compared with the transduced cell pool. Southern blot and DNA-polymerase chain reaction (PCR) analyses specific for the tRNA-alpha rev cassette in the 5' or 3' LTR of the retroviral vector suggested that the transfer of the 3' LTR U3 region to the 5' LTR was incorrect in most proviruses. These data were confirmed by DNA sequence analyses of several clonal lines demonstrating deletions and insertions. In summary, our results indicate that this retroviral vector design with direct repeats flanking the polymerase III transcription unit plus the alpha rev insert is prone to genetic rearrangements and consequently not useful for the development of gene therapy protocols.

RevM10-mediated inhibition of HIV-1 replication in chronically infected T cells

Two clinical regimens have been proposed for gene therapies of acquired immunodeficiency syndrome (AIDS): (i) Genetic modification of differentiated peripheral mononuclear cells ex vivo and (ii) gene delivery into hematopoietic stem/progenitor cells ex vivo. Various antiviral strategies targeted at different molecular processes in the human immunodeficiency virus type 1 (HIV-1) life cycle are currently being pursued, all with the goal of reducing HIV-1 replication. Until now, all successful studies have reported inhibition in acutely HIV-infected cells that had been genetically modified prior to infection. These promising results do not address a clinically relevant question: What is the contribution of already infected peripheral mononuclear and hematopoietic stem/progenitor cells to disease progression? In this report, we demonstrate inhibition of both HIV-1 replication and production of infectious particles in chronically infected human T leukemia cell lines. The antiviral effect on the transduced cell population correlates with the expression of the dominant-negative RevM10 protein. This is the first demonstration that a gene therapy-based treatment can achieve antiviral efficacy in human T leukemia cells chronically infected with HIV-1.

Scanning mutagenesis of the arginine-rich region of the human immunodeficiency virus type 1 Rev trans activator

The structural proteins of human immunodeficiency virus type 1, for example, Gag and Env, are encoded by unspliced and incompletely spliced viral transcripts. The expression of these mRNAs in the cytoplasm, along with their commensurate translation, is absolutely dependent on the virally encoded Rev trans activator. Previous studies have demonstrated that Rev binds directly to its substrate mRNAs via an arginine-rich element that also serves as its nuclear localization sequence. In an attempt to define the specific amino acid residues that are important for in vivo activity, we have constructed a series of missense mutations that scan across this region. Our data demonstrate that all eight arginine residues within this element can, individually, be substituted for either leucine or lysine with no apparent loss of function. Importantly, these findings suggest that no single amino acid within the arginine-rich domain of Rev is, by itself, essential for activity and that considerable functional redundancy is therefore likely to exist within this region. Interestingly, one mutant in which a tryptophan had been substituted for a serine failed to accumulate exclusively in the nucleus but still bound RNA in a manner that was indistinguishable from that of the wild-type protein. This observation indicates that features of the arginine-rich region that are additional to those required for RNA binding are important for Rev's correct accumulation in the nucleus.

Constitutive expression of chimeric neo-Rev response element transcripts suppresses HIV-1 replication in human CD4+ T lymphocytes

We have previously reported that chimeric neomycin phosphotransferase (neo)-Rev response element (RRE) transcripts suppress the function of the human immunodeficiency virus type 1 (HIV-1) Rev trans-activator protein in HeLa cells. In an extension of these experiments, human CD4+ CEM cells (G418-resistant cell populations and clonal isolates) stably expressing chimeric neo-RRE genes (2, 3, or 6 RRE copies) were generated using retroviral-mediated gene transfer. The transduced CEM clones were infected with the HIV-1 HTLVIIIB isolate and the following three phenotypes were observed: (i) the transduced CEM cells were readily infected with HIV-1 indistinguishable from the control CEM cells; (ii) the appearance of HIV-1 replication markers was significantly delayed; (iii) no signs of HIV-1 replication were detectable although proviral HIV-1 DNA sequences could be detected in these cells. Furthermore, HIV antigen expression was limited in neo-resistant CEM cell populations inoculated with the HIV-1 HTLVIIIB isolate. Only 10% of the CEM-pX17-3xRRE cells and 20% of the CEM-pX17-2xRRE cells displayed HIV-1 antigens 43 days after challenge and had retained CD4 surface expression on 47% and 64% of the cells, respectively. In sharp contrast, 80% of the CEM-pX17 or the CEM-pX17-6xRRE cells expressed HIV-1 antigens but no CD4 antigens were detectable in these cultures. These results clearly indicate that RRE decoys could be developed into an effective somatic gene therapy approach against HIV-1 induced acquired immunodeficiency syndrome (AIDS).

Reduction in replication of the human immunodeficiency virus type 1 in human T cell lines by polymerase III-driven transcription of chimeric tRNA-antisense RNA genes

Inhibition of human immunodeficiency virus type 1 (HIV-1) replication was demonstrated by using tat- and rev-directed antisense oligoribonucleotides 68 and 69 nucleotides in length. In this study, human T-lymphoid cells were transduced with a murine amphotropic retroviral vector containing a polymerase III-driven chimeric gene consisting of the human tRNA(imet) sequence and the short tat- and rev-directed antisense sequences that had been shown before to inhibit HIV-1 replication. Pools of transduced, G418-resistant human T-lymphoid Jurkat or CEM cells showed reduced replication of HIV-1 in the presence of antisense-containing chimeric transcripts, but not with sense sequence-containing transcripts. These results demonstrate that short inhibitory antisense RNA transcripts can be stably expressed endogenously using polymerase III promoters, which can reduce replication of HIV-1. The approach described in this work combines the advantages of short and, usually, synthetic oligonucleotides with the stable intracellular expression of inhibitory genes for HIV-1 in target cells. Considering the small size of the described chimeric polymerase III genes, it appears feasible to combine multiple antiviral genes with the currently available retroviral vectors as gene delivery systems.

Human T-lymphotropic virus type I tax regulates the expression of the human lymphotoxin gene

Human T-lymphotropic virus type-I (HTLV-I)-infected T-cell lines constitutively produce high levels of lymphotoxin (LT). To analyze the mechanisms that lead to the expression of LT in HTLV-I-infected cell lines, we studied regulatory regions of the human LT promoter involved in the activation of the human LT gene. As determined by deletional analysis, sequences between +137 and -116 (relative to the transcription initiation site) are sufficient to direct expression of a reporter gene in the HTLV-I-infected cell line MT-2. Site-directed mutation of a of the single kappa B-like motif present in the LT promoter region (positions -99 to -89) completely abrogated LT promoter activity in MT-2 cells, suggesting that this site plays a critical role in the activation of the human LT gene. Transfection of LT constructs into HTLV-I-uninfected and -unstimulated Jurkat and U937 cell lines showed little to no activity of the LT promoter. Cotransfection of the same constructs with a tax expression plasmid into Jurkat cells led to detectable promoter activity, which could be significantly increased by stimulation of the cells with phorbol myristate acetate (PMA). Similarly, cotransfection of the LT promoter constructs and the tax expression plasmid into U937 cells led to significant promoter activity upon stimulation with PMA. These data suggest that HTLV-I tax is involved in the upregulation of LT gene expression in HTLV-I-infected cells.

Inhibition of human immunodeficiency virus type 1 replication in human T cells by retroviral-mediated gene transfer of a dominant-negative Rev trans-activator

Human immunodeficiency virus type 1 (HIV-1) is the causative agent of the acquired immunodeficiency syndrome (AIDS). Currently, no satisfactory treatment for this viral disease is available. Somatic gene therapy has been proposed as an alternative to conventional therapies. Several antiviral gene therapy approaches including ribozymes, antisense inhibition, and RNA-decoy strategies, as well as dominant-negative mutants of HIV-1 proteins (Gag, Tat, and Rev) have been suggested. To prove the concept of trans-dominant inhibition of HIV-1 replication, we transduced CEM cells with a retroviral vector encoding a dominant-negative rev gene. Amplification of integrase-specific proviral sequences from high molecular weight DNA indicated successful HIV-1 human T-lymphotropic virus type IIIB (HTLV-IIIB) infection of all cells. In contrast to CEM cells and CEM cells expressing the rev wild-type (wt) gene, infection of two CEM-RevM10 clones with HIV-1 did not result in the release of significant levels of p24 Gag antigen as measured by antigen capture assay, indicating a block in HIV-1 replication due to the presence of the trans-dominant Rev protein. Furthermore, the parental CEM cells as well as CEM cells expressing the Rev wt protein were effectively killed in the course of the HIV-1 infection, whereas all CEM cells expressing the RevM10 protein were unaffected in their growth rate.

Dominant-negative mutants are clustered in a domain of the human T-cell leukemia virus type I Rex protein: implications for trans dominance

The 27-kDa Rex trans-acting protein appears to be essential for replication of human T-cell leukemia virus type I. Mutations introduced outside of the Rex RNA-binding domain-nucleolar localization signal display either wild-type activity or, conversely, yield dominant-negative proteins. We generated missense mutations in a particular domain of the Rex protein (amino acid residues 54 to 69) which is characterized by a cluster of dominant-negative mutants. Our results indicate that amino acids 57 to 67 are critically important for Rex function mediated through the RxRE cis-acting RNA sequence. Within this domain, only amino acids 61 to 63 could be mutated without loss of function. All other missense and deletion mutants yielded dominant-negative proteins. In vitro RNA-binding studies performed with glutathione S-transferase-Rex fusion proteins demonstrated that all of the mutant Rex proteins interacted specifically with RxRE RNA. Analysis of chimeric Rex-Rev proteins suggests that this Rex domain is important for oligomerization.

Definition of the human immunodeficiency virus type 1 Rev and human T-cell leukemia virus type I Rex protein activation domain by functional exchange

The human retroviruses human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type I (HTLV-I) are characterized by complex regulation of gene expression. Each virus encodes a posttranscriptional regulator, the 19-kDa HIV-1 Rev protein and the 27-kDa HTLV-I Rex protein, which is required for viral replication. Expression of these trans activators results in the cytoplasmic accumulation of unspliced or singly spliced viral mRNA which encode the gag, pol, and env gene products. The finding that the HTLV-I Rex protein is able to functionally substitute for the Rev protein of HIV-1 indicates that HIV-1 Rev and HTLV-I Rex may interact with the same component of a cellular pathway involved in either mRNA splicing or transport. In this study, we have generated functional Rev/Rex hybrid proteins by domain exchange. We have defined, using in vivo and in vitro analyses, the activation domains of Rev and Rex which are the putative targets of a common host cell factor(s) required for Rev and Rex function.

Expression of chimeric neo-Rev response element sequences interferes with Rev-dependent HIV-1 Gag expression

Recombinant plasmids containing reiterated human immunodeficiency virus type 1 (HIV-1) Rev response element (RRE) sequences were constructed to suppress Rev-dependent HIV-1 Gag expression. The mammalian expression vectors pMAMneo containing one, three, or six repeats of the RRE sequence were cotransfected with a HIV-1 HTLV-IIIB proviral DNA into HeLa cells. All three RRE expression plasmids reduced replication of HIV-1 with similar efficacy. Furthermore, the chimeric expression vector pCMV neoRRE6 x ----(containing six copies of the RRE sequence) was used to establish HeLa cell lines constitutively expressing RRE. A plasmid encoding a Rev-dependent HIV-1 p24 Gag protein was cotransfected with the wild-type Rev expression plasmid into three different RRE-expressing HeLa cell lines. p24 Gag protein production in the culture supernatants of the HeLaneoRRE cells was compared with two neo-expressing cell lines. Although all cell lines (HeLaneoRRE, HeLaneo) displayed similar transfection efficiencies, p24 Gag protein synthesis was markedly reduced in the RRE-expressing cell lines in comparison to the control cells.

Functional mapping of the human immunodeficiency virus type 1 Rev RNA binding domain: new insights into the domain structure of Rev and Rex

Expression of human immunodeficiency virus type 1 (HIV-1) structural proteins requires the direct interaction of the viral trans-activator protein Rev with its cis-acting RNA sequence (Rev-response element [RRE]). A stretch of 14 amino acid residues of the 116-amino-acid Rev protein is sufficient to impose nucleolar localization onto a heterologous protein. Our results demonstrated that these same amino acid residues confer Rev-specific RRE binding to the heterologous human T-cell leukemia virus type I Rex protein. In addition, our results indicated that amino acids distinct from the nuclear localization signal are important for Rex-specific RRE RNA binding.

Mutational analysis of functional domains in the HIV-1 Rev trans-regulatory protein

HIV-1 replication depends on the expression of trans-regulatory genes (tat, rev) encoded in the 3' part of the retroviral genome. HIV-1 Rev trans-activator protein allows the cytoplasmic translocation of incompletely spliced retroviral mRNA which is required for the translational switch from regulatory (Tat, Rev, Nef) to structural proteins (Gag, Pol, Env). The HIV-1 Rev regulatory protein comprises an activation domain (RAD) and a RNA binding domain (RBD). Both functional domains are not well defined and the RBD appears to overlap with the nuclear localization signal (NLS). Our mutational analysis localized the Rev protein domain important for RRE (nucleotide 7781 to 8000) binding in vitro to amino acid residues 31 to 50. Mutations in this domain always resulted in exclusion from the nucleoli. Furthermore, these mutants did not support Rev-dependent p24 Gag production in vivo. Sequences immediately upstream of this domain (RevM4, RevM19) were attenuated in their in vivo activity possibly indicating a role in Rev protein oligomerization. The observed tight correlation between subcellular localization and RNA binding in vitro indicates that this short stretch of amino acids supports two essential functions required for HIV-1 replication.

Functional analysis of human T-cell leukemia virus type I rex-response element: direct RNA binding of Rex protein correlates with in vivo activity

The human T-cell leukemia virus type I rex gene product plays a critical role in the expression of the retroviral structural proteins Gag and Env from incompletely spliced mRNAs. Rex protein acts through a cis element (rex-response element [RxRE]) which is located in the U3/R region of the 3' long terminal repeat and is present on all human T-cell leukemia virus type I-specific mRNAs. Two domains of the predicted secondary structure of the RxRE are crucially important for Rex action in vivo as measured by two assay systems. In vitro studies using highly purified recombinant Rex protein revealed a specific and direct interaction with radiolabeled RxRE sequences. The correlation between our in vivo results and the direct binding of Rex protein to mutant and wild-type RxRE sequences supports both the existence of the predicted secondary structure and the importance of this direct interaction with the cis-acting RNA sequence for Rex function in vivo.

trans-activation of the HIV-1 LTR by the HIV-1 Tat and HTLV-I Tax proteins is mediated by different cis-acting sequences

Human immunodeficiency virus type 1 (HIV-1) gene expression is regulated by viral and cellular factors interacting with cis-elements located in the retroviral long terminal repeat (LTR). In this report we analyzed HIV-1 LTR-specific regulatory sequences responsive to the HIV-1 Tat and HTLV-I Tax trans-activator proteins. Our results indicate that the Sp1 binding sites in the HIV-1 LTR are crucially involved in Tat-mediated gene expression in human Jurkat T-cells whereas they are dispensable for HTLV-I Tax-induced activation. In contrast, the NF-kB binding sites within the HIV-1 LTR are essential for Tax-mediated transcription but had only marginal effect on Tat-induced reporter gene expression.

Mutational analysis of the human T-cell leukemia virus type I trans-acting rex gene product

Expression of the human T-cell leukemia virus type I (HTLV-I) rex gene is a prerequisite for the expression of the retroviral structural proteins. We have generated internal deletion mutants of this 27-kDa nucleolar trans-acting gene product to define functional domains in the Rex protein. The phenotype of the various mutant proteins was tested on the homologous HTLV-I rex response element sequence and the heterologous human immunodeficiency virus type 1 (HIV-1) rev response element sequence. Our results indicate that a region between amino acid residues 55 and 132 in the 189-amino-acid Rex protein is required for Rex-mediated trans activation on both retroviral response element sequences. In addition, substitution of the Rex nuclear localization signal by a sequence of the HIV-1 rev gene product targets the Rex protein to the correct subcellular compartment required for Rex function.

The lentivirus regulatory proteins REV and REX are site specific RNA binding proteins

These studies demonstrate that HIV-1 REV and HTLV-1 REX are site specific RNA binding proteins. In addition, the REV protein studies indicate a protein domain essential for biological function that is not involved in RRE binding. Lentiviruses are unique among retroviruses in providing gene products to switch expression from early to late genes. Rather than transcriptional control, this is accomplished by regulating RNA transport. A further understanding of these lentiviral genes may identify means of inhibiting viruses responsible for insidious human disease.

Activation of the interleukin-2 receptor alpha gene: regulatory role for DNA-protein interactions flanking the kappa B enhancer

The human interleukin-2 receptor alpha (IL2R alpha) gene is transcriptionally activated by both phorbol esters and the HTLV-I trans-activator (Tax) protein through a mechanism that involves the interaction of inducible DNA binding proteins with a kappa B-like enhancer element (-267 to -256). Using mutated IL2R alpha promoter constructs in transient transfection and DNA binding assays, we now demonstrate that sequences located immediately upstream and downstream of the kappa B enhancer also contribute to the regulation of IL2R alpha gene expression. One upstream sequence termed UE-1 is preferentially required for phorbol ester relative to Tax-induced activation and specifically interacts with a constitutively expressed 56-kD cellular factor. In contrast, two overlapping downstream elements between nucleotides -252 and -239 appear to be required for both phorbol ester and Tax-induced activation. One of these elements, an Sp1-like sequence, binds a constitutively expressed 100-kD T-cell protein consistent in size with Sp1 isolated from HeLa cells. The second element, located between the kappa B and Sp1 sites, resembles the decanucleotide core of the serum response element (SRE) from the c-fos gene and interacts with a constitutively expressed factor. Together, these findings implicate a functional role for multiple constitutively expressed DNA binding proteins, in addition to the inducible kappa B-specific factors, in the overall regulation of IL2R alpha gene activation.

HIV-1, HTLV-1 and normal T-cell growth: transcriptional strategies and surprises

In this review, Warner Greene and colleagues discuss recent studies that have revealed an intriguing molecular interplay between two pathogenic human retroviruses, HIV-1 and HTLV-1, and certain cellular genes that normally control T-cell growth. Activation of T cells during an immune response results in the induction of select transcription factors that bind specifically to kappa B enhancer elements present in both the IL-2R alpha and IL-2 genes. Normal T-cell growth is in part regulated by the transient expression of these genes. The Tax protein of HTLV-1 induces these same kappa B-specific proteins, but in contrast to immune stimulation, HTLV-1 infection of T cells leads to constitutive IL-2R alpha gene expression and immortalization. A second human retrovirus, HIV-1, can subvert the normal action of the kappa B-binding factors induced by these immune stimuli. Rather than promoting T-cell growth, these factors may augment viral replication and promote T-cell death.

Functional characterization of a complex protein-DNA-binding domain located within the human immunodeficiency virus type 1 long terminal repeat leader region

Transcriptional trans activation of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) by the viral tat trans activator is mediated by an LTR-specific sequence located immediately 3' to the start of transcription initiation. We have used a range of molecular techniques to examine DNA-protein interactions that occur in the vicinity of this cis-acting sequence. Our results demonstrate the existence of a sequence-specific DNA-protein interaction involving the HIV-1 leader DNA and map this binding event to between -2 and +21 base pairs relative to the HIV-1 LTR transcription start site. Evidence suggesting that this interaction involves three distinct protein-DNA contact sites extending along one side of the DNA helix is presented. Mutation of these sites was found to ablate protein-DNA binding yet was observed to have no effect on either the basal or tat trans-activated level of HIV-1 LTR-specific gene expression. We therefore conclude that this DNA-protein interaction has a function distinct from the regulation of HIV-1 LTR-specific gene expression.

Induction of interleukin-2 receptor-alpha gene expression is regulated by post-translational activation of kappa B specific DNA binding proteins

T cell mitogens induce the expression of specific trans-acting DNA binding proteins that in turn regulate the expression of the interleukin-2 receptor-alpha (IL-2R alpha) gene. To investigate whether de novo protein synthesis is required for the activation of these transacting factors and the induced expression of this receptor gene, Jurkat T cells were incubated with various inhibitors of protein synthesis prior to stimulation with phytohemagglutinin and phorbol 12-myristate 13-acetate (PMA). Despite the presence of cycloheximide or anisomycin at concentrations sufficient to block greater than 97% of cellular protein synthesis, phytohemagglutinin and phorbol 12-myristate 13-acetate effectively induced the expression of the IL-2R alpha gene as measured at the mRNA level. Similarly, gel retardation, DNA footprinting, and DNA-protein cross-linking studies revealed that these mitogens induced the activation of two predominant DNA binding proteins (50-55 and 80-90 kDa) in the presence or absence of cycloheximide and anisomycin. Both of these proteins specifically interacted with a kappa B-like binding site present in the IL-2R alpha promoter (-267 to -256) that is requisite for mitogen-induced expression of this receptor gene. These findings support a post-translational mechanism of induction of pre-existing, but inactive, DNA binding proteins which in turn bind to and activate the IL-2R alpha gene.

Tumor necrosis factor-alpha activation of the IL-2 receptor-alpha gene involves the induction of kappa B-specific DNA binding proteins

TNF-alpha induces the expression of IL-2R and promotes the proliferation and differentiation of T and B cells. In this report, we have studied the biochemical basis for TNF-alpha activation of the IL-2R alpha (Tac, p55) gene. Transfection of human T cell lines with selectively mutated forms of the IL-2R alpha promoter revealed that a kappa B element (nucleotides -267 to -256), as well as 5' flanking sequences (nucleotides -281 to -271) are required for TNF-alpha induction of this transcriptional unit. DNA binding studies demonstrated that this IL-2R alpha kappa B control element is specifically bound by a set of TNF-alpha inducible T cell nuclear proteins of relative Mr 80 to 90, 50 to 55, and 38 to 42 kDa. This protein recognition site from the IL-2R alpha promoter, as well as related kappa B motifs from the long terminal repeat of the type I human immunodeficiency virus, proved sufficient to impart TNF-alpha inducibility to an unresponsive heterologous promoter. These findings suggest that TNF-alpha-stimulated expression of the IL-2R alpha gene involves the induction of specific DNA binding proteins that in turn interact with a kappa B-like promoter element and facilitate activation of this transcription unit.

Tumor necrosis factor-alpha activation of the IL-2 receptor-alpha gene involves the induction of kappa B-specific DNA binding proteins

TNF-alpha induces the expression of IL-2R and promotes the proliferation and differentiation of T and B cells. In this report, we have studied the biochemical basis for TNF-alpha activation of the IL-2R alpha (Tac, p55) gene. Transfection of human T cell lines with selectively mutated forms of the IL-2R alpha promoter revealed that a kappa B element (nucleotides -267 to -256), as well as 5' flanking sequences (nucleotides -281 to -271) are required for TNF-alpha induction of this transcriptional unit. DNA binding studies demonstrated that this IL-2R alpha kappa B control element is specifically bound by a set of TNF-alpha inducible T cell nuclear proteins of relative Mr 80 to 90, 50 to 55, and 38 to 42 kDa. This protein recognition site from the IL-2R alpha promoter, as well as related kappa B motifs from the long terminal repeat of the type I human immunodeficiency virus, proved sufficient to impart TNF-alpha inducibility to an unresponsive heterologous promoter. These findings suggest that TNF-alpha-stimulated expression of the IL-2R alpha gene involves the induction of specific DNA binding proteins that in turn interact with a kappa B-like promoter element and facilitate activation of this transcription unit.

Kappa B-specific DNA binding proteins: role in the regulation of human interleukin-2 gene expression

Transcriptional activation of the human interleukin-2 (IL-2) gene, like induction of the IL-2 receptor alpha (IL-2R alpha) gene and the type 1 human immunodeficiency virus (HIV-1), is shown to be modulated by a kappa B-like enhancer element. Mutation of a kappa B core sequence identified in the IL-2 promoter (-206 to -195) partially inhibits both mitogen- and HTLV-I Tax-mediated activation of this transcription unit and blocks the specific binding of two inducible cellular factors. These kappa B-specific proteins (80 to 90 and 50 to 55 kilodaltons) similarly interact with the functional kappa B enhancer present in the IL-2R alpha promoter. These data suggest that these kappa B-specific proteins have a role in the coordinate regulation of this growth factor-growth factor receptor gene system that controls T cell proliferation.

Tumor necrosis factor alpha induces proteins that bind specifically to kappa B-like enhancer elements and regulate interleukin 2 receptor alpha-chain gene expression in primary human T lymphocytes

We have investigated the biochemical basis for the activation of interleukin 2 receptor alpha-subunit (IL-2R alpha) gene expression in primary human T lymphocytes by a cytokine (tumor necrosis factor alpha), a T-cell mitogen (phorbol 12-myristate 13-acetate), and the transactivator protein (Tax) from the type I human T-cell leukemia virus. Using in vivo transfection techniques specificially designed for these primary T cells in conjunction with in vitro gel retardation and DNA footprinting assays, we found that activation of the IL-2R alpha promoter by each of these agents involves the induction of nuclear proteins that specifically interact with a kappa B-like enhancer element (i.e., an element resembling the immunoglobulin kappa-chain enhancer sequence recognized by transcription factor NF-kappa B). DNA-protein crosslinking studies revealed that primary T cells express at least three different inducible DNA-binding proteins (50-55, 70-75, and 80-90 kDa) that specifically interact with this IL-2R alpha kappa B element.

Stimulation of the human immunodeficiency virus type 1 enhancer by the human T-cell leukemia virus type I tax gene product involves the action of inducible cellular proteins

The human immunodeficiency virus type 1 (HIV-1) preferentially infects CD4+ T lymphocytes and may exist as a latent provirus within these cells for extended periods. The transition to a productive retroviral infection results in T-cell death and clinically may lead to the acquired immune deficiency syndrome. Accelerated production of infectious HIV-1 virions appears to be closely linked to a heightened state of T-cell activation. The transactivator (Tax) protein of the type I human T-cell leukemia virus (HTLV-I) can produce such an activated T-cell phenotype and augments activity of the HIV-1 long terminal repeat. One Tax-responsive region within the HIV-1 long terminal repeat has been mapped to a locus composed of two 10-base-pair direct repeats sharing homology with the binding site for the eucaryotic transcription factor NF-kappaB (GGGACTTTCC). Tax-expressing Jurkat T cells contain one or more inducible cellular proteins that specifically associate with the HIV-1 enhancer at these binding sites. Microscale DNA affinity precipitation assays identified a Tax-inducible 86-kilodalton protein, HIVEN86A, as one of these HIV-1 enhancer-binding factors. The interaction of HIVEN86A, and presumably other cellular proteins, with the HIV-1 enhancer appears functionally important as oligonucleotides corresponding to this enhancer were sufficient to impart Tax inducibility to an unresponsive heterologous promoter. These findings suggest that the Tax-inducible cellular protein HIVEN86A plays an important role in the transcriptional activation of the HIV-1 enhancer. These specific protein-DNA interactions may also be important for the transition of HIV-1 from a latent to a productive mode of infection. Furthermore, these findings highlight an intriguing biological interplay between HTLV-1 and HIV-1 through a cellular transcriptional pathway that is normally involved in T-cell activation and growth.

HIV-1, HTLV-I and the interleukin-2 receptor: insights into transcriptional control

In this study, we present direct evidence for the binding of the inducible cellular protein, HIVEN86A, to a 12-bp element present in the IL-2R alpha promoter. This element shares significant sequence similarity with the NF-kappa B binding sites present in the HIV-1 and kappa immunoglobulin enhancers. Transient transfection studies indicate that this kappa B element is both necessary and sufficient to confer tax or mitogen inducibility to a heterologous promoter. As summarized schematically in Fig. 5, the findings suggest that the HIVEN86A protein may play a central role in the activation of cellular genes required for T-cell growth, specifically the IL-2R alpha gene. In addition, the induced HIVEN86A protein also binds to a similar sequence present in the HIV-1 LTR leading to enhanced viral gene expression and ultimately T-cell death. Thus, mitogen activation of the HIV-1 LTR appears to involve the same inducible transcription factor(s) that normally regulates IL-2R alpha gene expression and T-cell growth. These findings further underscore the importance of the state of T-cell activation in the regulation of HIV-1 replication. Our results also demonstrate that HIVEN86A is induced by the tax protein of HTLV-I. Thus, in HTLV-I infected cells, normally the tight control of the transient expression of the IL-2R alpha gene is lost. The constitutive high-level display of IL-2 receptors may play a role in leukemic transformation mediated by HTLV-I (ATL). Apparently by the same mechanism, the tax protein also activates the HIV-1 LTR through the induction of HIVEN86A.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and amplification in transgenic mice of a polyoma virus mutant regulatory region

Two hybrid gene constructs consisting of wild-type and mutant polyoma regulatory regions fused to a bacterial reporter gene were inserted in the mouse germline. Both transgenes were expressed in a large number of different organs. However, marker gene expression controlled by the polyoma wild-type regulatory region was not detectable in the early embryo and remained low throughout the life of the animal while expression controlled by the polyoma F9-1 mutation was detectable in blastocysts and was significantly higher at later stages of development. The F9-1 hybrid gene was also amplifiable when large T-antigen was supplied in trans to mice or to kidney cells derived from these transgenic mice. Amplification resulted in the appearance of several hundred copies of episomal transgenes and a marked increase of marker gene RNA and protein. Our results suggest that the F9-1 mutation does not alter the target spectrum of gene expression in vivo but does create a more efficient enhancer element in the polyoma early control region. Transgene amplification based upon use of the polyoma regulatory elements may be a means of increasing expression of genes in transgenic mice.