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Biomedical subjects

B B Aggarwal

Publications and source records attributed to B B Aggarwal.

At least 109 records · Page 6Linked to original sources
PubMed1996

Transcriptional up-regulation of interleukin 4 receptors by human immunodeficiency virus type 1 tat gene.

The human immunodeficiency virus type 1 (HIV-1) regulatory gene, tat, encodes an early transactivator protein (Tat) necessary for virus replication. We have reported that the HIV-1 tat gene can up-regulate interleukin 4 receptors (IL-4R) however, the mechanism of this up-regulation is not understood. We now show that in Raji cells, 125I-labeled IL-4 cross-linked to three proteins of 140, 70, and 63 kDa, which were immunoprecipitated with an antibody to the human IL-4R. Although this level of all three IL-4 binding proteins increased in tat-transfected cells, the binding characteristics of IL-4R on control or mock transfected control and tat-transfected cells remained similar. The exogenous recombinant Tat protein or supernatant of tat transfected Raji cells also up-regulated the expression of the IL-4R on two renal cell carcinoma cell lines in a concentration-dependent manner. The actinomycin D chase experiments revealed that the half-lives of the IL-4R protein (t1/2 3.5 hr) and mRNA transcripts (t1/2 2.5 hr) were similar in both control and tat-transfected cells. In contrast, nuclear run-on experiments revealed that the rate of the IL-4R mRNA transcription increased 3- to 5-fold in Raji-tat compared to Raji cells. These data indicate that the HIV-1 tat gene up-regulates IL-4R expression by increasing the transcription rate rather than posttranscriptional stabilization of either the mRNA or the protein. HIV-tat inducible exogenous tumor necrosis factor (TNF-alpha) did not up-regulate IL-4R and IL-4R inducible activation of signal transducers and activators of transcription (STAT-6) was not observed by Tat even though IL-4R were up-regulated. These results allow us to speculate that HIV-1 tat may interact directly with the IL-4R gene and up-regulate IL-4R transcription.

Antigens, CD↗
PubMed1996

Differential activation of the nuclear factor-kappa B by TNF muteins specific for the p60 and p80 TNF receptors.

Human TNF is a highly pleiotropic cytokine that mediates its effects by binding to two distinct receptors, viz p60 and p80, which transmit their signals independently of each other. Activation of the transcription factor NF-kappa B is one of the earliest events induced by TNF, but whether it is mediated through one or both forms of the TNF receptor is controversial. in the present studies, we examined the role of each receptor in the activation of NF-kappa B by using TNFs that has been designed by site-specific mutagenesis to bind either the p60 (R32W; S86T) or the p80 (D143N; A145R) form of the receptor. Human myelogenous leukemic ML-1 a cells known to express almost equal amounts of the two receptors were used. The binding of TNF to these cell could be inhibited equally by either TNF(p60) or TNF(p80) mutein. Treatment of these cells with TNF(p60) mutein activate NF-kappa B within 30 min, whereas TNF(p80) mutein, even at a 1000-fold excess, had no effect, suggesting that the activation of NF-kappa B is differentially regulated through the p60 receptor. Consistent with these results, treatment with either anti-p80 monoclonal or polygonal Abs blocked the binding of TNF to the p80 receptor without affecting TNF-mediated activation of NF-kappa B TNF(p60) mutein was also effective in cell killing, but the TNF(p80) mutein was totally ineffective. The effect was not cell type-specific, since other p80-expressing cell lines were also unresponsive. Overall, our results clearly demonstrate that the activation of NF-kappa B and cytotoxicity by TNF is differentially regulated through the p60 receptor.

Antibodies↗
PubMed1996

Caffeic acid phenethyl ester is a potent and specific inhibitor of activation of nuclear transcription factor NF-kappa B.

Caffeic acid phenethyl ester (CAPE), an active component of propolis from honeybee hives, is known to have antimitogenic, anticarcinogenic, antiinflammatory, and immunomodulatory properties. The molecular basis for these diverse properties is not known. Since the role of the nuclear factor NF-kappa B in these responses has been documented, we examined the effect of CAPE on this transcription factor. Our results show that the activation of NF-kappa B by tumor necrosis factor (TNF) is completely blocked by CAPE in a dose- and time-dependent manner. Besides TNF, CAPE also inhibited NF-kappa B activation induced by other inflammatory agents including phorbol ester, ceramide, hydrogen peroxide, and okadaic acid. Since the reducing agents reversed the inhibitory effect of CAPE, it suggests the role of critical sulfhydryl groups in NF-kappa B activation. CAPE prevented the translocation of the p65 subunit of NF-kappa B to the nucleus and had no significant effect on TNF-induced I kappa B alpha degradation, but did delay I kappa B alpha resynthesis. The effect of CAPE on inhibition of NF-kappa B binding to the DNA was specific, in as much as binding of other transcription factors including AP-1, Oct-1, and TFIID to their DNA were not affected. When various synthetic structural analogues of CAPE were examined, it was found that a bicyclic, rotationally constrained, 5,6-dihydroxy form was superactive, whereas 6,7-dihydroxy variant was least active. Thus, overall our results demonstrate that CAPE is a potent and a specific inhibitor of NF-kappa B activation and this may provide the molecular basis for its multiple immunomodulatory and antiinflammatory activities.

Base Sequence↗
PubMed1996

Acidic sphingomyelinase-generated ceramide is needed but not sufficient for TNF-induced apoptosis and nuclear factor-kappa B activation.

Previously we have shown that treatment of ML-1a cells with TNF in the presence of cycloheximide triggers apoptosis within 90 min. In the present report we used this system to investigate the role of ceramide in TNF action. We found that while maximum DNA fragmentation response was induced by 1 nM TNF, the synthetic membrane-permeable C-2, C-6, and C-8 ceramides had no effect even up to 40 microM concentration. To investigate the roles of ceramide in TNF action, we used ((2-isopropyl-1-(4-[3-N-methyl-N-(3,4-dimethoxy-phenethyl)amino] propyloxy)benzenesulfonyl))indolizine (SR33557), a potent inhibitor of acidic but not neutral sphingomyelinase (SMase). Even though ceramides by themselves did not mimic TNF, we found that SR33557 inhibited TNF-induced apoptosis and the addition of ceramide reversed this effect, indicating that ceramide generated by acidic SMase is involved in TNF action. The addition of SR33557 to cells at 0 or at 30 min after TNF treatment showed inhibition, but the addition 60 min later had no effect, indicating that an SR33557-sensitive step is located between 30 and 60 min of signal transduction. Since ceramide has been shown to play a role in TNF-mediated activation of nuclear factor-kappa B (NF-kappa B), we examined the effect of SR33557 on this early cellular response of TNF. Surprisingly, this inhibitor of ceramide production was found to have no effect on TNF-mediated NF-kappa B activation, thus suggesting that SR33557-sensitive acidic SMase is not involved in this process. From these results, we concluded that ceramide is needed for certain TNF-mediated cellular responses, but it alone may not be sufficient.

Apoptosis↗
PubMed1996

Qualitative and quantitative differences in the cellular responses mediated through Fas antigen and tumor necrosis factor receptor.

Like tumor necrosis factor (TNF), antibodies against the Fas antigen (anti-Fas) are cytotoxic to some and induce proliferation of other Fas-expressing cells. In this study, we compared cellular responses mediated through TNF with anti-Fas using a T cell line (Jurkat) and a macrophage cell line (U-937). These two cell types differed in that the Jurkat cells expressed higher levels of Fas antigen than U-937 cells, whereas the latter expressed higher levels of the p80 form of the TNF receptor than Jurkat cells. Treatment for 72 h with anti-Fas inhibited the growth of both Jurkat and U-937 cells, the 50% inhibitory concentrations (IC50) being 10 and 100 ng/ml, respectively. Under similar conditions, the IC50 for TNF was > 100 and 0.8 ng/ml for Jurkat and U-937 cells, respectively. Like TNF, the cytotoxic effects of anti-Fas were potentiated by cycloheximide, showing they did not require protein synthesis. Interestingly, in the presence of cycloheximide, the kinetics of cell killing was more rapid for TNF than anti-Fas (50% inhibition occurred at 3 versus 6h). Treatment of both cell types with anti-Fas led to time-dependent DNA fragmentation, but TNF-induced DNA fragmentation occurred only in the presence of cycloheximide. Pretreatment of cells with TNF led to resistance to TNF but not to anti-Fas, suggesting that the receptors for the two are not cross-modulated. Furthermore, TNF activated the nuclear transcriptional factor NF-kappa B in both cell types, whereas anti-Fas had no effect. Overall, our results demonstrate that anti-Fas and TNF transduce over-lapping and nonoverlapping signals in macrophage-like and T cell lines through distinct pathways.

Base Sequence↗
PubMed1995

Activation of transcription factor NF-kappa B is suppressed by curcumin (diferuloylmethane) [corrected].

When activated, NF-kappa B, a ubiquitous transcription factor, binds DNA as a heterodimeric complex composed of members of the Rel/NF-kappa B family of polypeptides. Because of its intimate involvement in host defense against disease, this transcription factor is an important target for therapeutic intervention. In the present report we demonstrate that curcumin (diferuloylmethane), a known anti-inflammatory and anticarcinogenic agent, is a potent inhibitor of NF-kappa B activation. Treatment of human myeloid ML-1a cells with tumor necrosis factor (TNF) rapidly activated NF-kappa B, which consists of p50 and p65 subunits, and this activation was inhibited by curcumin. AP-1 binding factors were also found to be down-modulated by curcumin, whereas the Sp1 binding factor was unaffected. Besides TNF, curcumin also blocked phorbol ester- and hydrogen peroxide-mediated activation of NF-kappa B. The TNF-dependent phosphorylation and degradation of I kappa B alpha was not observed in curcumin-treated cells; the translocation of p65 subunit to the nucleus was inhibited at the same time. The mechanism of action of curcumin was found to be different from that of protein tyrosine phosphatase inhibitors. Our results indicate that curcumin inhibits NF-kappa B activation pathway at a step before I kappa B alpha phosphorylation but after the convergence of various stimuli.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1995

Transfection of cells with basic fibroblast growth factor and Kaposi fibroblast growth factor genes induce resistance to and receptor modulation of tumor necrosis factor.

Tumor necrosis factor (TNF) has been shown to inhibit the growth of some cell types and stimulate the proliferation of others by a mechanism that is not understood. In the present study, we investigated the effect of transfection of NIH-3T3 cells with either the basic fibroblast growth factor gene (bFGF) or the kaposi FGF gene (K-fgf) on the growth-modulatory effects of TNF. Our results show that transformation of cells with either gene leads to resistance to the growth-inhibitory effects of TNF. The K-fgf gene was found to be a more potent inducer of cellular resistance than the bFGF gene. The cellular resistance correlated with the inhibition of TNF-induced activation of phospholipase A2 and down-modulation of TNF receptors. Overall, our results indicate that both K-fgf and bFGF play an important role in suppression of antiproliferative effects of TNF.

3T3 Cells↗
PubMed1995

Protease inhibitors differentially regulate tumor necrosis factor-induced apoptosis, nuclear factor-kappa B activation, cytotoxicity, and differentiation.

We investigated the effect of various protease inhibitors on several tumor necrosis factor (TNF)-mediated cellular responses. Treatment of a human myelogenous leukemia cell line, ML-1a, with TNF in the presence of cycloheximide triggers endonucleolytic activity and apoptotic cell death within 90 minutes. The general serine protease inhibitor diisopropyl fluorophosphate (DFP) and the chymotrypsin-like protease inhibitor N-tosyl-L-lysyl chloromethyl ketone (TPCK) completely abrogated TNF-induced DNA fragmentation and the formation of apoptotic bodies. However, 13 other protease inhibitors, including serine protease inhibitors, did not. The addition of TPCK to cells 30 minutes after TNF treatment completely inhibited the cytokine action, indicating that TPCK-sensitive proteases are not involved in the early stages of signal transduction. TNF is cytotoxic and induces differentiation in ML-1a cells after a 3-day incubation. TPCK had no effect on the TNF-induced cytotoxicity and differentiation, indicating that TPCK-sensitive proteases are specific for DNA fragmentation. TPCK also blocked TNF-induced activation of nuclear factor (NF)-kappa B. The dose-response and the time-course of the inhibitor, however, indicated that the site of action of TPCK for NF-kappa B activation and for DNA fragmentation are quite distinct. Therefore, we conclude that TNF activates two distinct TPCK-sensitive pathways, one leading to apoptosis and the other to NF-kappa B activation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

The p60 tumor necrosis factor (TNF) receptor-associated kinase (TRAK) binds residues 344-397 within the cytoplasmic domain involved in TNF signaling.

The p60 form of the tumor necrosis factor (TNF) receptor lacks motifs characteristic of tyrosine or serine/threonine protein kinases. Our recent observations have indicated that a p60 TNF receptor-associated kinase (p60-TRAK) from U-937 cells physically interacts with and causes the phosphorylation of the cytoplasmic domain of the TNF receptor. To define which region of the cytoplasmic domain is necessary for physical interaction with p60-TRAK, we constructed a series of deletions (grouped into three sets delta 1-delta 5, delta 6-delta 12, and delta 13-delta 16) of the p60 cytoplasmic domain, expressed them as glutathione S-transferase (GST) fusion proteins, and used them in affinity precipitations, followed by in vitro kinase assays. Our detailed analysis indicated that a serine-, threonine-, and proline-rich region (residues 243-274, delta 2) and the N-terminal half of the cytoplasmic domain (residues 243-323, delta 3) neither associated with p60-TRAK nor underwent phosphorylation. We found that out of 222 residues (205-426) in the cytoplasmic domain, only 54 (344-397, delta 12) were sufficient for binding p60-TRAK and for phosphorylation of the cytoplasmic domain. A region of approximately 30 residues (397-426) at the C-terminal end was found to interfere with optimal binding of the p60-TRAK activity. Thus, our results indicate that the minimal region of the cytoplasmic domain necessary for interacting with p60-TRAK and for phosphorylation resides within the domain previously reported to be needed for signaling the cytotoxic effect of TNF.

Binding Sites↗
PubMed1995

Retinoids downregulate both p60 and p80 forms of tumor necrosis factor receptors in human histiocytic lymphoma U-937 cells.

Because retinoids are known to modulate the growth and differentiation effects of tumor necrosis factor (TNF), we investigated the effect of all-trans-retinoic acid (RA) on the cell surface expression of TNF receptors in human histiocytic lymphoma U-937 cells. RA decreased the specific binding of 125I-labeled TNF to these cells in a dose- and time-dependent manner. The maximal decrease occurred when cells were treated with 1 mumol/L RA for 24 hours at 37 degrees C. Scatchard analysis of the binding indicated that the decrease by RA was caused by a decrease in receptor number and not by a decrease in affinity. The downmodulation of TNF receptors was also confirmed by covalent receptor-ligand cross-linking studies. Receptor-mediated internalization of the ligand was also found to be decreased on treatment of cells with RA. Northern blot analysis also indicated a decrease in the transcript of the receptor. By using antibodies specific to either the p60 or p80 form of the TNF receptor, we found that both receptors were downregulated by RA. RA treatment also decreased TNF receptors on acute monocytic leukemia cell line THP-1. Other analogues of RA, specifically 9-cis-RA, (E)-4-[2-(5,6,7,8- tetrahydro-2-naphthalenyl)-1-propenyl]-benzoic acid (TTNPB), and 3-methyl-TTNPB, which differ in their specificity towards different RA receptors, were also active in downregulating TNF receptors. 3-Methyl-TTNPB, which is more specific for the RXR form of the RA receptor, was found to be most potent. The downregulation of TNF receptors by RA correlated with the downmodulation of the antiproliferative effects of TNF against U-937 cells. Overall, our results indicate that RA downmodulates both the p60 and p80 form of the TNF receptor on cells of myeloid origin, which correlates with the cellular response.

Down-Regulation↗
PubMed1995

Protein-tyrosine phosphatase inhibitors block tumor necrosis factor-dependent activation of the nuclear transcription factor NF-kappa B.

Most of the inflammatory and proviral effects of tumor necrosis factor (TNF) are mediated through the activation of the nuclear transcription factor NF-kappa B. How TNF activates NF-kappa B, however, is not well understood. We examined the role of protein phosphatases in the TNF-dependent activation of NF-kappa B. Treatment of human myeloid ML-1a cells with TNF rapidly activated (within 30 min) NF-kappa B; this effect was abolished by treating cells with inhibitors of protein-tyrosine phosphatase (PTPase), including phenylarsine oxide (PAO), pervanadate, and diamide. The inhibition was dependent on the dose and occurred whether added before or at the same time as TNF. PAO also inhibited the activation even when added 15 min after the TNF treatment of cells. In contrast to inhibitors of PTPase, okadaic acid and calyculin A, which block serine-threonine phosphatase, had no effect. The effect of PTPase inhibitors was not due to the modulation of TNF receptors. Since both dithiothreitol and dimercaptopropanol reversed the inhibitory effect of PAO, critical sulfhydryl groups in the PTPase must be involved in NF-kappa B activation by TNF. PTPase inhibitors also blocked NF-kappa B activation induced by phorbol ester, ceramide, and interleukin-1 but not that activated by okadaic acid. The degradation of I kappa B protein, a critical step in NF-kappa B activation, was also abolished by the PTPase inhibitors as revealed by immunoblotting. Thus, overall, we demonstrate that PTPase is involved either directly or indirectly in the pathway leading to the activation of NF-kappa B.

Adenosine Triphosphate↗
PubMed1995

Fas antigen signals proliferation of normal human diploid fibroblast and its mechanism is different from tumor necrosis factor receptor.

Recent cloning of the cDNA for Fas/Apo-1 and its ligand has revealed that they belong to the tumor necrosis factor (TNF) receptor and TNF family, respectively, and play an important role in apoptosis (programmed cell death). Like TNF, antibodies against the Fas antigen (anti-Fas) have been shown to be cytotoxic to Fas-expressing cells. Whether Fas, like TNF receptor, also mediates proliferation of normal human diploid fibroblasts (HDF), is not known. In this study, we show that HDF expresses Fas antigen and the engagement of this antigen signals proliferation of these cells in a dose-dependent manner. Unlike TNF receptor, however, Fas-mediated proliferation of HDF could not be blocked by orthovanadate, a tyrosine phosphatase inhibitor. The difference in the signaling was further evident from our observation that TNF induced the expression of interleukin-6 but anti-Fas did not. Overall, our results demonstrate for the first time that besides cell killing, Fas also mediates proliferation of HDF and that its mechanism is different from that of TNF receptor.

Antibodies↗
PubMed1995

Characterization of the apoptotic effects of human tumor necrosis factor: development of highly rapid and specific bioassay for human tumor necrosis factor and lymphotoxin using human target cells.

Currently available bioassays for most cytokines require several days and therefore must be performed under sterile conditions. In this report we describe a bioassay for tumor necrosis factor (TNF) and lymphotoxin (LT) that is extremely rapid and specific and does not require sterile conditions. Using tritiated thymidine release, we could conveniently monitor degradation of DNA into small fragments following the incubation of human myelogenous leukemia ML-1a cells with TNF. The assay showed that TNF-dependent DNA fragmentation was potentiated by cycloheximide and occurred within 90 min. Treatment of cells to TNF lead to apoptosis as indicated by thymidine release, DNA laddering on agarose gels and morphological alterations. Under these conditions, plasma membrane were not damaged as indicated by lack of chromium release. This effect was linear with TNF concentration. This assay had high throughput, did not require sterile conditions, could be carried out in the absence of serum, and was sensitive only to TNF and LT and not to interferon (IFN)-alpha, IFN-beta, IFN-gamma, transforming growth factor beta, interleukin-4, leukemia inhibitory factor and granulocyte-monocyte colony stimulating factor; all cytokines known to inhibit different cell types. Besides detection of TNF in biological fluids, this assay may prove useful for the identification of novel inhibitors of TNF action.

Apoptosis↗
PubMed1995

Suppression of antiproliferative effects of tumor necrosis factor by transfection of cells with human platelet-derived growth factor B/c-sis gene.

The growth of cells is determined by the balance between growth-stimulatory and growth-inhibitory signals. In the present study, we demonstrate that the transfection of NIH 3T3 cells with a platelet-derived growth factor (PDGF-Blc-sis) gene induces resistance to the anticellular effects of tumor necrosis factor (TNF). Human tumor cell lines that express elevated levels of c-sis (e.g. epidermoid carcinoma, A-431) are also TNF resistant, whereas those that express no significant levels of this gene (e.g. breast adenocarcinoma, MCF-7) are TNF sensitive. Transfection of cells with the c-sis gene leads to down-modulation of TNF receptors and also a decrease in intracellular glutathione levels. Thus, our results demonstrate that over-expression of PDGF-Blc-sis by certain tumor cells can lead to their protection from the anticellular effects of TNF.

3T3 Cells↗
PubMed1995

Effect of cell cycle on the regulation of the cell surface and secreted forms of type I and type II human tumor necrosis factor receptors.

The cell cycle has been shown to regulate the biological effects of human tumor necrosis factor (TNF), but to what extent that regulation is due to the modulation of TNF receptors is not clear. In the present report we investigated the effect of the cell cycle on the expression of surface and soluble TNF receptors in human histiocytic lymphoma U-937. Exposure to hydroxyurea, thymidine, etoposide, bisbensimide, and demecolcine lead to accumulation of cells primarily in G1/S, S, S/G2/M, G2/M, and M stages of the cell cycle, respectively. While no significant change in TNF receptors occurred in cells arrested in G1/S or S/G2 stages, about a 50% decrease was observed in cells at M phase of the cycle. Scatchard analysis showed a reduction in receptor number rather than affinity. In contrast, cells arrested at S phase (thymidine) showed an 80% increase in receptor number. The decrease in the TNF receptors was not due to changes in cell size or protein synthesis. The increase in receptors, however, correlated with an increase in total protein synthesis (to 3.8-fold of the control levels). A proportional change was observed in the p60 and p80 forms of the TNF receptors. A decrease in the surface receptors in cells arrested in M phase correlated with an increase in the amount of soluble receptors. The cellular response to TNF increased to 8- and 2-fold in cells arrested in G1 and S phase, respectively; but cells at G2/M phase showed about 6-fold decrease in response. In conclusion, our results demonstrate that the cell cycle plays an important role in regulation of cell-surface and soluble TNF receptors and also in the modulation of cellular response.

Cell Cycle↗
PubMed1995

Diminished responsiveness of senescent normal human fibroblasts to TNF-dependent proliferation and interleukin production is not due to its effect on the receptors or on the activation of a nuclear factor NF-kappa B.

The limited life span in culture of normal human diploid fibroblasts (HDF) has provided a model of cellular senescence. The short-term growth of these cells in culture is regulated by a number of different cytokines, including tumor necrosis factor (TNF), interleukin-1 (IL-1), and fibroblast growth factor (FGF). However, the effect of senescence on the responsiveness of HDF to these cytokines is not known. In the present report, we examined the effects of TNF on foreskin-derived HDF at different passage levels. We compared the response of HDF cells at population doubling (PD) 23 (young) with that of cells at PD 70 (senescent). Young cells proliferated in response to TNF in a dose-dependent manner. Under these conditions TNF had no effect on senescent HDF. The decrease in TNF responsiveness was found to be dependent on PD. The lack of response of senescent HDF was not unique to TNF, since FGF and IL-1 were also ineffective. In contrast to senescent HDF, TNF-dependent proliferation of young HDF could be further potentiated by IL-1 and FGF, suggesting an independent signaling mechanism. On exposure to TNF, senescent HDF produced IL-6 and IL-8, but to a much lower degree than that produced by young HDF. The diminished responsiveness of senescent HDF to TNF does not appear to be due to the difference in either receptor number or affinity, since senescent cells had two- to threefold higher number of TNF receptors than young HDF but the same affinity. TNF induced the activation of a nuclear transcriptional factor, NF-kappa B, equally in both young and senescent cells, which indicates the lack of a defect in the early events of TNF signal transduction in senescent fibroblasts. Overall, our results indicate that there is an age-dependent decline in TNF-induced proliferation and in the production of interleukins by fibroblasts; this unresponsiveness appears not to be due to TNF receptors or NF-kappa B activation. These results may have importance in understanding the diminished immune response, inflammation, and wound healing associated with aging.

Base Sequence↗
PubMed1995

Constitutive expression of human immunodeficiency virus type 1 tat gene inhibits interleukin 2 and interleukin 2 receptor expression in a human CD4+ T lymphoid (H9) cell line.

Human immunodeficiency virus (HIV-1) tat, a trans-activator of the HIV long terminal repeat, is essential for HIV replication and causes inhibition of antigen-mediated T cell proliferation. To understand the mechanism of inhibition of T cell proliferation, we have investigated the regulation of IL-2 production and its receptor expression on a human CD4+ T lymphoid cell line (H9) transfected with HIV-1 tat gene. When cells were activated by mitogens, as compared to control cells, a significant decrease in both IL-2 mRNA and protein was observed in tat-transfected cells. Similarly, mitogen-induced IL-2R alpha and IL-2R beta mRNA and surface expression of IL-2R alpha and IL-2R beta chains were also significantly decreased in tat-transfected cells compared to control cells. Only IL-2 receptor density was decreased; the affinity of the ligand for the receptor appeared to be unchanged. In contrast to our previous studies with B-lymphoblastoid cell line (Puri RK and Aggarwal BB: Cancer Res 1992; 52:3787-3790), IL-4R expression was unaltered by HIV tat transfection in the H9 T cell line, indicating a cell type-specific phenomenon. Owing to the central role of IL-2 immunoregulation, our data suggest that immunosuppressive effects of HIV-1 tat may be mediated at least in part through the inhibition of both IL-2 production and IL-2 receptor expression.

CD4-Positive T-Lymphocytes↗