Microbial ligand-independent regulation of lymphopoiesis by NOD1

Aberrant differentiation of progenitor cells in the hematopoietic system is known to severely impact host immune responsiveness. Here we demonstrate that NOD1, a cytosolic innate sensor of bacterial peptidoglycan, also functions in murine hematopoietic cells as a major regulator of both the generation and differentiation of lymphoid progenitors as well as peripheral T lymphocyte homeostasis. We further show that NOD1 mediates these functions by facilitating STAT5 signaling downstream of hematopoietic cytokines. In steady-state, loss of NOD1 resulted in a modest but significant decrease in numbers of mature T, B and natural killer cells. During systemic protozoan infection this defect was markedly enhanced, leading to host mortality. Lack of functional NOD1 also impaired T cell-dependent anti-tumor immunity while preventing colitis. These findings reveal that, in addition to its classical role as a bacterial ligand receptor, NOD1 plays an important function in regulating adaptive immunity through interaction with a major host cytokine signaling pathway.

Increased Activity of a NK-Specific CAR-NK Framework Targeting CD3 and CD5 for T-Cell Leukemias

Simple Summary

Chimeric antigen receptors (CAR) can redirect the activity of NK cells to target T-cell malignancies. Our results identify that recognition of CD5 molecules in malignant T cells by the CAR leads to improved antitumor response compared to targeting CD3, due to strong downregulation of the CD3 antigen after CD3-CAR treatment. We have also identified that a specific CAR-NK framework has superior activity than a CAR-T framework on NK effector cells.

Abstract

NK effector cells expressing a CAR construct may be used to target T-lineage markers. In this work, we compared the activity of a NK-specific CAR-NK and a CAR-T framework when expressed on NK effector cells to target CD3 and CD5 in T-cell malignancies. Our results show that CD3-CAR-T is more active than CD5-CAR-T to eliminate malignant T cells in vitro, however, CD3-CAR-T were less efficient to eliminate tumor cells in vivo, while CD5-CAR-T had antitumor activity in a diffuse xenograft model. Lack of in vivo efficacy correlated with downregulation of CD3 levels in target T cells after coculture with CD3-CAR effector cells. The CAR-NK framework greatly improved the efficacy of CARs leading to increased degranulation, cytokine secretion and elimination of the tumor xenograft by CD5-CAR-NK effector cells. Finally, all CAR constructs were similarly effective to eliminate malignant T cells in vitro. Our results show that the NK-CAR framework improves the activity of CARs in NK cells and that CD5 would be a better target than CD3 for T-cell malignancies, as dynamic downregulation of target expression may affect in vivo efficacy.

Generation of Tumor Antigen-Specific iPSC-Derived Thymic Emigrants Using a 3D Thymic Culture System

Induced pluripotent stem cell (iPSC)-derived T cells may provide future therapies for cancer patients, but those generated by current methods, such as the OP9/DLL1 system, have shown abnormalities that pose major barriers for clinical translation. Our data indicate that these iPSC-derived CD8 single-positive T cells are more like CD4⁺CD8⁺ double-positive T cells than mature naive T cells because they display phenotypic markers of developmental arrest and an innate-like phenotype after stimulation. We developed a 3D thymic culture system to avoid these aberrant developmental fates, generating a homogeneous subset of CD8αβ⁺ antigen-specific T cells, designated iPSC-derived thymic emigrants (iTEs). iTEs exhibit phenotypic and functional similarities to naive T cells both in vitro and in vivo, including the capacity for expansion, memory formation, and tumor suppression. These data illustrate the limitations of current methods and provide a tool to develop the next generation of iPSC-based antigen-specific immunotherapies.

PD-1 Inhibitory Receptor Downregulates Asparaginyl Endopeptidase and Maintains Foxp3 Transcription Factor Stability in Induced Regulatory T Cells

CD4⁺ T cell differentiation into multiple T helper (Th) cell lineages is critical for optimal adaptive immune responses. This report identifies an intrinsic mechanism by which programmed death-1 receptor (PD-1) signaling imparted regulatory phenotype to Foxp3⁺ Th1 cells (denoted as Tbet⁺iTreg_PDL1 cells) and inducible regulatory T (iTreg) cells. Tbet⁺iTreg_PDL1 cells prevented inflammation in murine models of experimental colitis and experimental graft versus host disease (GvHD). Programmed death ligand-1 (PDL-1) binding to PD-1 imparted regulatory function to Tbet⁺iTreg_PDL1 cells and iTreg cells by specifically downregulating endo-lysosomal protease asparaginyl endopeptidase (AEP). AEP regulated Foxp3 stability and blocking AEP imparted regulatory function in Tbet⁺iTreg cells. Also, Aep^-/- iTreg cells significantly inhibited GvHD and maintained Foxp3 expression. PD-1-mediated Foxp3 maintenance in Tbet⁺ Th1 cells occurred both in tumor infiltrating lymphocytes (TILs) and during chronic viral infection. Collectively, this report has identified an intrinsic function for PD-1 in maintaining Foxp3 through proteolytic pathway.

Abstract 313: Tbata induces G2/M cell cycle arrest and sensitizes osteosarcoma cells to etoposide in a p53-independent manner

Thymus, brain, and testes-associated (Tbata) is a negative control cell-cycle gene highly expressed in murine thymic epithelial cells (TECs). Tbata protein binds to Uba3, inhibiting formation of Nedd8 E1 and subsequent target degradation via neddylation of several cell cycle control proteins needed for G2/M transition, which may be a major mechanism of TEC growth arrest during thymic involution. Etoposide is a cytotoxic drug which targets the enzyme toposimerase II — increased 2-3 fold during the G2 phase. To further characterize effect of Tbata on the cell cycle, we modified p53 wild-type U2OS cells derived from human osteosarcoma to express a Tbata/mCherry fusion protein when mifepristone is added to culture media. Tbata-expressing cells identified on flow cytometry did exhibit growth arrest, with quantitative assessment of DNA content in U2OS cells by flow cytometry establishing that 32% of Tbata/mCherry-expressing cells were in the G2 phase when exposed to mifepristone for 24 hours, compared to 11% of mCherry-expressing cells. Gene expression studies were consistent with these results. Cells expressing Tbata/mCherry were also more sensitive to etoposide at 0.5, 1, and 5 times the IC50 dose. To test whether p53 function was required, we further modified the cells to overexpress a dominant negative p53 mutant along with Tbata/mCherry. Similar G2 arrest and increased sensitivity to etoposide were observed, indicating that the effects of Tbata did not require normal p53 function. Potential Tbata analogues or mimetics may therefore be used as an adjunct to G2-targeted chemotherapy.

Citation Format: Milos D. Miljkovic, Francis A. Flomerfelt, Ronald E. Gress. Tbata induces G2/M cell cycle arrest and sensitizes osteosarcoma cells to etoposide in a p53-independent manner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 313. doi:10.1158/1538-7445.AM2017-313

In vivo kinetics and nonradioactive imaging of rapidly proliferating cells in graft-versus-host disease

Hematopoietic stem cell transplantation (HSCT) offers a cure for cancers that are refractory to chemotherapy and radiation. Most HSCT recipients develop chronic graft-versus-host disease (cGVHD), a systemic alloimmune attack on host organs. Diagnosis is based on clinical signs and symptoms, as biopsies are risky. T cells are central to the biology of cGVHD. We found that a low Treg/CD4+ T effector memory (Tem) ratio in circulation, lymphoid, and target organs identified early and established mouse cGVHD. Using deuterated water labeling to measure multicompartment in vivo kinetics of these subsets, we show robust Tem and Treg proliferation in lymphoid and target organs, while Tregs undergo apoptosis in target organs. Since deuterium enrichment into DNA serves as a proxy for cell proliferation, we developed a whole-body clinically relevant deuterium MRI approach to nonradioactively detect cGVHD and potentially allow imaging of other diseases characterized by rapidly proliferating cells.

Systemic toxoplasma infection triggers a long-term defect in the generation and function of naive T lymphocytes

Kugler et al. show that systemic infection with Toxoplasma gondii triggers a long-term impairment in thymic function, which leads to an immunodeficient state reflected in decreased antimicrobial resistance.

Because antigen-stimulated naive T cells either die as effectors or enter the activated/memory pool, continuous egress of new T lymphocytes from thymus is essential for maintenance of peripheral immune homeostasis. Unexpectedly, we found that systemic infection with the protozoan Toxoplasma gondii triggers not only a transient increase in activated CD4⁺ Th1 cells but also a persistent decrease in the size of the naive CD4⁺ T lymphocyte pool. This immune defect is associated with decreased thymic output and parasite-induced destruction of the thymic epithelium, as well as disruption of the overall architecture of that primary lymphoid organ. Importantly, the resulting quantitative and qualitative deficiency in naive CD4⁺ T cells leads to an immunocompromised state that both promotes chronic toxoplasma infection and leads to decreased resistance to challenge with an unrelated pathogen. These findings reveal that systemic infectious agents, such as T. gondii, can induce long-term immune alterations associated with impaired thymic function. When accumulated during the lifetime of the host, such events, even when occurring at low magnitude, could be a contributing factor in immunological senescence.

Analysis of Cell Proliferation and Homeostasis Using EdU Labeling

Determination of cellular proliferation and population turnover is an important tool for research on lymphoid cell function. Historically this has been done using radiolabeled nucleotides or nucleoside analogs, such as BrdU (5-bromo-2-deoxyuridine), that are incorporated into nascent DNA during S-phase. Recently, a new procedure was developed to label nascent DNA using EdU (5-Ethynyl-2-deoxyuridine). This new method overcomes limitations imposed by the procedure used to detect BrdU because EdU detection is based on an easily performed chemical reaction that does not require DNA denaturation, is quick and reproducible, and has a superior signal-to-noise ratio. This technique offers a wide range of opportunities to analyze cellular proliferation, population homeostasis, and cell marking procedures.

Distinct IL-7 signaling in recent thymic emigrants versus mature naïve T cells controls T-cell homeostasis

IL-7 is essential for T-cell survival but its availability is limited in vivo. Consequently, all peripheral T cells, including recent thymic emigrants (RTEs) are constantly competing for IL-7 to survive. RTEs are required to replenish TCR diversity and rejuvenate the peripheral T-cell pool. However, it remains unknown how RTEs successfully compete with resident mature T cells for IL-7. Moreover, RTEs express low levels of IL-7 receptors, presumably rendering them even less competitive. Here, we show that, surprisingly, RTEs are more responsive to IL-7 than mature naïve T cells as demonstrated by markedly increased STAT5 phosphorylation upon IL-7 stimulation. Nonetheless, adoptive transfer of RTE cells into lymphopenic host mice resulted in slower IL-7-induced homeostatic proliferation and diminished expansion compared to naïve donor T cells. Mechanistically, we found that IL-7 signaling in RTEs preferentially upregulated expression of Bcl-2, which is anti-apoptotic but also anti-proliferative. In contrast, naïve T cells showed diminished Bcl-2 induction but greater proliferative response to IL-7. Collectively, these data indicate that IL-7 responsiveness in RTE is designed to maximize survival at the expense of reduced proliferation, consistent with RTE serving as a subpopulation of T cells rich in diversity but not in frequency.

Toxoplasma gondii infection triggers a long-term defect in the generation and function of naive CD4+ T lymphocytes

Since Ag-stimulated naïve T cells either die as effectors or enter the activated/memory pool, continuous egress of new T lymphocytes from thymus is essential for maintenance of peripheral immune homeostasis. Unexpectedly, we found that systemic infection with the protozoan Toxoplasma gondii triggers not only a transient increase in activated CD4+ Th1 cells, but also a profound and persistent reduction in the size of the peripheral naïve CD4+ T cell pool. We further showed that the resulting perturbation in T cell homeostasis is mechanistically associated with parasite-induced thymic atrophy and more specifically with a loss in the architectural integrity of the thymic epithelium. This structural degeneration is accompanied by impaired thymic selection as evidenced by decreased CD5 expression on the few recent thymic emigrants that reach the periphery. The resulting quantitative and qualitative deficiency in naïve CD4+ T cells leads to an immunocompromised state that both promotes chronic toxoplasma infection and leads to decreased resistance to challenge with an unrelated pathogen. Interestingly, the changes in thymic structure and function induced by toxoplasma closely resemble those associated with the thymic involution that occurs during aging suggesting a possible influence of infection-induced alterations in the thymus on immunologic senescence.

This work was supported by the Intramural Research Program of the National Institute of Allergy and Infectious diseases.

High levels of IL-7 cause dysregulation of thymocyte development

IL-7 signaling is required for thymocyte development and its loss has a severe deleterious effect on thymus function. Thymocyte-stromal cell interactions and other mechanisms tightly regulate IL-7 expression. We show that disruption of that regulation by over-expression of IL-7 inhibits T-cell development and promotes extensive B-cell lymphopoiesis in the thymus. Our data reveal that high levels of IL-7 negate Notch-1 function in thymocytes found in IL-7 transgenic mice and in co-culture with OP9-DL1 cells. While high levels of IL-7R are present on thymocytes, increased suppressor of cytokine signaling-1 expression blunts IL-7 downstream signaling, resulting in hypo-phosphorylation of proteins in the PI3K-Akt pathway. Consequently, GSK3β remains active and inhibits Notch-1 signaling as observed by decreased Hes-1 and Deltex expression in thymic progenitors. This is the first demonstration that high levels of IL-7 antagonize Notch-1 signaling and suggest that IL-7 may affect T- versus B-lineage choice in the thymus.

Quantitative analysis of T cell receptor diversity in clinical samples of human peripheral blood

The analysis of T cell receptor diversity provides a clinically relevant and sensitive marker of repertoire loss, gain, or skewing. Spectratyping is a broadly utilized technique to measure global TCR diversity by the analysis of the lengths of CDR3 fragments in each Vβ family. However the common use of large numbers of T cells to obtain a global view of TCR Vβ CDR3 diversity has restricted spectratyping analyses when limited T-cell numbers are available in clinical setting, such as following transplant regimens. We here demonstrate that one hundred thousand T cells are sufficient to obtain a robust, highly reproducible measure of the global TCR Vβ repertoire diversity among twenty Vβ families in human peripheral blood. We also show that use of lower cell number results not in a dwindling of observed diversity but rather in non-reproducible patterns in replicate spectratypes. Finally, we report here a simple to use but sensitive method to quantify repertoire divergence in patient samples by comparison to a standard repertoire profile we generated from fifteen normal donors. We provide examples using this method to statistically evaluate the changes in the global TCR Vβ repertoire diversity that may take place during T subset immune reconstitution after hematopoietic stem cell transplantation or after immune modulating therapies.

Tbata modulates thymic stromal cell proliferation and thymus function

Niche availability provided by stromal cells is critical to thymus function. Thymi with diminished function contain fewer stromal cells, whereas thymi with robust function contain proliferating stromal cell populations. Here, we show that the thymus, brain, and testes-associated gene (Tbata; also known as SPATIAL) regulates thymic epithelial cell (TEC) proliferation and thymus size. Tbata is expressed in thymic stromal cells and interacts with the enzyme Uba3, thereby inhibiting the Nedd8 pathway and cell proliferation. Thymi from aged Tbata-deficient mice are larger and contain more dividing TECs than wild-type littermate controls. In addition, thymic reconstitution after bone marrow transplantation occurred more rapidly in Rag2(-/-)Tbata(-/-) mice than in Rag2(-/-)Tbata(+/+) littermate controls. These findings suggest that Tbata modulates thymus function by regulating stromal cell proliferation via the Nedd8 pathway.

Rapamycin generates anti-apoptotic human Th1/Tc1 cells via autophagy for induction of xenogeneic GVHD

Murine T cells exposed to rapamycin maintain flexibility towards Th1/Tc1 differentiation, thereby indicating that rapamycin promotion of regulatory T cells (Tregs) is conditional. The degree to which rapamycin might inhibit human Th1/Tc1 differentiation has not been evaluated. In the presence of rapamycin, T cell costimulation and polarization with IL-12 or IFN-α permitted human CD4+ and CD8+ T cell differentiation towards a Th1/Tc1 phenotype; activation of STAT1 and STAT4 pathways essential for Th1/Tc1 polarity was preserved during mTOR blockade but instead abrogated by PI3 kinase inhibition. Such rapamycin-resistant human Th1/Tc1 cells: (1) were generated through autophagy (increased LC3BII expression; phenotype reversion by autophagy inhibition via 3-MA or siRNA for Beclin1); (2) expressed anti-apoptotic bcl-2 family members (reduced Bax, Bak; increased phospho-Bad); (3) maintained mitochondrial membrane potentials; and (4) displayed reduced apoptosis. In vivo, type I polarized and rapamycin-resistant human T cells caused increased xenogeneic graft-versus-host disease (x-GVHD). Murine recipients of rapamycin-resistant human Th1/Tc1 cells had: (1) persistent T cell engraftment; (2) increased T cell cytokine and cytolytic effector function; and (3) T cell infiltration of skin, gut, and liver. Rapamycin therefore does not impair human T cell capacity for type I differentiation. Rather, rapamycin yields an anti-apoptotic Th1/Tc1 effector phenotype by promoting autophagy.

Aging, immunity and cancer

Immunosenescence, the progressive decline in immune function that develops with age, results from cumulative alterations in critical B- and T-cell subpopulations. Decreases in circulating memory B cells and in germinal center formation are evident in the elderly, possibly due to diminished follicular dendritic-cell function. T-cell dysfunction is associated with reduced thymic generation of naïve T cells, virus-induced expansion of terminal effectors and increased levels of memory cells producing type I and II cytokines. The diversity of the T-cell receptor repertoire is diminished by the first two changes, and elevated type I cytokines might contribute to the pro-inflammatory cytokine milieu present in the elderly.

Characterization of the mouse gene, human promoter and human cDNA of TSCOT reveals strong interspecies homology

The regulation of gene expression in thymic epithelial cells is critical for T cell development. The mouse thymic epithelial gene Tscot encodes a protein with weak homology to bacterial 12 transmembrane co-transporters. Using competitive reverse transcription-polymerase chain reaction (RT-PCR), we show that low level Tscot expression is detectable in several other tissues. Tscot was mapped to chromosome 4 and was also detected in other mammalian species by Southern blotting. The human cDNA clone showed 77% amino acid identity with the mouse sequence. The highest conservation was in the TM regions and in a small segment of the central cytoplasmic loop. Genomic clones spanning 17164 bases of the Tscot gene revealed four exons with nine of the TM domains encoded in the first exon. The major transcriptional start site in mouse was identified by a primer extension analysis and confirmed by RT-PCR. Comparison of 1.7 kb of the human and mouse promoters identified six conserved possible regulatory elements, one containing a potential binding site for an interferon alpha inducible factor. Finally, as a functional test, 3 kb of the murine promoter was used to create a transgenic mouse that expresses enhanced green fluorescent protein message strongly in the thymus, weakly in the kidney and undetectably in the spleen, liver and heart.

Spatial, a gene expressed in thymic stromal cells, depends on three-dimensional thymus organization for its expression

Although the importance of thymic stroma in thymopoiesis has been recognized, the underlying molecular details regarding stromal cell biology remain obscure. To study this area, we have cloned genes expressed in thymic stromal cells. Spatial is alternatively spliced to generate two mRNAs in thymus and lymph node (LN) but it is not expressed in the spleen. In mouse embryos, the short form begins expression at day 10 while the long form is not detected until day 12. Both mRNAs encode proline rich proteins and their closest homology is to homeobox and POU domain transcription factors. Spatial is not expressed in thymocytes, but it is expressed in 2-deoxyguanosine-treated day 14 fetal thymic organ culture (FTOC) and in reaggregated FTOC. These data suggest that a normal three-dimensional organization of stromal cells is required for Spatial expression. An antiserum raised against a C-terminal peptide detected proteins of 38 and 32 kDa in Western blots of total thymus proteins. In frozen thymus sections, subcapsular epithelial cells were stained with the anti-Spatial antiserum. Paracortical subcapsular cells of unknown function were also stained in the LN. Both forms of Spatial fused to the green fluorescent protein (GFP) localize to the nucleus in transfected cells.

A putative 12 transmembrane domain cotransporter expressed in thymic cortical epithelial cells

We have isolated a full-length cDNA clone (thymic stromal origin (TSO)-1C12) from a SCID thymus library using a probe from a PCR-based subtractive library enriched for sequences from fetal thymic stromal cells. TSO-1C12 mRNA is expressed mainly in the thymic cortex and is highly enriched in SCID thymus. Expression per cell is highest during fetal thymus development and decreases after day 16. Antipeptide Abs immunoprecipitated a hydrophobic, plasma membrane glycoprotein (thymic stromal cotransporter, TSCOT) whose translated sequence has weak homology to bacterial antiporters and mammalian cation cotransporters with 12 transmembrane domains. TSCOT represents a new member of this superfamily that is highly expressed in thymic cortical epithelial cells.

A subtractive PCR-based cDNA library made from fetal thymic stromal cells

We describe our initial approach to clone and characterize genes expressed preferentially in thymic stromal cells, in an attempt to generate molecular reagents to study the role of these cells in thymopoiesis and thymic function. Thymic stromal cells were prepared from fetal thymic organ cultures by treating them with 2-deoxyguanosine and depleting the remaining hematopoietic cells with anti-CD45 antibody. A cDNA library was then prepared after subtraction and amplification by PCR. The cloned inserts were sequenced and compared for homology with known genes in the data base. Unidentified cDNAs were then examined for expression in normal and SCID thymus and in a set of SV40-transformed thymic epithelial cell lines, by Northern blotting and a dot blot assay. In this report we describe the development of the library and present a general description of the genes identified from the initial 249 cDNAs sequenced. Among these, a relatively high percentage (55%) do not show any homology to previously identified genes. Several genes with a limited expression pattern were selected for further study.

A cell-specific and selective effect on transactivation by the androgen receptor

The androgen (AR) and glucocorticoid receptors (GR) are related ligand-activated transcriptional regulators which bind the same cis-acting element and are coexpressed in a variety of cell types. Despite a shared DNA binding site, these receptors mediate diverse cellular responses. To explain this paradox, the existence of cell-specific factors that interact with, and modulate the function of, distinct receptors has been proposed. Prostate epithelial cell growth is sensitive to androgens, but is not affected by glucocorticoids, even though both AR and GR are expressed in these cells. We have recently isolated a unique panel of prostate epithelial cell lines from normal rats and have used these cell lines to examine cell-specific steroid responses. In this study, we compared the abilities of AR and GR to enhance transcription of several different reporter genes regulated by simple (i.e., noncompsite) hormone response elements (HREs) in prostate and nonprostate cell lines. The cell-specific effect occurred independently of the AR hormone binding domain and could be observed with a GAL4 fusion protein containing only the AR N-terminal regulatory domain. Gel shift analyses showed that the relative DNA binding affinity of AR for a probe containing a simple HRE was similar in prostate and nonprostate cell extracts. Presently, the only factors known to mediate steroid receptor-specific gene regulation are cJun and cFos, but there were no cell-specific differences in the functional levels of these proteins which could account for a preferential effect on AR-dependent transcription. Taken together, these results suggest that cell-specific activities exist which can preferentially modulate transcriptional transactivation by AR.

Recessive mutations in a common pathway block thymocyte apoptosis induced by multiple signals

The glucocorticoid receptor (GR) is a ligand-regulated transcription factor that controls genes necessary to initiate glucocorticoid-induced thymocyte apoptosis. We have performed a genetic analysis of thymocyte cell death by isolating and characterizing a panel of GR+ dexamethasone-resistant mutants of the murine WEHI7.2 thymocyte cell line. These apoptosis-defective (Apt-) mutants were used to identify previously unknown early steps in the apoptotic pathway. The Apt- mutants contain nonglucocorticoid receptor, recessive mutations in genes that represent multiple complementation groups. These mutations block apoptosis induced by dexamethasone, gamma irradiation, and c-AMP treatment before the point where Bcl-2 exerts its protective effect. We propose that different signals share a common apoptotic pathway, and that the induction of apoptosis involves multiple precommitment steps that can be blocked by recessive mutations.

Elevated glutathione S-transferase gene expression is an early event during steroid-induced lymphocyte apoptosis

Based on the finding that glutathione S-transferase Yb1 (GST) gene expression is elevated in the regressing prostate of androgen-ablated rats, we analyzed GST transcript levels during steroid-induced lymphocyte cell death. It was found that GST gene expression was induced in steroid-sensitive cells within 4 hr of dexamethasone treatment, required functional glucocorticoid receptor, and was dose-dependent with regard to hormone. GST expression was not induced in an apoptosis-defective variant that contained normal levels of functional receptor, indicating that GST up-regulation was the result of secondary events that occur during steroid-mediated apoptosis. Using the calcium ionophore A23817 to induce lymphocyte cell death, GST RNA levels were increased in both steroid-sensitive and steroid-resistant cell lines, supporting the conclusion that elevated GST expression was the result of cellular processes associated with apoptosis, rather than a direct consequence of steroid-mediated transcriptional control. The cells were also treated with dibutyryl cAMP to cause cell death; however, this mode of killing did not result in GST up-regulation. Taken together, these results suggest that GST induction in dexamethasone-treated T-lymphocytes occurs early in the steroid-regulated apoptotic pathway and that this may be a marker of calcium-stimulated cell death. Based on the known function of GST as an antioxidant defense enzyme and its transcriptional regulation by reactive oxygen intermediates, we propose that the gene product of a primary GR target gene(s) directly or indirectly effects the redox state of the cell. Thus activation of GST gene expression in apoptotic lymphocytes is likely a indicator of oxidative stress, rather than a required step in the pathway.

Transcriptional analyses of steroid-regulated gene networks

It has been proposed that cell-specific responses to steroid action are the result of coordinate expression of steroid gene networks. Using three different cell systems, we have performed transcriptional analyses to determine if the observed hormone-induced alterations in gene expression are consistent with a limited number of potential target genes in any one cell type. Our results indicate that greater than 95% of the transcripts in dexamethasone-treated rat hepatoma (HTC), or mouse lymphoma (WEH17) cells, are similar to the mRNAs in untreated cells based on subtraction hybridization. In addition, we find that although the castration-induced expression of androgen-regulated transcripts in the rat ventral prostate (RVP) is significantly different between normal and castrated rats (19%), the majority of these mRNAs are accounted for by the over abundance of sulfated glycoprotein-2 sequences. Specifically, analysis of an RVP subtracted cDNA library revealed that sulfated glycoprotein-2 mRNA masked the presence of less abundant differentially expressed sequences, confirming that the actual size of the RVP androgen gene network is small. We conclude that steroid-mediated changes in transcription accurately reflect the expression of a few cell-specific target genes, and thus support the model of steroid gene networks. The potential to characterize key elements which determine both the time course and magnitude of cell-specific hormone responses is discussed.

Cadmium produces a delayed mitogenic response and modulates the EGF response in quiescent NRK cells

Recent studies have shown that cadmium, at subtoxic levels, may induce a response characteristic of that elicited by a type of growth factor that supports the anchorage independent growth of cells that are not fully transformed. That is, Cd++ was found to replace transforming growth factor beta in supporting soft agar growth of NRK-49F cells. To test the extent to which Cd++ further mimics transforming growth factor beta in its effects and to establish response patterns that suggest possible molecular mechanisms of action, we have determined the effects of Cd++ and/or epidermal growth factor (EGF) on DNA synthesis in quiescent NRK-49F cells. We found that subtoxic doses of Cd++ modulate EGF-induced DNA synthesis in a dose-dependent fashion. Although Cd++ effects on early (16-24 hr) EGF-induced DNA synthesis are primarily inhibitory, later effects involve stimulation as well. Subtoxic doses of Cd++ did not stimulate DNA synthesis in quiescent cells within 24 hr of addition. At later times (40 or 64 hr), however, an increase in DNA synthesis of up to threefold was induced by 0.25 microM Cd++. This pattern of mitogenic response, involving inhibition of early growth-factor induced DNA synthesis and stimulation of late DNA synthesis, is consistent with that reported to be effected in some instances by transforming growth factor beta. Because a defined pattern of gene expression also is associated with the mitogenic responses to transforming growth factor beta, future studies at the molecular level can definitively test the degree to which Cd++ and transforming growth factor beta effects are common.

Expression of the art/trs protein of HIV and study of its role in viral envelope synthesis

The art/trs transactivator protein of human immunodeficiency virus (HIV) was expressed in mammalian cells as a 19-kilodalton protein that was immunoreactive with sera from HIV-infected patients. Separate plasmids encoding the art/trs protein, the tat protein, or the envelope glycoprotein gp120 were used to demonstrate that both art/trs and tat are absolutely required for the synthesis of gp120 from its cognate messenger RNA. In addition, both the tat and art/trs proteins influence the level of envelope RNA. The results suggest that art/trs and tat may be ideal targets for potential anti-HIV agents in AIDS therapy.