Biomedical subjects

T Pohl

Publications and source records attributed to T Pohl.

At least 37 records · Page 2Linked to original sources

PubMed2001

Conservation of microstructure between a sequenced region of the genome of rice and multiple segments of the genome of Arabidopsis thaliana.

The nucleotide sequence was determined for a 340-kb segment of rice chromosome 2, revealing 56 putative protein-coding genes. This represents a density of one gene per 6.1 kb, which is higher than was reported for a previously sequenced segment of the rice genome. Sixteen of the putative genes were supported by matches to ESTs. The predicted products of 29 of the putative genes showed similarity to known proteins, and a further 17 genes showed similarity only to predicted or hypothetical proteins identified in genome sequence data. The region contains a few transposable elements: one retrotransposon, and one transposon. The segment of the rice genome studied had previously been identified as representing a part of rice chromosome 2 that may be homologous to a segment of Arabidopsis chromosome 4. We confirmed the conservation of gene content and order between the two genome segments. In addition, we identified a further four segments of the Arabidopsis genome that contain conserved gene content and order. In total, 22 of the 56 genes identified in the rice genome segment were represented in this set of Arabidopsis genome segments, with at least five genes present, in conserved order, in each segment. These data are consistent with the hypothesis that the Arabidopsis genome has undergone multiple duplication events. Our results demonstrate that conservation of the genome microstructure can be identified even between monocot and dicot species. However, the frequent occurrence of duplication, and subsequent microstructure divergence, within plant genomes may necessitate the integration of subsets of genes present in multiple redundant segments to deduce evolutionary relationships and identify orthologous genes.

Arabidopsis↗

PubMed2001

Influence on collateral flow of recanalising chronic total coronary occlusions: a case-control study.

OBJECTIVE: To assess the effect of recanalisation on collateral flow in a case-control study in patients with and without chronic total coronary occlusions. DESIGN: In 54 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) (mean (SD) age 61 (6) years), coronary collateral flow was measured by intracoronary pressure or Doppler guide wires at the end of repeated balloon occlusions. Coronary collateral flow index (collateral flow relative to normal antegrade flow) during the first two balloon inflations in 27 patients with a chronic total occlusion (occlusion group) was compared with that of 27 patients matched for age, sex, and collateral flow index at the first occlusion and with a coronary artery diameter stenosis </= 80% (stenosis group). RESULTS: Following revascularisation, collateral flow index decreased in 17 of the patients in the occlusion group (63%) and in eight of the patients in the stenosis group (30%) (p = 0.03 between groups). The overall change of collateral flow index between the first and the second balloon occlusion was -0.04 (0.01) in the occlusion group (p = 0.07 for paired comparison; from 0.29 (0.17) to 0.25 (0.14)), and +0.02 (0.06) in the stenosis group (p = 0.06 for paired comparison; from 0.27 (0.13) to 0.30 (0.15)). The trend to collateral enhancement in the stenosis group differed significantly from the occlusion group (p = 0.01). CONCLUSIONS: While repeated coronary balloon occlusions induce collateral recruitment in the majority of patients with moderate stenoses, recanalisation of chronic total coronary occlusions is more often associated with collateral flow reduction. A later decrease in collateral flow by involution of collateral channels cannot be excluded by this study but has not been reported so far.

Angioplasty, Balloon, Coronary↗

PubMed2001

Disease progression in chronic relapsing experimental allergic encephalomyelitis is associated with reduced inflammation-driven production of corticosterone.

In this study, we demonstrate that disruption of neuroendocrine signaling is a major factor driving disease progression in myelin oligodendrocyte glycoprotein-induced chronic relapsing experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Although the initial episode of chronic relapsing experimental autoimmune encephalomyelitis is associated with a robust hypothalamic-pituitary-adrenocortical axis response, we show that subsequent disease progression is associated with a selective desensitization of hypothalamic-pituitary-adrenocortical responsiveness to inflammatory mediators. Inflammatory activity in the central nervous system during relapse is therefore unable to produce an endogenous immunosuppressive corticosterone response, and disease progresses into an ultimately lethal phase. However, disease progression is inhibited if the circulating corticosterone level is maintained at levels seen during the initial phase of disease. The effect of hypothalamic-pituitary-adrenocortical axis desensitization on the clinical course of experimental autoimmune encephalomyelitis is aggravated by a marked reduction in proinflammatory cytokine synthesis in the central nervous system in the later stages of disease, reflecting an increasing involvement of antibody, rather than T cell-dependent effector mechanisms, in disease pathogenesis, with time. Thus, our data indicate that distinct immune-endocrine effects play a decisive role in determining disease progression in multiple sclerosis, a concept supported by reports that a subpopulation of multiple sclerosis patients shows evidence of hypothalamic-pituitary-adrenocortical axis desensitization.

Animals↗

PubMed2000

Sequence and analysis of chromosome 5 of the plant Arabidopsis thaliana.

The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.

Animals↗

PubMed2000

The HTLV-I tax protein transcriptionally modulates OX40 antigen expression.

OX40 is a member of the TNF receptor family, expressed on activated T cells. It is the only costimulatory T cell molecule known to be specifically up-regulated in human T cell leukemia virus type-I (HTLV-I)-producing cells. In a T cell line, OX40 surface expression was shown to be induced by HTLV-I Tax alone. To understand molecular mechanisms of OX40 gene regulation and modulation by HTLV-I Tax, we have cloned the human OX40 gene and analyzed its 5'-flanking region. By reporter gene analysis with progressive 5' deletions from nucleotides -1259 to -64, we have defined a 157-bp DNA fragment as a minimal promoter for constitutive expression. In addition, we show that in the OX40+ cell line, Co, Tax is able to further increase OX40 surface expression. Up-regulation of OX40 promoter activity by Tax requires two upstream NF-kappaB sites, which are not active in the constitutive OX40 expression. Their deletion abrogates Tax responsiveness in reporter gene analysis. The site-directed mutagenesis of each NF-kappaB site demonstrates that cooperative NF-kappaB binding is a prerequisite for Tax-directed activity as neither site alone is sufficient for a full Tax responsiveness of the OX40 promoter. Upon Tax expression, both sites bind p65 and c-Rel. These data provide new insight into the direct regulation of OX40 by Tax and add to our understanding of the possible role of the OX40/OX40 ligand system in the proliferation of HTLV-I+ T cells.

Amino Acid Motifs↗

PubMed2000

An interleukin-2-IgG-Fas ligand fusion protein suppresses delayed-type hypersensitivity in mice by triggering apoptosis in activated T cells as a novel strategy for immunosuppression.

BACKGROUND: Cell-mediated immune responses can be down-regulated by induction of apoptosis of immunoreactive lymphocytes. In the present study, we have tested the feasibility of a strategy for immunosuppression by the selective induction of apoptosis in activated, interleukin (IL)-2 receptor-positive lymphocytes, using a triple IL-2-IgG-FasL fusion protein. The IL-2-IgG-FasL fusion protein combines IL-2 for the selection of activated T cells, with the extracellular domain of the FasL molecule for inducing T-cell apoptosis. These components were separated by the Fc part of IgG1 serving as a spacer as well as for half-life prolongation. METHODS: The gene for the chimeric protein was created by fusing DNA sequences encoding for the three functional components: human IL-2, the Fc part of human IgG1, and the extracellular domain of murine FasL. When the fusion gene was expressed in murine J558L cells, we obtained soluble dimeric immunoglobulin-like proteins in the supernatant. After analyzing the function of the IL-2 and FasL portions individually in vitro, a delayed-type hypersensitivity (DTH) reaction to sheep red blood cells as model for cell-mediated immune responses was investigated to evaluate the IL-2-IgG-FasL-mediated immunosuppression in vivo. RESULTS: In vitro, the IL-2-IgG-FasL fusion protein supported IL-2-dependent proliferation of Fas-resistant CTLL-2 cells, whereas concanavalin A-T blasts were induced to undergo apoptosis by the FasL portion. In vivo, this fusion protein potently inhibited a murine DTH. This was associated with an increased rate of apoptosis in activated lymphocytes in the spleen, even at very low doses of the fusion protein. Furthermore, a second antigen challenge 10 days after IL-2-IgG-FasL treatment still failed to elicit a DTH response. CONCLUSION: The abrogation of a standard T cell-dependent immune response in vivo demonstrates that IL-2-IgG-FasL can be successfully exploited to trigger the death of deleterious T cells, presenting a potentially useful strategy in the management of autoimmune diseases and allotransplant rejections.

Animals↗

PubMed2000

Progress in Arabidopsis genome sequencing and functional genomics.

Arabidopsis thaliana has a relatively small genome of approximately 130 Mb containing about 10% repetitive DNA. Genome sequencing studies reveal a gene-rich genome, predicted to contain approximately 25000 genes spaced on average every 4.5 kb. Between 10 to 20% of the predicted genes occur as clusters of related genes, indicating that local sequence duplication and subsequent divergence generates a significant proportion of gene families. In addition to gene families, repetitive sequences comprise individual and small clusters of two to three retroelements and other classes of smaller repeats. The clustering of highly repetitive elements is a striking feature of the A. thaliana genome emerging from sequence and other analyses.

Agriculture↗

PubMed2000

The restricted expression pattern of the Hodgkin's lymphoma-associated cytokine receptor CD30 is regulated by a minimal promoter.

One of the most peculiar immunohistological characteristics of the tumour cells of Hodgkin's lymphoma, anaplastic large cell lymphoma (ALCL), and embryonal carcinoma of the testis is the expression of the CD30 antigen. Physiologically, CD30 expression is restricted to a few activated lymphocytes in normal lymphoid tissue and a small population of decidual cells. To clarify the reasons behind this highly restricted expression pattern and to learn about the combination of transcription factors involved in this regulation in Hodgkin's lymphoma and other CD30(+) malignancies, the 5'-flanking regulatory region of the cd30 gene was analysed. The major transcription start site was determined to be 270 bases upstream of the translational start codon in the Hodgkin's lymphoma-derived cell lines L591 and L428. Reporter gene assays revealed that the CD30 promoter (-413 to 84) induces a 50- to 1000-fold higher luciferase expression in CD30(+) human lymphoid cell lines (Co, Jurkat, and the Hodgkin's lymphoma-derived cell line L540) than in CD30(-) human lymphoid cell lines (DG75, SUP-T1, and U698M), CD30(-) human carcinoma cell lines (HeLa and MCF-7), or COS1 cells. Deletion analysis defined a TATA-less, minimal promoter sequence from -164 to 84. The transcription factor Sp1 and members of the Ets family induce CD30 expression, whereas the transcription factor Sp3 diminishes its induction. These data suggest that a high Sp1/Sp3 expression ratio and a peculiar expression pattern of the Ets transcription factors are involved in the overexpression of CD30 and might contribute to the transformation of CD30(+) tumour cells.

Base Sequence↗

PubMed2000

Rel/NF-kappaB transcription factors: key mediators of B-cell activation.

The Rel/nuclear factor (NF)-kappaB family of transcription factors have been implicated in the regulation of a wide variety of genes, in particular those encoding proteins crucial to the function of the immune system. Through the use of mutant mice that lack one or more of these proteins, we have begun to examine the individual and combined roles of Rel, RelA and NF-kappaB1 in B-cell development and function. Here we outline and discuss how these transcription factors operate as differentiation stage-specific regulators of B-cell development, survival, division and immunoglobulin expression, emphasizing those Rel/NF-kappaB-regulated genes that mediate these functions.

Animals↗

PubMed1999

Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana.

The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.

Animals↗

PubMed1999

Genetic approaches in mice to understand Rel/NF-kappaB and IkappaB function: transgenics and knockouts.

Rel/NF-kappaB transcription factors have been implicated in regulating a wide variety of genes important in cellular processes that include cell division, cell survival, differentiation and immunity. Here genetic models in which various Rel/NF-kappaB and IkappaB proteins have either been over-expressed or deleted in mice will be reviewed. Although expressed fairly ubiquitously, homozygous disruption of individual Rel/NF-kappaB genes generally affects the development of proper immune cell function. One exception is rela, which is essential for embryonic liver development. The disruption of genes encoding the individual subunits of the IkappaB kinase, namely IKKalpha and IKKbeta, has demonstrated that IKKbeta transmits the response to most common NF-kappaB inducing agents, whereas IKKalpha has an unexpected role in keratinocyte differentiation. Future studies will no doubt focus on the effect of multiple gene disruptions of members of this signaling pathway, on tissue-specific disruptions of these genes, and on the use of these mice as models for human diseases.

Animals↗

PubMed1999

Chronic selective hypertriglyceridemia impairs endothelium-dependent vasodilatation in rats.

OBJECTIVE/METHODS: In order to investigate whether selective hypertriglyceridemia impairs endothelium-dependent vasodilatation in the rat hindlimb, rats were selectively bred to establish two strains, one with a pronounced hypertriglyceridemia (HT) and the other with normal plasma levels of triglycerides (LT). RESULTS: Carotid arteries and aortae removed from 3, 6, 9 and 12 month old LT- and HT-rats exhibited a normal morphology. However, marked morphological differences were observed between vessels from 18-20 month old HT- and LT-rats. The endothelium-dependent vasodilator acetylcholine (2 to 50 micrograms/kg), administered into the iliac artery, elicited a concentration-dependent increase in hindlimb blood flow which was not different in 3, 6 and 9 month old LT- or HT-rats but was impaired in 12 and 18-20 month old HT-rats. In contrast the endothelium-independent vasodilator sodium nitroprusside enhanced blood flow in both strains to a similar extent. Neither administration of the nitric oxide (NO) synthase (NOS) substrate, L-arginine, nor the NOS inhibitor NGnitro-L-arginine, affected the responsiveness to endothelium-dependent vasodilators in 12 month old HT-rats. These attenuated responses could not be attributed to a decrease in endothelial NOS expression as Western blot analysis revealed identical levels of this enzyme in the aortae and carotid arteries from LT- and HT-rats. Determination of superoxide anion (O2-) formation however, demonstrated a markedly elevated production of O2- in aortae from HT-rats. CONCLUSION: We conclude that chronic selective hypertriglyceridemia, an independent risk factor in the development and progression of atherosclerosis, leads to an endothelial dysfunction which is associated with an increased vascular O2- production and a subsequent decrease in bioavailable NO.

Acetylcholine↗

PubMed1999

Death deflected: IL-15 inhibits TNF-alpha-mediated apoptosis in fibroblasts by TRAF2 recruitment to the IL-15Ralpha chain.

Interleukin-15 (IL-15) is a potent inhibitor of several apoptosis pathways. One prominent path toward apoptosis is the ligand-induced association of TNF receptor 1 (TNFR1) with death domain adaptor proteins. Studying if and how IL-15 blocks TNFR1-mediated apoptosis in a murine fibroblast cell line (L929), we show here that IL-15 blocks TNFR1-induced apoptosis via IL-15Ralpha chain signaling. The intracellular tail of IL-15Ralpha shows sequence homologies to the TRAF2 binding motifs of CD30 and CD40. Most important, binding of IL-15 to IL-15Ralpha successfully competes with the TNFR1 complex for TRAF2 binding, which may impede assembly of key adaptor proteins to the TNFR1 complex, and induces IkappaBalpha phosphorylation. Thus, IL-15Ralpha chain stimulation is a powerful deflector of cell death very early in the apoptosis signaling cascade, while TNF-alpha and IL-15 surface as major opponents in apoptosis control.

Amino Acid Sequence↗

PubMed1998

Vaccination with tumor cells engineered to secrete interleukin 2-immunoglobulin G fusion protein induces tumor rejection.

Here we provide proof that the injection of tumor cells engineered to secrete interleukin 2 (IL-2)-IgG chimeric proteins locally induces potent antitumor responses, which are more effective than tumor transfection with IL-2 alone. Murine plasmacytoma cells (J558L) were stably transfected with DNA coding for a human IL-2-IgG1 or a murine IL-2-IgG2b fusion protein and were injected s.c. into syngeneic BALB/c mice. Evaluation of tumor growth and rejection patterns showed that IL-2-IgG secretion by transfected J558L tumor cells induced their rejection in all animals tested, similar to the rejection of J558L cells engineered to secrete IL-2 alone, whereas treatment with parental cells was lethal. However, mice treated with IL-2-IgG-secreting J558L cells (human IL-2-IgG1 and murine IL-2-IgG2b) exhibited a significantly stronger tumor immunity against a later challenge with parental J558L cells than mice treated with IL-2-secreting tumor cells.

Animals↗

PubMed1998

IL-15-IgG2b fusion protein accelerates and enhances a Th2 but not a Th1 immune response in vivo, while IL-2-IgG2b fusion protein inhibits both.

We have explored how IL-15 influences Th1 or Th2 type immune response in vivo. Intraperitoneal application of an IL-15-IgG2b fusion protein (FP) to mice did neither significantly affect the footpad swelling nor the production of hemagglutinizing antibodies in a delayed type hypersensitivity reaction to sheep red blood cells. In contrast, in an established murine Th2 model of sensitization to ovalbumin (OVA), IL-15-IgG2b FP plus OVA sensitization resulted in massively accelerated and enhanced allergen-specific IgE and IgG1 antibody production. In vitro, stimulation of spleen cells from OVA-sensitized mice with OVA+IL-15 or OVA+IL-15-IgG2b resulted in a significantly enhanced IgE production. IL-4 secretion was significantly induced by IL-15 but not by IL-15-IgG2b. An IL-2-IgG2b FP with the same Fc tail as the IL-15-IgG2b FP was used as control in both models. In striking contrast to the IL-15-IgG2b FP, IL-2-IgG2b significantly inhibited the Th2 type antibody production in vivo. The current study suggests that IL-15-IgG2b may be employed as a potent accelerator and enhancer of Th2 type immune responses in vivo, while IL-2-IgG2b can suppress the latter.

Allergens↗

PubMed1998

Prolongation of corneal allograft survival by an interleukin-2-immunoglobulin fusion protein in mice.

BACKGROUND: Interleukin 2 (IL2) production by activated T-helper cells leads to activation and proliferation of cytotoxic T cells. Recently, an IL2-IgG fusion protein was found to suppress cell-mediated and humoral immune responses in mice. METHODS: We used the genetically engineered murine IL2-IgG2b fusion protein in a fully MHC-mismatched mouse keratoplasty model. The DTH reaction against sheep red blood cells was investigated as a measure of IL2-IgG2b-mediated immunosuppression. The animals were divided into three control groups (n > or = 6) [no treatment, subconjunctival (SQ) treatment with saline or mouse serum], two IL2 SQ-treated groups (14 micrograms or 140 micrograms), and four IL2-IgG2b-treated groups (14 micrograms, 140 micrograms or 280 micrograms SQ or 280 micrograms i.p.). RESULTS: Administration of 20 micrograms of IL2-IgG2b twice daily from the time of immunization until the time of challenge resulted in almost complete prevention of footpad swelling. The 140 micrograms SQ application of IL2 (allograft reaction on day 20.5 +/- 4.04) and the 280 micrograms SQ (day 19.2 +/- 2.48) or i.p. (day 19.7 +/- 1.5) application of IL2-IgG2b fusion protein significantly prolonged the corneal graft survival in comparison to the untreated group (day 13.4 +/- 1.35) (P < 0.01) or saline control group (P < 0.01) and the mouse-serum-treated group (day 14.7 +/- 3.5) (P < 0.05). CONCLUSION: Our results indicate that, at a total dose of 280 micrograms, the fusion protein IL2-IgG2b causes no detectable side effects and very effectively suppresses the immune response of the corneal allograft in mice. This fusion protein could prove useful in the treatment of allograft rejections and autoimmune diseases.

Animals↗

PubMed1998

Wild-type p53-mediated down-modulation of interleukin 15 and interleukin 15 receptors in human rhabdomyosarcoma cells.

We recently reported that rhabdomyosarcoma cell lines express and secrete interleukin 15 (IL-15), a tightly regulated cytokine with IL-2-like activity. To test whether the p53-impaired function that is frequently found in this tumour type could play a role in the IL-15 production, wild-type p53 gene was transduced in the human rhabdomyosarcoma cell line RD (which harbours a mutated p53 gene), and its effect on proliferation and expression of IL-15 was studied. Arrest of proliferation was induced by wild-type p53; increased proportions of G1-arrested cells and of apoptotic cells were observed. A marked down-modulation of IL-15 expression, at both the mRNA and protein level, was found in p53-transduced cells. Because a direct effect of IL-15 on normal muscle cells has been reported, the presence of IL-15 membrane receptors was studied by cytofluorometric analysis. Rhabdomyosarcoma cells showed IL-15 membrane receptors, which are down-modulated by wild-type p53 transfected gene. In conclusion, wild-type p53 transduction in human rhabdomyosarcoma cells induces the down-modulation of both IL-15 production and IL-15 receptor expression.

Cell Division↗

PubMed1997

Regulation of IL-15 secretion via the leader peptide of two IL-15 isoforms.

The secretion of IL-15, a potent modulator of T, B, and NK lymphocyte functions, is likely to be tightly controlled. Here, we show that human T lymphoblasts transcribe the IL-15 gene and generate an alternative splicing product that codes for the same amino acid composition as the mature IL-15 protein, but produces an IL-15 precursor protein with a shorter signal peptide. Both alternative splicing products are transcribed by non-IL-15-secreting lymphocytes, suggesting that IL-15 secretion is not primarily controlled at the level of transcription. We generated an in vitro system for correlating the expression, translation, and secretion of IL-15 or IL-15-IgG1 fusion protein. This revealed that the two isoforms of IL-15 or a truncated IL-15 variant, both alone and fused to human IgG1, are all transcribed and translated, but not efficiently secreted. After replacing the IL-15 leader peptide with a foreign one, translation and secretion clearly increase. These results suggest that IL-15 is mainly controlled at the level of translation and secretion.

Alternative Splicing↗