Biomedical subjects

Raif Yücel

Publications and source records attributed to Raif Yücel.

7 recordsLinked to original sources

PubMed2005

Cellular uptake and cytotoxic potential of respirable bentonite particles with different quartz contents and chemical modifications in human lung fibroblasts.

Considering the biological reactivity of pure quartz in lung cells, there is a strong interest to clarify the cellular effects of respirable siliceous dusts, like bentonites. In the present study, we investigated the cellular uptake and the cytotoxic potential of bentonite particles (Ø< 10 microm) with an alpha-quartz content of up to 6% and different chemical modifications (activation: alkaline, acidic, organic) in human lung fibroblasts (IMR90). Additionally, the ability of the particles to induce apoptosis in IMR90-cells and the hemolytic activity was tested. All bentonite samples were tested for endotoxins with the in vitro-Pyrogen test and were found to be negative. Cellular uptake of particles by IMR90-cells was studied by transmission electron microscopy (TEM). Cytotoxicity was analyzed in IMR90-cells by determination of viable cells using flow cytometry and by measuring of the cell respiratory activity. Induced apoptotic cells were detected by AnnexinV/Propidiumiodide-staining and gel electrophoresis. Our results demonstrate that activated bentonite particles are better taken up by IMR90-cells than untreated (native) bentonite particles. Also, activated bentonite particles with a quartz content of 5-6% were more cytotoxic than untreated bentonites or bentonites with a quartz content lower than 4%. The bentonite samples induced necrotic as well as apoptotic cell death. In general, bentonites showed a high membrane-damaging potential shown as hemolytic activity in human erythrocytes. We conclude that cellular effects of bentonite particles in human lung cells are enhanced after chemical treatment of the particles. The cytotoxic potential of the different bentonites is primarily characterized by a strong lysis of the cell membrane.

Air Pollutants↗

PubMed2005

The transcriptional repressor Gfi1 controls STAT3-dependent dendritic cell development and function.

The mechanisms controlling the differentiation of dendritic cells (DCs) remain largely unknown. Using a transcriptional profiling approach, we identified Gfi1 as a novel critical transcription factor in DC differentiation. Gfi1-/- mice showed a global reduction of myeloid and lymphoid DCs in all lymphoid organs whereas epidermal Langerhans cells were enhanced in number. In vivo, Gfi1-/- DCs showed striking phenotypic and functional alterations such as defective maturation and increased cytokine production. In vitro, Gfi1-/- hematopoietic progenitor cells were unable to develop into DCs. Instead, they differentiated into macrophages, suggesting that Gfi1 is a critical modulator of DC versus macrophage development. Analysis of hematopoietic chimeras and retrovirus-reconstituted hematopoietic progenitor cells established a cell autonomous and nonredundant role for Gfi1 in DC development. The developmental defect of Gfi1-/- progenitor cells was associated with decreased STAT3 activation. In conclusion, we have identified Gfi1 as a critical transcription factor that controls DC versus macrophage development and dissociates DC maturation and activation.

Animals↗

PubMed2004

Transcription factor Gfi1 regulates self-renewal and engraftment of hematopoietic stem cells.

The generation of all blood cells depends on the ability of hematopoietic stem cells (HSCs) for self-renewal and multilineage differentiation. We show here that the transcription factor Gfi1 is expressed in HSCs and in more mature cells such as common lymphoid progenitors (CLPs) and granulo/monocytic progenitors, but is absent in common myeloid progenitors and megakaryocyte/erythroid progenitors. When Gfi1 is deleted in mice, HSC frequencies are significantly reduced and CLPs all but disappear from the bone marrow. This specific requirement of Gfi1 for the maintenance of HSC numbers is cell autonomous. Transplantation of Gfi1-deficient bone marrow results in a compromised radioprotection and lower numbers of colony forming units in the spleen of wild-type recipients. Strikingly, Gfi1-/- bone marrow cells are severely impaired in competitive long-term reconstituting abilities after transplantation and show a surprisingly high proportion of actively cycling HSCs, suggesting that Gfi1 restrains proliferation of HSCs and thereby regulates their self-renewal and long-term engraftment abilities.

Alleles↗

PubMed2004

Transcription profiling of inner ears from Pou4f3(ddl/ddl) identifies Gfi1 as a target of the Pou4f3 deafness gene.

Pou4f3 (Brn3.1, Brn3c) is a class IV POU domain transcription factor that has a central function in the development of all hair cells in the human and mouse inner ear sensory epithelia. A mutation of POU4F3 underlies human autosomal dominant non-syndromic progressive hearing loss DFNA15. Through a comparison of inner ear gene expression profiles of E16.5 wild-type and Pou4f3 mutant deaf mice using a high density oligonucleotide microarray, we identified the gene encoding growth factor independence 1 (Gfi1) as a likely in vivo target gene regulated by Pou4f3. To validate this result, we performed semi-quantitative RT-PCR and in situ hybridizations for Gfi1 on wild-type and Pou4f3 mutant mice. Our results demonstrate that a deficiency of Pou4f3 leads to a statistically significant reduction in Gfi1 expression levels and that the dynamics of Gfi1 mRNA abundance closely follow the pattern of expression for Pou4f3. To examine the role of Gfi1 in the pathogenesis of Pou4f3-related deafness, we performed comparative analyses of the embryonic inner ears of Pou4f3 and Gfi1 mouse mutants using immunohistochemistry and scanning electron microscopy. The loss of Gfi1 results in outer hair cell degeneration, which appears comparable to that observed in Pou4f3 mutants. These results identify Gfi1 as the first downstream target of a hair cell specific transcription factor and suggest that outer hair cell degeneration in Pou4f3 mutants is largely or entirely a result of the loss of expression of Gfi1.

Animals↗

PubMed2004

Gfi1:green fluorescent protein knock-in mutant reveals differential expression and autoregulation of the growth factor independence 1 (Gfi1) gene during lymphocyte development.

The Gfi1 gene encodes a 55-kDa transcriptional repressor protein with important functions in T-cell development, in granulopoiesis, and in the regulation of the innate immune response. To follow expression of the Gfi1 gene during the differentiation of specific immune cells, we have generated a mouse mutant in which the Gfi1 coding region is replaced by the gene for the green fluorescent protein (GFP). We found that Gfi1 gene expression is highest in early B-cell subpopulation and differentially expressed during T-cell development with peak levels at stages where pre-TCR or positive/negative selection takes place. Gfi1 is absent in mature B-cells, whereas in peripheral T-cells Gfi1 gene expression is low but rises significantly upon T-cell receptor triggering and decreases again in T-memory cells. Constitutive expression of an lck promoter-driven Gfi1 transgene led to transcriptional silencing of the Gfi1:GFP allele in T-cells. Because Gfi1 was found to occupy genomic sites of its own promoter in thymocytes and was able to repress its own transcription in vitro we propose that transcription of the Gfi1 gene is regulated through an autoregulatory feedback loop.

Alleles↗

PubMed2003

The transcriptional repressor Gfi1 affects development of early, uncommitted c-Kit+ T cell progenitors and CD4/CD8 lineage decision in the thymus.

In the thymus, several steps of proliferative expansion and selection coordinate the maturation of precursors into antigen-specific T cells. Here we identify the transcriptional repressor Gfi1 as an important regulator of this maturation process. Mice lacking Gfi1 show reduced thymic cellularity due to an increased cell death rate, lack of proliferation, and a differentiation block in the very early uncommitted CD4-/CD8-/c-Kit+ cytokine-dependent T cell progenitors that have not yet initiated VDJ recombination. In addition, Gfi1-deficient mice show increased major histocompatibility complex class I-restricted positive selection and develop significantly more CD8+ cells suggesting a requirement of Gfi1 for a correct CD4/CD8 lineage decision. Absence of Gfi1 correlates with high level expression of the genes for lung Krüppel-like factor (LKLF), inhibitor of DNA binding (Id)1 and Id2, suggesting the existence of new regulatory pathways in pre-T cell development and thymic selection in which Gfi1 acts upstream of LKLF as well as the E-proteins, which are negatively regulated by Id1 and Id2.

Animals↗

PubMed2003

Loss of p27(Kip1) cooperates with cyclin E in T-cell lymphomagenesis.

Cyclin E and p27(Kip1) are key regulators for cyclin-dependent kinases (Cdks) acting at the G1-/S-phase transition of the cell cycle. Whereas cyclin E is required for the activation of Cdk2, p27(Kip1) is a specific Cdk inhibitor and can block cell division. High levels of cyclin E and low levels of p27(Kip1) expression have been associated with malignant lymphomas in humans; the level of p27(Kip1) is even considered of prognostic significance. However, mice that lack p27(Kip1) do not develop any malignant lymphomas despite a pronounced lymphoid hyperplasia in thymus and spleen. We have previously described transgenic mice that carry a construct in which the cyclin E cDNA is under the control of the CD2 promoter/enhancer region and thus express high levels of cyclin E in the T-cell compartment (CD2-cyclin E). These animals are not predisposed for T-cell lymphomas in the absence of other cooperating events. Here we show that T-cells from CD2-cyclin E mice that at the same time are deficient for p27(Kip1) show a significantly higher Cdk2 activity than cells from wild-type or single mutant animals. Accordingly, a higher percentage of T cells in S/G2/M phase is found in CD2-cyclin E/p27(Kip1-/-) mice. After a long latency period of over 200 days, these animals develop spontaneous monoclonal T cell lymphoma whereas none of the single CD2-cyclin E transgenic or the p27(Kip1)-deficient mice showed any sign of lymphoid malignancies. Our findings demonstrate that a deregulation of control mechanisms at the G1/S transition by the combination of high cyclin E levels in the absence of p27(Kip1) is sufficient to predispose mice to develop lymphoid malignancies and further support a role of p27(Kip1) as a tumor suppressor and of cyclin E as a dominant oncogene.

Animals↗