Biomedical subjects

Tomohiko Tamura

Publications and source records attributed to Tomohiko Tamura.

26 records · Page 2Linked to original sources

PubMed2003

Nramp1-mediated innate resistance to intraphagosomal pathogens is regulated by IRF-8, PU.1, and Miz-1.

Natural resistance-associated macrophage protein 1 (Nramp1) is a proton/divalent cation antiporter exclusively expressed in monocyte/macrophage cells with a unique role in innate resistance to intraphagosomal pathogens. In humans, it is linked to several infectious diseases, including leprosy, pulmonary tuberculosis, visceral leishmaniasis, meningococcal meningitis, and human immunodeficiency virus as well as to autoimmune diseases such as rheumatoid arthritis and Crohn's disease. Here we demonstrate that the restricted expression of Nramp1 is mediated by the macrophage-specific transcription factor IRF-8. This factor exerts its activity via protein-protein interaction, which facilitates its binding to target DNA. Using yeast two-hybrid screen we identified Myc Interacting Zinc finger protein 1 (Miz-1) as new interacting partner. This interaction is restricted to immune cells and takes place on the promoter Nramp1 in association with PU.1, a transcription factor essential for myelopoiesis. Consistent with these data, IRF-8 knockout mice are sensitive to a repertoire of intracellular pathogens. Accordingly, IRF-8-/- mice express low levels of Nramp1 that can not be induced any further. Thus, our results explain in molecular terms the role of IRF-8 in conferring innate resistance to intracellular pathogens and point to its possible involvement in autoimmune diseases.

Animals↗

PubMed2003

Cutting edge: IFN consensus sequence binding protein/IFN regulatory factor 8 drives the development of type I IFN-producing plasmacytoid dendritic cells.

IFN consensus sequence binding protein (ICSBP/IFN regulatory factor 8) is a hematopoietic cell-specific transcription factor essential for the generation of CD8 alpha(+) dendritic cells (DCs). We found that ICSBP(-/-) mice lack B220(+)CD11b(-) plasmacytoid DCs (pDCs) in addition to CD8 alpha(+) DCs. Although ICSBP(-/-) mice have B220(-)CD11b(+) myeloid DCs (mDCs), they fail to mature upon Toll-like receptor signaling. Accordingly, ICSBP(-/-) bone marrow progenitor cells were defective in generating pDCs in the fms-like tyrosine kinase 3 ligand-based culture system and mDCs generated in this system were defective in maturation. We demonstrate that introduction of ICSBP rescues the development of pDCs from -/- bone marrow progenitors. ICSBP also restored the ability of both pDCs and mDCs to mature after Toll-like receptor signals. ICSBP-restored DCs produced IFN-alpha and IL-12p40 in a DC subset-selective manner with the amounts comparable to those by +/+ DCs. Together, ICSBP is essential for early pDC development and final maturation of both pDCs and mDCs.

Animals↗

PubMed2002

ICSBP/IRF-8 retrovirus transduction rescues dendritic cell development in vitro.

Dendritic cells (DCs) develop from bone marrow (BM) progenitor cells and mature in response to external signals to elicit functions important for innate and adaptive immunity. Interferon consensus sequence binding protein (ICSBP; also called interferon regulatory factor 8 [IRF-8]) is a hematopoietic cell-specific transcription factor expressed in BM progenitor cells that contributes to myeloid cell development. In light of our earlier observation that ICSBP(-/-) mice lack CD8alpha(+) DCs, we investigated the role of ICSBP in DC development in vitro in the presence of Flt3 ligand. Immature ICSBP(-/-) DCs developed from BM progenitor cells showed assorted defects, did not mature in response to activation signals, and failed to express CD8alpha and interleukin 12 (IL-12) p40, a feature consistent with ICSBP(-/-) DCs in vivo. We show that retroviral introduction of ICSBP restores the development of immature DCs that can fully mature on activation signals. All the defects seen with ICSBP(-/-) DCs were corrected after ICSBP transduction, including the expression of CD8alpha and IL-12 p40 as well as major histocompatability complex class II and other costimulatory molecules. ICSBP is known to regulate gene expression by interacting with partner proteins PU.1 and IRFs, thereby binding to target elements ISRE and EICE. Analysis of a series of ICSBP mutants showed that the intact DNA-binding activity as well as the ability to interact with partner proteins are required for the restoration of DC development/maturation, pointing to the transcriptional function of ICSBP as a basis of restoration. Taken together, this study identifies ICSBP as a factor critical for both early differentiation and final maturation of DCs.

Animals↗

PubMed2002

IFN consensus sequence binding protein/IFN regulatory factor-8 guides bone marrow progenitor cells toward the macrophage lineage.

IFN consensus sequence binding protein (ICSBP; IFN regulatory factor-8) is a transcription factor of the IFN regulatory factor family. Disruption of this gene results in a leukemia-like disease in mice. To investigate the role of ICSBP in myeloid cell development, lineage marker-negative (Lin(-)) bone marrow progenitor cells were purified from ICSBP(+/+) and ICSBP(-/-) mice and tested for gene expression and colony-forming ability. ICSBP was expressed in Lin(-) progenitor cells, and its levels were markedly increased by IFN-gamma. The colony-forming potential of ICSBP(-/-) progenitor cells was grossly abnormal, as they gave rise to a disproportionately high number of granulocyte colonies and many fewer macrophage colonies. IFN-gamma inhibited colony formation, while promoting macrophage maturation in ICSBP(+/+) cells. In contrast, the effects of IFN-gamma were completely absent in ICSBP(-/-) progenitors. By retrovirus transduction we tested whether reintroduction of ICSBP restores a normal colony-forming potential in -/- progenitor cells. The wild-type ICSBP, but not transcriptionally defective mutants, corrected abnormal colony formation by increasing macrophage colonies and decreasing granulocyte colonies. Taken together, ICSBP plays a critical role in myeloid cell development by controlling lineage selection and is indispensable for IFN-gamma-dependent modulation of progenitor cell maturation.

Animals↗

PubMed2002

ICSBP/IRF-8: its regulatory roles in the development of myeloid cells.

Interferon (IFN) consensus sequence binding protein (ICSBP)/IFN regulatory factor (IRF)-8 is an IFNgamma-inducible transcription factor of the IRF family and regulates transcription through multiple target DNA elements, such as IFN-stimulated response element (ISRE), Ets/IRF composite element, and IFN-gamma activation site (GAS). ICSBP(-/-) mice are immunodeficient and susceptible to various pathogens. They have defects in the macrophage function, including the ability to induce interleukin-12 (IL-12) p40 and some IFN-gamma-responsible genes. In addition, ICSBP(-/-) mice develop a chronic myelogenous leukemia (CML)-like syndrome, where a systemic expansion of granulocytes is followed by a fatal blast crisis. ICSBP(-/-) mice harbor an increased number of myeloid progenitor cells, and the -/- progenitors preferentially give rise to granulocytes, although they cannot efficiently generate another descendant of the myeloid lineage, macrophages. Studies with myeloid progenitor cells have shown that ICSBP drives their differentiation toward macrophage, whereas it inhibits granulocyte differentiation. Furthermore, myeloid cells from ICSBP(-/-) mice are resistant to apoptosis. These results illustrate the mechanism by which the loss of ICSBP leads to immunodeficiency and CML-like syndrome and suggest ICSBP's critical role in the development of myeloid cells.

Animals↗

PubMed2002

A Mammalian bromodomain protein, brd4, interacts with replication factor C and inhibits progression to S phase.

Brd4 belongs to the BET family of nuclear proteins that carry two bromodomains implicated in the interaction with chromatin. Expression of Brd4 correlates with cell growth and is induced during early G(1) upon mitogenic stimuli. In the present study, we investigated the role of Brd4 in cell growth regulation. We found that ectopic expression of Brd4 in NIH 3T3 and HeLa cells inhibits cell cycle progression from G(1) to S. Coimmunoprecipitation experiments showed that endogenous and transfected Brd4 interacts with replication factor C (RFC), the conserved five-subunit complex essential for DNA replication. In vitro analysis showed that Brd4 binds directly to the largest subunit, RFC-140, thereby interacting with the entire RFC. In line with the inhibitory activity seen in vivo, recombinant Brd4 inhibited RFC-dependent DNA elongation reactions in vitro. Analysis of Brd4 deletion mutants indicated that both the interaction with RFC-140 and the inhibition of entry into S phase are dependent on the second bromodomain of Brd4. Lastly, supporting the functional importance of this interaction, it was found that cotransfection with RFC-140 reduced the growth-inhibitory effect of Brd4. Taken as a whole, the present study suggests that Brd4 regulates cell cycle progression in part by interacting with RFC.

3T3 Cells↗

PubMed2002

Gamma interferon triggers interaction between ICSBP (IRF-8) and TEL, recruiting the histone deacetylase HDAC3 to the interferon-responsive element.

ICSBP (IRF-8) is a transcription factor of the IRF family expressed only in the immune system. It is induced in macrophages by gamma interferon (IFN-gamma) and contributes to macrophage functions. By interacting with Ets family protein PU.1, ICSBP binds to the IRF/Ets composite element and stimulates transcription. ICSBP binds to another DNA element, the IFN-stimulated response element (ISRE), a common target of the IRF family. Limited knowledge as to how ICSBP and other IRF proteins regulate ISRE-dependent transcription in IFN-gamma-activated macrophages is available. By mass-spectrometric analysis of ISRE-bound proteins in macrophages, we identified TEL, another Ets member, as a factor recruited to the element in an IFN-gamma-dependent manner. In vitro analysis with recombinant proteins indicated that this recruitment is due to a direct interaction between ICSBP and TEL, which is enhanced by the presence of ISRE. Significantly, the interaction with TEL in turn resulted in the recruitment of the histone deacetytase HDAC3 to the ISRE, causing increased repression of IFN-gamma-mediated reporter activity through the ISRE. This repression may provide a negative-feedback mechanism operating after the initial transcriptional activation by IFN-gamma. By associating with two different Ets family proteins, ICSBP exerts a dual function in IFN-gamma-dependent gene regulation in an immune system-specific manner.

Animals↗

PubMed2002

Toll-like receptor signaling and regulation of cytokine gene expression in the immune system.

Dendritic cells, macrophages, and granulocytes are derived from hematopoietic stem cells and provide a first line of defense against infectious pathogens. Toll-like receptors (TLRs) expressed on these cells recognize molecular stuctures present in the pathogens. Upon binding of a pathogen ligand, TLRs trigger a cascade of signaling pathways that is conserved from insect to plants to humans, which ultimately activates NFkappaB. In mammalian cells, this leads to the induction of cytokine genes and the establishment of innate immunity. For example, TLR signals induce type I interferons (IFN alpha/beta) in dendritic cells conferring an antiviral state upon host cells. Moreover, TLR signals stimulate not only pro-inflammatory cytokines such as IFNs, IL-1, TNFalpha, and IL-12 but also anti-inflammatory cytokines such as IL-10 and IL-6 IL-12 and IL-10 are cytokines that bridge early innate responses and the ensuing specific immune responses. TLR signals also enhance an antigen presentation capacity in dendritic cells and macrophages. Recent studies with mouse and human cells indicate that TLRs activate multiple signaling cascades that involve chromatin structure alterations as well as activation of many transcription factors (e.g., IRF-3, IRF-8/ICSBP, and PU.1). Together, although the basic backbone is conserved throughout evolution, the TLR signaling system in mammalian species has an added complexity to accommodate a mechanism that links innate and adaptive immunity.

Animals↗