| Budget Amount *help |
¥3,890,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥390,000)
Fiscal Year 2007: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000)
Fiscal Year 2006: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
TRAP/Mediator complex is a multiprotein coactivator complex that mediates the signals of a variety of activators. The TRAP220/MED1 subunit is known to act as a coactivator for ligand-dependent nuclear receptor signals and some other activators such as the GATA family proteins. We have recently shown that TRAP220 plays a key role in mediating signals of nuclear receptor-dependent differentiation of not only adipocytes but white blood cells (granulocytes and monocytes). Bone marrow hematopoiesis is achieved by both hematopoietic cells and niche cells, the latter of which are comprised of osteoblasts and other type(s) of mesenchymal cells. In this study we have evaluated the role of TRAP220 in niche cells.
Although the TRAP220 knockout mice am lethal before definitive hematopoiesis is dominant, the knockout mouse embryonic fibroblasts (MEF) are successfully prepared. Therefore, the MEFs, known to support hematopoietic stem/progenitor cells (HSPCs)in vitro, are used to check the ability to
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support the HSPCs. Indeed, the colony formation within the methylcellulose media was prominently decreased for bone marrow cells cultured for 6 to 8 weeks on mitomycin C-treated knockout MEFs, compared to those cultured on control MEFs. This result apparently demonstrates the role of TRAP220 in niche cells, which induce signals that mediate long-term support of HSPCs.
In order to see the short-term role of TRAP220 in MEF to support bone marrow cells, we then evaluated growth and survival of bone marrow cells cultured on knockout and control MEFs. The counts of bone marrow cells on knockout MEFs were significantly decreased compared to the control ever after the 2-days culture. To know the mechanism of decreased cell numbers, we analyzed DNA synthesis and apoptosis of bone marrow cells cultured on MEFs for one or two weeks. The incorporation of BrdU into bone marrow cells cultured on knockout MEFs was prominently decreased compared to the control. Furthermore, the apoptotic cells on knockout MEFs were less than those on the control. These results indicate that the MEFs secret the signal molecules that induce proliferation stress in bone marrow cells that eventually causes apoptosis simultaneously.
Thus, the TRAP220 in niche cells might mediate the signals both of the HSPCs support and the growth stress in hematopoietic progenitors. This is the first finding that the basic transctiptional coactivator complex might play a role in the hematopoietic niche. Less
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