Hematopoietic stem ell support through transcriptional coactivator TRAP220

TRAP/Mediator复合物是一种多蛋白共激活因子复合物，介导多种激活因子的信号。已知TRAP 220/MED 1亚基作为配体依赖性核受体信号的共激活剂和一些其它激活剂如加塔家族蛋白。我们最近发现TRAP 220不仅在脂肪细胞而且在白色血细胞（粒细胞和单核细胞）的核受体依赖性分化信号的介导中起关键作用。骨髓造血是通过造血细胞和龛细胞实现的，后者由成骨细胞和其他类型的间充质细胞组成。本研究探讨了TRAP 220在小生境细胞中的作用，尽管TRAP 220基因敲除小鼠在造血功能恢复之前是致死的，但我们成功地制备了敲除小鼠胚胎成纤维细胞（MEF）。因此，已知在体外支持造血干细胞/祖细胞（HSPC）的MEF用于检查以下能力： ...更多信息 支持HSPC。事实上，与在对照MEF上培养的骨髓细胞相比，在丝裂霉素C处理的敲除MEF上培养6至8周的骨髓细胞在甲基纤维素培养基内的殖民地形成显著减少。为了观察TRAP 220在MEF中支持骨髓细胞的短期作用，我们评估了在敲除和对照MEF上培养的骨髓细胞的生长和存活。与对照组相比，在2天培养后，敲除MEFs上的骨髓细胞计数显著降低。为了了解细胞数量减少的机制，我们分析了在MEFs上培养一周或两周的骨髓细胞的DNA合成和凋亡。与对照组相比，在敲除MEFs上培养的骨髓细胞中BrdU的掺入显著降低。此外，敲除MEFs上的凋亡细胞少于对照组。这些结果表明，MEFs分泌的信号分子可诱导骨髓细胞的增殖应激，并最终导致细胞凋亡，因此，微生态位细胞中的TRAP 220可能同时介导了造血祖细胞对HSPCs的支持和对造血祖细胞的生长应激。这是第一个发现，基本的transtiptional辅激活复合物可能发挥作用的造血生态位。少

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 … More 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