Molecular mechanisms regulating the growth and differentiation of hematopoietic stem cells

(1)干细胞因子（Stem cell factor， SCF）通过与c-Kit受体（c-Kit receptor， KIT）结合，在造血干细胞的增殖、存活和分化中起着至关重要的作用。我们制作了一系列22个KIT突变体，其中Tyr (Y)残基替换为细胞质域的Phe (F)，并引入BAF3细胞。在SCF刺激下，表达KIT^<WT>(WT)的BAF3表现出细胞迁移和Ca^<2+>动员。在22YF突变体中，Y567F和Y719F显著降低了细胞迁移和Ca^<2+>的动员。信号级联分析表明，Y567介导的Src家族激酶（SFK）激活导致Ca^<2+>内流和迁移，P38MAPK （P38MAPK）和Erk1/2也受Y567/SFK调控并参与细胞迁移。此外，y719介导的PI3K通路也参与了迁移。这些结果表明，两个主要的KIT信号通路导致细胞迁移，一个是Y567-SFK-p38MAPK-Erk，另一个是Y719-PI3激酶。(2)血小板生成素（T…More PO）及其受体c-mpl在造血干细胞的生长和巨核细胞分化中起着至关重要的作用。我们发现Ras激活参与了血小板生成素（TPO）诱导的巨核细胞分化。此外，我们证明了GATA-1活性是ras介导的巨核细胞分化所必需的，并且GATA-1活性受到其他谱系特异性转录因子PU.1和c-Myb的直接相互作用的负调控。(3) AIM-1属于Aurora/Ipl1丝氨酸苏氨酸激酶家族，在有丝分裂中起关键作用。在人造血细胞中，AIM-1的表达仅限于细胞周期的G2/M期。相反，AIM-1在巨核细胞多倍体化过程中持续受到抑制。通过诱导表达野生型AIM-1来补充AIM-1活性，可以消除tpa诱导的K562细胞的多倍体化，而显性阴性AIM-1抑制AIM-1活性导致多倍体化。这些结果提示M期AIM-1的下调可能与巨核细胞有丝分裂流产和多倍体形成有关。少

(1) Stem cell factor (SCF) has crucial roles in proliferation, survival and differentiation of hematopoietic stem cells through binding to c-Kit receptor (KIT). We made a series of 22 KIT mutants, in which Tyr (Y) residue was substituted to Phe (F) in the cytoplasmic domain, and introduced into BAF3 cells. On stimulation with SCF, BAF3 expressing KIT^<WT>(WT) showed cell migration and Ca^<2+> mobilization. Among 22YF mutants, Y567F and Y719F showed significantly reduced cell migration and Ca^<2+> mobilization. Analysis on signaling cascades suggested that Y567-mediated Src family kinase (SFK) activation led to Ca^<2+> influx and migration, and that P38MAPkinase (P38MAPK) and Erk1/2 were also regulated by Y567/SFK and involved in cell migration. Also, Y719-mediated PI3K pathway was suggested to be involved in the migration. These results indicate that two major KIT signaling pathways lead to cell migration, one is Y567-SFK-p38MAPK-Erk and another is Y719-PI3 kinase.(2) Thrombopoietin (T … More PO) and its receptor c-mpl play crucial roles in growth and megakaryocytic differentiation of hematopoietic stem cells. We found that Ras activation was involved in thrombopoietin (TPO)-induced megakaryocytic differentiation. Furthermore, we demonstrated that GATA-1 activities was required for the Ras-mediated megakaryocytic differentiation, and that GATA-1 activities were regulated negatively by the direct interaction with other lineage-specific transcription factors, PU.1 and c-Myb.(3) AIM-1 belongs to an Aurora/Ipl1 serine threonine kinase family, and is supposed to play key roles in mitosis. In human hematopoietic cells, expression of AIM-1 was restrictedly observed at G2/M phase of cell cycle. In contrast, AIM-1 was continuously repressed during megakaryocytic polyploidization. Supplement of AIM-1 activities by the induced expression of wild-type AIM-1 canceled TPA-induced polyploidization of K562 cells, and the suppression of AIM-1 activities by dominant-negative AIM-1 led to polyploidization. These results suggested that down-regulation of AIM-1 at M phase may be involved in abortive mitosis and polyploid formation of megakaryocytes. Less