Receptor-mediated signalings-regulating proliferation, differentiation and neoplastic transformation of hematopoietic cells

c-kit受体酪氨酸激酶（KIT）及其配体干细胞因子（SCF）是造血细胞中的重要信号分子。我们发现，两个点突变，Val 559 →Gly（G559）突变的质膜结构域和Asp 814 →瓦尔（V814）突变的激酶结构域，导致组成性和致癌激活的KIT。为了确定突变型KIT的哪一部分在SCF不存在的情况下对于受体二聚化或自缔合是必不可少的，我们构建了一系列KIT的缺失和嵌合突变体，包括胞外结构域截短型KIT和嵌合型KIT，其中胞外和跨膜结构域被src肉豆蔻基化信号肽取代。通过使用小鼠白细胞介素（IL）-3依赖性Ba/F3细胞，这些细胞经历了各种c-kit基因的转染，我们表明KIT的胞膜和激酶结构域的组成性激活突变可能不一定需要它们的细胞外和跨膜表达。 关于我们 KIT突变体的受体自结合可能对激活下游效应子起重要作用，这些效应子是非依赖因子的生长和致瘤性所必需的。除SCF/KIT系统外，血小板生成素（TPO）/c-mpl系统在造血中也起重要作用。为了阐明TPO诱导的增殖和分化的机制，将c-mpl引入人IL-3依赖性F-36 P细胞中。发现F-36 P-mpl细胞响应于TPO以高速率增殖和分化成成熟巨核细胞。通过使用显性阴性（dn）形式的STATs和ras，这表明TPO诱导的增殖可能是通过激活STAT 5和ras介导的，延长的ras激活可能参与TPO诱导的巨核细胞分化。此外，我们发现，STAT 5，除了ras信号，似乎介导的转录调控细胞周期蛋白D1在造血细胞中依赖于精氨酸的生长。少

The c-kit receptor tyrosine kinase (KIT) and its ligand, stem cell factor (SCF) transduce crucial signals in hematopoietic cells. We revealed that two point mutations, Val559→Gly (G559) mutation in the juxtamembrane domain and Asp814→Val (V814) mutation in the kinase domain, lead to constitutive and oncogenic activation of KIT. In order to determine as to which portion of mutant KITs is indispensable for receptor dimerization or self-association in the absence of SCF, we have constructed a series of deletion and chimeric mutants of KIT, including the extracellular domain truncated type KIT and chimeric type KIT in which extracellular and transmembrane domains are replaced by src myristylation signal peptide. By using murine interleukin (IL)-3-dependent Ba/F3 cells that were subjected to transfection of various c-kit genes, we showed that the constituvely activating mutations at both the juxtamembrane and kinase domains of KIT may not necessarily require their extracellular and transmem … More brane domains for their formation of receptor self-association, and that the receptor self-association of mutant KIT may be important for activation of downstream effectors that are required for factor-independent growth and tumorigenicity.In addition to the SCF/KIT system, thrombopoietin (TPO)/c-mpl system also plays a fundamental role in hematopoiesis. In an effort to clarify the mechanisms of TPO-induced proliferation and differentiation, c-mpl was introduced into human IL-3-dependent F-36P cells. F-36P-mpl cells were found to proliferate and differentiate at a high rate into mature megakaryocytes in response to TPO. By using dominant-negative (dn) forms of STATs and ras, it was suggested that TPO-induced proliferation may be mediated through activation of STAT5 and ras, and that prolonged ras activation may be involved in TPO-induced megakaryocytic differentiation. Furthermore, we found that STAT5, in addition to ras signaling, appeared to mediate transcriptional regulation of cyclin D1 during cytokine-dependent growth in hematopoietic cells. Less