Neurofibromatosis Type 1 Gene Regulates Myelopoiesis

描述（申请人提供）：NF 1肿瘤抑制基因突变导致1型神经纤维瘤病（NF-1）。NF 1编码一种称为神经纤维蛋白的p21 ras（Ras）的GTP酶激活蛋白（GAP）。神经纤维蛋白将p21 ras从其活性GTP转化为其非活性GDP结合构象。具有NFl的个体具有获得良性和恶性肿瘤的倾向。此外，患有NF 1的儿童易患青少年骨髓单核细胞白血病（JMML）。来自JMML骨髓细胞的髓样祖细胞（CFU-GM）的标志是它们响应于低剂量的生长因子粒细胞巨噬细胞集落刺激因子（GM-CSF）而过度增殖的倾向。Nf 1的纯合破坏在子宫内是致命的，然而，我们发现，小鼠Nf 1缺陷的胎儿造血细胞显示CFU-GM生长和Ras效应器响应多种生长因子，包括GM-CSF和干细胞因子（SCF），c-kit受体酪氨酸激酶的配体的超活化的异常模式。C-kit由鼠显性白色斑点位点编码，W）。由于W和Nfl基因座似乎沿着共同的发育途径起作用，因此产生了在两个基因座处具有突变的小鼠。我们发现Nfl单倍不足部分挽救了W 41小鼠的肥大细胞和毛色缺陷。这些数据提供了遗传证据，即Nfl处的单倍不足在体外和体内调节在患有NFl的个体中受影响的两个谱系中的细胞命运。这些结果支持了一个新的概念，杂合失活的肿瘤抑制基因可能有重要的生物学effects.While损失的神经纤维蛋白增加p21 ras活性在特定的细胞系，识别不同的p21 ras效应通路，控制增殖和生存的NF-1缺陷细胞的改变是不完整的，理解疾病的发病机制是至关重要的。大多数先前的研究认为，神经纤维蛋白的损失导致经典的p21 ras-Raf-Mek-ERK通路的激活增加。然而，我们有初步的数据来支持一个替代的生物化学模型，其中Nfl 1缺陷细胞的生长优势是通过从p21 ras到小Rho GT3，Rac 2，一种仅在造血细胞中表达的Rac同种型的信号增加来介导的。我们建议研究如何激活p21 ras和Rac亚型合作，以改变生物学的Nf 1 +/-肥大细胞和Nf 1 -/-干细胞和骨髓祖细胞利用小鼠在这些基因座的基因突变。

DESCRIPTION (provided by applicant): Mutatons in the NF1 tumor suppressor gene cause neurofibromatosis type 1 (NF-1). NF1 encodes a GTPase activating protein (GAP) for p21 ras (Ras) called neurofibromin. Neurofibromin converts p21 ras from its active GTP to its inactive GDP bound conformation. Individuals with NFl have a propensity to acquire benign and malignant tumors. Additionally, children with NFl are predisposed to juvenile myelomonocytic leukemia (JMML). A hallmark of myeloid progenitors (CFU-GM) from JMML bone marrow cells is their propensity to hyperproliferate in response to low doses of the growth factor granulocyte macrophage colony stimulating factor (GM-CSF). Homozygous disruption of Nfl is lethal in utero; however we found that murine Nf1 -deficient fetal hematopoletic cells show an abnormal pattern of CFU-GM growth and hyperactivation of Ras effectors in response to multiple growth factors, including GM-CSF and stem cell factor (SCF), the ligand for the c-kit receptor tyrosine kinase. C-kit is encoded by the murine dominant white spotting locus, W). Since the W and Nfl loci appeared to function along a common developmental pathway, mice with mutations at both loci were generated. We found that haploinsufficiency of Nfl partially rescued the mast cell and coat color defects in W41 mice. These data offered genetic evidence that haploinsufficiency at Nfl modulates cell fates in vitro and in vivo in two lineages that are affected in individuals with NFl. The results support the emerging concept that heterozygous inactivation of tumor suppressor genes may have important biological effects.While loss of neurofibromin increases p21 ras activity in specific cell lineages, identification of alterations in distinct p21 ras effector pathways that control proliferation and survival in NF1-deficient cells is incomplete and critical for understanding disease pathogenesis. Most previous studies argue that loss of neurofibromin results in increased activation of the classical p21 ras-Raf-Mek-ERK pathway. However, we have preliminary data to support an alternative biochemical model where the growth advantage of Nfl1-deficient cells is mediated through increased signals from p21 ras to the small Rho GTPase, Rac2, a Rac isoform expressed only in hematopoietic cells. We propose studies to examine how activation of p21 ras and Rac isoforms cooperate to alter the biology of Nfl +/- mast cells and Nf 1 -/- stem and myeloid progenitor cells utilizing mice with genetic mutations in these loci.