C-, N-, AND L-MYC EFFECTS ON HEMATOPOIETIC CELLS

MYC癌蛋白参与细胞增殖、分化、细胞周期进程和细胞凋亡。三种主要的myc蛋白，c-myc，N-myc和L-myc，也参与了诸如Burkitt‘s和AIDS相关的淋巴瘤、乳腺癌、神经母细胞瘤和肺癌等恶性肿瘤的发病机制。人们对这些蛋白质的功能相似性知之甚少。我们已经证明了c-、N-和L-myc在调节c-myc反应启动子方面的能力不同。C-myc的过度表达与造血细胞对化疗药物的敏感性增加有关，而N-myc和L-myc则产生耐药。在缺乏p53的细胞中，c-myc的过度表达也会导致基因组的不稳定。在具体目标I中，我们将比较c-myc、N-和L-myc通过c-myc依赖的癌基因在c-myc/-成纤维细胞中恢复正常增殖和转化的能力。在特定的目标II中，嵌合和突变的myc蛋白将被用来绘制负责传递对造血细胞的药理敏感性或耐药性的区域。在特定目的III中，我们将确定半胱氨酸蛋白酶(“Caspase”)在c-、N-和L-myc介导的细胞凋亡中的作用。最后，在特定的目标IV中，我们将再次使用突变的myc蛋白来定位导致缺乏p53的造血细胞基因组不稳定的区域。我们将询问单个c-myc调控基因的过度表达是否足以产生基因组不稳定性。将检查细胞周期蛋白及其激酶的异常。我们还将探讨c-myc以外的基因是否可以替代c-myc诱导四倍体。还将测试两种不同的诱导四倍体的模型。上述研究应该为Myc癌蛋白在赋予造血细胞的表型方面如何彼此不同提供新的见解。

Myc oncoproteins are involved in proliferation, differentiation, cell cycle progression, and apoptosis. The three major myc proteins, c-myc, N-myc, and L-myc, are also implicated in the pathogenesis of malignancies such as Burkitt's and AIDS-related lymphomas, breast cancer, neuroblastoma, and lung cancer. Little is known regarding the functional similarities of these proteins. We have shown that c-, N-, and L-myc differ in their ability to modulate c-myc-responsive promoters. Overexpression of c-myc is associated with increased sensitivity of hematopoietic cells to chemotherapeutic drugs whereas N-myc and L-myc produce resistance. In cells lacking p53, c-myc overexpression also produces genomic instability. In Specific Aim I, we will compare the abilities of c-, N-, and L-myc to restore normal levels of proliferation and transformation by c-myc-dependent oncogenes in c-myc-/- fibroblasts. In Specific Aim II, chimeric and mutant myc proteins will be used to map the domains responsible for imparting pharmacologic sensitivity or resistance to hematopoietic cells. In Specific Aim III, we will determine the role of cysteine proteases ("Caspases") in apoptosis mediated by c-, N-, and L-myc. Finally, in Specific Aim IV, we will again use mutant myc proteins to map the regions responsible for imparting genomic instability to hematopoietic cells lacking p53. We will ask if the overexpression of individual c-myc-regulated genes, is sufficient to produce genomic instability. Abnormalities of cyclins and their kinases will be examined. We will also ask if genes other than c-myc, which can induce unscheduled S-phase can substitute for c-myc in the induction of tetraploidy. Two different models for the induction of tetraploidy will also be tested. The above studies should provide new insights into how myc oncoproteins differ from one another with respect to the phenotypes they impart to hematopoietic cells.