Multi step tumorigenesis, control of cell cycle entry

癌变是由多种协同作用的遗传病变引起的，导致细胞信号和细胞周期限制点控制的逐渐解除。所涉及的突变导致癌基因激活或肿瘤抑制基因功能的丧失。然而，这些突变基因在恶性细胞转化中的合作机制在很大程度上是未知的。我们的实验室已经证明，致癌病变的合作涉及多种信号的整合，这些信号聚集在细胞周期依赖性激酶复合物的调节上。在这里，我们建议研究c-myc癌基因与活化的Ras/Raf信号通路合作的分子机制。c-myc癌基因在人类癌症中经常被激活，是一种有效的增殖和凋亡诱导剂。myc诱导增殖的一个重要步骤是细胞周期蛋白E依赖性激酶（Cyclin E/Cdk2）的激活。利用组织培养中的遗传和生化方法，我们最近取得了令人惊讶的发现，c-myc激活周期蛋白E/Cdk2需要D周期蛋白隔离Gl细胞周期抑制剂p27Kip1和p21Cip1 （Ckis）的能力。我们现在提议研究D细胞周期蛋白隔离Ckis的能力是否在完整生物体中通过激活c-myc诱导细胞分裂中起重要作用。此外，我们计划验证D细胞周期蛋白对Ckis的抑制可能在器官发育和多步骤癌变过程中发挥重要作用的假设。这项工作将为开发基于信号通路的人类癌症治疗策略提供见解。

Carcinogenesis is caused by multiple co-operating genetic lesions leading to a progressive deregulation of cellular signaling and cell cycle restriction point control. The mutations involved result in oncogene activation or loss of tumor-suppressor gene function. However, the mechanisms by which these mutant genes co-operate in malignant cell transformation are largely unknown. Our laboratory has shown that the co-operation of oncogenic lesions involves integration of multiple signals converging on the regulation of cell cycle-dependent kinase complexes. Here we propose to investigate the molecular mechanisms by which the c-myc oncogene co-operates with activated Ras/Raf signaling. The c-myc oncogene is frequently activated in human cancer and is a potent inducer of proliferation and apoptosis. One essential step in Myc-induced proliferation is the activation of Cyclin E-dependent kinase (Cyclin E/Cdk2). Using genetic and biochemical approaches in tissue culture, we recently made the surprising finding that activation of cyclin E/Cdk2 by c-myc requires the ability of D cyclins to sequester Gl cell cycle inhibitors p27Kip1 and p21Cip1 (Ckis). We now propose to investigate whether the capability of D cyclins to sequester Ckis plays an important role in the induction of cell division by activated c-myc in an intact organism. Moreover, we plan to tea the hypothesis that sequestration of Ckis by D cyclins may play a significant role in organ development and during multi-step carcinogenesis. This work will provide insight into developing signaling pathway-based strategies for cancer therapy in humans.