Signaling Pathways in Proliferation and Differentiation

描述(申请人提供)：视网膜母细胞瘤肿瘤抑制基因产物，pRb，调节细胞周期进程，这代表了其肿瘤抑制功能之一。PRb也是许多分化计划的关键参与者；然而，没有令人信服的遗传或体内证据表明pRb在控制细胞分化中的作用有助于其肿瘤抑制功能。像Rb一样，三个ras原癌基因调节分化和增殖。Rb和ras共同发挥作用，控制小鼠的分化。K-ras杂合子或N-ras杂合子(I)通过影响分化而不是增殖来挽救许多以Rb缺陷胚胎为特征的发育缺陷，(Ii)显著提高Rb杂合子产生的垂体腺癌的分化程度，从而延长其生存时间。总之，这些观察表明，pRb影响分化的能力是其肿瘤抑制功能的一个方面。 Rb+/-小鼠也会患上髓样(C细胞)甲状腺腺瘤。相比之下，RbN-ras杂合子发生转移性C细胞癌，其中一部分表现出剩余的N-ras等位基因丢失。这一违反直觉的观察可能是合理的，因为观察到神经内分泌源性肿瘤很少显示RAS突变，并且将致癌RAS引入此类肿瘤的株系中促进了它们的分化。将进行的研究通过实验分析来检验N-ras的缺失如何促进大型原发甲状腺肿瘤及其相关转移的发展。在Rb N-ras突变动物中出现的C细胞肿瘤的转移行为可能与获得C细胞在胚胎发生过程中所具有的正常迁移和侵袭行为有关。第二项研究将解决在转化过程中对不同ras亚型的需求。具体地说，K-和N-ras在SV40T抗原介导的小鼠胚胎成纤维细胞转化中的作用将被讨论。第三条线调查的动机是观察到Rb ras突变动物的骨骼肌继续显示出持续增殖的证据，尽管分化得到了挽救。详细的研究将集中在pRB和成肌因子MyoD在成肌分化过程中维持细胞周期终末停滞的分子机制，重点是对已知的参与细胞周期重新进入的基因的调节。

DESCRIPTION (provided by applicant): The retinoblastoma tumor suppressor gene product, pRb, regulates cell cycle progression, and this represents one of its tumor suppressor functions. pRb is also a key participant in a number of differentiation programs; however, there is no compelling genetic or in vivo evidence that pRb's role in the control of cellular differentiation contributes to its tumor suppressor function. Like Rb, the three ras proto-oncogenes regulate differentiation and proliferation. Rb and ras function together to control differentiation in the mouse. Heterozygosity for K-ras or nullizygosity for N-ras (i) rescues many of the developmental defects that characterize Rb-deficient embryos by affecting differentiation, but not proliferation and (ii) significantly enhances the degree of differentiation of pituitary adenocarcinomas arising in Rb heterozygotes, leading to their prolonged survival. Together, these observations suggest that the ability of pRb to affect differentiation is a facet of its tumor suppressor function. Rb+/- mice also develop medullary (C-cell) thyroid adenomas. By contrast, Rb N-ras heterozygotes develop metastatic C-cell carcinomas, with a fraction of these showing loss of the remaining N-ras allele. This counterintuitive observation might be rationalized by the observations that tumors of neuroendocrine origin rarely display mutations in ras and introduction of oncogenic Ras into lines derived from such tumors promotes their differentiation. Research to be conducted examines how loss of N-ras contributes to the development of large primary thyroid tumors and their associated metastases using experimental assays. The possibility that the metastatic behavior of C-cell tumors arising in Rb N-ras mutant animals might be associated with acquisition of the normal migratory and invasive behavior C-cells possess during embryo genesis will be explored. A second line of research will address the requirement for different ras isoforms in transformation. Specifically, the role of K- and N-ras in SV40 T antigen-mediated transformation of murine embryo fibroblasts will be addressed. A third line of investigation is motivated by the observation that skeletal muscle in Rb ras mutant animals continues to display evidence of ongoing proliferation, despite a rescue in differentiation. Detailed research will be focused here on the molecular mechanism by which pRb and the myogenic factor, MyoD, maintain a terminal cell cycle arrest during myogenic differentiation, with emphasis on the regulation of genes known to participate in cell cycle re-entry.