The Role of p53 and 14-3-3 in Genomic Instability

描述（由申请人提供）：基因组不稳定性是癌症的标志，也是促进肿瘤发展和进展为恶性肿瘤的有利特征。众所周知，p53 肿瘤抑制因子在基因组的稳定中发挥着重要作用。然而，p53 执行“基因组守护者”功能的机制尚不清楚。在初步研究中，我们已确定 14-3-3gamma（一种已知与 p53 肿瘤抑制因子相互作用的蛋白质）可导致某种形式的基因组不稳定，表现为核内复制和 DNA 含量 > 4N 的细胞的产生。我们发现这种活性发生在缺乏功能性 p53 的细胞中，但不会发生在 p53 保持活性的细胞中。由于多倍体是非整倍体之前的不稳定状态，因此我们假设 14-3-3gamma 在水平升高时可能会降低基因组稳定性。为了支持这一点，有报道称 14-3-3 表达在肺癌中升高，我们的初步数据表明 14-3-3gamma 是这些肿瘤中过度表达的亚型之一。因为 14-3-3gamma 与 p53 蛋白发生物理相互作用，并且因为 14-3-3gamma 介导的再复制表型发生在功能性 p53 不存在的情况下，所以我们假设 p53 通过两种蛋白之间的直接物理相互作用抑制 14-3-3gamma 导致基因组不稳定的能力。为了测试这一点，我们将通过检查 14-3-3gamma 对细胞周期控制蛋白功能、DNA 复制起始和细胞周期检查点的影响来确定 14-3-3gamma 是否会引起核内复制，2) 野生型 p53 是否可以抑制核内复制以及这是否需要与 14-3-3gamma 直接物理相互作用，3) 表征人肺肿瘤中 14-3-3 的表达。

DESCRIPTION (provided by applicant): Genomic instability is a hallmark of cancer and an enabling feature that facilitates tumor development and advancement to malignancy. The p53 tumor suppressor is known to play a major role in the stabilization of the genome. However, the mechanism by which p53 executes it's function as "guardian of the genome" is unclear. In preliminary studies we have determined that 14-3-3gamma, a protein known to interact with the p53 tumor suppressor, can cause a form of genomic instability that is manifested by endoreduplication and production of cells with > 4N DNA content. We have found that this activity occurs in cells that lack a functional p53, but does not occur in cells where p53 remains active. Because polyploidy is an unstable condition that precedes aneuploidy, we postulate that 14-3-3gamma may decrease genomic stability when present at elevated levels. In support of this it has been reported that 14-3-3 expression is elevated in lung cancer and our preliminary data indicates that 14-3-3gamma is one of the isoforms that is overexpressed in these tumors. Because 14-3-3gamma physically interacts with the p53 protein and because the 14-3-3gamma-mediated rereplication phenotype occurs in the absence of a functional p53 we hypothesize that p53 suppresses 14-3-3gamma's ability to cause genomic instability through a direct physical interaction between the two proteins. To test this we will determine 1) whether 14-3-3gamma causes endoreduplication by examining its affect on the function of cell cycle control proteins, initiation of DNA replication, and cell cycle checkpoints, 2) whether wild-type p53 can suppress the endoreduplication and whether this requires a direct physical interaction with 14-3-3gamma and 3) characterize 14-3-3 expression in human lung tumors.