Regulation and Function of ECK in Apoptosis

然而，P53和E2F-1如何介导细胞凋亡的机制尚不清楚。我们发现，P53和E2F-1共同调节Eck的表达，Eck是一种上皮细胞受体蛋白-酪氨酸激酶，Eck介导氧化应激后的细胞凋亡。在P53诱导系统中，Eck在P53激活的基础上显著上调。氧化应激后Eck的表达以P53依赖的方式增加。我们克隆了人Eck基因的启动子区域，并在Eck转录起始点的700bp范围内确定了两个潜在的P53结合位点。我们发现，P53极大地诱导了含有该序列的荧光素酶报告基因上游的荧光素酶活性。有趣的是，在Eck启动子中也有一个E2F结合位点。将含有潜在E2F-1结合位点的荧光素酶报告基因与E2F-1基因共转染，可激活该启动子报告基因。我们的研究结果表明，P53和E2F-1是Eck的转录调节因子，Eck是P53和E2F-1途径中的细胞死亡受体。在这项拨款申请中，我们提出了一系列实验方法来将Eck归类为P53下游基因家族的新成员和P53和E2F-1的双重靶点。我们将确定Eck是否以及如何受到这两个基本肿瘤抑制因子的调控。我们的特定目标的成功实现将为P53和E2F-1如何协同调节蛋白质受体提供证据，蛋白质受体接收损伤信号并介导细胞死亡。Eck作为一种细胞死亡受体的特性可能揭示基因治疗的新靶点，或导致开发有效的癌症治疗化疗策略。

Transcription factors p53 and E2F-1 coordinate and mediate apoptosis in response to genotoxic stress. However, the mechanism whereby how p53 and E2F-1 mediate apoptosis is unclear. We found that p53 and E2F-1 co-regulate the expression of ECK, an epithelial cell receptor protein-tyrosine kinase and that ECK mediates apoptosis following oxidative stress. In p53 inducible systems, ECK is greatly upregulated upon the activation of p53. The expression of ECK is increased following oxidative stress in a p53-dependent manner. We have cloned the promoter region of human ECK gene and identified two potential p53-binding sites within a 700 bp from the transcriptional initiation site of ECK. We show that p53 greatly induces luciferase activity of the luciferase reporter containing this sequence upstream of the luciferase gene. Interestingly, there is also an E2F-binding site in the ECK promoter. Cotransfection of E2F-1 with the luciferase reporter containing the potential E2F-1 binding site leads to the activation of this promoter reporter. We further demonstrate that the ectopic expression of E2F-1 elevates the levels of ECK protein. Finally, overexpression of ECK greatly increases cellular susceptibility to apoptosis and suppresses colony formation in soft agar. Our findings indicate that p53 and E2F-1 are transcriptional regulators of ECK and that ECK is a cell death receptor in the p53 and E2F-1 pathways. This is the first evidence that p53 and E2F-1 share a common target gene in signaling apoptosis. In this grant application, we propose a series of experimental approaches to classify ECK as a new member of the p53-downstream gene family and a dual target for p53 and E2F-1. We will determine whether and how ECK is regulated by these two fundamental tumor suppressors. We will demonstrate the importance of ECK in signaling oxidative cell death by apoptosis and its potential role in tumorigenesis. Successful achievement of our specific aims will provide evidence for how p53 and E2F-1 cooperatively regulate a protein receptor, which receives damage signals and mediates cell death. Characterization of ECK as a cell death receptor may reveal a new target for gene therapy or lead to the development of effective chemotherapeutical strategies in cancer treatment.