P53 AND ESTROGEN IN PCNA EXPRESSION OSTEOSARCOMA CELLS

这项研究的目的是分析人骨肉瘤细胞中肿瘤抑制蛋白P53和雌激素信号通路之间的相互作用。P53基因是各种人类癌症中最常见的突变基因。P53的失活被认为是骨肉瘤发生发展的重要一步。雌激素在成骨细胞系的发育和功能中起重要作用，雌激素刺激骨肉瘤细胞的增殖。然而，在存在和不存在功能性野生型P53的情况下，雌激素作用的后果尚不清楚。虽然已知p300/CBP是P53和雌激素受体介导的基因调控的共同激活子，但P53和雌激素功能之间的关系仍不清楚。我们以骨肉瘤细胞中增殖细胞核抗原基因的表达为模型，研究P53和雌激素介导的基因调控途径之间的功能相互关系及其与细胞增殖和细胞周期紊乱的关系。增殖细胞核抗原是细胞DNA复制和DNA修复机制的重要组成部分。骨肉瘤细胞中增殖细胞核抗原的表达受P53调控。我们的结果表明，增殖细胞核抗原基因是雌激素诱导的。此外，初步实验表明，p300/CBP在P53对增殖细胞核抗原表达的调节中起着重要作用。基于早期的研究和初步数据，我们假设P53和雌激素信号通路之间在调节增殖细胞核抗原表达方面存在显著的串扰。为了验证这一假设，我们将分析P300/CBP，P53和雌激素受体的共同激活剂，调节P53介导的增殖细胞核抗原基因表达的机制。我们建议确定P53-CBP通路在雌激素诱导的骨肉瘤细胞增殖和增殖中的作用。由于增殖细胞核抗原的相对数量在确定其与其他对细胞周期重要的蛋白质的相互作用方面是重要的，因此还假设在细胞周期的不同阶段，增殖细胞核抗原的表达受P53和雌激素的协同作用的不同调控。为了验证这一假设，我们将分析细胞周期中p53和雌激素对增殖细胞核抗原转录的调控。这项拟议的研究将提供重要的信息，在存在和不存在功能性P53的情况下，雌激素在细胞增殖和细胞周期检查点功能中的作用。它还将为分析类固醇激素和p53在调节正常和异常细胞过程(如肿瘤发生)中的基因表达方面的相互作用提供一个范例。

The objective of the proposed study is to analyze the cross-talk between the tumor suppressor protein p53 and estrogen signaling pathways in human osteosarcoma cells. The p53 gene is the most frequently altered gene in various human cancers. Inactivation of p53 is considered to be an important step in the development of osteosarcomas. Estrogens are important in the development and functioning of the osteoblast lineage and estrogens stimulate proliferation of osteosarcoma cells. However, consequence of estrogen action in the presence and in the absence of functional wild type p53 is not clear. Although it is known that p300/CBP is a coactivator for both p53-mediated and estrogen receptor-mediated gene regulation, the relationship between p53 and estrogen functions remains unknown. We propose to investigate the functional interrelationship between pathways of p53-mediated and estrogen-mediated gene regulation and its relevance to cell proliferation and perturbation of cell cycle, using PCNA gene expression in osteosarcoma cells as a model. PCNA is a critical component of the cellular DNA replication and DNA repair machineries. PCNA expression in osteosarcoma cells is regulated by p53. Our results show that the PCNA gene is estrogen-inducible. Furthermore, preliminary experiments have revealed a major role for p300/CBP in mediating regulation of PCNA expression by p53. Based on earlier studies and preliminary data, we hypothesize that there is significant cross-talk between p53 and estrogen signaling pathways in regulating PCNA expression. To test this hypothesis, we will analyze the mechanisms by which p300/CBP, a coactivator for both p53 and estrogen receptor, regulates p53-mediated PCNA gene expression. We propose to determine the role of p53-CBP pathway in estrogen-induced PCNA expression and proliferation of osteosarcoma cells. Since the relative amount of PCNA is important in specifying its interaction with other proteins important for the cell cycle, it is also hypothesized that PCNA expression is differentially regulated by coordinated action of p53 and estrogen in different stages of the cell cycle. To test this hypothesis, PCNA transcriptional regulation by p53 and estrogen during the cell cycle will be analyzed. The proposed study will provide important information on the role of estrogen in proliferation and cell cycle checkpoint function in the presence and in the absence of functional p53. It will also provide a paradigm for analyzing cross-talk between steroid hormones and p53 in regulating gene expression in both normal and abnormal cellular processes such as oncogenesis.