DISRUPTION OF STAT SIGNALING PATHWAYS

信号转导和转录激活因子(STATs)是转录因子被发现的关键信号成分，参与调节对细胞因子刺激的反应。越来越多的证据表明STAT蛋白在肿瘤发生中的运动。在此之前，我们首次观察到在由Src癌蛋白转化的成纤维细胞系中，STAT家族成员STAT3被结构性激活。对显性阴性的STAT3蛋白的研究进一步证明，Src癌蛋白激活STAT3信号导致基因表达的特异性调节，这是细胞转化所必需的。此外，STAT3信号在细胞系中被高频激活，另有研究表明，STAT3信号在乳腺癌和各种淋巴系统恶性肿瘤中起着重要作用。在这个项目中，我们建议测试假设，即特定的STAT3信号抑制剂将在相关的人类肿瘤模型中降低致瘤性，而不会产生显著的毒性。这一目标将通过以下具体目标来实现：(1)为了确定可能干扰STAT3功能的候选先导肽，我们将筛选与STAT3蛋白结合的线性和环肽噬菌体展示文库。(2)候选的先导肽，以及在项目1中合成的多肽模拟物和组合化学文库，将在体外测试它们破坏STAT3二聚和DNA结合活性的能力。有关活性、多肽和其他化合物的信息将反馈给项目1，以进行线索优化。(3)将测试有希望的化合物在完整细胞中干扰STAT3信号的能力，并阻止由Src癌蛋白进行的细胞转化。(4)利用细胞培养和STAT3经常被激活的人类癌症动物模型，将评估干扰STAT3信号转导的化合物的抗肿瘤效果和毒性。此外，这些STAT3干扰物将被用于探索STAT3如何促进肿瘤发生的生物学机制，包括对细胞增殖和凋亡的调控。这些研究的结果将促进我们对STAT3在人类癌症中的作用的理解，并评估STAT3抑制剂作为新型抗癌药物的治疗潜力。

Signal transducers and activators of transcription (STATs) are transcription factors that were discovered as key signaling components involved in mediating responses to cytokine stimulation. Increasingly, evidence has been accumulating that points to the movement of STAT proteins in oncogenesis. Previously, we made the original observation that one STAT family member, STAT3, is constitutively activated in fibroblast cell lines transformed by the Src oncoprotein. Studies with dominant-negative STAT3 proteins further demonstrate that activation of STAT3 signaling by the Src oncoprotein leads to specific regulation of gene expression and is required for cell transformation. In addition, STAT3 signaling is activated with high frequency in cell lines and by others suggest that STAT3 signaling has an important role in breast carcinoma and various lymphoid malignancies. In this project, we propose to test the hypothesis that specific inhibitors of STAT3 signaling will reduce tumorigenicity in relevant human tumor models without inducing significant toxicity. This goal will be pursued through the following specific aims: (1) To identify candidate lead peptides that potentially disrupt STAT3 function, we will screen linear and cyclic peptide phage display libraries for sequences that bind to STAT3 protein. (2) Candidate lead peptides, together with peptidomimetics and combinatorial chemical libraries synthesized in Project 1, will be tested in vitro assays for their abilities to disrupt STAT3 dimerization and DNA- binding activity. Information on activities peptides and other compounds will be fed back to Project 1 for lead optimization. (3) Promising compounds will be assayed for their abilities to disrupt STAT3 signaling in intact cells and to block cell transformation by the Src oncoprotein. (4) Using cell culture and animal models of human cancers where STAT3 is frequently activated, compounds that disrupt STAT3 signaling will be evaluated for their anti-tumor efficacy and toxicity. In addition, these STAT3 disruptors will be used to explore the biological mechanisms of how STAT3 contributes to oncogenesis, including regulation of cell proliferation and apoptosis. Results of these studies will advance our understanding of the role of STAT3 in human cancer and assess the therapeutic potential of STAT3 inhibitors as novel anti-cancer drugs.