ISGF3 TRANSCRIPTION FACTOR FAMILY IN CYTOKINE SIGNALING

细胞因子信号传导涉及被称为信号转导子和转录激活子（Stat）的转录因子家族，其由Janus激酶（Jak）家族的受体结合酪氨酸激酶激活，在该项目的早期发现和表征。Stat 1主要由干扰素（IFN）系统激活，但在IFN系统外具有其他作用，而其最近的亲戚Stat 3是许多细胞因子受体的共同靶点。Stat 3也被经典生长因子受体酪氨酸激酶和细胞质原癌基因酪氨酸激酶及其致癌衍生物激活。Stat 3的功能在早期胚胎发育过程中是必不可少的，但其在后期发育和成熟动物中的作用仍有待确定。Stat 2仅由IFN α激活，是Stat家族中最有效的转录激活因子。该提案将采取遗传和生物化学方法来继续研究Stat信号传导和功能。我们以前创造的动物没有Stat 1，并将继续我们的研究所产生的表型，集中在新发现的IFN-独立的行动Stat 1的机制。这些包括在基础基因表达中的组成性作用以及在软骨细胞生长和骨发育中的作用。Stat 1的结构/功能分析将检查其在基因表达中的作用，并确定Stat 1突变抑制FGF引起的骨异常的能力。通过创建携带Stat 3基因的条件无效突变的细胞系和动物，我们将在特定的发育时间、特定的组织和培养的细胞系中消除Stat 3功能，并在其缺失的情况下测量各种反应。我们将评估Stat 3-null细胞对胚胎和成年小鼠不同组织的贡献能力。使用胚胎成纤维细胞，我们将确定Stat 3在生长因子，细胞因子和IFN信号转导反应，细胞增殖和酪氨酸激酶癌基因转化中的作用。我们还将评估Stat 3在正常细胞周期进展、生长和凋亡过程中的作用。作为转录因子，Stat 3与Stat 1二聚化，但这种合作的后果尚不清楚。将在存在和不存在Stat 1和Stat 3的情况下测量Stat靶基因的调节。Stat 2的转录反式激活机制将通过对人类和小鼠同源物的结构/功能分析来表征，并将评估组蛋白乙酰化酶的作用。这些研究的结果将增强我们对细胞因子网络、协同转录因子、细胞生长和致癌转化的理解。

Cytokine signaling involves a family of transcription factors known as Signal Transducer and Activators of Transcription (Stat) that are activated by receptor-bound tyrosine kinases of the Janus Kinase (Jak) family, discovered and characterized during the earlier years of this project. Stat1 is activated mainly by the interferon (IFN) system but has additional roles outside the IFN system, while its closest relative, Stat3, is a common target for many cytokine receptors. Stat3 is also activated by classical growth factor receptor tyrosine kinases and by cytoplasmic proto-oncogene tyrosine kinases and their oncogenic derivatives. Stat3 function is essential during early embryogenesis, but its role in later development and in mature animals remains to be determined. Stat2 is activated exclusively by IFNalpha and is the most potent transcriptional activator of the Stat family. This proposal will take a genetic and biochemical approach to continued studies of Stat signaling and function. We have previously created animals devoid of Stat1 and will continue our studies of the resulting phenotype, concentrating on the mechanisms underlying newly discovered IFN- independent actions of Stat1. These include a constitutive role in basal gene expression as well as a role in chondrocyte growth and bone development. Structure/function analysis of Stat1 will examine its role in gene expression, and the ability of a Stat1 mutation to suppress bone abnormalities caused by FGF will be determined. By creating cell lines and animals that carry a conditionally null mutation of the Stat3 gene, we will ablate Stat3 function at specific times of development, in specific tissues, and in cultured cell lines, and measure a variety of responses in its absence. We will assess the ability of Stat3-null cells to contribute to different tissues of the embryo and adult mouse. Using embryonic fibroblasts, we will determine the role of Stat3 in growth factor, cytokine, and IFN signaling responses, in cell proliferation, and in transformation in response to tyrosine kinase oncogenes. We will also assess the role of Stat3 during normal cell cycle progression, growth, and apoptosis. As a transcription factor, Stat3 dimerizes with Stat1, but the consequences of this cooperation are unknown. Regulation of Stat target genes will be measured in the presence and absence of Stat1 and Stat3. Mechanisms of transcriptional transactivation by Stat2 will be characterized by structure/function analysis of human and mouse homologues, and the role of histone acetylases will be evaluated. Results from these studies will enhance our understanding of cytokine networks, cooperating transcription factors, cell growth, and oncogenic transformation.