ISGF3 TRANSCRIPTION FACTOR FAMILY IN CYTOKINE SIGNALING

细胞因子信号转导涉及一系列被称为信号转导和转录激活因子(Stat)的转录因子，这些转录因子由Janus Kinase(JAK)家族的受体结合酪氨酸激酶(JAK)激活，该家族是在该项目的早期发现和表征的。STAT1主要由干扰素系统激活，但在干扰素系统之外还有其他作用，而它的近亲STAT3是许多细胞因子受体的共同靶标。STAT3也被经典的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。STAT3的功能在早期胚胎发育中是必不可少的，但它在后期发育和成熟动物中的作用仍有待确定。STAT2被IFNpha独占激活，是STAT家族中最有效的转录激活因子。这项提议将采用遗传和生化方法来继续研究STAT信号和功能。我们之前已经创造了缺乏STAT1的动物，并将继续我们对由此产生的表型的研究，集中在新发现的STAT1不依赖于干扰素的作用的机制上。这些包括在基础基因表达中的构成作用以及在软骨细胞生长和骨发育中的作用。STAT1的结构/功能分析将检验其在基因表达中的作用，并将确定STAT1突变抑制成纤维细胞生长因子引起的骨骼异常的能力。通过创造携带STAT3基因条件性零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去除STAT3的功能，并测量在它缺失的情况下的各种反应。我们将评估STAT3缺失细胞对胚胎和成年小鼠不同组织的贡献能力。利用胚胎成纤维细胞，我们将确定STAT3在生长因子、细胞因子和干扰素信号反应中的作用，在细胞增殖和酪氨酸激酶癌基因反应的转化中的作用。我们还将评估STAT3在正常细胞周期进程、生长和凋亡中的作用。作为一种转录因子，STAT3与STAT1二聚化，但这种合作的结果尚不清楚。在存在和不存在STAT1和STAT3的情况下，将测量对STAT靶基因的调节。STAT2转录反式激活的机制将通过对人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基酶的作用。这些研究的结果将加深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.