BIOCHEMICAL STUDIES OF STAT NUCLEAR LOCALIZATION

描述（由申请人提供）： 该研究计划的广泛和长期目标是揭示Jak/STAT介导的信号转导和转录激活的分子机制。STAT之所以如此命名，是因为它们是细胞质中的信号转导子和细胞核中的转录激活子。在由配体结合诱导的受体二聚化后，Jak或受体酪氨酸激酶被激活，并且它们进而使受体上的酪氨酸磷酸化。含SH 2的STAT分子被募集到细胞表面，并被Jak或受体激酶酪氨酸磷酸化。它们随后同源或异源二聚化并易位到细胞核中，在那里它们结合到特定的DNA靶标并指导特定的转录起始。Jak/STAT通路参与几乎所有细胞因子和生长因子的信号传导过程。该途径的失调导致组成性激活STAT蛋白以及随后的凋亡抑制剂和细胞周期调节剂基因的上调。组成性激活的STAT与许多癌细胞系和实体瘤（包括白血病和乳腺癌）有关。因此，它们已成为癌症药物发现的重要靶点。本研究的重点是阐明STAT核定位的原子分辨率的分子机制。拟议研究的具体目标包括：（1）确定非磷酸化全长STAT的晶体结构;（2）使用生物化学、生物物理学和细胞生物学工具研究观察到的非磷酸化STAT二聚体结构的生理意义;（3）使用生物化学、结构和细胞生物学工具研究STAT 1：NPI 1相互作用及其在STAT 1核定位中的作用。

DESCRIPTION (provided by applicant): The broad and long-term objectives of the research program are to uncover the molecular mechanism of Jak/STAT-mediated signal transduction and transcription activation. STATs are so named since they are signal transducers in the cytoplasm and activators of transcription in the nucleus. Upon receptor dimerization induced by ligand binding, Jak or receptor tyrosine kinases are activated and they in turn phosphorylate tyrosines on the receptors. The SH2-containing STAT molecules are recruited to the cell surface and become tyrosine phosphorylated by Jak or receptor kinases. They subsequently homo- or hetero-dimerize and translocate into the nucleus, where they bind to specific DNA targets and direct specific transcription initiation. The Jak/STAT pathway is involved in the signaling process of virtually every cytokine and growth factor. Dysregulation of this pathway leads to constitutively activated STAT proteins and the subsequent up-regulation of the genes of apoptosis inhibitors and cell cycle regulators. Constitutively activated STATs have been linked to numerous cancer cell lines and solid tumors including leukemia and breast cancer. Thus they have become important targets for cancer drug discovery. The major focus of this research is to elucidate the molecular mechanism underlying STAT nuclear localization at atomic resolution. The specific aims of the proposed research include (1) to determine the crystal structure of an unphosphorylated full-length STAT; (2) to study the physiological significance of the observed unphosphorylated STAT dimer structure using biochemical, biophysical, and cell biological tools; and (3) to study STAT1:NPI1 interaction and its role in STAT1 nuclear localization using biochemical, structural, and cell biological tools.