Regulation of STAT Activity by Tyrosine Phosphatases

描述（由申请人提供）：细胞因子通过酪氨酸磷酸化激活STAT（信号传感器和转录激活因子）家族的潜在细胞质转录因子。酪氨酸磷酸化的STATs转移到细胞核中，在那里它们与DNA结合以激活转录。STAT的活性依赖于酪氨酸磷酸化，其在细胞核中的失活是由一种以前未知的蛋白酪氨酸磷酸酶完成的。组成型STAT激活与癌症有关。通过结合生化和遗传方法，我们现在已经确定TC45是一种蛋白磷酸酶，可以使细胞核中的Stat1失活。本课题的总体目标是研究STAT酪氨酸去磷酸化的分子机制、调控和特异性。这些研究可能会提高我们利用细胞因子设计合理治疗策略的能力。

DESCRIPTION (provided by applicant): Cytokines activate the STAT (signal transducer and activator of transcription) family of latent cytoplasmic transcription factors by tyrosine phosphorylation. Tyrosine phosphorylated STATs translocate into the nucleus where they bind to DNA to activate transcription. The activity of STAT is dependent on tyrosine phosphorylation and its inactivation in the nucleus is accomplished by a previously unknown protein tyrosine phosphatase. Constitutive STAT activation has been associated with cancer. Using combined biochemical and genetic approaches, we have now identified TC45 as a protein phosphatase that can inactivate Stat1 in the nucleus. The overall goal of this proposal is to study the molecular mechanism, the regulation, and the specificity of STAT tyrosine dephosphorylation. These studies may enhance our ability to design rational therapeutic strategies employing cytokines. To study the molecular mechanism of STAT dephosphorylation, we will test if TC45 preferentially dephosphorylates Stat1 dimer or monomers by in vitro and in vivo interaction assays. Protein domains involved in the recognition of Stat1 by TC45 will be examined by mutational analysis and genetic reconstitution experiments. To study the regulation of STAT dephosphorylation, we will investigate if Stat1 DNA binding activity as well as Stat1-interacting proteins may regulate Stat1 dephosphorylation. The possible regulation of TC45 by cytokines at transcriptional or post-transcriptional levels will be analyzed. A mutant Stat1 resistant to tyrosine dephosphorylation will be examined for possible defects in the regulation of Stat1 dephosphorylation. To study the specificity of STAT dephosphorylation, we will further characterize the specificity of TC45-mediated STAT dephosphorylation in different types of TC45-null cells. We will test the hypothesis that TC45 has intrinsic substrate specificity toward STATs by biochemical assays and domain-swapping analysis. The dephosphorylation of other STATs will be examined.