Mechanism of heterochromatin regulation by STAT

STAT调节异染色质的机制 异染色质是DNA的一种紧密堆积形式，对染色体紧凑和转录非常重要 沉默以及基因组稳定性、动物寿命和肿瘤抑制。异染色质如何 动力学，即它的建立、维持和损失是否受到控制，目前还不完全清楚。我们 之前已经证明了uSTAT在异染色质维持中的生理作用，但 机制尚不清楚。这个项目的总体目标是在分子水平上研究 STAT在建立和维持异染色质中的作用，并了解STAT磷酸化如何 作为一个分子开关，将基因沉默转化为活跃的转录。我们之前已经展示了 免疫染色显示，STAT的一部分没有在700氨基酸附近的临界酪氨酸处磷酸化 (称为uSTAT)与异染色质蛋白1(HP1)一起定位于细胞核。我们有 从基因上看，STAT对于异染色质的维持是必不可少的，STAT的激活(通过 酪氨酸的磷酸化)与异染色质的破坏有关。我们已经进一步表明， 人uSTAT5A具有促进异染色质形成和抑制肿瘤生长的作用。在新的 使用染色质免疫沉淀和深度测序(CHIP-SEQ)的初步研究，我们有 发现大多数染色质结合的果蝇STAT定位于异染色质，并且丢失 STAT导致全球异染色质减少，其标志是组蛋白3在lys9三甲基化 (H3K9me3)。我们进一步发现，当被迫与常染色质结合时，uSTAT可以在附近抑制 基因以依赖于HP1的方式。这些结果表明，uSTAT可能不仅在 维持并启动异染色质的形成。HP1和H3K9me3是 异染色质，HP1为中心成分。研究表明，招募HP1为常染色质 足以形成异染色质。然而，HP1不直接与DNA结合，只有弱的 与H3K9me3的亲和力，因此可能需要DNA结合蛋白因子才能最初招募到 异染色质基因座，或加强其与H3K9me3的结合。我们假设uSTAT在 由于uSTAT二聚体的分子确认，异染色质的建立和维持。 我们将使用基因组、遗传和生化工具的组合来调查导致 异染色质的建立，STAT和HP1在异染色质维持中的各自作用， USTAT结合和HP1募集对顺式元件的要求以及uSTAT和pSTAT的性质 DNA和HP1结合的二聚体。理解非正则STAT功能的分子机制 异染色质调控不仅要阐明异染色质的基本细胞生物学过程 与肿瘤抑制和表观遗传学有关的动力学和异染色质基因沉默 疾病。

Mechanism of heterochromatin regulation by STAT Heterochromatin is a tightly packed form of DNA important for chromosomal compaction and transcriptional silencing as well as for genome stability, animal longevity, and tumor suppression. How heterochromatin dynamics, i.e., its establishment, maintenance, and loss, is controlled remains incompletely understood. We have previously demonstrated a physiological role of uSTAT in heterochromatin maintenance, but the mechanism remains unclear. The overall goal of this project is to investigate, at the molecular level, the role of STAT in establishing and maintaining heterochromatin, and to understand how STAT phosphorylation can serve as a molecular switch converting gene silencing to active transcription. We have previously shown by immunostaining that a fraction of STAT not phosphorylated at the critical tyrosine around amino acid 700 (termed uSTAT) is localized in the nucleus in association with Heterochromatin Protein 1 (HP1). We have shown genetically that STAT is essential for heterochromatin maintenance, and that STAT activation (by phosphorylation on this tyrosine) is associated with heterochromatin disruption. We have further shown that human uSTAT5A is capable of promoting heterochromatin formation and suppressing tumor growth. In new preliminary studies using chromatin immunoprecipitation followed by deep sequencing (ChIP-seq), we have found that the majority of chromatin-bound Drosophila STAT is localized in heterochromatin, and that loss of STAT leads to a global decrease in heterochromatin, which is marked by trimethylated histone 3 at lys9 (H3K9me3). We have further found that, when forced to bind to euchromatin, uSTAT can repress nearby genes in an HP1-dependent manner. These results suggest that uSTAT may play an important role not only in maintaining but also in initiating heterochromatin formation. HP1 and H3K9me3 are hallmarks of heterochromatin, with HP1 being the central component. It has been shown that recruiting HP1 to euchromatin is sufficient for heterochromatin formation. However, HP1 does not bind DNA directly and has only weak affinity for H3K9me3, and thus may require DNA-binding protein factors for its initial recruitment to heterochromatic loci, or for strengthening its binding to H3K9me3. We hypothesize that uSTAT plays roles in both establishment and maintenance of heterochromatin due to the molecular confirmation of uSTAT dimers. We will use a combination of genomic, genetic, and biochemical tools to investigate the initial events leading to heterochromatin establishment, the respective roles of STAT and HP1 in heterochromatin maintenance, the requirement for cis-element in uSTAT binding and HP1 recruitment, and the properties of uSTAT and pSTAT dimers in DNA and HP1 binding. Understanding the molecular mechanism of noncanonical STAT function in heterochromatin regulation should shed light on not only the basic cell biological process of heterochromatin dynamics but also heterochromatic gene silencing relevant to tumor suppression and epigenetic human diseases.