USP22调控雌激素受体α介导基因转录的机制及其在乳腺癌中的作用

Estrogen receptor α (ERα) is a member of steroid hormone receptor superfamily. It is a ligand dependent transcription factor. ERα exerts its biological function by regulating transcription of target genes. Co-regulators are important for modulating these processes. ERα plays a key role in normal growth and function of the female reproductive system. It is also involved in epithelial cell differentiation, proliferation, and DNA replication process in breast cancer. ERα is an essential molecular target of endocrine therapy in breast cancer. In the previous published paper, the applicant has identified a histone deubiquitinase USP22, a component of STAGA complex is involved in deubiquitination of histone H2A/H2B, and participates in counteracting heterochromatin silencing. In the recent year, we found that USP22 expression had a significant correlation with that of ERα. USP22 participates in co-activating ERα-mediated trasactivation. Knockdown of USP22 attenuates the recruitment of ERα to estrogen response elements (ERE) of ERα target gene. Interestingly, our results have revealed that USP22 enhances ERα protein expression. Furthermore, our results have demonstrated that USP22 promotes MCF7 cell proliferation, attenuates the sensitivity of BT474 cells to tamoxifen. All above results indicate that USP22 may participate in modulation of chromatin structure through the recruitment of other important histone modification enzymes to promote ERα-mediated transcriptional activity, and play a crucial role in breast cancer progression. Using ChIP, ChIP-re-IP, Co-IP, Real time qRT-PCR, and RNA-seq, the aim of our project is to analyze the epigenetic mechanism for USP22 involved in modulation of ERα-mediated transactivation and biological function analysis. We will continue elucidating the role of USP22 in breast cancer progression and endocrine therapy resistance, and try to provide experimental evidences and new target for breast cancer.

雌激素受体α（ERα）以配体依赖方式介导基因转录，并招募一系列辅调节因子参与转录调控，发挥其生物学功能。ERα分别在女性生殖系统发育及乳腺癌发生发展中起关键作用。据文献报道去泛素化酶USP22是STAGA复合物组分之一，对组蛋白H2A/H2B去泛素化，并拮抗异染色质沉默状态；近年我们发现在乳腺癌组织中USP22与ERα表达水平显著正相关，并参与上调ERα介导基因转录；USP22敲低减弱了ERα靶基因反应元件(ERE) 区ERα的招募；有趣的是，我们还发现USP22能增加ERα蛋白本身的表达；此外，USP22的敲低抑制了乳腺癌细胞MCF7增殖能力，增强了BT474细胞对他莫昔芬的敏感性。本项目试图阐明USP22调控ERα功能的分子新机制，并深入研究USP22在乳腺癌发生发展、肿瘤侵袭转移及内分泌治疗耐受等方面的作用及其分子机制，为该疾病的早期诊断和治疗提供理论依据和新靶点。

雌激素受体α（Estrogen Receptor，ERα）阳性乳腺癌中ERα信号转导通路的异常调节会促进肿瘤的进展，并可能促进对内分泌治疗的抵抗。ERα激活后，ERα会募集辅调节因子，以通过染色质结构的改变，转录后修饰或ERα蛋白稳定性的调节来参与调节ERα介导的基因转录调控。一系列ERα辅助调节因子与乳腺癌的增殖，侵袭或内分泌抵抗有关。因此，开发ERα功能靶向调节的疗法可能为ERα阳性乳腺癌提供有效的治疗手段。先前我们已经证明USP22促进雄激素受体介导的基因转录调控。另外，USP22通过去泛素化非组蛋白发挥生物学功能。最近的研究表明，在许多癌症中，USP22的高表达与预后不良呈正相关。但是，USP22在肿瘤进展中的潜在分子机制仍然知之甚少。.这篇文章我们证实与癌旁组织相比，USP22在乳腺癌组织中呈高表达，而且与ERα成正相关，并且USP22的高表达患者总体存活时间短。在哺乳动物细胞中USP22与ERα相互作用。通过泛素化实验证实USP22能够去泛素化ERα从而稳定ERα蛋白，并且这一作用与USP22的去泛素化酶活性相关。之后我们证实了在哺乳动物细胞中，USP22能够上调ERα介导的转录激活，并且与USP22的去泛素化酶活性有关。ChIP实验证明USP22与ERα一起募集到ERα靶基因c-Myc的顺式调控元件上。细胞功能实验证实USP22能够促进ERα阳性乳腺癌细胞的生长和增殖，并且USP22增加了乳腺癌细胞对内分泌治疗药物的抗性。.总之，我们的研究表明USP22与ERα结合，作为ERα蛋白水平的调节因子参与ERα的K48和K63连接的泛素链的去泛素化，从而抑制了ERα的降解。另一方面，USP22作为ER信号通路新的辅激活因子，促进乳腺癌细胞的生长和增殖。这些结果证实USP22可能是乳腺癌进展的主要驱动力，也是乳腺癌及内分泌治疗抵抗的潜在治疗靶标。