调控Twist1的蛋白磷酸酶在乳腺癌中的机制和功能研究

Metastasis is the leading factor which causes death in breast cancer. Transcription factor Twist1 is an inducer in cancer metastasis. Both AKT1 and AKT2 are important kinases which regulate Twist1. Akt2 only phosphorylates Twist1 at S42, which increases the protein stability of Twist1 and promotes breast cancer metastasis. Akt1 phosphorylates Twist1 at S42, T121 and S123, which promotes protein degradation of Twist1 and inhibits breast cancer metastasis. It could be seen that phosphorylation level of Twist1 at T121 and S123 plays a crucial role in regulating Twist1 protein stability. However, the de-phosphorylation mechanism for T121 and S123 on Twist1 still remains elusive. In this study, we plan to screen an existing human protein phosphatase pool, find the protein phosphatase (PPOI) which is the most effective in de-phosphorylating T121(P) and S123(P)-Twist1, clarify the molecular mechanism of PPOI in Twist1 signaling. Then, we will reveal the effects of PPOI on the breast cancer cell function from both cellular and animal level. Lastly, we will find the expression correlation between PPOI and Twist1 using clinical samples and evaluate the potential clinical prognostic value of PPOI . This study will provide new idea and theoretical foundation for developing targeted drugs to treat Twist1 high-expressing type of breast cancer.

转移是乳腺癌致死的最主要原因，转录因子Twist1在癌症转移上起促进作用。AKT1和AKT2均是Twist1的调节激酶。AKT2仅磷酸化Twist1的S42位点，增强Twist1的蛋白稳定性并促进乳腺癌转移；AKT1磷酸化Twist1的S42，T121和S123三个位点，促进Twist1蛋白的降解并抑制乳腺癌转移。由此看出，Twist1在T121和S123的磷酸化水平对其蛋白稳定性至关重要，但以上两个位点的去磷酸化调控机制至今仍不明确。本项目拟筛选一套已有的人源蛋白磷酸酶库，鉴定出对Twist1上T121和S123去磷酸作用最强的磷酸酶-PPOI。而后分别在细胞水平以及动物水平上揭示其对乳腺癌细胞功能的影响。最后，利用临床样本检测PPOI与Twist1表达水平的相关性并评估PPOI的潜在临床预后价值。此研究将为治疗Twist1高表达类乳腺癌的靶向药物研发提供新的思路和理论基础。

Twist1 是属于碱性螺旋-环-螺旋家族的转录因子。近年来发现在多种癌症中Twist1 的表达量均有显著上调，Twist1 在肿瘤中的高表达与肿瘤转移能力及不良临床预后紧密相关。Twist1 受多种翻译后水平调控。既往研究表明Twist1 上 T121 和 S123 位点的磷酸化水平对其蛋白的稳定性有重要影响。本项目对调控Twist1的T121 和 S123 位点的蛋白磷酸酶进行了筛选和鉴定，探明了PP2A通过其调节亚基B56δ对Twist1的T121 和 S123进行去磷酸化修饰。接着，我们在体内及体外证实了B56δ对乳腺癌细胞的迁移、侵袭及转移起到促进作用。最后，我们利用临床在线工具揭示了在已经出现淋巴结转移的乳腺癌患者中，B56δ的高表达预示着较低的无复发生存率。