MST4-14-3-3复合物介导胰腺癌转移的功能机制

MST4, a member of the serine/threonine protein kinase family, plays vital roles in regulating cell growth, transformation, polarity and migration. The regulatory molecules 14-3-3 proteins are highly conserved in eukaryotes, which can interact with a variety of signaling proteins, such as kinases and phosphatases, and are involved in the regulation of mitosis, apoptosis and cell cycle. Aberrant expression of MST4 and 14-3-3 have been reported to be closely related to tumorigenesis and cancer progression; and STK25, a MST4 homolog, can interact with 14-3-3 to promote cell migration. However, there is still no evidence on whether MST4 can bind to and function together with 14-3-3 proteins. Pancreatic cancer is a serious danger to the mankind. In the previous studies, the applicant of this project has partially uncovered the mechanism of MST4-MOB4 complex in the proliferation and migration of pancreatic cancer cells; and found that MST4 can interact with 14-3-3 to synergistically enhance pancreatic cancer cell migration. Based on the previous work, this project will take full advantage of techniques regarding biochemistry, molecular biology, structural biology and cellular biology to explore the underlying molecular mechanisms of MST4-14-3-3 complex in the metastasis of pancreatic cancer at the molecular, cellular and animal levels; and to screen potential anti-pancreatic cancer drugs targeting MST4-14-3-3. This project will benefit the drug discovery and clinical treatment of pancreatic cancer.

MST4是丝氨酸／苏氨酸蛋白激酶家族成员，主要参与调控细胞生长、转化、极性和迁移等重要生理过程。14-3-3蛋白在真核生物中高度保守，能够与激酶、磷酸酶等信号蛋白结合，在有丝分裂、细胞凋亡和细胞周期过程中发挥作用。MST4和14-3-3的异常表达与多种癌症的发生发展密切相关；且MST4的同源蛋白STK25能结合14-3-3，促进细胞迁移。然而，MST4是否能与14-3-3结合并协同发挥作用尚不清楚。胰腺癌是严重威胁人类健康的重大疾病，本项目申请人前期部分揭示了MST4-MOB4复合物促进胰腺癌细胞增殖和迁移的机制；并且发现MST4能与14-3-3结合，协同促进胰腺癌细胞的迁移。本项目拟在前期工作基础上，综合运用生化分子、结构和细胞生物学技术手段，在分子、细胞和动物水平上深入探究MST4-14-3-3复合物调控胰腺癌转移的分子机制，并进行药物筛选，为胰腺癌的药物研发和临床治疗奠定理论基础。

MST4和14-3-3的异常表达与多种癌症的发生发展密切相关。MST4激酶参与调控细胞增殖、迁移、极性、自噬以及炎症反应等若干生物学过程。我们发现了MST4调控Wnt信号通路，建立了MST4-pβ-cateninThr40这一信号轴，揭示了该信号轴在肠干细胞介导的肠稳态维持及肠癌发生发展过程中的调控功能与作用机制。具体而言，MST4能够响应Wnt3a信号刺激，直接结合并磷酸化β-catenin的T40位点，进而抑制GSK3β对β-catenin Ser33位点的磷酸化，阻断β-TrCP识别并降解β-catenin，最终促进β-catenin入核，从而诱导Wnt信号通路的完全激活。小鼠实验表明，细胞类型特异性敲除Stk26（Stk26为MST4基因名）导致β-catenin蛋白水平明显下降，ISC数量大幅减少，抑制肠癌发生发展。反之，细胞类型特异性激活MST4（Stk26TE，持续激活突变体）能够显著提高β-catenin活性，促进ISC扩增，加剧肠癌发生发展。进一步，模拟β-catenin Thr40位点持续磷酸化的基因敲入小鼠具有和Stk26TE基因敲入小鼠高度类似的表型，为MST4-pβ-cateninThr40信号轴的调控功能提供了体内证据。更为重要的是，我们观察到MST4-pβ-cateninThr40信号轴在结直肠癌病人组织样品中存在过度激活现象，且与病人不良预后高度相关。在本项目的支持下，共发表2篇SCI 论文，其中项目负责人以共同第一作者在J Exp Med上发表论文1篇，以共同作者在国际高水平杂志Cancer Cell发表论文1篇。