Tonini Tiziana, Bagella Luigi, D'Andrilli Giuseppina, Claudio Pier Paolo, Giordano Antonio
Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, Temple University, Philadelphia, PA 19122, USA.
Oncogene. 2004 Jun 17;23(28):4930-7. doi: 10.1038/sj.onc.1207608.
The polycomb group (PcG) proteins are known to be involved in maintaining the silenced state of several developmentally regulated genes. Enhancer of zeste homolog 2 (Ezh2), a member of this large protein family, has also been shown to be deregulated in different tumor types and its role, both as a potential primary effector and as a mediator of tumorigenesis, has become a subject of increased interest. We observed that Ezh2 binds to pRb2/p130, a member of the retinoblastoma family; as such, we were led to consider the possible ability of Ezh2 to modulate cell cycle progression. Both Ezh2 and pRb2/p130 repress gene expression by recruiting histone deacetylase (HDAC1), which decreases DNA accessibility for activating transcription factors. Additionally, we observed that Ezh2 interacts with the C-terminal region of pRb2/p130, essential for interaction with HDAC1. We show that Ezh2 is able to reverse pRb2/p130-HDAC1-mediated repression of the cyclin A promoter. This indicates a functional role of this complex in regulating cyclin A expression, known to be crucial in mediating cell cycle advancement. We also detected a significant decrease in the retention of HDAC1 activity associated with pRb2/p130 when Ezh2 was overexpressed. Finally, electromobility shift assays (EMSA) demonstrated that overexpression of Ezh2 caused the abrogation of the pRb2/p130-HDAC1 complex on the cyclin A promoter. These data, taken together, suggest that Ezh2 competes with HDAC1 in binding to pRb2/p130, disrupting their occupancy on the cyclin A promoter. In this study, we propose a new mechanism for the functional inactivation of pRb2/p130 that ultimately contributes to cell cycle progression and malignant transformation.
已知多梳蛋白家族（PcG）参与维持多个发育调控基因的沉默状态。该大型蛋白家族的成员之一——zeste同源物2增强子（Ezh2），在不同肿瘤类型中也被证明存在失调，其作为潜在的主要效应因子和肿瘤发生介导因子的作用，已成为人们日益关注的焦点。我们观察到Ezh2与视网膜母细胞瘤家族成员pRb2/p130结合；因此，我们开始考虑Ezh2调节细胞周期进程的可能性。Ezh2和pRb2/p130均通过招募组蛋白脱乙酰基酶（HDAC1）来抑制基因表达，这会降低DNA对激活转录因子的可及性。此外，我们观察到Ezh2与pRb2/p130的C末端区域相互作用，该区域对于与HDAC1的相互作用至关重要。我们发现Ezh2能够逆转pRb2/p130 - HDAC1介导的细胞周期蛋白A启动子的抑制作用。这表明该复合物在调节细胞周期蛋白A表达中具有功能性作用，已知细胞周期蛋白A在介导细胞周期进程中至关重要。当Ezh2过表达时，我们还检测到与pRb2/p130相关的HDAC1活性保留显著降低。最后，电泳迁移率变动分析（EMSA）表明，Ezh2的过表达导致细胞周期蛋白A启动子上pRb2/p130 - HDAC1复合物的消失。综合这些数据表明，Ezh2在与pRb2/p130结合时与HDAC1竞争，破坏它们在细胞周期蛋白A启动子上的占据。在本研究中，我们提出了一种pRb2/p130功能失活的新机制，该机制最终有助于细胞周期进程和恶性转化。
