The Function of PNUTS (Phosphatase Nuclear Targeting Subunit) in the Cell Cycle

描述(申请人提供)：在癌细胞中，在没有信号的情况下发生分裂和复制。许多控制细胞分裂的蛋白质都参与了癌症的发展。肿瘤抑制蛋白视网膜母细胞瘤(RB)的活性在癌细胞中经常被解除调控。Rb抑制活跃的细胞的增殖，但在不活跃的时候允许细胞增殖。Rb的活性受其磷酸化状态的控制，该状态受细胞周期蛋白依赖性蛋白激酶(CDKs)和蛋白磷酸酶1(PP1)的调节。PP1的活性是通过靶向与特定底物结合并将其定向到特定底物的亚基来控制的。有一个新发现的PP1靶向亚基，称为PNUTS(磷酸酶核靶向亚基)，它在体外抑制PP1对Rb的活性。PNUTS蛋白在两种类型的乳腺癌细胞中都有高表达，因此本项目旨在阐明PNUTS在细胞周期调控中的功能和调控。为了研究PNUTS在细胞分裂周期中的作用，我们打算利用RNA干扰(RNAi)来阻断PNUTS在乳腺癌细胞中的表达，并检测其对PP1酶活性、Rb磷酸化状态和细胞增殖的影响。此外，还将研究磷酸化对PNUTS活性的调节及其与PP1的关系。阐明PNUTS在细胞分裂周期中的功能将有助于深入研究细胞增殖的控制和调控。在癌症中，细胞以不受控制的方式分裂和增殖。因此，对控制细胞分裂的分子的研究可能会带来了解癌细胞发育和生长所需的信息。该项目旨在研究一种名为PNUTS的蛋白质的功能，该蛋白质被认为是乳腺癌中细胞增殖的激活剂。

DESCRIPTION (provided by applicant): In cancer cells, division and replication occurs in the absence of signals to do so. Many proteins that control cell division are involved in cancer development. The activity of the tumor suppressor protein, Retinoblastoma (Rb), is often deregulated in cancer cells. Rb inhibits proliferation in cells in which it is active, but allows cell proliferation when it is inactive. Rb activity is controlled by its phosphorylation state which is regulated by cyclin dependent kinases (cdks) and Protein phosphatase 1 (PP1). PP1 activity is controlled by targeting subunits that bind to and direct it to specific substrates. There is a newly identified PP1-targeting subunit called PNUTS (Phosphatase Nuclear Targeting Subunit) which inhibits PP1 activity toward Rb in vitro. The PNUTS protein is highly expressed in two types of breast cancer cells, therefore the specific aims of this project are designed to elucidate the function of and regulation of PNUTS in cell cycle control. To investigate the role of PNUTS in the cell division cycle, we intend to use RNA interference (RNAi) to block PNUTS expression in breast cancer cells and examine the effects on the enzyme activity of PP1, Rb phosphorylation status and cell proliferation. In addition, the regulation of PNUTS activity by phosphorylation and its association with PP1 will be investigated. The elucidation of PNUTS function in the cell division cycle will provide insight into the control and regulation of cell proliferation. In cancer, cells divide and proliferate in an uncontrolled manner. Thus, the investigation of the molecules that control cell division may lead to information needed to understand cancer cell development and growth. This project is designed to study the function of a protein called PNUTS which is proposed to be an activator of cell proliferation in breast cancer.