A PTEN-dependent cell size checkpoint in human cells

描述(由申请人提供)：无法强制执行细胞周期抑制是癌症的一个标志。执行这些抑制的遗传和生化机制被称为检查点，由几个最常见的突变肿瘤抑制基因编码，如p53和p16INK4a。PTEN是人类肿瘤中最常见的失活抑癌基因之一。我们之前已经证明，PTEN在辐射诱导的细胞周期停滞过程中，在执行细胞大小停滞方面发挥着核心作用。这种依赖于PTEN的细胞大小检查点的发现有助于解释PTEN突变果蝇和小鼠中存在显著增大的细胞，并为遗传PTEN突变导致易患错构瘤的事实提供了洞察，错构瘤的特征是细胞增大。我们假设细胞大小检查点的丢失直接导致肿瘤的发生。在这笔赠款的第一个周期中，我们进行了一些与检查点大小直接相关的观察：(I)与癌细胞中常见的缺陷检查点一样，依赖于PTEN的细胞大小检查点可以被电离辐射和破坏DNA的化疗药物诱导。(Ii)依赖PTEN的细胞大小检查点是Akt不依赖的；(Iii)依赖PTEN的肌动蛋白重塑是细胞大小检查点控制所必需的；(Iv)内源性PTEN在膜上与PIP2调节的新的肌动蛋白重塑复合体相互作用；(V)PTEN的突变失活导致P53的激活，表明大小检查点和G1/G2检查点之间存在串扰。这第一次竞争性更新旨在建立在这些进展的基础上，进一步评估人类细胞中依赖PTEN的大小检查点的机制基础和表型后果。在目标1中，我们将确定细胞大小检查点控制是否需要PTEN对肌动蛋白动力学的调节。在目标#2中，我们建议确定含有PTEN的肌动蛋白重塑复合体的组成和功能。在目标3中，我们将确定PTEN介导的肿瘤抑制是否需要调节细胞大小和检查点控制。

DESCRIPTION (provided by applicant): The inability to enforce cell cycle arrests is one hallmark of cancer. The genetic and biochemical mechanisms that enforce these arrests are known as checkpoints, and are encoded by several of the most commonly mutated tumor suppressor genes such as p53 and p16INK4a. PTEN is one of the most commonly inactivated tumor suppressor genes in human cancer. We have previously demonstrated that PTEN plays a central role in enforcing cell size arrest during radiation-induced cell cycle arrest. The discover of this PTEN-dependent cell size checkpoint helped to explain the existence of dramatically enlarged cells in PTEN mutant flies and mice, and provided insight into the fact that inherited PTEN mutations cause a predisposition to hamartomas, which are characterized by enlarged cells. We hypothesize that loss of the cell size checkpoint contributes directly to tumorigenesis. In the first cycle of this grant, we made a number of observations directly related to the size checkpoint: (i) Like other checkpoints that are commonly defective in cancer cells, the PTEN- dependent cell size checkpoint is inducible by ionizing radiation and DNA-damaging chemotherapeutic drugs. (ii) The PTEN-dependent cell size checkpoint is Akt-independent; (iii) PTEN-dependent actin remodeling is required for cell size checkpoint control; (iv) Endogenous PTEN interacts at the membrane with a novel, PIP2-regulated actin remodeling complex; (v) Mutational inactivation of PTEN leads to activation of p53, suggesting the existence of crosstalk between the size checkpoint and the G1/G2 checkpoints. This first competitive renewal is designed to build on these advances to further evaluate the mechanistic basis and phenotypic consequences of the PTEN-dependent size checkpoint in human cells. In Aim #1 we will determine if regulation of actin dynamics by PTEN is required for cell size checkpoint control. In Aim #2 we propose to identify the composition and function of a PTEN-containing actin remodeling complex. In Aim #3 we will determine if regulation of cell size checkpoint control is required for PTEN-mediated tumor suppression.