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停滞是癌症的标志之一。执行这些逮捕的遗传和生化机制被称为检查点，由几种最常见的突变肿瘤抑制基因（例如 p53 和 p16INK4a）编码。 PTEN 是人类癌症中最常见的失活肿瘤抑制基因之一。我们之前已经证明，PTEN 在辐射诱导的细胞周期停滞期间强制细胞大小停滞中发挥着核心作用。这种 PTEN 依赖性细胞大小检查点的发现有助于解释 PTEN 突变果蝇和小鼠中细胞显着增大的存在，并提供了对遗传性 PTEN 突变导致错构瘤易感性这一事实的深入了解，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发生。在这笔资助的第一个周期中，我们进行了一些与大小检查点直接相关的观察：（i）与癌细胞中通常有缺陷的其他检查点一样，PTEN依赖性细胞大小检查点可以通过电离辐射和DNA损伤性化疗药物诱导。 (ii) PTEN 依赖性细胞大小检查点与 Akt 无关； (iii) 细胞大小检查点控制需要 PTEN 依赖性肌动蛋白重塑； (iv) 内源性 PTEN 在膜上与新型 PIP2 调节的肌动蛋白重塑复合物相互作用； (v) PTEN 突变失活导致 p53 激活，表明大小检查点和 G1/G2 检查点之间存在串扰。首次竞争性更新旨在以这些进展为基础，进一步评估人类细胞中 PTEN 依赖性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 调节肌动蛋白动力学。在目标#2 中，我们建议鉴定包含 PTEN 的肌动蛋白重塑复合物的组成和功能。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.