The Role of PHLPP in Colon Cancer

描述（由申请人提供）： 结直肠癌（CRC）是美国癌症相关死亡的第二大原因。预计2013年约有142 000例新病例和51 000例死亡。为了提高CRC患者的总体生存率，需要更好地了解导致癌症进展和化疗耐药性的分子事件。我们的实验室一直致力于阐明一个新的蛋白磷酸酶家族PHLPP（PH结构域富含亮氨酸重复序列的蛋白磷酸酶）在抑制CRC发生和发展中的作用。我们在了解PHLPP作为肿瘤抑制因子的功能重要性以及PHLPP调控的分子机制方面取得了实质性进展。在这项拟议的研究中，我们将确定PHLPP损失对调节CRC脂质代谢的影响。尽管癌症代谢研究的最新进展已经开始阐明代谢变化如何支持癌细胞生长和存活，但CRC中脂质代谢改变的调节和功能重要性仍然难以捉摸。这一提议基于一个新的假设，即PHLPP-丢失通过促进脂肪生成在驱动CRC进展中起关键作用。在令人兴奋的最新研究结果中，我们证明了PHLPP表达的下调导致激活的SREBP 1表达的增加，SREBP 1是脂质生物合成的关键激活剂。一致地，从PHLPP敲除小鼠分离的MEF细胞在分化成脂肪细胞期间具有增强的脂肪生成。此外，我们发现沉默PHLPP表达导致CRC细胞中葡萄糖摄取、乳酸盐产生、克雷布斯循环活性和三酰甘油酯积累增加，表明PHLPP在调节细胞代谢中的作用。推动这项拟议研究的中心假设是，PHLPP通过负调节PI 3 K/Akt/mTOR通路在抑制脂肪生成中起重要作用，并且PHLPP表达的丧失作为代谢重编程的结果促进CRC进展。提出以下具体目标：1）阐明PHLPP调节CRC细胞中脂肪生成的分子机制。我们将进行稳定同位素解析代谢组学（SIRM）分析，以确定PHLPP损失如何影响CRC细胞中的脂质代谢; 2）确定PHLPP介导的脂肪生成调节的功能重要性。我们将测试PHLPP-损失是否使CRC细胞对代谢应激和化疗药物更具抗性，这是脂肪生成改变的结果;和3）确定PHLPP在体内抑制脂肪生成中的作用。将使用遗传修饰的小鼠模型和患者来源的异种移植物模型来确定PHLPP损失对调节脂质代谢的影响。我们的研究结果将填补一个重要的知识空白，改变脂肪生成如何影响结直肠癌患者的预后和治疗效果。最终，通过深入了解PHLPP介导的脂肪生成机制，我们的研究结果将有助于开发CRC患者的新治疗策略。

DESCRIPTION (provided by applicant): Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the United States. Approximately 142,000 new cases and 51,000 deaths are predicted for the year 2013. A better understanding of the molecular events leading to cancer progression and chemoresistance is needed in order to improve the overall survival of CRC patients. Our lab has been intensively focused on elucidating the role of a novel family of protein phosphatases, PHLPP (PH domain Leucine-rich-repeats Protein Phosphatase), in inhibiting CRC initiation and progression. We have made substantial progress in understanding the functional importance of PHLPP as a tumor suppressor as well as the molecular mechanism underlying PHLPP regulation. In this proposed study, we will determine the effect of PHLPP-loss on modulating lipid metabolism in CRC. Although recent advances in cancer metabolism research have begun to elucidate how metabolic changes support cancer cell growth and survival, the regulation and functional importance of altered lipid metabolism in CRC remain elusive. This proposal centers on a novel hypothesis that PHLPP-loss plays a pivotal role in driving CRC progression by promoting lipogenesis. In exciting recent findings, we demonstrate that downregulation of PHLPP expression results in an increase in the expression of activated SREBP1, a key activator of lipid biosynthesis. Consistently, MEF cells isolated from PHLPP knockout mice have enhanced lipogenesis during differentiation into adipocytes. In addition, we have found that silencing PHLPP expression leads to increased glucose uptake, lactate production, Krebs cycle activity, and triacylglycerides accumulation in CRC cells, suggesting a role of PHLPP in regulating cellular metabolism. The central hypothesis driving this proposed study is that PHLPP plays an essential role in inhibiting lipogenesis by negatively regulating the PI3K/Akt/mTOR pathway, and loss of PHLPP expression promotes CRC progression as the result of metabolic reprogramming. The following specific aims are proposed: 1) to delineate the molecular mechanism by which PHLPP regulates lipogenesis in CRC cells. We will perform the Stable Isotope-Resolved Metabolomics (SIRM) analysis to determine how PHLPP-loss affects lipid metabolism in CRC cells; 2) to determine the functional importance of PHLPP-mediated regulation of lipogenesis. We will test if PHLPP-loss renders CRC cells more resistant to metabolic stress and chemotherapy drugs as the result of alterations in lipogenesis; and 3) to define the role of PHLPP in suppressing lipogenesis in vivo. The effect of PHLPP-loss on modulating lipid metabolism will be determined using both genetically modified mouse models and patient-derived xenograft models. Results from our studies will fill an important knowledge gap on how altered lipogenesis affects the prognosis and treatment efficacy in CRC patients. Ultimately, by providing insight into the mechanisms by which PHLPP-mediated lipogenesis, our findings will help to develop new treatment strategies in CRC patients.