The Role of PHLPP in Colon Cancer

描述(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。为了提高结直肠癌患者的总体生存率，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域富含亮氨酸重复蛋白磷酸酶)在抑制结直肠癌的发生和发展中的作用。我们在理解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已经取得了实质性的进展。在这项拟议的研究中，我们将确定PHLPP缺失在调节结直肠癌脂质代谢中的作用。虽然最近癌症代谢研究的进展已经开始阐明代谢变化如何支持癌细胞的生长和生存，但在结直肠癌中，脂代谢改变的调节和功能重要性仍然是未知的。这一建议的核心是一个新的假设，即PHLPP缺失通过促进脂肪生成在推动结直肠癌进展中发挥关键作用。在令人兴奋的最新发现中，我们证明了PHLPP表达下调导致激活的SREBP1表达增加，SREBP1是脂质生物合成的关键激活剂。一直以来，从PHLPP基因敲除小鼠分离的MEF细胞在分化为脂肪细胞的过程中促进了脂肪的生成。此外，我们还发现，沉默PHLPP的表达导致结直肠癌细胞葡萄糖摄取、乳酸产生、Krebs循环活性和三酰甘油积累增加，这表明PHLPP在调节细胞代谢中发挥作用。支持这项研究的中心假设是，PHLPP通过负调控PI3K/Akt/mTOR途径在抑制脂肪生成方面发挥重要作用，而PHLPP表达的缺失作为代谢重编程的结果促进了CRC的进展。具体目的如下：1)阐明PHLPP调控结直肠癌细胞脂肪生成的分子机制。我们将进行稳定同位素分辨代谢组学(SIRM)分析，以确定PHLPP缺失如何影响结肠癌细胞中的脂代谢；2)确定PHLPP介导的脂肪生成调控的功能重要性。我们将测试PHLPP缺失是否会由于脂肪生成的改变而使CRC细胞对代谢压力和化疗药物更具抵抗力；以及3)确定PHLPP在体内抑制脂肪生成中的作用。PHLPP缺失对调节脂质代谢的影响将使用转基因小鼠模型和患者来源的异种移植模型来确定。我们的研究结果将填补关于脂肪生成改变如何影响结直肠癌患者预后和治疗效果的重要知识空白。最终，通过洞察PHLPP介导的脂肪生成的机制，我们的发现将有助于开发新的结直肠癌患者的治疗策略。

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.