丙酮酸激酶同工酶2（PKM2）在肿瘤发生中的作用和机制

Aerobic glycolysis (Warburg effect) promotes the use of glucose for biosynthetic pathways necessary for cell proliferation and tumor growth. Overexpression of the M2 isoform of glycolytic enzyme pyruvate kinase (PKM2) is found in various tumors. Studies using in vitro culture systems and xenografting tumors in immunodeficient nude mice revealed the critical role of PKM2 in both aerobic glycolysis and anabolic metabolism as well as enhancement of tumor development in cancer cells. However, knockout of PKM2 accelerated but not diminished tumorigenesis in mice, implicating PKM2 in tumor suppression. To resolve the controversy over those reported conflicting roles of PKM2 in tumor development, we mimicked the overexpression of PKM2 in human tumors by knocking-in PKM2 gene in mice (Pkm2-KI). Spontaneous tumors were formed with low frequency in multiple organs of Pkm2-KI mice control mice while no tumors were found in control mice. Long-term observation of expanded colonies will be applied to ascertain the incidence and tumor types in Pkm2-KI mice. As tumorigenesis is a multiple-step pathological process, Diethylnitrosamine and Azoxymethane will be used to induce mouse liver cancer and colon cancer, respectively, in the presence (Pkm2-KI) or absence (control) of PKM2 overexpession. The impact of PKM2 on carcinogen-induced carcinogenesis will thus help us determine the role of PKM2 in tumor development. mRNA array and metabolic profiling of non-tumor and tumor tissues with or without overexpressed PKM2 will be taken for dissection of potential effectors of PKM2 in tumorigenesis. Characterization of these effectors may yield putative targets for cancer treatment.

有氧糖酵解(Warburg效应) 通过消耗大量葡萄糖，供给细胞快速增殖所需底物，促进肿瘤发展。糖酵解关键酶丙酮酸激酶同工酶2（PKM2）在人肿瘤组织高表达，通过体外细胞培养及裸鼠移植瘤等实验，发现 PKM2促进Warburg效应和肿瘤发展。可是，体内敲除Pkm2不是降低而是促进小鼠肿瘤的发展，为了澄清PKM2促进肿瘤还是抑制肿瘤，我们构建了PKM2基因敲入小鼠（Pkm2-KI），模拟临床肿瘤PKM2高表达， Pkm2-KI小鼠在多个器官低频率自发肿瘤，提示体内过表达PKM2可能促进肿瘤的发生。本研究将长期大样本观察Pkm2-KI小鼠自发肿瘤情况，分别用二乙基亚硝胺和氧化偶氮甲烷诱导Pkm2-KI和对照小鼠产生肝癌、结肠癌，确定PKM2高表达在化学诱导肿瘤发生中的作用，并通过检测组织mRNA表达谱及糖代谢谱，发现关键效应分子，阐明PKM2的作用机制，为肿瘤的发生和靶向治疗提供新的思路和策略。

肿瘤细胞倾向于利用有氧糖酵解(Warburg效应)满足其快速生长增殖的物质和能量需要。丙酮酸激酶（PKM）是催化糖酵解反应的限速酶之一，包括PKL，PKR，PKM1和PKM2四种同工酶，其中PKM2在人肿瘤组织高表达。通过体外细胞培养及裸鼠移植瘤等实验，发现 PKM2促进Warburg效应和肿瘤发展。可是，体内敲除Pkm2不是降低而是促进小鼠肿瘤的发展，为了澄清PKM2促进肿瘤还是抑制肿瘤，我们构建了PKM2基因敲入小鼠（Pkm2-KI），模拟临床肿瘤PKM2高表达。长期观察发现Pkm2-KI小鼠全身多器官低频率自发肿瘤，包括肾，肠和乳腺，提示体内过表达PKM2可能促进肿瘤的发生。根据人肝细胞肝癌（HCC）临床样本中PKM2高表达的现象，我们用二乙基亚硝胺（DEN））诱导小鼠HCC模型，以研究PKM2高表达在HCC中的作用。结果发现PKM2高表达促进DEN 诱导的肝脏肿瘤的发生发展。为阐明PKM2的作用机制，我们构建了PKM2过表达的小鼠胚胎成纤维细胞（MEF），发现PKM2过表达加速了MEF细胞的生长增殖，增强了细胞的糖酵解和线粒体呼吸能力。本研究阐明了PKM2过表达促进肝癌发生，为肿瘤的发生和靶向治疗提供新的思路和策略。