beta-连环素与GRP78相互作用调控大肠癌细胞能量代谢的分子机制研究

Remodeling of glucose and glutamine metabolism is one of the important characteristics of tumor cells. β-catenin (β-cat), which is a crucial protein of Wnt signal pathway, plays important roles in the formation of several types of tumors, especially in colorectal cancer adenoma. Glucose regulated protein 78 (GRP78) is referred as an important chaperone located in the endoplasmic reticulum. It is highly expressed in a few human cancers. Our previous study indicated that the expression of GRP78 and c-Myc were significantly elaveted in colorectal cancer cells under the glucose-deprived conditions. We further identified the interactions of GRP78 with β-catenin and glucose transporter 1 (Glut-1). Those interactions may promote the nuclear translocation of β-catenin and subsequent activation of c-Myc expression. We speculate that glucose deprivation-induced c-Myc is likely to accelerate the glutamine metabolism and play a compensatory effect on glucose metabolism. In this project, we intend to identify the role of the induced c-Myc protein in glutamine metabolism under the glucose-starved conditions. The molecular mechanism of GRP78-β-catenin and β-catenin-c-Myc promoter interactions will be studied in detail. Furthermore, the regulation of GRP78 on Glut-1 expression and its membrane translocation will be investigated. The project will implicate a possible molecular mechanism between glucose and glutamine metabolism, and provide molecular targets for cancer therapy.

葡萄糖和谷氨酰胺代谢重塑是肿瘤细胞的重要特征之一。beta-连环素是Wnt信号通路中的关键成员，在多种肿瘤尤其是肠癌腺瘤的形成中起重要作用。葡萄糖调节蛋白78（GRP78）是位于内质网中的重要分子伴侣，在多种人类肿瘤组织中高表达。本课题前期研究表明，葡萄糖饥饿条件下大肠癌细胞中GRP78和谷氨酰胺代谢调控因子c-Myc蛋白呈明显高表达，且发现GRP78与beta-连环素、葡萄糖转运蛋白-1（Glut-1）有相互作用，这些相互作用可能促进了beta-连环素细胞核转位并激活c-Myc的表达，以加快谷氨酰胺代谢来补偿葡萄糖缺乏。本课题将研究葡萄糖饥饿诱导下，c-Myc在谷氨酰胺代谢和细胞存活中的作用；GRP78与beta-连环素相互作用促进c-Myc表达的分子机制；GRP78变化对Glut-1表达和细胞膜转位的影响。以新的视角阐明葡萄糖和谷氨酰胺代谢之间的关系，为肿瘤治疗提供新的思路和靶点。

糖酵解是肿瘤细胞中主要进行的代谢类型。糖酵解过程会产生大量的代谢中间产物，用于肿瘤细胞在快速增殖过程中合成生物大分子。已知肿瘤细胞由于生长过快，常常处于葡萄糖饥饿的微环境中，而糖酵解代谢又需要消耗大量葡萄糖，肿瘤细胞是通过怎样的机制维持其正常的生理功能呢？我们的研究发现，葡萄糖调节蛋白GRP78能够感受微环境中葡萄糖的变化。当细胞处于缺糖环境时，GRP78大量表达，过量的GRP78能够与β-catenin相互作用，首先通过自噬调节的NF-κB/β-catenin/c-myc信号直接激活肿瘤细胞中的谷氨酰胺代谢，利用谷氨酰胺为其自身提供能量；其次促进了葡萄糖转运蛋白Glut-1的表达以及膜转位，帮助细胞尽量多的汲取微环境中的葡萄糖；然后能够促进PDHA和PDHB等TCA循环关键酶的表达，促进肿瘤细胞中的TCA循环，提高葡萄糖的利用率；最后能够通过自噬调节的NF-κB信号抑制糖酵解途径中的关键酶PKM2的表达。PKM2的低表达不仅起到了抑制糖酵解，防止能量过度消耗的作用，而且还通过miR-200a进一步激活β-catenin/c-Myc信号以及谷氨酰胺代谢途径，为其增殖和存活提供能量。本项目从多个方面阐明了肿瘤细胞在葡萄糖饥饿环境下，各代谢通路的相互代偿关系，同时也证明了GRP78与β-catenin相互作用在这一系列调控中所发挥的关键作用，为以GRP78和β-catenin为靶点的肿瘤靶向治疗提供了重要依据。