FoxM1/c-Met正反馈环路促进舌鳞癌细胞糖代谢重编程的机制

It has been widely recognized that deregulating cellular energetics is emerging as one of the most important hallmarks of cancer cells and a key contributor to tumor development. Among the many adjustments of the metabolic pathways that are found in tumor cells, a key role is played by an enhanced aerobic glycolysis. Reprogramming of glucose metabolism is a hallmark in various tumor origins, and serves cancer cells in proliferation and survival through maintenance of biosynthesis and redox homeostasis. However, it is still not completely clear why such a less efficient metabolism is selected by proliferating cancer cells. The c-Met amplification results in continuous activation of the AKT signaling pathway, the ERKs signaling pathway and the STAT3 signaling pathway, which are the major upstream signaling routes of FoxM1. Our results showed that FoxM1 bound directly to the c-Met, GLUT1 and HK2 promoter regions and regulated the promoter activities and the expression of them at the transcriptional level. Inhibition of FoxM1 or c-Met by specific shRNAs markedly reduced the expression of FoxM1 and c-Met in tongue squamous carcinoma cells. Spearman rank correlation analysis showed significant positive correlations between FoxM1 and c-Met levels in tongue squamous cell carcinoma. Our hypothesis is that FoxM1 lies both downstream and upstream of the c-Met signaling pathway, and creates a positive feedback loop to promote reprogramming of glucose metabolism via regulation of GLUT1 and HK2 expression in tongue squamous cell carcinoma. In order to further understand mechanisms of glucose metabolism in tongue squamous cell carcinoma, we will further confirm the effects of FoxM1 on glucose metabolism by in vitro and in vivo experiments. This project is helpful for deeply investigating abnormal energy metabolism of tongue squamous cell carcinoma and possibly provide new drug targets and therapeutic strategy clues.

糖代谢重编程是肿瘤细胞能量代谢失调的主要方面，在生物合成与氧化还原反应中提供能量和物质前体，但肿瘤细胞这种低效供能方式的分子机制尚不明确。c-Met活化后可激活ERKs、AKT和STAT3等信号通路，这些信号通路均可以调控转录因子FoxM1。我们发现FoxM1可以增强c-Met、GLUT1和HK2的启动子活性促进它们的转录与表达，干涉FoxM1或c-Met表达后，FoxM1和c-Met的表达均有一定程度的降低，且FoxM1与c-Met在舌鳞癌组织中表达正相关。因此，我们推测FoxM1与c-Met在舌鳞癌细胞中能够相互调节形成一个正反馈环路，通过调控GLUT1和HK2促进舌鳞癌细胞糖代谢重编程。本课题拟在此基础上，深入研究FoxM1促进舌鳞癌细胞糖代谢重编程的分子网络调控机制。本项目可进一步加深舌鳞癌能量代谢异常的理解，并针对肿瘤代谢为靶点的治疗提供新线索。

本研究发现在舌鳞癌细胞中存在FoxM1与c-Met的相互调节机制，形成一个正反馈环路促进其发生EMT、糖代谢重编程和侵袭转移，并可能是AKT信号通路持续激活的重要因素。第一部分：FoxM1与c-Met对舌鳞癌细胞糖代谢重编程的影响。在舌鳞癌细胞SCC9和SCC25中干涉FoxM1或c-Met表达后，细胞葡萄糖摄取、糖酵解速率以及乳酸生成均有一定程度的下降，而氧消耗则相对升高；小动物PET/CT显像结果显示，FoxM1干涉组移植瘤的18F-FDG摄取率明显降低。第二部分：FoxM1参与细胞糖代谢重编程的机制研究。Real time PCR和Western blot结果显示，GLUT1和HK2的表达随FoxM1的表达下调而下降。ChIP结果显示，转录因子FoxM1中能够与GLUT1和HK2的DNA启动子结合。荧光素酶报告基因结果显示，FoxM1能显著增强GLUT1和HK2的DNA启动子活性。第三部分：FoxM1通过c-Met信号通路促进舌鳞癌EMT及侵袭转移的机制研究。在SCC9和SCC25中下调FoxM1后，pc-Met, c-Met, pAKT和Vimentin的蛋白表达随之降低，E-cadherin的表达有所升高，细胞的侵袭迁移能力下降。过表达FoxM1后，pc-Met, c-Met, pAKT和Vimentin的蛋白表达随之升高，E-cadherin的表达有所降低，细胞的侵袭迁移能力升高，LY294002有一定的抑制作用。ChIP结果显示，转录因子FoxM1能够与c-Met的DNA启动子结合。荧光素酶报告基因结果显示，FoxM1能显著增强c-Met的DNA启动子活性。第四部分 c-Met信号通路在舌鳞癌细胞中反向调控FoxM1的机制研究。在SCC9和SCC25中下调c-Met后，FoxM1，pAKT和Vimentin的蛋白表达随之降低，E-cadherin的表达有所升高，细胞的侵袭迁移能力下降。过表达c-Met后，FoxM1，pAKT和Vimentin的表达随之升高，E-cadherin的表达有所降低，细胞的侵袭迁移能力升高，LY294002有一定的抑制作用。免疫组化结果显示，FoxM1、c-Met和pAKT在58例舌鳞癌组织中的表达明显高于癌旁组织，任意两分子的表达正相关，且它们的表达均与T分期、TNM分期、淋巴结转移相关。