Role Of PI3K/Akt-HIF-1α Signaling Pathways On Glycolysis In Esophageal Carcinoma Cells

Background:Esophageal cancer as a kind of malignant tumor is common in China, with characteristics of fast infiltrating, early metastasis, chemoradiotherapy tolerance and poor prognosis. Studies showed that hypoxia within esophageal cancer tissue plays a important role in promoting tumor invasion, metastasis and chemoradiotherapy tolerance with relating to cancer cell’s energy metabolism and others. Tumour cells show a striking rate of glycolysis and lactate production, even in the presence of oxygen (Warburg effect). Warburg effect makes tumor cells showing a stronger capability of glucose metabolism than normal cells, which provides more ATP supplies to meet the required of cells with rapid proliferation and stronger hypoxia tolerance. Synergy effect with hypoxic environment and the Warburg effect in tumor tissue may paly a key role in promoting tumor metastasis and radiotherapy and chemotherapy resistant. Hypoxia-inducible factor1(HIF-1α) is a key regulator of tissue cells adapting to the hypoxic environment, which has been found overexpressed in esophageal carcinoma and related to lymph node metastasis and chemoradiotherapy tolerance. PI3K/Akt pathway is one of the signal transduction pathways of cancer cells which most closely related to the regulation of glucose metabolism (Akt, also known as the Warburg kinase), and also involved in regulation of HIF-1α expression. But it is unclear the role of PI3K/Akt-HIF-1α pathway on hypoxia and Warburg effect in esophageal cancer cells. Aim:To explore the role of PI3K/Akt-HIF-1α pathway on the regulation of glycolysis in esophageal cancer cells.Method:1) to observe the change of lactate concentration outside esophageal cancer cell lines Eca109or TE13and the expression of HIF-la and GLUT1, HKⅡ, LDHA (rate-limiting enzymes related to glycolysis) in different oxygen concentration;2) to explore the expression of HIF-la and the change of glycolysis after blocking PI3K/Akt pathway by wortmannin or rapamycin in Eca109and TE13cells;3) to inhibit the expression of HIF-la with siRNA interference and then to observe the activity changes of rate-limiting enzymes related to glycolysis and the change of glycolysis;4) to observe the variation of glycolysis in HIF-la silence cells after activating PI3K/Akt pathway with EGF.Results:With environmental oxygen concentration dropping, the expression of HIF-la and ensymes related to glycolysis(GLUT1, HKII, LDHA) increased in Eca109, and TE13cells. Meanwhile, the activity of glycolysis enzymes and concentration of lactic acid were increased. Wortmannin or rapamycin was applied to block the PI3K/Akt pathway, the expression of glycolysis enzymes and the concentration of lactic acid outside esophageal cancer cells decreased significantly in both normoxia and hypoxia environment. After downregulating the expression of HIF-la by siRNA, the expression and activity of glycolysis enzymes and concentration of lactic acid decreased more in hypoxia than in normoxia; EGF was applied to activate the PI3K/Akt pathway in HIF-la silence cells, the expression of glycolysis enzymes and the level of glycolysis increase highly in normoxia than in hypoxia.Conclusion:Hypoxia can promote the level of glycolysis at esophageal cancer cell, which related to the overexpression of HIF-1α. PI3K/Akt and HIF-1α pathways are involved in the glycolysis, HKII, GLUT1and LDHA may be located in downstream sites. Activation of PI3K/Akt pathway with EGF play an important role in the regulation of glycolysis through HIF-1α in hypoxia. But this process might be independent of HIF-1α at normoxia. Inhibition of PI3K/Akt-HIF-1α pathway can decrease the level of glycolysis effectively at esophageal cancer cells, which may be applied to treat patients with esophageal cancer in the future.