科學家知道腫瘤細胞會高度依賴醣解作用提供能量的現象已經超過七十年。過去發現，惡性腫瘤細胞偏好以無氧醣解產生細胞所需能量並降低有氧呼吸作用，此現象稱為瓦式效應。透過控制將葡萄糖磷酸化成六-磷酸葡萄糖的化學反應，六碳醣激酶是醣解作用的第一個並且是速率決定步驟的關鍵酵素，並藉此維持細胞內外醣濃度梯度使得葡萄糖更容易進入到細胞中並開始啟動所有和葡萄糖利用相關的代謝路徑，正因為調控著細胞葡萄糖的供給和利用，六碳醣激酶在細胞中扮演了維持生命所必須的角色。因為腫瘤細胞高度活化的醣解作用，觀察沉默醣解作用第一個酵素”六碳醣激酶”對腫瘤細胞所造成的影響是十分令人感興趣的。在哺乳動物的器官中，有四種高度同源性的六碳醣激酶同功酵素，分別位在不同位置的基因上。因為六碳醣激酶III和六碳醣激酶IV僅在特殊的組織中表現，我們選擇了六碳醣激酶I和六碳醣激酶II作為RNAi沉默對象。在這次的研究中令人注意的是，穩定沉默六碳醣激酶I會對細胞的外形產生非常戲劇性的變化，細胞從原本上皮性的外觀轉變成間質細胞挾長的型態，而穩定沉默六碳醣激酶II並不會對細胞的外形產生影響。更近一步發現穩定沉默六碳醣激酶I 會使得細胞在生長速度、移動能力和侵襲能力上有顯著的提升。此外相較於控制組HeLa、HeLa-vector-1，HeLa-vector-2，穩定沉默六碳醣激酶I的細胞株中粒線體膜電位以及活性氧化物都是處在相當低的情況。活體動物實驗的結果也證實穩定沉默六碳醣激酶I的細胞株腫瘤形成速度和轉移能力都有明顯的增強。在我們的研究中，有許多的證據證明穩定沉默六碳醣激酶I 會造成細胞有上皮－間質細胞轉型(epithelial-mesenchymal transition, EMT)的現象。從我們的研究發現，不正常的六碳醣激酶I表現量可能是影響腫瘤細胞是否惡化轉移的重要因素之一。

For over 70 years, it has been known that tumor cells exhibit a high rate of glycolysis. By catalyzing the ATP-dependent phosphorylation of glucose to yield glucose-6-phosphate, hexokinase controls the first committed and rate-limiting step of glycolysis, thereby sustaining the concentration gradient that permits facilitated glucose entry into cells and initiates all major pathways of glucose utilization. It plays a vital role in the cellular uptake and utilization of glucose. Because the high rate of glycolysis in cancer cells, it’s interesting to observe the effects of cancer cells when we knockdown the first enzyme of glycolysis, hexokinase. Four highly homologous hexokinase isoforms, encoded by separate genes, have been described in mammalian tissues. Because the HKIII and HKIV isoforms are tissue specific expression, we chose HKI and HKII to be our RNAi-mediated gene silencing targets. In this study, stable knockdown HKI induced dramatically morphological changes from epithelial to fibroblast-like phenotype, whereas stable knockdown HKII showed no distinct phenotype changes. Moreover, the constant HKI knockdown cells exhibited a conspicuous rise not only in cell proliferation, but also in cell motility and invasiveness. Furthermore, the mitochondrial membrane potential (Δψm) and reactive oxygen species (ROS) of HKI-knockdown cells were at an extremely low level as compared with control mock and vector-transfected cells. In vivo experiments also demonstrate that HKI-knockdown cells have highly tumorgenesis and metastasis ability. In our study, there were many evidences indicated that persistent knockdown HKI induced the epithelial-mesenchymal transition (EMT). The abnormal expression of hexokianse I may be one of the important factors for cancer cell metastasis.

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