腫瘤的代謝與增生能力有密不可分的關係,本實驗室先前的研究證實Nodal會增強腦瘤細胞增生與侵襲。在腦瘤細胞代謝中已知葡萄糖轉運蛋白-1(Glut-1;glucose transporter-1)表現與腦瘤的增生相關。在本實驗中首先證實Nodal在腦瘤細胞的表現與葡萄糖轉運蛋白-1表現呈正相關。利用專一性Nodal小髮夾RNA與Nodal受器(Receptor)藥理抑制劑,證明當降低Nodal時葡萄糖轉運蛋白-1蛋白表現量與攝取葡萄糖能力也會降低,並且,粒線體中調控克氏循環的酵素丙酮酸去氫脢(PDH, pyruvate dehydrogenase) 則出現被活化的情形。反之,若利用Nodal重組蛋白或利用載體增加Nodal的表現則細胞之葡萄糖轉運蛋白-1增加且攝取葡萄糖能力上升,丙酮酸去氫脢活性被抑制。動物實驗中也證實,Nodal的存在會影響腫瘤在活體的侵襲能力。在分子機制方面,實驗中證實腦瘤細胞經Nodal刺激後,透過增加ERK(Extracellular signal-regulated kinase)活性而影響缺氧誘導因子-1(Hypoxia inducible factor-1α;HIF-1α)影響葡萄糖轉運蛋白-1蛋白的表現。而利用血癌用藥5’-AzadC可以誘發分裂原活化蛋白質激脢去磷酸脢(MAP kinase phosphatase-1;MKP-1),抑制分裂原活化蛋白質激脢(MAPK; Mitogen-activated protein kinase)活性,進而降低細胞攝取葡萄糖之能力。 此外,於研究中也發現Nodal可能會影響癌細胞之分化情形,使惡性腦瘤細胞表現類星狀細胞之特徵(astrocytic-like phenotype;GFAP/Vimentin ratio改變)。綜合以上,Nodal可能具有調控癌細胞代謝行為及抑制其分化的能力,而 MKP-1則有潛力作為此由Nodal所導致的癌惡性行為之抑制分子。
It is well known that tumor growth rate is correlated with metabolism. Previous work from our laboratory, had show that Nodal promotes cell proliferation rate and cell invasiveness ability in glioma cells in vitro. In the present study, we demonstrated that expression of Nodal was correlated with Glut-1 (glucose transporter-1) expression and capacity of glucose uptake. Treatment of glioma cell lines with recombinant Nodal increases Glut-1 expression and glucose uptake ability in glioma cell lines. The ectopic expression of Nodal in GBM glioma cells that expressed Nodal at a low level resulted in increased Glut-1 expression, enhanced glucose uptake capacity, inactivated PDH (pyruvate dehydrogenase) and increased tumor growth in vivo. In contrast, knockdown of Nodal expression in U87MG glioma cells that has a high Nodal expression level reduced expression of Glut-1, capacity of glucose uptake, activated PDH and decreased tumor growth in vivo. These data is consistent to our previous study that Nodal increases cell proliferation rate in vitro, and suggest that Nodal might enhance glycolysis effect and reduce mitochondrial respiration in glioma cells. In addition, Nodal promotes the reversion of malignant glioma cells toward a differentiated astrocytic-like phenotype (GFAP/Vimentin ratio). We also demonstrated that the ERK and HIF-1α might play a major role in Nodal-induced effect on glioma cells. 5’-AzadC has been demonstrated that induces MKP-1 expression and reduces MAPK ( Mitogen-activated protein kinase) activity. We found that 5’-AzadC reduces glucose uptake capacity through MKP-1 dependent pathway. Taken together, these data suggest that Nodal might regulate tumor metabolism and cell differentiated phenotype, MKP-1 might use as a molecular therapeutic target to Nodal-induced malignant tumor.
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