厭氧糖酵解(anaerobic glycolysis)以及糖質新生(gluconeogenesis)被認為對於癌細胞的生長是重要的。磷酸烯醇式丙酮酸羧激酶(Phosphoenolpyruvate carboxykinase；PEPCK)是調控糖質新生及甘油新生(glycerogenesis)(參與脂質新生過程)的重要酵素，此反應需要GTP催化將草醯乙酸(oxaloacetate)轉變為磷酸烯醇式丙酮酸(phosphoenolpyruvate)。PEPCK有兩種同功酶(isozymes)，一種是位於粒線體的PEPCK-M；另ㄧ種是位於細胞質的PEPCK-C。在本篇研究中，我們著重於研究PEPCK-M在癌細胞的功能。我們發現在Huh-7和ML-1肝癌細胞中，PEPCK-M mRNA和蛋白質的表現會受到內質網壓力(ER stress)的誘導物，tunicamycin及brefeldin A所增強，此誘導並不會受到促細胞分裂劑活化性蛋白激酶(mitogen-activated protein kinase；MAPK) inhibitor影響，然而卻會受糖原合酶激酶3β(glycogen synthase kinase-3β；GSK-3β) inhibitor所抑制。我們利用核醣核酸干擾(RNAi)技術抑制Huh-7細胞株的內生PEPCK-M。PEPCK-M的缺乏抑制了細胞生長以及在軟膠(soft agar)中anchorage-independent的生長能力，並且降低調控脂質生成相關酵素基因的表現，如脂肪酸合酶(fatty acid synthase；FAS)和乙醯輔酶A羧化酶(acetyl-CoA carboxylase；ACC)。另一方面，利用Boyden chamber assay和傷口癒合(wound-healing assay)分析細胞爬行，發現PEPCK-M缺失明顯增加細胞爬行速度，爬行速度的增加可能有部份是因為乳酸(lactate)累積所造成的。總而言之，PEPCK-M減少可以抑制癌細胞生長，但也許有可能會促進癌細胞爬行。PEPCK siRNA 是否能作為新的癌症治療分子而不會誘發腫瘤轉移，未來將會在動物實驗進行更進一步的測試。

Anaerobic glycolysis and gluconeogenesis have been suggested to be important for the growth of cancer cells. Phosphoenolpyruvate carboxykinase (PEPCK) is a pace-setting enzyme in gluconeogenesis and glycerogenesis for lipogenesis. The reaction requires GTP to catalyze the conversion from oxaloacetate to phosphoenolpyruvate. Two isozymes of PEPCK are compartmentalized to the mitochondria (PEPCK-M) and cytosol (PEPCK-C). In this report, we aimed to study the function of PEPCK-M in cancer. The expression of PEPCK-M mRNA and protein was enhanced by artificial inducers of endoplasmic reticulum stress, tunicamycin and brefeldin A, in Huh-7 and ML-1 hepatoma cells. The induction was not affected by mitogen-activated protein kinase (MAPK) inhibitor, but was attenuated with glycogen synthase kinase-3β (GSK-3β) inhibitor. The endogenous PEPCK-M was suppressed by small interference RNA in Huh-7 cells. Downregulation of PEPCK-M inhibited the cell growth in 10% serum and anchorage-independent growth in soft agar. Decrease of PEPCK-M inhibited the expression of for lipogenic enzymes, such as fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC). It was interesting to note that PEPCK-M-knockdown significantly increased cellular migration rate, as demonstrated with Boyden chamber assay and wound-healing assay. The increase of migration may be in part due to accumulation of lactate in PEPCK-M knockdown cells. In summary, downregulation of PEPCK-M can inhibit the oncogenic growth of cancer cells, but may enhance the migration of cancer cells. Whether the PEPCK siRNA can function as novel cancer therapeutic agent without inducing metastasis will be tested in animal experiments in the future.

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