Faculté de Médecine, Institut de Génétique et Signalisation Moléculaire, Université de Nice-Sophia Antipolis, Nice, France.
Diabetologia. 2011 Apr;54(4):954-64. doi: 10.1007/s00125-010-2032-1. Epub 2011 Jan 15.
AIMS/HYPOTHESIS: A high-fat diet and obesity are associated with increased risk of liver cancer. Because increased delivery of NEFA to the liver occurs in these conditions, we investigated the involvement of the unsaturated fatty acid oleate in hepatocarcinoma cell proliferation using human-derived hepatocarcinoma cell lines as model systems.
Western blotting, FACS analysis and [(3)H]thymidine incorporation were used to study the signalling pathways and the proliferation of cells cultured for up to 72 h with or without a concentration of oleate considered to be relevant to human pathophysiology (50 μmol/l) or a concentration considered elevated (1 mmol/l).
In HepG2 cells, proliferation was increased in the presence of 50 μmol/l oleate, but was decreased at 1 mmol/l. This differential effect was correlated with the activation of the mammalian target of rapamycin complex 1 (mTORC1) and with increased translation of cell cycle regulators. Oleate-mediated mTORC1 activation required phospholipase D activation, which produces phosphatidic acid and is known to render mTORC1 rapamycin resistant. Remarkably, rapamycin resistance was found to affect specifically the mTORC1/eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) branch of the mTORC1 pathway in the presence of 50 μmol/l oleate. Furthermore, inhibition of phosphatidic acid production abolished oleate-induced increases in mTORC1 activity and cyclin A production. Importantly, the same differential effects of oleate on mTORC1 activation, cell cycle regulators and rapamycin resistance were found in SK-Hep1 cells.
CONCLUSIONS/INTERPRETATION: Oleate stimulates mTORC1 activation and rapamycin resistance. We propose that rapamycin-derived mTOR inhibitors are likely to be of limited therapeutic use to restrain hepatic tumour growth, particularly in the context of associated obesity.
目的/假设：高脂肪饮食和肥胖与肝癌风险增加有关。由于这些情况下肝脏中 NEFA 的输送增加，我们使用人源性肝癌细胞系作为模型系统，研究了不饱和脂肪酸油酸在肝癌细胞增殖中的作用。
使用 Western blot、FACS 分析和 [(3)H]胸腺嘧啶掺入法，研究了在浓度为 50μmol/L（被认为与人类病理生理学相关）或 1mmol/L（被认为升高）的油酸存在下培养长达 72 小时的细胞信号通路和增殖情况。
在 HepG2 细胞中，50μmol/L 油酸存在时细胞增殖增加，但在 1mmol/L 时减少。这种差异效应与哺乳动物雷帕霉素靶蛋白复合物 1（mTORC1）的激活以及细胞周期调节剂的翻译增加有关。油酸介导的 mTORC1 激活需要磷脂酶 D 激活，产生磷脂酸，已知使 mTORC1 对雷帕霉素产生抗性。值得注意的是，在 50μmol/L 油酸存在下，雷帕霉素抗性被发现专门影响 mTORC1/eIF4E 结合蛋白 1（4E-BP1）分支的 mTORC1 通路。此外，抑制磷脂酸产生可消除油酸诱导的 mTORC1 活性和细胞周期蛋白 A 的产生。重要的是，在 SK-Hep1 细胞中也发现了油酸对 mTORC1 激活、细胞周期调节剂和雷帕霉素抗性的相同差异效应。
结论/解释：油酸刺激 mTORC1 激活和雷帕霉素抗性。我们提出，雷帕霉素衍生的 mTOR 抑制剂可能在限制肝肿瘤生长方面的治疗用途有限，特别是在肥胖相关的情况下。
