Loss of protein targeting to glycogen sensitizes human hepatocellular carcinoma cells towards glucose deprivation mediated oxidative stress and cell death.
Loss of protein targeting to glycogen sensitizes human hepatocellular carcinoma cells towards glucose deprivation mediated oxidative stress and cell death.
复制标题
DOI：
10.1042/bsr20150090
复制
发表时间：
2015-05-01
影响因子：
4
通讯作者：
Cheng A
中科院分区：
文献类型：
--
作者：
Yang R;Zhang M;Gustafson AR;Wang E;Cole MP;Tooley CE;Cheng A
PTG是一种蛋白质，对各种组织（如肝脏）的糖原积累至关重要。我们目前的研究表明，它的丧失使肝癌细胞对代谢和氧化应激敏感。靶糖原蛋白（PTG）是一种普遍表达的支架蛋白，在许多组织中，包括肝脏、肌肉和大脑中，对糖原水平起关键调节作用。然而，它在转化细胞中的重要性尚未被详细探讨。由于最近的研究已经证明糖原代谢在癌细胞中起重要作用，我们决定评估PTG水平对人肝细胞癌（HepG2）细胞对代谢应激反应能力的影响。虽然在正常培养条件下，PTG的表达对HepG2细胞的增殖没有显著影响，但我们确定PTG在葡萄糖剥夺过程中发挥了重要作用。在缺乏葡萄糖的情况下，PTG的过表达保护细胞免于死亡，而通过乳酸脱氢酶（LDH）释放到培养基中来测量，敲低PTG进一步促进细胞毒性。此外，我们证明了PTG减弱葡萄糖剥夺诱导的血红素氧化酶-1 （HO-1）表达，这表明PTG可以保护葡萄糖剥夺诱导的氧化应激。事实上，用抗氧化剂n -乙酰半胱氨酸（NAC）处理细胞可以使细胞免受葡萄糖剥夺引起的细胞毒性。最后，我们发现PTG的缺失导致自噬增强。在对照细胞中，葡萄糖剥夺抑制自噬，这是由自噬底物p62水平的增加决定的。然而，在敲低细胞中，这种抑制被缓解。阻断自噬也可减轻PTG敲低细胞中葡萄糖剥夺引起的细胞毒性。综上所述，我们的研究结果确定了PTG在保护肝癌细胞免受代谢应激的新作用，部分是通过调节氧化应激和自噬。
PTG is a protein that is critical for glycogen accumulation in various tissues such as the liver. Our present study shows that its loss sensitizes liver cancer cells towards metabolic and oxidative stress. Protein targeting to glycogen (PTG) is a ubiquitously expressed scaffolding protein that critically regulates glycogen levels in many tissues, including the liver, muscle and brain. However, its importance in transformed cells has yet to be explored in detail. Since recent studies have demonstrated an important role for glycogen metabolism in cancer cells, we decided to assess the effect of PTG levels on the ability of human hepatocellular carcinoma (HepG2) cells to respond to metabolic stress. Although PTG expression did not significantly affect the proliferation of HepG2 cells under normal culture conditions, we determined that PTG plays an important role during glucose deprivation. Overexpression of PTG protected cells from cell death in the absence of glucose, whereas knocking down PTG further promoted cytotoxicity, as measured by the release of lactate dehydrogenase (LDH) into the media. Additionally, we demonstrated that PTG attenuates glucose deprivation induced haeme oxygenase-1 (HO-1) expression, suggesting that PTG protects against glucose deprivation-induced oxidative stress. Indeed, treating cells with the antioxidant N-acetyl cysteine (NAC) rescued cells from cytotoxicity caused by glucose deprivation. Finally, we showed that loss of PTG resulted in enhanced autophagy. In control cells, glucose deprivation suppressed autophagy as determined by the increase in the levels of p62, an autophagy substrate. However, in knockdown cells, this suppression was relieved. Blockade of autophagy also attenuated cytotoxicity from glucose deprivation in PTG knockdown cells. Taken together, our findings identify a novel role for PTG in protecting hepatocellular carcinoma cells from metabolic stress, in part by regulating oxidative stress and autophagy.