IDH3α调节肿瘤相关成纤维细胞有氧糖酵解的机制研究

We found that the aerobic glycolysis is increased not only in tumor cells but also in cancer-associated fibroblasts (CAF), and the inhibition of aerobic glycolysis dramatically attenuates its tumor promoting effects, which is consistant with the finding from the Lisanti group. Our recent data also show that the critical enzyme in citric acid cycle, isocitrate dehydrogenase IDH3α is down-regulated in CAF cells, and the down-regulation of IDH3α increases the protein level of HIF1α. However, how the aerobic glycolysis is regualted is still not clear. Based on previous observations, we propose that IDH3α modulates the activity of proline hydroxylase PHD2 through decreasing the production of its motabolites, α-Ketoglutarate, which is an allosteric regulator of PHD2. Since the PHD2 regulates the HIF1α acetylation which promotes the ubiquitin-dependent degradation of HIF1α, the loss of α-Ketoglutarate inactivates PHD2 and increases the stability of HIF1α, the later induces the aerobic glycolysis.

我们的研究发现，不仅肿瘤细胞存在着有氧糖酵解，而且癌相关成纤维细胞（CAF）也存在着类似肿瘤细胞的有氧糖酵解，对CAF细胞有氧糖酵解的抑制明显减弱了其促肿瘤生长的作用，这与美国Lisanti实验室的发现一致。我们的研究还发现，CAF细胞中三羧酸循环关键性限速酶异柠檬酸脱氢酶IDH3α表达下调，而IDH3α表达下调导致成纤维细胞的有氧糖酵解增加；另外，IDH3α表达下调增加HIF1α的蛋白水平。然而，CAF细胞中有氧糖酵解的调节机制目前还知之甚少。基于前期的发现，我们推测IDH3α可能通过影响其代谢产物α-KG的含量，调节α-KG依赖的脯氨酸羟化酶PHD2的活性，从而减少HIF1α的羟基化修饰，增加HIF1α的稳定性，导致CAF细胞有氧糖酵解的发生。本研究拟在证实IDH3α是否通过影响HIF1α蛋白的稳定性调节有氧糖酵解，并探索IDH3α上游的调控因子，阐明CAF细胞中有氧糖酵解的可能起因。

肿瘤的发生、发展不仅依赖于肿瘤细胞本身，肿瘤间质特别是肿瘤相关成纤维细胞（CAF）也调节了肿瘤细胞的增殖和侵袭能力。CAF细胞也存在着类似肿瘤细胞的有氧糖酵解，抑制CAF 细胞的有氧糖酵解可明显减弱其促肿瘤生长的作用，但是对于CAF代谢变化的机制目前鲜有研究。我们研究发现，转化生长因子β1（TGF-β1）或血小板衍生因子（PDGF）诱导CAF有氧糖代谢的变化是由异柠檬酸脱氢酶催化亚基（IDH3a）介导的，CAF细胞通过miR-424抑制IDH3a的表达。IDH3a通过下调有效“α-KG”（α-酮戊二酸，α-ketoglutarate; α-KG）与延胡索酸（fumarate）琥珀酸盐（succinate）比值）抑制脯氨酸羟化酶 PHD2，从而通过调控低氧诱导转录因子HIF1-α的水平来调控细胞中糖酵解关键基因的表达，并通过调控NDUFA4L2的水平来调控细胞的氧化磷酸化。肿瘤标本中CAF细胞IDH3a表达下调。过表达IDH3a抑制成纤维细胞CAF转变。本研究发现IDH3a介导了CAF细胞的有氧糖酵解的代谢转变。