Role of FH loss in development of HLRCC heriditary kidney cancer

具有半合子生殖系富马酸水合酶（FH）突变的个体易患肾癌。这些肿瘤主要表现出剩余野生型等位基因的功能失活，暗示FH失活是肿瘤促进事件。缺氧诱导因子在许多癌症中表达，并且在肾透明细胞癌中增加。在常氧条件下，HIF由于VHL依赖性蛋白酶体降解而不稳定，但在缺氧条件下由于HIF脯氨酰羟化酶（HPH）失活而稳定，这阻止了HIF羟基化和VHL识别。我们证明，FH抑制，连同升高的细胞内富马酸，符合HIF上调。此外，我们表明，富马酸作为一个竞争性抑制剂的HPH。这些数据描绘了一种新的谷氨酸依赖性途径，用于调节HPH活性和HIF蛋白水平。此外，我们证明了在HLRCC衍生的细胞系中FH的失活突变导致葡萄糖介导的细胞活性氧（ROS）和ROS依赖性HIF-1 α稳定化的产生。此外，我们发现在永生化的肾上皮细胞中FH的稳定敲低导致ROS依赖的HIF-1 α稳定化。这些数据表明，专性糖酵解开关存在于HLRCC是至关重要的HIF稳定通过ROS的产生。

Individuals with hemizygous germline fumarate hydratase (FH) mutations are predisposed to renal cancer. These tumors predominantly exhibit functional inactivation of the remaining wild-type allele, implicating FH inactivation as a tumor-promoting event. Hypoxia-inducible factors are expressed in many cancers and are increased in clear cell renal carcinomas. Under normoxia, the HIFs are labile due to VHL-dependent proteasomal degradation, but stabilization occurs under hypoxia due to inactivation of HIF prolyl hydroxylase (HPH), which prevents HIF hydroxylation and VHL recognition. We demonstrate that FH inhibition, together with elevated intracellular fumarate, coincides with HIF upregulation. Further, we show that fumarate acts as a competitive inhibitor of HPH. These data delineate a novel fumarate-dependent pathway for regulating HPH activity and HIF protein levels. Additionally, we demonstrate that inactivating mutations of FH in an HLRCC-derived cell line result in glucose-mediated generation of cellular reactive oxygen species (ROS) and ROS-dependent HIF-1alpha stabilization. Further, we have found that stable knockdown of FH in immortalized renal epithelial cells results in ROS-dependent HIF-1alpha stabilization. These data reveal that the obligate glycolytic switch present in HLRCC is critical to HIF stabilization via ROS generation.