Role of FH loss in development of HLRCC heriditary kidney cancer

具有半合子胚系富马酸水合酶(FH)突变的个体容易患肾癌。这些肿瘤主要表现为剩余的野生型等位基因的功能失活，暗示FH失活是肿瘤促进事件。低氧诱导因子在许多癌症中表达，并在透明细胞肾癌中增加。在常氧条件下，由于依赖VHL的蛋白酶体降解，HIF是不稳定的，但在低氧条件下，由于HIF Pro羟基酶(HPH)的失活，使HIF稳定，从而阻止HIF羟化和VHL识别。我们证明，FH抑制和细胞内富马酸升高与HIF上调是一致的。此外，我们还发现富马酸对HPH具有竞争性抑制作用。这些数据描绘了一种新的富马酸依赖的调节HPH活性和HIF蛋白水平的途径。此外，我们证明了在HLRCC来源的细胞系中FH的失活突变导致葡萄糖介导的细胞活性氧物种(ROS)的产生和ROS依赖的HIF-1α的稳定。此外，我们还发现，在永生化的肾上皮细胞中稳定地敲除FH会导致ROS依赖的HIF-1α的稳定。这些数据表明，HLRCC中存在的专性糖酵解开关对于通过产生ROS稳定HIF至关重要。

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.