Wohlrab Christina, Vissers Margreet C M, Phillips Elisabeth, Morrin Helen, Robinson Bridget A, Dachs Gabi U
Mackenzie Cancer Research Group, Department of Pathology and Biomedical Science, University of Otago, Christchurch, New Zealand.
Centre for Free Radical Research, Department of Pathology and Biomedical Science, University of Otago, Christchurch, New Zealand.
Front Oncol. 2018 Nov 30;8:574. doi: 10.3389/fonc.2018.00574. eCollection 2018.
Hypoxia-inducible transcription factors (HIFs) drive angiogenesis and cancer cell growth, contributing to an aggressive tumor phenotype. HIF-α protein levels and activity are controlled at the post-translational level by HIF hydroxylases. Hydroxylated HIF-α is recognized by the von Hippel Lindau (VHL) tumor suppressor and targeted for degradation. The HIF hydroxylases are members of the iron and 2-oxoglutarate-dependent dioxygenases, which require ascorbate as cofactor for activity. Clear cell renal cell carcinomas (ccRCC) harbor mutations in the gene, whereas papillary RCC (pRCC) have a functional VHL. These natural occurring variants in RCC enable the testing, in clinical samples, of the hypothesis that ascorbate modulates HIF-α levels through its role as a cofactor for the HIF hydroxylases. We measured ascorbate, HIF-1α, and HIF-2α protein and HIF downstream targets BNIP3, CA9, cyclin D1, GLUT1, and VEGF (combined to generate the HIF pathway score) in VHL-defective ccRCC ( = 73) and VHL-proficient pRCC human tumor tissue ( = 41). HIF and ascorbate levels were increased in ccRCC and pRCC tumors compared to matched renal cortex. HIF-1 and total HIF pathway activation scores were decreased with higher ascorbate in pRCC tumors (Spearman = -0.38, < 0.05 and = -0.35, < 0.05). This was not evident for ccRCC tumors. In mechanistic studies , ascorbate influenced HIF-1 activity in VHL-proficient, but not VHL-defective ccRCC cells. Our results indicate that ccRCC, which lacks a functional VHL, does not respond to ascorbate-mediated modulation of the HIF response. This contrasts with the demonstrated association between ascorbate content and the HIF pathway observed in pRCC and other tumors with a functional VHL. The results support a role for ascorbate as a modulator of HIF activity and tumor aggression in cancer types with a functional hypoxic response.
缺氧诱导转录因子（HIFs）驱动血管生成和癌细胞生长，促使肿瘤呈现侵袭性表型。HIF-α蛋白水平和活性在翻译后水平受HIF羟化酶调控。羟化的HIF-α被冯·希佩尔-林道（VHL）肿瘤抑制蛋白识别并靶向降解。HIF羟化酶是铁和2-氧戊二酸依赖性双加氧酶家族成员，其活性需要抗坏血酸作为辅因子。透明细胞肾细胞癌（ccRCC）的VHL基因存在突变，而乳头状肾细胞癌（pRCC）的VHL功能正常。肾细胞癌中这些自然发生的变异使得在临床样本中能够检验抗坏血酸通过作为HIF羟化酶的辅因子来调节HIF-α水平这一假说。我们检测了VHL缺陷型ccRCC（n = 73）和VHL功能正常的pRCC人肿瘤组织（n = 41）中的抗坏血酸、HIF-1α和HIF-2α蛋白以及HIF下游靶点BNIP3、CA9、细胞周期蛋白D1、葡萄糖转运蛋白1（GLUT1）和血管内皮生长因子（VEGF）（合并生成HIF通路评分）。与匹配的肾皮质相比，ccRCC和pRCC肿瘤中的HIF和抗坏血酸水平升高。在pRCC肿瘤中，抗坏血酸水平越高，HIF-1和总HIF通路激活评分越低（斯皮尔曼相关系数r = -0.38，P < 0.05和r = -0.35，P < 0.05）。ccRCC肿瘤中未观察到这种现象。在机制研究中，抗坏血酸影响VHL功能正常但不影响VHL缺陷型ccRCC细胞中的HIF-1活性。我们的结果表明，缺乏功能性VHL的ccRCC对抗坏血酸介导的HIF反应调节无反应。这与在pRCC和其他具有功能性VHL的肿瘤中观察到的抗坏血酸含量与HIF通路之间的关联形成对比。这些结果支持抗坏血酸在具有功能性缺氧反应的癌症类型中作为HIF活性和肿瘤侵袭调节剂的作用。
