Xiao Xue, Zhao Weilin, Tian Fangyun, Zhou Xiaoying, Zhang Jinyan, Huang Tingting, Hou Bo, Du Chunping, Wang Shumin, Mo Yingxi, Yu Nana, Zhou Shiping, You Jinping, Zhang Zhe, Huang Guangwu, Zeng Xianjie
Department of Otolaryngology-Head and Neck Surgery, First Affiliated Hospital of Guangxi Medical University, 6# Shuangyong Road, Nanning, 530021, China.
Tumour Biol. 2014 Apr;35(4):3755-63. doi: 10.1007/s13277-013-1497-1. Epub 2013 Dec 12.
Cytochrome b5 reductase 2 (CYB5R2), a member of the flavoprotein pyridine nucleotide cytochrome reductase family, is associated with a number of physiological reactions. However, its role in cancer, especially nasopharyngeal carcinoma (NPC), has not been addressed. Here, we investigate the transcript levels and promoter methylation status of CYB5R2 in NPC derived cell lines and tumor biopsies and experimentally address its role as a tumor suppressor gene. We find that CYB5R2 transcript levels are decreased in NPC cell lines and tumor biopsies. Promoter hypermethylation of CYB5R2 was detected in all six tested NPC cell lines and in 84% of primary NPC tumor biopsies but not in normal nasopharyngeal epithelium. Clinically, CYB5R2 methylation was associated with lymph node metastasis in NPC patients (P < 0.05). The endogenous expression of CYB5R2 could be restored in vitro by the methyltransferase inhibitor 5-aza-2'-deoxycytidine in NPC cell lines. Ectopic expression of CYB5R2 had an inhibitory effect on proliferation, clonogenicity and migration of NPC cells. Moreover, in vivo tests in nude mice indicated that ectopic expression of CYB5R2 reduces the tumorigenicity of CYB5R2-negative NPC cells. Collectively, these findings suggest that CYB5R2 may be a functional tumor suppressor gene, frequently inactivated by hypermethylation of its promoter in NPC. We report here the first instance of epigenetic downregulation in NPC tumor biopsies of a key enzyme, CYB5R2, which is responsible for the detoxification of environmental carcinogens. We propose the possibility of utilizing CYB5R2 promoter methylation as a diagnostic biomarker of NPC in the future.
细胞色素b5还原酶2（CYB5R2）是黄素蛋白吡啶核苷酸细胞色素还原酶家族的成员之一，与多种生理反应相关。然而，其在癌症尤其是鼻咽癌（NPC）中的作用尚未得到研究。在此，我们研究了CYB5R2在NPC来源的细胞系和肿瘤活检组织中的转录水平及启动子甲基化状态，并通过实验探讨了其作为肿瘤抑制基因的作用。我们发现NPC细胞系和肿瘤活检组织中CYB5R2的转录水平降低。在所有六个检测的NPC细胞系以及84%的原发性NPC肿瘤活检组织中检测到CYB5R2启动子高甲基化，而在正常鼻咽上皮中未检测到。临床上，CYB5R2甲基化与NPC患者的淋巴结转移相关（P < 0.05）。NPC细胞系中甲基转移酶抑制剂5-氮杂-2'-脱氧胞苷可在体外恢复CYB5R2的内源性表达。CYB5R2的异位表达对NPC细胞的增殖、克隆形成能力和迁移具有抑制作用。此外，裸鼠体内实验表明，CYB5R2的异位表达降低了CYB5R2阴性NPC细胞的致瘤性。总体而言，这些发现表明CYB5R2可能是一个功能性肿瘤抑制基因，在NPC中常因启动子高甲基化而失活。我们在此首次报道了NPC肿瘤活检组织中一种关键酶CYB5R2的表观遗传下调，该酶负责环境致癌物的解毒。我们提出了未来将CYB5R2启动子甲基化用作NPC诊断生物标志物的可能性。
