Section on Medical Neuroendocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA.
Neuro-Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892, USA.
BMC Cancer. 2018 Mar 13;18(1):286. doi: 10.1186/s12885-018-4127-x.
The role of the hypoxia signaling pathway in the pathogenesis of pheochromocytoma/paraganglioma (PPGL)-polycythemia syndrome has been elucidated. Novel somatic mutations in hypoxia-inducible factor type 2A (HIF2A) and germline mutations in prolyl hydroxylase type 1 and type 2 (PHD1 and PHD2) have been identified to cause upregulation of the hypoxia signaling pathway and its target genes including erythropoietin (EPO) and its receptor (EPOR). However, in a minority of patients presenting with this syndrome, the genetics and molecular pathogenesis remain unexplained. The aim of the present study was to uncover novel genetic causes of PPGL-polycythemia syndrome.
A female presented with a history of JAK2 positive PV, diagnosed in 2007, and right adrenal pheochromocytoma diagnosed and resected in 2011. Her polycythemia symptoms and hematocrit levels continued to worsen from 2007 to 2011, with an increased frequency of phlebotomies. Postoperatively, until early 2013, her hematocrit levels remained normalized. Following this, the hematocrit levels ranged between 46.4 and 48.9% [35-45%]. Tumor tissue from the patient was further tested for mutations in genes related to upregulation of the hypoxia signaling pathway including iron regulatory protein 1 (IRP1), which is a known regulator of HIF-2α mRNA translation. Functional studies were performed to investigate the consequences of these mutations, especially their effect on the HIF signaling pathway and EPO. Indel mutations (c.267-1_267delGGinsTA) were discovered at the exon 3 splicing site of IRP1. Minigene construct and splicing site analysis showed that the mutation led to a new splicing site and a frameshift mutation of IRP1, which caused a truncated protein. Fluorescence in situ hybridization analysis demonstrated heterozygous IRP1 deletions in tumor cells. Immunohistochemistry results confirmed the truncated IRP1 and overexpressed HIF-2α, EPO and EPOR in tumor cells.
This is the first report which provides direct molecular genetic evidence of association between a somatic IRP1 loss-of-function mutation and PHEO and secondary polycythemia. In patients diagnosed with PHEO/PGL and polycythemia with negative genetic testing for mutations in HIF2A, PHD1/2, and VHL, IRP1 should be considered as a candidate gene.
缺氧信号通路在嗜铬细胞瘤/副神经节瘤（PPGL）-红细胞增多症综合征发病机制中的作用已被阐明。已发现缺氧诱导因子 2A 型（HIF2A）的新体细胞突变和脯氨酰羟化酶 1 型和 2 型（PHD1 和 PHD2）的种系突变导致缺氧信号通路及其靶基因（包括促红细胞生成素（EPO）及其受体（EPOR））的上调。然而，在少数出现这种综合征的患者中，遗传和分子发病机制仍未得到解释。本研究的目的是揭示 PPGL-红细胞增多症综合征的新的遗传原因。
一名女性曾患有 JAK2 阳性 PV（真性红细胞增多症），于 2007 年确诊，2011 年诊断出右侧肾上腺嗜铬细胞瘤并接受手术切除。她的红细胞增多症症状和血细胞比容水平从 2007 年到 2011 年持续恶化，放血治疗的频率增加。手术后，直到 2013 年初，她的血细胞比容水平仍保持正常。此后，血细胞比容水平在 46.4%至 48.9%之间波动[35-45%]。进一步检测患者肿瘤组织中与缺氧信号通路上调相关的基因（包括铁调节蛋白 1（IRP1））的突变，IRP1 是 HIF-2α mRNA 翻译的已知调节剂。进行功能研究以调查这些突变的后果，特别是它们对 HIF 信号通路和 EPO 的影响。在 IRP1 的外显子 3 剪接位点发现插入缺失突变（c.267-1_267delGGinsTA）。小基因构建体和剪接位点分析表明，该突变导致新的剪接位点和 IRP1 的移码突变，导致截短蛋白。荧光原位杂交分析显示肿瘤细胞中存在杂合性 IRP1 缺失。免疫组织化学结果证实肿瘤细胞中存在截断的 IRP1 和过表达的 HIF-2α、EPO 和 EPOR。
这是第一个提供与体细胞 IRP1 功能丧失突变与 PHEO 和继发性红细胞增多症之间关联的直接分子遗传学证据的报告。在诊断为 PHEO/PGL 和红细胞增多症且 HIF2A、PHD1/2 和 VHL 基因突变检测阴性的患者中，应考虑 IRP1 作为候选基因。
