Department of Medicine, Center for Esophageal Diseases, Baylor University Medical Center and Center for Esophageal Research, Baylor Scott & White Research Institute, 2 Hoblitzelle, Suite 252, 3500 Gaston Avenue, Dallas, TX, 75246, USA.
Department of Liver Surgery, the First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, Guangdong, China.
Cell Commun Signal. 2019 Nov 21;17(1):152. doi: 10.1186/s12964-019-0458-8.
Overexpression of erythropoietin (EPO) and EPO receptor (EPO-R) is associated with poor prognosis in non-small-cell lung carcinoma (NSCLC). Hypoxia, a potent EPO inducer, is a major stimulating factor in the growth of solid tumors. However, how EPO-R expression is regulated under hypoxia is largely unknown.
The role of EPO-R in NSCLC cell proliferation was assessed by RNA interference in vitro. Luciferase reporter assays were performed to map the promoter elements involved in the EPO-R mRNA transcription. Nuclear co-immunoprecipitation and chromatin immunoprecipitation were performed to assess the interaction among transcription factors HIF1α, SP1, and EGR1 in the regulation of EPO-R under hypoxia. The expression of key EPO-R transcription factors in clinical specimens were determined by immunohistochemistry.
Hypoxia induced a dosage and time dependent EPO-R mRNA expression in NSCLC cells. Knockdown of EPO-R reduced NSCLC cell growth under hypoxia (P < 0.05). Mechanistically, a SP1-EGR1 overlapped DNA binding sequence was essential to the hypoxia induced EPO-R transcription. In the early phase of hypoxia, HIF1α interacted with EGR1 that negatively regulated EPO-R. With the exit of EGR1 in late phase, HIF1α positively regulated EPO-R expression through additive interaction with SP1. In clinical NSCLC specimen, SP1 was positively while EGR1 was negatively associated with active EPO-R expression (P < 0.05).
HIF1α, SP1 and EGR1 mediated EPO-R expression played an essential role in hypoxia-induced NSCLC cell proliferation. Our study presents a novel mechanism of EPO-R regulation in the tumor cells, which may provide information support for NSCLC diagnosis and treatment.
促红细胞生成素（EPO）及其受体（EPO-R）的过表达与非小细胞肺癌（NSCLC）的预后不良有关。缺氧是一种强烈的 EPO 诱导剂，是实体瘤生长的主要刺激因素。然而，EPO-R 的表达在缺氧下是如何调节的，在很大程度上尚不清楚。
通过体外 RNA 干扰评估 EPO-R 在 NSCLC 细胞增殖中的作用。进行荧光素酶报告基因检测，以绘制参与 EPO-R mRNA 转录的启动子元件图谱。进行核共免疫沉淀和染色质免疫沉淀，以评估缺氧下转录因子 HIF1α、SP1 和 EGR1 之间的相互作用，调节 EPO-R 的表达。通过免疫组织化学测定临床标本中关键 EPO-R 转录因子的表达。
缺氧诱导 NSCLC 细胞中 EPO-R mRNA 的剂量和时间依赖性表达。EPO-R 的敲低降低了缺氧下 NSCLC 细胞的生长（P<0.05）。在机制上，SP1-EGR1 重叠的 DNA 结合序列对于缺氧诱导的 EPO-R 转录是必不可少的。在缺氧的早期阶段，HIF1α 与 EGR1 相互作用，负调控 EPO-R。在后期，随着 EGR1 的退出，HIF1α 通过与 SP1 的附加相互作用正向调节 EPO-R 的表达。在临床 NSCLC 标本中，SP1 与活跃的 EPO-R 表达呈正相关，而 EGR1 呈负相关（P<0.05）。
HIF1α、SP1 和 EGR1 介导的 EPO-R 表达在缺氧诱导的 NSCLC 细胞增殖中起着重要作用。我们的研究提出了肿瘤细胞中 EPO-R 调节的新机制，可为 NSCLC 的诊断和治疗提供信息支持。
