NOR1调节wnt/β-catenin-ALDH1A1环路抑制鼻咽癌干性维持的作用和机制

Cancer stem-like cells (CSCs) or tumor initial cells(TICs) play a central role in the pathogenesis of malignancies including nasopharyngeal carcinoma(NPC) and contribute to both disease initiation and relapse. Over the past decade, increasing evidences have confirmed that CSCs are responsible for cancer metastasis,chemoradioresistance,radioresistance and recurrence. At present, the molecular mechanism of stemness maintenance in NPC is not fully understood. NOR1 is a novel tumor suppressor gene cloned by our lab and is down-regulated in nasopharyngeal carcinoma(NPC). We found the CSCs marker ALDH1A1 expression level and ALDH1 activity decreased in NOR1 expressing NPC cells, follwed by decreased cancer stem-like cell properties of NPC cells such as decreased tumor spheroids formation ability, less tumorigenecity in nude mice but increased sensitivity to chemotherapy agents. We also found activation of wnt/β-catenin signaling pathway induced ALDH1A1 expression and ALDH1 activity in NPC cells, while knockdown of ALDH1A1 also decreased β-catenin protein level, suggesting there was a wnt/β-catenin-ALDH1A1 feedback circuit in NPC cells. Over-experssion of NOR1 also decreased β-catenin protein level and its nuclear translocation.Thus, we hypothyze that NOR1 may suppression ALDH1A1 expression and cancer stem-like cell properties of NPC cells through inhibition of wnt/β-catenin signaling activation. In this project, we like to furtehr study the molecular mechanism and clinical value of NOR1/wnt/β-catenin/ALDH1A1 axis on NPC CSCs/TICs or stemness maintenance.

肿瘤干细胞样细胞/肿瘤起始细胞在肿瘤发生、演进和复发中具有关键作用。研究证实鼻咽癌（NPC)中存在肿瘤干细胞样细胞，然而对其干性维持机制的认识却十分有限。NOR1是申请人课题组自主克隆的抑瘤基因。申请人前期发现NOR1抑制了肿瘤干细胞标志分子ALDH1A1表达和干性生物学行为，同时发现NPC细胞中wnt/β-catenin通路与ALDH1A 1构成环路相互调节；稳定表达NOR1引起β-catenin蛋白下调、入核减少。据此提出NOR1可能通过影响wnt/β-catenin-ALDH1A1环路，从而抑制NPC干性生物学行为。本项目拟进一步深入研究NOR1在鼻咽癌干性行为中的作用，探讨NOR1是否通过影响wnt/β-catenin-ALDH1A1环路，抑制鼻咽癌干性生物学行为；检测NOR1、wnt/β-catenin-ALDH1A1环路分子在鼻咽癌干细胞和组织中的表达，并分析其临床意义。

肿瘤干细胞或肿瘤起始细胞是具有自我更新能力的肿瘤细胞亚群，被认为是恶性肿瘤的发生、演进、放化疗抵抗和肿瘤复发、转移的元凶。关于鼻咽癌肿瘤干细胞起源和干性维持的机制并不明确。在本研究中，我们聚焦于自主克隆的抑瘤基因NOR1在鼻咽癌干性维持中的作用和分子机制。首先我们发现Wnt/ β-catenin信号通路与肿瘤干细胞标志分子ALDH1A1存在调控环路。Wnt/β-catenin信号活化，促进TCF4结合ALDH1A1启动子，上调其表达，提高ALDH1活性。ALDH1A1高表达，激活Akt通路，抑制了GSK-3β活化，提高β-catenin蛋白稳定性。我们发现NOR1稳定表达下调了β-catenin和ALDH1A1蛋白水平，引起鼻咽癌ALDH1活性和干细胞标志分子表达水平下降，抑制了鼻咽癌细胞的成球能力，导致致瘤性细胞数量显著减少，提高了化疗敏感性。在机制上，NOR1是通过引起wnt受体LRP6下调，抑制了wnt1、wnt3a刺激引起的β-catenin蛋白增加。NOR1是通过促进β-catenin蛋白的降解，而不是影响它的转录水平，来抑制β-catenin的表达。在NOR1高表达的细胞中转染组成性活化的β-catenin 突变体，可以恢复ALDH1A1表达和ALDH1活性，并上调上皮-间质变转录因子Slug表达，引起鼻咽癌细胞恶性表型得以恢复。鼻咽癌组织中β-catenin、ALDH1A1蛋白表达上调，二者呈正相关；而NOR1 mRNA表达降低，LRP6 mRNA表达增高，二者存在负相关。本研究揭示了抑瘤基因NOR1通过抑制wnt/β-catenin-ALDH1A1调节环路，抑制鼻咽癌干细胞特性的作用和分子机制。项目发表SCI收录论文14篇，获得国家发明专利授权3项。通过项目研究，培养毕业博士研究生3名，硕士研究生3名。获得2016年度湖南省优秀博士学位论文和2017年中南大学优秀学术论文各1人次。

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