骨分化相关基因Nell-1调控肿瘤干细胞分化的分子机制研究

Cancer stem cells have recently been identified in many types of cancer and has been found to play an important role in cancer initiation, development ，drug resistance and recurrence. To uncover the mechanisms by which cancer stem cells sustain their stemness and know how to induce them differentiation and decrease drug resistance has become a critical scientific issue in attempts to develop a therapy to induce cancer stem cell differentiation and reverse their drug resistance. In our previous studies published in Molecular Cancer and Stem Cells, we demonstrated that CD133-positive cancer stem cells derived from malignant glioma present significant resistance to chemotherapy.Our recent pilot study found that Nell-1, a novel growth factor believed to promote osteoblast differentiation，is not expressed or exhibits a very low expression in malignant glioma tissue. We also found that over-expressing Nell-1 by plasmid transfection on glioma cancer stem cells induces differentiation, decreases CD133 expression and increase its sensitivity to chemotherapy drugs, which suggests Nell-1 plays a crucial role in cancer stem cell differentiation and decrease of its drug resistance, although further investigation is required to determine the mechanism involved. Based on our previous results, in this project we will explore the molecular mechanism and clarify the related signal pathway by which Nell-1 induces cancer stem cell differentiation and effects of drug resistance through a series of experiments, including studies using an in vivo animal model, as well as in vitro cell biology and molecular expression analysis using overexpression, RNAi, tissue array, FACS and living imaging technology. Our study should provide evidence to further understanding of the molecular mechanisms by which Nell-1 induces cancer stem cell differentiation, decreases drug resistance. Our goal is to contribute to the development of a novel therapy that can selectively target cancer stem cells.

肿瘤干细胞目前已在多种癌症中发现，并证实参与肿瘤发生、发展、耐药与复发，故如何调控和诱导肿瘤干细胞分化，降低耐药已成为针对肿瘤干细胞靶向治疗中的关键科学问题之一。申请人发在Molecular Cancer与Stem Cells杂志上的研究结果表明CD133+胶质瘤干细胞参与耐药。本课题组前期实验发现：1）骨分化相关基因Nell-1在胶质瘤组织中低表达或不表达；2）在胶质瘤干细胞中过表达Nell-1，促进干细胞分化，降低CD133表达并提高对化疗药物的敏感性，提示Nell-1可能参与肿瘤干细胞分化，但调控功能与分子机制需深入探索。为此，在前期基础上项目拟用过表达、RNAi、组织芯片、FACS、活体成像等技术从分子、细胞与动物水平研究Nell-1诱导肿瘤干细胞分化的功能及临床意义，阐明Nell-1调控肿瘤干细胞分化的分子机制，为今后临床上开展肿瘤干细胞靶向分化治疗提供依据。

肿瘤干细胞被认为是导致肿瘤发生、发展、耐药、复发与转移的元凶，如何调控肿瘤干细胞分化、降低耐药，特异性地针对肿瘤干细胞开展靶向治疗是当前急需解决的一个重大科学问题。基于Nell-1具有促进成骨细胞分化及抑癌的双重功能，本项目提出如下科学假设：Nell-1具有诱导肿瘤干细胞分化并降低其耐药性的生物学功能。我们开展了以下四个方面的研究，对这一假设进行验证：1）在脑胶质瘤干细胞中过表达Nell-1蛋白，探讨其在肿瘤干细胞分化中的功能；2）分析Nell-1对肿瘤干细胞耐药表型的作用；3）利用动物模型研究Nell-1对肿瘤干细胞在体内分化的作用；4）检测脑神经胶质瘤组织样品中Nell-1的表达，分析其临床意义。通过这一系列的研究，我们在分子、细胞和动物水平确认了Nell-1具有诱导肿瘤干细胞分化的生物学功能，抑制其在模型动物体内的成瘤，并降低其对化疗药物的耐药性；同时我们结合临床肿瘤标本的分析，证实了Nell-1的表达与神经胶质瘤临床参数存在相关性，表达Nell-1的脑胶质瘤患者具有更长的生存期。本项目所取得的结果将加深我们对Nell-1在肿瘤干细胞中作用的认识，为肿瘤干细胞的靶向性分化治疗提供一定的理论基础和实验依据。