Elimination of Carcinogen-Induced Tumor Stem Cells by ATF5 Loss of Function.

描述（由申请人提供）：激活转录因子5（ATF 5）在神经干/祖细胞中高度表达，当这些细胞分化为神经元和星形胶质细胞时消失。外源性ATF 5的过表达可维持神经干/祖细胞处于未分化状态。相比之下，通过过表达其显性负性或通过小干扰RNA丧失ATF 5表达而实现的功能性ATF 5的丧失加速神经元和神经胶质分化。ATF 5的高表达发生在胶质母细胞瘤肿瘤中。显性负性ATF 5的表达促进神经肿瘤的凋亡，但在体外和体内的非肿瘤细胞。长期目标是确定由环境致癌物引起的脑肿瘤是否促进神经干细胞向肿瘤干细胞的转化，从而支持肿瘤的生长。我们提出：（1）在小鼠模型中建立类似于生长因子扩增途径突变和DNA加合物遗传病变的脑肿瘤。(2)显示神经干细胞/祖细胞组成型过表达内源性ATF 5，导致肿瘤转化。3)ATF 5功能的阻断防止肿瘤，并导致预先存在的神经肿瘤细胞及其肿瘤干细胞的细胞死亡，但保留同一脑内的非肿瘤细胞。(4)最后，我们将证实以前的工作，以表明阻断ATF 5促进非肿瘤干/祖细胞的细胞周期退出，但肿瘤转化通过禁止细胞周期退出和/或限制营养需求而导致细胞凋亡。我们希望这些先驱实验将为靶向ATF 5治疗患者脑肿瘤的治疗干预提供未来的见解。公共卫生相关性：尽管在治疗癌症方面取得了持续的成功，但在治愈神经肿瘤如恶性神经胶质瘤方面仅取得了有限的进展。本实验室最近的研究对增殖的神经干/祖细胞成为成熟神经元和胶质细胞的机制有了深入的了解。其中一种方法是通过与DNA结合并打开或关闭基因的转录因子。我们发现，一个这样的转录因子，命名为ATF 5，关闭基因，将导致增殖干/祖细胞变成神经元或神经胶质。我们的假设是，ATF 5在脑干肿瘤细胞中被永久打开，并且这些细胞被指示继续分裂，并且无法变成成熟的非分裂神经元或神经胶质细胞。我们发现，通过干扰ATF 5的功能或将其从增殖的神经祖细胞中去除，后者停止或减缓细胞分裂，并能够转变为正常的神经元和神经胶质。在胶质母细胞瘤脑肿瘤细胞模型系统中，我们发现干扰ATF 5功能会导致肿瘤细胞死亡。因此，ATF 5可能是治疗干预的潜在靶点，也可能是脑癌的治疗方法。

DESCRIPTION (provided by applicant): Activating transcription factor 5 (ATF5) is highly expressed in neural stem/progenitor cells, and disappears when these cells differentiate into neurons and astrocytes. Over expression of exogenous ATF5 maintains neural stem/progenitor cells in their undifferentiated state. By contrast, loss of functional ATF5, achieved through overexpression of its dominant negative or loss of ATF5 expression by small interfering RNA, accelerates neuronal and glial differentiation. High expression of ATF5 occurs in glioblastoma tumors. Expression of dominant negative ATF5 promotes apoptosis in neural tumors, but not in non-neoplastic cells both in vitro and in vivo. Long-term objectives are to determine whether brain neoplasm, arising from environmental carcinogens, promotes transformations of neural stem cells to tumor stem cells that in turn support the growth of tumors. We propose: (1) To create brain tumors in mouse models that resemble mutations of a growth factor amplified pathway and DNA- adduct genetic lesions. (2) Show that neural stem/progenitors constitutively overexpress endogenous ATF5 resulting from neoplastic conversion. 3) Blockage of ATF5 function prevents neoplasm, and leads to cell death of pre- existing neural tumor cells and their tumor stem cells, but spares non-neoplastic cells within the same brain. (4) Finally, we will substantiate previous work to show that blocked ATF5 promotes cell cycle exit in non-neoplastic stem/ progenitor cells, but neoplasm conversion globally leads to apoptosis through prohibited cell cycle exit and/or restriction in nutrient requirements. We hope these pioneer experiments will provide future insight for therapeutic intervention aimed at targeting ATF5 to treat brain tumors in patients. PUBLIC HEALTH RELEVANCE: Despite the continuing success in treatment of cancer, there has been only limited advancement in curing neural tumors such as malignant gliomas. Recent research in our laboratory has gained insight on the mechanism by which proliferating neural stem/progenitor cells become mature neurons and glia. One of the ways is through transcription factors that bind to DNA and turn on or off genes. We found that one such transcription factor, designated ATF5, turns off genes that would lead a proliferating stem/progenitor cell to turn into either a neuron or glia. Our hypothesis is that ATF5 is permanently turned on in brain stem tumor cells and that these cells are instructed to continue to divide, and are unable to change into mature non-dividing neurons or glial cells. We found that by interfering with the function of ATF5 or by removing it from proliferating neural progenitor cells, the latter cease or slow down cell division, and are able to turn into normal neurons and glia. In a glioblastoma brain tumor cell model system, we found that interference with ATF5 function causes death of the tumor cells. Thus, ATF5 may be a potential target for therapeutic intervention and a possible treatment for brain cancer.