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 （ATF5）在神经干/祖细胞中高表达，当这些细胞分化为神经元和星形胶质细胞时消失。外源性ATF5的过度表达维持神经干/祖细胞处于未分化状态。相反，通过过表达ATF5的显性阴性或通过小干扰RNA导致ATF5表达缺失，功能ATF5的丧失会加速神经元和胶质细胞的分化。ATF5在胶质母细胞瘤中高表达。在体外和体内实验中，显性负ATF5的表达促进神经肿瘤细胞的凋亡，但在非肿瘤细胞中没有作用。长期目标是确定由环境致癌物引起的脑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。我们建议：(1)在小鼠模型中创建类似生长因子扩增途径突变和DNA加合物遗传病变的脑肿瘤。(2)表明神经干/祖细胞组成性过表达由肿瘤转化引起的内源性ATF5。3)阻断ATF5功能可防止肿瘤发生，导致已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，我们将证实先前的工作，表明阻断ATF5促进非肿瘤干细胞/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/或限制营养需求导致细胞凋亡。我们希望这些开创性的实验将为针对ATF5的治疗干预提供未来的见解，以治疗脑肿瘤患者。公共卫生相关性：尽管在治疗癌症方面取得了持续成功，但在治疗神经肿瘤（如恶性胶质瘤）方面的进展有限。我们实验室最近的研究已经深入了解了增殖的神经干细胞/祖细胞成为成熟的神经元和胶质细胞的机制。其中一种方法是通过与DNA结合并开启或关闭基因的转录因子。我们发现一种这样的转录因子，称为ATF5，可以关闭导致增殖干细胞/祖细胞转变为神经元或神经胶质细胞的基因。我们的假设是，ATF5在脑干肿瘤细胞中被永久激活，这些细胞被指示继续分裂，不能转变为成熟的非分裂神经元或神经胶质细胞。我们发现，通过干扰ATF5的功能或将其从增殖的神经祖细胞中移除，后者可以停止或减缓细胞分裂，并能够转变为正常的神经元和胶质细胞。在胶质母细胞瘤脑肿瘤细胞模型系统中，我们发现干扰ATF5功能可导致肿瘤细胞死亡。因此，ATF5可能是治疗干预的潜在靶点，并可能成为脑癌的一种治疗方法。

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.