ATF2 Oncogenic Addiction in Melanoma

描述(由申请人提供)：鉴于癌基因成瘾在推动肿瘤发生中的作用，了解致癌基因成瘾的机制具有重要意义。这项提议聚焦于一项新的发现，借此我们揭示了癌基因成瘾的一种新机制。一个遗传的N-RAS/INK4A小鼠黑色素瘤模型证实了转录因子ATF2在黑色素瘤中的致癌作用。这是通过其结构性核定位实现的，其中ATF2作为转录因子和DNA损伤反应蛋白发挥作用。我们最近发现，ATF2的结构性核定位损害了该蛋白在胞浆中的一个新发现的功能。在细胞暴露于遗传毒性后，ATF2从细胞核输出，使其能够定位在线粒体外膜(MOM)，在那里它削弱MOM的电位并促进细胞凋亡。这个过程是新公布的ATF2促进细胞死亡的机制的基础。虽然ATF2的这种线粒体功能在大多数细胞类型中都能看到， 它在黑色素瘤中减弱或消失。此外，ATF2结合MOM的能力由PKC epsilon(PKC？)控制。黑色素瘤细胞表达高水平的PKC，有效地将ATF2锁定在细胞核内，阻止其在线粒体上的输出和功能。这些观察结果构成了我们假设的基础，即PKC？控制ATF2核输出构成了黑色素瘤致癌基因成瘾的新范例，因此为研究黑色素瘤发生和进展的未知途径提供了独特的机会，可用于开发创新的治疗方式。我们提议的研究旨在回答我们最近发现的ATF2对PKC上瘾的关键问题，使用细胞生物学和新的相关遗传小鼠黑色素瘤模型。我们将解决的主要问题包括：在黑色素瘤中PKC上调的基础是什么，ATF2‘S肿瘤抑制活性的意义以及致癌ATF2活性的潜在机制。我们将建立条件性ATF2敲入小鼠，这将使我们能够分别定义ATF2的致癌和肿瘤抑制功能。最后，我们将使用已经建立的高含量筛查来鉴定促进黑色素瘤细胞ATF2核输出的天然化合物，从而为黑色素瘤提供一种新的治疗方式。

DESCRIPTION (provided by applicant): Understanding the mechanism underlying oncogene addiction is of major importance given their role in driving tumorigenesis. This proposal focuses on a new discovery, whereby we reveal a novel mechanism for oncogene addiction. A genetic N-RAS/Ink4a mouse melanoma model established the oncogenic role of the transcription factor ATF2 in melanoma. This is achieved through its constitutive nuclear localization, where ATF2 is active as a transcription factor and DNA damage response protein. We recently discovered that constitutive nuclear localization of ATF2 impairs a newly identified function for this protein in te cytosol. Following exposure of cells to genotoxic, ATF2 is exported from the nucleus to enable its localization at the mitochondrial outer membrane (MOM), where it impairs MOM potential and augments apoptosis. This process underlies a newly disclosed mechanism by which ATF2 contributes to cell death. Although this mitochondrial function of ATF2 is seen in most cell types, it is attenuated or lost in melanoma. Moreover, the ability of ATF2 to localize to the MOM is controlled by PKC epsilon (PKC¿). Melanoma cells express high levels of PKC¿, which effectively locks ATF2 in the nucleus and prevents its export and function at the mitochondria. These observations form the basis for our hypothesis that PKC¿ control of ATF2 nuclear export constitutes a novel paradigm for oncogene addiction in melanoma, and therefore offers unique opportunities for studying unrecognized pathways underlying melanoma development & progression, which can be exploited for development of innovative therapeutic modalities. Our proposed studies are designed to answer key questions that emerge from our recent discovery of ATF2 addiction to PKC¿, using cell biology, and new relevant genetic mouse melanoma models. Among the cardinal questions we will address are: what underlies PKC¿ upregulation in melanoma, the significance of ATF2's tumor suppressor activities and the mechanisms underlying oncogenic ATF2 activity. We will establish conditional ATF2 knock-in mice, which will allow us to define oncogenic and tumor suppressor functions of ATF2, respectively. Lastly, we will use a high- content screen, already established, to identify natural compounds that promote nuclear export of ATF2 in melanoma cells, thereby offering a novel therapeutic modality for melanoma.