The 26S Proteasome in Cancer Stem Cells

描述（由申请人提供）： 最近的数据表明，大多数（如果不是全部的话）实体癌具有分级结构，并且含有少量的癌症干细胞或癌症起始细胞（CIC）。只有这个群体具有自我更新和重新填充肿瘤的能力，而它们的后代缺乏这种能力。因此，癌症治愈需要消除所有CIC。最近已经基于表面标志物谱在脑肿瘤、乳腺癌、前列腺癌、结肠癌、胰腺癌、头颈癌和黑色素瘤中前瞻性地鉴定了富含CIC的细胞群。然而，到目前为止，还没有发现唯一区分个体CIC的标志物。在我们的初步数据中，我们报告了CIC和非CIC之间的根本差异的发现，即CIC几乎没有26S蛋白酶体活性。我们发现这使用一个报告基因系统，目标ZsGreen蛋白降解特异性通过26 S蛋白酶体凭借添加一个羧基末端降解决定子的鸟氨酸脱羧酶。我们已经使用该系统来跟踪胶质母细胞瘤细胞系中的CIC，并研究它们对体外和体内癌症治疗的反应。此外，我们已经使用相同的降解决定子去稳定胸苷激酶，并使用更昔洛韦靶向它，从而消除胶质母细胞瘤细胞群中的CIC。我们假设CIC和非CIC之间蛋白酶体活性的这种根本差异有助于CIC对已建立的治疗方式的相对抗性，并且靶向低26S蛋白酶体活性可用于治疗癌块内最相关和最重要的细胞亚群。在这个项目中，我们将进一步描述胶质母细胞瘤中CIC的低蛋白酶体活性及其与其他干细胞标志物表达的关系。我们将研究导致CIC中26S蛋白酶体功能低下的机制，以及这是否与表达的蛋白酶体类型有关。我们将研究蛋白酶体活性低与辐射抗性之间的功能关系。最后，我们将探讨潜在的机制，我们将修改相关的途径，以增加蛋白酶体活性和辐射敏感性。 公共卫生相关性： 癌症干细胞对常规抗癌疗法具有相对抗性，并且被认为是肿瘤中唯一导致大多数治疗失败的细胞。目前，肿瘤必须被切除和分解以检测癌症干细胞。该提案利用癌症干细胞的一种新特征，使它们在活体动物中可见，研究其潜在机制，并应用这一特征来了解这些细胞对放射等癌症治疗的抵抗力。

DESCRIPTION (provided by applicant): Recent data indicate that most, if not all, solid cancers have a hierarchical structure and contain a small number of cancer stem or cancer initiating cells (CICs). Only this population has the ability to self-renew and to repopulate a tumor while their progeny lack this ability. Elimination of all CICs will therefore be required for cancer cure. Cell populations enriched for CICs have been recently prospectively identified in brain tumors, breast cancer, prostate cancer, colon cancer, pancreatic cancer, cancer of the head and neck, and melanoma based on surface marker profiles. However, so far no marker has been found that uniquely distinguishes individual CICs. In our preliminary data, we report the discovery of a fundamental difference between CICs and non-CICs, namely that CICs have little if any 26S proteasome activity. We discovered this using a reporter gene system that targets the ZsGreen protein for degradation specifically through the 26S proteasome by virtue of the addition of a carboxy-terminal degron of ornithine decarboxylase. We have used this system to trace CICs in glioblastoma cell lines and to study their response to cancer treatment in vitro and in vivo. Furthermore, we have used the same degron to destabilize thymidine kinase and to target it using ganciclovir, in so doing eliminating CICs from glioblastoma cell populations. We hypothesize that this fundamental difference in proteasome activity between CICs and non-CICs contributes to the relative resistance of CICs against established therapy modalities and that targeting low 26S proteasome activity can be utilized to treat the most relevant and important subpopulation of cells within a cancer mass. In this project, we will further characterize CICs in glioblastoma with respect to low proteasome activity and how it relates to expression of other stem cell markers. We will investigate the mechanisms that lead to low 26S proteasome function in CICs and whether this is associated with the type of proteasomes that are expressed. We will investigate the functional relationship between low proteasome activity and radiation resistance. Finally, we will explore the underlying mechanisms and we will modify the involved pathways in order to increase proteasome activity and radiation sensitivity. PUBLIC HEALTH RELEVANCE: Cancer stem cells are relatively resistant to conventional anti-cancer therapies and are believed to be the only cells in a tumor responsible for most treatment failures. Currently, tumors have to be explanted and disintegrated to detect cancer stem cells. This proposal uses a novel feature of cancer stem cells to make them visible in living animals, investigates the underlying mechanisms, and applies this feature to understand the resistance of these cells to cancer therapies like radiation.