The ARF Tumor Suppressor

描述（由申请人提供）：ARF肿瘤抑制蛋白由Ink 4a/ARF基因编码，Ink 4a/ARF基因是人类癌症中第二个最常突变的遗传基因座。迄今为止，大多数关于ARF的研究都集中在其肿瘤抑制功能上。这项建议的重点是我们最近发现的ARF的一种新的生存功能，并且存在于突变/无效p53的肿瘤子集中。我们发现，ARF在饥饿诱导的自噬中起着不可或缺的作用。自噬是一种自我分解代谢过程，它促进了暴露于营养剥夺的细胞的存活。由于肿瘤细胞存在于独特的代谢应激条件下，许多肿瘤细胞严重依赖这一途径生存。与这一事实相一致，自噬抑制剂已显示出作为抗癌剂的前景。我们发现，ARF蛋白显着上调响应营养剥夺。我们发现，沉默ARF阻碍自噬，并降低营养缺乏细胞的存活率。最后，我们表明，沉默ARF在淋巴瘤损害自噬和生存，实际上阻碍了这些肿瘤的发展。该建议的中心假设是，ARF介导的自噬被具有突变p53的肿瘤子集利用，以使它们能够在代谢应激事件中存活。 我们认为，自噬的生存功能的要求是肿瘤的“阿喀琉斯之踵”。我们需要更好地了解这一途径，以便将其用于癌症治疗。在拟议的研究中，我们将阐明ARF诱导自噬的机制。我们将确定营养缺乏如何导致ARF蛋白水平增加。我们已经发现ARF表达对某些肿瘤（淋巴瘤）有益，但对其他肿瘤（肉瘤）无益;我们将定义ARF介导的自噬有益的肿瘤子集。我们将确定自噬的关键介质，如ARF和Beclin 1，是否决定肿瘤对调节这一过程的小分子的反应，如氯喹（抑制自噬）和海藻糖（诱导自噬）。最后，我们将阐明p53基因对ARF基因座的转录抑制机制，因为这导致了p53突变型肿瘤中ARF的上调。综合数据将作为利用自噬途径进行癌症治疗的必要基础。 公共卫生相关性：ARF基因由Ink 4a/ARF基因座编码，Ink 4a/ARF基因座是人类癌症中第二个最常见的突变基因座;高达50%的人类肿瘤含有Ink 4a/ARF突变。这一事实表明，旨在了解ARF在人类癌症中的基本功能的研究是必要的。我们表明，ARF控制肿瘤细胞的一个关键生存途径。我们相信ARF和自噬的需要可能是肿瘤细胞的致命弱点。这项研究旨在了解这一途径，并找到操纵这一途径来对抗癌症的方法。

DESCRIPTION (provided by applicant): The ARF tumor suppressor protein is encoded by the Ink4a/ARF gene, which is the second most frequently mutated genetic locus in human cancer. To date the majority of research on ARF has focused on its tumor suppressor functions. This proposal focuses instead on a novel survival function for ARF that we have recently uncovered, and that exists for a subset of tumors with mutant/null p53. We show that ARF plays an integral role in starvation-induced autophagy. Autophagy is a self-catabolic process that promotes the survival of cells exposed to nutrient deprivation. Because tumor cells exist under uniquely metabolically-stressed conditions, many rely heavily on this pathway in order to subsist. Consistent with this fact, autophagy inhibitors have shown promise as anti-cancer agents. We show that ARF protein is markedly up-regulated in response to nutrient deprivation. We show that silencing ARF impedes autophagy and decreases the survival of nutrient-deprived cells. Finally, we show that silencing ARF in lymphomas impairs autophagy and survival, and actually impedes the development of these tumors. The central hypothesis of this proposal is that ARF-mediated autophagy is utilized by a subset of tumors with mutant p53 to allow them to survive episodes of metabolic stress. We contend that the requirement for the survival function of autophagy is an 'Achilles heel' for tumors. We need to better understand this pathway in order to exploit it for cancer therapy. In proposed research we will elucidate the mechanism(s) whereby ARF induces autophagy. We will determine how nutrient deprivation leads to increased ARF protein levels. We have found that ARF expression is beneficial for some tumors (lymphoma) but not others (sarcoma); we will define the subset of tumors that are benefited by ARF-mediated autophagy. We will determine whether critical mediators of autophagy, such as ARF and Beclin1, dictate tumor response to small molecules that modulate this process, such as chloroquine (inhibits autophagy), and trehalose (induces autophagy). Finally we will elucidate the mechanism of transcriptional repression of the ARF locus by p53, as this leads to ARF up-regulation in p53-mutant tumors. The combined data will serve as a necessary foundation for exploiting the pathway of autophagy for cancer therapy. PUBLIC HEALTH RELEVANCE: The ARF gene is encoded by the Ink4a/ARF locus, which is the second most commonly mutated genetic locus in human cancer; up to 50% of human tumors contain mutations in Ink4a/ARF. This fact argues that research aimed at understanding the basic function of ARF in human cancer is warranted. We show that ARF controls a key survival pathway for tumor cells. We believe that the requirement for ARF and autophagy may be an Achilles Heel for tumor cells. This research is aimed at understanding this pathway, and at finding ways to manipulate this pathway to combat cancer.