The ARF Tumor Suppressor

描述（由申请人提供）：ARF肿瘤抑制蛋白由Ink4a/ARF基因编码，该基因是人类癌症中第二常发生突变的基因位点。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。我们最近发现了一种新的ARF存活功能，这种功能存在于p53突变/缺失的肿瘤亚群中。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，促进细胞在营养缺乏的情况下存活。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来生存。与这一事实相一致，自噬抑制剂已显示出抗癌药物的前景。我们发现，在营养剥夺的情况下，ARF蛋白明显上调。我们发现沉默ARF会阻碍自噬并降低营养缺乏细胞的存活率。最后，我们发现在淋巴瘤中沉默ARF会损害自噬和生存，实际上会阻碍这些肿瘤的发展。该建议的中心假设是，arf介导的自噬被p53突变的肿瘤亚群利用，使它们能够在代谢应激发作时存活下来。我们认为，对自噬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。我们将确定营养剥夺如何导致ARF蛋白水平升高。我们发现ARF表达对某些肿瘤（淋巴瘤）有益，但对其他肿瘤（肉瘤）无益；我们将定义受益于arf介导的自噬的肿瘤亚群。我们将确定自噬的关键介质，如ARF和Beclin1，是否指示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对ARF基因座的转录抑制机制，因为这导致p53突变肿瘤中ARF的上调。这些综合数据将为开发自噬途径用于癌症治疗提供必要的基础。

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.