The Role of Non-C anonical Bax/Bak Direct Activators in Hematological Cancers

描述（由申请人提供）：肿瘤发生的一个重要组成部分是逃避程序性细胞死亡（也称为“凋亡”），这是肿瘤抑制的重要机制，因为逃避细胞凋亡是导致转移表型的六个获得性特性之一。逃避细胞凋亡抵消了不受控制的增殖，并可能导致化疗耐药性，因为许多化疗药物依赖于诱导细胞凋亡来杀死细胞。细胞凋亡，特别是线粒体内在通路，依赖于两个Bcl-2家族蛋白Bax和Bak。一旦被激活，Bax和Bak寡聚并产生线粒体外膜通透性，导致膜间空间蛋白释放到细胞质中，从而参与下游信号级联反应（如半胱天冬酶激活），导致细胞死亡。迄今为止，已知只有三种蛋白可以直接激活Bax和/或Bak: Bim、Bid和细胞质p53。然而，最近的遗传和生化数据表明，在缺乏这三种蛋白的情况下，线粒体凋亡可以正常进行，这表明存在Bax和Bak的其他“直接激活因子”。本提案的目标是识别和表征这些非规范的直接激活剂，并探索它们在血液学癌症中的作用。利用遗传学方法，我们将创建缺乏Bim， Bid和p53表达的细胞，以研究缺乏已知的Bax和Bak直接激活因子的细胞的凋亡反应。作为研究非规范直接激活剂的第二种方法，我们将从E？-myc小鼠缺乏Bim和Bid表达，以检验此类肿瘤是否含有功能性非规范直接激活因子。最后，作为第三种方法，我们将对可以作为直接激活剂的新型蛋白质进行大规模筛选。p53、Bim和Bid的缺失可促进癌变。因此，非规范直接激活剂的丧失可能也有助于癌症的进展。这些蛋白在血液恶性肿瘤中的特性将增强我们对癌变的认识，并为研究人员提供重要的新治疗靶点。

DESCRIPTION (provided by applicant): An important component of oncogenesis is the evasion of programmed cell death (also known as "apoptosis"), which is an essential mechanism of tumor suppression, as evasion of apoptosis is one of six acquired properties that result in a metastatic phenotype. Evasion of apoptosis offsets uncontrolled proliferation and can contribute to chemotherapeutic resistance, as many chemotherapeutic agents rely on induction of apoptosis in order to kill the cell. Apoptosis, and specifically the intrinsic mitochondrial pathway, relies on two Bcl-2 family proteins, Bax and Bak. Once activated, Bax and Bak oligomerize and produce mitochondrial outer membrane permeabilization, resulting in the release of intermembrane space proteins into the cytosol, thereby engaging downstream signaling cascades (such as caspase activation) that lead to the demise of the cell. To date, only three proteins are known to directly activate Bax and/or Bak: Bim, Bid and cytosolic p53. However, recent genetic and biochemical data suggest that mitochondrial apoptosis can proceed normally in the absence of these three proteins, indicating the existence of other "direct activators" of Bax and Bak. The goal of this proposal is to identify and characterize these non-canonical direct activators, and to explore their role in hematological cancers. Using genetic approaches, we will create cells that lack Bim, Bid and p53 expression in order to study the apoptotic response of cells lacking known direct activators of Bax and Bak. As a second approach to studying non-canonical direct activators, we will generate tumor cell lines from E?-myc mice lacking Bim and Bid expression, in order to examine whether such tumors contain functional non-canonical direct activators. Lastly, as a third approach, we will perform a large-scale screen for novel proteins that can act as direct activators. Loss of p53, Bim and Bid can contribute to carcinogenesis. It is therefore probable that loss of non-canonical direct activators can also contribute to cancer progression. Characterization of these proteins in hematological malignancies will enhance our knowledge of carcinogenesis, and provide researchers with important new therapeutic targets. Relevance: Cancer cells persist, in part, because they find ways to evade cell death, often through reducing expression of molecules that promote cell death, such as the proteins Bax and Bak and their activators, Bim, Bid and cytosolic p53. Recent genetic and biochemical evidence suggests proteins other than Bim, Bid and cytosolic p53 may exist, and if they do, they are likely dysregulated in cancer cells. Identifying and characterizing these non-canonical direct Bax/Bak activators and exploring their role in carcinogenesis will enhance our knowledge of carcinogenesis, and provide researchers with important new therapeutic targets.