Apoptotic Network Integrated at the Mitochondrion

描述(由申请人提供)：细胞凋亡在多细胞生物体内动态平衡的发展和维持中起着至关重要的作用。细胞凋亡的损害不仅是癌症发展的中心，而且也使肿瘤对细胞毒治疗难以产生作用。Bcl-2家族蛋白由抗凋亡和促凋亡两种成员组成，构成了细胞死亡途径中的关键检查点。我们之前的研究已经帮助描绘了哺乳动物的核心凋亡途径。只有BH3的分子激活多结构域促凋亡的Bax和BAK，释放细胞色素c以激活caspase，并启动caspase非依赖性线粒体功能障碍。相反，抗凋亡的bcl2/bclxl仅将BH3分子隔离成惰性复合体，从而阻止Bax和BAK的激活。遗传学研究表明，缺乏促凋亡的Bax和BAK会对包括癌症治疗在内的多种死亡信号所引发的细胞凋亡产生深远的阻碍作用。因此，多域成员BAX或BAK的激活似乎是线粒体介导的细胞死亡程序的必由之路。然而，目前还不清楚是否所有的BH3-Only分子都能够激活Bax和BAK，BH3-Only分子是如何激活Bax和BAK的，以及哪个BH3-Only分子以及它是如何被每个特定的死亡信号激活来启动凋亡信号级联反应的。新的证据表明，抗凋亡的bcl-2成员被不同的BH3-only分子选择性地灭活，但单个BH3-only分子对抗抗凋亡的bcl2成员的详细功能图仍然缺乏。此外，抗凋亡的bcl-2成员是否通过直接抑制Bax/BAK和/或隔离BH3-Only分子来抑制细胞凋亡仍存在争议。最后，关键是要确定BAX和BAK在活细胞中是如何受到控制的。它们是被抗凋亡的bcl2成员抑或是其他相关蛋白如VDAC2所控制？为了解决这些问题，我们建议对BH3-Only分子进行表征，指定和识别BH3-Only分子，以整合凋亡信号级联和线粒体依赖的死亡程序，剖析BH3-Only分子激活Bax和BAK的机制，并在不同的bcl2亚家族之间建立一个差异调控的功能网络。我们的最终目标是将bcl2家族决定死亡/生存的机制转化为抗癌策略。

DESCRIPTION (provided by applicant): Apoptosis plays an essential role in the development and maintenance of homeostasis within multicellular organisms. Impairment of apoptosis is not only central to cancer development but also renders tumors refractory to cytotoxic therapy. The BCL-2 family proteins, consisting of both anti-apoptotic and proapoptotic members, constitute a crucial checkpoint in the cell death pathway. Our prior studies have helped delineate the core apoptotic pathway in mammals. The BH3-only molecules activate multidomain proapoptotic BAX and BAK to releases cytochrome c for caspase activation and initiate caspase-independent mitochondrial dysfunction. Conversely, anti-apoptotic BCL-2/BCL-XL sequesters BH3-only molecules into inert complexes, thus preventing the activation of BAX and BAK. Genetic studies revealed that absence of proapoptotic BAX and BAK creates a profound block in apoptosis triggered by diverse death signals including cancer therapeutics. Thus, activation of a multidomain member, BAX or BAK, appears to be an obligate gateway to the mitochondrion-mediated cell death program. However, it remains unclear whether all the BH3-only molecules are capable of activating BAX and BAK, how the BH3-only molecules activate BAX and BAK, and which BH3-only molecule and how it is activated by each specific death signal to initiate the apoptotic signaling cascade. Emerging evidence suggests that anti-apoptotic BCL-2 members are selectively inactivated by different BH3-only molecules, but detailed functional map of individual BH3-only molecules in antagonizing anti-apoptotic BCL-2 members is still missing. Moreover, it remains debated whether anti- apoptotic BCL-2 members inhibit apoptosis through direct inhibition of BAX/BAK and/or sequestration of BH3-only molecules. Finally, it is critical to determine how BAX and BAK are kept in check in viable cells. Are they kept in check by anti-apoptotic BCL-2 members or by other associated proteins such as VDAC2? To address these questions, we propose to characterize the BH3-only molecules, assign and identify individual BH3-only molecules to integrate apoptotic signaling cascades and mitochondrion-dependent death program, dissect the mechanisms by which BH3-only molecules activate BAX and BAK, and establish a functional network of differential regulation among various BCL-2 subfamilies. Our ultimate goal is to translate the mechanisms governing death/survival decision by BCL-2 family into anti-cancer strategies.