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稳态的发展和维持中起着重要作用。细胞凋亡受损不仅是癌症发展的核心，而且还使肿瘤对细胞毒治疗产生耐药性。 BCL-2 家族蛋白由抗凋亡和促凋亡成员组成，构成细胞死亡途径中的关键检查点。我们之前的研究帮助描绘了哺乳动物的核心细胞凋亡途径。仅 BH3 的分子激活多域促凋亡 BAX 和 BAK，释放细胞色素 c 以激活 caspase，并引发不依赖 caspase 的线粒体功能障碍。相反，抗凋亡 BCL-2/BCL-XL 将 BH3-only 分子隔离成惰性复合物，从而防止 BAX 和 BAK 的激活。遗传学研究表明，促凋亡 BAX 和 BAK 的缺失会严重阻碍由包括癌症治疗在内的多种死亡信号触发的细胞凋亡。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然途径。然而，目前尚不清楚是否所有 BH3-only 分子都能够激活 BAX 和 BAK、BH3-only 分子如何激活 BAX 和 BAK、哪种 BH3-only 分子以及它如何被每个特定死亡信号激活以启动凋亡信号级联。新出现的证据表明，抗凋亡 BCL-2 成员被不同的 BH3-only 分子选择性失活，但单个 BH3-only 分子拮抗抗凋亡 BCL-2 成员的详细功能图谱仍然缺失。此外，抗凋亡 BCL-2 成员是否通过直接抑制 BAX/BAK 和/或仅隔离 BH3 分子来抑制凋亡仍存在争议。最后，确定如何在活细胞中控制 BAX 和 BAK 至关重要。它们是否受到抗凋亡 BCL-2 成员或其他相关蛋白（例如 VDAC2）的控制？为了解决这些问题，我们建议表征 BH3-only 分子，分配和识别单个 BH3-only 分子以整合凋亡信号级联和线粒体依赖性死亡程序，剖析 BH3-only 分子激活 BAX 和 BAK 的机制，并建立不同 BCL-2 亚家族之间差异调节的功能网络。我们的最终目标是将 BCL-2 家族控制死亡/生存决策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.