BCL-2 family proteins regulate apoptosis by initiating mitochondrial outer membrane permeabilization (MOMP). Activation of the MOMP effectors BAX and BAK is controlled by the interplay of anti-apoptotic BCL-2 proteins (e.g., MCL-1) and pro-apoptotic BH3-only proteins (e.g., BIM). Using a genome-wide CRISPR-dCas9 transactivation screen we identified BNIP5 as an inhibitor of BAK-, but not BAX-induced apoptosis. BNIP5 blocked BAK activation in different cell types and in response to various cytotoxic therapies. The BH3 domain of BNIP5 was both necessary and sufficient to block BAK activation. Mechanistically, the BH3 domain of BNIP5 acts as a selective BAK activator, but a poor de-repressor of complexes between BAK and pro-survival BCL-2 family proteins. By promoting the binding of activated BAK to MCL-1 or BCL-xL, BNIP5 inhibits apoptosis when BAX is absent. Based on our observations, BNIP5 can act functionally as an anti-apoptotic BH3-only protein.

BCL-2 家族蛋白通过启动线粒体外膜透化 （MOMP） 来调节细胞凋亡。MOMP 效应子 BAX 和 BAK 的激活受抗凋亡 BCL-2 蛋白（例如 MCL-1）和促凋亡 BH3 蛋白（例如 BIM）的相互作用控制。使用全基因组 CRISPR-dCas9 反式激活筛选，我们确定 BNIP5 是 BAK- 的抑制剂，而不是 BAX 诱导的细胞凋亡的抑制剂。BNIP5 阻断了不同细胞类型中的 BAK 活化以及对各种细胞毒性疗法的反应。BNIP5 的 BH3 结构域对于阻断 BAK 激活既必要又足够。从机制上讲，BNIP5 的 BH3 结构域充当选择性 BAK 激活剂，但对 BAK 和促存活 BCL-2 家族蛋白之间复合物的去抑制作用较差。通过促进活化的 BAK 与 MCL-1 或 BCL-xL 的结合，BNIP5 在 BAX 缺失时抑制细胞凋亡。根据我们的观察，BNIP5 在功能上可以作为一种仅抗凋亡的 BH3 蛋白发挥作用。