Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ, United States.
Graduate Program in Cellular and Molecular Pharmacology, Rutgers University, Piscataway, NJ, United States.
Front Immunol. 2021 Oct 20;12:670338. doi: 10.3389/fimmu.2021.670338. eCollection 2021.
Proteins controlling mitochondrial fission have been recognized as essential regulators of mitochondrial functions, mitochondrial quality control and cell apoptosis. In the present study, we identified the critical B cell survival regulator TRAF3 as a novel binding partner of the key mitochondrial fission factor, MFF, in B lymphocytes. Elicited by our unexpected finding that the majority of cytoplasmic TRAF3 proteins were localized at the mitochondria in resting splenic B cells after culture for 2 days, we found that TRAF3 specifically interacted with MFF as demonstrated by co-immunoprecipitation and GST pull-down assays. We further found that in the absence of stimulation, increased protein levels of mitochondrial TRAF3 were associated with altered mitochondrial morphology, decreased mitochondrial respiration, increased mitochondrial ROS production and membrane permeabilization, which eventually culminated in mitochondria-dependent apoptosis in resting B cells. Loss of TRAF3 had the opposite effects on the morphology and function of mitochondria as well as mitochondria-dependent apoptosis in resting B cells. Interestingly, co-expression of TRAF3 and MFF resulted in decreased phosphorylation and ubiquitination of MFF as well as decreased ubiquitination of TRAF3. Moreover, lentivirus-mediated overexpression of MFF restored mitochondria-dependent apoptosis in TRAF3-deficient malignant B cells. Taken together, our findings provide novel insights into the apoptosis-inducing mechanisms of TRAF3 in B cells: as a result of survival factor deprivation or under other types of stress, TRAF3 is mobilized to the mitochondria through its interaction with MFF, where it triggers mitochondria-dependent apoptosis. This new role of TRAF3 in controlling mitochondrial homeostasis might have key implications in TRAF3-mediated regulation of B cell transformation in different cellular contexts. Our findings also suggest that mitochondrial fission is an actionable therapeutic target in human B cell malignancies, including those with deletion or relevant mutations.
调控线粒体裂变的蛋白质已被认为是线粒体功能、线粒体质量控制和细胞凋亡的重要调节因子。在本研究中，我们鉴定出关键的 B 细胞存活调节剂 TRAF3 是 B 淋巴细胞中线粒体分裂关键因子 MFF 的新结合伴侣。在培养 2 天后，我们发现大多数细胞质 TRAF3 蛋白在静止的脾 B 细胞中位于线粒体，这一意外发现促使我们进行了研究，结果显示，TRAF3 通过免疫共沉淀和 GST 下拉实验特异性与 MFF 相互作用。我们进一步发现，在没有刺激的情况下，线粒体 TRAF3 蛋白水平的增加与线粒体形态的改变、线粒体呼吸的减少、线粒体 ROS 产生的增加和膜通透性的增加有关，最终导致静止 B 细胞中线粒体依赖性凋亡。TRAF3 的缺失对静止 B 细胞中线粒体的形态和功能以及线粒体依赖性凋亡具有相反的影响。有趣的是，TRAF3 和 MFF 的共表达导致 MFF 的磷酸化和泛素化减少以及 TRAF3 的泛素化减少。此外，慢病毒介导的 MFF 过表达恢复了 TRAF3 缺陷恶性 B 细胞中线粒体依赖性凋亡。总之，我们的研究结果为 TRAF3 在 B 细胞中诱导凋亡的机制提供了新的见解：由于生存因子的缺乏或其他类型的应激，TRAF3 通过与 MFF 的相互作用被募集到线粒体，在那里它触发线粒体依赖性凋亡。TRAF3 在控制线粒体动态平衡方面的这一新作用可能对 TRAF3 在不同细胞环境中调节 B 细胞转化具有关键意义。我们的研究结果还表明，线粒体裂变是人类 B 细胞恶性肿瘤的一个可行的治疗靶点，包括缺失或相关突变的肿瘤。
