Wang Lili, Chang Xixi, Feng Jinli, Yu Jiyun, Chen Guozhu
Institute of Military Cognition and Brain Sciences, Academy of Military Medical Sciences, Beijing, China.
Department of Neurology, The Eighth Medical Center of Chinese PLA General Hospital, Beijing, China.
Front Cell Dev Biol. 2020 Jan 22;7:393. doi: 10.3389/fcell.2019.00393. eCollection 2019.
As a programmed necrotic cell death, necroptosis has the intrinsic initiators, including receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like protein (MLKL), which combine to form necroptotic signaling pathway and mediate necroptosis induced by various necroptotic stimuli, such as tumor necrosis factor (TNF). Although chemical inhibition of RIPK1 blocks TNF-induced necroptosis, genetic elimination of RIPK1 does not suppress but facilitate necroptosis triggered by TNF. Moreover, RIPK3 has been reported to mediate the RIPK1-independent necroptosis, but the involved mechanism is unclear. In this study, we found that TRADD was essential for TNF-induced necroptosis in RIPK1-knockdown L929 and HT-22 cells. Mechanistic study demonstrated that TRADD bound RIPK3 to form new protein complex, which then promoted RIPK3 phosphorylation via facilitating RIPK3 oligomerization, leading to RIPK3-MLKL signaling pathway activation. Therefore, TRADD acted as a partner of RIPK3 to initiate necroptosis in RIPK1-knockdown L929 and HT-22 cells in response to TNF stimulation. In addition, TRADD was critical for the accumulation of reactive oxygen species (ROS), which contributed to RIPK1-independent necroptosis triggered by TNF. Collectively, our data demonstrate that TRADD acts as the new target protein for TNF-induced RIPK3 activation and the subsequent necroptosis in a RIPK1-independent manner.
作为一种程序性坏死性细胞死亡，坏死性凋亡具有内在的启动因子，包括受体相互作用丝氨酸/苏氨酸蛋白激酶1（RIPK1）、RIPK3和混合谱系激酶结构域样蛋白（MLKL），它们结合形成坏死性凋亡信号通路，并介导由各种坏死性凋亡刺激物（如肿瘤坏死因子（TNF））诱导的坏死性凋亡。虽然对RIPK1的化学抑制可阻断TNF诱导的坏死性凋亡，但RIPK1的基因敲除并不能抑制反而促进了TNF触发的坏死性凋亡。此外，据报道RIPK3介导不依赖RIPK1的坏死性凋亡，但其涉及的机制尚不清楚。在本研究中，我们发现TRADD对于TNF诱导的RIPK1敲低的L929和HT-22细胞中的坏死性凋亡至关重要。机制研究表明，TRADD与RIPK3结合形成新的蛋白质复合物，然后通过促进RIPK3寡聚化来促进RIPK3磷酸化，导致RIPK3-MLKL信号通路激活。因此，在TNF刺激下，TRADD作为RIPK3的伙伴在RIPK1敲低的L929和HT-22细胞中启动坏死性凋亡。此外，TRADD对于活性氧（ROS）的积累至关重要，ROS促成了TNF触发的不依赖RIPK1的坏死性凋亡。总的来说，我们的数据表明，TRADD作为TNF诱导的RIPK3激活以及随后以不依赖RIPK1的方式发生的坏死性凋亡的新靶蛋白。
