Department of Gastroenterology, The 983rd Hospital of Chinese PLA Joint Logistics Support Force, Tianjin 300142, China.
Institute of Military Cognition and Brain Sciences, Academy of Military Medical Sciences, Beijing 100850, China.
Cytokine. 2020 May;129:155046. doi: 10.1016/j.cyto.2020.155046. Epub 2020 Feb 28.
Necroptosis is a recently identified programmed cell death, which is initiated by receptor-interacting serine/threonine-protein kinase 1 (RIP1), RIP3 and mixed-lineage kinase domain-like protein (MLKL). It has been reported that necroptosis induced by tumor necrosis factor (TNF) was inhibited by the inhibitor of phosphatidylinositol-3-kinase (PI3K) and its substrate protein AKT, indicating that PI3K-AKT signaling pathway was involved in mediating TNF-induced necroptosis, whereas it is unclear how PI3K initiates necroptosis. In this study, we found that TNF-induced necroptosis was inhibited by chemical inhibition or genetic deletion of PI3K. Moreover, knockdown of p110α, the catalytic subunit of PI3K, significantly suppressed the phosphorylation of PI3K substrate protein AKT, and TNF-induced necroptosis was blocked by AKT inhibitors. Furthermore, we found that p110α knockdown also suppressed the phosphorylation and oligomerization of RIP1, RIP3 and MLKL in response to TNF stimulation. In addition to the critical role in mediating TNF-induced necrosome formation, p110α was also essential for the spontaneous phosphorylation of RIP1 and RIP3. Finally, we found that p110α bound to RIP3, but not RIP1, to form protein complex in the process of TNF-induced necroptosis, and mediated TNF-induced necroptosis in the absence of RIP1. Our results demonstrate that PI3K is essential for TNF-induced necroptosis, which may act as the partner of RIP3 to initiate the activation of RIP1-RIP3-MLKL signal pathway and the subsequent necroptosis.
细胞程序性坏死是近年来新发现的一种细胞死亡方式，其发生过程由受体相互作用丝氨酸/苏氨酸蛋白激酶 1（RIP1）、RIP3 和混合谱系激酶结构域样蛋白（MLKL）所启动。有报道称，肿瘤坏死因子（TNF）诱导的细胞程序性坏死可被磷脂酰肌醇-3-激酶（PI3K）抑制剂及其底物蛋白 AKT 所抑制，提示 PI3K-AKT 信号通路参与了 TNF 诱导的细胞程序性坏死的调控，然而 PI3K 如何启动细胞程序性坏死尚不清楚。本研究发现，PI3K 的化学抑制或基因敲除均可抑制 TNF 诱导的细胞程序性坏死。此外，PI3K 的催化亚基 p110α 敲低可显著抑制 PI3K 底物蛋白 AKT 的磷酸化，而 AKT 抑制剂则可阻断 TNF 诱导的细胞程序性坏死。进一步研究发现，p110α 敲低还可抑制 TNF 刺激后 RIP1、RIP3 和 MLKL 的磷酸化和寡聚化。p110α 不仅在介导 TNF 诱导的坏死体形成中起关键作用，而且对于 RIP1 和 RIP3 的自发磷酸化也必不可少。最后，我们发现 p110α 在 TNF 诱导的细胞程序性坏死过程中与 RIP3 而非 RIP1 结合形成蛋白复合物，并在缺乏 RIP1 的情况下介导 TNF 诱导的细胞程序性坏死。本研究结果表明，PI3K 是 TNF 诱导的细胞程序性坏死所必需的，它可能作为 RIP3 的伴侣，启动 RIP1-RIP3-MLKL 信号通路的激活及随后的细胞程序性坏死。
