HTLV-1 Tax Induces Formation of the Active Macromolecular IKK Complex by Generating Lys63- and Met1-Linked Hybrid Polyubiquitin Chains.
HTLV-1 Tax Induces Formation of the Active Macromolecular IKK Complex by Generating Lys63- and Met1-Linked Hybrid Polyubiquitin Chains.
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DOI：
10.1371/journal.ppat.1006162
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发表时间：
2017-01
期刊：
影响因子：
6.7
通讯作者：
Inoue JI
中科院分区：
文献类型：
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作者：
Shibata Y;Tokunaga F;Goto E;Komatsu G;Gohda J;Saeki Y;Tanaka K;Takahashi H;Sawasaki T;Inoue S;Oshiumi H;Seya T;Nakano H;Tanaka Y;Iwai K;Inoue JI
人类T细胞白血病病毒1型(HTLV-1)的Tax蛋白在成人T细胞白血病(ATL)的发生发展中起着至关重要的作用，ATL是一种高度恶性的CD4+T细胞肿瘤。在税收对细胞过程的多种异常影响中，转录因子NF-κB的持续激活是白血病发生的关键，它只在生理刺激下短暂激活。我们和其他人已经证明，TAX通过产生Lys63连接的多泛素链，诱导IκB激酶(IKK)复合体的激活，这是NF-κB激活的关键步骤。然而，税收诱导IKK激活的分子机制仍存在争议，而且还不完全清楚。在这里，我们证明了TAX招募线性(MET1连接的)泛素链组装复合体(LUBAC)到IKK复合体，并且未能在缺乏LUBAC活性的细胞中诱导IKK激活。质谱分析表明，Lys63连接的和MET1连接的多泛素链都与IKK复合体相关。此外，用MET1链特异性脱泛素酶(OTULIN)处理IKK相关的多泛素链，可导致高分子量多泛素链的减少和Lys63连接的短泛素链的产生，这表明Tax可以诱导Lys63和MET1连接的杂合多泛素链的产生。我们还证明了Tax诱导活性的大分子IKK复合体的形成，以及Tax诱导的多泛素链合成的阻断抑制了大分子复合体的形成。综上所述，这些结果导致我们提出了一个新的模型，在该模型中，由税收引发的IKK复合体的杂合链依赖的寡聚导致了反式自磷酸化介导的IKK激活。核因子-κB是一种关键的转录因子，调节着许多重要的生理过程。然而，NF-κB的持续激活会导致慢性炎症、自身免疫和恶性转化。人类逆转录病毒HTLV-1感染成人T细胞白血病，HTLV-1Tax介导的持续的NF-κB激活在白血病的发生中起关键作用。因此，更好地了解NF-κB异常激活的确切机制对于开发新的治疗方法至关重要。泛素化是主要的翻译后修饰之一，调节多种细胞内信号通路。我们和其他人已经证明，TAX通过激活IκB激酶(IKK)复合体来激活NF-κB，途径是产生Lys63连接的多泛素链。然而，税收诱导的IKK激活的分子机制仍然不太清楚。在这里，我们准确地展示了HTLV-1 Tax如何利用泛素系统激活IKK复合体。IKK复合体相关的Lys63/MET1连接的杂化多泛素链是通过税收介导的线性泛素链组装复合体(LUBAC)招募到IKK复合体上而产生的。此外，杂化链是税收诱导形成活性大分子IKK络合物所必需的。因此，我们提出了一个新的模型，在该模型中，TAX触发Lys63/MET1连接的杂交链依赖的IKK复合体齐聚，导致反式自动磷酸化介导的IKK激活。
The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) is crucial for the development of adult T-cell leukemia (ATL), a highly malignant CD4+ T cell neoplasm. Among the multiple aberrant Tax-induced effects on cellular processes, persistent activation of transcription factor NF-κB, which is activated only transiently upon physiological stimulation, is essential for leukemogenesis. We and others have shown that Tax induces activation of the IκB kinase (IKK) complex, which is a critical step in NF-κB activation, by generating Lys63-linked polyubiquitin chains. However, the molecular mechanism underlying Tax-induced IKK activation is controversial and not fully understood. Here, we demonstrate that Tax recruits linear (Met1-linked) ubiquitin chain assembly complex (LUBAC) to the IKK complex and that Tax fails to induce IKK activation in cells that lack LUBAC activity. Mass spectrometric analyses revealed that both Lys63-linked and Met1-linked polyubiquitin chains are associated with the IKK complex. Furthermore, treatment of the IKK-associated polyubiquitin chains with Met1-linked-chain-specific deubiquitinase (OTULIN) resulted in the reduction of high molecular weight polyubiquitin chains and the generation of short Lys63-linked ubiquitin chains, indicating that Tax can induce the generation of Lys63- and Met1-linked hybrid polyubiquitin chains. We also demonstrate that Tax induces formation of the active macromolecular IKK complex and that the blocking of Tax-induced polyubiquitin chain synthesis inhibited formation of the macromolecular complex. Taken together, these results lead us to propose a novel model in which the hybrid-chain-dependent oligomerization of the IKK complex triggered by Tax leads to trans-autophosphorylation-mediated IKK activation. NF-κB is a key transcription factor that regulates many physiologically important cellular processes. However, persistent activation of NF-κB leads to chronic inflammation, autoimmunity and malignancy. Infection with the human retrovirus HTLV-1 causes adult T-cell leukemia, and HTLV-1 Tax-mediated persistent NF-κB activation is crucial for leukemogenesis. Therefore, a better understanding of the precise mechanism underlying aberrant NF-κB activation is essential to develop new therapeutic approaches. Ubiquitination is one of the major post-translational modifications that regulate various intracellular signaling pathways. We and others have shown that Tax activates NF-κB through activation of the IκB kinase (IKK) complex by generating Lys63-linked polyubiquitin chains. However, the molecular mechanism underlying Tax-induced IKK activation remains less well understood. Here, we demonstrate precisely how HTLV-1 Tax utilizes the ubiquitin system to activate the IKK complex. The IKK complex-associated Lys63/Met1-linked hybrid polyubiquitin chains are generated through the Tax-mediated recruitment of linear ubiquitin chain assembly complex (LUBAC) to the IKK complex. Furthermore, the hybrid chains are required for the Tax-induced formation of the active macromolecular IKK complex. Accordingly, we propose a novel model in which Tax triggers Lys63/Met1-linked hybrid-chain-dependent oligomerization of the IKK complex, leading to trans-autophosphorylation-mediated IKK activation.