Coupling of a Signal Response Domain in IkBato Multiple Pathways for NF-kB Activation
Coupling of a Signal Response Domain in IkBato Multiple Pathways for NF-kB Activation
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发表时间：
1995
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通讯作者：
J. Brockman;D. Scherer;T. McKinsey;S. M. Hall;X. Qi;Wha-Young Lee;Anddean W. Ballard
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作者：
J. Brockman;D. Scherer;T. McKinsey;S. M. Hall;X. Qi;Wha-Young Lee;Anddean W. Ballard
真核转录因子NF-kB在人类免疫缺陷病毒1型的诱导表达中以及在介导正常T细胞活化和生长的遗传程序的许多方面中起核心作用。NF-κ B的核活性由称为IkBa的抑制性亚基从细胞质区室严格调节。这种细胞质抑制剂迅速磷酸化和降解，以响应一组不同的NF-κ B诱导剂，包括T细胞有丝分裂原，促炎细胞因子和病毒反式激活因子，如人T细胞白血病病毒1型的Tax蛋白。为了探索这些IkBa依赖的NF-kB诱导机制，我们鉴定了IkBa的新突变体，其在人T淋巴细胞中解偶联其抑制和信号转导功能。具体而言，去除IkBa的N-末端36个氨基酸未能破坏其在细胞质中与NF-kB形成潜在复合物的能力。然而，这种缺失突变阻止了Tax表达细胞中诱导的磷酸化、降解损失和IkBa从NF-κ B的功能释放。在IkBa的N-末端调控区内的两个丝氨酸残基处引入丙氨酸取代也产生了组成型阻遏物，其从Tax诱导的周转中逃脱，并有效地抑制NF-κ B诱导的免疫活化途径，包括从抗原和细胞因子受体起始的免疫活化途径。相比之下，在这些位点引入磷酸丝氨酸模拟物纠正了这种功能缺陷，这一发现与这种细胞质抑制剂的磷酸化状态和蛋白水解稳定性之间的因果关系一致。总之，这些体内研究定义了IkBa中的关键信号应答结构域，其协调控制IkBa和NF-κ B in对病毒和免疫刺激的应答的生物活性。
The eukaryotic transcription factor NF-kB plays a central role in the induced expression of human immunodeficiency virus type 1 and in many aspects of the genetic program mediating normal T-cell activation and growth. The nuclear activity of NF-kB is tightly regulated from the cytoplasmic compartment by an inhibitory subunit called IkBa. This cytoplasmic inhibitor is rapidly phosphorylated and degraded in response to a diverse set of NF-kB-inducing agents, including T-cell mitogens, proinflammatory cytokines, and viral transactivators such as the Tax protein of human T-cell leukemia virus type 1. To explore these IkBa-dependent mechanisms for NF-kB induction, we identified novel mutants of IkBa that uncouple its inhibitory and signal-transducing functions in human T lymphocytes. Specifically, removal of the N-terminal 36 amino acids of IkBa failed to disrupt its ability to form latent complexes with NF-kB in the cytoplasm. However, this deletion mutation prevented the induced phosphorylation, degradative loss, and functional release of IkBa from NF-kB in Tax-expressing cells. Alanine substitutions introduced at two serine residues positioned within this N-terminal regulatory region of IkBaalso yielded constitutive repressors that escaped from Tax-induced turnover and that potently inhibited immune activation pathways for NF-kB induction, including those initiated from antigen and cytokine receptors. In contrast, introduction of a phosphoserine mimetic at these sites rectified this functional defect, a finding consistent with a causal linkage between the phosphorylation status and proteolytic stability of this cytoplasmic inhibitor. Together, these in vivo studies define a critical signal response domain in IkBa that coordinately controls the biologic activities of IkBa and NF-k Bi n response to viral and immune stimuli.