Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Sci Signal. 2019 Apr 30;12(579):eaau3568. doi: 10.1126/scisignal.aau3568.
Over the last decade, multiple studies have shown that signaling proteins activated in different temporal patterns, such as oscillatory, transient, and sustained, can result in distinct gene expression patterns or cell fates. However, the molecular events that ensure appropriate stimulus- and dose-dependent dynamics are not often understood and are difficult to investigate. Here, we used single-cell analysis to dissect the mechanisms underlying the stimulus- and dose-encoding patterns in the innate immune signaling network. We found that Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) signaling dynamics relied on a dose-dependent, autoinhibitory loop that rendered cells refractory to further stimulation. Using inducible gene expression and optogenetics to perturb the network at different levels, we identified IL-1R-associated kinase 1 (IRAK1) as the dose-sensing node responsible for limiting signal flow during the innate immune response. Although the kinase activity of IRAK1 was not required for signal propagation, it played a critical role in inhibiting the nucleocytoplasmic oscillations of the transcription factor NF-κB. Thus, protein activities that may be "dispensable" from a topological perspective can nevertheless be essential in shaping the dynamic response to the external environment.
在过去的十年中，多项研究表明，在不同时间模式下激活的信号蛋白，如振荡、瞬时和持续，可导致不同的基因表达模式或细胞命运。然而，确保适当的刺激和剂量依赖性动力学的分子事件通常不被理解，并且难以研究。在这里，我们使用单细胞分析来剖析先天免疫信号网络中刺激和剂量编码模式的机制。我们发现 Toll 样受体 (TLR) 和白细胞介素 1 受体 (IL-1R) 信号动力学依赖于剂量依赖性的自抑制环，使细胞对进一步刺激产生抗性。使用诱导型基因表达和光遗传学在不同水平上扰动网络，我们确定了 IL-1R 相关激酶 1 (IRAK1) 作为剂量感应节点，负责限制先天免疫反应期间信号流。尽管 IRAK1 的激酶活性对于信号传播不是必需的，但它在抑制转录因子 NF-κB 的核质振荡中起着关键作用。因此，从拓扑学的角度来看，可能“可有可无”的蛋白质活性，但对于塑造对外界环境的动态反应却是必不可少的。
