Department of Biological Chemistry and Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Biochemistry. 2010 Sep 28;49(38):8240-50. doi: 10.1021/bi101052d.
The regulated activation of NF-κB by antigen receptor signaling is required for normal B and T lymphocyte activation during the adaptive immune response. Dysregulated NF-κB activation is associated with several types of lymphoma, including diffuse large B cell lymphoma (DLBCL). During normal antigen receptor signaling, the multidomain scaffold protein CARD11 undergoes a transition from a closed, inactive state to an open, active conformation that recruits several signaling proteins into a complex, leading to IKK kinase activation. This transition is regulated by the CARD11 inhibitory domain (ID), which participates in intramolecular interactions that prevent cofactor binding to CARD11 prior to signaling, but which is neutralized after receptor engagement by phosphorylation. Several oncogenic CARD11 mutations have been identified in DLBCL that enhance activity and that are mostly found in the coiled-coil domain. However, the mechanisms by which these mutations cause CARD11 hyperactivity and spontaneous NF-κB activation are poorly understood. In this report, we provide several lines of evidence that oncogenic mutations F123I and L225LI induce CARD11 hyperactivity by disrupting autoinhibition by the CARD11 ID. These mutations disrupt ID-mediated intramolecular interactions and ID-dependent inhibition and bypass the requirement for ID phosphorylation during T cell receptor signaling. Intriguingly, these mutations selectively enhance the apparent affinity of CARD11 for Bcl10, but not for other signaling proteins that are recruited to CARD11 in an ID-dependent manner during normal antigen receptor signaling. Our results establish a mechanism that explains how DLBCL-associated mutations in CARD11 can initiate spontaneous, receptor-independent activation of NF-κB.
抗原受体信号转导调控的 NF-κB 激活对于适应性免疫反应中正常 B 和 T 淋巴细胞的激活是必需的。NF-κB 激活失调与几种类型的淋巴瘤有关，包括弥漫性大 B 细胞淋巴瘤（DLBCL）。在正常的抗原受体信号转导过程中，多结构域支架蛋白 CARD11 经历从封闭、无活性状态到开放、活性构象的转变，募集几种信号蛋白形成复合物，导致 IKK 激酶的激活。这种转变受 CARD11 抑制结构域（ID）的调节，该结构域参与阻止信号转导前辅助因子与 CARD11 结合的分子内相互作用，但在受体结合后通过磷酸化被中和。在 DLBCL 中已经发现了几种致癌的 CARD11 突变，这些突变增强了 CARD11 的活性，并且大多数存在于卷曲螺旋结构域中。然而，这些突变导致 CARD11 过度活跃和 NF-κB 自发激活的机制尚不清楚。在本报告中，我们提供了几条证据表明，致癌突变 F123I 和 L225LI 通过破坏 CARD11 ID 的自身抑制作用导致 CARD11 过度活跃。这些突变破坏了 ID 介导的分子内相互作用和 ID 依赖性抑制作用，并绕过了 T 细胞受体信号转导过程中 ID 磷酸化的要求。有趣的是，这些突变选择性地增强了 CARD11 与 Bcl10 的表观亲和力，但不增强在正常抗原受体信号转导过程中以 ID 依赖性方式募集到 CARD11 的其他信号蛋白的亲和力。我们的结果建立了一种机制，解释了 DLBCL 相关的 CARD11 突变如何引发 NF-κB 的自发、受体非依赖性激活。
