Regulation of SIGNALLING PATHWAYS INVOLVING NUCLEAR FACTOR KAPPA B

许多免疫反应基因的调节依赖于一个称为kappaB的10个碱基对的DNA序列。这个序列被一系列与rel癌基因相关的蛋白质因子结合在一起。与该序列结合的原型转录复合体称为NF-kappaB，通常被定义为p50 DNA结合蛋白和p65(RelA)激活蛋白之间的异源二聚体，后者通常被一种称为I-kappaB的蛋白隔离在细胞质中。在对细胞进行某些类型的刺激后，一种称为I-kappaB的特殊蛋白激酶复合体导致I-kappaB的磷酸化，随后它被泛素化和降解。在可以释放核因子-kappaB的刺激中，有一种是在免疫反应中由抗原触发T细胞受体(TCR)或B细胞受体(BCR)。然而，这种转录因子在体内对数百种不同诱导剂的不同基因集的诱导中发挥作用。在研究一种罕见的免疫缺陷的临床情况时，我们还发现了CARD11的第一个胚系突变，CARD11是一种在B和T淋巴细胞的抗原受体之间形成重要信号联系的蛋白质，在1971年首次报道的一个先天性淋巴增生症家庭中，以及在第二个家庭中从中国收养的一个孩子中，我们发现了第一个胚系突变。受影响的家庭成员表现出B淋巴细胞过度聚集和分化缺陷，但T淋巴细胞没有。发现的主要错义突变将结构性地激活B和T细胞中的核因子-kappaB，从而促进B细胞的下游增殖。然而，它会导致T细胞明显的无反应或无能，从而导致IL-2的产生和增殖能力低下。因此，我们已经确定了这种遗传性B细胞疾病的潜在遗传原因，并发现了为什么CARD11突变可能易患B而不是T淋巴样恶性肿瘤的潜在分子解释。这可以用2信号模型来理解，在该模型中，T淋巴细胞需要抗原受体(信号1)和共刺激(信号2)，这两者都是T细胞增殖所必需的，而仅提供信号1会导致较差的反应性或无能。我们在我们的患者中观察到了这种现象，因为在没有伴随信号2的情况下，E127G CARD11会导致信号1的重要特征成分--核因子-kappaB的内部结构性激活。相反，B细胞的增殖可以单独由BCR交联剂触发，这是由突变的CARD11驱动的核因子-kappaB活性模拟的。我们假设，当专业的抗原提呈细胞提供适当的共刺激(信号2)时，由突变的CARD11提供的慢性TCR样信号1可以在体内转化为患者T细胞的增殖信号。T细胞辅助B细胞的缺陷与T细胞的低反应性有关，这可能是这些患者生发中心缺乏和自身免疫表现的部分原因。另一方面，T细胞非依赖性体液对多糖类抗原反应的不足也表明E127G CARD11存在的B细胞信号和效应器功能的内在缺陷。我们在CARD11中的一个种系功能获得突变的发现阐明了抗原受体信号在B细胞和T细胞中是如何被不同地调节的，即使近端的信号机制几乎相同。弥漫性大细胞B细胞淋巴瘤的体细胞CARD11突变并没有显示出这种惊人的差异，在弥漫性大细胞B细胞淋巴瘤中，只有B细胞含有这种突变，这可能可以解释为什么B细胞淋巴瘤而不是T细胞淋巴瘤与该基因的激活突变有关。我们对这一常染色体显性遗传性淋巴增殖性疾病的分子分析揭示了通过CARD11选择性调节NF-kappaB的异常可能导致B细胞选择性增殖和分化停止，但T细胞的增殖和功能缺陷。通过重新检查几十年前首次报道的一种罕见遗传疾病的分子基础，我们的发现可能会打开治疗这种淋巴增殖性疾病的新途径，并通过可以阻断核因子-kB的药物来防止淋巴瘤的发展。

Regulation of many immune response genes depend on a 10 bp DNA sequence termed kappaB. This sequence is bound by a family of protein factors related to the Rel oncogene. The prototype transcription complex binding to the sequence, termed NF-kappaB, has been conventionally defined as a heterodimer between a P50 DNA binding protein and a P65 (RelA) activation protein that is typically sequestered in the cytoplasm by a protein called I-kappaB. Following certain types of stimulation to the cell, a specific protein kinase complex called I-kappaB kinase causes the phosphorylation of I-kappaB followed by its ubiquitination and degradation. Among the stimuli that can release NF-kappaB is the triggering of the T cell receptor (TCR) or B cell receptor (BCR) by antigen during an immune response. However, this transcription factor plays a role in the induction of diverse sets of genes throughout the body in response to hundreds of different inducers. While studying a rare clinical condition of immunodeficiency, We have also discovered the first germline mutation in CARD11, a protein that forms a vital signaling link between the antigen receptor in both B and T lymphocytes, in one family with congenital lymphoid hyperplasia first reported in The New England Journal of Medicine in 1971 as well as in a child adopted from China in a second family. The affected family members exhibit excessive accumulation and defective differentiation of B lymphocytes but not T lymphocytes. The dominant missense mutations identified will constitutively activate NF-kappaB in both B and T cells contributing to downstream proliferation in B cells. However,it causes apparent non-responsivenes or anergy in T cells resulting in poor IL-2 production and proliferation. Thus, we have identified the underlying genetic cause of this hereditary B cell disorder and have uncovered a potential molecular explanation for why CARD11 mutations may predispose to B but not T lymphoid malignancies. This can be understood in terms of the 2 signal model in which T lymphocytes require antigen receptor(signal 1) as well as costimulatory (signal 2)both required for T cell proliferation, whereas the provision solely of signal 1 leads to poor responsiveness or anergy. We observed this phenomenon in our patients, since E127G CARD11 causes internal constitutive activation of NF-kappaB, an important feature component of signal 1, in the absence of a concomitant signal 2. In contrast, B cell proliferation can be triggered by BCR crosslinking alone, which is mimicked by mutant CARD11-driven NF-kappaB activity. We posit that a chronic TCR-like signal 1 provided through mutant CARD11 can be converted to a proliferative signal for the patients T cells in vivo when proper costimulation (signal 2) is provided by professional antigen presenting cells. Defects in T cell help to B cells, related to T cell hyporesponsiveness, may partly explain the paucity of germinal centers and autoimmune manifestations in these patients. On the other hand, deficiencies in T cell-independent humoral responses to polysaccharide antigens also point to intrinsic defects in B cell signaling and effector function with E127G CARD11 present. Our discovery of a germline gain-of-function mutation in CARD11 illuminates how antigen receptor signaling is regulated differently in B and T cells, even though the proximal signaling machinery is nearly identical. This surprising difference has not been revealed by somatic CARD11 mutations in diffuse large cell B cell lymphoma, in which only B cells harbor the mutation and can potentially explain the preponderance of B cell rather than T-cell lymphomas associated with activating mutations in this gene. Our molecular analysis of this autosomal dominant lymphoproliferative disorder, which may represent a novel precursor state for B cell malignancies like B-chronic lymphocytic leukemia, reveals how selective dysregulation of NF-kappaB via CARD11 may predispose to selective proliferation and differentiation arrest in B cells, but defective proliferation and function of T cells. By re-examining the molecular basis of a rare genetic disorder first reported for decades ago, our discovery may open new avenues to treat this lymphoproliferative disease and prevent development of lymphoma by agents that can block NF-kB.