Laboratory of B Cell Biology, Karches Center for Chronic Lymphocytic Leukemia Research, Feinstein Institute for Medical Research, Manhasset, NY 11030, USA.
J Immunol. 2012 Jun 15;188(12):6093-108. doi: 10.4049/jimmunol.1103037. Epub 2012 May 18.
Resting mature human B cells undergo a dynamic process of clonal expansion, followed by clonal contraction, during an in vitro response to surrogate C3d-coated Ag and innate immune system cytokines, IL-4 and BAFF. In this study, we explore the mechanism for clonal contraction through following the time- and division-influenced expression of several pro- and anti-apoptotic proteins within CFSE-labeled cultures. Several findings, involving both human and mouse B cells, show that a mitochondria-dependent apoptotic pathway involving p53 contributes to the high activation-induced cell death (AICD) susceptibility of replicating blasts. Activated B cell clones exhibit elevated p53 protein and elevated mRNA/protein of proapoptotic molecules known to be under direct p53 transcriptional control, Bax, Bad, Puma, Bid, and procaspase 6, accompanied by reduced anti-apoptotic Bcl-2. Under these conditions, Bim levels were not increased. The finding that full-length Bid protein significantly declines in AICD-susceptible replicating blasts, whereas Bid mRNA does not, suggests that Bid is actively cleaved to short-lived, proapoptotic truncated Bid. AICD was diminished, albeit not eliminated, by p53 small interfering RNA transfection, genetic deletion of p53, or Bcl-2 overexpression. DNA damage is a likely trigger for p53-dependent AICD because susceptible lymphoblasts expressed significantly elevated levels of both phosphorylated ataxia telangiectasia mutated-Ser(1980) and phospho-H2AX-Ser(139). Deficiency in activation-induced cytosine deaminase diminishes but does not ablate murine B cell AICD, indicating that activation-induced cytosine deaminase-induced DNA damage is only in part responsible. Evidence for p53-influenced AICD during this route of T cell-independent clonal expansion raises the possibility that progeny bearing p53 mutations might undergo positive selection in peripherally inflamed tissues with elevated levels of IL-4 and BAFF.
静止成熟的人类 B 细胞在体外对替代 C3d 包被的 Ag 和先天免疫系统细胞因子 IL-4 和 BAFF 作出反应时，经历克隆扩增，随后是克隆收缩的动态过程。在这项研究中，我们通过跟踪 CFSE 标记培养物中几种促凋亡和抗凋亡蛋白的时间和分裂影响的表达，探索了克隆收缩的机制。涉及人和小鼠 B 细胞的几项发现表明，涉及 p53 的线粒体依赖性凋亡途径导致复制性 blast 高激活诱导的细胞死亡（AICD）易感性。激活的 B 细胞克隆表现出升高的 p53 蛋白和升高的 mRNA/蛋白，这些蛋白是已知受 p53 转录控制的促凋亡分子，包括 Bax、Bad、Puma、Bid 和 procaspase 6，同时抗凋亡的 Bcl-2 减少。在这些条件下，Bim 水平没有增加。发现在易发生 AICD 的复制性 blast 中，全长 Bid 蛋白显著下降，而 Bid mRNA 没有，这表明 Bid 被主动切割成短寿命的、促凋亡的截断 Bid。AICD 被减少，尽管没有消除，通过 p53 小干扰 RNA 转染、p53 的基因缺失或 Bcl-2 的过表达。DNA 损伤可能是 p53 依赖性 AICD 的触发因素，因为易感性淋巴细胞表达显著升高的磷酸化 ataxia telangiectasia 突变体 Ser(1980)和磷酸化 H2AX-Ser(139)。激活诱导的胞嘧啶脱氨酶缺乏减少但没有消除小鼠 B 细胞 AICD，表明激活诱导的胞嘧啶脱氨酶诱导的 DNA 损伤仅部分负责。在这种 T 细胞非依赖性克隆扩增途径中，p53 影响 AICD 的证据提出了携带 p53 突变的后代在具有高水平 IL-4 和 BAFF 的外周炎症组织中可能经历阳性选择的可能性。
