Signal Regulation Mechanisms for B Cell Development and Self-Tolerance Establishment.

Pre-B细胞受体(Pre-B cell Receptor，Pre-Bcr)信号诱导大的Pre-B细胞的增殖和随后向小的Pre-B细胞的分化(Pre-B细胞转变)，并抑制IgH基因VH到DJH的重排(IgH等位基因排除)，后者也解释了表达Dμ蛋白的前B细胞的逆向选择(Dμ选择)。我们以前已经证明，B细胞特异性接头蛋白Bash(或BLNK/SLP-65)对B细胞抗原受体(BCR)信号转导至关重要，对B细胞前转化是重要的，但不是必需的。在这项研究中，我们发现了CD19在BCR前信号转导中的增强作用，CD19是BCR的B细胞特异性辅助受体。在Bash/CD19双突变小鼠中，Bash/CD19双突变小鼠完全取消了前B细胞的转变，增加了大的非周期的、表达前bcr的细胞的积累。然而，即使在双突变小鼠中，IgH等位基因排斥也是完整的，而在Bash-和双突变小鼠中，Dμ选择被取消。因此，di…这些事件需要更强烈的信号。此外，这些小鼠死于前B细胞白血病，表明Bash(和CD19)有助于肿瘤抑制。我们还通过检测Bash缺失的抗DNA抗体敲入小鼠，发现自结合抗原受体的编辑显著依赖于Bash。因此，受体编辑在建立自我耐受性方面的贡献被清楚地记录下来。BASH与Btk、PLCγ、Vav、Grb2、HPK1等信号分子相互作用，这种相互作用在bcr信号转导中具有重要意义。我们已经鉴定出与Bash保守的N-末端结构域结合的新蛋白，并将其命名为BNAS1和BNAS2。它们都是一种膜跨度为4倍的蛋白，定位于内质网、高尔基体和核周。利用基因打靶方法进行的功能研究目前正在进行中。较少

Pre-B cell receptor (pre-BCR) signaling induces proliferative expansion of large pre-B cells and the following differentiation into small pre-B cells (pre-B cell transition), and inhibits V_H to DJ_H rearrangement of IgH locus (IgH allelic exclusion), the latter also accounting for counter-selection of pro-B cells expressing Dμ protein (Dμ selection). We have previously shown that a B-cell specific adaptor protein, BASH (or BLNK/SLP-65), which is critical for B-cell antigen receptor(BCR) signaling, is important, but not essential, for pre-B cell transition. In this study we have discovered a buck-up role in the pre-BCR signaling for CD19, a B-cell specific co-receptor for BCR. The pre-B cell transition was completely abolished and accumulation of large non-cycling, pre-BCR-expressing cells was augmented in BASH/CD19 double-mutant mice. However, IgH allelic exclusion was intact even in the double-mutant mice, while Dμ selection was abolished in BASH- and the double-mutant mice. Thus, di … More stinct signals are required for these events. In addition, these mice succumbed to pre-B cell leukemia, indicating BASH (and CD19) contributes to tumor suppression.We also found that editing of self-binding antigen receptors is significantly dependent on BASH, through examining anti-DNA-antibody knock-in mice deficient for BASH. Thus contribution of the receptor editing in the establishment of self-tolerance is clearly documented. In addition, BASH has turned out to be unnecessary for T-independent secondary and memory response, as well as affinity maturation of antibodies.BASH interacts with signaling molecules such as Btk, PLCγ, Vav, Grb2, HPK1, and the significance of such interactions in BCR signal transduction has been shown. We have identified novel proteins that bind to a conserved N-terminal domain of BASH, and termed them BNAS1 and BNAS2. They are both presumed to be a 4-times membrane-span protein and localize at endoplasmic reticulum, Golgi apparatus and peri-nuclear region. Functional studies utilizing gene targeting methodology are currently underway. Less