Analysis of B-cell antigen receptor signal regulation and dys-regulation emerged as autoimmune diseases

自身免疫性疾病是免疫系统自身耐受性丧失的结果，其机制尚不完全清楚。自我耐受主要是通过克隆缺失或识别自身抗原的淋巴细胞无能来建立的。因此，抗原受体信号的异常会导致不成功的自我耐受，最终导致自身免疫性疾病。B细胞抗原受体(BCR)参与诱导酪氨酸激酶的激活，如Lyn和Syk，它们负责磷酸化和激活多种信号成分。在Lyn基因敲除小鼠中，BCR介导的B细胞反应上调，该动物产生更丰富的抗体和抗自身抗体，并经常患有自身免疫性疾病，如肾炎。这些结果表明，LYN对BCR信号转导具有负性调节作用。我们利用Lyn缺失的鸡B细胞系DT40，研究了Lyn介导的调节机制。我们发现bcr介导的…在Lyn缺陷的鸡B细胞中，c-myc启动子活性和PKC活性的诱导显著增加，但功能性PKC的表达水平并未显著增加。这种增强作用被外源LYN的表达逆转到野生型细胞的水平。这些结果表明，Lyn以一种不依赖于激酶的方式抑制了BCR介导的大部分PKC同工酶的激活。这一发现揭示了LYN在BCR信号负调控中的新作用。进一步的分析表明，在表达于DT40细胞中的α亚型中，bcr结扎和PMA处理对PKC DNA活性的上调作用比其他处理更强。然而，在DT40细胞中没有观察到Lyn与PKCα之间的直接相互作用。此外，携带非功能性SH2或SH3结构域的Lyn突变形式分别抑制了在Lyn缺失的DT40细胞中观察到的夸大的BCR信号。因此，Lyn的剩余N-末端结构域可能间接地与PKCα相互作用并干扰其激活。较少

Autoimmune disease is a consequence of abrogated self-tolerance of immune system, the mechanism of which is not fully understood. Self-tolerance is established mainly by clonal deletion or anergy of lymphocytes that recognizes self antigen. Therefore, abnormal antigen receptor signaling will result in unsuccessful self-tolerance and eventually in the autoimmune disease. Engagement of B cell antigen receptor (BCR) induces activation of tyrosine kinases such as Lyn and Syk, which are responsible for phosphorylation and activation of multiple signaling components. In Lyn-knockout mice, BCR-mediated B cell responses are up-regulated, and the animal produces more abundant antibodies and also anti-self antibodies, and frequently suffers from autoimmune diseases like nephritis. These results suggest that Lyn negatively regulates BCR signal transduction. We have studied the mechanism of Lyn-mediated regulation using chicken B cell line, DT40, deficient for Lyn. We have found that BCR-mediated … More induction of c-myc promoter activity and of PKC activity, but not the expression level of functional PKC, was markedly augmented in Lyn-deficient chicken B cells. This enhancement was reversed to the level of wild-type cells by the expression of exogenous Lyn of kinase-inactive form. These results indicate that Lyn inhibits BCR-mediated activation of a large portion of PKC isozymes in a kinase-independent fashion. This finding reveals a novel role of Lyn in negative regulation of BCR-signaling. Further analyses revealed that, among PKC isotypes expressing in DT40 cells, the activity of PKCα was more potently upregulated by BCR-ligation as well as PMA treatment than others. However, direct interaction between Lyn and PKCα was not observed in DT40 cells. Furthermore, mutant forms of Lyn carrying non-functional SH2 or SH3 domains, respectively, suppressed the exaggerated BCR-signaling observed in Lyn-deficient DT40 cells. Therefore, the remaining N-terminal domain of Lyn may indirectly interact with PKCα and interfere its activation. Less