Search for CD45 ligand

在最初的提案中，我们计划寻找CD45的配体。最近的研究表明，CD45的催化活性受二聚化的调节，二聚化可能依赖于CD45的细胞外结构域，因此CD45RO比CD45RABC更容易受到二聚化的影响。这些发现表明，调节CD45活性可能不需要反式作用的配体。因此，我们试图阐明CD45调控的信号通路。(1) CD45对丝裂原活化蛋白激酶（MAPKs）的调控：我们之前发现CD45对代表不同不饱和阶段的两种B细胞系WEHI-231和BAL-17的B细胞受体（BCR）信号传导有不同的影响。在这项研究中，我们检测了CD45对bcr诱导的MAPK家族成员激活的贡献。我们发现，在未成熟的WEHI-231细胞中，CD45负调控bcr诱导的c-Jun nh_2末端激酶（INK）和p38的激活，而在成熟的BAL-17细胞中，CD45正调控JNK和p38的激活，负调控细胞外信号调节激酶（ERK）的活性。此外，JNK和p38的协同作用决定了bcr诱导的生长抑制。因此，CD45似乎对bcr诱导的MAPK成员的激活有差异调节，并且可以在不同的细胞环境中对JNK和p38施加相反的作用，从而控制B细胞的命运。(2) CD45对CD40介导的信号通路的调控：在BAL-17细胞中，CD40连接不能恢复bcr诱导的生长抑制，但它本身抑制增殖。这种作用依赖于CD45。此外，cd40诱导的增殖抑制受JNK和p38的控制，其活性也受CD45的调节。然而，cd40介导的细胞表面分子的诱导不受CD45的调节。因此，这些结果表明CD45对cd40介导的选择性信号通路具有决定性作用，决定了B细胞的命运。

In the original proposal, we planed to search for the ligand for CD45. Recent studies demonstrated that CD45 catalytic activity is regulated by dimerization and that dimerization may be dependent on the extracellular domain of CD45 such that CD45RO is more susceptible to dimerization than CD45RABC. These findings suggest that ligands acting in trans may not be required for the regulation of CD45 activity. We therefore pursued to elucidate the signaling pathways regulated by CD45.(1) Regulation ofmitogen-activated protein kinases (MAPKs) by CD45: We previously showed that CD45 exerts differential effects on B cell receptor (BCR) signaling in two B cell lines, WEHI-231 and BAL-17, which represent different inaturational stages. In this study, we examined the contribution made by CD45 to BCR-induced activation of MAPK family members. We found that CD45 negatively regulated BCR-induced c-Jun NH_2-terminal kinase (INK) and p38 activation in immature WEHI-231 cells, whereas in mature BAL-17 cells, CD45 positively regulated JNK and p38 activation and negatively regulated extracellular signal-regulated kinase (ERK) activity. Furthermore, cooperative action of JNK and p38 dictated BCR-induced inhibition of growth. Thus, CD45 appears to differentially regulate BCR-induced activation of MAPK members, and can exert opposing effects on JNK and p38 in different cellular milieus, controlling the B cell fate.(2) Regulation of CD40-mediated signaling pathways by CD45: In BAL-17 cells, CD40 ligation did not rescue BCR-induced growth inhibition but itself inhibited proliferation. This effect was dependent on CD45. Furthermore, CD40-induced inhibition of proliferation was controlled by JNK and p38, the activity of which was also regulated by CD45. However, CD40-mediated induction of cell surface molecules was not regulated by CD45. Thus, these results suggest that CD45 exerts a decisive effect on selective sets of CD40-mediated signaling pathways, dictating B cell fate.