B cell signaling molecules which regulated by protein tyrosine phosphatase CD45

CD 45是T和B细胞活化的关键调节因子。然而，关于CD 45的作用模式，存在相互矛盾的结果。为了深入了解这个问题，我们试图鉴定B细胞中CD 45的底物PTK，并确定Src家族PTK的去磷酸化位点。结果表明，在来自未成熟B细胞系的CD 45缺陷型克隆中，林恩在没有B细胞受体（BCR）连接的情况下被选择性过度磷酸化和活化。CD 45通过使阳性（394）和阴性（508）酪氨酸残基去磷酸化而组成性地使林恩失活（J. Immunol.163：1321-1326，1999）。我们还研究了CD 45对BCR诱导的丝裂原活化蛋白激酶（MAPK）家族成员活化的贡献。我们发现，CD 45调节BCR诱导的c-Jun氨基末端激酶（JNK）和p38。有趣的是，这种调节依赖于B细胞分化水平（FEBS Lett. 490：97-101，2001）。CD 45对CD 40介导的信号传导途径的选择性集合发挥决定性作用，决定B细胞的命运（J. Biol. Chem. 276：8550-8556，2001）。为了阐明这些观察结果的分子基础，我们现在正试图确定CD 45与Src家族PTK的精确定位，我们利用糖脂富集膜部分（GEM）（通常称为脂筏）作为标记物。初步结果显示，CD 45在BCR连接前存在于筏中，并且在刺激后从筏中隔离。这些结果表明，与脂筏组成性结合的CD 45使脂筏失活，Src家族的PTK和BCR连接以某种方式将CD 45从脂筏上隔离，从而启动激活级联反应，因此，我们正在揭示CD 45对脂筏BCR信号的调控机制。

CD45 is a critical regulator of T and B cell activation. However, there have been conflicting results as to the mode of CD45 action.1. To obtain some insights into this problem, we tried to identify substrate PTKs for CD45 in B cells and to determine the dephosphory lation sites of the Src-family PTKs. The results demonstrated that in CD45-deficient clones from the immature B cell line, Lyn was selectively hyperphosphorylated and activated in the absence of B cell receptor (BCR) ligation. CD45 constitutively inactivates Lyn by dephosphorylating both the positive (394) and negative (508) tyrosine residues (J.Immunol. 163 : 1321-1326, 1999).2. We also examined contribution made by CD45 to BCR-induced activation of mitogen-activated protein kinase (MAPK) family members. We found that CD45 regulated BCR-induced c-Jun NH2-terminal kinase (JNK) and p38. Interestingly, the regulation was depend on B cell differentiation level (FEBS Lett. 490 : 97-101, 2001).3. CD45 exerts a decisive effect on selective sets of CD40-mediated signaling pathway, dictating B cell fate (J.Biol. Chem. 276 : 8550-8556, 2001).4. To elucidate the molecular basis of these observations, we are now trying to determine the precise localization of CD45 with Src-family PTK, we utilized glycolipid-enriched membrane fraction (GEM), commonly referred to as lipid raft, as a marker. The preliminary results revealed that CD45 is present in the raft before BCR ligation and is sequestered from the raft after stimulation. These results suggest that CD45 constitutively associated with the raft inactivates, Src-family PTK and BCR ligation somehow sequesters CD45 from the raft, thereby initiating activation cascades.Thus, we are in the process of revealing the regulatory mechanism of BCR signals by CD45 on lipid raft.