Murakami K, Sato S, Nagasawa S, Yamashita T
Department of Hygienic Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-ku, Sapporo 060-0812, Japan.
Int Immunol. 2000 Feb;12(2):169-76. doi: 10.1093/intimm/12.2.169.
The transmembrane tyrosine phosphatase CD45 regulates the activity of src family protein tyrosine kinases (PTK) and thereby influences the signaling via such receptors as T and B cell antigen receptors associated with these PTK. However, its implication in signaling through the mast cell receptor with high affinity for IgE (FcepsilonRI) is less clear, although Lyn, a member of the src family, plays an important role in FcepsilonRI-mediated signaling. To define a role for CD45 in FcepsilonRI signal transduction, we established CD45 high expressing rat basophilic leukemia cell lines (RBL-CD45H) and cell lines expressing trace amounts of CD45 (RBL-CD45L). We demonstrate that although all RBL-CD45L cell lines degranulate following IgE- and antigen-induced FcepsilonRI aggregation, the response is significantly reduced at a low dose of antigen. The cells show a delayed and slowed Ca(2+) mobilization even though at a higher dose where the cells degranulate to a similar extent as RBL-CD45H. This diminished Ca(2+) response is restored by reconstitution of RBL-CD45L with a chimeric molecule containing the cytoplasmic phosphatase domains of rat CD45. Furthermore, tyrosine phosphorylation of FcepsilonRI, association of FcepsilonRI with Lyn and PTK activity associated with FcepsilonRI, all of which are enhanced upon FcepsilonRI aggregation in RBL-CD45H, are impaired in RBL-CD45L. Finally, we show that FcepsilonRI is physically associated with CD45 in RBL-CD45H prior to receptor aggregation. Thus, we propose that, although not indispensable in mast cell degranulation, CD45 positively regulates the signaling through FcepsilonRI by promoting the activation of FcepsilonRI-associated Lyn.
跨膜酪氨酸磷酸酶CD45调节src家族蛋白酪氨酸激酶（PTK）的活性，从而影响通过与这些PTK相关的T和B细胞抗原受体等受体的信号传导。然而，其在通过对IgE具有高亲和力的肥大细胞受体（FcepsilonRI）进行信号传导中的作用尚不清楚，尽管src家族成员Lyn在FcepsilonRI介导的信号传导中起重要作用。为了确定CD45在FcepsilonRI信号转导中的作用，我们建立了高表达CD45的大鼠嗜碱性白血病细胞系（RBL-CD45H）和表达微量CD45的细胞系（RBL-CD45L）。我们证明，尽管所有RBL-CD45L细胞系在IgE和抗原诱导的FcepsilonRI聚集后都会脱颗粒，但在低剂量抗原时反应会显著降低。即使在较高剂量下细胞脱颗粒程度与RBL-CD45H相似，这些细胞仍显示出延迟和缓慢的Ca(2+)动员。通过用含有大鼠CD45细胞质磷酸酶结构域的嵌合分子重建RBL-CD45L，这种减弱的Ca(2+)反应得以恢复。此外，FcepsilonRI的酪氨酸磷酸化、FcepsilonRI与Lyn的结合以及与FcepsilonRI相关的PTK活性，在RBL-CD45H中FcepsilonRI聚集时都会增强，但在RBL-CD45L中却受损。最后，我们表明在受体聚集之前，FcepsilonRI在RBL-CD45H中与CD45存在物理关联。因此，我们提出，尽管CD45在肥大细胞脱颗粒中并非不可或缺，但它通过促进与FcepsilonRI相关的Lyn的激活来正向调节通过FcepsilonRI的信号传导。
