Taetle R, Ostergaard H, Smedsrud M, Trowbridge I
Division of Hematology/Oncology, University of California, San Diego.
Leukemia. 1991 Apr;5(4):309-14.
The CD45 antigen cluster identifies a family of transmembrane glycoprotein tyrosine phosphatases (PTPases) present on nearly all hemopoietic cells. Recent studies suggest that CD45 may play a role in the control of receptor mediated blood cell responses, and that expression of the CD45 gene varies during bone marrow cell maturation. However, relatively little is known of the mechanisms controlling CD45 expression and function. Here we show that the induction of granulocyte or monocyte differentiation of HL60 leukemia cells is accompanied by a rapid increase in CD45 antigen expression and CD45 PTPase activity. In contrast, other leukemia cell lines induced for monocyte/macrophage differentiation did not show increased CD45. Immunoprecipitation of radiolabelled CD45 glycoprotein from dimethyl sulphoxide (DMSO) treated HL60 cells indicated that the cells expressed 200 and 180 kD isoforms. Northern blots of steady-state RNA from HL60 cells showed a 4-11-fold increase in CD45 transcripts after DMSO treatment, but no alteration in the half-life of CD45 mRNA. Nuclear transcription assays showed that CD45 expression was controlled at the level of gene transcription. Namalwa Burkitt leukemia cells expressing the heterologous epidermal growth factor (EGF) receptor protein tyrosine kinase were used to assess the specificity of CD45 PTPase activity. Co-clustering of CD45 and the EGF receptor with specific monoclonal antibodies failed to alter the EGF stimulated tyrosine phosphorylation of the EGF receptor. These studies indicate that CD45 increases during myeloid maturation, and the expression of the CD45 gene is controlled at the level of gene transcription. Preliminary studies suggest that CD45 does not alter the protein tyrosine kinase activity of the EGF receptor in intact cells, suggesting substrate specificity in vivo.
CD45抗原簇可识别几乎所有造血细胞上存在的一类跨膜糖蛋白酪氨酸磷酸酶（PTP酶）。最近的研究表明，CD45可能在受体介导的血细胞反应控制中发挥作用，并且CD45基因的表达在骨髓细胞成熟过程中会发生变化。然而，对于控制CD45表达和功能的机制了解相对较少。在这里我们表明，HL60白血病细胞向粒细胞或单核细胞的分化诱导伴随着CD45抗原表达和CD45 PTP酶活性的快速增加。相比之下，其他诱导为单核细胞/巨噬细胞分化的白血病细胞系并未显示CD45增加。从经二甲基亚砜（DMSO）处理的HL60细胞中免疫沉淀放射性标记的CD45糖蛋白表明，这些细胞表达200 kD和180 kD的异构体。来自HL60细胞的稳态RNA的Northern印迹显示，DMSO处理后CD45转录本增加了4至11倍，但CD45 mRNA的半衰期没有改变。细胞核转录分析表明，CD45的表达在基因转录水平受到控制。使用表达异源表皮生长因子（EGF）受体蛋白酪氨酸激酶的Namalwa伯基特白血病细胞来评估CD45 PTP酶活性的特异性。用特异性单克隆抗体使CD45和EGF受体共聚集未能改变EGF刺激的EGF受体酪氨酸磷酸化。这些研究表明，CD45在髓系成熟过程中增加，并且CD45基因的表达在基因转录水平受到控制。初步研究表明，CD45不会改变完整细胞中EGF受体的蛋白酪氨酸激酶活性，提示在体内存在底物特异性。
