Ma Bruce Y, Mikolajczak Sebastian A, Yoshida Tetsuya, Yoshida Ryoko, Kelvin David J, Ochi Atsuo
Department of Biological Chemistry, Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto, Japan.
Biochem Biophys Res Commun. 2004 Apr 23;317(1):60-7. doi: 10.1016/j.bbrc.2004.03.012.
CD28 is a cell surface glycoprotein expressed on T cells that modulates immune responses through its ability to transduce costimulatory signals. Even though nearly 50% of the molecular mass of CD28 is N-glycan, the physiological significance of CD28 glycosylation is at present unknown. In this report, we have investigated the function of hypoglycosylated wildtype CD28 and its splice variant, CD28i. When N-glycosylation was prevented through point mutations in N-glycosylation sites in CD28, or reduced by glycosidase inhibitors, the binding of CD28 to CD80 significantly increased. Stimulation of hypoglycosylated CD28 induced IL-2 promoter activity greater than that induced through the stimulation of wildtype CD28. Unlike hypoglycosylated wildtype CD28, hypoglycosylation of CD28i did not alter CD28i functions. Our data indicate that N-glycans of CD28 negatively regulate CD28/CD80 interactions, resulting in diminished CD28 signaling. It is also suggested that N-glycans regulate the density of CD28 clustering upon ligation with CD80/CD86. The results support the hypothesis that the N-glycosylation negatively regulates CD28-mediated T cell adhesion and costimulation.
CD28是一种表达于T细胞表面的糖蛋白，它通过转导共刺激信号来调节免疫反应。尽管CD28近50%的分子质量是N-聚糖，但目前CD28糖基化的生理意义尚不清楚。在本报告中，我们研究了低糖基化野生型CD28及其剪接变体CD28i的功能。当通过CD28中N-糖基化位点的点突变阻止N-糖基化，或用糖苷酶抑制剂降低N-糖基化时，CD28与CD80的结合显著增加。低糖基化CD28的刺激诱导的IL-2启动子活性大于野生型CD28刺激诱导的活性。与低糖基化野生型CD28不同，CD28i的低糖基化并未改变CD28i的功能。我们的数据表明，CD28的N-聚糖负向调节CD28/CD80相互作用，导致CD28信号减弱。还表明，N-聚糖在与CD80/CD86连接时调节CD28聚集的密度。这些结果支持了N-糖基化负向调节CD28介导的T细胞黏附和共刺激的假说。
