Sitrin R G, Pan P M, Blackwood R A, Huang J, Petty H R
Pulmonary and Critical Care Medicine Division, Department of Internal Medicine, University of Michigan, Ann Arbor MI 48109, USA.
J Immunol. 2001 Apr 15;166(8):4822-5. doi: 10.4049/jimmunol.166.8.4822.
Leukocyte urokinase plasminogen activator receptors (uPARs) cluster at adhesion interfaces and at migratory fronts where they participate in adhesion, chemotaxis, and proteolysis. uPAR aggregation triggers activation signaling even though this glycolipid-anchored protein must associate with membrane-spanning proteins to access the cell interior. This study demonstrates a novel partnership between uPAR and L-selectin in human polymorphonuclear neutrophils. Fluorescence resonance energy transfer demonstrated a direct physical association between uPAR and L-selectin. To examine the role of L-selectin in uPAR-mediated signaling, uPAR was cross-linked and intracellular Ca(2+) concentrations were measured by spectrofluorometry. A mAb reactive against the carbohydrate binding domain (CBD) of L-selectin substantially inhibited uPAR-mediated Ca(2+) mobilization, whereas mAbs against the beta(2) integrin complement receptor 3 (CR3), another uPAR-binding adhesion protein, had no effect. Similarly, fucoidan, a sulfated polysaccharide that binds to L-selectin CBD, inhibited the Ca(2+) signal. We conclude that uPAR associates with the CBD region of L-selectin to form a functional signaling complex.
白细胞尿激酶型纤溶酶原激活物受体（uPARs）聚集在黏附界面和迁移前沿，在那里它们参与黏附、趋化作用和蛋白水解。尽管这种糖脂锚定蛋白必须与跨膜蛋白结合才能进入细胞内部，但uPAR聚集会触发激活信号。本研究证明了uPAR与人类多形核中性粒细胞中的L-选择素之间存在一种新的伙伴关系。荧光共振能量转移证明了uPAR与L-选择素之间存在直接的物理关联。为了研究L-选择素在uPAR介导的信号传导中的作用，对uPAR进行交联，并通过荧光分光光度法测量细胞内Ca(2+)浓度。一种针对L-选择素碳水化合物结合结构域（CBD）的单克隆抗体显著抑制了uPAR介导的Ca(2+)动员，而针对另一种uPAR结合黏附蛋白β(2)整合素补体受体3（CR3）的单克隆抗体则没有作用。同样，与L-选择素CBD结合的硫酸化多糖岩藻依聚糖也抑制了Ca(2+)信号。我们得出结论，uPAR与L-选择素的CBD区域结合形成功能性信号复合物。
