Altieri D C, Wiltse W L, Edgington T S
Department of Immunology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
J Immunol. 1990 Jul 15;145(2):662-70.
A variety of monocyte/neutrophil adhesive functions is coordinated by the CD11b/CD18 complex, a leukocyte-restricted member of integrin receptors. Previous studies have shown that the adenine nucleotide ADP produces a transient and high affinity recognition state of CD11b/CD18 for its complementary ligands fibrinogen and factor X. We have now characterized the process of intracellular signalling initiated in monocytes by ADP. Further, we have causally related these events to the qualitative upregulation of CD11b/CD18, as exemplified by its inducible binding of factor X. Micromolar concentrations of ADP or ATP produce dose-dependent increase in monocyte cytosolic free [Ca2+]i through mobilization from intracellular stores coupled with a sustained, EGTA-sensitive, influx of Ca2+ from the external compartment. This Ca2+ response was kinetically and quantitatively heterogeneous when analyzed at the single cell level. Ca2+ channel antagonists nifedipine or verapamil blocked the sustained phase of ADP-induced Ca2+ entry and inhibited 125I-factor X binding to CD11b/CD18 in a dose-dependent manner. Nifedipine-sensitive Ca2+ channels are gated by variations in transmembrane potential in a variety of cells. In monocytes, depolarizing conditions by high external [K+] or by the Na+ ionophore gramicidin D mimicked the stimulatory effect of ADP, inducing increased cytosolic free [Ca2+]i and 125I-factor X binding to CD11b/CD18. In contrast, these responses were both abrogated by hyperpolarization with the K+ ionophore valinomycin. These data suggest that a sustained increase in monocyte cytosolic free [Ca2+]i coupled with variations in transmembrane potential regulate the high affinity receptor function of CD11b/CD18. Although prototypically exemplified for monocyte stimulation with adenine nucleotides, this pathway of intracellular signalling might provide a general mechanism for transient and qualitative functional upregulation of integrin receptors.
多种单核细胞/中性粒细胞黏附功能由CD11b/CD18复合物协调，该复合物是整合素受体中白细胞特异性成员。先前的研究表明，腺嘌呤核苷酸ADP可使CD11b/CD18对其互补配体纤维蛋白原和因子X产生短暂的高亲和力识别状态。我们现在已对ADP在单核细胞中引发的细胞内信号传导过程进行了表征。此外，我们已将这些事件与CD11b/CD18的定性上调建立了因果关系，例如其对因子X的诱导性结合。微摩尔浓度的ADP或ATP通过从细胞内储存库中动员Ca2+并伴随着外部隔室中Ca2+的持续、EGTA敏感的内流，使单核细胞胞质游离[Ca2+]i呈剂量依赖性增加。在单细胞水平分析时，这种Ca2+反应在动力学和定量上是异质性的。Ca2+通道拮抗剂硝苯地平或维拉帕米可阻断ADP诱导的Ca2+内流的持续阶段，并以剂量依赖性方式抑制125I-因子X与CD11b/CD18的结合。硝苯地平敏感的Ca2+通道在多种细胞中受跨膜电位变化的调控。在单核细胞中，高细胞外[K+]或Na+离子载体短杆菌肽D引起的去极化条件模拟了ADP的刺激作用，诱导胞质游离[Ca2+]i增加以及125I-因子X与CD11b/CD18的结合。相反，K+离子载体缬氨霉素引起的超极化可消除这些反应。这些数据表明，单核细胞胞质游离[Ca2+]i的持续增加以及跨膜电位的变化调节了CD11b/CD18的高亲和力受体功能。尽管以腺嘌呤核苷酸刺激单核细胞作为典型例子，但这种细胞内信号传导途径可能为整合素受体的短暂和定性功能上调提供一种普遍机制。
