Galluzzo E, Albi N, Fiorucci S, Merigiola C, Ruggeri L, Tosti A, Grossi C E, Velardi A
Department of Clinical Medicine, Pathology and Pharmacology, University of Perugia, Italy.
Eur J Immunol. 1995 Oct;25(10):2932-9. doi: 10.1002/eji.1830251033.
The standard, 85-95-kDa form of the hyaluronic acid (HA) receptor CD44 and a number of CD44 mRNA splice variants play important roles in immune responses and tumor metastasis. Variants carrying exon 6 (v6), or 9 (v9) products are transiently expressed on activated human T cells. Here, modulation experiments with specific monoclonal antibodies (mAb) indicate that v6 and v9 are expressed independently on distinct sets of CD44 molecules, and that their combined expression is necessary for HA adhesion. Moreover, the finding that mAb-mediated cross-linking of v6 and v9 promoted cytosolic free Ca2+ mobilization and co-stimulated CD3-triggered T cell proliferation indicates that v6 and v9 possess signaling and effector function activation ability. Finally, HA-mediated signaling appears to be required for variant-dependent adhesion to HA. The observation that soluble HA promoted cytosolic free Ca2+ mobilization indicates that HA-induced Ca2+ mobilization can occur during T cell-HA interaction. Since Ca2+ mobilization was inhibited by pretreatment of cells with an anti-CD44 mAb directed against the HA-binding domain of CD44, CD44 receptors appear to be involved in HA-mediated signal transduction. The requirement of cytosolic free Ca2+ for adhesion is shown by the fact that ionomycin (a Ca2+ ionophore) stimulated, and EGTA (a Ca2+ chelator), inhibited HA adhesion. In addition, cytoskeletal functional activation is required for cell adhesion to HA, since drugs that block actin polymerization, such as cytochalasin B, or actomyosin contraction, such as the calmodulin antagonist W-7, inhibited cell adhesion to HA. As this adhesion is also ADP ribosylation-sensitive, it may involve a GTP-dependent function of CD44v, i.e. ankyrin binding. Our data indicate that there is a functional hierarchy among the CD44 molecules expressed on human peripheral blood T cells and that the splice variants, as compared to the standard form, exhibit a greater HA binding ability which involves CD44-mediated signaling and effector function activation.
透明质酸（HA）受体CD44的标准85 - 95 kDa形式以及一些CD44 mRNA剪接变体在免疫反应和肿瘤转移中发挥重要作用。携带外显子6（v6）或9（v9）产物的变体在活化的人T细胞上短暂表达。在这里，用特异性单克隆抗体（mAb）进行的调节实验表明，v6和v9在不同的CD44分子组上独立表达，并且它们的联合表达对于HA黏附是必需的。此外，mAb介导的v6和v9交联促进胞质游离Ca2+动员并共同刺激CD3触发的T细胞增殖这一发现表明，v6和v9具有信号传导和效应功能激活能力。最后，HA介导的信号传导似乎是变体依赖性黏附于HA所必需的。可溶性HA促进胞质游离Ca2+动员的观察结果表明，HA诱导的Ca2+动员可在T细胞与HA相互作用期间发生。由于用针对CD44的HA结合域的抗CD44 mAb预处理细胞可抑制Ca2+动员，CD44受体似乎参与了HA介导的信号转导。离子霉素（一种Ca2+离子载体）刺激而EGTA（一种Ca2+螯合剂）抑制HA黏附这一事实表明黏附需要胞质游离Ca2+。此外，细胞黏附于HA需要细胞骨架功能激活，因为阻断肌动蛋白聚合的药物（如细胞松弛素B）或抑制肌动球蛋白收缩的药物（如钙调蛋白拮抗剂W - 7）可抑制细胞黏附于HA。由于这种黏附对ADP核糖基化敏感，它可能涉及CD44v的GTP依赖性功能，即锚蛋白结合。我们的数据表明，人外周血T细胞上表达的CD44分子之间存在功能层次结构，并且与标准形式相比，剪接变体表现出更大的HA结合能力，这涉及CD44介导的信号传导和效应功能激活。
