Haskell C A, Cleary M D, Charo I F
Gladstone Institute of Cardiovascular Disease, San Francisco, California 94141-9100, USA.
J Biol Chem. 2000 Nov 3;275(44):34183-9. doi: 10.1074/jbc.M005731200.
The chemokine fractalkine (FK) has two structural features that make it unique in the chemokine family: a CX(3)C motif and an extended carboxyl terminus that anchors it to the cell surface. This mucin-like stalk or an equivalent spacer is required for FK to mediate the adhesion of cells expressing its receptor, CX(3)CR1. To determine whether the ability of FK to act as a cell adhesion molecule is due to the unique presentation of a chemokine domain on a stalk or to properties of the chemokine domain itself, we created a series of chimeras in which other soluble chemokines (RANTES (regulated on activation normal T cell expressed), monocyte chemoattractant protein 1, macrophage inflammatory protein 1 beta, secondary lymphoid tissue chemokine, and interleukin 8) were fused to the mucin stalk. When tested in a static-cell adhesion assay, many of these chemokine chimeras demonstrated activity equivalent to that of FK. In flow assays, however, none of the chimeras captured cells as efficiently as FK. Interestingly, FK captured cells expressing either CX(3)CR1 or the viral receptor US28. Cells bound to FK without rolling or detaching, whereas the interleukin 8 and monocyte chemoattractant protein 1 chimeras induced primarily cell rolling and detaching, respectively. In binding studies, FK has a significantly slower off-rate from its receptors than any of the other chemokine chimeras had for their cognate receptors. We conclude that presentation of a chemokine atop a mucin-like stalk is not, in and of itself, sufficient to capture cells. The unique ability of FK to mediate adhesion under flow may be a function of its slow receptor off-rate.
趋化因子fractalkine（FK）具有两个结构特征，使其在趋化因子家族中独树一帜：一个CX(3)C基序和一个将其锚定在细胞表面的延长羧基末端。这种黏蛋白样茎或等效间隔区是FK介导表达其受体CX(3)CR1的细胞黏附所必需的。为了确定FK作为细胞黏附分子的能力是由于茎上趋化因子结构域的独特呈现还是趋化因子结构域本身的特性，我们构建了一系列嵌合体，其中其他可溶性趋化因子（RANTES（活化正常T细胞表达上调）、单核细胞趋化蛋白1、巨噬细胞炎性蛋白1β、二级淋巴组织趋化因子和白细胞介素8）与黏蛋白茎融合。在静态细胞黏附试验中进行测试时，许多这些趋化因子嵌合体表现出与FK相当的活性。然而，在流动试验中，没有一个嵌合体能像FK那样有效地捕获细胞。有趣的是，FK捕获表达CX(3)CR1或病毒受体US28的细胞。与FK结合的细胞不会滚动或脱离，而白细胞介素8和单核细胞趋化蛋白1嵌合体分别主要诱导细胞滚动和脱离。在结合研究中，FK与其受体的解离速率明显慢于任何其他趋化因子嵌合体与其同源受体的解离速率。我们得出结论，在黏蛋白样茎上呈现趋化因子本身并不足以捕获细胞。FK在流动状态下介导黏附的独特能力可能是其受体解离速率缓慢的结果。
