Study of the regulation mechanism of cell adhesion caused by a nobel modification of sialic acid

有许多报道表明粘附分子与唾液酸糖缀合物的反应性是由于它们识别唾液酸的羧基。最近我们发现了一种新的代谢途径，将唾液酸修饰成一种新的环状形式，称为“环状唾液酸”，缺少其羧基。这种修饰应该调节唾液酸介导的细胞粘附的强度。在本研究中，我们试图通过分离编码唾液酸环化酶的cDNA来研究细胞粘附的调节机制，该酶催化上述修饰，在唾液酸环化酶cDNA的表达克隆过程中，我们获得了编码人干扰素-γ的cDNA克隆，该人干扰素-γ作为增强环唾液酸6-磺基刘易斯x表达的因子。当用干扰素γ处理表达sialyl 6-sulfo刘易斯x的细胞时，以时间和剂量依赖的方式观察到环sialyl 6-sulfo刘易斯x的表达。这些影响是可逆的，在人淋巴细胞上检测到的速度比在上皮细胞衍生的细胞上更快。这是第一个报告，以确定自然发生的因素，可以诱导表达的环唾液酸。另一方面，识别环唾液酸6-磺基刘易斯x抗原的单克隆抗体（mAb）G159对YT或HUT-102等细胞系呈阳性染色，而识别环唾液酸6-磺基刘易斯x前体的mAb对YT或HUT-102等细胞系不呈阳性染色。我们检查了固定和透化细胞的细胞内染色模式，并在细胞被膜区域检测到载体中的前体唾液酸糖缀合物。结果表明，在细胞被膜区有环唾液酸的形成。

There are many reports indicating that the reactivity of adhesion molecules with sialoglycoconjugates is due to their recognition of the carboxyl group of sialic acid. Recently we found a novel metabolic pathway to modify the sialic acid to be a novel ring form named "cyclic sialic acid", lacking its carboxyl group. This modification should regulate the strength of cell adhesion mediated by sialic acid. In this study, we tried to investigate the mechanism of regulation of cell adhesion by isolation of a cDNA encoding an enzyme named sialic acid cyclase, which catalyzes above modification.In the process of the expression cloning of the sialic acid cyclase cDNA, we obtained a cDNA clone encoding human interferon-gamma as a factor that enhances the expression of cyclic sialyl 6-sulfo Lewis x. The expression of cyclic sialyl 6-sulfo Lewis x was observed in time-and dose-dependent manner, when the sialyl 6-sulfo Lewis x expressing cells were treated with interferon-gamma. These effects were reversible and detected on human lymphoid cells more rapidly than on cells derived from epithelial cells. This is the first report to identify the naturally occurring factor which can induce the expression of cyclic sialic acid. Investigation of the mechanism induced by interferon-gamma to express cyclic sialyl 6-sulfo Lewis x will clarify the function of this metabolic pathway.In the other hand, the cell lines such as YT or HUT-102 stained positively by monoclonal antibody (mAb) G159, which recognizes cyclic silayl 6-sulfo Lewis x antigen, are not stained positively with the mAbs recognizing precursor of cyclic silayl 6-sulfo Lewis x. We examined the intracellular staining pattern of the fixed and permeabilized cells and detected the precursor sialoglycoconjugates in vehicles in cell coat region. It is suggested that some formation of cyclic sialic acid is occurred in cell coat region.