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

有许多报道表明，黏附分子与唾液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，将唾液酸修饰为一种新的环状结构，命名为“环唾液酸”，其羧基缺失。这种修饰可以调节唾液酸介导的细胞粘附强度。在这项研究中，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，我们获得了一个编码人干扰素- γ的cDNA克隆，干扰素- γ是促进环唾液酸6-磺酰Lewis x表达的因子。当表达环唾液酸6-磺酰Lewis x的细胞经干扰素- γ处理后，观察到环唾液酸6-磺酰Lewis x的表达呈时间和剂量依赖性。这些作用是可逆的，并且在人淋巴样细胞上比在上皮细胞衍生的细胞上更快地被检测到。本文首次报道了诱导环唾液酸表达的天然因子。研究干扰素诱导表达环sialyl 6-sulfo Lewis x的机制将阐明这一代谢途径的功能。另一方面，如YT或HUT-102等细胞系被识别环硅基6-磺基Lewis x抗原的单克隆抗体（mAb） G159染色呈阳性，而识别环硅基6-磺基Lewis x前体的单克隆抗体染色呈阴性。我们检测了固定和渗透细胞的细胞内染色模式，并在细胞外壳区域的载具中检测到前体唾液糖缀合物。提示环唾液酸的形成可能发生在细胞外壳区。

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.