Molecular mechanism of leukocyte activation by galectin via integrin family

半乳糖凝集素是动物凝集素家族的成员，能特异性识别糖结合物的P-半乳糖苷结构。本研究试图分析Galectins串联重复序列Galectins-8和Galectins-9在免疫细胞中的作用及其信号转导的分子机制。首先，我们比较了Galectins-8和Galectins-9对不同免疫细胞系的细胞凋亡和细胞黏附的影响。Galectin-9诱导Tell细胞(Jurkat和Molt-4)的凋亡，但Galectin-8不能同时介导B细胞系(Namalwa和RPM-8866)和单核细胞系(THP-1)的细胞黏附。在本研究中，我们检测了Galectin-9介导的Jurkat T细胞死亡的特性。Galectin-9NC(野生型)由两个CRD(N端和C端糖识别域)及其衍生物Galectins-9-NN和-9-CC诱导Jurkat T细胞凋亡。然而，单一的CRD(Galectin-9NT或-CT)没有作用，这表明两个CRD的稳定的二聚体结构是活性所必需的。N-葡聚糖合成抑制剂可抑制细胞凋亡，表明N-葡聚糖在Galectin-9诱导的细胞凋亡中起重要作用。我们先前的研究表明，Galectin-9通过钙依赖的钙-钙蛋白酶-半胱氨酸蛋白酶-caspase-1途径介导MOLT-4细胞的凋亡。在Jurkat细胞中，Galectin-9引起的细胞死亡不能被caspase抑制剂、Ca~(2+)-螯合剂或Calain抑制剂所充分抑制。此外，我们观察到在Galectin-9处理的细胞中，线粒体膜电位的丧失和AIF的显著释放。这些发现提示Jurkat细胞中存在caspase依赖和非依赖的死亡途径，其主要途径可能因T细胞类型而异。

Galectins are members of an animal lectin family, which specifically recognizes P-galactoside structure of glycoconjugates. In this study, we attempted to analyze the molecular mechanism of the functions and their signaling of tandem repeat galectins, such as galectins-8 and-9 in immune cells. First, we compared the effects of galectins-8 and-9on the apoptosis and cell adhesion in various immune cell lines. Galectin-9 induced apoptosis of Tell lines (Jurkat and Molt-4), but galectin-8 did not Both of galectins mediated the cell adhesion to plastic culture plates in B-cell lines(Namalwa, and RPM-8866) and a monocytic cell (THP-1) in addition of T-cell lines. In the present study, we examined the properties of galectin-9-mediated cell death of Jurkat T-cells. Galectin-9NC (wild-type), consisting of two CRDs (N-terminal and C-terminal carbohydrate recognition domains), and derivatives of it, galectins-9-NN and-9-CC, induced Jurkat T-cell apoptosis. However, a single CRD (galectin-9NT or-CT) had no effect, suggesting the stable dimeric structure of two CRDs is required for the activity. The apoptosis was inhibited by pretreatment with an N-glycan synthesis inhibitor, indicating that the expression of N-glycans in the cells is essential for galectin-9-induced apoptosis. We previously showed that the apoptosis of MOLT-4 cell is mediated by galectin-9 via a Ca^<2+>-calpain-caspase-1-dependent pathway. In Jurkat cells, the cell death by galectin-9, was insufficiently suppressed by caspase inhibitors, Ca^<2+>-chelator or calpain inhibitor. Furthermore, we observed the loss of mitochondrial membrane potential and significant AIF release in galectin-9-treated cells. These findings suggest that caspase-dependent and-independent death pathways exist in Jurkat cells, and the main pathway might vary with the T-cell type.