Studies of nucleolin, a shuttle protein between the nucleus, cytoplasm, and cell surface

我们以前发现，诱导人Jurkat T细胞凋亡的结果在短暂的封盖的CD 43糖蛋白，在比磷脂酰丝氨酸暴露的阶段，其sialylpolylactosaminyl链作为巨噬细胞的吞噬识别的配体。我们还发现细胞表面核仁素参与识别早期凋亡细胞的唾液酸聚乳糖胺链簇。核仁素是一种多功能穿梭蛋白，存在于某些类型细胞的细胞核、细胞质和表面。人核仁素由710个氨基酸组成，其氨基端第三个结构域为酸性和碱性交替结构域，中间部分为四个共有RNA结合结构域（RBD），羧基端为富含甘氨酸/甘氨酸的结构域。E.大肠杆菌（rNUC）对巨噬细胞的作用。使用rNUCs的流式细胞术分析显示，巨噬细胞结合位点位于核仁素的中心区域，含有RBD。以往的研究表明核仁素295-302位的某些残基可能是早期凋亡细胞识别所必需的，这些结果表明核仁素通过295-302位的某些残基与早期凋亡细胞上的唾液酸聚乳糖胺链簇结合，而核仁素通过RBD与巨噬细胞相互作用，作为桥接分子促进巨噬细胞对早期凋亡细胞的识别。

We previously found that induction of apoptosis in human Jurkat T cells results in transient capping of CD43 glycoprotein, at the stage earlier than that of phosphatidylserine exposure, and its sialylpolylactosaminyl chains serve as ligands for phagocytic recognition by macrophages. We have also shown that cell-surface nucleolin is involved in the recognition of sialylpolylactosaminyl chains cluster of early apoptotic cells.Nucleolin is a multifunctional shuttling protein present in nucleus, cytoplasm, and on the surface of some types of cells. Human nucleolin is composed of 710 amino acids and it's amino-terminal third contains alternating acidic and basic domains, its middle section contains four consensus RNA-binding domains (RBDs), and its carboxy-terminus contains a glycine/arginine-rich domain.In order to examine how cell-surface nucleolin is located on the cell surface, where it might be accessible to function as a receptor for apoptotic cells, the binding of various deletion constructs of recombinant nucleolins produced in E. coli (rNUCs) to macrophages were examined. Flowcytometric analysis using rNUCs revealed that the macrophage-binding site is located in the center region of nucleolin, containing RBDs. Previous studies suggested that some residues within the 295-302 of nucleolin are likely to be required for the recognition of early apoptotic cells.These results suggest that nucleolin binds to sialylpolylactosaminyl chains cluster on early apoptotic cells via some residues within the 295-302, whereas it interacts with macrophage via RBDs, then promoting macrophage recognition of early apoptotic cells as a bridging molecule.