Lark M W, Laterra J, Culp L A
Fed Proc. 1985 Feb;44(2):394-403.
The fibroblast cell line Balb/c 3T3 makes both close and tight-focal adhesive contacts with the plasma fibronectin (pFn)-coated tissue culture substratum. Detachment of these cells mediated by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid leaves tight-focal contacts and a subset of close contacts as substratum-attached material (SAM). The enrichment of heparan sulfate (HS) proteoglycan (HS-PG) in SAM under specific attachment conditions, as well as the recent demonstration of HS binding to pFn or cellular Fn, has evolved a series of experiments with the selective HS-binding protein platelet factor-4 to analyze the requirement of the HS-binding activity of pFn in the formation of these two types of adhesive contacts. In addition, the cell-binding domain (CBD) of pFn, which recognizes an unidentified cell surface receptor, has been isolated free of HS-binding domains after proteolytic cleavage of pFn. These functional studies indicate that the binding of pFn on the substratum to cell surface HS-PG is necessary and sufficient to generate close contacts with transmembrane signaling of this proteoglycan to reorganize lengthy microfilament bundles in the cytoplasm. Cells spread incompletely on CBD alone, form only close contacts, and reorganize highly concentrated actin filaments only in their spiky projections. Furthermore, the formation of tight-focal contacts with associated stress fibers appears to require both reactions of pFn, binding to cell surface HS-PG and to its unidentified receptor. The importance of HS-PG in these functional studies has led to its better biochemical characterization in SAM. Initially formed close contacts of these cells contain principally a large HS-PG that aggregates into high-molecular-weight complexes by some unknown mechanism. With time, there are two different mechanisms of catabolism of HS-PG, one of which includes the liberation of single-chain HS. The importance of these changes in the HS-PG in SAM are now being analyzed with regard to the formation and disappearance of close and tight-focal adhesions.
成纤维细胞系Balb/c 3T3与血浆纤连蛋白（pFn）包被的组织培养基质形成紧密和紧密聚焦的黏附接触。由乙二醇双（β-氨基乙醚）-N，N，N'，N'-四乙酸介导的这些细胞脱离会留下紧密聚焦接触和一部分紧密接触作为基质附着材料（SAM）。在特定附着条件下SAM中硫酸乙酰肝素（HS）蛋白聚糖（HS-PG）的富集，以及最近HS与pFn或细胞纤连蛋白（Fn）结合的证明，促使人们进行了一系列使用选择性HS结合蛋白血小板因子-4的实验，以分析pFn的HS结合活性在这两种黏附接触形成中的需求。此外，pFn的细胞结合结构域（CBD）可识别未鉴定的细胞表面受体，在pFn经蛋白水解切割后已从HS结合结构域中分离出来。这些功能研究表明，基质上的pFn与细胞表面HS-PG的结合对于产生紧密接触以及该蛋白聚糖的跨膜信号传导以重组细胞质中长长的微丝束是必要且充分的。细胞仅在CBD上不完全铺展，仅形成紧密接触，并且仅在其尖刺状突起中重组高度浓缩的肌动蛋白丝。此外，与相关应力纤维形成紧密聚焦接触似乎需要pFn的两种反应，即与细胞表面HS-PG结合以及与未鉴定的受体结合。HS-PG在这些功能研究中的重要性促使人们对SAM中的HS-PG进行更好的生化表征。这些细胞最初形成的紧密接触主要包含一种大的HS-PG，它通过某种未知机制聚集成高分子量复合物。随着时间的推移，HS-PG有两种不同的分解代谢机制，其中一种包括单链HS的释放。现在正在分析SAM中HS-PG的这些变化对于紧密和紧密聚焦黏附的形成和消失的重要性。
