Kzhyshkowska Julia, Workman Gail, Cardó-Vila Marina, Arap Wadih, Pasqualini Renata, Gratchev Alexei, Krusell Liis, Goerdt Sergij, Sage E Helene
Department of Dermatology, University Medical Centre Mannheim, Ruprecht-Karls University of Heidelberg, Theodor-Kutzer Ufer 1-3, D-68167 Mannheim, Germany.
J Immunol. 2006 May 15;176(10):5825-32. doi: 10.4049/jimmunol.176.10.5825.
The matricellular protein SPARC (secreted protein acidic and rich in cysteine) has been implicated in development, differentiation, response to injury, and tumor biology by virtue of its regulation of extracellular matrix production/assembly and its antiadhesive and antiproliferative effects on different cell types. Despite numerous biological activities described for SPARC, cell surface receptors for this protein have not been identified. By phage display and in vitro-binding assays, we now show that SPARC interacts with stabilin-1, a scavenger receptor expressed by tissue macrophages and sinusoidal endothelial cells. The interaction is mediated by the extracellular epidermal growth factor-like region of stabilin-1 containing the sequence FHGTAC. Using FACS analysis and confocal microscopy, we demonstrate that stabilin-1 internalizes and targets SPARC to an endosomal pathway in Chinese hamster ovary cells stably transfected with this receptor. In human macrophages, stabilin-1 expression is required for receptor-mediated endocytosis of SPARC. SPARC was efficiently endocytosed by alternatively activated macrophages stimulated by IL-4 and dexamethasone, but not solely by Th1 or Th2 cytokines. A time course of ligand exposure to alternatively activated macrophages revealed that stabilin-1-mediated endocytosis of SPARC was followed by its targeting for degradation, similar to the targeting of acetylated low density lipoprotein, another stabilin-1 ligand. We propose that alternatively activated macrophages coordinate extracellular matrix remodeling, angiogenesis, and tumor progression via stabilin-1-mediated endocytosis of SPARC and thereby regulate its extracellular concentration.
基质细胞蛋白SPARC（分泌性酸性富含半胱氨酸蛋白）因其对细胞外基质产生/组装的调节以及对不同细胞类型的抗黏附和抗增殖作用，而与发育、分化、损伤反应及肿瘤生物学相关。尽管已描述了SPARC的众多生物学活性，但该蛋白的细胞表面受体尚未被鉴定。通过噬菌体展示和体外结合试验，我们现在表明SPARC与稳定素-1相互作用，稳定素-1是一种由组织巨噬细胞和窦状内皮细胞表达的清道夫受体。这种相互作用由稳定素-1的细胞外表皮生长因子样区域介导，该区域包含序列FHGTAC。使用流式细胞术分析和共聚焦显微镜，我们证明在稳定转染该受体的中国仓鼠卵巢细胞中，稳定素-1内化并将SPARC靶向至内体途径。在人类巨噬细胞中，稳定素-1的表达是SPARC受体介导的内吞作用所必需的。SPARC被白细胞介素-4和地塞米松刺激的替代性活化巨噬细胞有效内吞，但不仅仅由Th1或Th2细胞因子介导。配体与替代性活化巨噬细胞接触的时间进程显示，稳定素-1介导的SPARC内吞作用之后是其靶向降解，类似于另一种稳定素-1配体乙酰化低密度脂蛋白的靶向作用。我们提出，替代性活化巨噬细胞通过稳定素-1介导的SPARC内吞作用协调细胞外基质重塑、血管生成和肿瘤进展，从而调节其细胞外浓度。
