Rees C, Clemmons D R
Department of Medicine, University of North Carolina School of Medicine, Chapel Hill 27599, USA.
J Cell Biochem. 1998 Dec 1;71(3):375-81.
Insulin-like growth factor binding protein-5 (IGFBP-5) is synthesized and secreted by smooth muscle cells (SMC). IGFBP-5 synthesis is stimulated five- to sixfold by IGF-I, and IGFBP-5 has been shown to augment IGF-I-stimulated DNA synthesis in this cell type. The ability of IGFBP-5 to augment the SMC response to IGF-I is dependent upon its binding to extracellular matrix. A highly charged region of IGFBP-5 that contains amino acids in positions 201-218 has been shown to mediate binding of IGFBP-5 to human fibroblast extracellular matrix (ECM), and a synthetic peptide containing this sequence inhibits IGFBP-5 binding to fibroblast ECM. In this study we show that exposure of SMC cultures that are constitutively synthesizing IGFBP-5 to a synthetic peptide (termed peptide A) containing this sequence has no effect on its synthesis but reduces its abundance within the ECM. The addition of increasing concentrations of the peptide to SMC cultures resulted in a concentration-dependent reduction in ECM-associated IGFBP-5. In contrast, a control peptide (peptide B), which contained the region of amino acids in positions 131-141 and had a similar charge-to-mass ratio, caused a minimal decrease in ECM binding. This effect was functionally significant since the addition of 10 microg/ml of peptide A inhibited the cellular replication response to 10 ng/ml IGF-I by 51%, and peptide B had no effect. The effects of peptide A were not due to nonspecific cytotoxicity since it had no inhibitory effect on the response of these cells to human serum and was associated with only minimal inhibition of the cellular response to platelet-derived growth factor. The findings suggest that inhibiting IGFBP-5 binding to porcine SMC ECM results in reduced cellular responses to IGF-I.
胰岛素样生长因子结合蛋白-5（IGFBP-5）由平滑肌细胞（SMC）合成并分泌。IGF-I可使IGFBP-5的合成增加5至6倍，并且已表明IGFBP-5可增强该细胞类型中IGF-I刺激的DNA合成。IGFBP-5增强SMC对IGF-I反应的能力取决于其与细胞外基质的结合。已表明IGFBP-5中一个包含201-218位氨基酸的高电荷区域介导IGFBP-5与人成纤维细胞细胞外基质（ECM）的结合，并且包含该序列的合成肽可抑制IGFBP-5与成纤维细胞ECM的结合。在本研究中，我们表明将持续合成IGFBP-5的SMC培养物暴露于含有该序列的合成肽（称为肽A）对其合成没有影响，但会降低其在ECM中的丰度。向SMC培养物中添加浓度不断增加的该肽会导致与ECM相关的IGFBP-5呈浓度依赖性降低。相比之下，包含131-141位氨基酸区域且电荷质量比相似的对照肽（肽B）导致ECM结合的最小减少。这种作用在功能上具有重要意义，因为添加10μg/ml的肽A可使细胞对10ng/ml IGF-I的复制反应抑制51%，而肽B没有作用。肽A的作用并非由于非特异性细胞毒性，因为它对这些细胞对人血清的反应没有抑制作用，并且仅对细胞对血小板衍生生长因子的反应有最小程度的抑制。这些发现表明，抑制IGFBP-5与猪SMC ECM的结合会导致细胞对IGF-I的反应降低。
