Hsieh Tzefu, Gordon Rebecca E, Clemmons David R, Busby Walker H, Duan Cunming
Department of Molecular, Cellular, and Developmental Biology, the University of Michigan, Ann Arbor, Michigan 48109, USA.
J Biol Chem. 2003 Oct 31;278(44):42886-92. doi: 10.1074/jbc.M303835200. Epub 2003 Aug 12.
Insulin-like growth factor (IGF)-I is a pleiotropic hormone that regulates vascular smooth muscle cell (VSMC) migration, proliferation, apoptosis, and differentiation. These actions are mediated by the IGF-I receptor. How activation of the same receptor by the same ligand leads to these diverse cellular responses is not well understood. Here we describe a novel mechanism specifying VSMC responses to IGF-I stimulation, distinctive for the pivotal roles of local IGF-binding proteins (IGFBPs). The role of local IGFBPs was indicated by comparing the activities of IGF-I and des-1-3-IGF-I, an IGF-I analog with reduced binding affinity to IGFBPs. Compared with IGF-I, des-1-3-IGF-I was more potent in stimulating DNA synthesis but much less potent in inducing directed migration of VSMCs. When the effects of individual IGFBPs were tested, IGFBP-2 and IGFBP-4 were found to inhibit IGF-I-stimulated DNA synthesis and migration. IGFBP-5 had an inhibitory effect on IGF-I-stimulated DNA synthesis, but it strongly potentiated IGF-I-induced VSMC migration. By using a non-IGF-binding IGFBP-5 mutant and an IGF-I-neutralizing antibody, it was demonstrated that IGFBP-5 also stimulates VSMC migration in an IGF-independent manner. This effect of IGFBP-5 was inhibited by soluble heparin and by treating cells with heparinase. Mutation of the heparin-binding motif of IGFBP-5 reduced its migration promoting activity. These findings suggest that local IGFBPs are important determinants of cellular responses to IGF-I stimulation, and a key player in this paradigm is IGFBP-5. IGFBP-5 not only modulates IGF-I actions, but it also stimulates cell migration by interacting with cell-surface heparan sulfate proteoglycans.
胰岛素样生长因子（IGF）-I是一种多效性激素，可调节血管平滑肌细胞（VSMC）的迁移、增殖、凋亡和分化。这些作用是由IGF-I受体介导的。目前尚不清楚同一配体对同一受体的激活如何导致这些不同的细胞反应。在这里，我们描述了一种新的机制，该机制明确了VSMC对IGF-I刺激的反应，其独特之处在于局部IGF结合蛋白（IGFBP）的关键作用。通过比较IGF-I和des-1-3-IGF-I（一种与IGFBP结合亲和力降低的IGF-I类似物）的活性，表明了局部IGFBP的作用。与IGF-I相比，des-1-3-IGF-I在刺激DNA合成方面更有效，但在诱导VSMC定向迁移方面效力要小得多。当测试单个IGFBP的作用时，发现IGFBP-2和IGFBP-4可抑制IGF-I刺激的DNA合成和迁移。IGFBP-5对IGF-I刺激的DNA合成有抑制作用，但它强烈增强了IGF-I诱导的VSMC迁移。通过使用非IGF结合的IGFBP-5突变体和IGF-I中和抗体，证明IGFBP-5也以IGF非依赖性方式刺激VSMC迁移。IGFBP-5的这种作用被可溶性肝素和用肝素酶处理细胞所抑制。IGFBP-5肝素结合基序的突变降低了其迁移促进活性。这些发现表明，局部IGFBP是细胞对IGF-I刺激反应的重要决定因素，在这一模式中的关键参与者是IGFBP-5。IGFBP-5不仅调节IGF-I的作用，还通过与细胞表面硫酸乙酰肝素蛋白聚糖相互作用来刺激细胞迁移。
