Department of Internal Medicine, School of Medicine, Chonbuk National University, Jeonju 56-182, South Korea.
J Biol Chem. 2011 May 20;286(20):17898-909. doi: 10.1074/jbc.M111.231035. Epub 2011 Mar 7.
Insulin-like growth factor-binding protein-3 (IGFBP-3) is a multifunctional protein known for modulating mitogenic and metabolic actions of IGFs as well as exerting a variety of biological actions not involving IGFs. Here, we show that IGFBP-3 blocks specific physiological consequences of asthma in an IGF-independent manner in vitro and in vivo. IGFBP-3 treatment effectively reduced all physiological manifestations of asthma examined in vivo (airway hyper-responsiveness, cellular and pathological changes in bronchoalveolar lavage fluid and lung tissue, and expression of numerous proinflammatory molecules). These unique IGFBP-3 effects were further confirmed in IGFBP-3-transgenic mice, thus strengthening the notion of IGFBP-3 actions within the respiratory system. Using human epithelial cells, we demonstrated the following: 1) IGFBP-3 blocks TNF-α-induced expression of proinflammatory molecules; 2) IGFBP-3 attenuates the TNF-α-induced migratory response of eosinophils; and 3) IGFBP-3 negatively regulates TNF-α-induced expression of the key NF-κB regulatory molecules IκBα and p65-NF-κB at the post-translational level. We identified that IGFBP-3 degrades IκBα and p65-NF-κB proteins through IGFBP-3 receptor (IGFBP-3R)-mediated activation of caspases thereby inhibiting TNF-α-induced activation of NF-κB signaling cascades. This unique IGFBP-3/IGFBP-3R action was further confirmed by demonstrating complete inhibition of IGFBP-3 action in the presence of caspase inhibitors as well as IGFBP-3R siRNAs. Non-IGF-binding IGFBP-3 mutants further proved the IGF-independent action of IGFBP-3. Our findings indicate that IGFBP-3 inhibits airway inflammation and hyper-responsiveness via an IGF-independent mechanism that involves activation of IGFBP-3R signaling and cross-talk with NF-κB signaling. The IGFBP-3/IGFBP-3R system therefore plays a pivotal role in the pathogenesis of asthma and can serve as a newly identified potential therapeutic target for this debilitating disease.
胰岛素样生长因子结合蛋白-3（IGFBP-3）是一种多功能蛋白，已知其可调节 IGF 的有丝分裂和代谢作用，以及发挥不涉及 IGF 的多种生物学作用。在这里，我们表明 IGFBP-3 以 IGF 独立的方式在体外和体内阻断哮喘的特定生理后果。IGFBP-3 治疗有效降低了体内检查的所有哮喘生理表现（气道高反应性、支气管肺泡灌洗液和肺组织中的细胞和病理变化，以及众多促炎分子的表达）。这些独特的 IGFBP-3 作用在 IGFBP-3 转基因小鼠中得到进一步证实，从而加强了 IGFBP-3 在呼吸系统中的作用的概念。使用人上皮细胞，我们证明了以下几点：1）IGFBP-3 阻断 TNF-α诱导的促炎分子表达；2）IGFBP-3 减弱 TNF-α诱导的嗜酸性粒细胞迁移反应；3）IGFBP-3 负调节 TNF-α诱导的关键 NF-κB 调节分子 IκBα 和 p65-NF-κB 在翻译后水平的表达。我们确定 IGFBP-3 通过 IGFBP-3 受体（IGFBP-3R）介导的半胱天冬酶激活来降解 IκBα 和 p65-NF-κB 蛋白，从而抑制 TNF-α诱导的 NF-κB 信号级联的激活。通过在存在半胱天冬酶抑制剂和 IGFBP-3R siRNA 的情况下完全抑制 IGFBP-3 作用，进一步证实了这种独特的 IGFBP-3/IGFBP-3R 作用。非 IGF 结合的 IGFBP-3 突变体进一步证明了 IGFBP-3 的 IGF 独立作用。我们的研究结果表明，IGFBP-3 通过涉及 IGFBP-3R 信号激活和与 NF-κB 信号交叉对话的 IGF 独立机制抑制气道炎症和高反应性。因此，IGFBP-3/IGFBP-3R 系统在哮喘的发病机制中起着关键作用，并可作为这种衰弱性疾病的新确定的潜在治疗靶点。
