Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
Am J Physiol Gastrointest Liver Physiol. 2018 Aug 1;315(2):G206-G219. doi: 10.1152/ajpgi.00349.2017. Epub 2018 Apr 6.
Insulin-like growth factor-binding protein-4 (IGFBP-4) is a binding protein that modulates the action of insulin-like growth factor-1 (IGF-1), a growth factor whose presence is required for the intestinotrophic effects of glucagon-like peptide-2 (GLP-2). GLP-2 is a gut hormone that uses both IGF-1 and epidermal growth factor (EGF) as intermediary factors to promote intestinal growth. Therefore, to elucidate the mechanism through which IGFBP-4 regulates IGF-1 activity in the intestine, proliferation assays were conducted using rat intestinal epithelial cells (IEC-6). IGF-1 and EGF synergistically enhanced proliferation, an effect that was dose-dependently decreased by IGFBP-4 ( P < 0.05-0.001) in an IGF-1 receptor (R)- and MEK1/2- but not a phosphatidylinositol 3-kinase-dependent manner ( P > 0.05 for IGFBP-4 effects with IGF-1R and MEK1/2 inhibitors). Intestinal organoids derived from IGFBP-4 knockout mice demonstrated significantly greater Ki-67 expression and an enhanced surface area increase in response to IGF-1 treatment, compared with organoids from control mice ( P < 0.05-0.01). GLP-2 is also known to increase the mucosal expression of IGFBP-4 mRNA. To investigate whether this occurs through the actions of its intermediaries, IGF-1 and EGF, inducible intestinal epithelial-IGF-1R knockout and control mice were treated for 10 days with and without the pan-ErbB inhibitor, CI-1033. However, no differences in mucosal IGFBP-4 mRNA expression were found for any of the treatment groups ( P > 0.05). Consistently, IEC-6 cells treated with IGF-1 and/or EGF displayed no alteration in IGFBP-4 mRNA or in cellular and secreted IGFBP-4 protein ( P > 0.05). Overall, this study establishes that endogenous IGFBP-4 plays an important role in inhibiting IGF-1-induced intestinal epithelial proliferation and that mucosal IGFBP-4 expression is independent of IGF-1 and EGF. NEW & NOTEWORTHY This study demonstrates, for the first time, the inhibitory role of locally expressed insulin-like growth factor-binding protein-4 (IGFBP-4) on the intestinal proliferative actions of IGF-1 and supports the notion of the synergistic roles of IGF-1 and EGF in promoting intestinal epithelial growth. In turn, intestinal IGFBP-4 expression was not found to be regulated by IGF-1 and/or EGF.
胰岛素样生长因子结合蛋白-4（IGFBP-4）是一种结合蛋白，可调节胰岛素样生长因子-1（IGF-1）的作用，IGF-1 是一种生长因子，其存在是胰高血糖素样肽-2（GLP-2）肠营养作用所必需的。GLP-2 是一种肠道激素，它使用 IGF-1 和表皮生长因子（EGF）作为中间因子来促进肠道生长。因此，为了阐明 IGFBP-4 调节 IGF-1 在肠道中活性的机制，使用大鼠肠上皮细胞（IEC-6）进行了 IGF-1 增殖测定。IGF-1 和 EGF 协同增强增殖，IGFBP-4 以剂量依赖性方式降低该效应（P<0.05-0.001），但不依赖 IGF-1 受体（R）和 MEK1/2（IGFBP-4 对 IGF-1R 和 MEK1/2 抑制剂的作用 P>0.05）。与来自对照小鼠的类器官相比，来自 IGFBP-4 基因敲除小鼠的肠类器官对 IGF-1 处理显示出显著更高的 Ki-67 表达和增强的表面面积增加（P<0.05-0.01）。已知 GLP-2 也会增加 IGFBP-4 mRNA 在粘膜中的表达。为了研究这是否是通过其中间物 IGF-1 和 EGF 的作用发生的，用诱导型肠上皮 IGF-1R 敲除和对照小鼠用 pan-ErbB 抑制剂 CI-1033 处理 10 天，并进行处理。然而，对于任何治疗组，粘膜 IGFBP-4 mRNA 表达均无差异（P>0.05）。一致地，用 IGF-1 和/或 EGF 处理的 IEC-6 细胞显示 IGFBP-4 mRNA 或细胞内和分泌的 IGFBP-4 蛋白无变化（P>0.05）。总的来说，这项研究确立了内源性 IGFBP-4 在抑制 IGF-1 诱导的肠上皮增殖中起重要作用，并且粘膜 IGFBP-4 表达独立于 IGF-1 和 EGF。本研究首次证明了局部表达的胰岛素样生长因子结合蛋白-4（IGFBP-4）对 IGF-1 诱导的肠上皮增殖作用的抑制作用，并支持 IGF-1 和 EGF 协同促进肠上皮生长的观点。反过来，发现肠 IGFBP-4 表达不受 IGF-1 和/或 EGF 调节。
