The insulin-like growth factors (IGFs) I and II bind to articular cartilage via the IGF-binding proteins
The insulin-like growth factors (IGFs) I and II bind to articular cartilage via the IGF-binding proteins
复制标题
DOI：
10.1074/jbc.275.8.5860
复制
发表时间：
2000-02-25
影响因子：
4.8
通讯作者：
Morales, TI
中科院分区：
文献类型：
--
作者：
Bhakta, NR;Garcia, AM;Morales, TI
牛关节软骨盘（3 mm直径× 400 μ m厚）在含有I-125-胰岛素样生长因子（IGF）-I的缓冲液中平衡（4 ℃）+/-未标记的IGF-I或IGF-II，每种未标记的IGF与软骨盘结合的竞争是浓度依赖性的，IGF-I和IGF-II抑制I-125-IGF-I结合的ED 50值分别为11和10 nM，饱和度为50 nM。相反，对胰岛素样生长因子结合蛋白（IGF-BP）具有非常低亲和力的IGF-I类似物，des-（1-3）-IGF-I与I-125-IGF-I在软骨结合方面没有竞争性，即使在100-400 nM时也是如此。I-125标记的IGF-II亚型与软骨的结合受到未标记的ICE-I或ICE-II的竞争，艾德（50）分别为160和8 nM。这可能反映了内源性IGF-BP（IGF-BP-6和-2）对IGF-II/IGF-I的不同亲和力。I-125-IGF-I的转运也在仅允许扩散穿过盘（400 μ m）的装置中测量，通过添加到一侧并连续监测另一侧的流出。I-125-IGF的运输时滞为266分钟，比基质中自由扩散的理论预测长一个数量级。I-125-IGF-I转运然后达到稳态速率（总加入的I-125-IGF的流出%/单位时间），随后通过加入过量的未标记的IGF-I将其加速约2倍。总之，这些结果表明，IGF与软骨的结合（主要通过IGF-BP）调节IC的转运;关节软骨中的Fs，可能有助于控制其旁分泌活动。
Bovine articular cartilage discs (3 mm diameter x 400 mu m thick) were equilibrated in buffer containing I-125-insulin-like growth factor (IGF)-I (4 degrees C) +/- unlabeled IGF-I or IGF-II, Competition for binding to cartilage discs by each unlabeled IGF was concentration-dependent, with ED50 values for inhibition of I-125-IGF-I binding of 11 and 10 nM for IGF-I and -II, respectively, and saturation by 50 nM, By contrast, an analog of IGF-I with very low affinity for the insulin-like growth factor-binding proteins (IGF-BPs), des-(1-3)-IGF-I, was not competitive with I-125-IGF-I for cartilage binding even at 100-400 nM. Binding of the I-125-labeled IGF-II isoform to cartilage was competed for by unlabeled ICE-I or -II, with ED(50)s of 160 and 8 nM, respectively. This probably reflected the differential affinities of the endogenous IGF-BPs (IGF-BP-6 and -2) for IGF-II/IGF-I. Transport of I-125-IGF-I was also measured in an apparatus that allows diffusion only across the discs (400 mu m), by addition to one side and continuous monitoring of efflux on the other side. The time lag for transport of I-125-IGF was 266 min, an order of magnitude longer than the theoretical prediction for free diffusion in the matrix. I-125-IGF-I transport then reached a steady state rate (% efflux of total added I-125-IGF/unit time), which was subsequently accelerated similar to 2-fold by addition of an excess of unlabeled IGF-I, Taken together, these results indicate that IGF binding to cartilage, mostly through the IGF-BPs, regulates the transport of IC;Fs in articular cartilage, probably contributing to the control of their paracrine activities.