Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus, Denmark.
Department of Molecular and Clinical Medicine, University of Liverpool, Liverpool L69 3BX, United Kingdom.
J Biol Chem. 2019 Oct 18;294(42):15495-15504. doi: 10.1074/jbc.RA119.008844. Epub 2019 Sep 4.
Destruction of the cartilage matrix in joints is an important feature of arthritis. Proteolytic degradation of cartilage glycoproteins can contribute to the loss of matrix integrity. Human inter-α-inhibitor (IαI), which stabilizes the extracellular matrix, is composed of the light-chain serine proteinase inhibitor bikunin and two homologous heavy chains (HC1 and HC2) covalently linked through chondroitin 4-sulfate. Inflammation promotes the transfer of HCs from chondroitin 4-sulfate to hyaluronan by tumor necrosis factor-stimulated gene-6 protein (TSG-6). This reaction generates a covalent complex between the heavy chains and hyaluronan that can promote leukocyte invasion. This study demonstrates that both IαI and the HC-hyaluronan complex are substrates for the extracellular matrix proteases ADAMTS-5 and matrix metalloprotease (MMP) -3, -7, and -13. The major cleavage sites for all four proteases are found in the C terminus of HC2. ADAMTS-5 and MMP-7 displayed the highest activity toward HC2. ADAMTS-5 degradation products were identified in mass spectrometric analysis of 29 of 33 arthropathic patients, indicating that ADAMTS-5 cleavage occurs in synovial fluid in arthritis. After cleavage, free HC2, together with TSG-6, is able to catalyze the transfer of heavy chains to hyaluronan. The release of extracellular matrix bound HC2 is likely to increase the mobility of the HC2/TSG-6 catalytic unit and consequently increase the rate of the HC transfer reaction. Ultimately, ADAMTS-5 cleavage of HC2 could alter the physiological and mechanical properties of the extracellular matrix and contribute to the progression of arthritis.
关节软骨基质的破坏是关节炎的一个重要特征。软骨糖蛋白的蛋白水解降解可能导致基质完整性的丧失。人相互-α-抑制物(IαI)稳定细胞外基质,由轻链丝氨酸蛋白酶抑制剂 bikunin 和两个同源重链(HC1 和 HC2)通过软骨素 4-硫酸盐共价连接组成。炎症通过肿瘤坏死因子刺激基因-6 蛋白(TSG-6)促进 HC 从重硫酸盐向透明质酸的转移。该反应在重链和透明质酸之间生成一个共价复合物,可促进白细胞浸润。本研究表明,IαI 和 HC-透明质酸复合物都是细胞外基质蛋白酶 ADAMTS-5 和基质金属蛋白酶(MMP)-3、-7 和-13 的底物。所有四种蛋白酶的主要切割位点都位于 HC2 的 C 端。ADAMTS-5 和 MMP-7 对 HC2 的活性最高。在对 33 名关节病患者中的 29 名进行质谱分析时,鉴定出 ADAMTS-5 对 HC2 的降解产物,表明 ADAMTS-5 切割发生在关节炎的滑液中。切割后,游离 HC2 与 TSG-6 一起能够催化重链向透明质酸的转移。细胞外基质结合的 HC2 的释放可能会增加 HC2/TSG-6 催化单元的迁移率,并因此增加 HC 转移反应的速率。最终,ADAMTS-5 对 HC2 的切割可能会改变细胞外基质的生理和机械特性,并导致关节炎的进展。