Department of Biochemistry, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
Biochem Biophys Res Commun. 2011 May 6;408(2):202-7. doi: 10.1016/j.bbrc.2011.02.127. Epub 2011 Mar 1.
Mechanical stress plays a key role in bone remodeling. Previous studies showed that loading of mechanical stretch induces a rapid Ca(2+) influx and subsequent activation of stress-activated protein kinase pathways in osteoblasts. However, the activation mechanism and its significance in bone remodeling have not been fully elucidated. Here we show that TAK1 MAPKKK was activated by cyclic stretch loading of MC3T3-E1 cells. Knockdown of TAK1 attenuated the stretch-induced activation of JNK, p38, and NF-κB. Extracellular (EGTA) or intracellular (BAPTA/AM) Ca(2+) chelator prevented the stretch-induced activation of TAK1. Activation of TAK1 and its associated downstream signaling pathways were also suppressed by CaMKII inhibitors (KN-93 and KN-62). Furthermore, TAK1-mediated downstream pathways cooperatively induced the expression of IL-6 mRNA in the stretched MC3T3-E1 cells. We also confirmed that TAK1 mediates cyclic stretch-induced IL-6 protein synthesis in the cells using immunoblotting and ELISA. Finally, stretch loading of murine primary osteoblasts induced the expression of IL-6 mRNA via TAK1. Collectively, these data suggest that stretch-dependent Ca(2+) influx activates TAK1 via CaMKII, leading to the enhanced expression of IL-6 through JNK, p38, and NF-κB pathways in osteoblasts.
机械应力在骨重塑中起着关键作用。先前的研究表明，机械拉伸加载会导致成骨细胞中 Ca(2+)快速内流，并随后激活应激激活蛋白激酶途径。然而，其激活机制及其在骨重塑中的意义尚未完全阐明。在这里，我们表明 TAK1 MAPKKK 被 MC3T3-E1 细胞的循环拉伸加载激活。TAK1 的敲低减弱了拉伸诱导的 JNK、p38 和 NF-κB 的激活。细胞外（EGTA）或细胞内（BAPTA/AM）Ca(2+)螯合剂可防止拉伸诱导的 TAK1 激活。TAK1 的激活及其相关的下游信号通路也被 CaMKII 抑制剂（KN-93 和 KN-62）抑制。此外，TAK1 介导的下游通路共同诱导拉伸 MC3T3-E1 细胞中 IL-6 mRNA 的表达。我们还通过免疫印迹和 ELISA 证实 TAK1 介导了细胞中环拉伸诱导的 IL-6 蛋白合成。最后，鼠原代成骨细胞的拉伸加载通过 TAK1 诱导 IL-6 mRNA 的表达。总的来说，这些数据表明，依赖于拉伸的 Ca(2+)内流通过 CaMKII 激活 TAK1，从而通过 JNK、p38 和 NF-κB 途径增强成骨细胞中 IL-6 的表达。
