Yang Yanmei, Lei Hong, Qiang Ya-Wei, Wang Bin
Center for Translational Medicine, Department of Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107.
College of Food Science and Engineering, Nanjing University of Finance and Economics, Nanjing 210023, China.
Mol Biol Cell. 2017 Jul 1;28(13):1792-1803. doi: 10.1091/mbc.E17-02-0096. Epub 2017 May 11.
The anabolic action of PTH in bone is mostly mediated by cAMP/PKA and Wnt-independent activation of β-catenin/T-cell factor (TCF) signaling. β-Catenin switches the PTH receptor (PTHR) signaling from cAMP/PKA to PLC/PKC activation by binding to the PTHR. Ixazomib (Izb) was recently approved as the first orally administered proteasome inhibitor for the treatment of multiple myeloma; it acts in part by inhibition of pathological bone destruction. Proteasome inhibitors were reported to stabilize β-catenin by the ubiquitin-proteasome pathway. However, how Izb affects PTHR activation to regulate β-catenin/TCF signaling is poorly understood. In the present study, using CRISPR/Cas9 genome-editing technology, we show that Izb reverses β-catenin-mediated PTHR signaling switch and enhances PTH-induced cAMP generation and cAMP response element-luciferase activity in osteoblasts. Izb increases active forms of β-catenin and promotes β-catenin translocation, thereby dissociating β-catenin from the PTHR at the plasma membrane. Furthermore, Izb facilitates PTH-stimulated GSK3β phosphorylation and β-catenin phosphorylation. Thus Izb enhances PTH stimulation of β-catenin/TCF signaling via cAMP-dependent activation, and this effect is due to its separating β-catenin from the PTHR. These findings provide evidence that Izb may be used to improve the therapeutic efficacy of PTH for the treatment of osteoporosis and other resorptive bone diseases.
甲状旁腺激素（PTH）在骨骼中的合成代谢作用主要由环磷酸腺苷（cAMP）/蛋白激酶A（PKA）以及β-连环蛋白/ T细胞因子（TCF）信号通路的非Wnt依赖性激活介导。β-连环蛋白通过与甲状旁腺激素受体（PTHR）结合，将PTHR信号从cAMP / PKA转换为磷脂酶C（PLC）/蛋白激酶C（PKC）激活。伊沙佐米（Izb）最近被批准为首个用于治疗多发性骨髓瘤的口服蛋白酶体抑制剂；它部分通过抑制病理性骨破坏发挥作用。据报道，蛋白酶体抑制剂可通过泛素-蛋白酶体途径稳定β-连环蛋白。然而，Izb如何影响PTHR激活以调节β-连环蛋白/ TCF信号通路尚不清楚。在本研究中，我们使用CRISPR/Cas9基因组编辑技术表明，Izb可逆转β-连环蛋白介导的PTHR信号转换，并增强成骨细胞中PTH诱导的cAMP生成及cAMP反应元件荧光素酶活性。Izb增加β-连环蛋白的活性形式并促进β-连环蛋白易位，从而使β-连环蛋白在质膜处与PTHR解离。此外，Izb促进PTH刺激的糖原合成酶激酶3β（GSK3β）磷酸化和β-连环蛋白磷酸化。因此，Izb通过cAMP依赖性激活增强PTH对β-连环蛋白/ TCF信号通路的刺激，这种作用是由于其使β-连环蛋白与PTHR分离。这些发现提供了证据，表明Izb可用于提高PTH治疗骨质疏松症和其他吸收性骨疾病的疗效。
