Department of General Surgery, The First Affiliated Hospital of Dalian Medical University, Dalian, China.
Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
FASEB J. 2018 Jan;32(1):230-242. doi: 10.1096/fj.201700415RR. Epub 2017 Sep 5.
The tumor necrosis factor receptor-associated factor 2 (TRAF2) is a second messenger adaptor protein that plays an essential role in propagating TNF-α-mediated signaling pathways. Modulation of TRAF2 activity by ubiquitination is well studied; however, the deubiquitinating enzyme (DUB), which regulates TRAF2 stability, has not been identified. Here we reveal USP48 as the first identified DUB to deubiquitinate and stabilize TRAF2 in epithelial cells. Down-regulation of USP48 increases K48-linked polyubiquitination of TRAF2 and reduces TRAF2 protein levels. Interestingly, USP48 only targets the TRAF2 related to JNK pathway, not the TRAF2 related to NF-κB and p38 pathways. USP48 is serine phosphorylated in response to TNF-α. The phosphorylation is catalyzed by glycogen synthase kinase 3β (GSK3β), ultimately resulting in increases in USP48 DUB activity. Furthermore, we reveal a new biologic function of TRAF2 that contributes to epithelial barrier dysfunction, which is attenuated by knockdown of USP48. Inhibition of TRAF2/JNK pathway increases E (epithelial)-cadherin expression and enhances epithelial barrier integrity, while knockdown of USP48 attenuates TNF-α/JNK pathway and increases E-cadherin expression and cell-cell junction in epithelial cells. These data, taken together, indicate that USP48 stabilizes TRAF2, which is promoted by GSK3β-mediated phosphorylation. Further, down-regulation of USP48 increases E-cadherin expression and epithelial barrier integrity through reducing TRAF2 stability.-Li, S., Wang, D., Zhao, J., Weathington, N. M., Shang, D., Zhao, Y. The deubiquitinating enzyme USP48 stabilizes TRAF2 and reduces E-cadherin-mediated adherens junctions.
肿瘤坏死因子受体相关因子 2（TRAF2）是一种第二信使衔接蛋白，在传播 TNF-α 介导的信号通路中发挥着重要作用。TRAF2 活性的泛素化调节得到了深入研究；然而，调节 TRAF2 稳定性的去泛素化酶（DUB）尚未被鉴定。在这里，我们揭示 USP48 是第一个被鉴定为能够去泛素化和稳定上皮细胞中 TRAF2 的 DUB。USP48 的下调会增加 TRAF2 的 K48 连接多泛素化，并降低 TRAF2 蛋白水平。有趣的是，USP48 仅靶向与 JNK 通路相关的 TRAF2，而不靶向与 NF-κB 和 p38 通路相关的 TRAF2。USP48 会响应 TNF-α 而发生丝氨酸磷酸化。磷酸化由糖原合酶激酶 3β（GSK3β）催化，最终导致 USP48 的 DUB 活性增加。此外，我们揭示了 TRAF2 的一个新的生物学功能，该功能有助于上皮屏障功能障碍，而 USP48 的敲低会减弱这种功能障碍。抑制 TRAF2/JNK 通路会增加 E（上皮）-钙粘蛋白的表达并增强上皮屏障的完整性，而 USP48 的敲低会减弱 TNF-α/JNK 通路并增加上皮细胞中的 E-钙粘蛋白表达和细胞-细胞连接。这些数据表明，USP48 通过 GSK3β 介导的磷酸化稳定 TRAF2。此外，下调 USP48 通过降低 TRAF2 的稳定性增加 E-钙粘蛋白的表达和上皮屏障的完整性。
