Division of Molecular Internal Medicine, Department of Internal Medicine II, University Hospital Würzburg, 97070 Würzburg, Germany.
J Immunol. 2013 Sep 1;191(5):2308-18. doi: 10.4049/jimmunol.1202899. Epub 2013 Aug 5.
We found recently that TNF-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor-inducible-14 (Fn14) by virtue of their strong capability to reduce the freely available cytoplasmic pool of TNFR-associated factor (TRAF)2 and cellular inhibitors of apoptosis (cIAPs) antagonize the functions of these molecules in TNFR1 signaling, resulting in sensitization for apoptosis and inhibition of classical NF-κB signaling. In this study, we demonstrate that priming of cells with TWEAK also interferes with activation of the classical NF-κB pathway by CD40. Likewise, there was strong inhibition of CD40 ligand (CD40L)-induced activation of MAPKs in TWEAK-primed cells. FACS analysis and CD40L binding studies revealed unchanged CD40 expression and normal CD40L-CD40 interaction in TWEAK-primed cells. CD40L immunoprecipitates, however, showed severely reduced amounts of CD40 and CD40-associated proteins, indicating impaired formation or reduced stability of CD40L-CD40 signaling complexes. The previously described inhibitory effect of TWEAK on TNFR1 signaling has been traced back to reduced activity of the TNFR1-associated TRAF2-cIAP1/2 ubiquitinase complex and did not affect the stability of the immunoprecipitable TNFR1 receptor complex. Thus, the inhibitory effect of TWEAK on CD40 signaling must be based at least partly on other mechanisms. In line with this, signaling by the CD40-related TRAF2-interacting receptor TNFR2 was also attenuated but still immunoprecipitable in TWEAK-primed cells. Collectively, we show that Fn14 activation by soluble TWEAK impairs CD40L-CD40 signaling complex formation and inhibits CD40 signaling and thus identify the Fn14-TWEAK system as a potential novel regulator of CD40-related cellular functions.
我们最近发现，肿瘤坏死因子样弱凋亡诱导因子（TWEAK）和成纤维细胞生长因子诱导蛋白 14（Fn14）通过其强大的能力，降低肿瘤坏死因子受体相关因子（TRAF）2 和细胞凋亡抑制剂（cIAPs）的细胞质游离池，拮抗这些分子在 TNFR1 信号转导中的作用，导致细胞凋亡敏感和经典 NF-κB 信号转导抑制。在这项研究中，我们证明细胞的 TWEAK 预激活也会干扰 CD40 激活经典 NF-κB 途径。同样，在 TWEAK 预激活的细胞中，强烈抑制了 CD40 配体（CD40L）诱导的 MAPK 的激活。FACS 分析和 CD40L 结合研究表明，TWEAK 预激活的细胞中 CD40 表达不变，CD40L-CD40 相互作用正常。然而，CD40L 免疫沉淀物显示 CD40 和 CD40 相关蛋白的含量严重减少，表明 CD40L-CD40 信号复合物的形成受损或稳定性降低。先前描述的 TWEAK 对 TNFR1 信号转导的抑制作用可追溯到 TNFR1 相关 TRAF2-cIAP1/2 泛素连接酶复合物活性降低，而不影响可沉淀的 TNFR1 受体复合物的稳定性。因此，TWEAK 对 CD40 信号的抑制作用至少部分基于其他机制。与此一致，CD40 相关 TRAF2 相互作用受体 TNFR2 的信号转导也在 TWEAK 预激活的细胞中减弱，但仍可被免疫沉淀。总之，我们表明可溶性 TWEAK 激活 Fn14 会损害 CD40L-CD40 信号复合物的形成，并抑制 CD40 信号转导，从而确定 Fn14-TWEAK 系统作为 CD40 相关细胞功能的潜在新型调节剂。
