Department of Biochemistry and Medical Chemistry, Medical Faculty, University of Pecs, Szigeti Str. 12, Pecs 7624, Hungary.
J Nutr Biochem. 2013 May;24(5):819-23. doi: 10.1016/j.jnutbio.2012.04.017. Epub 2012 Aug 24.
Resveratrol was suggested to inhibit Toll-like receptor (TLR)4-mediated activation of nuclear factor-κB (NF-κB) and Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-β (TRIF)-(TANK)-binding kinase 1, but the myeloid differentiation primary response gene 88-tumor necrosis factor receptor-associated factor 6 (TRAF6) pathway is not involved in this effect. However, involvement of TRAF6 in this process is still elusive since cross talk between TRIF and TRAF6 has been reported in lipopolysaccharide (LPS)-induced signaling. Using RAW 264.7 macrophages, we determined the effect of resveratrol on LPS-induced TRAF6 expression, ubiquitination as well as activation of mitogen-activated protein (MAP) kinases and Akt in order to elucidate its involvement in TLR4 signaling. LPS-induced transient elevation in TRAF6 mRNA and protein expressions is suppressed by resveratrol. LPS induces the ubiquitination of TRAF6, which has been reported to be essential for Akt activation and for transforming growth factor-β activated kinase-1-NAP kinase kinase 6 (MKK6)-mediated p38 and c-Jun N-terminal kinase (JNK) activation. We found that resveratrol diminishes the effect of LPS on TRAF6 ubiquitination and activation of JNK and p38 MAP kinases, while it has no effect on the activation of extracellular-signal-regulated kinase (ERK)1/2. The effect of resveratrol on MAP kinase inhibition is significant since TRAF6 activation was reported to induce activation of JNK and p38 MAP kinase while not affecting ERK1/2. Moreover, Akt was identified previously as a direct target of TRAF6, and we found that, similarly to MAPKs, phosphorylation pattern of Akt followed the activation of TRAF6, and it was inhibited by resveratrol at all time points. Here, we provide the first evidence that resveratrol, by suppressing LPS-induced TRAF6 expression and ubiquitination, attenuates the LPS-induced TLR4-TRAF6, MAP kinase and Akt pathways that can be significant in its anti-inflammatory effects.
白藜芦醇被认为可以抑制 Toll 样受体 (TLR)4 介导的核因子-κB (NF-κB) 和 Toll/白细胞介素-1 受体结构域包含衔接诱导干扰素-β (TRIF)-(TANK)-结合激酶 1 的激活，但髓样分化初级反应基因 88-肿瘤坏死因子受体相关因子 6 (TRAF6) 途径不参与这种作用。然而，由于已经报道了脂多糖 (LPS) 诱导的信号转导中 TRIF 和 TRAF6 之间的串扰，因此 TRAF6 是否参与该过程仍不清楚。使用 RAW 264.7 巨噬细胞，我们确定了白藜芦醇对 LPS 诱导的 TRAF6 表达、泛素化以及丝裂原活化蛋白 (MAP) 激酶和 Akt 激活的影响，以阐明其在 TLR4 信号转导中的作用。白藜芦醇抑制 LPS 诱导的 TRAF6 mRNA 和蛋白表达的瞬时升高。LPS 诱导 TRAF6 的泛素化，这对于 Akt 的激活以及转化生长因子-β激活激酶-1-NAP 激酶激酶 6 (MKK6)介导的 p38 和 c-Jun N-末端激酶 (JNK) 的激活是必不可少的。我们发现，白藜芦醇减弱了 LPS 对 TRAF6 泛素化和 JNK 和 p38 MAP 激酶激活的作用，而对细胞外信号调节激酶 (ERK)1/2 的激活没有影响。白藜芦醇对 MAP 激酶抑制的作用是显著的，因为 TRAF6 的激活被报道会诱导 JNK 和 p38 MAP 激酶的激活，而不影响 ERK1/2。此外，Akt 先前被鉴定为 TRAF6 的直接靶标，我们发现，与 MAPKs 类似，Akt 的磷酸化模式遵循 TRAF6 的激活，并且它在所有时间点都被白藜芦醇抑制。在这里，我们提供了第一个证据，即白藜芦醇通过抑制 LPS 诱导的 TRAF6 表达和泛素化，减弱了 LPS 诱导的 TLR4-TRAF6、MAP 激酶和 Akt 途径，这在其抗炎作用中可能是重要的。
