Department of Physiology and Division of Pathology, Michigan State University, East Lansing, MI 48824, USA.
Biochem J. 2009 Dec 14;425(1):169-78. doi: 10.1042/BJ20090908.
Tumor necrosis factor-α (TNFα) is a multifunctional cytokine involved in the pathophysiology of many chronic inflammatory diseases. TNFα activation of the nuclear factor κB (NFκB) signaling pathway particularly in macrophages has been implicated in many diseases. We demonstrate here that G-protein coupled receptor kinase-2 and 5 (GRK2 and 5) regulate TNFα-induced NFκB signaling in Raw264.7 macrophages. RNAi knockdown of GRK2 or 5 in macrophages significantly inhibits TNFα-induced IκBα phosphorylation and degradation, NFκB activation, and expression of the NFκB-regulated gene, macrophage inflammatory protein-1β. Consistent with these results, over-expression of GRK2 or 5 enhances TNFα-induced NFκB activity. In addition,we show that GRK2 and 5 interact with IκBα via the N-terminal domain of IκBα and that IκBα isa substrate for GRK2 and 5 in vitro. Furthermore, we also find that GRK5 but not GRK2 phosphorylates IκBα at the same amino acid residues (Ser32/36) as that of IKKβ. Interestingly,associated with these results, knockdown of IKKβ in Raw264.7 macrophages did not affect TNFα-induced IκBα phosphorylation. Taken together, these results demonstrate that both GRK2 and 5 are important and novel mediators of a non-traditional IκBα-NFκB signaling pathway.
肿瘤坏死因子-α（TNFα）是一种多功能细胞因子，参与许多慢性炎症性疾病的病理生理学过程。TNFα 激活核因子 κB（NFκB）信号通路，特别是在巨噬细胞中，与许多疾病有关。我们在这里证明，G 蛋白偶联受体激酶 2 和 5（GRK2 和 5）调节 Raw264.7 巨噬细胞中 TNFα 诱导的 NFκB 信号转导。巨噬细胞中 GRK2 或 5 的 RNAi 敲低显著抑制 TNFα 诱导的 IκBα 磷酸化和降解、NFκB 激活以及 NFκB 调节基因巨噬细胞炎症蛋白-1β的表达。与这些结果一致，GRK2 或 5 的过表达增强了 TNFα 诱导的 NFκB 活性。此外，我们表明 GRK2 和 5 通过 IκBα 的 N 端结构域与 IκBα 相互作用，并且 IκBα 是 GRK2 和 5 的体外底物。此外，我们还发现 GRK5 但不是 GRK2 在 IKKβ 相同的氨基酸残基（Ser32/36）上磷酸化 IκBα。有趣的是，与这些结果一致，Raw264.7 巨噬细胞中 IKKβ 的敲低不影响 TNFα 诱导的 IκBα 磷酸化。总之，这些结果表明，GRK2 和 5 都是非传统 IκBα-NFκB 信号通路的重要和新型介质。
