We found that AKT1, a primary effector molecule of PI3K-AKT signaling, distinctively suppressed Toll-like receptor (TLR)-mediated MyD88-dependent and Toll/IL-1R domain-containing adaptor inducing IFN-β (TRIF)-dependent signaling by inhibiting NF-κB activation and IRF3 activity independently of its kinase activity. In AKT1 knockout RAW264.7 cells, lipopolysaccharide (LPS)-induced transcription and protein production of cytokines including IL-1β and TNF-α (regulated by the MyD88-dependent pathway), as well as IFN-β and RANTES (C-C motif chemokine ligand 5: CCL-5; regulated by the TRIF-dependent pathways) was enhanced compared to wild type cells. In response to LPS stimulation, AKT1 knockout cells also exhibited enhanced NF-κB and IFN-β promoter activities, which were reduced to a level comparable to that in wild type cells by complementation with either AKT1 or its kinase-dead mutant (AKT1-KD). Expression of AKT1 or AKT1-KD similarly suppressed NF-κB and IFN-β promoter activities induced by LPS and other TLR ligands in wild type cells. Analysis of NF-κB activation caused by transient expression of proteins involved in the MyD88-dependent pathway in TLR signaling revealed that AKT1 suppressed signaling that occurs between activation of IKKβ and that of NF-κB. In contrast, AKT1 appeared to suppress the IFN-β promoter through inhibition of IRF3 activity itself. These results demonstrate a novel, non-kinase function of AKT1 that inhibits TLR signaling, and suggest the multifunctional nature of AKT1.

我们发现AKT1，PI3K-AKT信号的主要效应分子，通过抑制Toll样受体（TLR）介导的MyD88依赖和包含Toll / IL-1R的适配器明显抑制了Toll样受体介导的IFN-β（TRIF）依赖信号转导。抑制NF-κB活化和IRF3活性，而与其激酶活性无关。在AKT1基因敲除的RAW264.7细胞中，脂多糖（LPS）诱导细胞因子的转录和蛋白质生成，包括IL-1β和TNF-α（受MyD88依赖性途径调节），以及IFN-β和RANTES（CC基序趋化因子）与野生型细胞相比，配体5：CCL-5；受TRIF依赖性途径调节）增强。响应LPS刺激，AKT1敲除细胞还表现出增强的NF-κB和IFN-β启动子活性，通过与AKT1或其激酶死亡突变体（AKT1-KD）互补，其活性降低至与野生型细胞相当的水平。AKT1或AKT1-KD的表达同样抑制了LPS和其他TLR配体在野生型细胞中诱导的NF-κB和IFN-β启动子活性。由TLR信号中MyD88依赖性途径中涉及的蛋白质的瞬时表达引起的NF-κB活化分析表明，AKT1抑制了IKKβ活化与NF-κB活化之间发生的信号传导。相反，AKT1似乎通过抑制IRF3活性本身来抑制IFN-β启动子。这些结果证明了抑制TLR信号传导的AKT1的新型非激酶功能，并暗示了AKT1的多功能性质。