Tesz Gregory J, Guilherme Adilson, Guntur Kalyani V P, Hubbard Andrea C, Tang Xiaoqing, Chawla Anil, Czech Michael P
Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
J Biol Chem. 2007 Jul 6;282(27):19302-12. doi: 10.1074/jbc.M700665200. Epub 2007 May 11.
Tumor necrosis factor alpha (TNFalpha) is a cytokine secreted by macrophages and adipocytes that contributes to the low grade inflammation and insulin resistance observed in obesity. TNFalpha signaling decreases peroxisome proliferator-activated receptor gamma and glucose transporter isoform 4 (GLUT4) expression in adipocytes, impairing insulin action, and this is mediated in part by the yeast Ste20 protein kinase ortholog Map4k4. Here we show that Map4k4 expression is selectively up-regulated by TNFalpha, whereas the expression of the protein kinases JNK1/2, ERK1/2, p38 stress-activated protein kinase, and mitogen-activated protein kinase kinases 4/7 shows little or no response. Furthermore, the cytokines interleukin 1beta (IL-1beta) and IL-6 as well as lipopolysaccharide fail to increase Map4k4 mRNA levels in cultured adipocytes under conditions where TNFalpha elicits a 3-fold effect. Using agonistic and antagonistic antibodies and small interfering RNA (siRNA) against TNFalpha receptor 1 (TNFR1) and TNFalpha receptor 2 (TNFR2), we show that TNFR1, but not TNFR2, mediates the increase in Map4k4 expression. TNFR1, but not TNFR2, also mediates a potent effect of TNFalpha on the phosphorylation of JNK1/2 and p38 stress-activated protein kinase and their downstream transcription factor substrates c-Jun and activating transcription factor 2 (ATF2). siRNA-based depletion of c-Jun and ATF2 attenuated TNFalpha action on Map4k4 mRNA expression. Consistent with this concept, the phosphorylation of ATF2 along with the expression and phosphorylation of c-Jun by TNFalpha signaling was more robust and prolonged compared with that of IL-1beta, which failed to modulate Map4k4. These data reveal that TNFalpha selectively stimulates the expression of a key component of its own signaling pathway, Map4k4, through a TNFR1-dependent mechanism that targets the transcription factors c-Jun and ATF2.
肿瘤坏死因子α（TNFα）是一种由巨噬细胞和脂肪细胞分泌的细胞因子，它会导致肥胖中出现的低度炎症和胰岛素抵抗。TNFα信号传导会降低脂肪细胞中过氧化物酶体增殖物激活受体γ和葡萄糖转运蛋白异构体4（GLUT4）的表达，损害胰岛素作用，这部分是由酵母Ste20蛋白激酶直系同源物Map4k4介导的。在此我们表明，Map4k4的表达被TNFα选择性上调，而蛋白激酶JNK1/2、ERK1/2、p38应激激活蛋白激酶以及丝裂原活化蛋白激酶激酶4/7的表达几乎没有反应或无反应。此外，在TNFα产生3倍效应的条件下，细胞因子白细胞介素1β（IL-1β）和IL-6以及脂多糖未能增加培养的脂肪细胞中Map4k4的mRNA水平。使用针对TNFα受体1（TNFR1）和TNFα受体2（TNFR2）的激动性和拮抗性抗体以及小干扰RNA（siRNA），我们表明TNFR1而非TNFR2介导了Map4k4表达的增加。TNFR1而非TNFR2也介导了TNFα对JNK1/2和p38应激激活蛋白激酶及其下游转录因子底物c-Jun和激活转录因子2（ATF2）磷酸化的强效作用。基于siRNA的c-Jun和ATF2缺失减弱了TNFα对Map4k4 mRNA表达的作用。与此概念一致的是，与未能调节Map4k4的IL-1β相比，TNFα信号传导导致的ATF2磷酸化以及c-Jun的表达和磷酸化更强且持续时间更长。这些数据表明，TNFα通过靶向转录因子c-Jun和ATF2的TNFR1依赖性机制选择性地刺激其自身信号通路的关键成分Map4k4的表达。
