Ruan Hong, Pownall Henry J, Lodish Harvey F
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.
J Biol Chem. 2003 Jul 25;278(30):28181-92. doi: 10.1074/jbc.M303141200. Epub 2003 May 5.
Troglitazone (TGZ), a member of the thiazolidinedione class of anti-diabetic compounds and a peroxisome proliferator activator receptor-gamma (PPAR-gamma) agonist, restores systemic insulin sensitivity and improves the full insulin resistance syndrome in vivo. The mechanisms underlying its in vivo function are not understood. Here we investigated the potential functional interaction between PPAR-gamma and NF-kappaB in adipocytes. We show that TGZ selectively blocked tumor necrosis factor-alpha-induced and NF-kappaB-dependent repression of multiple adipocyte-specific genes and induction of growth phase and other genes. This occurs without interfering with NF-kappaB expression, activation, nuclear translocation, or DNA binding and without suppressing NF-kappaB-dependent survival signals. Notably, the expressions of some tumor necrosis factor-alpha-induced genes in adipocytes were unaffected by PPAR-gamma activation. In reporter gene assays in HeLa cells, ectopic expression of PPAR-gamma abolished induction of a NF-kappaB-responsive reporter gene by the p65 subunit (RelA) of NF-kappaB, and the inhibition was further enhanced in the presence of TGZ. Conversely, overexpression of p65 inhibited induction of a PPAR-gamma-responsive reporter gene by activated PPAR-gamma in a dose-dependent manner. The inhibitory effect was independent of the presence of NF-kappaB-binding sites in the promoter region. Other NF-kappaB family members, p50 and c-Rel as well as the S276A mutant of p65, blocked PPAR-gamma-mediated gene transcription less effectively. Thus, p65 antagonizes the transcriptional regulatory activity of PPAR-gamma in adipocytes, and PPAR-gamma activation can at least partially override the inhibitory effects of p65 on the expression of key adipocyte genes. Our data suggest that inhibition of NF-kappaB activity is a mechanism by which PPAR-gamma agonists improve insulin sensitivity in vivo and that adipocyte NF-kappaB is a potential therapeutic target for obesity-linked type 2 diabetes.
曲格列酮（TGZ）是噻唑烷二酮类抗糖尿病化合物的一员，也是过氧化物酶体增殖物激活受体γ（PPAR-γ）激动剂，可恢复全身胰岛素敏感性并改善体内完全胰岛素抵抗综合征。其体内功能的潜在机制尚不清楚。在此，我们研究了脂肪细胞中PPAR-γ与核因子κB（NF-κB）之间潜在的功能相互作用。我们发现，TGZ选择性地阻断了肿瘤坏死因子α诱导的以及NF-κB依赖的多个脂肪细胞特异性基因的抑制作用，以及生长阶段和其他基因的诱导作用。这一过程并不干扰NF-κB的表达、激活、核转位或DNA结合，也不抑制NF-κB依赖的存活信号。值得注意的是，脂肪细胞中一些肿瘤坏死因子α诱导基因的表达不受PPAR-γ激活的影响。在HeLa细胞的报告基因检测中，PPAR-γ的异位表达消除了NF-κB的p65亚基（RelA）对NF-κB反应性报告基因的诱导作用，并且在TGZ存在的情况下抑制作用进一步增强。相反，p65的过表达以剂量依赖的方式抑制了活化的PPAR-γ对PPAR-γ反应性报告基因的诱导作用。这种抑制作用与启动子区域中NF-κB结合位点的存在无关。其他NF-κB家族成员，p50和c-Rel以及p65的S276A突变体，对PPAR-γ介导的基因转录的阻断作用较弱。因此，p65拮抗脂肪细胞中PPAR-γ的转录调节活性，并且PPAR-γ激活至少可以部分克服p65对关键脂肪细胞基因表达的抑制作用。我们的数据表明，抑制NF-κB活性是PPAR-γ激动剂在体内改善胰岛素敏感性的一种机制，并且脂肪细胞NF-κB是肥胖相关2型糖尿病的一个潜在治疗靶点。
