Department of Pharmacology and Therapeutic Chemistry, IBUB (Institut de Biomedicina de la Universitat de Barcelona) and CIBERDEM, Faculty of Pharmacy, University of Barcelona, Barcelona, Spain.
PLoS One. 2011;6(5):e19724. doi: 10.1371/journal.pone.0019724. Epub 2011 May 23.
Pyruvate dehydrogenase kinase 4 (PDK4) inhibition by nuclear factor-κB (NF-κB) is related to a shift towards increased glycolysis during cardiac pathological processes such as cardiac hypertrophy and heart failure. The transcription factors estrogen-related receptor-α (ERRα) and peroxisome proliferator-activated receptor (PPAR) regulate PDK4 expression through the potent transcriptional coactivator PPARγ coactivator-1α (PGC-1α). NF-κB activation in AC16 cardiac cells inhibit ERRα and PPARβ/δ transcriptional activity, resulting in reduced PGC-1α and PDK4 expression, and an enhanced glucose oxidation rate. However, addition of the NF-κB inhibitor parthenolide to these cells prevents the downregulation of PDK4 expression but not ERRα and PPARβ/δ DNA binding activity, thus suggesting that additional transcription factors are regulating PDK4. Interestingly, a recent study has demonstrated that the transcription factor E2F1, which is crucial for cell cycle control, may regulate PDK4 expression. Given that NF-κB may antagonize the transcriptional activity of E2F1 in cardiac myocytes, we sought to study whether inflammatory processes driven by NF-κB can downregulate PDK4 expression in human cardiac AC16 cells through E2F1 inhibition. Protein coimmunoprecipitation indicated that PDK4 downregulation entailed enhanced physical interaction between the p65 subunit of NF-κB and E2F1. Chromatin immunoprecipitation analyses demonstrated that p65 translocation into the nucleus prevented the recruitment of E2F1 to the PDK4 promoter and its subsequent E2F1-dependent gene transcription. Interestingly, the NF-κB inhibitor parthenolide prevented the inhibition of E2F1, while E2F1 overexpression reduced interleukin expression in stimulated cardiac cells. Based on these findings, we propose that NF-κB acts as a molecular switch that regulates E2F1-dependent PDK4 gene transcription.
核因子-κB（NF-κB）对丙酮酸脱氢酶激酶 4（PDK4）的抑制作用与心脏病理过程中糖酵解增加有关，如心脏肥大和心力衰竭。转录因子雌激素相关受体-α（ERRα）和过氧化物酶体增殖物激活受体（PPAR）通过强效转录共激活因子过氧化物酶体增殖物激活受体γ共激活因子-1α（PGC-1α）调节 PDK4 的表达。AC16 心脏细胞中 NF-κB 的激活抑制 ERRα 和 PPARβ/δ 的转录活性，导致 PGC-1α 和 PDK4 的表达减少，葡萄糖氧化率增加。然而，向这些细胞中添加 NF-κB 抑制剂小白菊内酯可防止 PDK4 表达的下调，但不能防止 ERRα 和 PPARβ/δ DNA 结合活性的下调，因此表明其他转录因子正在调节 PDK4。有趣的是，最近的一项研究表明，细胞周期控制的关键转录因子 E2F1 可能调节 PDK4 的表达。鉴于 NF-κB 可能在心肌细胞中拮抗 E2F1 的转录活性，我们试图研究 NF-κB 驱动的炎症过程是否可以通过抑制 E2F1 来下调人心脏 AC16 细胞中的 PDK4 表达。蛋白质免疫共沉淀表明，PDK4 的下调需要 NF-κB 的 p65 亚基与 E2F1 之间增强的物理相互作用。染色质免疫沉淀分析表明，p65 向核内易位阻止了 E2F1 募集到 PDK4 启动子及其随后的 E2F1 依赖性基因转录。有趣的是，NF-κB 抑制剂小白菊内酯可防止 E2F1 的抑制，而 E2F1 的过表达可减少刺激心脏细胞中的白细胞介素表达。基于这些发现，我们提出 NF-κB 作为一种分子开关，调节 E2F1 依赖性 PDK4 基因转录。
