Department of Biomedical Sciences, Center for Pharmacogenomics and Molecular Therapy, University of Rhode Island, Kingston, RI 02881, USA.
Biochem Pharmacol. 2012 Sep 15;84(6):864-71. doi: 10.1016/j.bcp.2012.06.025. Epub 2012 Jul 6.
Carboxylesterase-1 (CES1), the most versatile human carboxylesterase, plays critical roles in drug metabolism and lipid mobilization. This enzyme is highly induced by antioxidants and sensitizers in various cell lines. These compounds are known to activate nuclear factor-E2 related factor-2 (Nrf2) by reacting to kelch-like ECH-associated protein-1 (Keap1). The aims of this study were to determine whether antioxidant sulforaphane (SFN) and sensitizer trinitrobenzene sulfonate (TNBS) target Keap1 similarly and whether they use the same element for CES1 induction. Cells over-expressing Keap1 were treated with TNBS or SFN and the formation of disulfide bonds among Keap1 molecules were determined. SFN promoted intramolecular disulfide formation whereas TNBS promoted intermolecular disulfide formation of Keap1. Two elements, sensitizing/antioxidant response element (S/ARE) and ARE4, were identified to support Nrf2 in the regulated expression of CES1A1. Both elements were bound by Nrf2, however, the S/ARE element supported, whereas the ARE4 element repressed Nrf2 transactivation. The repression required higher amounts of Nrf2, suggesting that the transactivation through the S/ARE element dominates the trans-repression through the ARE4 element under normal antioxidative condition. These findings conclude that compounds, although triggering the Keap1-Nrf2 pathway, may differ in the mode of reacting with Keap1. These findings also conclude that both positive and negative Nrf2 elements exist even within the same gene, and such opposing mechanisms provide fine-tuning in transcriptional regulation by the Keap1-Nrf2 pathway. High levels of CES1 are linked to lipid retention. Excessive induction of CES1 by antioxidants and sensitizers likely provides a mechanism for potential detrimental effect on human health.
羧基酯酶 1（CES1）是最具多功能性的人类羧基酯酶，在药物代谢和脂质动员中发挥关键作用。这种酶在各种细胞系中被抗氧化剂和敏化剂高度诱导。这些化合物通过与 Kelch 样 ECH 相关蛋白 1（Keap1）反应来激活核因子-E2 相关因子-2（Nrf2）是已知的。本研究旨在确定抗氧化剂萝卜硫素（SFN）和敏化剂三硝基苯磺酸（TNBS）是否以类似的方式靶向 Keap1，以及它们是否使用相同的元素来诱导 CES1。用 TNBS 或 SFN 处理过表达 Keap1 的细胞，并确定 Keap1 分子之间形成二硫键的情况。SFN 促进 Keap1 分子内二硫键的形成，而 TNBS 促进 Keap1 分子间二硫键的形成。两个元素，敏化/抗氧化反应元件（S/ARE）和 ARE4，被鉴定为支持 Nrf2 在 CES1A1 的调节表达。两个元件都被 Nrf2 结合，但 S/ARE 元件支持，而 ARE4 元件抑制 Nrf2 反式激活。这种抑制需要更多的 Nrf2，这表明在正常抗氧化条件下，通过 S/ARE 元件的反式激活主导了通过 ARE4 元件的反式抑制。这些发现表明，尽管化合物触发了 Keap1-Nrf2 途径，但它们与 Keap1 反应的方式可能不同。这些发现还表明，即使在同一个基因中，也存在正向和负向的 Nrf2 元件，这种对立的机制为 Keap1-Nrf2 途径的转录调节提供了精细的调整。CES1 的高水平与脂质保留有关。抗氧化剂和敏化剂对 CES1 的过度诱导可能为其对人类健康的潜在有害影响提供了一种机制。
