Department of Radio-Oncology, Nanjing Medical University Affiliated Suzhou Hospital; Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104.
School of Radiation Medicine and Protection, Soochow University, Suzhou 205123, China; Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104.
J Biol Chem. 2012 Oct 12;287(42):35161-35169. doi: 10.1074/jbc.M112.367367. Epub 2012 Aug 29.
Activation of peroxisome proliferator-activated receptor α (PPARα) has been demonstrated to inhibit tumor growth and angiogenesis, yet the mechanisms behind these actions remain to be characterized. In this study, we examined the effects of PPARα activation on the hypoxia-inducible factor-1α (HIF-1α) signaling pathway in human breast (MCF-7) and ovarian (A2780) cancer cells under hypoxia. Incubation of cancer cells under 1% oxygen for 16 h significantly induced HIF-1α expression and activity as assayed by Western blotting and reporter gene analysis. Treatment of the cells with PPARα agonists, but not a PPARγ agonist, prior to hypoxia diminished hypoxia-induced HIF-1α expression and activity, and addition of a PPARα antagonist attenuated the suppression of HIF-1α signaling. Activation of PPARα attenuated hypoxia-induced HA-tagged HIF-1α protein expression without affecting the HA-tagged HIF-1α mutant protein level, indicating that PPARα activation promotes HIF-1α degradation in these cells. This was further confirmed using proteasome inhibitors, which reversed PPARα-mediated suppression of HIF-1α expression under hypoxia. Using the co-immunoprecipitation technique, we found that activation of PPARα enhances the binding of HIF-1α to von Hippel-Lindau tumor suppressor (pVHL), a protein known to mediate HIF-1α degradation through the ubiquitin-proteasome pathway. Following PPARα-mediated suppression of HIF-1α signaling, VEGF secretion from the cancer cells was significantly reduced, and tube formation by endothelial cells was dramatically impaired. Taken together, these findings demonstrate for the first time that activation of PPARα suppresses hypoxia-induced HIF-1α signaling in cancer cells, providing novel insight into the anticancer properties of PPARα agonists.
过氧化物酶体增殖物激活受体 α（PPARα）的激活已被证明可抑制肿瘤生长和血管生成，但这些作用的机制仍有待阐明。在这项研究中，我们研究了在缺氧条件下 PPARα 激活对人乳腺癌（MCF-7）和卵巢癌细胞（A2780）中缺氧诱导因子-1α（HIF-1α）信号通路的影响。将癌细胞在 1%氧气中孵育 16 小时，通过 Western blot 和报告基因分析显著诱导 HIF-1α 的表达和活性。在缺氧之前用 PPARα 激动剂而不是 PPARγ 激动剂处理细胞，可减少缺氧诱导的 HIF-1α 表达和活性，并且添加 PPARα 拮抗剂可减弱 HIF-1α 信号的抑制。PPARα 的激活减弱了缺氧诱导的 HA 标记的 HIF-1α 蛋白表达，而不影响 HA 标记的 HIF-1α 突变蛋白水平，表明 PPARα 激活促进了这些细胞中的 HIF-1α 降解。这通过使用蛋白酶体抑制剂进一步得到证实，蛋白酶体抑制剂逆转了缺氧下 PPARα 介导的 HIF-1α 表达抑制。使用共免疫沉淀技术，我们发现 PPARα 的激活增强了 HIF-1α 与 von Hippel-Lindau 肿瘤抑制因子（pVHL）的结合，pVHL 是一种已知通过泛素-蛋白酶体途径介导 HIF-1α 降解的蛋白。在 PPARα 介导的 HIF-1α 信号抑制后，癌细胞中 VEGF 的分泌显著减少，内皮细胞的管形成也受到严重损害。总之，这些发现首次证明了 PPARα 的激活可抑制癌细胞中缺氧诱导的 HIF-1α 信号，为 PPARα 激动剂的抗癌特性提供了新的见解。
