Centre for Biotechnology, Anna University, Chennai 600025, India.
Br J Cancer. 2011 Sep 27;105(7):953-60. doi: 10.1038/bjc.2011.349. Epub 2011 Sep 6.
Hypoxia-inducible factor 1 (HIF1) has been implicated in regulating many of the genes responsible for angiogenesis, erythropoiesis, glucose metabolism and cancer pathogenesis. In this study, we demonstrate that exposure of human breast cancer lines to 17β-oestradiol (E2) rapidly induced the expression of HIF-1α, the regulated subunit of HIF1, in normoxic condition. Hypoxia-inducible factor-1α is normally degraded in normoxia through ubiquitination-mediated proteolysis, whereas hypoxia modulates HIF-1α level by inhibiting ubiquitination-mediated degradation.
Oestradiol-induced accumulation of HIF-1α in breast cancer lines was detected by western blot analysis and its promoter activity was measured by HIF1 reporter assay. Molecular signalling of oestradiol-mediated HIF-1α expression was studied using specific pharmacological inhibitors and small interference RNA by co-immunoprecipitation and western blotting analysis.
Oestradiol has been observed to rapidly activate the nongenomic signalling cascade leading to HIF-1α protein synthesis. The results define a signalling pathway in breast cancer cells whereby oestradiol induces a rapid protein-protein interaction of ERα-c-Src-PI3K, resulting in the activation of PI3K/AKT pathway leading to mammalian target of rapamycin (mTOR) phosphorylation. The mTOR then stimulates translation by phosphorylating p70 S6 kinase and 4EB-P1, modulating HIF-1α protein synthesis. Oestradiol-stimulated HIF-1α activity was inhibited by either siRNA or pharmacological inhibitors to ERα, c-Src, PI3K and mTOR, providing a mechanism for the modulation of HIF-1α protein synthesis.
These results show oestradiol-induced expression of HIF-1α, downstream of the ERα/c-Src/PI3K/AKT/mTOR pathway in human breast cancer cells.
缺氧诱导因子 1（HIF1）被认为参与调节许多与血管生成、红细胞生成、葡萄糖代谢和癌症发病机制相关的基因。在这项研究中，我们证明了在常氧条件下，暴露于 17β-雌二醇（E2）的人乳腺癌细胞系迅速诱导 HIF1 的调节亚基 HIF-1α的表达。在常氧条件下，HIF-1α 通过泛素化介导的蛋白水解而正常降解，而缺氧通过抑制泛素化介导的降解来调节 HIF-1α 水平。
通过 Western blot 分析检测乳腺癌细胞系中雌二醇诱导的 HIF-1α 积累，通过 HIF1 报告基因测定测量其启动子活性。使用特异性药理学抑制剂和小干扰 RNA 通过共免疫沉淀和 Western blot 分析研究雌二醇介导的 HIF-1α 表达的分子信号。
雌二醇已被观察到快速激活导致 HIF-1α 蛋白合成的非基因组信号级联。结果定义了乳腺癌细胞中的信号通路，其中雌二醇诱导 ERα-c-Src-PI3K 的快速蛋白-蛋白相互作用，导致 PI3K/AKT 通路激活，导致哺乳动物雷帕霉素靶蛋白（mTOR）磷酸化。mTOR 通过磷酸化 p70 S6 激酶和 4EB-P1 来刺激翻译，调节 HIF-1α 蛋白合成。用 siRNA 或 ERα、c-Src、PI3K 和 mTOR 的药理学抑制剂抑制雌二醇刺激的 HIF-1α 活性，为调节 HIF-1α 蛋白合成提供了一种机制。
这些结果表明，在人乳腺癌细胞中，雌激素诱导的 HIF-1α 表达是 ERα/c-Src/PI3K/AKT/mTOR 通路的下游事件。
