Glait Chen, Tencer Lilach, Ravid Dana, Sarfstein Rive, Liscovitch Mordechai, Werner Haim
Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
Exp Cell Res. 2006 Nov 15;312(19):3899-908. doi: 10.1016/j.yexcr.2006.08.016. Epub 2006 Aug 26.
The insulin-like growth factor (IGF) system plays an important role in the biology of breast cancer. Most of the biological actions of IGF-I and IGF-II are mediated by the IGF-I receptor (IGF-IR), a membrane-bound heterotetramer with potent antiapoptotic and cell survival activities. Caveolin-1 (Cav-1) is one of the main components of caveolae, and it has been shown to interact with multiple signaling molecules. In view of the important roles of IGF-IR and Cav-1 in oncogenically transformed mammary gland cells, in the present study we addressed the potential regulation of IGF-IR gene expression by Cav-1. The results obtained showed that MCF7/Cav-1 cells, expressing the Cav-1 gene in a stable manner, contain significantly higher levels of IGF-IR protein and mRNA than native MCF7 cells. These elevated levels of expression are mediated at the level of transcription, as shown by the results of experiments showing that the activity of the proximal IGF-IR promoter was higher in Cav-1-expressing MCF7 cells than in untransfected MCF7 cells. Furthermore, in subcellular localization studies, intensive IGF-IR staining in membrane ruffles and projections in MCF7/Cav-1 cells were noted, in contrast to typical membrane staining in MCF7 cells. In addition, we demonstrated that transcriptional activation of the IGF-IR gene by Cav-1 requires an intact p53 signaling pathway, since Cav-1 was unable to elevate IGF-IR levels in p53-null cells. Finally, the effect of Cav-1 was associated with an elevation in the levels of Sp1, a zinc-finger protein with important roles in IGF-IR gene transactivation. In summary, we identified the IGF-IR gene as a downstream target for Cav-1 action in breast cancer cells.
胰岛素样生长因子（IGF）系统在乳腺癌生物学中发挥着重要作用。IGF-I和IGF-II的大多数生物学作用是由IGF-I受体（IGF-IR）介导的，IGF-IR是一种具有强大抗凋亡和细胞存活活性的膜结合异源四聚体。小窝蛋白-1（Cav-1）是小窝的主要成分之一，已证明它能与多种信号分子相互作用。鉴于IGF-IR和Cav-1在致癌转化的乳腺细胞中的重要作用，在本研究中，我们探讨了Cav-1对IGF-IR基因表达的潜在调控作用。所得结果表明，稳定表达Cav-1基因的MCF7/Cav-1细胞中，IGF-IR蛋白和mRNA水平显著高于天然MCF7细胞。实验结果表明，IGF-IR近端启动子在表达Cav-1的MCF7细胞中的活性高于未转染的MCF7细胞，这表明这些升高的表达水平是在转录水平介导的。此外，在亚细胞定位研究中，与MCF7细胞典型的膜染色不同，在MCF7/Cav-1细胞的膜皱褶和突起中观察到强烈的IGF-IR染色。此外，我们证明Cav-1对IGF-IR基因的转录激活需要完整的p53信号通路，因为Cav-1在p53基因缺失的细胞中无法提高IGF-IR水平。最后，Cav-1的作用与Sp1水平的升高有关，Sp1是一种在IGF-IR基因反式激活中起重要作用的锌指蛋白。总之，我们确定IGF-IR基因是Cav-1在乳腺癌细胞中作用的下游靶点。
