Cherlet Tracy, Murphy Leigh C
Manitoba Institute of Cell Biology, Department of Biochemistry & Medical Genetics, University of Manitoba, Winnipeg, MB, Canada R3E 0V9.
Mol Cell Biochem. 2007 Dec;306(1-2):33-42. doi: 10.1007/s11010-007-9551-1. Epub 2007 Jul 28.
Breast tumorigenesis and breast cancer progression involves the deregulation or hyperactivation of intracellular signaling proteins that leads to uncontrolled cellular proliferation, invasion and metastasis. For example, the expression and cellular responses to estogen receptor (ER) and transforming growth factor beta (TGFbeta) signaling pathways change during breast tumorigenesis and breast cancer progression. While the expression and activity of ER and TGFbeta maybe significant in the development of breast cancer, alterations in the cross-talk between these pathways may be equally important. Autocrine and paracrine effects of TGFbeta on breast cancer cell growth have been known for some time, but only recently have direct interactions between ER and TGFbeta been described. The purpose of this article was to further characterize the cross-talk between ER and TGFbeta, by examining ER interaction with Smad3, a downstream mediator of TGFbeta signaling. Transient transfection of Cos1 cells with p3TP-lux, demonstrate that ERalpha and ERbeta(1) repress Smad3 transcriptional activity in an estradiol-dependent manner and that this effect is inhibited by antiestrogen treatment. The ERbeta variants, ERbeta(2) and ERbeta(5), did not have any effect on Smad3 transcriptional activity. Further experiments attempted to characterize the molecular mechanism by which activated ER inhibits Smad3 transcriptional activity. Results indicate that ligand-bound ER does not affect Smad3 protein expression levels and that ER does not form direct protein interactions with Smad3. Transient transfection of Cos1 cells with the Ap-1 transcription factor c-Jun but not c-Fos was able to rescue the inhibitory effect of estrogen on Smad3 transcriptional activity. Based on these results, a model is proposed whereby c-Jun is limiting in its ability to act as a Smad3 co-activator in the presence of E(2)-bound ER, possibly due to ER sequestering c-Jun away from the Smad3 responsive promoter.
乳腺肿瘤发生和乳腺癌进展涉及细胞内信号蛋白的失调或过度激活，这会导致细胞不受控制地增殖、侵袭和转移。例如，在乳腺肿瘤发生和乳腺癌进展过程中，雌激素受体（ER）和转化生长因子β（TGFβ）信号通路的表达及细胞反应会发生变化。虽然ER和TGFβ的表达及活性在乳腺癌发展过程中可能很重要，但这些通路之间相互作用的改变可能同样重要。TGFβ对乳腺癌细胞生长的自分泌和旁分泌作用已为人所知一段时间了，但直到最近才描述了ER和TGFβ之间的直接相互作用。本文的目的是通过研究ER与TGFβ信号下游介质Smad3的相互作用，进一步表征ER和TGFβ之间的相互作用。用p3TP-lux瞬时转染Cos1细胞，结果表明ERα和ERβ(1)以雌二醇依赖的方式抑制Smad3转录活性，且这种作用可被抗雌激素处理所抑制。ERβ变体ERβ(2)和ERβ(5)对Smad3转录活性没有任何影响。进一步的实验试图表征活化的ER抑制Smad3转录活性的分子机制。结果表明，配体结合的ER不影响Smad3蛋白表达水平，且ER不与Smad3形成直接的蛋白质相互作用。用Ap-1转录因子c-Jun而不是c-Fos瞬时转染Cos1细胞能够挽救雌激素对Smad3转录活性的抑制作用。基于这些结果，提出了一个模型，即在存在与E(2)结合的ER的情况下，c-Jun作为Smad3共激活因子的能力受到限制，这可能是由于ER将c-Jun从Smad3反应性启动子上隔离开。
