Vafaizadeh Vida, Graab Ulrike, Darvishi Tahmineh, Machado Rita, Groner Bernd
Horm Mol Biol Clin Investig. 2012 Jun;10(1):227-39. doi: 10.1515/hmbci-2012-0016.
Abstract Breast cancer patients with disseminated metastatic disease still have a very unfavorable prognosis. Investigations into the molecular mechanisms that underlie metastasis formation have a high priority and can possibly result in improved therapeutic interventions. The process of oncogenic epithelial to mesenchymal transition (EMT) has recently become a focus in cancer research because it encompasses many of the phenotypic traits characteristic of metastatic cells, e.g., increased motility, invasion, anoikis resistance, immunosuppression, and cancer stem cell potential. A number of central cellular signaling pathways and transcription factors have been implied in the control of EMT and metastasis formation, among them signal originating from the activation of the transforming growth factor β (TGFβ), epithelial growth factor, Wnt, Notch, and Hedgehog pathways. We have investigated the contribution of TGFβ signaling to metastasis-related cellular properties. TGFβ signaling can have tumor-suppressive and -promoting effects depending on the tumor type and the stage of tumor progression. TGFβ can inhibit the proliferation of mammary epithelial cells (MECs), but it can also induce EMT, invasion, and metastasis, possibly through Smad-independent signaling events. We investigated the effects of TGFβ pathway inhibition on the proliferation, differentiation, and invasion of both normal and malignant MECs. shRNA-mediated downregulation of the Smad4 protein in non-tumorigenic HC11 and tumorigenic 4T1 cells promotes the invasiveness of both cell lines. Mammary gland reconstitution studies, with primary MECs expressing shSmad4, resulted only in subtle effects on the glandular morphogenesis. Orthotopic transplantation of shSmad4-transduced 4T1 tumor cells caused the accelerated growth of mammary tumors and enhanced colonization and macroscopic lung metastases when compared to control cells. Surprisingly, the expression of Smad4 was restored, and a strong activation of Stat3 was found in the metastatic lesions present in the lungs. These lesions express metastatic factors, such as angiopoietin-like-4 and the inhibitor of DNA binding/differentiation 1. We suggest that the downregulation of Smad4 inhibits the tumor-suppressive effects of TGFβ signaling and enhances tumor growth. The downregulation, however, was only transient, and the reactivation of Smad4 expression caused the reversal of EMT, mesenchymal to epithelial transition, and thereby promoted metastasis formation in the lungs.
摘要 患有播散性转移性疾病的乳腺癌患者预后仍然非常不佳。对转移形成背后分子机制的研究具有高度优先性，并且可能带来改进的治疗干预措施。致癌性上皮-间质转化（EMT）过程最近已成为癌症研究的焦点，因为它涵盖了许多转移细胞的表型特征，例如运动性增加、侵袭性、抗失巢凋亡、免疫抑制和癌症干细胞潜能。一些核心细胞信号通路和转录因子已被认为参与EMT和转移形成的调控，其中包括源自转化生长因子β（TGFβ）、上皮生长因子、Wnt、Notch和Hedgehog通路激活的信号。我们研究了TGFβ信号传导对转移相关细胞特性的贡献。TGFβ信号传导根据肿瘤类型和肿瘤进展阶段可具有肿瘤抑制和促进作用。TGFβ可抑制乳腺上皮细胞（MEC）的增殖，但它也可诱导EMT、侵袭和转移，可能通过不依赖Smad的信号事件。我们研究了TGFβ通路抑制对正常和恶性MEC增殖、分化和侵袭的影响。shRNA介导的非致瘤性HC11细胞和致瘤性4T1细胞中Smad4蛋白的下调促进了两种细胞系的侵袭性。用表达shSmad4的原代MEC进行乳腺重建研究，仅对腺形态发生产生轻微影响。与对照细胞相比，转导shSmad4的4T1肿瘤细胞的原位移植导致乳腺肿瘤加速生长，并增强了在肺部的定植和肉眼可见的肺转移。令人惊讶的是，Smad4的表达得以恢复，并且在肺部的转移病灶中发现Stat3强烈激活。这些病灶表达转移因子，如血管生成素样4和DNA结合/分化抑制剂1。我们认为Smad4的下调抑制了TGFβ信号传导的肿瘤抑制作用并增强了肿瘤生长。然而，这种下调只是暂时的，Smad4表达的重新激活导致EMT逆转，即间质向上皮转化，从而促进了肺部转移形成。
