Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
Oncogene. 2014 Mar 27;33(13):1649-57. doi: 10.1038/onc.2013.118. Epub 2013 Apr 29.
In the mammary gland, the stromal extracellular matrix (ECM) undergoes dramatic changes during development and in tumorigenesis. For example, normal adult breast tissue is largely devoid of the ECM protein fibronectin (FN) whereas high FN levels have been detected in the stroma of breast tumors. FN is an established marker for epithelial-mesenchymal transition (EMT), which occurs during development and has been linked to cancer. During EMT, epithelial cell adhesion switches from cell-cell contacts to mainly cell-ECM interactions, raising the possibility that FN may have a role in promoting this transition. Using MCF-10A mammary epithelial cells, we show that exposure to exogenous FN induces an EMT response including upregulation of the EMT markers FN, Snail, N-cadherin, vimentin, the matrix metalloprotease MMP2, α-smooth muscle actin and phospho-Smad2, as well as acquisition of cell migratory behavior. FN-induced EMT depends on Src kinase and extracellular signal-regulated kinase/mitogen-activated protein (ERK/MAP) kinase signaling but not on the immediate early gene EGR-1. FN initiates EMT under serum-free conditions; this response is partially reversed by a transforming growth factor (TGF)β-neutralizing antibody, suggesting that FN enhances the effect of endogenous TGFβ. EMT marker expression is upregulated in cells on a fragment of FN containing the integrin-binding domain but not other domains. Differences in gene expression between FN and Matrigel are maintained with addition of a subthreshold level of TGFβ1. Together, these results show that cells interacting with FN are primed to respond to TGFβ. The ability of FN to induce EMT shows an active role for the stromal ECM in this process and supports the notion that the increased levels of FN observed in breast tumors facilitate tumorigenesis.
在乳腺中，基质细胞外基质（ECM）在发育和肿瘤发生过程中发生显著变化。例如，正常成年乳腺组织中大量缺乏 ECM 蛋白纤维连接蛋白（FN），而乳腺肿瘤基质中检测到高 FN 水平。FN 是上皮-间充质转化（EMT）的一个既定标志物，它发生在发育过程中，并与癌症有关。在 EMT 过程中，上皮细胞黏附从细胞-细胞接触转变为主要的细胞-ECM 相互作用，这使得 FN 可能在促进这种转化中发挥作用。使用 MCF-10A 乳腺上皮细胞，我们发现，暴露于外源性 FN 会诱导 EMT 反应，包括 EMT 标志物 FN、Snail、N-钙黏蛋白、波形蛋白、基质金属蛋白酶 MMP2、α-平滑肌肌动蛋白和磷酸化 Smad2 的上调，以及获得细胞迁移行为。FN 诱导的 EMT 依赖于Src 激酶和细胞外信号调节激酶/丝裂原活化蛋白（ERK/MAP）激酶信号通路，但不依赖于即刻早期基因 EGR-1。FN 在无血清条件下启动 EMT；这种反应部分被转化生长因子（TGF）β中和抗体逆转，表明 FN 增强了内源性 TGFβ 的作用。在包含整合素结合域的 FN 片段上，细胞中 EMT 标志物的表达上调，但不包括其他结构域。在添加亚阈值水平的 TGFβ1 后，FN 和 Matrigel 之间的基因表达差异得以维持。总之，这些结果表明，与 FN 相互作用的细胞已准备好对 TGFβ 作出反应。FN 诱导 EMT 的能力表明基质 ECM 在这一过程中发挥了积极作用，并支持这样一种观点，即乳腺肿瘤中观察到的 FN 水平升高促进了肿瘤的发生。
