Comprehensive Pneumology Center, University Hospital, Ludwig-Maximilians University and Helmholtz Zentrum München, 81377 Munich, Germany.
J Biol Chem. 2012 Sep 7;287(37):31393-405. doi: 10.1074/jbc.M112.357624. Epub 2012 Jul 9.
Although TGF-β acts as a tumor suppressor in normal tissues and in early carcinogenesis, these tumor suppressor effects are lost in advanced malignancies. Single cell migration and epithelial-mesenchymal transition (EMT), both of which are regulated by TGF-β, are critical steps in mediating cancer progression. Here, we sought to identify novel direct targets of TGF-β signaling in lung cancer cells and have indentified the zyxin gene as a target of Smad3-mediated TGF-β1 signaling. Zyxin concentrates at focal adhesions and along the actin cytoskeleton; as such, we hypothesized that cytoskeletal organization, motility, and EMT in response to TGF-β1 might be regulated by zyxin expression. We show that TGF-β1 treatment of lung cancer cells caused rapid phospho-Smad3-dependent expression of zyxin. Zyxin expression was critical for the formation and integrity of cell adherens junctions. Silencing of zyxin decreased expression of the focal adhesion protein vasodilator-activated phospho-protein (VASP), although the formation and morphology of focal adhesions remained unchanged. Zyxin-depleted cells displayed significantly increased integrin α5β1 levels, accompanied by enhanced adhesion to fibronectin and acquisition of a mesenchymal phenotype in response to TGF-β1. Zyxin silencing led to elevated integrin α5β1-dependent single cell motility. Importantly, these features are mirrored in the K-ras-driven mouse model of lung cancer. Here, lung tumors revealed decreased levels of both zyxin and phospho-Smad3 when compared with normal tissues. Our data thus demonstrate that zyxin is a novel functional target and effector of TGF-β signaling in lung cancer. By regulating cell-cell junctions, integrin α5β1 expression, and cell-extracellular matrix adhesion, zyxin may regulate cancer cell motility and EMT during lung cancer development and progression.
虽然 TGF-β 在正常组织和早期癌变中起肿瘤抑制作用，但这些肿瘤抑制作用在晚期恶性肿瘤中丧失。TGF-β 调节的单细胞迁移和上皮-间充质转化 (EMT) 都是介导癌症进展的关键步骤。在这里，我们试图确定肺癌细胞中 TGF-β 信号的新的直接靶标，并确定 zyxin 基因为 Smad3 介导的 TGF-β1 信号的靶标。Zyxin 集中在焦点粘连和肌动蛋白细胞骨架上；因此，我们假设细胞骨架组织、运动和 EMT 对 TGF-β1 的反应可能受 zyxin 表达的调节。我们表明，TGF-β1 处理肺癌细胞导致快速的磷酸化 Smad3 依赖的 zyxin 表达。Zyxin 表达对于细胞黏附连接的形成和完整性至关重要。沉默 zyxin 降低了焦点附着蛋白血管扩张激活磷酸化蛋白 (VASP) 的表达，尽管焦点附着的形成和形态保持不变。Zyxin 耗尽的细胞显示出明显增加的整合素 α5β1 水平，伴随着对纤维连接蛋白的增强黏附以及对 TGF-β1 的获得间充质表型。Zyxin 沉默导致整合素 α5β1 依赖性单细胞迁移增加。重要的是，这些特征在 K-ras 驱动的肺癌小鼠模型中得到了反映。在这里，与正常组织相比，肺癌肿瘤显示出 zyxin 和磷酸化 Smad3 的水平降低。因此，我们的数据表明 zyxin 是肺癌中 TGF-β 信号的新的功能靶标和效应物。通过调节细胞-细胞连接、整合素 α5β1 表达和细胞-细胞外基质黏附，zyxin 可能调节癌症细胞在肺癌发生和进展过程中的运动和 EMT。
