Tumor gene expression in vitro and in vivo

我们过去对生长的研究主要集中在ras癌基因及其正向调节因子，即RAS特异性鸟嘌呤核苷酸交换因子(RAS-GNEFs)，它们在信号转导中起着关键作用。我们最近将注意力转向E-钙粘蛋白及其在生长调节和信号转导中的作用。E-钙粘附素是一种重要的黏附蛋白，也是一种肿瘤抑制因子，在肿瘤中经常被沉默。E-钙粘蛋白最初被描述为一种结构蛋白，最近被认为是调节信号的。到目前为止，被认为受E-钙粘蛋白调控的主要生物相关信号分子是β-连环蛋白，它以非共价方式与E-钙粘蛋白结合，是Wnt信号通路的关键组成部分。然而，尽管黏附是E-钙粘蛋白的标志性功能，但其对β-连环蛋白的调节并不依赖于E-钙粘附素的黏附功能。我们现在发现，E-钙粘素可以以黏附依赖的方式负性调节不同类别受体酪氨酸激酶的配体依赖性激活，包括EGFR/Neu、IGF1R和c-Met。相反，E-钙粘素不调节结构性活性突变受体酪氨酸激酶(Neu*)，也不调节LPA受体或M受体的配体依赖性激活，这两个受体是两个G蛋白偶联受体。E-钙粘附素依赖的黏附限制了EGFR-CFP在质膜上的流动性，并消除了高亲和力的EGF和IGF-1结合部位，从而削弱了配体激活其同源受体的能力。结果表明，受体酪氨酸激酶的可溶性配体对受体酪氨酸激酶的负性调节是生理性的、特异性的和粘附性的。由于受体酪氨酸激酶参与了多种细胞过程，包括营养、生长和分化，这些数据表明E-钙粘素可以调节这些过程。受体酪氨酸激酶调节的取消也可能是肿瘤中E-钙粘蛋白频繁沉默的原因之一。

Much of our past research on growth has been concerned with the ras oncogene and its positive regulators, the Ras-specific guanine nucleotide exchange factors (Ras-GNEFs), which play a key role in signal transduction. We have recently turned our attention to E-cadherin and its role in the regulation of growth and signaling. E-cadherin is an essential adhesion protein that is also a tumor suppressor frequently silenced in tumors. Originally described as a structural protein, E-cadherin has more recently been recognized to regulate signaling. The principal biologically relevant signaling molecule thus far implicated as being regulated by E-cadherin is Beta-catenin, which binds non-covalently to E-cadherin and is a key component of the Wnt signaling pathway. However, although adhesion is the hallmark function of E-cadherin, its regulation of Beta-catenin does not depend on the adhesive function of E-cadherin. We have now found that E-cadherin can negatively regulate, in an adhesion-dependent manner, the ligand-dependent activation of divergent classes of receptor tyrosine kinases, including EGFR/Neu, IGF1R, and c-Met. By contrast, E-cadherin did not regulate a constitutively active mutant receptor tyrosine kinase (Neu*) or the ligand-dependent activation of LPA receptors or muscarinic receptors, which are two G protein coupled receptors. E-cadherin dependent adhesion restricted the mobility of EGFR-CFP in the plasma membrane and eliminated high affinity EGF and IGF-1 binding sites, thus impairing the ability of the ligands to activate their cognate receptors. The results indicated that negative regulation of receptor tyrosine kinases by their soluble ligands is physiologic, specific, and adhesion-dependent. Since receptor tyrosine kinases have been implicated in multiple cellular processes, including nutrition, growth, and differentiation, the data imply that E-cadherin can regulate these processes. Abrogation of receptor tyrosine kinase regulation may also contribute to the frequent silencing of E-cadherin in tumors.