Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 2010 Mar 16;107(11):5012-7. doi: 10.1073/pnas.1000896107. Epub 2010 Mar 1.
Aberrant activation of Notch receptors has been implicated in breast cancer; however, the mechanisms contributing to Notch-dependent transformation remain elusive because Notch displays dichotomous functional activities, promoting both proliferation and growth arrest. We investigated the cellular basis for the heterogeneous responses to Notch pathway activation in 3D cultures of MCF-10A mammary epithelial cells. Expression of a constitutively active Notch-1 intracellular domain (NICD) was found to induce two distinct types of 3D structures: large, hyperproliferative structures and small, growth-arrested structures with reduced cell-to-matrix adhesion. Interestingly, we found that these heterogeneous phenotypes reflect differences in Notch pathway activation levels; high Notch activity caused down-regulation of multiple matrix-adhesion genes and inhibition of proliferation, whereas low Notch activity maintained matrix adhesion and provoked a strong hyperproliferative response. Moreover, microarray analyses implicated NICD-induced p63 down-regulation in loss of matrix adhesion. In addition, a reverse-phase protein array-based analysis and subsequent loss-of-function studies identified STAT3 as a dominant downstream mediator of the NICD-induced outgrowth. These results indicate that the phenotypic responses to Notch are determined by the dose of pathway activation; and this dose affects the balance between growth-stimulative and growth-suppressive effects. This unique feature of Notch signaling provides insights into mechanisms that contribute to the dichotomous effects of Notch during development and tumorigenesis.
Notch 受体的异常激活与乳腺癌有关；然而，导致 Notch 依赖性转化的机制仍不清楚，因为 Notch 显示出双重功能活性，既能促进增殖又能促进生长停滞。我们研究了 Notch 途径激活在 MCF-10A 乳腺上皮细胞 3D 培养物中产生异质反应的细胞基础。发现组成性激活的 Notch-1 细胞内结构域（NICD）表达诱导两种不同类型的 3D 结构：大的、过度增殖的结构和小的、生长停滞的结构，细胞与基质的粘附减少。有趣的是，我们发现这些异质表型反映了 Notch 途径激活水平的差异；高 Notch 活性导致多种基质粘附基因下调和增殖抑制，而低 Notch 活性维持基质粘附并引发强烈的过度增殖反应。此外，微阵列分析表明，NICD 诱导的 p63 下调导致基质粘附丧失。此外，基于反相蛋白阵列的分析和随后的功能丧失研究表明，STAT3 是 NICD 诱导生长的主要下游介质。这些结果表明，对 Notch 的表型反应取决于途径激活的剂量；而这种剂量会影响生长刺激和生长抑制作用之间的平衡。Notch 信号的这种独特特征为解释 Notch 在发育和肿瘤发生过程中的双重作用的机制提供了线索。
