SNAIL-Dependent Regulation of EMT in Cancer

描述(申请人提供)：E-钙粘附素表达下调是称为上皮-间充质转化(EMT)的关键发育计划的标志，该过程通常被表现为侵袭性表型的癌细胞利用。锌指转录因子Snail是E-钙粘蛋白基因表达的强大抑制因子，它可以单独或与Wnt信号级联一起作用，在正常和肿瘤细胞中诱导EMT。在最近的研究中，我们证明了蜗牛蛋白中嵌入了β-连环素样基序，支持其被GSK3β磷酸化，以及随后的β-TrCP诱导的泛素化和蛋白酶体降解。此外，已经建立了一个可操作的模型，其中规范的Wnt信号以合作的方式稳定细胞内Snail和β-catenin的水平，以参与控制EMT程序的转录机制。基于一系列新的初步数据，我们现在确定了一个新的调节级联，其中规范的Wnt信号和β-catenin/TCF转录级联通过诱导依赖于Axin2的GSK3β核质运输调节来启动EMT。通过触发核GSK3β输出，核蜗牛蛋白的半衰期得到稳定，并通过与膜锚定金属蛋白酶基因家族成员表达相关的过程参与经典的EMT计划-包括癌细胞侵袭和血管内侵入。因此，我们现在建议：1)表征Wnt通过Snail/β-catenin/TCF轴启动的对癌细胞EMT的调控；ii)定义Axin2对β-catenin/TCF诱导的EMT的蜗牛依赖性调控；iii)确定Axin2核浆转运和蜗牛依赖性EMT的结构-功能关系；以及iv)表征Axin2依赖性GSK3β核浆转运的调控及其对蜗牛依赖性EMT的影响。这些研究不仅应该确定Wnt、β-catenin/Tcf和Snail在调节癌症EMT中的连锁作用，而且还应该确定治疗干预的新靶点。

DESCRIPTION (provided by applicant): Down-regulation of E-cadherin expression is a hallmark of a key developmental program termed the epithelial-mesenchymal transition (EMT), a process often exploited by cancer cells that display an invasive phenotype. The zinc finger transcription factor, Snail, is a powerful represser of E-cadherin gene expression that can function alone or together with the Wnt signaling cascade to induce EMT in normal as well neoplastic cells. In recent studies, we demonstrated that the Snail protein is embedded with beta-catenin-like motifs supporting its phosphorylation by GSK3beta and its subsequent beta-TrCP-directed ubiquitination and proteasomal degradation. Further, an operational model has been established wherein canonical Wnt signaling stabilizes intracellular levels of Snail and beta-catenin in cooperative fashion to engage transcriptional mechanisms that control the EMT program. Based on a body of new preliminary data, we now identify a novel regulatory cascade wherein canonical Wnt signaling and the beta- catenin/TCF transcriptional cascade initiate EMT by inducing the Axin2-dependent regulation of GSK3beta nucleo-cytoplasmic trafficking. By triggering nuclear GSK3beta export, nuclear Snail protein half-life is stabilized and a classic EMT program engaged - including cancer cell invasion and intravasation - via a process linked to the expression of membrane-anchored metalloproteinase gene family members. As such, we now propose to i) characterize the Wnt-initiated regulation of carcinoma cell EMT by the Snail/beta-catenin/TCF axis, ii) define the Snail-dependent regulation of beta-catenin/TCF-induced EMT by Axin2, iii) define the structure-function relationships underlying Axin2 nucleo-cytoplasmic trafficking and Snail-dependent EMT and iv) characterize the Axin2-dependent control of GSK3beta nucleo-cytoplasmic trafficking and its impact on Snail-dependent EMT. These studies should not only define the interlocking role of Wnt, beta-catenin/TCF and Snail in regulating EMT in cancer, but also identify new targets for therapeutic intervention.