Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston, 77030, USA.
Proc Natl Acad Sci U S A. 2010 Sep 7;107(36):15810-5. doi: 10.1073/pnas.1004060107. Epub 2010 Aug 23.
Defects in apical-basal cell polarity and abnormal expression of cell polarity determinants are often associated with cancer in vertebrates. In Drosophila, abnormal expression of apical-basal determinants can cause neoplastic phenotypes, including loss of cell polarity and overproliferation. However, the pathways through which apical-basal polarity determinants affect growth are poorly understood. Here, we investigated the mechanism by which the apical determinant Crumbs (Crb) affects growth in Drosophila imaginal discs. Overexpression of Crb causes severe overproliferation, and we found that loss of Crb similarly results in overgrowth of imaginal discs. Crb gain and loss of function caused defects in Hippo signaling, a key signaling pathway that controls tissue growth in Drosophila and mammals. Manipulation of Crb levels caused the up-regulation of Hippo target genes, genetically interacted with known Hippo pathway components, and required Yorkie, a transcriptional coactivator that acts downstream in the Hippo pathway, for target gene induction and overgrowth. Interestingly, Crb regulates growth and cell polarity through different motifs in its intracellular domain. A juxtamembrane FERM domain-binding motif is responsible for growth regulation and induction of Hippo target gene expression, whereas Crb uses a PDZ-binding motif to form a complex with other polarity factors. The Hippo pathway component Expanded, an apically localized adaptor protein, is mislocalized in both crb mutant cells and Crb overexpressing tissues, whereas the other Hippo pathway components, Fat and Merlin, are unaffected. Taken together, our data show that Crb regulates growth through Hippo signaling, and thus identify Crb as a previously undescribed upstream input into the Hippo pathway.
顶端-基底细胞极性缺陷和细胞极性决定因素的异常表达常与脊椎动物的癌症有关。在果蝇中，顶端-基底决定因素的异常表达可导致肿瘤表型，包括细胞极性丧失和过度增殖。然而，顶端-基底极性决定因素影响生长的途径知之甚少。在这里，我们研究了顶端决定因子 Crumbs（Crb）影响果蝇 imaginal discs 生长的机制。Crb 的过表达导致严重的过度增殖，我们发现 Crb 的缺失同样导致 imaginal discs 的过度生长。Crb 的功能获得和缺失导致 Hippo 信号通路的缺陷，Hippo 信号通路是控制果蝇和哺乳动物组织生长的关键信号通路。Crb 水平的操纵导致 Hippo 靶基因的上调，与已知的 Hippo 途径成分在遗传上相互作用，并需要 Yorkie，一种在 Hippo 途径下游起作用的转录共激活因子，用于靶基因诱导和过度生长。有趣的是，Crb 通过其细胞内结构域中的不同基序来调节生长和细胞极性。一个靠近膜的 FERM 结构域结合基序负责调节生长和 Hippo 靶基因表达的诱导，而 Crb 使用 PDZ 结合基序与其他极性因子形成复合物。Hippo 途径成分 Expanded，一种定位于顶端的衔接蛋白，在 crb 突变细胞和 Crb 过表达组织中都发生了定位错误，而其他 Hippo 途径成分 Fat 和 Merlin 则不受影响。总之，我们的数据表明 Crb 通过 Hippo 信号通路调节生长，从而将 Crb 鉴定为 Hippo 途径的一个以前未被描述的上游输入。
