No abstract

Epithelial cell-cell adhesion is mediated by E-cadherin, an intercellular N-glycoprotein adhesion receptor that functions in the assembly of multiprotein complexes anchored to the actin cytoskeleton named adherens junctions (AJs). E-cadherin ectodomains 4 and 5 contain three potential N-glycan addition sites, although their significance in AJ stability is unclear. Here we show that sparse cells lacking stable AJs produced E-cadherin that was extensively modified with complex N-glycans. In contrast, dense cultures with more stable AJs had scarcely N-glycosylated E-cadherin modified with high mannose/hybrid and limited complex N-glycans. This suggested that variations in AJ stability were accompanied by quantitative and qualitative changes in E-cadherin N-glycosylation. To further examine the role of N-glycans in AJ function, we generated E-cadherin N-glycosylation variants lacking selected N-glycan addition sites. Characterization of these variants in CHO cells, lacking endogenous E-cadherin, revealed that site 1 on ectodomain 4 was modified with a prominent complex N-glycan, site 2 on ectodomain 5 did not have a substantial oligosaccharide, and site 3 on ectodomain 5 was decorated with a high mannose/hybrid N-glycan. Removal of complex N-glycan from ectodomain 4 led to a dramatically increased interaction of E-cadherin-catenin complexes with vinculin and the actin cytoskeleton. The latter effect was further enhanced by the deletion of the high mannose/hybrid N-glycan from site 3. In MDCK cells, which produce E-cadherin, a variant lacking both complex and high mannose/hybrid N-glycans functioned like a dominant positive displaying increased interaction with ␥-catenin and vinculin compared with the endogenous E-cadherin. Collectively, our studies show that N-glycans, and complex oligosaccharides in particular, destabilize AJs by affecting their molecular organization.

Oral squamous cell carcinoma (OSCC) is a prevalent form of cancer that develops from the epithelium of the oral cavity. OSCC is on the rise worldwide, and death rates associated with the disease are particularly high. Despite progress in understanding of the mutational and expression landscape associated with OSCC, advances in deciphering these alterations for the development of therapeutic strategies have been limited. Further insight into the molecular cues that contribute to OSCC is therefore required. Here we show that the transcriptional regulators YAP (YAP1) and TAZ (WWTR1), which are key effectors of the Hippo pathway, drive pro-tumorigenic signals in OSCC. Regions of pre-malignant oral tissues exhibit aberrant nuclear YAP accumulation, suggesting that dysregulated YAP activity contributes to the onset of OSCC. Supporting this premise, we determined that nuclear YAP and TAZ activity drives OSCC cell proliferation, survival, and migration in vitro, and is required for OSCC tumor growth and metastasis in vivo. Global gene expression profiles associated with YAP and TAZ knockdown revealed changes in the control of gene expression implicated in pro-tumorigenic signaling, including those required for cell cycle progression and survival. Notably, the transcriptional signature regulated by YAP and TAZ significantly correlates with gene expression changes occurring in human OSCCs identified by “The Cancer Genome Atlas” (TCGA), emphasizing a central role for YAP and TAZ in OSCC biology.

The formation of acinar and ductal structures during epithelial tissue branching morphogenesis is not well understood. We report that in the mouse submandibular gland (SMG), acinar and ductal cell fates are determined early in embryonic morphogenesis with E-cadherin playing pivotal roles in development. We

Little is known about the mechanisms by which the lung epithelial progenitors are initially patterned and how proximaldistal boundaries are established and maintained when the lung primordium forms and starts to branch. Here we identified a number of Notch pathway components in respiratory progenitors of the early lung, and we investigated the role of Notch in lung pattern formation. By preventing ␥-secretase cleavage of Notch receptors, we have disrupted global Notch signaling in the foregut and in the lung during the initial stages of murine lung morphogenesis. We demonstrate that Notch signaling is not necessary for lung bud initiation; however, Notch is required to maintain a balance of proximal-distal cell fates at these early stages. Disruption of Notch signaling dramatically expands the population of distal progenitors, altering morphogenetic boundaries and preventing formation of proximal structures. Our data suggest a novel mechanism in which Notch and fibroblast growth factor signaling interact to control the proximaldistal pattern of forming airways in the mammalian lung.The mammalian respiratory system arises from the ventral foregut endoderm. Studies in mice show that at around embryonic day 9 (E9) 2 respiratory progenitors are collectively identified in the ventral foregut as a group of endodermal cells expressing Titf1 (thyroid transcription factor-1, or Nkx2.1). Besides being the earliest known marker of respiratory progenitors, Titf1 appears to be required to regulate lung epithelial cell fate (1). By E9.5, major morphogenetic changes occur in the respiratory field, leading to Fgf10 (fibroblast growth factor 10)-mediated expansion of these progenitors to form the lung primordia. Once primary lung buds have formed, lateral buds arise at stereotyped positions from these tubules (the main bronchi) and undergo branching morphogenesis and differentiation to give rise to the bronchial tree (2, 3).Little is known about the mechanisms by which the lung epithelial progenitors are expanded and patterned into proximal and distal compartments during the early stages of lung morphogenesis. Furthermore, it is still unclear how proximaldistal boundaries are established and maintained when lung epithelial buds form and start to branch. Studies in other foregut derivatives, such as the pancreas and stomach implicate signaling by Notch as a critical regulator of pattern during organ formation (4, 5).The Notch pathway orchestrates a highly evolutionarily conserved mechanism of control of cell fate decisions, which plays a prominent role in establishing asymmetries or differences in signaling between two cells. During development, Notch-mediated mechanisms give rise to cellular diversity while also serving to generate compartments and to establish tissue boundaries (6 -8). Notch signaling results from cell-cell contact via interactions of Notch receptors (in mammalians, Notch1 to -4) with ligands (Delta-like 1, 3, and 4 and Jagged1 and -2) in adjacent cells. Ligand-receptor engagement results in shedding of the Not...