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ObjectiveDeregulation of the Wnt signalling pathway by mutations in the Apc or β-catenin genes underlies colorectal carcinogenesis. As a result, β-catenin stabilises, translocates to the nucleus, and activates gene transcription. Intestinal tumours show a heterogeneous pattern of nuclear β-catenin, with the highest levels observed at the invasion front. Activation of receptor tyrosine kinases in these tumour areas by growth factors expressed by surrounding stromal cells phosphorylate β-catenin at tyrosine residues, which is thought to increase β-catenin nuclear translocation and tumour invasiveness. This study investigates the relevance of β-catenin tyrosine phosphorylation for Wnt signalling and intestinal tumorigenesis in vivo.DesignA conditional knock-in mouse model was generated into which the phospho-mimicking Y654E modification in the endogenous β-catenin gene was introduced.ResultsThis study provided in vivo evidence that β-cateninE654 is characterised by reduced affinity for cadherins, increased signalling and strongly increased phosphorylation at serine 675 by protein kinase A (PKA). In addition, homozygosity for the β-cateninE654 targeted allele caused embryonic lethality, whereas heterozygosity predisposed to intestinal tumour development, and strongly enhanced Apc-driven intestinal tumour initiation associated with increased nuclear accumulation of βcatenin. Surprisingly, the expression of β-cateninE654 did not affect histological grade or induce tumour invasiveness.ConclusionsA thus far unknown mechanism was uncovered in which Y654 phosphorylation of β-catenin facilitates additional phosphorylation at serine 675 by PKA. In addition, in contrast to the current belief that β-catenin Y654 phosphorylation increases tumour progression to a more invasive phenotype, these results show that it rather increases tumour initiation by enhancing Wnt signalling.

Background-New vessel formation contributes to organ development during embryogenesis and tissue repair in response to mechanical damage, inflammation, and ischemia in adult organisms. Early angiogenesis includes formation of an excessive primitive network that needs to be reorganized into a secondary vascular network with higher hierarchical structure. Vascular pruning, the removal of aberrant neovessels by apoptosis, is a vital step in this process. Although multiple molecular pathways for early angiogenesis have been identified, little is known about the genetic regulators of secondary network development. Methods and Results-Using a transcriptomics approach, we identified a new endothelial specific gene named FYVE, RhoGEF, and PH domain-containing 5 (FGD5) that plays a crucial role in vascular pruning. Loss-and gain-of-function studies demonstrate that FGD5 inhibits neovascularization, indicated by in vitro tube-formation, aortic-ring, and coated-bead assays and by in vivo coated-bead plug assays and studies in the murine retina model. FGD5 promotes apoptosis-induced vaso-obliteration via induction of the hey1-p53 pathway by direct binding and activation of cdc42. Indeed, FGD5 correlates with apoptosis in endothelial cells during vascular remodeling and was linked to rising p21 Key Words: angiogenesis-inducing agents Ⅲ apoptosis Ⅲ endothelium Ⅲ FGD5 Ⅲ models, animal V ascularization during development and regeneration plays a vital role in adult disease progression, including tumor growth and metastasis, arthritis, diabetic retinopathy, and cardiovascular disease. Vascular growth in both development and disease consists of a strictly orchestrated, multistep process that requires integrated activation of several molecular pathways. During early vascular growth, a dense primary vascular network without functional arterial and venous distinction is formed in response to low-oxygen conditions. This primitive system, consisting of small capillaries, is relatively unstable, with tip and stalk cell vessel structures expanding and collapsing at a high rate. Transition of this primary network into a stable secondary vasculature with a defined arterial/venous hierarchy of larger vessels that branch into a restricted capillary field requires intensive vascular remodeling, a late angiogenic process that includes neovessel stabilization and pruning of redundant vessel structures. 1,2 Editorial see p 3063 Clinical Perspective on p 3158The molecular regulation by angiogenic factors such as vascular endothelial growth factor (VEGF)-A and fibroblast growth factor that promote growth of the primary vasculature has been studied extensively. In contrast, the key molecular pathways that regulate the reorganization of this early network into the more mature secondary vascular structure are still largely undefined. For the process of vascular pruning, vaso-obliteration by apoptosis induced by hyperoxia has been described, 3 but little is known about the molecular regulation of this important aspect in vascular remodeling that dete...