The role of Wnt/β‐catenin signaling in proliferation and regeneration of the developing basilar papilla and lateral line

Canonical Wnt/β‐catenin signaling has been implicated in multiple developmental events including the regulation of proliferation, cell fate, and differentiation. In the inner ear, Wnt/β‐catenin signaling is required from the earliest stages of otic placode specification through the formation of the mature cochlea. Within the avian inner ear, the basilar papilla (BP), many Wnt pathway components are expressed throughout development. Here, using reporter constructs for Wnt/β‐catenin signaling, we show that this pathway is active throughout the BP (E6‐E14) in both hair cells (HCs) and supporting cells. To characterize the role of Wnt/β‐catenin activity in developing HCs, we performed gain‐ and loss‐of‐function experiments in vitro and in vivo in the chick BP and zebrafish lateral line systems, respectively. Pharmacological inhibition of Wnt signaling in the BP and lateral line neuromasts during the periods of proliferation and HC differentiation resulted in reduced proliferation and decreased HC formation. Conversely, pharmacological activation of this pathway significantly increased the number of HCs in the lateral line and BP. Results demonstrated that this increase was the result of up‐regulated cell proliferation within the Sox2‐positive cells of the prosensory domains. Furthermore, Wnt/β‐catenin activation resulted in enhanced HC regeneration in the zebrafish lateral line following aminoglycoside‐induced HC loss. Combined, our data suggest that Wnt/β‐catenin signaling specifies the number of cells within the prosensory domain and subsequently the number of HCs. This ability to induce proliferation suggests that the modulation of Wnt/β‐catenin signaling could play an important role in therapeutic HC regeneration. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 438–456, 2014     

Phosphorylation of PPP(S/T)P motif of the free LRP6 intracellular domain is not required to activate the Wnt/β‐catenin pathway and attenuate GSK3β activity

The canonical Wnt/β‐catenin signaling pathway plays a critical role in numerous physiological and pathological processes. LRP6 is an essential co‐receptor for Wnt/β‐catenin signaling; as transduction of the Wnt signal is strongly dependent upon GSK3β‐mediated phosphorylation of multiple PPP(S/T)P motifs within the membrane‐anchored LRP6 intracellular domain. Previously, we showed that the free LRP6 intracellular domain (LRP6‐ICD) can activate the Wnt/β‐catenin pathway in a β‐catenin and TCF/LEF‐1 dependent manner, as well as interact with and attenuate GSK3β activity. However, it is unknown if the ability of LRP6‐ICD to attenuate GSK3β activity and modulate activation of the Wnt/β‐catenin pathway requires phosphorylation of the LRP6‐ICD PPP(S/T)P motifs, in a manner similar to the membrane‐anchored LRP6 intracellular domain. Here we provide evidence that the LRP6‐ICD does not have to be phosphorylated at its PPP(S/T)P motif by GSK3β to stabilize endogenous cytosolic β‐catenin resulting in activation of TCF/LEF‐1 and the Wnt/β‐catenin pathway. LRP6‐ICD and a mutant in which all 5 PPP(S/T)P motifs were changed to PPP(A)P motifs equivalently interacted with and attenuated GSK3β activity in vitro, and both constructs inhibited the in situ GSK3β‐mediated phosphorylation of β‐catenin and tau to the same extent. These data indicate that the LRP6‐ICD attenuates GSK3β activity similar to other GSK3β binding proteins, and is not a result of it being a GSK3β substrate. Our findings suggest the functional and regulatory mechanisms governing the free LRP6‐ICD may be distinct from membrane‐anchored LRP6, and that release of the LRP6‐ICD may provide a complimentary signaling cascade capable of modulating Wnt‐dependent gene expression. J. Cell. Biochem. 108: 886–895, 2009. © 2009 Wiley‐Liss, Inc.     

Activation of Wnt/β‐catenin signalling is required for TGF‐β/Smad2/3 signalling during myofibroblast proliferation

Fibrosis in animal models and human diseases is associated with aberrant activation of the Wnt/β‐catenin pathway. Despite extensive research efforts, effective therapies are still not available. Myofibroblasts are major effectors, responsible for extracellular matrix deposition. Inhibiting the proliferation of the myofibroblast is crucial for treatment of fibrosis. Proliferation of myofibroblasts can have many triggering effects that result in fibrosis. In recent years, the Wnt pathway has been studied as an underlying factor as a primary contributor to fibrotic diseases. These efforts notwithstanding, the specific mechanisms by which Wnt‐mediated promotes fibrosis reaction remain obscure. The central role of the transforming growth factor‐β (TGF‐β) and myofibroblast activity in the pathogenesis of fibrosis has become generally accepted. The details of interaction between these two processes are not obvious. The present investigation was conducted to evaluate the level of sustained expression of fibrosis iconic proteins (vimentin, α‐SMA and collagen I) and the TGF‐β signalling pathway that include smad2/3 and its phosphorylated form p‐smad2/3. Detailed analysis of the possible molecular mechanisms mediated by β‐catenin revealed epithelial–mesenchymal transition and additionally demonstrated transitions of fibroblasts to myofibroblast cell forms, along with increased activity of β‐catenin in regulation of the signalling network, which acts to counteract autocrine TGF‐β/smad2/3 signalling. A major outcome of this study is improved insight into the mechanisms by which epithelial and mesenchymal cells activated by TGFβ1‐smad2/3 signalling through Wnt/β‐catenin contribute to lung fibrosis.     

Wnt/β‐catenin signaling in the mouse embryonic cranial mesenchyme is required to sustain the emerging differentiated meningeal layers

Cranial neural crest cells (CNCCs) give rise to cranial mesenchyme (CM) that differentiates into the forebrain meningeal progenitors in the basolateral and apical regions of the head. This occurs in close proximity to the other CNCC‐CM‐derivatives, such as calvarial bone and dermal progenitors. We found active Wnt signaling transduction in the forebrain meningeal progenitors in basolateral and apical populations and in the non‐meningeal CM preceding meningeal differentiation. Here, we dissect the source of Wnt ligand secretion and requirement of Wnt/β‐catenin signaling for the lineage selection and early differentiation of the forebrain meninges. We find persistent canonical Wnt/β‐catenin signal transduction in the meningeal progenitors in the absence of Wnt ligand secretion in the CM or surface ectoderm, suggesting additional sources of Wnts. Conditional mutants for Wntless and β‐catenin in the CM showed that Wnt ligand secretion and Wnt/β‐catenin signaling were dispensable for specification and proliferation of early meningeal progenitors. In the absence of β‐catenin in the CM, we found diminished laminin matrix and meningeal hypoplasia, indicating a structural and trophic role of mesenchymal β‐catenin signaling. This study shows that β‐catenin signaling is required in the CM for maintenance and organization of the differentiated meningeal layers in the basolateral and apical populations of embryonic meninges.     

The Tumor Suppressor SCRIB is a Negative Modulator of the Wnt/β‐Catenin Signaling Pathway

SCRIB is a scaffold protein containing leucine‐rich repeats (LRR) and PSD‐95/Dlg‐A/ZO‐1 domains (PDZ) that localizes at the basolateral membranes of polarized epithelial cells. Deregulation of its expression or localization leads to epithelial defects and tumorigenesis in part as a consequence of its repressive role on several signaling pathways including AKT, ERK, and HIPPO. In the present work, a proteomic approach is used to characterize the protein complexes associated to SCRIB and its paralogue LANO. Common and specific sets of proteins associated to SCRIB and LANO by MS are identified and an extensive landscape of their associated networks and the first comparative analysis of their respective interactomes are provided. Under proteasome inhibition, it is further found that SCRIB is associated to the β‐catenin destruction complex that is central in Wnt/β‐catenin signaling, a conserved pathway regulating embryonic development and cancer progression. It is shown that the SCRIB/β‐catenin interaction is potentiated upon Wnt3a stimulation and that SCRIB plays a repressing role on Wnt signaling. The data thus provide evidence for the importance of SCRIB in the regulation of the Wnt/β‐catenin pathway.     

MicroRNA‐300 promotes apoptosis and inhibits proliferation,migration, invasion and epithelial‐mesenchymal transition via the Wnt/β‐catenin signaling pathway by targeting CUL4B in pancreatic cancer cells

The study aims to verify the hypothesis that up‐regulation of microRNA‐300 (miR‐300) targeting CUL4B promotes apoptosis and suppresses proliferation, migration, invasion, and epithelial‐mesenchymal transition (EMT) of pancreatic cancer cells by regulating the Wnt/β‐catenin signaling pathway. Pancreatic cancer tissues and adjacent tissues were collected from 110 pancreatic cancer patients. Expression of miR‐300, CUL4B, Wnt, β‐catenin, E‐cadherin, N‐cadherin, Snail, GSK‐3β, and CyclinD1 were detected using qRT‐PCR and Western blot. CFPAC‐1, Capan‐1, and PANC‐1 were classified into blank, negative control (NC), miR‐300 mimics, miR‐300 inhibitors, siRNA‐CUL4B, and miR‐300 inhibitors + siRNA‐CUL4B groups. The proliferation, migration, invasion abilities, the cell cycle distribution, and apoptosis rates were measured in CCK‐8 and Transwell assays. Pancreatic cancer tissues showed increased CUL4B expression but decreased miR‐300 expression. When miR‐300 was lowly expressed, CUL4B was upregulated which in‐turn activated the Wnt/β‐catenin pathway to protect the β‐catenin expression and thus induce EMT. When miR‐300 was highly expressed, CUL4B was downregulated which in‐turn inhibited the Wnt/β‐catenin pathway to prevent EMT. Weakened cell migration and invasion abilities and enhanced apoptosis were observed in the CUL4B group. The miR‐300 inhibitors group exhibited an evident increase in growth rate accompanied the largest tumor volume. Smaller tumor volume and slower growth rate were observed in the miR‐300 mimics and siRNA‐CUL4B group. Our study concludes that lowly expressed miR‐300 may contribute to highly expressed CUL4B activating the Wnt/β‐catenin signaling pathway and further stimulating EMT, thus promoting proliferation and migration but suppressing apoptosis of pancreatic cancer cells.     

miR‐193b represses influenza A virus infection by inhibiting Wnt/β‐catenin signalling

Due to an increasing emergence of new and drug‐resistant strains of the influenza A virus (IAV), developing novel measures to combat influenza is necessary. We have previously shown that inhibiting Wnt/β‐catenin pathway reduces IAV infection. In this study, we aimed to identify antiviral human microRNAs (miRNAs) that target the Wnt/β‐catenin signalling pathway. Using a miRNA expression library, we identified 85 miRNAs that up‐regulated and 20 miRNAs that down‐regulated the Wnt/β‐catenin signalling pathway. Fifteen miRNAs were validated to up‐regulate and five miRNAs to down‐regulate the pathway. Overexpression of four selected miRNAs (miR‐193b, miR‐548f‐1, miR‐1‐1, and miR‐509‐1) that down‐regulated the Wnt/β‐catenin signalling pathway reduced viral mRNA, protein levels in A/PR/8/34‐infected HEK293 cells, and progeny virus production. Overexpression of miR‐193b in lung epithelial A549 cells also resulted in decreases of A/PR/8/34 infection. Furthermore, miR‐193b inhibited the replication of various strains, including H1N1 (A/PR/8/34, A/WSN/33, A/Oklahoma/3052/09) and H3N2 (A/Oklahoma/309/2006), as determined by a viral reporter luciferase assay. Further studies revealed that β‐catenin was a target of miR‐193b, and β‐catenin rescued miR‐193b‐mediated suppression of IAV infection. miR‐193b induced G0/G1 cell cycle arrest and delayed vRNP nuclear import. Finally, adenovirus‐mediated gene transfer of miR‐193b to the lung reduced viral load in mice challenged by a sublethal dose of A/PR/8/34. Collectively, our findings suggest that miR‐193b represses IAV infection by inhibiting Wnt/β‐catenin signalling.     

Proteomic analysis of β‐catenin activation in mouse liver by DIGE analysis identifies glucose metabolism as a new target of the Wnt pathway

The Wnt/β‐catenin signaling pathway has been increasingly implicated in liver development and physiology. Aberrant activation of this pathway is one of the major genetic events observed during the process of human HCC development. To gain insight into the mechanism underlying β‐catenin action in the liver, we conducted a quantitative differential proteomic analysis using 2‐D DIGE combined with MS, in mice with liver‐specific deletion of Apc resulting in acute activation of β‐catenin signaling (Apc^KOliv mice). We identified 94 protein spots showing differential expression between mutant Apc^KOliv and control mice, corresponding to 56 individual proteins. Most of the proteins identified were associated with metabolic pathways, such as ammonia and glucose metabolism. Our analysis showed an increase in lactate dehydrogenase activity together with a downregulation of two mitochondrial ATPase subunits (ATP5a1 and ATP5b). These observations indicate that β‐catenin signaling may induce a shift in the glucose metabolism from oxidative phosphorylation to glycolysis, known as the “Warburg effect”. Imaging with ¹⁸F‐fluoro‐2‐deoxy‐D ‐glucose‐positron emission tomography suggests that the specific metabolic reprogramming induced by β‐catenin in the liver does not imply the first step of glycolysis. This observation may explain why some HCCs are difficult to assess by fluoro‐2‐deoxy‐D ‐glucose‐positron emission tomography imaging.     

MiR‐30‐5p suppresses cell chemoresistance and stemness in colorectal cancer through USP22/Wnt/β‐catenin signaling axis

Colorectal cancer (CRC) remains both common and fatal, and its successful treatment is greatly limited by the development of stem cell‐like characteristics (stemness) and chemoresistance. MiR‐30‐5p has been shown to function as a tumor suppressor by targeting the Wnt/β‐catenin signaling pathway, but its activity in CRC has never been assessed. We hypothesized that miR‐30‐5p exerts anti‐oncogenic effects in CRC by regulating the USP22/Wnt/β‐catenin signaling axis. In the present study, we demonstrate that tissues from CRC patients and human CRC cell lines show significantly decreased miR‐30‐5p family expression. After identifying the 3’UTR of USP22 as a potential binding site of miR‐30‐5p, we constructed a luciferase reporter containing the potential miR‐30‐5p binding site and measured the effects on USP22 expression. Western blot assays showed that miR‐30‐5p decreased USP22 protein expression in HEK293 and Caco2 CRC cells. To evaluate the effects of miR‐30‐5p on CRC cell stemness, we isolated CD133 + CRC cells (Caco2 and HCT15). We then determined that, while miR‐30‐5p is normally decreased in CD133 + CRC cells, miR‐30‐5p overexpression significantly reduces expression of stem cell markers CD133 and Sox2, sphere formation, and cell proliferation. Similarly, we found that miR‐30‐5p expression is normally reduced in 5‐fluorouracil (5‐FU) resistant CRC cells, whereas miR‐30‐5p overexpression in 5‐FU resistant cells reduces sphere formation and cell viability. Inhibition of miR‐30‐5p reversed the process. Finally, we determined that miR‐30‐5p attenuates the expression of Wnt/β‐catenin signaling target genes (Axin2 and MYC), Wnt luciferase activity, and β‐catenin protein levels in CRC stem cells.     

Essential role of Dkk3 for head formation by inhibiting Wnt/β‐catenin and Nodal/Vg1 signaling pathways in the basal chordate amphioxus

To dissect the molecular mechanism of head specification in the basal chordate amphioxus, we investigated the function of Dkk3, a secreted protein in the Dickkopf family, which is expressed anteriorly in early embryos. Amphioxus Dkk3 has three domains characteristic of Dkk3 proteins—an N‐terminal serine rich domain and two C‐terminal cysteine‐rich domains (CRDs). In addition, amphioxus Dkk3 has a TGFβ‐receptor 2 domain, which is not present in Dkk3 proteins of other species. As vertebrate Dkk3 proteins have been reported to regulate either Nodal signaling or Wnt/β‐catenin signaling but not both in the same species, we tested the effects of Dkk3 on signaling by these two pathways in amphioxus embryos. Loss of function experiments with an anti‐sense morpholino oligonucleotide (MO) against amphioxus Dkk3 resulted in larvae with truncated heads and concomitant loss of expression of anterior gene markers. The resemblance of the headless phenotype to that from upregulation of Wnt/β‐catenin signaling with BIO, a GSK3β inhibitor, suggested that Dkk3 might inhibit Wnt/β‐catenin signaling. In addition, the Dkk3 MO rescued dorsal structures in amphioxus embryos treated with SB505124, an inhibitor of Nodal signaling, indicating that amphioxus Dkk3 can also inhibit Nodal signaling. In vitro assays in Xenopus animal caps showed that Nodal inhibition is largely due to domains other than the TGFβ domain. We conclude that amphioxus Dkk3 regulates head formation by modulating both Wnt/β‐catenin and Nodal signaling, and that these functions may have been partitioned among various vertebrate lineages during evolution of Dkk3 proteins.     

Wnt/β‐catenin‐signaling and the formation of Müller glia‐derived progenitors in the chick retina

Müller glia can be stimulated to de‐differentiate, proliferate, and form Müller glia‐derived progenitor cells (MGPCs) that are capable of producing retinal neurons. The signaling pathways that influence the de‐differentiation of mature Müller glia and proliferation of MGPCs may include the Wnt‐pathway. The purpose of this study was to investigate how Wnt‐signaling influences the formation of MGPCs in the chick retina in vivo. In NMDA‐damaged retinas where MGPCs are known to form, we find dynamic changes in retinal levels of potential readouts of Wnt‐signaling, including dkk1, dkk3, axin2, c‐myc, tcf‐1, and cd44. We find accumulations of nuclear β‐catenin in MGPCs that peaks at 3 days and rapidly declines by 5 days after NMDA‐treatment. Inhibition of Wnt‐signaling with XAV939 in damaged retinas suppressed the formation of MGPCs, increased expression of ascl1a and decreased hes5, but had no effect upon the differentiation of progeny produced by MGPCs. Activation of Wnt‐signaling, with GSK3β‐inhibitors, in the absence of retinal damage, failed to stimulate the formation of MGPCs, whereas activation of Wnt‐signaling in damaged retinas stimulated the formation of MGPCs. In the absence of retinal damage, FGF2/MAPK‐signaling stimulated the formation of MGPCs by activating a signaling network that includes Wnt/β‐catenin. In FGF2‐treated retinas, inhibition of Wnt‐signaling reduced numbers of proliferating MGPCs, whereas activation of Wnt‐signaling failed to influence the formation of proliferating MGPCs. Our findings indicate that Wnt‐signaling is part of a network initiated by FGF2/MAPK or retinal damage, and activation of canonical Wnt‐signaling is required for the formation of proliferating MGPCs. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 983–1002, 2016     

Trolox‐induced cardiac differentiation is mediated by the inhibition of Wnt/β‐catenin signaling in human embryonic stem cells

Cardiac differentiation of human pluripotent stem cells may be induced under chemically defined conditions, wherein the regulation of Wnt/β‐catenin pathway is often desirable. Here, we examined the effect of trolox, a vitamin E analog, on the cardiac differentiation of human embryonic stem cells (hESCs). 6‐Hydroxy‐2,5,7,8‐tetramethylchromane‐2‐carboxylic acid (Trolox) significantly enhanced cardiac differentiation in a time‐ and dose‐dependent manner after the mesodermal differentiation of hESCs. Trolox promoted hESC cardiac differentiation through its inhibitory activity against the Wnt/β‐catenin pathway. This study demonstrates an efficient cardiac differentiation method and reveals a novel Wnt/β‐catenin regulator.     

USP44 suppresses proliferation and enhances apoptosis in colorectal cancer cells by inactivating the Wnt/β‐catenin pathway via Axin1 deubiquitination

Colorectal cancer (CRC) is the leading cause of cancer death, and its 5‐year survival rate remains unsatisfactory. Recent studies have revealed that ubiquitin‐specific protease 44 (USP44) is a cancer suppressor or oncogene depending on the type of neoplasm. However, its role in CRC remains unclear. Here, we found that the USP44 expression level was markedly decreased in CRC, and USP44 overexpression inhibited proliferation while enhancing apoptosis in CRC cells, suggesting that USP44 is a cancer suppressor in CRC. We then investigated if USP44 functioned through regulating the Wnt/β‐catenin pathway. We found that USP44 overexpression increased the Axin1 protein while decreasing β‐catenin, c‐myc, and cyclin D1 proteins, suggesting that USP44 inhibited the activation of the Wnt/β‐catenin pathway. Moreover, we found that two Wnt/β‐catenin activators, LiCl and SKL2001, both attenuated oeUSP44‐mediated proliferation and apoptosis in CRC cells. Collectively, these data points indicated that USP44 inhibited proliferation while promoting apoptosis in CRC cells by inhibiting the Wnt/β‐catenin pathway. Interestingly, we observed that USP44 overexpression did not affect the Axin1 mRNA level. Further study uncovered that USP44 interacted with Axin1 and reduced the ubiquitination of Axin1. Furthermore, Axin1 knock‐down abolished the effects of oeUSP44 on proliferation, apoptosis, and Wnt/β‐catenin activity in CRC cells. Taken together, this study demonstrates that USP44 inhibits proliferation while enhancing apoptosis in CRC cells by inactivating the Wnt/β‐catenin pathway via Axin1 deubiquitination. USP44 is a cancer suppressor in CRC and a potential target for CRC therapy.