Heterogeneous murine peribiliary glands orchestrate compartmentalized epithelial renewal

The extrahepatic branches of the biliary tree have glands that connect to the surface epithelium through narrow pits. The duct epithelia undergo homeostatic renewal, yet the identity and multiplicity of cells that maintain this tissue is unknown. Using marker-free and targeted clonal fate mapping in mice, we provide evidence that the extrahepatic bile duct is compartmentalized. Pit cholangiocytes of extramural glands renewed the surface epithelium, whereas basally oriented cholangiocytes maintained the gland itself. In contrast, basally positioned cholangiocytes replenished the surface epithelium in mural glands. Single-cell sequencing identified genes enriched in the base and surface epithelial populations, with trajectory analysis showing graded gene expression between these compartments. Epithelia were plastic, changing cellular identity upon fasting and refeeding. Gain of canonical Wnt signaling caused basal cell expansion, gastric chief cell marker expression, and a decrease in surface epithelial markers. Our results identify the cellular hierarchy governing extrahepatic biliary epithelial renewal.

Wnt/β-Catenin-Signaling Modulates Megakaryopoiesis at the Megakaryocyte-Erythrocyte Progenitor Stage in the Hematopoietic System

The bone marrow (BM) hematopoietic system (HS) gives rise to blood cells originating from hematopoietic stem cells (HSCs), including megakaryocytes (MKs) and red blood cells (erythrocytes; RBCs). Many steps of the cell-fate decision remain to be elucidated, being important for cancer treatment. To explore the role of Wnt/β-catenin for MK and RBC differentiation, we activated β-catenin signaling in platelet-derived growth factor b (Pdgfb)-expressing cells of the HS using a Cre-lox approach (Ctnnb1BM-GOF). FACS analysis revealed that Pdgfb is mainly expressed by megakaryocytic progenitors (MKPs), MKs and platelets. Recombination resulted in a lethal phenotype in mutants (Ctnnb1BM-GOFwt/fl, Ctnnb1BM-GOFfl/fl) 3 weeks after tamoxifen injection, showing an increase in MKs in the BM and spleen, but no pronounced anemia despite reduced erythrocyte counts. BM transplantation (BMT) of Ctnnb1BM-GOF BM into lethally irradiated wildtype recipients (BMT-Ctnnb1BM-GOF) confirmed the megakaryocytic, but not the lethal phenotype. CFU-MK assays in vitro with BM cells of Ctnnb1BM-GOF mice supported MK skewing at the expense of erythroid colonies. Molecularly, the runt-related transcription factor 1 (RUNX1) mRNA, known to suppress erythropoiesis, was upregulated in Ctnnb1BM-GOF BM cells. In conclusion, β-catenin activation plays a key role in cell-fate decision favoring MK development at the expense of erythroid production.

β-Catenin signaling in alveolar macrophages enhances lung metastasis through a TNF-dependent mechanism

The main cause of malignancy-related mortality is metastasis. Although metastatic progression is driven by diverse tumor-intrinsic mechanisms, there is a growing appreciation for the contribution of tumor-extrinsic elements of the tumor microenvironment, especially macrophages, which correlate with poor clinical outcomes. Macrophages consist of bone marrow-derived and tissue-resident populations. In contrast to bone marrow-derived macrophages, the transcriptional pathways that govern the pro-metastatic activities of tissue-resident macrophages (TRMs) remain less clear. Alveolar macrophages (AMs) are a TRM population with critical roles in tissue homeostasis and metastasis. Wnt/β-catenin signaling is a hallmark of cancer and has been identified as a pathologic regulator of AMs in infection. We tested the hypothesis that β-catenin expression in AMs enhances metastasis in solid tumor models. Using a genetic β-catenin gain-of-function approach, we demonstrated that (a) enhanced β-catenin in AMs heightened lung metastasis; (b) β-catenin activity in AMs drove a dysregulated inflammatory program strongly associated with Tnf expression; and (c) localized TNF-α blockade abrogated this metastatic outcome. Last, β-catenin gene CTNNB1 and TNF expression levels were positively correlated in AMs of patients with lung cancer. Overall, our findings revealed a Wnt/β-catenin/TNF-α pro-metastatic axis in AMs with potential therapeutic implications against tumors refractory to the antineoplastic actions of TNF-α.

A novel decellularized matrix of Wnt signaling-activated osteocytes accelerates the repair of critical-sized parietal bone defects with osteoclastogenesis, angiogenesis, and neurogenesis

Cell source is the key to decellularized matrix (DM) strategy. This study compared 3 cell types, osteocytes with/without dominant active Wnt/β-catenin signaling (daCO and WTO) and bone marrow stromal cells (BMSCs) for their DMs in bone repair. Decellularization removes all organelles and >95% DNA, and retained >74% collagen and >71% GAG, maintains the integrity of cell basement membrane with dense boundaries showing oval and honeycomb structure in osteocytic DM and smooth but irregular shape in the BMSC-DM. DM produced higher cell survival rate (90%) and higher proliferative activity. In vitro, daCO-DM induces more and longer stress fibers in BMSCs, conducive to cell adhesion, spreading, and osteogenic differentiation. 8-wk after implantation of the critical-sized parietal bone defect model, daCO-DM formed tight structures, composed of a large number of densely-arranged type-I collagen under polarized light microscope, which is similar to and integrated with host bone. BV/TV (>54%) was 1.5, 2.9, and 3.5 times of WTO-DM, BMSC-DM, and none-DM groups, and N.Ob/T.Ar (3.2 × 10²/mm²) was 1.7, 2.9, and 3.3 times. At 4-wk, daCO-DM induced osteoclastogenesis, 2.3 times higher than WTO-DM; but BMSC-DM or none-DM didn't. daCO-DM increased the expression of RANKL and MCSF, Vegfa and Angpt1, and Ngf in BMSCs, which contributes to osteoclastogenesis, angiogenesis, and neurogenesis, respectively. daCO-DM promoted H-type vessel formation and nerve markers β3-tubulin and NeuN expression. Conclusion: daCO-DM produces metabolic and neurovascularized organoid bone to accelerate the repair of bone defects. These features are expected to achieve the effect of autologous bone transplantation, suitable for transformation application.

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Decellularized matrix of osteocytes with dominant-active β-catenin (daCO-DM) promotes osteogenesis for regenerative repair.

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daCO-DM induces BMSCs to form stress fibers, conducive to cell adhesion, spreading, and differentiation towards osteoblasts.

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daCO-DM-induced osteoblasts have strong activity secreting dense and orderly-arranged type I collagen as host bone’s.

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daCO-DM induces BMSCs to express pre-osteoclastogenic cytokine RANKL and MCSF for osteoclastogenesis of marrow monocytes.

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daCO-DM enhances BMSCs to express angiogenic Vegfa and Angpt1, and neurogenic Ngf potentially for neurovascularization.

Primary cilia control translation and the cell cycle in medulloblastoma

The primary cilium, a signaling organelle projecting from the surface of a cell, controls cellular physiology and behavior. The presence or absence of primary cilia is a distinctive feature of a given tumor type; however, whether and how the primary cilium contributes to tumorigenesis are unknown for most tumors. Medulloblastoma (MB) is a common pediatric brain cancer comprising four groups: SHH, WNT, group 3 (G3), and group 4 (G4). From 111 cases of MB, we show that primary cilia are abundant in SHH and WNT MBs but rare in G3 and G4 MBs. Using WNT and G3 MB mouse models, we show that primary cilia promote WNT MB by facilitating translation of mRNA encoding β-catenin, a major oncoprotein driving WNT MB, whereas cilium loss promotes G3 MB by disrupting cell cycle control and destabilizing the genome. Our findings reveal tumor type-specific ciliary functions and underlying molecular mechanisms. Moreover, we expand the function of primary cilia to translation control and reveal a molecular mechanism by which cilia regulate cell cycle progression, thereby providing new frameworks for studying cilium function in normal and pathologic conditions.

Spatiotemporal reprogramming of differentiated cells underlies regeneration and neoplasia in the intestinal epithelium

Although the mammalian intestinal epithelium manifests robust regenerative capacity after various cytotoxic injuries, the underlying mechanism has remained unclear. Here we identify the cyclin-dependent kinase inhibitor p57 as a specific marker for a quiescent cell population located around the +4 position of intestinal crypts. Lineage tracing reveals that the p57⁺ cells serve as enteroendocrine/tuft cell precursors under normal conditions but dedifferentiate and act as facultative stem cells to support regeneration after injury. Single-cell transcriptomics analysis shows that the p57⁺ cells undergo a dynamic reprogramming process after injury that is characterized by fetal-like conversion and metaplasia-like transformation. Population-level analysis also detects such spatiotemporal reprogramming widely in other differentiated cell types. In intestinal adenoma, p57⁺ cells manifest homeostatic stem cell activity, in the context of constitutively activated spatiotemporal reprogramming. Our results highlight a pronounced plasticity of the intestinal epithelium that supports maintenance of tissue integrity in normal and neoplastic contexts.

Rapid turnover and regeneration of intestinal epithelium requires distinct intestinal stem cell (ISC) populations. Here the authors show p57 marks quiescent ISCs, and that differentiated cells revert to stem cell state after injury, through dynamic reprogramming characterized by fetal- and metaplastic-like changes.

Fine-tuning of β-catenin in mouse thymic epithelial cells is required for postnatal T-cell development

In the thymus, the thymic epithelium provides a microenvironment essential for the development of functionally competent and self-tolerant T cells. Previous findings showed that modulation of Wnt/β-catenin signaling in mouse thymic epithelial cells (TECs) disrupts embryonic thymus organogenesis. However, the role of β-catenin in TECs for postnatal T-cell development remains to be elucidated. Here, we analyzed gain-of-function (GOF) and loss-of-function (LOF) of β-catenin highly specific in mouse TECs. We found that GOF of β-catenin in TECs results in severe thymic dysplasia and T-cell deficiency beginning from the embryonic period. By contrast, LOF of β-catenin in TECs reduces the number of cortical TECs and thymocytes modestly and only postnatally. These results indicate that fine-tuning of β-catenin expression within a permissive range is required for TECs to generate an optimal microenvironment to support postnatal T-cell development.

Bone-derived sclerostin and Wnt/β-catenin signaling regulate PDGFRα+ adipoprogenitor cell differentiation

The Wnt signaling antagonist, sclerostin, is a potent suppressor of bone acquisition that also mediates endocrine communication between bone and adipose. As a result, Sost^-/- mice exhibit dramatic increases in bone formation but marked decreases in visceral and subcutaneous adipose that are secondary to alterations in lipid synthesis and utilization. While interrogating the mechanism by which sclerostin influences adipocyte metabolism, we observed paradoxical increases in the adipogenic potential and numbers of CD45^- :Sca1⁺ :PDGFRα⁺ adipoprogenitors in the stromal vascular compartment of fat pads isolated from male Sost^-/- mice. Lineage tracing studies indicated that sclerostin deficiency blocks the differentiation of PDGFRα⁺ adipoprogenitors to mature adipocytes in association with increased Wnt/β-catenin signaling. Importantly, osteoblast/osteocyte-specific Sost gene deletion mirrors the accumulation of PDGFRα⁺ adipoprogenitors, reduction in fat mass, and improved glucose metabolism evident in Sost^-/- mice. These data indicate that bone-derived sclerostin regulates multiple facets of adipocyte physiology ranging from progenitor cell commitment to anabolic metabolism.

β-Catenin and FGFR2 regulate postnatal rosette-based adrenocortical morphogenesis

Rosettes are widely used in epithelial morphogenesis during embryonic development and organogenesis. However, their role in postnatal development and adult tissue maintenance remains largely unknown. Here, we show zona glomerulosa cells in the adult adrenal cortex organize into rosettes through adherens junction-mediated constriction, and that rosette formation underlies the maturation of adrenal glomerular structure postnatally. Using genetic mouse models, we show loss of β-catenin results in disrupted adherens junctions, reduced rosette number, and dysmorphic glomeruli, whereas β-catenin stabilization leads to increased adherens junction abundance, more rosettes, and glomerular expansion. Furthermore, we uncover numerous known regulators of epithelial morphogenesis enriched in β-catenin-stabilized adrenals. Among these genes, we show Fgfr2 is required for adrenal rosette formation by regulating adherens junction abundance and aggregation. Together, our data provide an example of rosette-mediated postnatal tissue morphogenesis and a framework for studying the role of rosettes in adult zona glomerulosa tissue maintenance and function.

Spatially Restricted Stromal Wnt Signaling Restrains Prostate Epithelial Progenitor Growth through Direct and Indirect Mechanisms

Cell-autonomous Wnt signaling has well-characterized functions in controlling stem cell activity, including in the prostate. While niche cells secrete Wnt ligands, the effects of Wnt signaling in niche cells per se are less understood. Here, we show that stromal cells in the proximal prostatic duct near the urethra, a mouse prostate stem cell niche, not only produce multiple Wnt ligands but also exhibit strong Wnt/β-catenin activity. The non-canonical Wnt ligand Wnt5a, secreted by proximal stromal cells, directly inhibits proliefration of prostate epithelial stem or progenitor cells whereas stromal cell-autonomous canonical Wnt/β-catenin signaling indirectly suppresses prostate stem or progenitor activity via the transforming growth factor β (TGFβ) pathway. Collectively, these pathways restrain the proliferative potential of epithelial cells in the proximal prostatic ducts. Human prostate likewise exhibits spatially restricted distribution of stromal Wnt/β-catenin activity, suggesting a conserved mechanism for tissue patterning. Thus, this study shows how distinct stromal signaling mechanisms within the prostate cooperate to regulate tissue homeostasis.

Targeting β-Catenin in GLAST-Expressing Cells: Impact on Anxiety and Depression-Related Behavior and Hippocampal Proliferation

β-catenin (key mediator in the Wnt signaling pathway) contributes to the pathophysiology of mood disorders, associated to neurogenesis and neuroplasticity. Decreased β-catenin protein levels have been observed in the hippocampus and prefrontal cortex of depressed subjects. Additionally, the antidepressants exert, at least in part, their neurogenic effects by increasing β-catenin levels in the subgranular zone of the hippocampus. To further understand the role of β-catenin in depression and anxiety, we generated two conditional transgenic mice in which β-catenin was either inactivated or stabilized in cells expressing CreERT under the control of the astrocyte-specific glutamate transporter (GLAST) promoter inducible by tamoxifen, which presents high expression levels on the subgranular zone of the hippocampus. Here, we show that β-catenin inactivation in GLAST-expressing cells enhanced anxious/depressive-like responses. These behavioral changes were associated with impaired hippocampal proliferation and markers of immature neurons as doublecortin. On the other hand, β-catenin stabilization induced an anxiolytic-like effect in the novelty suppressed feeding test and tended to ameliorate depressive-related behaviors. In these mice, the control over the Wnt/β-catenin pathway seems to be tighter as evidenced by the lack of changes in some proliferation markers. Moreover, animals with stabilized β-catenin showed resilience to some anxious/depressive manifestations when subjected to the corticosterone model of depression. Our findings demonstrate that β-catenin present in GLAST-expressing cells plays a critical role in the development of anxious/depressive-like behaviors and resilience, which parallels its regulatory function on hippocampal proliferation. Further studies need to be done to clarify the importance of these changes in other brain areas also implicated in the neurobiology of anxiety and depressive disorders.

Hepatocyte specific expression of an oncogenic variant of β-catenin results in cholestatic liver disease

BACKGROUND

The Wnt/β-catenin signaling pathway plays a crucial role in embryonic development, tissue homeostasis, wound healing and malignant transformation in different organs including the liver. The consequences of continuous β-catenin signaling in hepatocytes remain elusive.

RESULTS

Livers of Ctnnb1CA hep mice were characterized by disturbed liver architecture, proliferating cholangiocytes and biliary type of fibrosis. Serum ALT and bile acid levels were significantly increased in Ctnnb1CA hep mice. The primary bile acid synthesis enzyme Cyp7a1 was increased whereas Cyp27 and Cyp8b1 were reduced in Ctnnb1CA hep mice. Expression of compensatory bile acid transporters including Abcb1, Abcb4, Abcc2 and Abcc4 were significantly increased in Ctnnb1CA hep mice while Ntcp was reduced. Accompanying changes of bile acid transporters favoring excretion of bile acids were observed in intestine and kidneys of Ctnnb1CA hep mice. Additionally, disturbed bile acid regulation through the FXR-FGF15-FGFR4 pathway was observed in mice with activated β-catenin.

MATERIALS AND METHODS

Mice with a loxP-flanked exon 3 of the Ctnnb1 gene were crossed to Albumin-Cre mice to obtain mice with hepatocyte-specific expression of a dominant stable form of β-catenin (Ctnnb1CA hep mice). Ctnnb1CA hep mice were analyzed by histology, serum biochemistry and mRNA profiling.

CONCLUSIONS

Expression of a dominant stable form of β-catenin in hepatocytes results in severe cholestasis and biliary type fibrosis.

Hepatocyte specific expression of an oncogenic variant of β-catenin results in lethal metabolic dysfunction in mice

Background

Wnt/β-catenin signaling plays a crucial role in embryogenesis, tissue homeostasis, metabolism and malignant transformation of different organs including the liver. Continuous β-catenin signaling due to somatic mutations in exon 3 of the Ctnnb1 gene is associated with different liver diseases including cancer and cholestasis.

Results

Expression of a degradation resistant form of β-catenin in hepatocytes resulted in 100% mortality within 31 days after birth. Ctnnb1^CAhep mice were characterized by reduced body weight, significantly enlarged livers with hepatocellular fat accumulation around central veins and increased hepatic triglyceride content. Proteomics analysis using whole liver tissue revealed significant deregulation of proteins involved in fat, glucose and mitochondrial energy metabolism, which was also reflected in morphological anomalies of hepatocellular mitochondria. Key enzymes involved in transport and synthesis of fatty acids and cholesterol were significantly deregulated in livers of Ctnnb1^CAhep mice. Furthermore, carbohydrate metabolism was substantially disturbed in mutant mice.

Conclusion

Continuous β-catenin signaling in hepatocytes results in premature death due to severe disturbances of liver associated metabolic pathways and mitochondrial dysfunction.

Methods

To investigate the influence of permanent β-catenin signaling on liver biology we analyzed mice with hepatocyte specific expression of a dominant stable form of β-catenin (Ctnnb1^CAhep) and their WT littermates by serum biochemistry, histology, electron microscopy, mRNA profiling and proteomic analysis of the liver.

Wnt inhibition promotes vascular specification of embryonic cardiac progenitors

Several studies have demonstrated a multiphasic role for Wnt signaling during embryonic cardiogenesis and developed protocols that enrich for cardiac derivatives during in vitro differentiation of human pluripotent stem cells (hPSCs). However, few studies have investigated the role of Wnt signaling in the specification of cardiac progenitor cells (CPCs) toward downstream fates. Using transgenic mice and hPSCs, we tracked endothelial cells (ECs) that originated from CPCs expressing NKX2.5. Analysis of EC-fated CPCs at discrete phenotypic milestones during hPSC differentiation identified reduced Wnt activity as a hallmark of EC specification, and the enforced activation or inhibition of Wnt reduced or increased, respectively, the degree of vascular commitment within the CPC population during both hPSC differentiation and mouse embryogenesis. Wnt5a, which has been shown to exert an inhibitory influence on Wnt signaling during cardiac development, was dynamically expressed during vascular commitment of hPSC-derived CPCs, and ectopic Wnt5a promoted vascular specification of hPSC-derived and mouse embryonic CPCs.

mTORC1-Mediated Inhibition of 4EBP1 Is Essential for Hedgehog Signaling-Driven Translation and Medulloblastoma

Mechanistic target of rapamycin (MTOR) cooperates with Hedgehog (HH) signaling, but the underlying mechanisms are incompletely understood. Here we provide genetic, biochemical, and pharmacologic evidence that MTOR complex 1 (mTORC1)-dependent translation is a prerequisite for HH signaling. The genetic loss of mTORC1 function inhibited HH signaling-driven growth of the cerebellum and medulloblastoma. Inhibiting translation or mTORC1 blocked HH signaling. Depleting 4EBP1, an mTORC1 target that inhibits translation, alleviated the dependence of HH signaling on mTORC1. Consistent with this, phosphorylated 4EBP1 levels were elevated in HH signaling-driven medulloblastomas in mice and humans. In mice, an mTORC1 inhibitor suppressed medulloblastoma driven by a mutant SMO that is inherently resistant to existing SMO inhibitors, prolonging the survival of the mice. Our study reveals that mTORC1-mediated translation is a key component of HH signaling and an important target for treating medulloblastoma and other cancers driven by HH signaling.

Gut Microbiota Promotes Obesity-Associated Liver Cancer through PGE2-Mediated Suppression of Antitumor Immunity

Obesity increases the risk of cancers, including hepatocellular carcinomas (HCC). However, the precise molecular mechanisms through which obesity promotes HCC development are still unclear. Recent studies have shown that gut microbiota may influence liver diseases by transferring its metabolites and components. Here, we show that the hepatic translocation of obesity-induced lipoteichoic acid (LTA), a Gram-positive gut microbial component, promotes HCC development by creating a tumor-promoting microenvironment. LTA enhances the senescence-associated secretory phenotype (SASP) of hepatic stellate cells (HSC) collaboratively with an obesity-induced gut microbial metabolite, deoxycholic acid, to upregulate the expression of SASP factors and COX2 through Toll-like receptor 2. Interestingly, COX2-mediated prostaglandin E₂ (PGE₂) production suppresses the antitumor immunity through a PTGER4 receptor, thereby contributing to HCC progression. Moreover, COX2 overexpression and excess PGE₂ production were detected in HSCs in human HCCs with noncirrhotic, nonalcoholic steatohepatitis (NASH), indicating that a similar mechanism could function in humans.Significance: We showed the importance of the gut-liver axis in obesity-associated HCC. The gut microbiota-driven COX2 pathway produced the lipid mediator PGE₂ in senescent HSCs in the tumor microenvironment, which plays a pivotal role in suppressing antitumor immunity, suggesting that PGE₂ and its receptor may be novel therapeutic targets for noncirrhotic NASH-associated HCC. Cancer Discov; 7(5); 522-38. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 443.

Loss of SMAD4 Promotes Lung Metastasis of Colorectal Cancer by Accumulation of CCR1+ Tumor-Associated Neutrophils through CCL15-CCR1 Axis

PURPOSE

We have reported loss of SMAD4 promotes expression of CCL15 from colorectal cancer to recruit CCR1⁺ myeloid cells through the CCL15-CCR1 axis, which contributes to invasion and liver metastasis. However, the molecular mechanism of lung metastasis is yet to be elucidated. Our purpose is to determine whether similar mechanism is involved in the lung metastasis of colorectal cancer.

EXPERIMENTAL DESIGN

In a mouse model, we examined whether SMAD4 could affect the metastatic activity of colorectal cancer cells to the lung through the CCL15-CCR1 axis. We immunohistochemically analyzed expression of SMAD4, CCL15, and CCR1 with 107 clinical specimens of colorectal cancer lung metastases. We also characterized the CCR1⁺ myeloid cells using several cell-type-specific markers.

RESULTS

In a mouse model, CCL15 secreted from SMAD4-deficient colorectal cancer cells recruited CCR1⁺ cells, promoting their metastatic activities to the lung. Immunohistochemical analysis of lung metastases from colorectal cancer patients revealed that CCL15 expression was significantly correlated with loss of SMAD4, and that CCL15-positive metastases recruited approximately 1.9 times more numbers of CCR1⁺ cells than CCL15-negative metastases. Importantly, patients with CCL15-positive metastases showed a significantly shorter relapse-free survival (RFS) than those with CCL15-negative metastases, and multivariate analysis indicated that CCL15 expression was an independent predictor of shorter RFS. Immunofluorescent staining showed that most CCR1⁺ cells around lung metastases were tumor-associated neutrophil, although a minor fraction was granulocytic myeloid-derived suppressor cell.

CONCLUSIONS

CCL15-CCR1 axis may be a therapeutic target to prevent colorectal cancer lung metastasis. CCL15 can be a biomarker indicating poor prognosis of colorectal cancer patients with lung metastases. Clin Cancer Res; 23(3); 833-44. ©2016 AACR.

Wnt activation protects against neomycin-induced hair cell damage in the mouse cochlea

Recent studies have reported the role of Wnt/β-catenin signaling in hair cell (HC) development, regeneration, and differentiation in the mouse cochlea; however, the role of Wnt/β-catenin signaling in HC protection remains unknown. In this study, we took advantage of transgenic mice to specifically knockout or overactivate the canonical Wnt signaling mediator β-catenin in HCs, which allowed us to investigate the role of Wnt/β-catenin signaling in protecting HCs against neomycin-induced damage. We first showed that loss of β-catenin in HCs made them more vulnerable to neomycin-induced injury, while constitutive activation of β-catenin in HCs reduced HC loss both in vivo and in vitro. We then showed that loss of β-catenin in HCs increased caspase-mediated apoptosis induced by neomycin injury, while β-catenin overexpression inhibited caspase-mediated apoptosis. Finally, we demonstrated that loss of β-catenin in HCs led to increased expression of forkhead box O3 transcription factor (Foxo3) and Bim along with decreased expression of antioxidant enzymes; thus, there were increased levels of reactive oxygen species (ROS) after neomycin treatment that might be responsible for the increased aminoglycoside sensitivity of HCs. In contrast, β-catenin overexpression reduced Foxo3 and Bim expression and ROS levels, suggesting that β-catenin is protective against neomycin-induced HC loss. Our findings demonstrate that Wnt/β-catenin signaling has an important role in protecting HCs against neomycin-induced HC loss and thus might be a new therapeutic target for the prevention of HC death.

β-Catenin destruction complex-independent regulation of Hippo-YAP signaling by APC in intestinal tumorigenesis

Cai et al. show that, besides its role in Wnt–β-catenin signaling, APC functions as a scaffold protein that facilitates the Hippo kinase cascade by interacting with Sav1 and Lats1. They also find that YAP is absolutely required for the development of APC-deficient adenomas.

Mutations in Adenomatous polyposis coli (APC) underlie familial adenomatous polyposis (FAP), an inherited cancer syndrome characterized by the widespread development of colorectal polyps. APC is best known as a scaffold protein in the β-catenin destruction complex, whose activity is antagonized by canonical Wnt signaling. Whether other effector pathways mediate APC's tumor suppressor function is less clear. Here we report that activation of YAP, the downstream effector of the Hippo signaling pathway, is a general hallmark of tubular adenomas from FAP patients. We show that APC functions as a scaffold protein that facilitates the Hippo kinase cascade by interacting with Sav1 and Lats1. Consistent with the molecular link between APC and the Hippo signaling pathway, genetic analysis reveals that YAP is absolutely required for the development of APC-deficient adenomas. These findings establish Hippo–YAP signaling as a critical effector pathway downstream from APC, independent from its involvement in the β-catenin destruction complex.

Reducing DNA methylation suppresses colon carcinogenesis by inducing tumor cell differentiation

The forced reduction of global DNA methylation suppresses tumor development in several cancer models in vivo. Nevertheless, the mechanisms underlying these suppressive effects remain unclear. In this report, we describe our findings showing that a genome-wide reduction in the DNA methylation levels induces cellular differentiation in association with decreased cell proliferation in Apc (Min/+) mouse colon tumor cells in vivo. Colon tumor-specific DNA methylation at Cdx1 is reduced in the DNA-hypomethylated tumors accompanied by Cdx1 derepression and an increased expression of intestinal differentiation-related genes. Furthermore, a histological analysis revealed that Cdx1 derepression in the DNA-hypomethylated tumors is correlated with the differentiation of colon tumor cells. Similarly, the treatment of human colon cancer cell lines with a hypomethylating agent induces differentiation-related genes, including CDX1. We herein propose that DNA demethylation exerts a tumor suppressive effect in the colon by inducing tumor cell differentiation.

A specific nuclear DNA background is required for high frequency lymphoma development in transmitochondrial mice with G13997A mtDNA

We previously found that mouse mitochondrial DNA (mtDNA) with a G13997A mutation (G13997A mtDNA) controls not only the transformation of cultured lung carcinoma cells from poorly metastatic into highly metastatic cells, but also the transformation of lymphocytes into lymphomas in living C57BL/6 (B6) mice. Because the nuclear genetic background of the B6 strain makes the strain prone to develop lymphomas, here we examined whether G13997A mtDNA independently induces lymphoma development even in mice with the nuclear genetic background of the A/J strain, which is not prone to develop lymphomas. Our results showed that the B6 nuclear genetic background is required for frequent lymphoma development in mice with G13997A mtDNA. Moreover, G13997A mtDNA in mice did not enhance the malignant transformation of lung adenomas into adenocarcinomas or that of hepatocellular carcinomas from poorly metastatic into highly metastatic carcinomas. Therefore, G13997A mtDNA enhances the frequency of lymphoma development under the abnormalities in the B6 nuclear genome, and does not independently control tumor development and tumor progression.

SOXC proteins amplify canonical WNT signaling to secure nonchondrocytic fates in skeletogenesis

In skeletogenic mesenchyme, SOXC proteins enter the APC–Axin destruction complex to inhibit β-catenin phosphorylation by GSK3 and thereby synergize with canonical WNT signaling to inhibit chondrogenesis.

Canonical WNT signaling stabilizes β-catenin to determine cell fate in many processes from development onwards. One of its main roles in skeletogenesis is to antagonize the chondrogenic transcription factor SOX9. We here identify the SOXC proteins as potent amplifiers of this pathway. The SOXC genes, i.e., Sox4, Sox11, and Sox12, are coexpressed in skeletogenic mesenchyme, including presumptive joints and perichondrium, but not in cartilage. Their inactivation in mouse embryo limb bud caused massive cartilage fusions, as joint and perichondrium cells underwent chondrogenesis. SOXC proteins govern these cells cell autonomously. They replace SOX9 in the adenomatous polyposis coli–Axin destruction complex and therein inhibit phosphorylation of β-catenin by GSK3. This inhibition, a crucial, limiting step in canonical WNT signaling, thus becomes a constitutive event. The resulting SOXC/canonical WNT-mediated synergistic stabilization of β-catenin contributes to efficient repression of Sox9 in presumptive joint and perichondrium cells and thereby ensures proper delineation and articulation of skeletal primordia. This synergy may determine cell fate in many processes besides skeletogenesis.

CDC42 inhibition suppresses progression of incipient intestinal tumors

Mutations in the APC or β-catenin genes are well-established initiators of colorectal cancer, yet modifiers that facilitate the survival and progression of nascent tumor cells are not well defined. Using genetic and pharmacologic approaches in mouse colorectal cancer and human colorectal cancer xenograft models, we show that incipient intestinal tumor cells activate CDC42, an APC-interacting small GTPase, as a crucial step in malignant progression. In the mouse, Cdc42 ablation attenuated the tumorigenicity of mutant intestinal cells carrying single APC or β-catenin mutations. Similarly, human colorectal cancer with relatively higher levels of CDC42 activity was particularly sensitive to CDC42 blockade. Mechanistic studies suggested that Cdc42 may be activated at different levels, including at the level of transcriptional activation of the stem cell-enriched Rho family exchange factor Arhgef4. Our results indicate that early-stage mutant intestinal epithelial cells must recruit the pleiotropic functions of Cdc42 for malignant progression, suggesting its relevance as a biomarker and therapeutic target for selective colorectal cancer intervention.

Canonical WNT signaling components in vascular development and barrier formation

Canonical WNT signaling is required for proper vascularization of the CNS during embryonic development. Here, we used mice with targeted mutations in genes encoding canonical WNT pathway members to evaluate the exact contribution of these components in CNS vascular development and in specification of the blood-brain barrier (BBB) and blood-retina barrier (BRB). We determined that vasculature in various CNS regions is differentially sensitive to perturbations in canonical WNT signaling. The closely related WNT signaling coreceptors LDL receptor-related protein 5 (LRP5) and LRP6 had redundant functions in brain vascular development and barrier maintenance; however, loss of LRP5 alone dramatically altered development of the retinal vasculature. The BBB in the cerebellum and pons/interpeduncular nuclei was highly sensitive to decrements in canonical WNT signaling, and WNT signaling was required to maintain plasticity of barrier properties in mature CNS vasculature. Brain and retinal vascular defects resulting from ablation of Norrin/Frizzled4 signaling were ameliorated by stabilizing β-catenin, while inhibition of β-catenin-dependent transcription recapitulated the vascular development and barrier defects associated with loss of receptor, coreceptor, or ligand, indicating that Norrin/Frizzled4 signaling acts predominantly through β-catenin-dependent transcriptional regulation. Together, these data strongly support a model in which identical or nearly identical canonical WNT signaling mechanisms mediate neural tube and retinal vascularization and maintain the BBB and BRB.