Dedifferentiation maintains melanocyte stem cells in a dynamic niche

For unknow reasons, the melanocyte stem cell (McSC) system fails earlier than other adult stem cell populations1, which leads to hair greying in most humans and mice2,3. Current dogma states that McSCs are reserved in an undifferentiated state in the hair follicle niche, physically segregated from differentiated progeny that migrate away following cues of regenerative stimuli4-8. Here we show that most McSCs toggle between transit-amplifying and stem cell states for both self-renewal and generation of mature progeny, a mechanism fundamentally distinct from those of other self-renewing systems. Live imaging and single-cell RNA sequencing revealed that McSCs are mobile, translocating between hair follicle stem cell and transit-amplifying compartments where they reversibly enter distinct differentiation states governed by local microenvironmental cues (for example, WNT). Long-term lineage tracing demonstrated that the McSC system is maintained by reverted McSCs rather than by reserved stem cells inherently exempt from reversible changes. During ageing, there is accumulation of stranded McSCs that do not contribute to the regeneration of melanocyte progeny. These results identify a new model whereby dedifferentiation is integral to homeostatic stem cell maintenance and suggest that modulating McSC mobility may represent a new approach for the prevention of hair greying.

Targeted engagement of β-catenin-Ikaros complexes in refractory B-cell malignancies

In most cell types, nuclear β-catenin functions as prominent oncogenic driver and pairs with TCF7-family factors for transcriptional activation of MYC. Surprisingly, B-lymphoid malignancies not only lacked expression and activating lesions of β-catenin but critically depended on GSK3β for effective β-catenin degradation. Our interactome studies in B-lymphoid tumors revealed that β-catenin formed repressive complexes with lymphoid-specific Ikaros factors at the expense of TCF7. Instead of MYC-activation, β-catenin was essential to enable Ikaros-mediated recruitment of nucleosome remodeling and deacetylation (NuRD) complexes for transcriptional repression of MYC. To leverage this previously unrecognized vulnerability of B-cell-specific repressive β-catenin-Ikaros-complexes in refractory B-cell malignancies, we examined GSK3β small molecule inhibitors to subvert β-catenin degradation. Clinically approved GSK3β-inhibitors that achieved favorable safety prof les at micromolar concentrations in clinical trials for neurological disorders and solid tumors were effective at low nanomolar concentrations in B-cell malignancies, induced massive accumulation of β-catenin, repression of MYC and acute cell death. Preclinical in vivo treatment experiments in patient-derived xenografts validated small molecule GSK3β-inhibitors for targeted engagement of lymphoid-specific β-catenin-Ikaros complexes as a novel strategy to overcome conventional mechanisms of drug-resistance in refractory malignancies.

HIGHLIGHTS

Unlike other cell lineages, B-cells express nuclear β-catenin protein at low baseline levels and depend on GSK3β for its degradation.In B-cells, β-catenin forms unique complexes with lymphoid-specific Ikaros factors and is required for Ikaros-mediated tumor suppression and assembly of repressive NuRD complexes. CRISPR-based knockin mutation of a single Ikaros-binding motif in a lymphoid MYC superenhancer region reversed β-catenin-dependent Myc repression and induction of cell death. The discovery of GSK3β-dependent degradation of β-catenin as unique B-lymphoid vulnerability provides a rationale to repurpose clinically approved GSK3β-inhibitors for the treatment of refractory B-cell malignancies.

GRAPHICAL ABSTRACT

Abundant nuclear β-cateninβ-catenin pairs with TCF7 factors for transcriptional activation of MYCB-cells rely on efficient degradation of β-catenin by GSK3βB-cell-specific expression of Ikaros factors Unique vulnerability in B-cell tumors: GSK3β-inhibitors induce nuclear accumulation of β-catenin.β-catenin pairs with B-cell-specific Ikaros factors for transcriptional repression of MYC.

Dual blockade of macropinocytosis and asparagine bioavailability shows synergistic anti-tumor effects on KRAS-mutant colorectal cancer

Mutations of KRAS gene are found in various types of cancer, including colorectal cancer (CRC). Despite intense efforts, no pharmacological approaches are expected to be effective against KRAS-mutant cancers. Macropinocytosis is an evolutionarily conserved actin-dependent endocytic process that internalizes extracellular fluids into large vesicles called macropinosomes. Recent studies have revealed macropinocytosis's important role in metabolic adaptation to nutrient stress in cancer cells harboring KRAS mutations. Here we showed that KRAS-mutant CRC cells enhanced macropinocytosis for tumor growth under nutrient-depleted conditions. We also demonstrated that activation of Rac1 and phosphoinositide 3-kinase were involved in macropinocytosis of KRAS-mutant CRC cells. Furthermore, we found that macropinocytosis was closely correlated with asparagine metabolism. In KRAS-mutant CRC cells engineered with knockdown of asparagine synthetase, macropinocytosis was accelerated under glutamine-depleted condition, and albumin addition could restore the glutamine depletion-induced growth suppression by recovering the intracellular asparagine level. Finally, we discovered that the combination of macropinocytosis inhibition and asparagine depletion dramatically suppressed the tumor growth of KRAS-mutant CRC cells in vivo. These results indicate that dual blockade of macropinocytosis and asparagine bioavailability could be a novel therapeutic strategy for KRAS-mutant cancers.

Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/β-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of β-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, β-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted β-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This β-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by β-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

The therapeutic potential of multiclonal tumoricidal T cells derived from tumor infiltrating lymphocyte-1derived iPS cells

Tumor-infiltrating lymphocytes (TIL), which include tumor-specific T lymphocytes with frequency, are used for adoptive cell transfer therapy (ACT) in clinical practice. The optimization of TIL preparation has been investigated to reduce the senescence and increase the abundance of TIL, as both the quality and quantity of the transferred cells have great influence on the outcome of TIL-based ACT (TIL-ACT). Considering the effects of cell reprogramming on senescence, we expected that the anti-tumor effect could be enhanced by TIL regeneration. To confirm this hypothesis, we established tumor-specific TIL-derived iPS cells (TIL-iPSC) with human colorectal cancer specimens. T cells differentiated from TIL-iPSC (TIL-iPS-T) retained not only intrinsic T cell functions and tumor specificity, but also exhibited improved proliferation capacity and additional killing activity. Moreover, less differentiated profiles and prolonged persistency were seen in TIL-iPS-T compared with primary cells. Our findings imply that iPSC technology has great potential for TIL-ACT.

Resident mesenchymal vascular progenitors modulate adaptive angiogenesis and pulmonary remodeling via regulation of canonical Wnt signaling

Adaptive angiogenesis is necessary for tissue repair, however, it may also be associated with the exacerbation of injury and development of chronic disease. In these studies, we demonstrate that lung mesenchymal vascular progenitor cells (MVPC) modulate adaptive angiogenesis via lineage trace, depletion of MVPC, and modulation of β-catenin expression. Single cell sequencing confirmed MVPC as multipotential vascular progenitors, thus, genetic depletion resulted in alveolar simplification with reduced adaptive angiogenesis. Following vascular endothelial injury, Wnt activation in MVPC was sufficient to elicit an emphysema-like phenotype characterized by increased MLI, fibrosis, and MVPC driven adaptive angiogenesis. Lastly, activation of Wnt/β-catenin signaling skewed the profile of human and murine MVPC toward an adaptive phenotype. These data suggest that lung MVPC drive angiogenesis in response to injury and regulate the microvascular niche as well as subsequent distal lung tissue architecture via Wnt signaling.

Chemosensitivity of Patient-Derived Cancer Stem Cells Identifies Colorectal Cancer Patients with Potential Benefit from FGFR Inhibitor Therapy

Some colorectal cancer patients harboring FGFR (fibroblast growth factor receptor) genetic alterations, such as copy number gain, mutation, and/or mRNA overexpression, were selected for enrollment in several recent clinical trials of FGFR inhibitor, because these genetic alterations were preclinically reported to be associated with FGFR inhibitor sensitivity as well as poor prognosis, invasiveness, and/or metastatic potential. However, few enrolled patients were responsive to FGFR inhibitors. Thus, practical strategies are eagerly awaited that can stratify patients for the subset that potentially responds to FGFR inhibitor chemotherapy. In the present study, we evaluated the sensitivity to FGFR inhibitor erdafitinib on 25 patient-derived tumor-initiating cell (TIC) spheroid lines carrying wild-type RAS and RAF genes, both in vitro and in vivo. Then, we assessed possible correlations between the sensitivity and the genetic/genomic data of the spheroid lines tested. Upon their exposure to erdafitinib, seven lines (7/25, 28%) responded significantly. Normal colonic epithelial stem cells were unaffected by the inhibitors. Moreover, the combination of erdafitinib with EGFR inhibitor erlotinib showed stronger growth inhibition than either drug alone, as efficacy was observed in 21 lines (84%) including 14 (56%) that were insensitive to erdafitinib alone. The in vitro erdafitinib response was accurately reflected on mouse xenografts of TIC spheroid lines. However, we found little correlation between their genetic/genomic alterations of TIC spheroids and the sensitivity to the FGFR inhibitor. Accordingly, we propose that direct testing of the patient-derived spheroids in vitro is one of the most reliable personalized methods in FGFR-inhibitor therapy of colorectal cancer patients.

Tubular β-catenin and FoxO3 interactions protect in chronic kidney disease

The Wnt/β-catenin signaling pathway plays an important role in renal development and is reexpressed in the injured kidney and other organs. β-Catenin signaling is protective in acute kidney injury (AKI) through actions on the proximal tubule, but the current dogma is that Wnt/β-catenin signaling promotes fibrosis and development of chronic kidney disease (CKD). As the role of proximal tubular β-catenin signaling in CKD remains unclear, we genetically stabilized (i.e., activated) β-catenin specifically in murine proximal tubules. Mice with increased tubular β-catenin signaling were protected in 2 murine models of AKI to CKD progression. Oxidative stress, a common feature of CKD, reduced the conventional T cell factor/lymphoid enhancer factor-dependent β-catenin signaling and augmented FoxO3-dependent activity in proximal tubule cells in vitro and in vivo. The protective effect of proximal tubular β-catenin in renal injury required the presence of FoxO3 in vivo. Furthermore, we identified cystathionine γ-lyase as a potentially novel transcriptional target of β-catenin/FoxO3 interactions in the proximal tubule. Thus, our studies overturned the conventional dogma about β-catenin signaling and CKD by showing a protective effect of proximal tubule β-catenin in CKD and identified a potentially new transcriptional target of β-catenin/FoxO3 signaling that has therapeutic potential for CKD.

WNT/β-catenin directed metabolic choice uncouples lung-resident alveolar macrophage inflammatory activity from self-renewal

Fetal-derived tissue-resident macrophages exhibit stem cell-like features of self-renewal in adulthood to maintain macrophage population during homeostasis and/or various insults. However, little is known about the cellular and molecular mechanisms modulating proliferative and inflammatory fate decisions of tissue-resident macrophages in vivo. Here, we show that WNT-β-catenin signaling inhibited lung-resident alveolar macrophage (AM) self-renewal, while simultaneously promoted AM inflammatory activities in vitro and in vivo during influenza virus infection. Mechanistically, WNT engagement facilitated the binding of β-catenin with HIF-1α over its conventional binding partner TCF-4. Such a binding choice led to the elevated macrophage inflammation in a glycolysis-dependent manner, while inhibited AM self-renewal by causing mitochondrial damage and impairing oxidative phosphorylation. Thus, AM self-renewal and inflammatory activity are uncoupled by WNT-β-catenin signaling through HIF-1α-mediated cellular metabolic choice. Importantly, we showed that AM with high HIF-1α activity had limited proliferative capacity and produced inflammatory cytokines, while AM with low HIF-1α activity were highly proliferative and expressed genes associated with tissue repair function in vivo during influenza virus infection. In accordance, we demonstrated that AM proliferation and repopulation were needed for optimal lung repair following the clearance of influenza virus in the respiratory tract. Our results have revealed key mechanisms modulating macrophage fate choice between progeny production versus inflammatory effector activity, and subsequent effects on tissue inflammation and repair.

MicroRNA-9-5p-CDX2 Axis: A Useful Prognostic Biomarker for Patients with Stage II/III Colorectal Cancer

A lack of caudal-type homeobox transcription factor 2 (CDX2) protein expression has been proposed as a prognostic biomarker for colorectal cancer (CRC). However, the relationship between CDX2 levels and the survival of patients with stage II/III CRC along with the relationship between microRNAs (miRs) and CDX2 expression are unclear. Tissue samples were collected from patients with stage II/III CRC surgically treated at Kyoto University Hospital. CDX2 expression was semi-quantitatively evaluated by immunohistochemistry (IHC). The prognostic impacts of CDX2 expression on overall survival (OS) and relapse-free survival (RFS) were evaluated by multivariable statistical analysis. The expression of miRs regulating CDX2 expression and their prognostic impacts were analyzed using The Cancer Genome Atlas Program for CRC (TCGA-CRC). Eleven of 174 CRC tissues lacked CDX2 expression. The five-year OS and RFS rates of patients with CDX2-negative CRC were significantly lower than those of CDX2-positive patients. Multivariate analysis of clinicopathological features revealed that CDX2-negative status is an independent marker of poor prognosis in stage II/III CRC. miR-9-5p was shown to regulate CDX2 expression. TCGA-CRC analysis showed that high miR-9-5p expression was significantly associated with poor patient prognosis in stage II/III CRC. In conclusion, CDX2, the post-transcriptional target of microRNA-9-5p, is a useful prognostic biomarker in patients with stage II/III CRC.

A novel mouse model demonstrates that oncogenic melanocyte stem cells engender melanoma resembling human disease

Melanoma, the deadliest skin cancer, remains largely incurable at advanced stages. Currently, there is a lack of animal models that resemble human melanoma initiation and progression. Recent studies using a Tyr-CreER driven mouse model have drawn contradictory conclusions about the potential of melanocyte stem cells (McSCs) to form melanoma. Here, we employ a c-Kit-CreER-driven model that specifically targets McSCs to show that oncogenic McSCs are a bona fide source of melanoma that expand in the niche, and then establish epidermal melanomas that invade into the underlying dermis. Further, normal Wnt and Endothelin niche signals during hair anagen onset are hijacked to promote McSC malignant transformation during melanoma induction. Finally, molecular profiling reveals strong resemblance of murine McSC-derived melanoma to human melanoma in heterogeneity and gene signatures. These findings provide experimental validation of the human melanoma progression model and key insights into the transformation and heterogeneity of McSC-derived melanoma.

Currently, few mouse models exist to recapitulate human melanomagenesis. Here, the authors establish a c-Kit-CreER-driven model to target melanocyte stem cells (McSCs) and show that oncogenic McSCs give rise to epidermal melanoma that invade into the dermis, similar to human melanoma.

Low wnt/β-catenin signaling determines leaky vessels in the subfornical organ and affects water homeostasis in mice

The circumventricular organs (CVOs) in the central nervous system (CNS) lack a vascular blood-brain barrier (BBB), creating communication sites for sensory or secretory neurons, involved in body homeostasis. Wnt/β-catenin signaling is essential for BBB development and maintenance in endothelial cells (ECs) in most CNS vessels. Here we show that in mouse development, as well as in adult mouse and zebrafish, CVO ECs rendered Wnt-reporter negative, suggesting low level pathway activity. Characterization of the subfornical organ (SFO) vasculature revealed heterogenous claudin-5 (Cldn5) and Plvap/Meca32 expression indicative for tight and leaky vessels, respectively. Dominant, EC-specific β-catenin transcription in mice, converted phenotypically leaky into BBB-like vessels, by augmenting Cldn5⁺vessels, stabilizing junctions and by reducing Plvap/Meca32⁺ and fenestrated vessels, resulting in decreased tracer permeability. Endothelial tightening augmented neuronal activity in the SFO of water restricted mice. Hence, regulating the SFO vessel barrier may influence neuronal function in the context of water homeostasis.

Infections and diseases in the brain and spine can be very damaging and debilitating. Indeed, the central nervous system also needs a carefully controlled biochemical environment to survive. As such, all animals with a backbone have barriers and defenses to protect and preserve this key system. One of these is the blood-brain barrier, a physical barrier between the brain and the outside world. Where most blood vessels allow relatively free exchange of chemicals between the blood and surrounding cells, the blood-brain barrier controls what can move between the bloodstream and the brain.

Yet, there are gaps in the blood-brain barrier, specifically within structures in the brain called the circumventricular organs. These leaky vessels allow the brain cells in these regions to monitor the blood and respond to changes, for example, by triggering sensations such as hunger, thirst or nausea. It is not clear what stops the blood-brain barrier from forming in these regions and what effect the presence of a barrier would have on the brains activity, or the health and behavior of the animal.

Benz et al. have now used mice and zebrafish to examine the development and structure of the blood-brain barrier. The investigation revealed that the signals that induce the blood-brain barrier throughout the brain are absent in the circumventricular organs of both species. Next, by artificially activating a protein involved in cell-cell interactions in mice, Benz et al. created blood-brain barrier-like structures in circumventricular organs by converting the leaky vessels into tight ones. This change meant that the brain cells in these regions did not respond properly to water deprivation, which potentially may have affected the regulation of thirst in these mice.

Understanding the blood-brain barrier could have a variety of impacts on how we treat diseases in the central nervous system. This includes stroke, brain tumors and Alzheimers disease. These findings could particularly help scientists to better understand conditions that affect basic needs like thirst and hunger.

Edar is a downstream target of beta-catenin and drives collagen accumulation in the mouse prostate

Beta-catenin (CTNNB1) directs ectodermal appendage spacing by activating ectodysplasin A receptor (EDAR) transcription, but whether CTNNB1 acts by a similar mechanism in the prostate, an endoderm-derived tissue, is unclear. Here we examined the expression, function, and CTNNB1 dependence of the EDAR pathway during prostate development. In situ hybridization studies reveal EDAR pathway components including Wnt10b in the developing prostate and localize these factors to prostatic bud epithelium where CTNNB1 target genes are co-expressed. We used a genetic approach to ectopically activate CTNNB1 in developing mouse prostate and observed focal increases in Edar and Wnt10b mRNAs. We also used a genetic approach to test the prostatic consequences of activating or inhibiting Edar expression. Edar overexpression does not visibly alter prostatic bud formation or branching morphogenesis, and Edar expression is not necessary for either of these events. However, Edar overexpression is associated with an abnormally thick and collagen-rich stroma in adult mouse prostates. These results support CTNNB1 as a transcriptional activator of Edar and Wnt10b in the developing prostate and demonstrate Edar is not only important for ectodermal appendage patterning but also influences collagen organization in adult prostates.

This article has an associated First Person interview with the first author of the paper.

Summary: This study provides a rare connection between beta catenin and ectodysplasin A receptor in an endoderm derived tissue and presents a potential mechanism for collagen accumulation in the prostate.

Single-Cell Analysis Reveals a Hair Follicle Dermal Niche Molecular Differentiation Trajectory that Begins Prior to Morphogenesis

Delineating molecular and cellular events that precede appendage morphogenesis has been challenging due to the inability to distinguish quantitative molecular differences between cells that lack histological distinction. The hair follicle (HF) dermal condensate (DC) is a cluster of cells critical for HF development and regeneration. Events that presage emergence of this distinctive population are poorly understood. Using unbiased single-cell RNA sequencing and in vivo methods, we infer a sequence of transcriptional states through which DC cells pass that begins prior to HF morphogenesis. Our data indicate that Wnt/β-catenin signaling is required to progress into an intermediate stage that precedes quiescence and differentiation. Further, we provide evidence that quiescent DC cells are recent progeny of selectively proliferating cells present prior to morphogenesis and that are later identified in the peri-DC zone during DC expansion. Together, these findings provide an inferred path of molecular states that lead to DC cell differentiation.

SMAD4 Suppresses WNT-Driven Dedifferentiation and Oncogenesis in the Differentiated Gut Epithelium

The cell of origin of colon cancer is typically thought to be the resident somatic stem cells, which are immortal and escape the continual cellular turnover characteristic of the intestinal epithelium. However, recent studies have identified certain conditions in which differentiated cells can acquire stem-like properties and give rise to tumors. Defining the origins of tumors will inform cancer prevention efforts as well as cancer therapies, as cancers with distinct origins often respond differently to treatments. We report here a new condition in which tumors arise from the differentiated intestinal epithelium. Inactivation of the differentiation-promoting transcription factor SMAD4 in the intestinal epithelium was surprisingly well tolerated in the short term. However, after several months, adenomas developed with characteristics of activated WNT signaling. Simultaneous loss of SMAD4 and activation of the WNT pathway led to dedifferentiation and rapid adenoma formation in differentiated tissue. Transcriptional profiling revealed acquisition of stem cell characteristics, and colabeling indicated that cells expressing differentiated enterocyte markers entered the cell cycle and reexpressed stem cell genes upon simultaneous loss of SMAD4 and activation of the WNT pathway. These results indicate that SMAD4 functions to maintain differentiated enterocytes in the presence of oncogenic WNT signaling, thus preventing dedifferentiation and tumor formation in the differentiated intestinal epithelium.Significance: This work identifies a mechanism through which differentiated cells prevent tumor formation by suppressing oncogenic plasticity. Cancer Res; 78(17); 4878-90. ©2018 AACR.

A Chemosensitivity Study of Colorectal Cancer Using Xenografts of Patient-Derived Tumor-Initiating Cells

Current genomic and gene expression analyses provide versatile tools to improve cancer chemotherapy. However, it is still difficult to predict whether each patient responds to a particular regimen or not. To predict chemosensitivity in each patient with colorectal cancer, we developed an evaluation method using the primary tumor-initiating cells (TIC, aka cancer stem cells) xenografted in nude mice subcutaneously (patient-derived spheroid xenografts; PDSX). Simultaneously, we also prepared the conventional patient-derived xenografts (PDX) from the same patients' tumors and compared the dosing results with those of PDSXs. We further compared the chemosensitivities of PDSXs with those of 7 patients who had been given regimens such as FOLFOX and FOLFIRI to treat their metastatic lesions. As per the results, the PDSX method provided much more precise and predictable tumor growth with less variance than conventional PDX, although both retained the epithelial characteristics of the primary tumors. Likewise, drug-dosing tests showed essentially the same results in PDXs and PDSXs, with stronger statistical power in PDSXs. Notably, the cancer chemosensitivity in each patient was precisely reflected in that of the PDSX mice along the clinical course until the resistance emerged at the terminal stage. This "paraclinical" xenograft trials using PDSXs may help selection of chemotherapy regimens efficacious for each patient, and, more importantly, avoiding inefficient ones by which the patient can lose precious time and QOL. Furthermore, the PDSX method may be employed for evaluations of off-label uses of cancer chemotherapeutics and compassionate uses of yet-unapproved new drugs in personalized therapies. Mol Cancer Ther; 17(10); 2187-96. ©2018 AACR.

Composite regulation of ERK activity dynamics underlying tumour-specific traits in the intestine

Acting downstream of many growth factors, extracellular signal-regulated kinase (ERK) plays a pivotal role in regulating cell proliferation and tumorigenesis, where its spatiotemporal dynamics, as well as its strength, determine cellular responses. Here, we uncover the ERK activity dynamics in intestinal epithelial cells (IECs) and their association with tumour characteristics. Intravital imaging identifies two distinct modes of ERK activity, sustained and pulse-like activity, in IECs. The sustained and pulse-like activities depend on ErbB2 and EGFR, respectively. Notably, activation of Wnt signalling, the earliest event in intestinal tumorigenesis, augments EGFR signalling and increases the frequency of ERK activity pulses through controlling the expression of EGFR and its regulators, rendering IECs sensitive to EGFR inhibition. Furthermore, the increased pulse frequency is correlated with increased cell proliferation. Thus, ERK activity dynamics are defined by composite inputs from EGFR and ErbB2 signalling in IECs and their alterations might underlie tumour-specific sensitivity to pharmacological EGFR inhibition.

The ERK signalling pathway regulates homeostasis of the intestinal epithelium. Here the authors identify two modes of ERK activity generated independently from EGFR and ErbB2 receptor and whose balance in cancer is shifted by Wnt pathway activation, resulting in enhanced sensitivity to EGFR inhibitors.

An improved method for culturing patient-derived colorectal cancer spheroids

Recent advances allowed culturing and examination of patient-derived colorectal cancer (PD-CRC) cells as organoids or spheroids. To be applied to practical personalized medicine, however, current methods still need to be strengthened for higher efficiency. Here we report an improved method to propagate PD-CRC tumor initiating cells (TICs) in spheroid culture. We established > 100 cancer spheroid lines derived from independent colorectal cancer patients employing a serum-containing medium with additional inhibitors, Y27632 and SB431542. Because colorectal cancer spheroids showed wide-range growth rates depending on the patient tumors, we searched for supplementary factors that accelerated proliferation of slow-growing CRC-TIC spheroids. To this end, we introduced a convenient growth-monitoring method using a luciferase reporter. We found that epidermal growth factor (EGF) and/or basic fibroblast growth factor (bFGF) were critical for steady propagation of a subset of CRC-TIC spheroids carrying the wild-type RAS and RAF genes. We also identified 5'-(N-ethyl-carboxamido)-adenosine (NECA), an adenosine receptor agonist, as an essential supplement for another subset of spheroids. Based on these results, we propose to optimize culture conditions for CRC-TIC spheroids by adjusting to the respective tumor samples. Our method provides a versatile tool that can be applied to personalized chemotherapy evaluation in prospective clinical studies.

Dissecting Wnt Signaling for Melanocyte Regulation during Wound Healing

Abnormal pigmentation is commonly seen in the wound scar. Despite advancements in the research of wound healing, little is known about the repopulation of melanocytes in the healed skin. Previous studies have shown the capacity of melanocyte stem cells in the hair follicle to contribute skin epidermal melanocytes after injury in mice and humans. Here, we focused on the Wnt pathway, known to be a vital regulator of melanocyte stem cells in efforts to better understand the regulation of follicle-derived epidermal melanocytes during wound healing. We showed that transgenic expression of Wnt inhibitor Dkk1 in melanocytes reduced epidermal melanocytes in the wound scar. Conversely, forced activation of Wnt signaling by genetically stabilizing β-catenin in melanocytes increases epidermal melanocytes. Furthermore, we show that deletion of Wntless (Wls), a gene required for Wnt ligand secretion, within epithelial cells results in failure in activating Wnt signaling in adjacent epidermal melanocytes. These results show the essential function of extrinsic Wnt ligands in initiating Wnt signaling in follicle-derived epidermal melanocytes during wound healing. Collectively, our results suggest the potential for Wnt signal regulation to promote melanocyte regeneration and provide a potential molecular window to promote proper melanocyte regeneration after wounding and in conditions such as vitiligo.

Canonical WNT Signaling Regulates the Pituitary Organizer and Pituitary Gland Formation

The pituitary organizer is a domain within the ventral diencephalon that expresses Bmp4, Fgf8, and Fgf10, which induce the formation of the pituitary precursor, Rathke's pouch, from the oral ectoderm. The WNT signaling pathway regulates this pituitary organizer such that loss of Wnt5a leads to an expansion of the pituitary organizer and an enlargement of Rathke's pouch. WNT signaling is classified into canonical signaling, which is mediated by β-CATENIN, and noncanonical signaling, which operates independently of β-CATENIN. WNT5A is typically classified as a noncanonical WNT; however, other WNT family members are expressed in the ventral diencephalon and nuclear localized β-CATENIN is observed in the ventral diencephalon. Therefore, we sought to determine whether canonical WNT signaling is necessary for regulation of pituitary organizer function. Using a conditional loss-of-function approach, we deleted β-catenin within the mouse ventral diencephalon. Mutant embryos have a smaller Rathke's pouch, resulting from a reduced pituitary organizer, especially Fgf8. This result suggests that canonical WNT signaling promotes pituitary organizer function, instead of inhibiting it. To test this hypothesis, we stimulated canonical WNT signaling in the ventral diencephalon using an inducible gain-of-function allele of β-catenin and found that stimulating canonical WNT signaling expands the domain of Fgf8 and results in a dysmorphic Rathke's pouch. These results demonstrate that canonical WNT signaling in the ventral diencephalon is necessary for proper expression of pituitary organizer genes and suggests that a balance of both canonical and noncanonical WNT signaling is necessary to ensure proper formation of Rathke's pouch.

A Critical Role of Presynaptic Cadherin/Catenin/p140Cap Complexes in Stabilizing Spines and Functional Synapses in the Neocortex

The formation of functional synapses requires coordinated assembly of presynaptic transmitter release machinery and postsynaptic trafficking of functional receptors and scaffolds. Here, we demonstrate a critical role of presynaptic cadherin/catenin cell adhesion complexes in stabilizing functional synapses and spines in the developing neocortex. Importantly, presynaptic expression of stabilized β-catenin in either layer (L) 4 excitatory neurons or L2/3 pyramidal neurons significantly upregulated excitatory synaptic transmission and dendritic spine density in L2/3 pyramidal neurons, while its sparse postsynaptic expression in L2/3 neurons had no such effects. In addition, presynaptic β-catenin expression enhanced release probability of glutamatergic synapses. Newly identified β-catenin-interacting protein p140Cap is required in the presynaptic locus for mediating these effects. Together, our results demonstrate that cadherin/catenin complexes stabilize functional synapses and spines through anterograde signaling in the neocortex and provide important molecular evidence for a driving role of presynaptic components in spinogenesis in the neocortex.

Blocking TGF-β and β-Catenin Epithelial Crosstalk Exacerbates CKD

The TGF-β and Wnt/β-catenin pathways have important roles in modulating CKD, but how these growth factors affect the epithelial response to CKD is not well studied. TGF-β has strong profibrotic effects, but this pleiotropic factor has many different cellular effects depending on the target cell type. To investigate how TGF-β signaling in the proximal tubule, a key target and mediator of CKD, alters the response to CKD, we injured mice lacking the TGF-β type 2 receptor specifically in this epithelial segment. Compared with littermate controls, mice lacking the proximal tubular TGF-β receptor had significantly increased tubular injury and tubulointerstitial fibrosis in two different models of CKD. RNA sequencing indicated that deleting the TGF-β receptor in proximal tubule cells modulated many growth factor pathways, but Wnt/β-catenin signaling was the pathway most affected. We validated that deleting the proximal tubular TGF-β receptor impaired β-catenin activity in vitro and in vivo Genetically restoring β-catenin activity in proximal tubules lacking the TGF-β receptor dramatically improved the tubular response to CKD in mice. Deleting the TGF-β receptor alters many growth factors, and therefore, this ameliorated response may be a direct effect of β-catenin activity or an indirect effect of β-catenin interacting with other growth factors. In conclusion, blocking TGF-β and β-catenin crosstalk in proximal tubules exacerbates tubular injury in two models of CKD.

Disruption of lineage specification in adult pulmonary mesenchymal progenitor cells promotes microvascular dysfunction

Pulmonary vascular disease is characterized by remodeling and loss of microvessels and is typically attributed to pathological responses in vascular endothelium or abnormal smooth muscle cell phenotypes. We have challenged this understanding by defining an adult pulmonary mesenchymal progenitor cell (MPC) that regulates both microvascular function and angiogenesis. The current understanding of adult MPCs and their roles in homeostasis versus disease has been limited by a lack of genetic markers with which to lineage label multipotent mesenchyme and trace the differentiation of these MPCs into vascular lineages. Here, we have shown that lineage-labeled lung MPCs expressing the ATP-binding cassette protein ABCG2 (ABCG2+) are pericyte progenitors that participate in microvascular homeostasis as well as adaptive angiogenesis. Activation of Wnt/β-catenin signaling, either autonomously or downstream of decreased BMP receptor signaling, enhanced ABCG2+ MPC proliferation but suppressed MPC differentiation into a functional pericyte lineage. Thus, enhanced Wnt/β-catenin signaling in ABCG2+ MPCs drives a phenotype of persistent microvascular dysfunction, abnormal angiogenesis, and subsequent exacerbation of bleomycin-induced fibrosis. ABCG2+ MPCs may, therefore, account in part for the aberrant microvessel function and remodeling that are associated with chronic lung diseases.

Amino-terminal enhancer of split gene AES encodes a tumor and metastasis suppressor of prostate cancer

A major cause of cancer death is its metastasis to the vital organs. Few effective therapies are available for metastatic castration‐resistant prostate cancer (PCa), and progressive metastatic lesions such as lymph nodes and bones cause mortality. We recently identified AES as a metastasis suppressor for colon cancer. Here, we have studied the roles of AES in PCa progression. We analyzed the relationship between AES expression and PCa stages of progression by immunohistochemistry of human needle biopsy samples. We then performed overexpression and knockdown of AES in human PCa cell lines LNCaP, DU145 and PC3, and determined the effects on proliferation, invasion and metastasis in culture and in a xenograft model. We also compared the PCa phenotypes of Aes/Pten compound knockout mice with those of Pten simple knockout mice. Expression levels of AES were inversely correlated with clinical stages of human PCa. Exogenous expression of AES suppressed the growth of LNCaP cells, whereas the AES knockdown promoted it. We also found that AES suppressed transcriptional activities of androgen receptor and Notch signaling. Notably, AES overexpression in AR‐defective DU145 and PC3 cells reduced invasion and metastasis to lymph nodes and bones without affecting proliferation in culture. Consistently, prostate epithelium‐specific inactivation of Aes in Pten^flox/flox mice increased expression of Snail and MMP9, and accelerated growth, invasion and lymph node metastasis of the mouse prostate tumor. These results suggest that AES plays an important role in controlling tumor growth and metastasis of PCa by regulating both AR and Notch signaling pathways.

Expression of metastasis suppressor gene AES driven by a Yin Yang (YY) element in a CpG island promoter and transcription factor YY2

We recently found that the product of the AES gene functions as a metastasis suppressor of colorectal cancer (CRC) in both humans and mice. Expression of amino‐terminal enhancer of split (AES) protein is significantly decreased in liver metastatic lesions compared with primary colon tumors. To investigate its downregulation mechanism in metastases, we searched for transcriptional regulators of AES in human CRC and found that its expression is reduced mainly by transcriptional dysregulation and, in some cases, by additional haploidization of its coding gene. The AES promoter‐enhancer is in a typical CpG island, and contains a Yin‐Yang transcription factor recognition sequence (YY element). In human epithelial cells of normal colon and primary tumors, transcription factor YY2, a member of the YY family, binds directly to the YY element, and stimulates expression of AES. In a transplantation mouse model of liver metastases, however, expression of Yy2 (and therefore of Aes) is downregulated. In human CRC metastases to the liver, the levels of AES protein are correlated with those of YY2. In addition, we noticed copy‐number reduction for the AES coding gene in chromosome 19p13.3 in 12% (5/42) of human CRC cell lines. We excluded other mechanisms such as point or indel mutations in the coding or regulatory regions of the AES gene, CpG methylation in the AES promoter enhancer, expression of microRNAs, and chromatin histone modifications. These results indicate that Aes may belong to a novel family of metastasis suppressors with a CpG‐island promoter enhancer, and it is regulated transcriptionally.

Beta-catenin and estrogen signaling collaborate to drive cyclin D1 expression in developing mouse prostate

Androgen, beta-catenin (CTNNB1), and estrogen pathways stimulate proliferative growth of developing mouse prostate but how these pathways interact is not fully understood. We previously found that androgens induce CTNNB1 signaling in mouse urogenital sinus (UGS) epithelium from which prostatic ductal epithelium derives. Others have shown that low estradiol concentrations induce UGS epithelial proliferative growth. Here, we found that CTNNB1 signaling overlaps cyclin D1 (CCND1) expression in prostatic buds and we used a genetic approach to test whether CTNNB1 signaling induces CCND1 expression. We observed an unexpected sexually dimorphic response to hyperactive CCNTB1 signaling: in male mouse UGS it increased Ccnd1 mRNA abundance without increasing its protein abundance but in female UGS it increased Ccnd1 mRNA and protein abundance, suggesting a potential role for estrogens in stabilizing CCND1 protein. Treating wild type male UGS explants with androgen and either 17β-estradiol or a proteasome inhibitor increased CCND1 protein and KI67 labeling in prostatic bud epithelium. Together, our results are consistent with an epithelial proliferative growth mechanism linking CTNNB1-driven Ccnd1 transcription and estrogen-mediated CCND1 protein stabilization.

An interdigit signalling centre instructs coordinate phalanx-joint formation governed by 5'Hoxd-Gli3 antagonism

The number of phalanges and joints are key features of digit 'identity' and are central to limb functionality and evolutionary adaptation. Prior chick work indicated that digit phalanges and their associated joints arise in a different manner than the more sparsely jointed long bones, and their identity is regulated by differential signalling from adjacent interdigits. Currently, there is no genetic evidence for this model, and the molecular mechanisms governing digit joint specification remain poorly understood. Using genetic approaches in mouse, here we show that functional 5'Hoxd-Gli3 antagonism acts indirectly, through Bmp signalling from the interdigital mesenchyme, to regulate specification of joint progenitors, which arise in conjunction with phalangeal precursors at the digit tip. Phalanx number, although co-regulated, can be uncoupled from joint specification. We propose that 5'Hoxd genes and Gli3 are part of an interdigital signalling centre that sets net Bmp signalling levels from different interdigits to coordinately regulate phalanx and joint formation.

Manipulating Wnt signaling at different subcellular levels affects the fate of neonatal neural stem/progenitor cells

The canonical Wnt signaling pathway plays an important role in embryogenesis, and the establishment of neurogenic niches. It is involved in proliferation and differentiation of neural progenitors, since elevated Wnt/β-catenin signaling promotes differentiation of neural stem/progenitor cells (NS/PCs¹) towards neuroblasts. Nevertheless, it remains elusive how the differentiation program of neural progenitors is influenced by the Wnt signaling output. Using transgenic mouse models, we found that in vitro activation of Wnt signaling resulted in higher expression of β-catenin protein and Wnt/β-catenin target genes, while Wnt signaling inhibition resulted in the reverse effect. Within differentiated cells, we identified three electrophysiologically and immunocytochemically distinct cell types, whose incidence was markedly affected by the Wnt signaling output. Activation of the pathway suppressed gliogenesis, and promoted differentiation of NS/PCs towards a neuronal phenotype, while its inhibition led to suppressed neurogenesis and increased counts of cells of glial phenotype. Moreover, Wnt signaling hyperactivation resulted in an increased incidence of cells expressing outwardly rectifying K⁺ currents, together with inwardly rectifying Na⁺ currents, a typical current pattern of immature neurons, while blocking the pathway led to the opposite effect. Taken together, our data indicate that the Wnt signaling pathway orchestrates neonatal NS/PCs differentiation towards cells with neuronal characteristics, which might be important for nervous tissue regeneration during central nervous system disorders. Furthermore, the transgenic mouse strains used in this study may serve as a convenient tool to manipulate β-catenin-dependent signaling in neural progenitors in the neonatal brain.

Tcf7l1 protects the anterior neural fold from adopting the neural crest fate

The neural crest (NC) is crucial for the evolutionary diversification of vertebrates. NC cells are induced at the neural plate border by the coordinated action of several signaling pathways, including Wnt/β-catenin. NC cells are normally generated in the posterior neural plate border, whereas the anterior neural fold is devoid of NC cells. Using the mouse model, we show here that active repression of Wnt/β-catenin signaling is required for maintenance of neuroepithelial identity in the anterior neural fold and for inhibition of NC induction. Conditional inactivation of Tcf7l1, a transcriptional repressor of Wnt target genes, leads to aberrant activation of Wnt/β-catenin signaling in the anterior neuroectoderm and its conversion into NC. This reduces the developing prosencephalon without affecting the anterior-posterior neural character. Thus, Tcf7l1 defines the border between the NC and the prospective forebrain via restriction of the Wnt/β-catenin signaling gradient.

The WNT/MYB pathway suppresses KIT expression to control the timing of salivary proacinar differentiation and duct formation

Growth factor signaling is involved in the development of various organs, but how signaling regulates organ morphogenesis and differentiation in a coordinated manner remains to be clarified. Here, we show how WNT signaling controls epithelial morphogenetic changes and differentiation using the salivary gland as a model. Experiments using genetically manipulated mice and organ cultures revealed that WNT signaling at an early stage (E12-E15) of submandibular salivary gland (SMG) development inhibits end bud morphogenesis and differentiation into proacini by suppressing Kit expression through the upregulation of the transcription factor MYB, and concomitantly increasing the expression of distal progenitor markers. In addition, WNT signaling at the early stage of SMG development promoted end bud cell proliferation, leading to duct formation. WNT signaling reduction at a late stage (E16-E18) of SMG development promoted end bud maturation and suppressed duct formation. Thus, WNT signaling controls the timing of SMG organogenesis by keeping end bud cells in an undifferentiated bipotent state.

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.

Excessive Wnt/beta-catenin signaling promotes midbrain floor plate neurogenesis, but results in vacillating dopamine progenitors

The floor plate (FP), a ventral midline structure of the developing neural tube, has differential neurogenic capabilities along the anterior-posterior axis. The midbrain FP, unlike the hindbrain and spinal cord floor plate, is highly neurogenic and produces midbrain dopaminergic (mDA) neurons. Canonical Wnt/beta-catenin signaling, at least in part, is thought to account for the difference in neurogenic capability. Removal of beta-catenin results in mDA progenitor specification defects as well as a profound reduction of neurogenesis. To examine the effects of excessive Wnt/beta-catenin signaling on mDA specification and neurogenesis, we have analyzed a model wherein beta-catenin is conditionally stabilized in the Shh+domain. Here, we show that the Foxa2+/Lmx1a+ domain is extended rostrally in mutant embryos, suggesting that canonical Wnt/beta-catenin signaling can drive FP expansion along the rostrocaudal axis. Although excess canonical Wnt/beta-catenin signaling generally promotes neurogenesis at midbrain levels, less tyrosine hydroxylase (Th)+, mDA neurons are generated, particularly impacting the Substantia Nigra pars compacta. This is likely because of improper progenitor specification. Excess canonical Wnt/beta-catenin signaling causes downregulation of net Lmx1b, Shh and Foxa2 levels in mDA progenitors. Moreover, these progenitors assume a mixed identity to that of Lmx1a+/Lmx1b+/Nkx6-1+/Neurog1+ progenitors. We also show by lineage tracing analysis that normally, Neurog1+ progenitors predominantly give rise to Pou4f1+ neurons, but not Th+ neurons. Accordingly, in the mutant embryos, Neurog1+ progenitors at the midline generate ectopic Pou4f1+ neurons at the expense of Th+ mDA neurons. Our study suggests that an optimal dose of Wnt/beta-catenin signaling is critical for proper establishment of the mDA progenitor character. Our findings will impact embryonic stem cell protocols that utilize Wnt pathway reagents to derive mDA neuron models and therapeutics for Parkinson's disease.

Characterization of Aes nuclear foci in colorectal cancer cells

Amino-terminal enhancer of split (Aes) is a member of Groucho/Transducin-like enhancer (TLE) family. Aes is a recently found metastasis suppressor of colorectal cancer (CRC) that inhibits Notch signalling, and forms nuclear foci together with TLE1. Although some Notch-associated proteins are known to form subnuclear bodies, little is known regarding the dynamics or functions of these structures. Here, we show that Aes nuclear foci in CRC observed under an electron microscope are in a rather amorphous structure, lacking surrounding membrane. Investigation of their behaviour during the cell cycle by time-lapse cinematography showed that Aes nuclear foci dissolve during mitosis and reassemble after completion of cytokinesis. We have also found that heat shock cognate 70 (HSC70) is an essential component of Aes foci. Pharmacological inhibition of the HSC70 ATPase activity with VER155008 reduces Aes focus formation. These results provide insight into the understanding of Aes-mediated inhibition of Notch signalling.

Id2 deletion attenuates Apc-deficient ileal tumor formation

The expression level of inhibitor of DNA binding 2 (Id2) is increased in colorectal carcinomas and is positively correlated with poor prognosis. However, the functional significance of Id2 in intestinal tumorigenesis has not been fully defined using genetic approaches. Here, we show that Id2 promotes ileal tumor initiation in Apc-deficient mice. Expression of Id2 was stimulated by Wnt signaling through the enhancer region of the Id2 promoter at the early stage of tumorigenesis in Apc^+/Δ716 (Apc^Δ716) mice. Genetic depletion of Id2 in Apc^Δ716 mice caused ∼80% reduction in the number of ileal polyps, but had little effect on tumor size. Notably, the lack of Id2 increased the number of apoptotic cells in the normal crypt epithelium of the mice. Furthermore, DNA microarray analysis revealed that the expression level of Max dimerization protein 1 (Mxd1), known as a c-Myc antagonist, was specifically increased by Id2 deletion in the ileal intestinal epithelium of Apc^Δ716 mice. In contrast, the protein level of c-Myc, but not the mRNA level, was decreased by loss of Id2 in these mice. These results indicate that loss of Id2 inhibits tumor initiation by up-regulation of Mxd1 and down-regulation of c-Myc in Apc^Δ716 mice.

Canonical wnt signaling in dendritic cells regulates Th1/Th17 responses and suppresses autoimmune neuroinflammation

Breakdown in immunological tolerance to self-Ags or uncontrolled inflammation results in autoimmune disorders. Dendritic cells (DCs) play an important role in regulating the balance between inflammatory and regulatory responses in the periphery. However, factors in the tissue microenvironment and the signaling networks critical for programming DCs to control chronic inflammation and promote tolerance are unknown. In this study, we show that wnt ligand-mediated activation of β-catenin signaling in DCs is critical for promoting tolerance and limiting neuroinflammation. DC-specific deletion of key upstream (lipoprotein receptor-related protein [LRP]5/6) or downstream (β-catenin) mediators of canonical wnt signaling in mice exacerbated experimental autoimmune encephalomyelitis pathology. Mechanistically, loss of LRP5/6-β-catenin-mediated signaling in DCs led to an increased Th1/Th17 cell differentiation but reduced regulatory T cell response. This was due to increased production of proinflammatory cytokines and decreased production of anti-inflammatory cytokines such as IL-10 and IL-27 by DCs lacking LRP5/6-β-catenin signaling. Consistent with these findings, pharmacological activation of canonical wnt/β-catenin signaling delayed experimental autoimmune encephalomyelitis onset and diminished CNS pathology. Thus, the activation of canonical wnt signaling in DCs limits effector T cell responses and represents a potential therapeutic approach to control autoimmune neuroinflammation.

Promotion of colorectal cancer invasion and metastasis through activation of NOTCH-DAB1-ABL-RHOGEF protein TRIO

We have recently identified a metastasis suppressor gene for colorectal cancer: AES/Aes, which encodes an endogenous inhibitor of NOTCH signaling. When Aes is knocked out in the adenomatous epithelium of intestinal polyposis mice, their tumors become malignant, showing marked submucosal invasion and intravasation. Here, we show that one of the genes induced by NOTCH signaling in colorectal cancer is DAB1/Dab1. Genetic depletion of DAB1 suppresses cancer invasion and metastasis in the NOTCH signaling-activated mice. DAB1 is phosphorylated by ABL tyrosine kinase, which activates ABL reciprocally. Consistently, inhibition of ABL suppresses cancer invasion in mice. Furthermore, we show that one of the targets of ABL is the RAC/RHOGEF protein TRIO, and that phosphorylation at its Tyr residue 2681 (pY2681) causes RHO activation in colorectal cancer cells. Its unphosphorylatable mutation TRIO Y2681F reduces RHOGEF activity and inhibits invasion of colorectal cancer cells. Importantly, TRIO pY2681 correlates with significantly poorer prognosis of patients with colorectal cancer after surgery.

SIGNIFICANCE

These results indicate that TRIO pY2681 is one of the downstream effectors of NOTCH signaling activation in colorectal cancer, and can be a prognostic marker, helping to determine the therapeutic modality of patients with colorectal cancer.

CCR1-mediated accumulation of myeloid cells in the liver microenvironment promoting mouse colon cancer metastasis

To understand colon cancer metastasis, we earlier analyzed a mouse model that developed liver metastasis of cancer cells disseminated from the spleen. We suggested that CCR1(+) bone marrow (BM)-derived cells are recruited to the microenvironment of disseminated colon cancer cells, and produce metalloproteinases MMP9 and MMP2, helping metastatic colonization. In the present study, we have examined these myeloid cells expressing CCR1 and/or MMPs in detail. To this end, we have established bacterial artificial chromosome (BAC)-based transgenic mouse lines in which membrane-targeted Venus fluorescent protein (mVenus) was expressed under the control of Ccr1 gene promoter. Then, myeloid cells obtained from the BM and liver metastatic foci were analyzed by the combination of flow cytometry and cytology/immunohistochemistry, in situ RNA hybridization, or quantitative RT-PCR. We have found four distinct types of myeloid cells recruited to the metastatic foci; neutrophils, eosinophils, monocytes and fibrocytes. These cell types exhibited distinct expression patterns for CCR1, MMP2 and MMP9. Namely, neutrophils found in the early phase of cancer cell dissemination expressed CCR1 exclusively and MMP9 preferentially, whereas fibrocytes accumulated in later phase expressed MMP2 exclusively. Either genetic inactivation of Ccr1 or antibody-mediated neutrophil depletion reduced subsequent recruitment of fibrocytes. The recruitment of CCR1(+) neutrophils in early phase of colon cancer dissemination appears to cause that of fibrocytes in late phase. These results implicate the key role of CCR1 in colon cancer metastasis in this mouse model, and explain why both MMP9 and MMP2 are essential as genetically demonstrated previously. The results also suggest relevant mechanisms in humans.

IKKα promotes intestinal tumorigenesis by limiting recruitment of M1-like polarized myeloid cells

The recruitment of immune cells into solid tumors is an essential prerequisite of tumor development. Depending on the prevailing polarization profile of these infiltrating leucocytes, tumorigenesis is either promoted or blocked. Here, we identify IκB kinase α (IKKα) as a central regulator of a tumoricidal microenvironment during intestinal carcinogenesis. Mice deficient in IKKα kinase activity are largely protected from intestinal tumor development that is dependent on the enhanced recruitment of interferon γ (IFNγ)-expressing M1-like myeloid cells. In IKKα mutant mice, M1-like polarization is not controlled in a cell-autonomous manner but, rather, depends on the interplay of both IKKα mutant tumor epithelia and immune cells. Because therapies aiming at the tumor microenvironment rather than directly at the mutated cancer cell may circumvent resistance development, we suggest IKKα as a promising target for colorectal cancer (CRC) therapy.

Distinct populations within Isl1 lineages contribute to appendicular and facial skeletogenesis through the β-catenin pathway

Isl1 expression marks progenitor populations in developing embryos. In this study, we investigated the contribution of Isl1-expressing cells that utilize the β-catenin pathway to skeletal development. Inactivation of β-catenin in Isl1-expressing cells caused agenesis of the hindlimb skeleton and absence of the lower jaw (agnathia). In the hindlimb, Isl1-lineages broadly contributed to the mesenchyme; however, deletion of β-catenin in the Isl1-lineage caused cell death only in a discrete posterior domain of nascent hindlimb bud mesenchyme. We found that the loss of posterior mesenchyme, which gives rise to Shh-expressing posterior organizer tissue, caused loss of posterior gene expression and failure to expand chondrogenic precursor cells, leading to severe truncation of the hindlimb. In facial tissues, Isl1-expressing cells broadly contributed to facial epithelium. We found reduced nuclear β-catenin accumulation and loss of Fgf8 expression in mandibular epithelium of Isl1(-/-) embryos. Inactivating β-catenin in Isl1-expressing epithelium caused both loss of epithelial Fgf8 expression and death of mesenchymal cells in the mandibular arch without affecting epithelial proliferation and survival. These results suggest a Isl1→β-catenin→Fgf8 pathway that regulates mesenchymal survival and development of the lower jaw in the mandibular epithelium. By contrast, activating β-catenin signaling in Isl1-lineages caused activation of Fgf8 broadly in facial epithelium. Our results provide evidence that, despite its broad contribution to hindlimb mesenchyme and facial epithelium, the Isl1-β-catenin pathway regulates skeletal development of the hindlimb and lower jaw through discrete populations of cells that give rise to Shh-expressing posterior hindlimb mesenchyme and Fgf8-expressing mandibular epithelium.

Excessive Wnt/β-catenin signaling disturbs tooth-root formation

BACKGROUND AND OBJECTIVE

Wingless-type MMTV integration site family (Wnt)/β-catenin signaling plays an essential role in cellular differentiation and matrix formation during skeletal development. However, little is known about its role in tooth-root formation. In a previous study, we found excessive formation of dentin and cementum in mice with constitutive β-catenin stabilization in the dental mesenchyme. In the present study we analyzed the molar roots of these mice to investigate the role of Wnt/β-catenin signaling in root formation in more detail.

MATERIAL AND METHODS

We generated OC-Cre:Catnb(+/lox(ex3)) mice by intercrossing Catnb(+/lox(ex3)) and OC-Cre mice, and we analyzed their mandibular molars using radiography, histomorphometry and immunohistochemistry.

RESULTS

OC-Cre:Catnb(+/lox(ex3)) mice showed impaired root formation. At the beginning of root formation in mutant molars, dental papilla cells did not show normal differentiation into odontoblasts; rather, they were prematurely differentiated and had a disorganized arrangement. Interestingly, SMAD family member 4 was upregulated in premature odontoblasts. In 4-wk-old mutant mice, molar roots were about half the length of those in their wild-type littermates. In contrast to excessively formed dentin in crown, root dentin was thin and hypomineralized in mutant mice. Biglycan and dentin sialophosphoprotein were downregulated in root dentin of mutant mice, whereas dentin matrix protein 1 and Dickkopf-related protein 1 were upregulated. Additionally, ectonucleotide pyrophosphatase/phosphodiesterase 1 was significantly downregulated in the cementoblasts of mutant molars. Finally, in the cementum of mutant mice, bone sialoprotein was downregulated but Dickkopf-related protein 2 was upregulated.

CONCLUSION

These results suggest that temporospatial regulation of Wnt/β-catenin signaling plays an important role in cell differentiation and matrix formation during root and cementum formation.

Coordinated activation of Wnt in epithelial and melanocyte stem cells initiates pigmented hair regeneration

Melanocyte stem cells (McSCs) intimately interact with epithelial stem cells (EpSCs) in the hair follicle bulge and secondary hair germ (sHG). Together, they undergo activation and differentiation to regenerate pigmented hair. However, the mechanisms behind this coordinated stem cell behavior have not been elucidated. Here, we identified Wnt signaling as a key pathway that couples the behavior of the two stem cells. EpSCs and McSCs coordinately activate Wnt signaling at the onset of hair follicle regeneration within the sHG. Using genetic mouse models that specifically target either EpSCs or McSCs, we show that Wnt activation in McSCs drives their differentiation into pigment-producing melanocytes, while EpSC Wnt signaling not only dictates hair follicle formation but also regulates McSC proliferation during hair regeneration. Our data define a role for Wnt signaling in the regulation of McSCs and also illustrate a mechanism for regeneration of complex organs through collaboration between heterotypic stem cell populations.

Ras mutation cooperates with β-catenin activation to drive bladder tumourigenesis

Mutations in the Ras family of proteins (predominantly in H-Ras) occur in approximately 40% of urothelial cell carcinoma (UCC). However, relatively little is known about subsequent mutations/pathway alterations that allow tumour progression. Indeed, expressing mutant H-Ras within the mouse bladder does not lead to tumour formation, unless this is expressed at high levels. The Wnt signalling pathway is deregulated in approximately 25% of UCC, so we examined if this correlated with the activation of MAPK signalling in human UCC and found a significant correlation. To test the functional significance of this association we examined the impact of combining Ras mutation (H-Ras(Q61L) or K-Ras(G12D)) with an activating β-catenin mutation within the mouse bladder using Cre-LoxP technology. Although alone, neither Ras mutation nor β-catenin activation led to UCC (within 12 months), mice carrying both mutations rapidly developed UCC. Mechanistically this was associated with reduced levels of p21 with dependence on the MAPK signalling pathway. Moreover, tumours from these mice were sensitive to MEK inhibition. Importantly, in human UCC there was a negative correlation between levels of p-ERK and p21 suggesting that p21 accumulation may block tumour progression following Ras mutation. Taken together these data definitively show Ras pathway activation strongly cooperates with Wnt signalling to drive UCC in vivo.

beta-Catenin initiates tooth neogenesis in adult rodent incisors

beta-Catenin signaling is required for embryonic tooth morphogenesis and promotes continuous tooth development when activated in embryos. To determine whether activation of this pathway in the adult oral cavity could promote tooth development, we induced mutation of epithelial beta-catenin to a stabilized form in adult mice. This caused increased proliferation of the incisor tooth cervical loop, outpouching of incisor epithelium, abnormal morphology of the epithelial-mesenchymal junction, and enhanced expression of genes associated with embryonic tooth development. Ectopic dental-like structures were formed from the incisor region following implantation into immunodeficient mice. Thus, forced activation of beta-catenin signaling can initiate an embryonic-like program of tooth development in adult rodent incisor teeth.

Investigation of Frizzled-5 during embryonic neural development in mouse

Recent studies revealed that the Wnt receptor Frizzled-5 (Fzd5) is required for eye and retina development in zebrafish and Xenopus, however, its role during mammalian eye development is unknown. In the mouse embryo, Fzd5 is prominently expressed in the pituitary, distal optic vesicle, and optic stalk, then later in the progenitor zone of the developing retina. To elucidate the role of Fzd5 during eye development, we analyzed embryos with a germline disruption of the Fzd5 gene at E10.25, just before embryos die due to defects in yolk sac angiogenesis. We observed severe defects in optic cup morphogenesis and lens development. However, in embryos with conditional inactivation of Fzd5 using Six3-Cre, we observed no obvious early eye defects. Analysis of Axin2 mRNA expression and TCF/LEF-responsive reporter activation demonstrate that Fzd5 does not regulate the Wnt/beta-catenin pathway in the eye. Thus, the function of Fzd5 during eye development appears to be species-dependent.

Chemokine receptor CXCR3 promotes colon cancer metastasis to lymph nodes

Chemokines and their receptors are essential for leukocyte trafficking, and also implicated in cancer metastasis to specific organs. We have recently demonstrated that CXCR3 plays a critical role in metastasis of mouse melanoma cells to lymph nodes. Here, we show that some human colon cancer cell lines express CXCR3 constitutively. We constructed cells that expressed CXCR3 cDNA ('DLD-1-CXCR3'), and compared with nonexpressing controls by rectal transplantation in nude mice. Although both cell lines disseminated to lymph nodes at similar frequencies at 2 weeks, DLD-1-CXCR3 expanded more rapidly than the control in 4 weeks. In 6 weeks, 59% of mice inoculated with DLD1-CXCR3 showed macroscopic metastasis in para-aortic lymph nodes, whereas only 14% of those with the control (P<0.05). In contrast, metastasis to the liver or lung was rare, and unaffected by CXCR3 expression. In clinical colon cancer samples, we found expression of CXCR3 in 34% cases, most of which had lymph node metastasis. Importantly, patients with CXCR3-positive cancer showed significantly poorer prognosis than those without CXCR3, or those expressing CXCR4 or CCR7. These results indicate that activation of CXCR3 with its ligands stimulates colon cancer metastasis preferentially to the draining lymph nodes with poorer prognosis.

Wnt signaling and gastrointestinal tumorigenesis in mouse models

The canonical Wnt signaling plays important roles in embryonic development and tumorigenesis. For the latter, induced mutations in mice have greatly contributed to our understanding of the molecular mechanisms of cancer initiation and progression. Here, I will review recent reports on gastrointestinal cancer model mice, with an emphasis on the roles of the Wnt signal pathway. They include: mouse models for familial adenomatous polyposis; modifying factors that affect mouse intestinal polyposis, including the genes that help cancer progression; Wnt target genes that affect mouse intestinal polyposis; and a mouse model of gastric cancer that mimics Helicobacter pyroli infection.