[Show abstract][Hide abstract] ABSTRACT: Mutations in the APC or β-catenin genes are well established initiators of colorectal cancer (CRC), yet modifiers that facilitate the survival and progression of nascent tumor cells are not well defined. Using genetic and pharmacological approaches in mouse CRC and human CRC 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 CRC with relatively higher levels of CDC42 activity were 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 suggest 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 CRC intervention.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Otic fibrocytes tether the cochlear duct to the surrounding otic capsule but are also critically involved in maintenance of ion homeostasis in the cochlea, thus, perception of sound. The molecular pathways that regulate the development of this heterogenous group of cells from mesenchymal precursors are poorly understood. Here, we identified epithelial Wnt7a and Wnt7b as possible ligands of Fzd-mediated ⎕-catenin (Ctnnb1)-dependent (canonical) Wnt signaling in the adjacent undifferentiated periotic mesenchyme (POM). Mice with a conditional deletion of Ctnnb1 in the POM exhibited a complete failure of fibrocyte differentiation, a severe reduction of mesenchymal cells surrounding the cochlear duct, loss of pericochlear spaces, a thickening and partial loss of the bony capsule and a secondary disturbance of cochlear duct coiling shortly before birth. Analysis at earlier stages revealed that radial patterning of the POM in two domains with highly condensed cartilaginous precursors and more loosely arranged inner mesenchymal cells occurred normally but that proliferation in the inner domain was reduced and cytodifferentiation failed. Cells with mis/overexpression of a stabilized form of Ctnnb1 in the entire POM mesenchyme sorted to the inner mesenchymal compartment and exhibited increased proliferation. Our analysis suggests that Wnt signals from the cochlear duct epithelium are crucial to induce differentiation and expansion of fibrocyte precursor cells. Our findings emphasize the importance of epithelial-mesenchymal signaling in inner ear development.
[Show abstract][Hide abstract] ABSTRACT: Wnt/β-catenin signaling is critical for tissue regeneration. However, it is unclear how β-catenin controls stem cell behaviors to coordinate organized growth. Using live imaging, we show that activation of β-catenin specifically within mouse hair follicle stem cells generates new hair growth through oriented cell divisions and cellular displacement. β-Catenin activation is sufficient to induce hair growth independently of mesenchymal dermal papilla niche signals normally required for hair regeneration. Wild-type cells are co-opted into new hair growths by β-catenin mutant cells, which non-cell autonomously activate Wnt signaling within the neighboring wild-type cells via Wnt ligands. This study demonstrates a mechanism by which Wnt/β-catenin signaling controls stem cell-dependent tissue growth non-cell autonomously and advances our understanding of the mechanisms that drive coordinated regeneration.
[Show abstract][Hide abstract] ABSTRACT: The intestinal epithelium maintains homeostasis by a self-renewal process involving resident stem cells, including Lgr5+ crypt-base columnar (CBC) cells, but core mechanisms and their contributions to intestinal cancer are not fully defined. In this study, we examined an hypothesized role for KLF5, a zinc-finger transcription factor that is critical to maintain the integrity of embryonic and induced pluripotent stem cells, in intestinal stem cell integrity and cancer in the mouse. Klf5 was indispensable for the integrity and oncogenic transformation of intestinal stem cells. In mice, inducible deletion of Klf5 in Lgr5+ stem cells suppressed their proliferation and survival in a manner associated with nuclear localization of ß-catenin, generating abnormal apoptotic cells in intestinal crypts. Moreover, production of lethal adenomas and carcinomas by specific expression of an oncogenic mutant of ß-catenin in Lgr5+ stem cells was suppressed completely by Klf5 deletion in the same cells. Given that activation of the Wnt/ß-catenin pathway is the most frequently altered pathway in human colorectal cancer, our results argue that KLF5 acts as a fundamental core regulator of intestinal oncogenesis at the stem cell level, and they suggest KLF5 targeting as a rational strategy to eradicate stem-like cells in colorectal cancer.
[Show abstract][Hide abstract] ABSTRACT: The regulation of the balance between proliferation and differentiation in the mesenchymal compartment of the lung is largely uncharacterized, unlike its epithelial counterpart. In this study, we determined that miR-142-3p contributes to the proper proliferation of mesenchymal progenitors by controlling the level of WNT signaling. miR-142-3p can physically bind to adenomatous polyposis coli mRNA, functioning to regulate its expression level. In miR-142-3p loss-of-function experiments, proliferation of parabronchial smooth muscle cell progenitors is significantly impaired, leading to premature differentiation. Activation of WNT signaling in the mesenchyme, or Apc loss of function, can both rescue miR-142-3p knockdown. These findings show that in the embryonic lung mesenchyme, the microRNA machinery modulates the level of WNT signaling, adding an extra layer of control in the feedback loop between FGFR2C and β-catenin-mediated WNT signaling.
[Show abstract][Hide abstract] ABSTRACT: The embryonic epicardium is a source of smooth muscle cells and fibroblasts of the coronary vasculature and of the myocardium, but the signaling pathways that control mobilization and differentiation of epicardial cells are only partly known. We aimed to (re-)evaluate the relevance of canonical Wnt-, Hedgehog (Hh)-, Fibroblast growth factor receptor (Fgfr)1/2- and platelet derived growth factor receptor alpha (Pdgfra)-signaling in murine epicardial development.Methods and ResultsWe used a T-box 18 (Tbx18)(cre)-mediated conditional approach to delete and to stabilize, respectively, the downstream mediator of canonical Wnt-signaling, beta-catenin (Ctnnb1), to delete and activate the mediator of Hh-signaling, smoothened (Smo), and to delete Fgfr1/Fgfr2 and Pdgfra in murine epicardial development. We show that epicardial loss of Ctnnb1, Smo or Fgfr1/Fgfr2 does not affect cardiac development whereas loss of Pdgfra prevents differentiation of epicardium-derived cells into mature fibroblasts. Epicardial expression of a stabilized version of Ctnnb1 results in formation of hyperproliferative epicardial cell clusters; epicardial expression of a constitutively active version of Smo leads to epicardial thickening and loss of epicardial mobilization.
Canonical Wnt-, Hh- and Fgfr1/Fgfr2-signaling are dispensable for epicardial development, but Pdgfra-signaling is crucial for differentiation of cardiac fibroblasts from epicardium-derived cells.
Cardiovascular Research 09/2013; · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Müllerian duct differentiation and development into the female reproductive tract is essential for fertility, but mechanisms regulating these processes are poorly understood. WNT signaling is critical for proper development of the female reproductive tract as evident by the phenotypes of Wnt4, Wnt5a, Wnt7a and beta-catenin (Ctnnb1) mutant mice. Here we extend these findings by determining the effects of constitutive CTNNB1 activation within the mesenchyme of the developing M üllerian duct and its differentiated derivatives. This was accomplished by crossing Amhr2-Cre knock-in mice with Ctnnb1 exon (ex) 3(f/f) mice. Amhr2-Cre(Δ/+); Ctnnb1 ex3(f/+) females did not form an oviduct, had smaller uteri, endometrial gland defects, and were infertile. At the cellular level, stabilization of CTNNB1 in the mesenchyme caused alterations within the epithelium, including less proliferation, delayed uterine gland formation, and induction of an epithelial-mesenchymal transition (EMT) event. This EMT event is observed before birth and is complete within five days after birth. Misexpression of estrogen receptor alpha (ESR1) in the epithelia correlated with the EMT before birth, but not after. These studies indicate that regulated CTNNB1 in mesenchyme is important for epithelial cell differentiation during female reproductive tract development.
[Show abstract][Hide abstract] ABSTRACT: Loss of the tumor suppressor SMAD4 correlates with progression of colorectal cancer (CRC). In mice, colon tumors that express CCL9 recruit CCR1(+) myeloid cells, which facilitate tumor invasion and metastasis by secreting matrix metalloproteinase (MMP) 9.
We used human CRC cell lines to investigate the ability of SMAD4 to regulate expression of CCL15, a human ortholog of mouse Ccl9. We used immunohistochemistry to compare levels of CCL15 and other proteins in 141 samples of human liver metastases.
In human CRC cell lines, knockdown of SMAD4 increased CCL15 expression, whereas overexpression of SMAD4 decreased it. SMAD4 bound directly to the promoter region of the CCL15 gene to negatively regulate its expression; transforming growth factor increased binding of SMAD4 to the CCL15 promoter and transcriptional repression. In livers of nude mice, SMAD4-deficient human CRC cells upregulated CCL15 to recruit CCR1(+) cells and promote metastasis. In human tumor samples, there was a strong inverse correlation between levels of CCL15 and SMAD4; metastases that expressed CCL15 contained 3-fold more CCR1(+) cells than those without CCL15. Patients with CCL15(+) metastases had significantly shorter times of disease-free survival than those with CCL15-negative metastases. CCR1(+) cells in the metastases expressed the myeloid cell markers CD11b and myeloperoxidase, and also MMP9.
In human CRC cells, loss of SMAD4 leads to upregulation of CCL15 expression. Human liver metastases that express CCL15 contain higher numbers CCR1(+) cells; patients with these metastases have shorter times of disease-free survival. Reagents designed to block CCL15 recruitment of CCR1(+) cells could prevent metastasis of CRC to liver.
[Show abstract][Hide abstract] ABSTRACT: Adenomyosis is defined by the presence of endometrial glands and stroma within the myometrium. Despite its frequent occurrence, the precise etiology and physiopathology of adenomyosis is still unknown. WNT/β-catenin signaling molecules are important and should be tightly regulated for uterine function. To investigate the role of β-catenin signaling in adenomyosis, the expression of β-catenin was examined. Nuclear and cytoplasmic β-catenin expression was significantly higher in epithelial cells of human adenomyosis compared to control endometrium. To determine if constitutive activation of β-catenin in the murine uterus leads to development of adenomyosis, mice were used which expressed a dominant stabilized β-catenin in the uterus by crossing the PR-Cre mouse with Ctnnb1(f(ex3)/+) mice . Uteri of PR(cre) (/+) Ctnnb1(f(ex3)/+) mice displayed an abnormal irregular structure and highly active proliferation in the myometrium, and subsequently developed adenomyosis. Interestingly, the expression of E-cadherin was repressed in epithelial cells of PR(cre) (/+) Ctnnb1(f(ex3)/+) mice compared to control mice. Repression of E-cadherin is one of the hallmarks of epithelial mesenchymal transition (EMT). The expression of SNAIL and ZEB1 was observed in some epithelial cells of the uterus in PR(cre) (/+) Ctnnb1(f(ex3)/+) mice but not in control mice. Vimentin and COUP-TFII, mesenchymal cell markers, were expressed in some epithelial cells of PR(cre) (/+) Ctnnb1(f(ex3)/+) mice. In human adenomyosis, the expression of E-cadherin was decreased in epithelial cells compared to control endometrium, while CD10, endometrial stromal marker, was expressed in some epithelial cells of human adenomyosis. These results suggest that abnormal activation of β-catenin contributes to adenomyosis development through the induction of EMT.
The Journal of Pathology 06/2013; · 7.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Injury to the adult kidney induces a number of developmental genes thought to regulate repair, including Wnt4. During kidney development, early nephron precursors and medullary stroma both express Wnt4, where it regulates epithelialization and controls smooth muscle fate, respectively. Expression patterns and roles for Wnt4 in the adult kidney, however, remain unclear. In this study, we used reporters, lineage analysis, and conditional knockout or activation of the Wnt/β-catenin pathway to investigate Wnt4 in the adult kidney. Proliferating, medullary, interstitial myofibroblasts strongly expressed Wnt4 during renal fibrosis, whereas tubule epithelia, except for the collecting duct, did not. Exogenous Wnt4 drove myofibroblast differentiation of a pericyte-like cell line, suggesting that Wnt4 might regulate pericyte-to-myofibroblast transition through autocrine signaling. However, conditional deletion of Wnt4 in interstitial cells did not reduce myofibroblast proliferation, cell number, or myofibroblast gene expression during fibrosis. Because the injured kidney expresses multiple Wnt ligands that might compensate for the absence of Wnt4, we generated a mouse model with constitutive activation of canonical Wnt/β-catenin signaling in interstitial pericytes and fibroblasts. Kidneys from these mice exhibited spontaneous myofibroblast differentiation in the absence of injury. Taken together, Wnt4 expression in renal fibrosis defines a population of proliferating medullary myofibroblasts. Although Wnt4 may be dispensable for myofibroblast transformation, canonical Wnt signaling through β-catenin stabilization is sufficient to drive spontaneous myofibroblast differentiation in interstitial pericytes and fibroblasts, emphasizing the importance of this pathway in renal fibrosis.
Journal of the American Society of Nephrology 06/2013; · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Wnt signaling is critical for cell fate specification and cell differentiation in many organs, but its function in pulmonary neuroendocrine cell (PNEC) differentiation has not been fully addressed. In this study, we examined the role of canonical Wnt signaling by targeting the gene for Adenomatous Polyposis Coli (Apc), which controls Wnt signaling activity via mediating phosphorylation of beta-catenin (Ctnnb). Targeting the Apc gene in lung epithelial progenitors by Nkx2.1-cre stabilized Ctnnb and activated canonical Wnt signaling. Apc deficiency altered lung epithelial cell fate by inhibiting Clara and ciliated cell differentiation and activating Uchl1, a marker of neuroendocrine cells. Similar to PNEC in normal lung, Uchl1(positive) cells were innervated. In mice with targeted inactivation of Ctnnb by Nkx2.1-cre, PNEC differentiation was not interrupted. These indicate that, after lung primordium formation, Wnt signaling is not essential for PNEC differentiation; however, its over-activation promotes PNEC features. Interestingly, Nkx2.1 was extinguished in Apc deficient epithelial progenitors before activation of Uchl1. Examination of Nkx2.1 null lungs suggested that early deletion of Nkx2.1 inhibits PNEC differentiation, while late repression does not. Nkx2.1 was specifically inhibited in Apc deficient lungs but not in Ctnnb gain-of-function lungs indicating a functional difference between Apc deletion and Ctnnb stabilization, both of which activate Wnt signaling. Further analysis revealed that Apc deficiency led to increased TGF-beta signaling, which inhibited Nkx2.1 in cultured lung endodermal explants. In contrast, TGF-beta activity was not increased in Ctnnb gain-of-function lungs. Therefore, our studies revealed an important mechanism involving Apc and TGF-beta signaling in regulating the key transcriptional factor, Nkx2.1, for lung epithelial progenitor cell fate determination.
[Show abstract][Hide abstract] ABSTRACT: Fetal prostate development is initiated by androgens and patterned by androgen dependent and independent signals. How these signals integrate to control epithelial cell differentiation and prostatic bud patterning is not fully understood. To test the role of beta-catenin (Ctnnb1) in this process, we used a genetic approach to conditionally delete or stabilize Ctnnb1 in urogenital sinus (UGS) epithelium from which the prostate derives. Two opposing mechanisms of action were revealed. By deleting Ctnnb1, we found it is required for separation of UGS from cloaca, emergence or maintenance of differentiated UGS basal epithelium and formation of prostatic buds. By genetically inducing a patchy subset of UGS epithelial cells to express excess CTNNB1, we found its excess abundance increases Bmp expression and leads to a global impairment of prostatic bud formation. Addition of NOGGIN partially restores prostatic budding in UGS explants with excess Ctnnb1. These results indicate a requirement for Ctnnb1 in UGS basal epithelial cell differentiation, prostatic bud initiation and bud spacing and suggest some of these actions are mediated in part through activation of BMP signaling.
[Show abstract][Hide abstract] ABSTRACT: Prostate cancer is a major cause of male death in the Western world, but few frequent genetic alterations that drive prostate cancer initiation and progression have been identified. β-Catenin is essential for many developmental processes and has been implicated in tumorigenesis in many tissues, including prostate cancer. However, expression studies on human prostate cancer samples are unclear on the role this protein plays in this disease. We have used in vivo genetic studies in the embryo and adult to extend our understanding of the role of β-Catenin in the normal and neoplastic prostate. Our gene deletion analysis revealed that prostate epithelial β-Catenin is required for embryonic prostate growth and branching but is dispensable in the normal adult organ. During development, β-Catenin controls the number of progenitors in the epithelial buds and regulates a discrete network of genes, including c-Myc and Nkx3.1. Deletion of β-Catenin in a Pten deleted model of castration-resistant prostate cancer demonstrated it is dispensable for disease progression in this setting. Complementary overexpression experiments, through in vivo protein stabilization, showed that β-Catenin promotes the formation of squamous epithelia during prostate development, even in the absence of androgens. β-Catenin overexpression in combination with Pten loss was able to drive progression to invasive carcinoma together with squamous metaplasia. These studies demonstrate that β-Catenin is essential for prostate development and that an inherent property of high levels of this protein in prostate epithelia is to drive squamous fate differentiation. In addition, they show that β-Catenin overexpression can promote invasive prostate cancer in a clinically relevant model of this disease. These data provide novel information on cancer progression pathways that give rise to lethal prostate disease in humans.
[Show abstract][Hide abstract] ABSTRACT: Cell-type plasticity within a tumor has recently been suggested to cause a bidirectional conversion between tumor-initiating stem cells and nonstem cells triggered by an inflammatory stroma. NF-κB represents a key transcription factor within the inflammatory tumor microenvironment. However, NF-κB's function in tumor-initiating cells has not been examined yet. Using a genetic model of intestinal epithelial cell (IEC)-restricted constitutive Wnt-activation, which comprises the most common event in the initiation of colon cancer, we demonstrate that NF-κB modulates Wnt signaling and show that IEC-specific ablation of RelA/p65 retards crypt stem cell expansion. In contrast, elevated NF-κB signaling enhances Wnt activation and induces dedifferentiation of nonstem cells that acquire tumor-initiating capacity. Thus, our data support the concept of bidirectional conversion and highlight the importance of inflammatory signaling for dedifferentiation and generation of tumor-initiating cells in vivo.
[Show abstract][Hide abstract] ABSTRACT: There is great interest in tumor stem cells (TSCs) as potential therapeutic targets; however, cancer therapies targeting TSCs are limited. A drawback is that TSC markers are often shared by normal stem cells (NSCs); thus, therapies that target these markers may cause severe injury to normal tissues. To identify a potential TSC-specific marker, we focused on doublecortin-like kinase 1 (Dclk1). Dclk1 was reported as a candidate NSC marker in the gut, but recent reports have implicated it as a marker of differentiated cells (for example, Tuft cells). Using lineage-tracing experiments, we show here that Dclk1 does not mark NSCs in the intestine but instead marks TSCs that continuously produce tumor progeny in the polyps of Apc(Min/+) mice. Specific ablation of Dclk1-positive TSCs resulted in a marked regression of polyps without apparent damage to the normal intestine. Our data suggest the potential for developing a therapy for colorectal cancer based on targeting Dclk1-positive TSCs.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Periodontal Research 10/2012; · 1.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dysregulated WNT/β-catenin signaling in murine testes results in a phenotype with complete germ cell loss that resembles human Sertoli cell-only syndrome. In other systems, including the ovary, dysregulated WNT/β-catenin induces tumorigenesis but no tumors are observed in the mutant testes without deletion of a tumor suppressor, such as phosphatase and tensin homolog (PTEN). Müllerian inhibiting substance (MIS, also known as AMH), a member of the transforming growth factor-β family of growth factors responsible for Müllerian duct regression in fetal males, has been shown to inhibit tumor growth in vitro and in vivo but its role as an endogenous tumor suppressor has never been reported. We have deleted the MIS type 2 receptor (MISR2), and thus MIS signaling, in mice with dysregulated WNT/β-catenin and show that these mice develop testicular stromal tumors with 100% penetrance within a few months postnatal. The tumors are highly proliferative and have characteristics of either Sertoli cell tumors or progenitor Leydig cell tumors based on their marker profiles and histology. Phosphorylated Sma and mothers against decapentaplegic-related homolog 1/5/8 is absent in the tumors and β-catenin target genes are induced. The tumor suppressor TP53 is also highly expressed in the tumors, as is phosphorylated γH2AX, which is indicative of DNA damage. The phenotype of these tumors closely resembles those observed when PTEN is also deleted in mice with dysregulated WNT/β-catenin. Tumorigenesis in these mice provides conclusive evidence that physiological MIS signaling is a tumor suppressor mechanism and suggests that targeted treatment of MISR2-expressing cancers with therapeutic MIS should have a beneficial effect on tumor progression.