Kegg Pathway: Wnt signaling pathway

PLoS One. 2009; 4(7): e6129
Kategaya LS, Changkakoty B, Biechele T, Conrad WH, Kaykas A, Dasgupta R, Moon RT

BACKGROUND: Insights into how the Frizzled/LRP6 receptor complex receives, transduces and terminates Wnt signals will enhance our understanding of the control of the Wnt/ss-catenin pathway. METHODOLOGY/PRINCIPAL FINDINGS: In pursuit of such insights, we performed a genome-wide RNAi screen in Drosophila cells expressing an activated form of LRP6 and a beta-catenin-responsive reporter. This screen resulted in the identification of Bili, a Band4.1-domain containing protein, as a negative regulator of Wnt/beta-catenin signaling. We found that the expression of Bili in Drosophila embryos and larval imaginal discs significantly overlaps with the expression of Wingless (Wg), the Drosophila Wnt ortholog, which is consistent with a potential function for Bili in the Wg pathway. We then tested the functions of Bili in both invertebrate and vertebrate animal model systems. Loss-of-function studies in Drosophila and zebrafish embryos, as well as human cultured cells, demonstrate that Bili is an evolutionarily conserved antagonist of Wnt/beta-catenin signaling. Mechanistically, we found that Bili exerts its antagonistic effects by inhibiting the recruitment of AXIN to LRP6 required during pathway activation. CONCLUSIONS: These studies identify Bili as an evolutionarily conserved negative regulator of the Wnt/beta-catenin pathway.

Endocr J. 2009 Jul 1;
Urano T, Shiraki M, Usui T, Sasaki N, Ouchi Y, Inoue S

Wnt signaling is an important regulator of bone homeostasis. The Wnt co-receptor, namely, low-density lipoprotein receptor-related protein 5 (LRP5), initiates Wnt signal transduction. Recently, we and several other groups have shown that there is a single nucleotide polymorphism (SNP) located in the exon 18 of the LRP5 gene that leads to an amino acid change (3989C > T, A1330V), and is associated with lumbar spine, femoral neck, and radial bone mineral density (BMD), and incidence of fracture. These data suggest that the A1330V variation in the LRP5 gene may affect the pathogenesis of osteoporosis. However, the functional basis of the A1330V variation remains unclear. In the present study, we analyzed the effect of the A1330V variation on Wnt activity. We also investigated the association between this LRP5 SNP and total body BMD using 739 postmenopausal women. LRP5 with the A1330V SNP were transiently coexpressed with Wnt3a in 293T cells and their activity was evaluated by the TCF-Lef reporter assay. In vitro, the TCF-Lef activity in presence of Wnt3a in cells expressing LRP5 and carrying the T allele (Valine at 1330 (V1330)) of exon 18 was significantly reduced as compared to the wild-type allele. The association between the A1330V SNP and total body BMD were replicated in 739 postmenopausal Japanese women (AA vs. VV; P = 0.0026). These data suggest that the V1330 variant in the LRP5 gene decreases Wnt activity, which in turn decreases the BMD.

Development. 2009 Jul 1;
Shaham O, Smith AN, Robinson ML, Taketo MM, Lang RA, Ashery-Padan R

The developing ocular lens provides an excellent model system with which to study the intrinsic and extrinsic cues governing cell differentiation. Although the transcription factors Pax6 and Sox2 have been shown to be essential for lens induction, their later roles during lens fiber differentiation remain largely unknown. Using Cre/loxP mutagenesis, we somatically inactivated Pax6 and Sox2 in the developing mouse lens during differentiation of the secondary lens fibers and explored the regulatory interactions of these two intrinsic factors with the canonical Wnt pathway. Analysis of the Pax6-deficient lenses revealed a requirement for Pax6 in cell cycle exit and differentiation into lens fiber cells. In addition, Pax6 disruption led to apoptosis of lens epithelial cells. We show that Pax6 regulates the Wnt antagonist Sfrp2 in the lens, and that Sox2 expression is upregulated in the Pax6-deficient lenses. However, our study demonstrates that the failure of differentiation following loss of Pax6 is independent of beta-catenin signaling or Sox2 activity. This study reveals that Pax6 is pivotal for initiation of the lens fiber differentiation program in the mammalian eye.

Clin Calcium. 2009 Jul; 19(7): 911-8
Kobayashi T

Treatment of osteoporosis aims to increase bone mass by suppressing bone resorption and/or stimulating bone formation. Among drugs clinically available for treatment of osteoporosis, only PTH stimulates bone formation. However, the mechanism by which PTH promotes bone formation is not clearly understood. PTH signaling in osteoblasts increases osteoblast progenitors. It appears that this effect of PTH is exerted mainly through multiple indirect pathways. Among them, the Wnt signaling pathway is of particular interest because of the strong human genetic evidence that Wnt signaling positively regulates bone mass. Activation of the PTH receptor increases Wnt signaling by down-regulating expression of Dkk1 and sclerostin, endogenous inhibitors for Wnt signaling, and by directly activating LRP6, a Wnt co-receptor. Understanding the mechanisms of the anabolic effect of PTH may lead to development of novel drugs to stimulate bone formation.

Methods Mol Biol. 2009; 542: 363-77
Jeong S, Lee HK, Kim MY

Aptamers are in vitro evolved molecules that bind to target proteins with high affinity and specificity by adapting three-dimensional structures upon binding. Because cancer cells exhibit the activation of signaling pathways that are not usually activated in normal cells, RNA aptamers against such a cancer cell-specific signal can be useful lead molecules for cancer gene therapy. The Wnt/beta-catenin signaling pathway plays important roles in a critical initiating event in the formation of various human cancers. Because mutations in beta-catenin have been found to be responsible for human tumorigenesis, beta-catenin is the molecular target for effective anticancer therapies. Here, we describe the selection of RNA aptamers against beta-catenin/T-Cell Factor (TCF) proteins and their intracellular expression as intramers. The RNA aptamers acted as central inhibitory players for multiple oncogenic functions of beta-catenin in colon cancer cells. These data provide the proof-of-principle for the use of RNA aptamers for an effective anticancer gene therapy.

Cancer. 2009 Jun 26;
Hirata H, Hinoda Y, Nakajima K, Kikuno N, Yamamura S, Kawakami K, Suehiro Y, Tabatabai ZL, Ishii N, Dahiya R

BACKGROUND:: Epigenetic silencing of several wingless-type mouse mammary tumor virus integration site (Wnt) pathway-related genes has been reported in renal cancer. Except for the T-cell factor 4 gene TCF4, there are no reports regarding Wnt pathway gene polymorphisms in renal cancer. Therefore, the authors of this report hypothesized that the polymorphisms in Wnt signaling genes may be risk factors for renal cancer. METHODS:: In total, 210 patients (145 men and 65 women) with pathologically confirmed renal cell carcinoma (RCC) and 200 age-matched and sex-matched control individuals were enrolled in this study. We genotyped 14 single nucleotide polymorphisms (SNPs) in 6 genes. including Dickkopf 2 (DKK2) (reference SNP identification number 17037102 [rs17037102], rs419558, and rs447372), DKK3 (rs3206824, rs11022095, rs1472189, rs7396187, and rs2291599), DKK4 (rs2073664), secreted frizzled-related protein 4 (sFRP4) (rs1802073 and rs1802074), mothers against decapentaplegic homolog (SMAD) family member 7 or SMAD7 (rs12953717), and disheveled associated activator of morphogenesis 2 or DAAM2 (rs6937133 and rs2504106) using polymerase chain reaction-restriction fragment length polymorphism analysis and direct sequencing in the patients with RCC and in the healthy, age-matched control group. The relations also were tested between these polymorphisms and clinicopathologic data, including sex, tumor grade, tumor stage, lymph node involvement, distant metastasis, and overall survival. RESULTS:: A significant decrease in the frequency of the guanine/adenine (G/A) + A/A genotypes in the DKK3 codon 335 rs3206824 was observed in the patients with RCC compared with the control group. The frequency of the rs3206824 (G/A) A-rs7396187 (guanine/cytosine [G/C]) C haplotype was significantly lower in patients with RCC compared with other haplotypes. In addition, DKK3 rs1472189 cytosine/thymine (C/T) was associated with distant metastasis, and, DKK2 rs17037102 G-homozygous patients had a decreased risk for death in multivariate Cox regression analysis. CONCLUSIONS:: To the authors' knowledge, this is the first report documenting that DKK3 polymorphisms are associated with RCC and that the DKK2 rs17037102 polymorphism may be a predictor for survival in patients with RCC after radical nephrectomy. Cancer 2009. (c) 2009 American Cancer Society.

J Cell Biochem. 2009 Jun 26;
Bi Y, Huang J, He Y, Zhu GH, Su Y, He BC, Luo J, Wang Y, Kang Q, Luo Q, Chen L, Zuo GW, Jiang W, Liu B, Shi Q, Tang M, Zhang BQ, Weng Y, Huang A, Zhou L, Feng T, Luu HH, Haydon RC, He TC, Tang N

Wnt/beta-catenin pathway plays an important role in regulating embryonic development. Hepatocytes differentiate from endoderm during development. Hepatic progenitor cells (HPCs) have been isolated from fetal liver and extrahepatic tissues. Most current studies in liver development and hepatic differentiation have been focused on Wnts, beta-catenin, and their receptors. Here, we sought to determine the role of Wnt antagonists in regulating hepatic differentiation of fetal liver-derived HPCs. Using mouse liver tissues derived from embryonic day E12.5 to postnatal day (PD) 28, we found that 13 of the 19 Wnt genes and almost all of Wnt receptors/co-receptors were expressed in most stages. However, Wnt antagonists SFRP2, SFRP3, and Dkk2 were only detected in the early stages. We established and characterized the reversible stable HPCs derived from E14.5 mouse fetal liver (HP14.5). HP14.5 cells were shown to express high levels of early liver progenitor cell markers, but low levels or none of late liver markers. HP14.5 cells were shown to differentiate into mature hepatocytes upon dexamethasone (Dex) stimulation. Dex-induced late marker expression and albumin promoter activity in HP14.5 cells were inhibited by exogenous expression of SFRP3. Furthermore, Dex-induced glycogen synthesis of PAS-positive HP14.5 cells was significantly inhibited by SFRP3. Therefore, our results have demonstrated that the expression of Wnt antagonists decreases as hepatic differentiation progresses, suggesting that a balanced Wnt signaling may be critical during mouse liver development and hepatic differentiation. J. Cell. Biochem. (c) 2009 Wiley-Liss, Inc.

Nat Genet. 2009 Jun 28;
Tuupanen S, Turunen M, Lehtonen R, Hallikas O, Vanharanta S, Kivioja T, Björklund M, Wei G, Yan J, Niittymäki I, Mecklin JP, Järvinen H, Ristimäki A, Di-Bernardo M, East P, Carvajal-Carmona L, Houlston RS, Tomlinson I, Palin K, Ukkonen E, Karhu A, Taipale J, Aaltonen LA

Homozygosity for the G allele of rs6983267 at 8q24 increases colorectal cancer (CRC) risk approximately 1.5 fold. We report here that the risk allele G shows copy number increase during CRC development. Our computer algorithm, Enhancer Element Locator (EEL), identified an enhancer element that contains rs6983267. The element drove expression of a reporter gene in a pattern that is consistent with regulation by the key CRC pathway Wnt. rs6983267 affects a binding site for the Wnt-regulated transcription factor TCF4, with the risk allele G showing stronger binding in vitro and in vivo. Genome-wide ChIP assay revealed the element as the strongest TCF4 binding site within 1 Mb of MYC. An unambiguous correlation between rs6983267 genotype and MYC expression was not detected, and additional work is required to scrutinize all possible targets of the enhancer. Our work provides evidence that the common CRC predisposition associated with 8q24 arises from enhanced responsiveness to Wnt signaling.

Nat Neurosci. 2009 Jun 28;
Hayashi Y, Hirotsu T, Iwata R, Kage-Nakadai E, Kunitomo H, Ishihara T, Iino Y, Kubo T

The molecular mechanism by which neurites are selected for elimination or incorporation into the mature circuit during developmental pruning remains unknown. The trophic theory postulates that local cues provided by target or surrounding cells act to inhibit neurite elimination. However, no widely conserved factor mediating this trophic function has been identified. We found that the developmental survival of specific neurites in Caenorhabditis elegans largely depends on detection of the morphogen Wnt by the Ror kinase CAM-1, which is a transmembrane tyrosine kinase with a Frizzled domain. Mutations in Wnt genes or in cam-1 enhanced neurite elimination, whereas overexpression of cam-1 inhibited neurite elimination in a Wnt-dependent manner. Moreover, mutations in these genes counteracted the effect of a mutation in mbr-1, which encodes a transcription factor that promotes neurite elimination. These results reveal the trophic role of an atypical Wnt pathway and reinforce the classical model of developmental pruning.

Exp Mol Med. 2009 Jun 29;
Jung H, Kim HJ, Lee SK, Kim R, Kopachik W, Han JK, Jho EH

Wnt signaling is known to be important for diverse embryonic and post-natal cellular events and be regulated by the proteins Dishevelled (Dvl) and Axin. Although Dvl is activated by Wnt and involved in signal transduction, it is not clear how Dvl-mediated signaling is turned off. We report that guanine nucleotide binding protein beta 2 (Gnb2; Gb2) bound to Axin and Gb2 inhibited Wnt mediated reporter activity. The inhibition involved reduction of the level of Dvl, and the Gb2g2 mediated reduction of Dvl was countered by increased expression of Axin. Consistent with these effects in HEK293T cells, injection of Gb2g2 into Xenopus embryos inhibited the formation of secondary axes induced either by XWnt8 or Dvl, but not by b-catenin. The DEP domain of Dvl is necessary for both interaction with Gb2g2 and subsequent degradation of Dvl via the lysosomal pathway. signaling induced by Gb2g2 is required because a mutant of Gb2, Gb2(W332A) with lower signaling activity, had reduced ability to downregulate the level of Dvl. Activation of Wnt signaling by either of two methods, increased Frizzled (FZD) signaling or transient transfection of Wnt, also led to increased degradation of Dvl and the induced Dvl loss is dependent on Gb1 and Gb2. Other studies with agents that interfere with phospholipase C (PLC) action and calcium signaling suggested that loss of Dvl is mediated through the following pathway: Wnt/FZD-->Gbg-->PLC-->Ca+2/PKC signaling. Together the evidence suggests a novel negative feedback mechanism in which Gb2g2 inhibits Wnt signaling by degradation of Dvl.

J Biol Chem. 2009 Jun 26;
Qin Y, Li L, Pan W, Wu D

Wnt signaling plays important roles in various physiological and pathophysiological processes. The pathway that leads to beta-catenin stabilization is initiated by Wnt binding to its cell surface receptors, which induces the formation of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] via activation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K) type I. Here, we show that Wnt also stimulated the production of phosphatidylinositol 4-phosphate [PtdIns(4)P], which depended on Frizzled (Fz), Disheveled (Dvl) and phosphatidylinositol 4-kinase (PI4K) type IIalpha in HEK293 cells. Dvl directly interacted with and activated PI4KIIalpha by increasing its Vmax for ATP and PtdIns. In addition, Dvl regulated PI4KIIalpha and PIP5KI via different domains. Moreover, Dvl, PI4KIIalpha and PIP5KI appeared to form a ternary complex upon Wnt3a stimulation. This complex may allow efficient production of PtdIns(4,5)P2 from PtdIns, which is far more abundant than PtdIns(4)P in cells. Therefore, this study provides new insights into the mechanism by which Wnt3a regulates the production of PtdIns(4,5)P2.

BMB Rep. 2009 Jun 30; 42(6): 338-43
Luo X, Li HX, Liu RX, Wu ZS, Yang YJ, Yang GS

The Wnt/beta-catenin signaling pathway alters adipocyte differentiation by inhibiting adipogenic gene expression. beta-catenin plays a central role in the Wnt/beta-catenin signaling pathway. In this study, we revealed that tumour necrosis factor-alpha (TNF-alpha), a potential negative regulator of adipocyte differentiation, inhibits porcine adipogenesis through activation of the Wnt/beta-catenin signaling pathway. Under the optimal concentration of TNF-alpha, the intracellular beta-catenin protein was stabilized. Thus, the intracellular lipid accumulation of porcine preadipocyte was suppressed and the expression of important adipocyte marker genes, including peroxisome proliferator-activated receptor-gamma (PPARgamma) and CCAAT/enhancer binding protein-alpha (C/EBPalpha), were inhibited. However, a loss of beta-catenin in porcine preadipocytes enhanced the adipogenic differentiation and attenuated TNF-alpha induced anti-adipogenesis. Taken together, this study indicated that TNF-alpha inhibits adipogenesis through stabilization of beta-catenin protein in porcine preadipocytes. [BMB reports 2009; 42(6): 338-343].

PLoS One. 2009; 4(6): e6067
Guo X, Mak KK, Taketo MM, Yang Y

Sequential proliferation, hypertrophy and maturation of chondrocytes are required for proper endochondral bone development and tightly regulated by cell signaling. The canonical Wnt signaling pathway acts through beta-catenin to promote chondrocyte hypertrophy whereas PTHrP signaling inhibits it by holding chondrocytes in proliferating states. Here we show by genetic approaches that chondrocyte hypertrophy and final maturation are two distinct developmental processes that are differentially regulated by Wnt/beta-catenin and PTHrP signaling. Wnt/beta-catenin signaling regulates initiation of chondrocyte hypertrophy by inhibiting PTHrP signaling activity, but it does not regulate PTHrP expression. In addition, Wnt/beta-catenin signaling regulates chondrocyte hypertrophy in a non-cell autonomous manner and Gdf5/Bmp signaling may be one of the downstream pathways. Furthermore, Wnt/beta-catenin signaling also controls final maturation of hypertrophic chondrocytes, but such regulation is PTHrP signaling-independent.

Mol Endocrinol. 2009 Jun 25;
Wang L, Gesty-Palmer D, Fields TA, Spurney RF

Activation of Wnt signaling pathways causes release and stabilization of the transcription regulator beta-catenin from a destruction complex composed of axin and the adenomatous polyposis coli (APC) protein (canonical signaling pathway). Assembly of this complex is facilitated by a protein-protein interaction between APC and an RGS domain in axin. Because GRK2 has a RGS domain that is closely related to the RGS domain in axin, we determined if GRK2 regulated canonical signaling. We found that GRK2 inhibited Wnt1-induced activation of a reporter construct as well as reduced Wnt3a-dependent stabilization and nuclear translocation of beta-catenin. GRK2 enzymatic activity was required for this negative regulatory effect, and depletion of endogenous GRK2 using siRNA enhanced canonical signaling. GRK2-dependent inhibition of canonical signaling is relevant to osteoblast (OB) biology because overexpression of GRK2 attenuated Wnt/beta-catenin signaling in calvarial OBs. Co-immunoprecipitation studies found that: 1. GRK2 bound APC, 2. The GRK2-APC interaction was promoted by GRK2 enzymatic activity, and 3. Deletion of the RGS domain in GRK2 prevented both the GRK2-APC interaction and GRK2-dependent inhibition of canonical signaling. These data suggest that: 1. GRK2 negatively regulates Wnt signaling, 2. GRK2-dependent inhibition of canonical signaling requires a protein-protein interaction between the RGS domain in GRK2 and APC, and 3. Enzymatic activity promotes the GRK2-APC interaction and is required for the negative regulatory effect on canonical signaling. We speculate that inhibiting GRK2 activity in bone forming OBs might be a useful therapeutic strategy for increasing bone mass.

Mol Endocrinol. 2009 Jun 25;
Liu S, Tang W, Fang J, Ren J, Li H, Xiao Z, Quarles LD

We used gene array analysis of cortical bone to identify Phex-dependent gene transcripts associated with abnormal Fgf23 production and mineralization in Hyp mice. We found evidence that elevation of Fgf23 expression in osteocytes is associated with increments in Fgf1, Fgf7, and Egr2 and decrements in Sost, an inhibitor in the Wnt-signaling pathway were observed in Hyp bone. beta-catenin levels were increased in Hyp cortical bone and Topflash luciferase reporter assay showed increased transcriptional activity in Hyp-derived osteoblasts, consistent with Wnt activation. Moreover, activation of Fgf and Wnt-signaling stimulated Fgf23 promoter activity in osteoblasts. We also observed reductions in Bmp1, a metalloproteinase that metabolizes the extracellular matrix protein Dmp1. In addition, we found that the Pcsk5 and the glycosyltransferase Galnt3 were decreased in Hyp bone, suggesting that reduced post-translational processing of FGF23 may also contribute to increased Fgf23 levels in Hyp mice. With regards to mineralization, we identified additional candidates to explain the intrinsic mineralization defect in Hyp osteoblasts, including increases in the mineralization inhibitors Mgp and Thbs4, as well as increases in local pH altering factors, carbonic anhydrase 12 (Car12) and 3 (Car3) and the sodium-dependent citrate transporter (Slc13a5). These studies demonstrate the complexity of gene expression alterations in bone that accompanies inactivating Phex mutations and identify novel pathways that may coordinate Fgf23 expression and mineralization of extracellular matrix in Hyp bone.

Dev Biol. 2009 Jun 22;
Roche DD, Liu KJ, Harland RM, Monsoro-Burq AH

The organization of the embryonic neural plate requires coordination of multiple signal transduction pathways, including fibroblast growth factors (FGFs), bone morphogenetic proteins (BMPs), and Wnts. Many studies have suggested that a critical component of this process is the patterning of posterior neural tissues by an FGF-caudal signaling cascade. Here, we have identified a novel player, Dazap2, and show that it is required in vivo for posterior neural fate. Loss of Dazap2 in embryos resulted in diminished expression of hoxb9 with a concurrent increase in the anterior marker otx2. Furthermore, we found that Dazap2 is required for FGF dependent posterior patterning; surprisingly, this is independent of Cdx activity. Furthermore, in contrast to FGF activity, Dazap2 induction of hoxb9 is not blocked by loss of canonical Wnt signaling. Functionally, we found that increasing Dazap2 levels alters neural patterning and induces posterior neural markers. This activity overcomes the anteriorizing effects of noggin, and is downstream of FGF receptor activation. Our results strongly suggest that Dazap2 is a novel and essential branch of FGF-induced neural patterning.

J Biol Chem. 2009 Jun 24;
Di Pasquale E, Brivanlou AH

BMP15 belongs to an unusual subgroup of the TGFbeta superfamily of signaling ligands as it lacks a key cystein residue in the mature region required for proper intermolecular dimerization. Naturally occurring BMP15 mutation leads to early ovarian failure in humans, and BMP15 has been shown to activate the Smad1/5/8 pathway in that context. Despite its important role in germ cell specification, the embryological function of BMP15 remains unknown. Surprisingly, we find that during early Xenopus embryogenesis BMP15 acts solely as an inhibitor of the Smad1/5/8 pathway, and the Wnt pathway. BMP15 gain-of-function leads to embryos with secondary ectopic heads, and to direct neural induction in intact explants. BMP15 inhibits BMP4-mediated epidermal induction in dissociated explants. BMP15 strongly inhibits BRE response induced by BMP4, and blocks phosphorylation, and activation of Smad1/5/8 MH2-domain. Mechanistically, BMP15 protein specifically interacts with BMP4 protein, suggesting inhibition upstream of receptor binding. Loss-of-function experiments using, morpholinos, or a naturally occurring human BMP15 dominant-negative mutant (BMP15-Y235C) leads to embryos lacking head. BMP15-Y235C also eliminates the inhibitory activity of BMP15 on BRE. Finally, we show that BMP15 inhibits the canonical branch of the Wnt pathway, upstream of beta-catenin. We thus demonstrate that BMP15 is necessary and sufficient for the specification of dorso-anterior structures, and highlight a novel mechanisms of BMP15 function that strongly suggest a re-interpretation of its function in ovaries specially for ovarian failure.

Biol Reprod. 2009 Jun 24;
Chang H, Guillou F, Taketo MM, Behringer RR

Overactive Wnt/beta-catenin signaling has been found in many forms of cancer in human patients. Mouse models with mutations in different components of the Wnt/beta-catenin signaling pathway have been generated to mimic tumorigenesis in humans. While mice with mutations that result in overactive Wnt/beta-catenin signaling developed tumors in some tissues, such as digestive tract, skin and ovary, they failed to develop tumors in other tissues, such as mammary gland, liver, kidney and primordial germ cells. To investigate whether overactive beta-catenin signaling is capable of inducing Sertoli cell tumorigenesis in testes, we generated Ctnnb1(tm1Mmt/+);Tg(AMH-cre)1Flor male mice that express a constitutively active form of beta-catenin specifically in Sertoli cells. While no tumors were observed at 4 mo of age, 70% of the mutant males developed Sertoli cell tumor at 8 mo of age. At one year of age, more than 90% of the mutant males developed tumors. No instances of extratesticular spread of the tumors were found in the mutant mice. These studies show a causal link between overactive Wnt/beta-catenin signaling and Sertoli cell tumor development and provide a novel mouse model for the study of Sertoli cell tumor biology.

Development. 2009 Jun 24;
Westenskow P, Piccolo S, Fuhrmann S

The retinal pigment epithelium (RPE) consists of a monolayer of cuboidal, pigmented cells that is located between the retina and the choroid. The RPE is vital for growth and function of the vertebrate eye and improper development results in congenital defects, such as microphthalmia or anophthalmia, or a change of cell fate into neural retina called transdifferentiation. The transcription factors microphthalmia-associated transcription factor (Mitf) and orthodenticle homolog 2 (Otx2) are crucial for RPE development and function; however, very little is known about their regulation. Here, by using a Wnt-responsive reporter, we show that the Wnt/beta-catenin pathway is activated in the differentiating mouse RPE. Cre-mediated, RPE-specific disruption of beta-catenin after the onset of RPE specification causes severe defects, resulting in microphthalmia with coloboma, disturbed lamination, and mislocalization of adherens junction proteins. Upon beta-catenin deletion, the RPE transforms into a multilayered tissue in which the expression of Mitf and Otx2 is downregulated, while retina-specific gene expression is induced, which results in the transdifferentiation of RPE into retina. Chromatin immunoprecipitation (ChIP) and luciferase assays indicate that beta-catenin binds near to and activates potential TCF/LEF sites in the Mitf and Otx2 enhancers. We conclude that Wnt/beta-catenin signaling is required for differentiation of the RPE by directly regulating the expression of Mitf and Otx2. Our study is the first to show that an extracellular signaling pathway directly regulates the expression of RPE-specific genes such as Mitf and Otx2, and elucidates a new role for the Wnt/beta-catenin pathway in organ formation and development.

Cancer Res. 2009 Jun 23;
Dimeo TA, Anderson K, Phadke P, Feng C, Perou CM, Naber S, Kuperwasser C

The establishment of metastasis depends on the ability of cancer cells to acquire a migratory phenotype combined with their capacity to recreate a secondary tumor in a distant tissue. In epithelial cancers, such as those of the breast, the epithelial-mesenchymal transition (EMT) is associated with basal-like breast cancers, generates cells with stem-like properties, and enables cancer cell dissemination and metastasis. However, the molecular mechanism(s) that connects stem cell-like characteristics with EMT has yet to be defined. Using an orthotopic model of human breast cancer metastasis to lung, we identified a poor prognosis gene signature, in which several components of the Wnt signaling pathway were overexpressed in early lung metastases. The Wnt genes identified in this signature were strongly associated with human basal-like breast cancers. We found that inhibiting Wnt signaling through LRP6 reduced the capacity of cancer cells to self-renew and seed tumors in vivo. Furthermore, inhibition of Wnt signaling resulted in the reexpression of breast epithelial differentiation markers and repression of EMT transcription factors SLUG and TWIST. Collectively, these results provide a molecular link between self-renewal, EMT, and metastasis in basal-like breast cancers. [Cancer Res 2009;69(13):5364-73].