Wnt signalling sees spots

Formin Binding Protein 1 (FNBP1) regulates non-canonical Wnt signaling and vertebrate gastrulation

The Formin protein Daam1 is required for Wnt-induced cytoskeletal changes during gastrulation, though how it accomplishes this remains unresolved. Here we report the characterization of Formin Binding Protein 1 (FNBP1) as a binding partner of Daam1. The interaction of Daam1 with FNBP1 and its domains required for this interaction were delineated. Immunofluorescence studies showed FNBP1 co-localizes with Daam1, and is an integral component of the actin cytoskeletal complex that is responsive to Wnt stimulation. Specifically, FNBP1 can induce intracellular tubule-like structures and localize to focal adhesions suggesting a role for FNBP1 in cell migration. Functional FNBP1 studies in Xenopus embryos uncover a critical role for FNBP1 in regulating vertebrate gastrulation. Additionally, suboptimal doses of Daam1 and FNBP1 synergize to produce severe gastrulation defects, indicating FNBP1 and Daam1 may function within the same signaling pathway. These results together show FNBP1 is an integral component of Daam1-regulated non-canonical Wnt signaling required for vertebrate gastrulation.

Millet seed oil activates β-catenin signaling and promotes hair growth

Alopecia, regardless of gender, exacerbates psychological stress in those affected. The rising prevalence of alopecia has fueled a research interest in preventing hair loss. This study investigates the potential of millet seed oil (MSO) in promoting the proliferation of hair follicle dermal papilla cells (HFDPC) and stimulating hair growth in animals with testosterone-dependent hair growth inhibition as part of a study on dietary treatments to improve hair growth. MSO-treated HFDPC significantly increased cell proliferation and phosphorylation of AKT, S6K1, and GSK3β proteins. This induces β-catenin, a downstream transcription factor, to translocate to the nucleus and increase the expression of factors related to cell growth. In a C57BL/6 mice model in which hair growth was inhibited by subcutaneous testosterone injection after shaving the dorsal skin, oral administration of MSO stimulated hair growth in the subject mice by increasing the size and number of hair follicles. These results suggest that MSO is a potent agent that may help prevent or treat androgenetic alopecia by promoting hair growth.

Dihydrotestosterone Regulates Hair Growth Through the Wnt/β-Catenin Pathway in C57BL/6 Mice and In Vitro Organ Culture

Dihydrotestosterone (DHT) is the most potent androgen that regulates hair cycling. Hair cycling involves cross-talk between the androgen and Wnt/β-catenin pathways. However, how DHT regulates hair follicle (HF) growth through the Wnt/β-catenin pathway has not been well investigated. This study aimed to investigate the roles of DHT in hair growth in vivo and in vitro. Human scalp HFs were treated with different concentrations of DHT (10^-5, 10^-6, 10^-7, 10^-8, and 10^-9 mol/L) for 10 days. The effects of DHT on hair shaft elongation, the proliferation of hair matrix cells, and the levels of β-catenin, GSK-3β, and phosphorylated GSK-3β (ser9) were evaluated in the cultured HFs. The effects of DHT were further investigated in C57BL/6 mice. Moreover, the growth of cultured human HFs was observed after interfering with the β-catenin pathway through inhibitors or activators in the presence or absence of DHT. We found that different concentrations of DHT had different effects on human HFs in vitro and C57BL/6 mice. At 10^-6 mol/L, DHT inhibited HF growth and β-catenin/p-GSK-3β expression, whereas 10^-7 mol/L DHT induced HF growth and β-catenin/p-GSK-3β expression. In addition, a β-catenin inhibitor (21H7) inhibited HF growth in vitro, while a β-catenin activator (IM12) promoted HF growth in vitro and antagonized the inhibition of HFs by high levels of DHT. These results suggest that DHT plays a pivotal role in region-specific hair growth, which may be related to the Wnt/β-catenin pathway.

LZTS2 and PTEN collaboratively regulate ß-catenin in prostatic tumorigenesis

The leucine zipper tumor suppressor 2 (LZTS2) was identified as a tumor susceptibility gene within the 10q24.3 chromosomal region, and is approximately 15Mb from the PTEN locus. This region containing the both loci is frequently deleted in a variety of human malignancies, including prostate cancer. LZTS2 is a ß-catenin-binding protein and a negative regulator of Wnt signaling. Overexpression of PTEN in prostate cancer cell lines reduces ß-catenin-mediated transcriptional activity. In this study, we examined the collaborative effect of PTEN and LZTS2 using multiple in vitro and in vivo approaches. Co-expression of PTEN and LZTS2 in prostate cancer cells shows stronger repressive effect on ß-catenin mediated transcription. Using a newly generated mouse model, we further assessed the effect of simultaneous deletion of Pten and Lzts2 in the murine prostate. We observed that mice with both Lzts2 and Pten deletion have an earlier onset of prostate carcinomas as well as an accelerated tumor progression compared to mice with Pten or Lzts2 deletion alone. Immunohistochemical analyses show that atypical and tumor cells from compound mice with both Pten and Lzts2 deletion are mainly composed of prostate luminal epithelial cells and possess higher levels of cytoplasmic and nuclear β-catenin. These cells also exhibit a higher proliferative capacity than cells isolated from single deletion mice. These data demonstrate the significance of simultaneous Pten and Lzts2 deletion in oncogenic transformation in prostate cells and implicates a new mechanism for the dysregulation of Wnt/β-catenin signaling in prostate tumorigenesis.

Efficient cardiomyogenic differentiation of bone marrow mesenchymal stromal cells by combination of Wnt11 and bone morphogenetic protein 2

Wnt11 and bone morphogenetic protein 2 (BMP-2) are key signaling factors for stem cell differentiation into functional cardiomyocytes (CMs). In this study, we elucidate the biological effect of BMP-2 and Wnt11 on bone marrow mesenchymal stromal cells (BM-MSCs) that differentiate into myocardial-like cells in a simulated myocardial microenvironment in vitro. A cell co-culture system was established with recombinant Wnt11 treatment of NIH/3T3 cells and CMs. BMP-2 was added in a diverse schedule to induce cardiomyogenic differentiation of BM-MSCs co-cultured under various conditions. The levels of cardiac-specific markers Nkx2.5, α-myosin heavy chain ( α-MHC), β-myosin heavy chain ( β-MHC) and cardiac troponin I (cTnI) were determined by reverse transcriptase polymerase chain reaction and immunocytochemistry to evaluate cardiomyogenic differentiation. Wnt11 or BMP-2 used on their own to differentiate BM-MSCs resulted in no expression of α-MHC and cTnI. Wnt11 alone in a myocardial microenvironment enhanced cardiomyogenic differentiation. BMP-2 demonstrated a dose-dependent effect on BM-MSC differentiation into myocardial-like cells. Addition of BMP to BM-MSCs at various time points resulted in varying effects on cardiomyogenic differentiation. The combination of Wnt11 and BMP-2 treatment in a temporal manner significantly enhanced cardiomyogenic differentiation of BM-MSCs, with high expressions of α-MHC, β-MHC, Nkx2.5 and cTnI upon co-culture with CMs. Our study demonstrates that the combination of Wnt11 and BMP-2 effectively promotes cardiomyogenic differentiation of BM-MSCs in vitro. The synergistic effect of Wnt11 and BMP-2 on the cardiomyogenic differentiation of BM-MSCs is further enhanced in a myocardial microenvironment.

Wnt3-frizzled 1 chimera as a model to study canonical Wnt signaling

Wnt proteins initiate signaling by binding to seven transmembrane spanning receptors of the frizzled (Fz) family together with the members of the low-density lipoprotein receptor-related protein (LRP) 5 and 6. A chimera of human Wnt3 and Fz1 receptor was developed that efficiently activated the TCF-luciferase reporter. Deletion of the cytoplasmic tail and point mutations in the PDZ binding region in the chimera resulted in the loss of Wnt signaling, suggesting a critical role for the Fz cytoplasmic region in Wnt signaling. The Fz CRD is also critical for Wnt signaling, as a deletion of 29 amino acids in the 2nd cysteine loop resulted in the total loss of TCF-luciferase activation. DKK-1 protein blocks upregulation of the TCF-luciferase reporter by the Wnt3-Fz1 chimera, suggesting involvement of LRP in Wnt3-Fz1 signaling. Expression of a Wnt3-Fz1 chimera in C3H10T1/2 cells resulted in the upregulation of alkaline phosphatase activity and inhibition of adipocyte formation, demonstrating that the Wnt3-Fz1 chimera is a potent activator of differentiation of C3H10T1/2 cells into osteoblasts and an inhibitor of their differentiation into the adipocyte lineage. In summary, the Wnt-Fz chimera approach has the potential to better our understanding of the mechanism of Wnt action and its role, particularly in stem cell differentiation. In addition, this methodology can be utilized to identify inhibitors of either Wnt, Fz or interactors of the canonical pathway, which may have potential therapeutic value in the treatment of cancers and other diseases.

Xenopus Wntless and the retromer complex cooperate to regulate XWnt4 secretion

Wnt signaling is implicated in a variety of developmental and pathological processes. The molecular mechanisms governing the secretion of Wnt ligands remain to be elucidated. Wntless, an evolutionarily conserved multipass transmembrane protein, is a dedicated secretion factor of Wnt proteins that participates in Drosophila melanogaster embryogenesis. In this study, we show that Xenopus laevis Wntless (XWntless) regulates the secretion of a specific Wnt ligand, XWnt4, and that this regulation is specifically required for eye development in Xenopus. Moreover, the Retromer complex is required for XWntless recycling to regulate the XWnt4-mediated eye development. Inhibition of Retromer function by Vps35 morpholino (MO) resulted in various Wnt deficiency phenotypes, affecting mesoderm induction, gastrulation cell movements, neural induction, neural tube closure, and eye development. Overexpression of XWntless led to the rescue of Vps35 MO-mediated eye defects but not other deficiencies. These results collectively suggest that XWntless and the Retromer complex are required for the efficient secretion of XWnt4, facilitating its role in Xenopus eye development.

Osteosarcoma development and stem cell differentiation

Osteosarcoma is the most common nonhematologic malignancy of bone in children and adults. The peak incidence occurs in the second decade of life, with a smaller peak after age 50. Osteosarcoma typically arises around the growth plate of long bones. Most osteosarcoma tumors are of high grade and tend to develop pulmonary metastases. Despite clinical improvements, patients with metastatic or recurrent diseases have a poor prognosis. Here, we reviewed the current understanding of human osteosarcoma, with an emphasis on potential links between defective osteogenic differentiation and bone tumorigenesis. Existing data indicate osteosarcoma tumors display a broad range of genetic and molecular alterations, including the gains, losses, or arrangements of chromosomal regions, inactivation of tumor suppressor genes, and the deregulation of major signaling pathways. However, except for p53 and/or RB mutations, most alterations are not constantly detected in the majority of osteosarcoma tumors. With a rapid expansion of our knowledge about stem cell biology, emerging evidence suggests osteosarcoma should be regarded as a differentiation disease caused by genetic and epigenetic changes that interrupt osteoblast differentiation from mesenchymal stem cells. Understanding the molecular pathogenesis of human osteosarcoma could ultimately lead to the development of diagnostic and prognostic markers, as well as targeted therapeutics for osteosarcoma patients.

Bone morphogenetic protein signaling inhibits hair follicle anagen induction by restricting epithelial stem/progenitor cell activation and expansion

Epithelial stem cells (EP-SCs) located in the bulge region of a hair follicle (HF) have the potential to give rise to hair follicle stem/progenitor cells that migrate down to regenerate HFs. Bone morphogenetic protein (BMP) signaling has been shown to regulate the HF cycle by inhibiting anagen induction. Here we show that active BMP signaling functions to prevent EP-SC activation and expansion. Dynamic expression of Noggin, a BMP antagonist, releases EP-SCs from BMP-mediated restriction, leading to EP-SC activation and initiation of the anagen phase. Experimentally induced conditional inactivation of the BMP type IA receptor (Bmpr1a) in EP-SCs leads to overproduction of HF stem/progenitor cells and the eventual formation of matricomas. This genetic manipulation of the BMP signaling pathway also reveals unexpected activation of beta-catenin, a major mediator of Wnt signaling. We propose that BMP activity controls the HF cycle by antagonizing Wnt/beta-catenin activity. This is at least partially achieved by BMP-mediated enhancement of transforming growth factor-beta-regulated epithelial cell-specific phosphatase (PTEN) function. Subsequently, PTEN, through phosphatidyl inositol 3-kinase-Akt, inhibits the activity of beta-catenin, the convergence point of the BMP and Wnt signaling pathways.

Differentiation-inducing factor-1 alters canonical Wnt signaling and suppresses alkaline phosphatase expression in osteoblast-like cell lines

Because DIF-1 has been shown to affect Wnt/beta-catenin signaling pathway, the effects of DIF-1 on osteoblast-like cell lines, SaOS-2 and MC3T3-E1, were examined. We found that DIF-1 inhibited this pathway, resulting in the suppression of ALP promoter activity through the TCF/LEF binding site.

INTRODUCTION

Differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium, inhibits cell proliferation and induces cell differentiation in several mammalian cells. Previous studies showed that DIF-1 activated glycogen synthase kinase-3beta, suggesting that this chemical could affect the Wnt/beta-catenin signaling pathway. This pathway has been shown to be involved in bone biology.

MATERIALS AND METHODS

We studied the effects of DIF-1 on SaOS-2 and MC3T3-E1, osteosarcoma cell lines widely used as a model system for ostoblastic cells and murine osteoblast-like cell line, respectively. Reporter gene assays were also carried out to examine the effect of DIF-1 on the Wnt/beta-catenin signaling pathway.

RESULTS

DIF-1 inhibited SaOS-2 proliferation and reduced alkaline phosphatase (ALP) activity in a concentration- and a time-dependent manner. The expression of ALP was markedly suppressed by DIF-1-treatment in protein and mRNA levels. DIF-1 also suppressed the expression of other osteoblast differentiation markers, including core binding factor alpha1, type I collagen, and osteocalcin, in protein and mRNA levels and inhibited osteoblast-mediated mineralization. Subsequently, we examined the effect of DIF-1 on the Wnt/beta-catenin signaling pathway. We found that DIF-1 suppressed the expression of beta-catenin protein and the activity of the reporter gene containing T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) consensus binding sites. We examined the effect of DIF-1 on a reporter gene driven by the human ALP promoter and found that DIF-1 significantly reduced the ALP reporter gene activity through the TCF/LEF binding site (-1023/-1017 bp). Furthermore, the effect of DIF-1 on MC3T3-E1, a murine osteoblast-like cell line, was examined, and it was found that DIF-1 suppressed ALP mRNA expression by the reduction of the ALP reporter gene activity through the TCF/LEF binding site.

CONCLUSIONS

Our data suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of ALP promoter activity. To our knowledge, this is the first report to analyze the role of the TCF/LEF binding site (-1023/-1017 bp) of the ALP gene promoter in osteoblast-like cell lines.

Differentiation-inducing factor-1 suppresses gene expression of cyclin D1 in tumor cells

To determine the mechanism by which differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium discoideum, inhibits tumor cell proliferation, we examined the effect of DIF-1 on the gene expression of cyclin D1. DIF-1 strongly reduced the expression of cyclin D1 mRNA and correspondingly decreased the amount of beta-catenin in HeLa cells and squamous cell carcinoma cells. DIF-1 activated glycogen synthase kinase-3beta (GSK-3beta) and inhibition of GSK-3beta attenuated the DIF-1-induced beta-catenin degradation, indicating the involvement of GSK-3beta in this effect. Moreover, DIF-1 reduced the activities of T-cell factor (TCF)/lymphoid enhancer factor (LEF) reporter plasmid and a reporter gene driven by the human cyclin D1 promoter. Eliminating the TCF/LEF consensus site from the cyclin D1 promoter diminished the effect of DIF-1. These results suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of cyclin D1 promoter activity.

Dvl2 silencing in postdevelopmental cells results in aberrant cell membrane activity and actin disorganization

The upstream events by which endothelial cells perceive the necessity for migration and how this signal results in coordinated movement is unknown. The synchrony underlying these events shares parallels to events occurring during the movement of tissues in embryogenesis. While Wnt signaling is an important pathway in development, components of the cascade exist in postdevelopment endothelial cells. The objective of this study was to determine whether Dishevelled, a key modulation protein in canonical and PCP-CE Wnt signaling was present in endothelium and its potential function. Western blots of cell lysates and immunolabeling studies confirmed that Dishevelled 2 (Dvl2) is an abundant phosphoprotein in endothelial cells. Dvl2 was localized within the cytoplasm of cells as either F-actin-free or F-actin-associated. The disappearance of F-actin-free Dvl2 in vesicle-like organelles and targeting of actin filaments correlated with a loss in cell motility. Gene silencing of Dishevelled by siRNA duplexes resulted in cells with aberrant membrane activity and an inability to extend lamellipodia. Underlying these abnormalities was a disorganization of the actin filament system, including loss of actin-rich densities, indistinct stress fibers and an accompanying increase in diffuse and aggregate cytoplasmic actin. This study represents the first documentation of Dvl2 in postdevelopmental endothelial cells and its possible role in cell migration via manipulation of actin filament bundles.

Wnt3a growth factor induces androgen receptor-mediated transcription and enhances cell growth in human prostate cancer cells

The Wnt signaling pathway plays a critical role in embryogenesis and tumorigenesis. However, biological roles of Wnt growth factors have not been fully characterized in prostate development and the pathogenesis of prostate cancer. In this study, we used Wnt3a-conditioned medium (Wnt3a-CM) and purified Wnt3a proteins to investigate whether there is a direct effect of Wnt3a on androgen receptor (AR)-mediated transcription and to determine its role in the growth of prostate cancer cells. We demonstrated that Wnt3a-CM either induces AR activity in the absence of androgens or enhances AR activity in the presence of low concentrations of androgens, whereas purified Wnt3a showed a pronounced effect in the presence of low concentrations of ligands. We also showed that Wnt3a-CM and the purified Wnt3a enhance the level of cytosolic and nuclear beta-catenin, suggesting an involvement of beta-catenin in this regulation. Moreover, treatment of LNCaP cells with Wnt3a-CM and purified Wnt3a significantly enhances cell growth in the absence of androgens. Our findings demonstrate that Wnt3a plays an important role in androgen-mediated transcription and cell growth. These results suggest a novel mechanism for the progression of prostate cancer.

Wnt11 facilitates embryonic stem cell differentiation to Nkx2.5-positive cardiomyocytes

Wnt signaling plays a crucial role in the control of morphogenesis in several tissues. Herein, we describe the role of Wnt11 during cardiac differentiation of embryonic stem cells. First, we examined the expression profile of Wnt11 during the course of differentiation in embryoid bodies, and then compared its expression in retinoic acid-treated embryoid bodies with that in untreated. In differentiating embryoid bodies, Wnt11 expression rose along with that of Nkx2.5 expression and continued to increase. When the embryoid bodies were treated with retinoic acid, Wnt11 expression decreased in parallel with the decreased expression of cardiac genes. Further, treatment of embryoid bodies with medium containing Wnt11 increased the expression of cardiac marker genes. Based on these results, we propose that Wnt11 plays an important role for cardiac development by embryoid bodies, and may be a key regulator of cardiac muscle cell proliferation and differentiation during heart development.

Polarity factor 'Frizzled' in the demosponge Suberites domuncula: identification, expression and localization of the receptor in the epithelium/pinacoderm(1)

Until recently, it was assumed that polarity and axis formation have evolved only in metazoan phyla higher than Cnidaria. One key molecule involved in the signal transduction causing tissue polarity is Frizzled, a seven-transmembrane receptor that is activated by the Wnt family of secreted proteins. We report the isolation and characterization of a Frizzled gene from the demosponge Suberites domuncula (Sd-Fz). The deduced polypeptide comprises all characteristic domains known from Frizzled receptors of higher metazoans. In situ hybridization studies show that Sd-Fz is expressed in cells close to the surface of the sponges and in the pinacocytes of some canals. Northern blot analysis demonstrates its upregulation during the formation of three-dimensional sponge cell aggregates in culture. These data provide for the first time experimental evidence that already in the lowest metazoan phylum (Porifera) genes are present which are very likely involved in tissue polarity.

Anti-Müllerian hormone, beta-catenin and Müllerian duct regression

The embryo is initially sexually indifferent, and correct sexual development is dependent on gonadal hormone production. Thus, in the male embryo, anti-Müllerian hormone (AMH), secreted by the Sertoli cells of the testis, induces regression of the Müllerian duct, the anlagen of female reproductive tract. This hormone causes ductal epithelial regression through a paracrine mechanism originating in periductal mesenchyme and the cross-talk between the mesenchymal and epithelial layers accounts for the cranial-to-caudal pattern of Müllerian regression. Here, we review and discuss recent developments concerning the relationship of apoptosis of Müllerian duct to tissue remodeling, mesenchymal-epithelial interactions, and involvement of beta-catenin in AMH signaling in periductal mesenchyme. Determining the role of beta-catenin/LEF-1 signaling is critical for understanding AMH action during Müllerian duct regression.

Multiple roles of the tuberous sclerosis complex genes

Soon after proposing the "two-hit" hypothesis for tumorigenesis, Knudson pursued further experimental validation of the concept by using a rat model of dominantly inherited renal tumor. Today, the Eker rat is one of the best characterized models of tuberous sclerosis complex (TSC) and has been used extensively for study of the function of the TSC2 tumor suppressor gene. Along with TSC1, these two genes behave as expected for tumor suppressor genes with evidence for loss of heterozygosity in tumors and suppression of growth when expressed in proliferating cells. Despite much experimental work, the mechanisms of these genes have remained elusive until recently. This review summarizes some of the current concepts in our understanding of the biological and biochemical function of the TSC genes.

Axin utilizes distinct regions for competitive MEKK1 and MEKK4 binding and JNK activation

Axin is a multidomain protein that plays a critical role in Wnt signaling, serving as a scaffold for down-regulation of beta-catenin. It also activates the JNK mitogen-activated protein kinase by binding to MEKK1. However, it is intriguing that Axin requires several additional elements for JNK activation, including a requirement for homodimerization, sumoylation at the extreme C-terminal sites, and a region in the protein phosphatase 2A-binding domain. In our present study, we have shown that another MEKK family member, MEKK4, also binds to Axin in vivo and mediates Axin-induced JNK activation. Surprisingly MEKK4 binds to a region distinct from the MEKK1-binding site. Dominant negative mutant of MEKK4 attenuates the JNK activation by Axin. Activation of JNK by Axin in MEKK1-/- mouse embryonic fibroblast cells supports the idea that another MEKK can mediate Axin-induced JNK activation. Expression of specific small interfering RNA against MEKK4 effectively attenuates JNK activation by the MEKK1 binding-defective Axin mutant in 293T cells and inhibits JNK activation by wild-type Axin in MEKK1-/- cells, confirming that MEKK4 is indeed another mitogen-activated protein kinase kinase kinase that is specifically involved in Axin-mediated JNK activation independently of MEKK1. We have also identified an additional domain between MEKK1- and MEKK4-binding sites as being required for JNK activation by Axin. MEKK1 and MEKK4 compete for Axin binding even though they bind to sites far apart, suggesting that Axin may selectively bind to MEKK1 or MEKK4 depending on distinct signals or cellular context. Our findings will provide new insights into how scaffold proteins mediate ultimate activation of different mitogen-activated protein kinase kinase kinases.

Secreted frizzled-related protein 4 is a potent tumor-derived phosphaturic agent

Tumors associated with osteomalacia elaborate the novel factor(s), phosphatonin(s), which causes phosphaturia and hypophosphatemia by cAMP-independent pathways. We show that secreted frizzled-related protein-4 (sFRP-4), a protein highly expressed in such tumors, is a circulating phosphaturic factor that antagonizes renal Wnt-signaling. In cultured opossum renal epithelial cells, sFRP-4 specifically inhibited sodium-dependent phosphate transport. Infusions of sFRP-4 in normal rats over 2 hours specifically increased renal fractional excretion of inorganic phosphate (FEPi) from 14% +/- 2% to 34% +/- 5% (mean +/- SEM, P < 0.01). Urinary cAMP and calcium excretion were unchanged. In thyro-parathyroidectomized rats, sFRP-4 increased FEPi from 0.7% +/- 0.2% to 3.8% +/- 1.2% (P < 0.05), demonstrating that sFRP-4 inhibits renal inorganic phosphate reabsorption by PTH-independent mechanisms. Administration of sFRP-4 to intact rats over 8 hours increased FEPi, decreased serum phosphate (1.95 +/- 0.1 to 1.53 +/- 0.09 mmol/l, P < 0.05) but did not alter serum 1alpha, 25-dihydroxyvitamin D, renal 25-hydroxyvitamin D 1alpha-hydroxylase cytochrome P450, and sodium-phosphate cotransporter mRNA concentrations. Infusion of sFRP-4 antagonizes Wnt action as demonstrated by reduced renal beta-catenin and increased phosphorylated beta-catenin concentrations. The sFRP-4 is detectable in normal human serum and in the serum of a patient with tumor-induced osteomalacia. Thus, sFRP-4 displays phosphatonin-like properties, because it is a circulating protein that promotes phosphaturia and hypophosphatemia and blunts compensatory increases in 1alpha, 25-dihydroxyvitamin D.