Molecular cloning and characterization of human Frizzled-4 on chromosome 11q14-q21

FZD4 in a Large Chinese Population With Familial Exudative Vitreoretinopathy: Molecular Characteristics and Clinical Manifestations

Purpose

The purpose of this study was to establish a genotype-phenotype correlation of familial exudative vitreoretinopathy (FEVR) caused by FZD4 gene mutations.

Methods

Six hundred fifty-one probands and their family members were recruited based on a clinical diagnosis of FEVR between 2015 and 2021 at Zhongshan Ophthalmic Center. Ocular examinations were performed in all participants. Targeted gene panel sequencing and whole-exome sequencing were performed in the probands, and Sanger sequencing was used to verify the mutations and segregation analysis was performed in the family members.

Results

Fifty-one FZD4 mutations (24 novels and 27 known) were detected in 84 families. Of these 168 eyes with FEVR, the eyes at stages 1, 2, 3, 4, and 5 were 29 (17.3%), 15 (8.9%), 19 (11.3%), 55 (32.7%), and 12 (7.1%), respectively. Exact stage of 38 (22.6%) eyes could not be determined. The FEVR phenotypes were more severe in the probands than the phenotypes in the family members (P < 0.001). The families were divided into two groups, probands that inherited the variant from the mother, and probands that inherited the variant from the father. In addition, the FEVR stage differences between these two groups were different (P < 0.05). Despite the mutations being located in different domains of FZD4, no significant differences were identified among the domains in terms of FEVR staging, retinal folds, retinal detachment, temporal midperipheral vitreoretinal interface abnormality, and foveal hypoplasia.

Conclusions

The FZD4 probands had severer phenotype than the family members, and the FEVR stage difference was greater between the probands and mothers than that between the probands and fathers.

Whole-Gene Deletions of FZD4 Cause Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by abnormalities in the retinal vasculature. The FZD4 gene is associated with FEVR, but the prevalence and impact of FZD4 copy number variation (CNV) on FEVR patients are unknown. The aim of this study was to better understand the genetic features and clinical manifestations of patients with FZD4 CNVs. A total of 651 FEVR families were recruited. Families negative for mutations in FEVR-associated genes were selected for CNV analysis using SeqCNV. Semiquantitative multiplex polymerase chain reaction and multiplex ligation-dependent probe amplification were conducted to verify the CNVs. Four probands were found to carry whole-gene deletions of FZD4, accounting for 5% (4/80) of probands with FZD4 mutations and 0.6% (4/651) of all FEVR probands. The four probands exhibited similar phenotypes of unilateral retinal folds. FEVR in probands with CNVs was not more severe than in probands with FZD4 missense mutations (p = 1.000). Although this is the first report of FZD4 CNVs and the associated phenotypes, the interpretation of FZD4 CNVs should be emphasized when analyzing the next-generation sequencing data of FEVR patients because of their high prevalence.

Up-Regulation of Nfat5 mRNA and Fzd4 mRNA as a Marker of Poor Outcome in Neonatal Hypoxic-Ischemic Encephalopathy

OBJECTIVE

To evaluate umbilical cord messenger RNA (mRNA) expression as biomarkers for the grade of hypoxic-ischemic encephalopathy (HIE) and long-term neurodevelopment outcome.

STUDY DESIGN

Infants were recruited from the BiHiVE1 study, Ireland (2009-2011), and the BiHiVE2 study, Ireland, and Sweden (2013-2015). Infants with HIE were assigned modified Sarnat scores at 24 hours and followed at 18-36 months. mRNA expression from cord blood was measured using quantitative real-time polymerase chain reaction.

RESULTS

We studied 124 infants (controls, n = 37; perinatal asphyxia, n = 43; and HIE, n = 44). Fzd4 mRNA increased in severe HIE (median relative quantification, 2.98; IQR, 2.23-3.68) vs mild HIE (0.88; IQR, 0.46-1.37; P = .004), and in severe HIE vs moderate HIE (1.06; IQR, 0.81-1.20; P = .003). Fzd4 mRNA also increased in infants eligible for therapeutic hypothermia (1.20; IQR, 0.92-2.37) vs those who were ineligible for therapeutic hypothermia group (0.81; IQR, 0.46-1.53; P = .017). Neurodevelopmental outcome was analyzed for 56 infants. Nfat5 mRNA increased in infants with severely abnormal (1.26; IQR, 1.17-1.39) vs normal outcomes (0.97; IQR, 0.83-1.24; P = .036), and also in infants with severely abnormal vs mildly abnormal outcomes (0.96; IQR, 0.80-1.06; P = .013). Fzd4 mRNA increased in infants with severely abnormal (2.51; IQR, 1.60-3.56) vs normal outcomes (0.74; IQR, 0.48-1.49; P = .004) and in infants with severely abnormal vs mildly abnormal outcomes (0.97; IQR, 0.75-1.34; P = .026).

CONCLUSIONS

Increased Fzd4 mRNA expression was observed in cord blood of infants with severe HIE; Nfat5 mRNA and Fzd4 mRNA expression were increased in infants with severely abnormal long-term outcomes. These mRNA may augment current measures as early objective markers of HIE severity at delivery.

The Role of Wnt Signalling in Chronic Kidney Disease (CKD)

Chronic kidney disease (CKD) encompasses a group of diverse diseases that are associated with accumulating kidney damage and a decline in glomerular filtration rate (GFR). These conditions can be of an acquired or genetic nature and, in many cases, interactions between genetics and the environment also play a role in disease manifestation and severity. In this review, we focus on genetically inherited chronic kidney diseases and dissect the links between canonical and non-canonical Wnt signalling, and this umbrella of conditions that result in kidney damage. Most of the current evidence on the role of Wnt signalling in CKD is gathered from studies in polycystic kidney disease (PKD) and nephronophthisis (NPHP) and reveals the involvement of β-catenin. Nevertheless, recent findings have also linked planar cell polarity (PCP) signalling to CKD, with further studies being required to fully understand the links and molecular mechanisms.

Familial Exudative Vitreoretinopathy-Related Disease-Causing Genes and Norrin/β-Catenin Signal Pathway: Structure, Function, and Mutation Spectrums

Familial exudative vitreoretinopathy (FEVR) is a hereditary ocular disorder characterized by incomplete vascularization/abnormality of peripheral retina. Four of the identified disease-causing genes of FEVR were NDP, FZD4, LRP5, and TSPAN12, the protein coded by which were the components of the Norrin/β-catenin signal pathway. In this review, we summarized and discussed the spectrum of mutations involving these four genes. By the end of 2017, the number of FEVR causing mutations reported for NDP, FZD4, LRP5, and TSPAN12 was, respectively, 26, 121, 58, and 40. Three most frequently reported mutations were c. 362G > A (p.R121Q) of NDP, c. 313A > G (p.M105V), and c.1282_1285delGACA (p.D428SfsX2) of FZD4. Mutations have a tendency to cluster in some “hotspots” domains which may be responsible for protein interactions.

Molecular genetics and targeted therapy of WNT-related human diseases (Review)

Canonical WNT signaling through Frizzled and LRP5/6 receptors is transduced to the WNT/β-catenin and WNT/stabilization of proteins (STOP) signaling cascades to regulate cell fate and proliferation, whereas non-canonical WNT signaling through Frizzled or ROR receptors is transduced to the WNT/planar cell polarity (PCP), WNT/G protein-coupled receptor (GPCR) and WNT/receptor tyrosine kinase (RTK) signaling cascades to regulate cytoskeletal dynamics and directional cell movement. WNT/β-catenin signaling cascade crosstalks with RTK/SRK and GPCR-cAMP-PKA signaling cascades to regulate β-catenin phosphorylation and β-catenin-dependent transcription. Germline mutations in WNT signaling molecules cause hereditary colorectal cancer, bone diseases, exudative vitreoretinopathy, intellectual disability syndrome and PCP-related diseases. APC or CTNNB1 mutations in colorectal, endometrial and prostate cancers activate the WNT/β-catenin signaling cascade. RNF43, ZNRF3, RSPO2 or RSPO3 alterations in breast, colorectal, gastric, pancreatic and other cancers activate the WNT/β-catenin, WNT/STOP and other WNT signaling cascades. ROR1 upregulation in B-cell leukemia and solid tumors and ROR2 upregulation in melanoma induce invasion, metastasis and therapeutic resistance through Rho-ROCK, Rac-JNK, PI3K-AKT and YAP signaling activation. WNT signaling in cancer, stromal and immune cells dynamically orchestrate immune evasion and antitumor immunity in a cell context-dependent manner. Porcupine (PORCN), RSPO3, WNT2B, FZD5, FZD10, ROR1, tankyrase and β-catenin are targets of anti-WNT signaling therapy, and ETC-159, LGK974, OMP-18R5 (vantictumab), OMP-54F28 (ipafricept), OMP-131R10 (rosmantuzumab), PRI-724 and UC-961 (cirmtuzumab) are in clinical trials for cancer patients. Different classes of anti-WNT signaling therapeutics are necessary for the treatment of APC/CTNNB1-, RNF43/ZNRF3/RSPO2/RSPO3- and ROR1-types of human cancers. By contrast, Dickkopf-related protein 1 (DKK1), SOST and glycogen synthase kinase 3β (GSK3β) are targets of pro-WNT signaling therapy, and anti-DKK1 (BHQ880 and DKN-01) and anti-SOST (blosozumab, BPS804 and romosozumab) monoclonal antibodies are being tested in clinical trials for cancer patients and osteoporotic post-menopausal women. WNT-targeting therapeutics have also been applied as reagents for in vitro stem-cell processing in the field of regenerative medicine.

Syndecan-1 Acts as an Important Regulator of CXCL1 Expression and Cellular Interaction of Human Endometrial Stromal and Trophoblast Cells

Successful implantation of the embryo into the human receptive endometrium is substantial for the establishment of a healthy pregnancy. This study focusses on the role of Syndecan-1 at the embryo-maternal interface, the multitasking coreceptor influencing ligand concentration, release and receptor presentation, and cellular morphology. CXC motif ligand 1, being involved in chemotaxis and angiogenesis during implantation, is of special interest as a ligand of Syndecan-1. Human endometrial stromal cells with and without Syndecan-1 knock-down were decidualized and treated with specific inhibitors to evaluate signaling pathways regulating CXC ligand 1 expression. Western blot analyses of MAPK and Wnt members were performed, followed by analysis of spheroid interactions between human endometrial cells and extravillous trophoblast cells. By mimicking embryo contact using IL-1β, we showed less ERK and c-Jun activation by depletion of Syndecan-1 and less Frizzled 4 production as part of the canonical Wnt pathway. Additionally, more beta-catenin was phosphorylated and therefore degraded after depletion of Syndecan-1. Secretion of CXC motif ligand 1 depends on MEK-1 with respect to Syndecan-1. Regarding the interaction of endometrial and trophoblast cells, the spheroid center-to-center distances were smaller after depletion of Syndecan-1. Therefore, Syndecan-1 seems to affect signaling processes relevant to signaling and intercellular interaction at the trophoblast-decidual interface.

Intrinsic disorder in spondins and some of their interacting partners

Spondins, which are proteins that inhibit and promote adherence of embryonic cells so as to aid axonal growth are part of the thrombospondin-1 family. Spondins function in several important biological processes, such as apoptosis, angiogenesis, etc. Spondins constitute a thrombospondin subfamily that includes F-spondin, a protein that interacts with Aβ precursor protein and inhibits its proteolytic processing; R-spondin, a 4-membered group of proteins that regulates Wnt pathway and have other functions, such as regulation of kidney proliferation, induction of epithelial proliferation, the tumor suppressant action; M-spondin that mediates mechanical linkage between the muscles and apodemes; and the SCO-spondin, a protein important for neuronal development. In this study, we investigated intrinsic disorder status of human spondins and their interacting partners, such as members of the LRP family, LGR family, Frizzled family, and several other binding partners in order to establish the existence and importance of disordered regions in spondins and their interacting partners by conducting a detailed analysis of their sequences, finding disordered regions, and establishing a correlation between their structure and biological functions.

Mutation spectrum of the FZD-4, TSPAN12 AND ZNF408 genes in Indian FEVR patients

BACKGROUND

Mutations in candidate genes that encode for a ligand (NDP) and receptor complex (FZD4, LRP5 and TSPAN12) in the Norrin β-catenin signaling pathway are involved in the pathogenesis of familial exudative vitreoretinopathy (FEVR, MIM # 133780). Recently, a transcription factor (ZNF408) has also been implicated in FEVR. We had earlier characterized the variations in NDP among FEVR patients from India. The present study aimed at understanding the involvement of the remaining genes (FZD4, TSPAN12 and ZNF408) in the same cohort.

METHODS

The DNA of 110 unrelated FEVR patients and 115 unaffected controls were screened for variations in the entire coding and untranslated regions of these 3 genes by resequencing. Segregation of the disease-associated variants was assessed in the family members of the probands. The effect of the observed missense changes were further analyzed by SIFT and PolyPhen-2 scores.

RESULTS

The screening of FZD4, TSPAN12 and ZNF408 genes identified 11 different mutations in 15/110 FEVR probands. Of the 11 identified mutations, 6 mutations were novel. The detected missense mutations were mainly located in the domains which are functionally crucial for the formation of ligand-receptor complex and as they replaced evolutionarily highly conserved amino acids with a SIFT score < 0.005, they are predicted to be pathogenic. Additionally 2 novel and 16 reported single nucleotide polymorphisms (SNP) were also detected.

CONCLUSIONS

Our genetic screening revealed varying mutation frequencies in the FZD4 (8.0 %), TSPAN12 (5.4 %) and ZNF408 (2.7 %) genes among the FEVR patients, indicating their potential role in the disease pathogenesis. The observed mutations segregated with the disease phenotype and exhibited variable expressivity. The mutations in FZD4 and TSPAN12 were involved in autosomal dominant and autosomal recessive families and further validates the involvement of these gene in FEVR development.

Complex genetics of familial exudative vitreoretinopathy and related pediatric retinal detachments

Familial exudative vitreoretinopathy (FEVR) is a hereditary vitreoretinal disorder that can cause various types of retinal detachments. The abnormalities in eyes with FEVR are caused by poor vascularization in the peripheral retina. The genetics of FEVR is highly heterogeneous, and mutations in the genes for Wnt signaling and a transcription factor have been reported to be responsible for FEVR. These factors have been shown to be the regulators of the pathophysiological pathways of retinal vascular development. Studies conducted to identify the causative genes of FEVR have uncovered a diverse and complex relationship between FEVR and other diseases; for example, Norrie disease, a Mendelian-inherited disease; retinopathy of prematurity, a multifactorial genetic disease; and Coats disease, a nongenetic disease, associated with pediatric retinal detachments.

Gastric cancer cell proliferation is suppressed by frizzled-2 short hairpin RNA

In order to identify novel targets for the molecular therapy of gastric cancer (GC), we investigated the mRNA and protein expression of frizzled-2 (Fz2), a Wnt signaling pathway receptor. Reverse-transcriptase polymerase chain reaction (PCR) amplification was utilized to determine the expression patterns of Fz genes in normal stomach and in the GC cell lines MKN45 and MKN74. Immunostaining was performed on surgical specimens of GC using an antibody against Fz2. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2- (4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay was performed on MKN45 cells and MKN74 cells transfected with Fz2 short-hairpin (sh) RNA. Cell motility was analyzed by scratch assay following Fz2 shRNA. Real-time quantitative PCR was performed to analyze the expression levels of cyclin D1 and matrix metallopeptidase 9 (MMP-9). Fz1, 3, 6 and 8 were expressed in normal stomach, and in MKN45 and MKN74 cells. Fz2 was expressed in normal stomach and in MKN45, but not in MKN74 cells. Well-differentiated GC tissue was weakly positive for Fz2 in cell membranes. Fz2 was positive in both the cell membrane and cytoplasm of GC tissues of moderately differentiated and poorly differentiated adenocarcinoma. Signet ring cells were positive for cytoplasmic Fz2. Proliferation of MKN45 and MKN74 cells was suppressed by Fz2 shRNA, and a scratch assay demonstrated that Fz2 shRNA suppressed also MKN45 and MKN74 cell motility. Furthermore, Fz2 shRNA application led to downregulated mRNA expression of both cyclin D1 and MMP-9. Fz2, 3, 6 and 8 were expressed in normal stomach, and in MKN45 and MKN74 GC cells. Fz2 shRNA suppressed cell proliferation and motility of MKN45 and MKN74 cells, and downregulated cyclin D1 and MMP-9 expression in these GC cell lines.

Frizzled homolog proteins, microRNAs and Wnt signaling in cancer

Wnt signaling pathways play important roles in tumorigenesis and are initiated by binding of Wnt to various receptors including frizzleds (FZDs). FZDs are one of several families of receptors comprised of FZD/LRP/ROR2/RYK in the Wnt signaling pathway. Expression of some FZD receptors are up regulated, thereby activating the Wnt signaling pathway and is correlated with cancer malignancy and patient outcomes (recurrence and survival) in many cancers. The FZD family contains ten genes in humans and their function has not been completely examined including the regulatory mechanisms of FZD genes in cancer. Knockdown of FZDs may suppress the Wnt signaling pathway resulting in decreased cell growth, invasion, motility and metastasis of cancer cells. Recently a number of microRNAs (miRNAs) have been identified and reported to be important in several cancers. MiRNAs regulate target gene expression at both the transcription and translation levels. The study of miRNA is a newly emerging field and promises to be helpful in understanding the pathogenesis of FZDs in cancer. In addition, miRNAs may be useful in regulating FZDs in cancer cells. Therefore, the aim of this review is to discuss current knowledge of the functional mechanisms of FZDs in cancer, including regulation by miRNAs and the potential for possible use of miRNAs and FZDs in future clinical applications.

Metallic gold slows disease progression, reduces cell death and induces astrogliosis while simultaneously increasing stem cell responses in an EAE rat model of multiple sclerosis

Multiple sclerosis (MS) is the most common neurodegenerative disease in the Western world affecting younger, otherwise healthy individuals. Today no curative treatment exists. Patients suffer from recurring attacks caused by demyelination and underlying neuroinflammation, ultimately leading to loss of neurons. Recent research shows that bio-liberation of gold ions from metallic gold implants can ameliorate inflammation, reduce apoptosis and promote proliferation of neuronal stem cells (NSCs) in a mouse model of focal brain injury. Based on these findings, the present study investigates whether metallic gold implants affect the clinical signs of disease progression and the pathological findings in experimental autoimmune encephalomyelitis (EAE), a rodent model of MS. Gold particles 20-45 μm suspended in hyaluronic acid were bilaterally injected into the lateral ventricles (LV) of young Lewis rats prior to EAE induction. Comparing gold-treated animals to untreated and vehicle-treated ones, a statistically significant slowing of disease progression in terms of reduced weight loss was seen. Despite massive inflammatory infiltration, terminal deoxynucleotidyl transferase dUTP nick end labeling staining revealed reduced apoptotic cell death in disease foci in the brain stem of gold-treated animals, alongside an up-regulation of glial fibrillary acidic protein-positive reactive astrocytes near the LV and in the brain stem. Cell counting of frizzled-9 and nestin-stained cells showed statistically significant up-regulation of NSCs migrating from the subventricular zone. Additionally, the neuroprotective proteins Metallothionein-1 and -2 were up-regulated in the corpus callosum. In conclusion, this study is the first to show that the presence of small gold implants affect disease progression in a rat model of MS, increasing the neurogenic response and reducing the loss of cells in disease foci. Gold implants might thus improve clinical outcome for MS patients and further research into the long-term effects of such localized gold treatment is warranted.

Characterization of Wnt2 overexpression in a rat granulosa cell line (DC3): effects on CTNNB1 activation

WNTs comprise a family of secreted glycoproteins that are essential for normal embryonic development of the female reproductive system. The functional role that WNTs play in the postnatal ovary is poorly defined. We have shown previously that Wnt2 and Fzd4 mRNAs are expressed in granulosa cells of the postnatal rat ovary. Here we examine the effects of Wnt2 overexpression in a rat granulosa cell line (DC3) that displays characteristics of granulosa cells at an early stage of follicular development. We show that DC3 cells express a 7.7-kb Fzd4 mRNA transcript similar in size to that detected in the rat and human ovary. Our results demonstrate that Wnt2 overexpression in DC3 promotes cytosolic and nuclear accumulation of beta-catenin (CTNNB1), but does not stimulate CTNNB1/TCF-dependent (pGL3-OT) transcriptional activity. We show that chibby (CBY1), a nuclear CTNNB1-associated antagonist of the WNT pathway, is expressed in DC3 cells and associates with CTNNB1 in the presence and absence of Wnt2 overexpression, suggesting that Cby1 contributes to suppression of CTNNB1/TCF-dependent transcription in these cells. Our results show that Wnt2 overexpression in DC3 cells increases follistatin (Fst) mRNA expression and promotes resistance to activin-induced cell deletion. Taken together, our results suggest that WNT2 opposes activin activity in granulosa cells by up-regulating expression of the activin antagonist Fst in a CTNNB1/TCF-independent manner, and that rat granulosa cells express factors, including Cby1, that suppress CTNNB1/TCF-dependent signal transduction in the presence of a WNT signal.

Small-molecule hydrophobic tagging-induced degradation of HaloTag fusion proteins

The ability to regulate any protein of interest in living systems with small molecules remains a challenge. We hypothesized that appending a hydrophobic moiety to the surface of a protein would mimic the partially denatured state of the protein, thus engaging the cellular quality control machinery to induce its proteasomal degradation. We designed and synthesized bifunctional small molecules that bind a bacterial dehalogenase (HaloTag protein) and present a hydrophobic group on its surface. Remarkably, hydrophobic tagging of the HaloTag protein with an adamantyl moiety induced the degradation of cytosolic, isoprenylated, and transmembrane fusion proteins in cell culture. We demonstrated the in vivo utility of hydrophobic tagging by degrading proteins expressed in zebrafish embryos and by inhibiting RasG12V-driven tumor progression in mice. Therefore, hydrophobic tagging of HaloTag fusion proteins affords small molecule control over any protein of interest, making it an ideal system for validating potential drug targets in disease models.

Structural diversity of G protein-coupled receptors and significance for drug discovery

G protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and also the targets of many drugs. Understanding of the functional significance of the wide structural diversity of GPCRs has been aided considerably in recent years by the sequencing of the human genome and by structural studies, and has important implications for the future therapeutic potential of targeting this receptor family. This article aims to provide a comprehensive overview of the five main human GPCR families--Rhodopsin, Secretin, Adhesion, Glutamate and Frizzled/Taste2--with a focus on gene repertoire, general ligand preference, common and unique structural features, and the potential for future drug discovery.

Networking of WNT, FGF, Notch, BMP, and Hedgehog signaling pathways during carcinogenesis

The biological functions of some orthologs within the human genome and model-animal genomes are evolutionarily conserved, but those of others are divergent due to protein evolution and promoter evolution. Because WNT signaling molecules play key roles during embryogenesis, tissue regeneration and carcinogenesis, the author's group has carried out a human WNT-ome project for the comprehensive characterization of human genes encoding WNT signaling molecules. From 1996 to 2002, we cloned and characterized WNT2B/WNT13, WNT3, WNT3A, WNT5B, WNT6, WNT7B, WNT8A, WNT8B, WNT9A/WNT14, WNT9B/WNT14B, WNT10A, WNT10B, WNT11, FZD1, FZD2, FZD3, FZD4, FZD5, FZD6, FZD7, FZD8, FZD10, FRAT1, FRAT2, NKD1, NKD2, VANGL1, RHOU/ARHU, RHOV/ARHV, GIPC2, GIPC3, FBXW11/betaTRCP2, SOX17, TCF7L1/TCF3, and established a cDNA-PCR system for snap-shot and dynamic analyses on the WNT-transcriptome. In 2003, we identified and characterized PRICKLE1, PRICKLE2, DACT1/DAPPER1, DACT2/DAPPER2, DAAM2, and BCL9L. After completion of the human WNT-ome project, we have been working on the stem cell signaling network. WNT signals are transduced to beta-catenin, NLK, NFAT, PKC, JNK and RhoA signaling cascades. FGF20, JAG1 and DKK1 are target genes of the WNT-beta-catenin signaling cascade. Cross-talk of WNT and FGF signaling pathways potentiates beta-catenin and NFAT signaling cascades. BMP signals induce IHH upregulation in co-operation with RUNX. Hedgehog signals induce upregulation of SFRP1, JAG2 and FOXL1, and then FOXL1 induces BMP4 upregulation. The balance between WNT-FGF-Notch and BMP-Hedgehog signaling networks is important for the maintenance of homoestasis among stem and progenitor cells. Disruption of the stem cell signaling network results in pathological conditions, such as congenital diseases and cancer.

Karyotype-phenotype insights from 11q14.1-q23.2 interstitial deletions: FZD4 haploinsufficiency and exudative vitreoretinopathy in a patient with a complex chromosome rearrangement

We detected a unique de novo complex chromosome rearrangement (CCR) in a patient with multiple abnormalities including growth retardation, facial anomalies, exudative vitreoretinopathy (EVR), cleft palate, and minor digital anomalies. Cytogenetic analysis, fluorescent in situ hybridization, and microsatellite genotyping showed a reciprocal translocation between chromosomes 5 and 8, and a complex translocation-deletion-inversion process in the formation of derivative chromosomes 11 and 16. High-density whole-genome oligonucleotide array comparative genomic hybridization (oaCGH) defined a 35-megabase interstitial deletion of 11q14.1-q23.2 and a 1 megabase deletion of 16q22.3-q23.1. The Frizzled-4 (FZD4) gene is located within this 11q deletion. Parental studies and sequencing analysis confirmed that the patient was hemizygous for FZD4 due to the loss of a paternal allele on the derivative chromosome 11. Mutations in FZD4 are known to cause autosomal dominant exudative vitreoretinopathy (EVR1). Our patient's findings suggest that haploinsufficiency of the FZD4 gene product can also be a disease-causing mechanism for EVR1. We reviewed the clinical manifestations of 23 cases with 11q14-q23 interstitial deletions, with particular scrutiny of the present case and four reported cases characterized by molecular cytogenetics. These findings were used to construct a regional deletion map consisting of a haplosufficient segment at 11q14.3, a flanking centromeric segment at 11q14.1-q14.2, and a flanking telomeric segment at 11q21-q23.3. We propose that deletions of the FZD4 gene located within the centromeric segment cause retinal dysgenesis, while deletions within the telomeric segment account for dysmorphic craniofacial features, growth and mental retardation, and mild digital anomalies. These results provide insight into karyotype-phenotype correlations and prompt a rational analytic approach to cases with interstitial deletions of the 11q14-q23 region.

Wnt/Frizzled signaling in the vasculature: new angiogenic factors in sight

Wnt growth factors function via Frizzled receptors to affect cellular proliferation, differentiation, apoptosis, and migration. Wnt/Frizzled signaling is now linked to human hereditary disorders with retinal vascular defects, implicating Wnts as angiogenic factors. Here, we discuss Wnts and a novel Frizzled ligand, Norrin, in physiological and pathological angiogenesis.

Cultured interstitial cells from human heart valves express both specific skeletal muscle and non-muscle markers

Cardiac valve interstitial cells are a phenotypically diverse and dynamic population, comprising myofibroblasts, fibroblasts and smooth muscle cells. To understand how these contribute to valve function and to optimize the choice of cells for seeding tissue-engineered valves, we are fingerprinting interstitial cells from all four human heart valves for useful phenotypic markers. We have begun by selecting markers indicated as of interest from previous work on myofibroblast-like cell lines. We show that interstitial cells express a variety of skeletal muscle contractile proteins and the skeletal muscle transcription factor myogenin, but not the related factors MyoD, myf-5 and MRF4, suggesting partial activation of the muscle programme in these cells. Expression of non-muscle isoforms of creatine kinase (CK-B) and AMP deaminase (AMPD2 and AMPD3) was found in contrast to muscle-restricted isoforms. Non-muscle isoforms of alpha- and beta-tropomyosins were detected specifically in contrast to skeletal muscle-specific isoforms. Several members of the Frizzled (FZD) family of Wnt receptors were also detected. In addition, intact cusps of all four valves from pig were capable of contacting to non-receptor and receptor-mediated stimulation in vitro. We conclude that interstitial cells from human heart valves express various sarcomeric proteins, and suggest that these cells have contractile potential due to a unique pattern of expression of both muscle-specific and non-muscle isoforms of metabolic and structural proteins. This may be under the control of myogenin, activated through specific Wnt/FZD signaling. Identifying such molecular markers could prove useful for engineering allogenic non-valve cell sources for seeding the synthetic valve.

Roles and regulation of Wnt signaling and beta-catenin in prostate cancer

The Wnt signaling pathway and its key component beta-catenin play critical roles in embryonic development as well as in human diseases, including various malignancies. Accumulated evidence has demonstrated a significant role for the Wnt pathway in the development and progression of human prostate cancer. The recent discovery of an interaction between beta-catenin and the androgen receptor (AR) suggests a possible mechanism of cross talk between Wnt and androgen signaling pathways. In this review, we summarize the recent progresses in this interesting and growing field. Particularly, we focus on the observation that the activation of the Wnt-mediated signal occurs in a different manner in prostate cancer than in colorectal cancer or other human malignancies. Since mutations in Adenomatous polyposis coli (APC), beta-catenin, and other components of the beta-catenin destruction complex are rare in prostate cancer cells, other regulatory mechanisms appear to play dominant roles in the activation of beta-catenin, such as loss or reduction of E-cadherin, a component of cell adhesion complex, and abnormal expression of Wnt ligands, receptors, inhibitors, and other co-regulators. Understanding the role and regulation of the Wnt signaling pathway in prostate cancer cells may help identify new targets for the prostate cancer therapy.

β-Catenin/T-cell factor-mediated transcription is modulated by cell density in human bronchial epithelial cells

The embryonic Wnt/beta-catenin ('canonical') pathway has been implicated in epithelial regeneration. To investigate the role of Wnt signal transduction in the airways, we characterised the expression of key pathway components in human bronchial epithelial cells (HBEC) and studied the influence of cell density on pathway activity, using sub-confluent cells in log-phase growth as a simple model of repairing epithelium. Primary HBEC and H292 bronchial epithelial cells were found to express TCF-4, TCF-3 and isoforms of LEF-1, transcription factors that are regulated by Wnt signalling. The cells also had the potential to respond to Wnt signalling through expression of several members of the Frizzled receptor family, including FZD-5 and -6. In confluent H292 cells, 20 mM lithium and 25% v/v Wnt-3a conditioned medium induced 4.5-fold (p = 0.008) and 1.4-fold (p = 0.006) increases in TOPflash activity, respectively. Under conditions of reduced cell density, TOPflash activity increased 1.8-fold (p = 0.002) in association with increased nuclear localisation of hypophosphorylated (active) beta-catenin and increased cell proliferation. This up-regulation in reporter activity occurred independently of EGF receptor activation and could not be recapitulated by use of low-calcium medium to disrupt cadherin-mediated cell-cell adhesion, but was associated with changes in FZD-6 expression. We conclude that reactivation of this embryonic pathway may play an important role in bronchial epithelial regeneration, and that modulation of Fzd-6 receptors may regulate Wnt signalling at confluence. Recognising that many chronic inflammatory disorders of the airways involve epithelial damage and repair, altered Wnt signalling might contribute to disease pathogenesis or progression.

Frizzled 4 gene (FZD4) mutations in patients with familial exudative vitreoretinopathy with variable expressivity

AIMS

To search for mutations in the frizzled 4 (FZD4) gene in patients with familial exudative vitreoretinopathy (FEVR) and to delineate the defective gene associated clinical features.

METHODS

Direct sequencing following polymerase chain reaction of exons of FZD4 was performed for 24 probands with FEVR (18 familial and six sporadic), and some of their families. Clinical symptoms among individuals with mutations were assessed.

RESULTS

Four novel mutations were identified in four patients with familial and one with sporadic FEVR. Three of these mutations were missense (M105V, R417Q, and G488D) and one was a nonsense change (W319X). M105V, R417Q, and G488D co-segregated with the disease. None of these sequence changes was found among 300 chromosomes from 150 healthy volunteers. The severity of vitreoretinopathy in the individuals involved in this study varied, but no patient with mutations in FZD4 exhibited rhegmatogenous retinal detachment although this pathology is thought to be the most common type of retinal detachment in FEVR.

CONCLUSION

FZD4 gene mutations were found in some cases of autosomal dominant and sporadic FEVR. FZD4 mutations were responsible for FEVR with variable clinical manifestations.

Expression of Wnt, Frizzled, sFRP, and DKK genes in adult human pancreas

Wnts are important signaling molecules involved in many normal developmental processes in the human body as well as some forms of cancer. Nineteen Wnt genes are found in the human genome, as well as 10 Wnt receptor genes called Frizzled. Two coreceptors called LRP 5 and 6 are critical for Wnt signal transduction. The interaction of the Wnts with the receptors is regulated by two classes of extracellular Wnt or LRP binding proteins called sFRP and Dickkopf (DKK), which modulate Wnt signaling. We have examined the expression of all Wnt family members both in the exocrine portion and in isolated islets of adult human pancreas. RT-PCR analysis of the 1-day cultured exocrine pellet fraction from the islet isolation procedure showed that Wnt 2, 2b, 3, 4, 5a, 5b, 7a, 7b, 14, and 15 were detectable. All 10 Frizzled (Frz) receptors were expressed but only Frizzled 1, 2, 4, 5, and 6 strongly. RT-PCR performed on purified human islets revealed that Wnt 2b, 3, 4, 5a, 7b, 10a, and 14 and Frz 4, 5, and 6 were the most highly expressed. DKK 1, 3, and 4 as well as sFRP 1, 4, and 5 were expressed in the exocrine fraction. sFRP 2 and 3 were detectable but only at low levels. In situ hybridization for Frz 1-7 showed that expression colocalized with the islets of Langerhans. Together the data suggest that active Wnt signaling occurs in adult pancreas and is probably important for physiological functions.

WNT2B2 mRNA, up-regulated in primary gastric cancer, is a positive regulator of the WNT- beta-catenin-TCF signaling pathway

Genetic alterations of WNT signaling molecules lead to carcinogenesis through activation of the beta-catenin-TCF signaling pathway. We have previously cloned and characterized WNT2B/WNT13 gene on human chromosome 1p13, which is homologous to proto-oncogene WNT2 on human chromosome 7q31. WNT2B1 and WNT2B2 mRNAs, generated from the WNT2B gene due to alternative splicing of the alternative promoter type, encode almost identical polypeptides with divergence in the N-terminal region. WNT2B2 mRNA rather than WNT2B1 mRNA is preferentially expressed in NT2 cells with the potential of neuronal differentiation. Here, we describe our investigations of expression of WNT2B mRNAs in various types of human primary cancer. Matched tumor/normal expression array analysis revealed that WNT2B mRNAs were significantly up-regulated in 2 of 8 cases of primary gastric cancer. WNT2B2 mRNA rather than WNT2B1 mRNA was found to be preferentially up-regulated in a case of primary gastric cancer (signet ring cell carcinoma). Function of WNT2B1 mRNA and that of WNT2B2 mRNA were investigated by using Xenopus axis duplication assay. Injection of synthetic WNT2B1 mRNA into the ventral marginal zone of fertilized Xenopus eggs at the 4-cell stage did not induce axis duplication. In contrast, ventral injection of synthetic WNT2B2 mRNA induced axis duplication in 90% of embryos (complete axis duplication, 24%). These results strongly suggest that WNT2B2 up-regulation in some cases of gastric cancer might lead to carcinogenesis through activation of the beta-catenin-TCF signaling pathway.

Molecular cloning and characterization of WNT3A and WNT14 clustered in human chromosome 1q42 region

Human WNT3A and WNT14 cDNAs were cloned and characterized. WNT3A and WNT14 encoded WNT family protein of 352 and 365 amino acids, respectively. The 3.0-kb WNT3A mRNA was moderately expressed in placenta, and the 4.4-kb WNT14 mRNA was moderately expressed in skeletal muscle and heart. Although WNT3A mRNA was not detected in 35 human cancer cell lines, WNT14 mRNA was expressed in gastric cancer cell lines TMK1, MKN7, MKN45 and KATO-III. WNT3A and WNT14 genes, clustered in the head to head manner with an interval of about 58.0 kb, were mapped to human chromosome 1q42 region by fluorescence in situ hybridization. WNT3 and WNT15, clustered in human chromosome 17q21 region, are related genes of WNT3A and WNT14, respectively. WNT3A-WNT14 gene cluster and WNT3-WNT15 gene cluster might be generated due to duplication of ancestral gene cluster, just like WNT10A-WNT6 gene cluster and WNT10B-WNT1 gene cluster. Integration sites of mouse mammary tumor virus (MMTV) are located in the mouse chromosomal regions corresponding to these human WNT gene clusters. These results strongly suggest that unidentified nucleotide motif responsible for susceptibility to recombination might exist within the intergenic regions of these WNT gene clusters.

WNT10A and WNT6, clustered in human chromosome 2q35 region with head-to-tail manner, are strongly coexpressed in SW480 cells

Human WNT10A and WNT6 were cloned and characterized. WNT10A encoded a 417-amino-acid polypeptide with WNT core domain, and WNT6 encoded a 365-amino-acid polypeptide with N-terminal signal peptide, WNT core domain, and RGD motif. WNT10A and WNT6 genes were clustered in the head-to-tail manner with an interval less than 7.0 kb in human chromosome 2q35 region. Among human WNT family, WNT10A was most homologous to WNT10B (59.2% amino-acid identity), and WNT6 was most homologous to WNT1 (47.4% amino-acid identity). WNT10B and WNT1 genes were also clustered in human chromosome 12q13 region. Two WNT gene clusters in human chromosome 2q35 and 12q13 regions might be generated due to duplication of ancestral gene cluster. The 3.0- and 2.4-kb WNT10A mRNAs were expressed in fetal kidney, placenta, adult spleen and kidney. The 2.0-kb WNT6 mRNA was coexpressed with WNT10A in placenta and adult spleen. WNT10A and WNT6 were strongly coexpressed in SW480 (colorectal cancer). In addition to SW480, WNT10A was strongly expressed in HL-60 (promyelocytic leukemia) and Raji (Burkitt's lymphoma), and WNT6 in HeLa S3 (cervical cancer). Overexpression WNT10A and WNT6 might play key roles in human carcinogenesis through activation of WNT-beta-catenin-TCF signaling pathway, just like Wnt10b and Wnt1.

FZD4S, a splicing variant of frizzled-4, encodes a soluble-type positive regulator of the WNT signaling pathway

Frizzled-1 (FZD1)-FZD10 are seven-transmembrane-type WNT receptors, and SFRP1-SFRP5 are soluble-type WNT antagonists. These molecules are encoded by mutually distinct genes. We have previously isolated and characterized the 7.7-kb FZD4 mRNA, encoding a seven-transmembrane receptor with the extracellular cysteine-rich domain (CRD). Here, we have cloned and characterized FZD4S, a splicing variant of the FZD4 gene. FZD4S, corresponding to the 10.0-kb FZD4 mRNA, consisted of exon 1, intron 1, and exon 2 of the FZD4 gene. FZD4S encoded a soluble-type polypeptide with the N-terminal part of CRD, and was expressed in human fetal kidney. Injection of synthetic FZD4S mRNA into the ventral marginal zone of Xenopus embryos at the 4-cell stage did not induce axis duplication by itself, but augmented the axis duplication potential of coinjected Xwnt-8 mRNA. These results indicate that the FZD4 gene gives rise to soluble-type FZD4S as well as seven-transmembrane-type FZD4 due to alternative splicing, and strongly suggest that FZD4S plays a role as a positive regulator of the WNT signaling pathway.

Molecular cloning and characterization of MFRP, a novel gene encoding a membrane-type Frizzled-related protein

The Frizzled-type cysteine-rich domain (CRD) is a binding motif for soluble-type glycoprotein WNTs, which play key roles in embryogenesis and carcinogenesis. Here, we have cloned and characterized a novel gene MFRP, encoding a type II transmembrane protein with CRD. In addition to CRD, two tandem-repeats containing the Cubilin domain approximately the MFRP domain were present in the extracellular region of MFRP. Although MFRP was homologous to Corin, FZDs, and SFRPs in CRD, amino-acid identities between CRD in MFRP and CRDs in these molecules were less than 40%. The MFRP gene on 11q23 consisted of at least 13 exons. The 4.0-kb MFRP was not detected by Northern blot analysis in normal tissues other than adult and fetal brain. The MFRP mRNA was undetectable in seven gastric cancer cell lines, seven brain tumor cell lines, and other eight tumor cell lines. Regional distribution of the MFRP mRNA in human brain was further investigated, and MFRP was found to be expressed strongly in medulla oblongata, and weakly in hippocampus and corpus callosum. Thus, MFRP with CRD might play key roles in medulla oblongata as a regulator of the WNT signaling pathway.

Isolation of Xenopus frizzled-10A and frizzled-10B genomic clones and their expression in adult tissues and embryos

Frizzled genes, encoding WNT receptors, play key roles in cell fate determination. Here, we isolated two Xenopus frizzled genes (Xfz10A and Xfz10B), probably reflecting pseudotetraploidy in Xenopus. Xfz10A (586 amino acids) and Xfz10B (580 amino acids) both encoded by a single exon, consisted of the N-terminal cysteine-rich domain, seven transmembrane domains, and the C-terminal Ser/Thr-X-Val motif. Xfz10A and Xfz10B were 97.0% identical at the amino acid level, and Xfz10B was 100% identical to previously reported Xfz9, yet Xfz10A was 85.3% and 62.4% identical to FZD10 and FZD9, respectively. Xfz10 mRNA appeared as 3.4 kb in adult tissues and embryos. RT-PCR analyses revealed the expression of more Xfz10A mRNA in stomach, kidney, eye, skeletal muscle, and skin, and more Xfz10B mRNA in heart and ovary, but in embryos, two mRNAs were equally expressed from the blastula stage with their peak expression at the late gastrula stage. The main site of Xfz10 mRNA expression was neural fold at the neurula stage and the dorsal region of midbrain, hindbrain, and spinal cord at the tadpole stage. These results suggest that Xfz10 has important roles in neural tissue formation.

Alternative splicing of the WNT-2B/WNT-13 gene

Secreted glycoprotein WNTs play important roles in carcinogenesis and development. We have previously reported molecular cloning of WNT-2B/WNT-13. Here, we have isolated a novel WNT-2B isoform (WNT-2B2), in addition to the original WNT-2B isoform (WNT-2B1). WNT-2B1 and WNT-2B2 are completely different in the 5'-UTR and in the N-terminal part of the coding region. The N-terminal hydrophobic domain is contained in WNT-2B1, but not in WNT-2B2. WNT-2B1 and WNT-2B2 share the WNT-core domain, and show 87.0% amino-acid identity. We have determined the structure of the WNT-2B gene. The WNT-2B1 mRNA consists of exons 1, 2, and 4-7, while the WNT-2B2 mRNA consists of exons 3-7. WNT-2B2 was expressed in fetal brain, fetal lung, fetal kidney, caudate nucleus, testis, glioblastoma cell lines A172, SW1783, gastric cancer cell lines MKN28, MKN74, and cervical cancer cell line HeLa S3. WNT-2B1 expression level was relatively higher in fetal brain and fetal lung than in other tissues or cell lines expressing WNT-2B2. These results indicate that the WNT-2B1 and WNT-2B2 mRNAs are transcribed due to alternative splicing with distinct expression profile. This is the first report on the WNT isoforms derived from the same gene due to alternative splicing.

Molecular cloning and characterization of human FGF-20 on chromosome 8p21.3-p22

The fibroblast growth factors (FGFs) play important roles in morphogenesis, angiogenesis, tissue remodeling, and carcinogenesis. Human FGF-20 has been cloned and characterized in this study. FGF-20 encodes a 211-amino-acid polypeptide with the FGF-core domain. A strong hydrophobic region was found in the FGF-core domain of FGF-20; however, no typical N-terminal signal sequence was found in FGF-20, just as in FGF-9 and FGF-16. Total amino acid identities are as follows: FGF-20 vs FGF-9, 71.6%; FGF-20 vs FGF-16, 66.2%; FGF-9 vs FGF-16, 72.4%. Phylogenic analysis indicated that FGF-20, FGF-9, and FGF-16 constitute a subfamily among the FGF family. FGF-20 mRNA of 2.4 kb in size was detected in colon cancer cell line SW480 by Northern blot analysis. Lower levels of FGF-20 mRNA were detected in human fetal tissues and primary cancers by cDNA-PCR. The nucleotide sequence of FGF-20 cDNA is split into three parts in the human genome sequence of the chromosome 8p21.3-p22 region (Accession No. AB020858). These results indicate that the FGF-20 gene, located on human chromosome 8p21.3-p22, consists of three exons. Compared with the nucleotide sequence of FGF-20 cDNA determined in this study, one nucleotide deletion and one nucleotide substitution in the putative coding region were identified in human genome sequence AB020858.

Identification, gene structure, and expression of human frizzled-3 (FZD3)

We report the identification, genomic structure, chromosomal localization, and expression analysis of human frizzled-3 (FZD3), a 7-transmembrane receptor belonging to the frizzled family. The cDNA obtained from adult human brain shows 91% identity at the nucleotide level and 98% at the amino acid level to mouse frizzled-3 (fzd3). The FZD3 locus is located on chromosome 8p21, spans 48 Kb and its coding sequence is distributed in 6 exons intercalated by 5 introns. FZD3 is expressed in all analyzed human tissues, with quantitatively higher expression in the CNS and in urogenital structures.

Molecular cloning and genomic structure of human frizzled-3 at chromosome 8p21

WNT receptors encoded by the Frizzled genes are implicated in carcinogenesis as well as in embryonic development. Human Frizzled-3 (FZD3) gene, encoding seven-transmembrane receptor with the N-terminal cysteine-rich domain, has been cloned and characterized. Expression of the FZD3 mRNAs was investigated by using three FZD3 specific probes: HF3S1, corresponding to the 5'-UTR and a part of the coding region; HF3S2, corresponding to a part of the coding region; HF3S3, corresponding to the 3'-UTR. HF3S1 and HF3S2 hybridized to the 14.0-, 9.0-, 4.0- and 1.8-kb FZD3 mRNA, while HF3S3 hybridized to the 14.0-, 9.0-, and 4.0-kb FZD3 mRNA. The 14. 0-kb FZD3 mRNA was the major transcript in fetal brain and adult cerebellum, while the 1.8-kb FZD3 mRNA was the major transcript in adult pancreas, and many cancer cell lines examined. The 1.8-kb FZD3 mRNA, alternatively polyadenylated by the internal AATAAA signal in the coding region, is predicted to encode the truncated FZD3 protein lacking the region through the second extracellular loop to the C-terminal tail, and might function as the transmembrane-type antagonist for WNTs. The FZD3 gene consists of 8 exons, and has been mapped to human chromosome 8p21.