Molecular cloning of human Frizzled-6

PD-L1 interacts with Frizzled 6 to activate β-catenin and form a positive feedback loop to promote cancer stem cell expansion

Cancer stem cells (CSCs) drive tumor initiation, progression, metastasis, and drug resistance. We report here that programmed cell death ligand 1 (PD-L1) is constitutively expressed in cancer cells to maintain and expand CSC through a novel mechanism in addition to promoting cancer cell immune evasion. We discovered that PD-L1 interacts with receptor Frizzled 6 to activate β-catenin signaling and increase β-catenin-targeted gene expression, such as a putative stem cell marker leucine-rich-repeat-containing G-protein-coupled receptor 5. Blockage of PD-L1 function, using a specific small hairpin RNA or a specific antibody, inhibits disease progression by reducing the CSC population in both colorectal and breast tumors. Moreover, β-catenin conversely regulates PD-L1 expression through a β-catenin complex binding site in the PD-L1 promoter. Our discoveries reveal that besides assistant tumor cell immune escaping, PD-L1 and β-catenin signaling form a positive feedback loop to promote cancer progression through CSC maintenance and expansion.

A novel FZD6 mutation revealed the cause of cleft lip and/or palate in a Chinese family

Cleft lip and/or palate (CL/P) is a most common craniofacial birth defect which has multifactorial etiology. In our study, we aimed to discover the underlying etiological gene variation in a Chinese family diagnosed as non-syndromic CL/P (NSCL/P). The blood sample of the proband and her parents were detected by whole exome sequencing. The Mendelian inheritance pattern, allele frequency, variation location, function analysis and literature search were applied to filtrate and screen the mutation. Besides, the candidates were confirmed by Sanger sequencing. We meanwhile explored the conservative analysis and protein homology simulation. As a result, a start-lost mutation c.1A > GAtg/Gtg in the Frizzled-6 (FZD6) gene predicting p.Met1 was detected. The variation has not been reported before and was predicted to be harmful. The alteration caused missing of two starting amino acids that are evolutionarily conserved for FZD6 protein. Moreover, the specific structure of the mutant protein obviously changed according to the results of the homologous model. In conclusion, the results suggest c.1A > GAtg/Gtg in the FZD6 (NM_001164616) might be the genetic etiology for non-syndromic CL/P in this pedigree. Furthermore, this finding provided new etiologic information, supplementing the evidence that FZD6 is a strong potential gene for CL/P.

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.

The prognostic role of FZD6 in esophageal squamous cell carcinoma patients

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a kind of cancer with heterogeneous biological characteristics, which is affected by a complex network of gene interactions. Identification of molecular biomarkers paves the way for individualized therapy based on gene expression profiles, which can overcome the heterogeneity of ESCC.

METHODS

In this study, GSE20347, GSE23400 and GSE45670 datasets were retrieved from Gene Expression Omnibus (GEO) database, and the overlapping differentially expressed genes (DEGs) in three datasets were screened. Then the overlapping DEGs function was annotated by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway-enrichment analysis. The prognostic value of the top five KEGG pathway-related genes were further validated in The Cancer Genome Atlas (TCGA) database. After extensive statistical analysis, four genes (CDC25B, CXCL8, FZD6 and MCM4) were identified as potential prognostic markers. Among the four candidate genes, the prognostic value of FZD6 in ESCC patients has not been evaluated. Therefore, we finally used immunohistochemistry method to evaluate the effect of FZD6 on the prognosis of patients with ESCC. Additionally, we detected the expression level of FZD6 in ESCC cell line and normal esophageal epithelial cell line, and observed the cell viability of ESCC cell line after FZD6 knockdown.

RESULTS

The results showed that the overexpression of FZD6 predicted poor overall survival (OS) (P = 0.005) and progression-free survival (PFS) (P = 0.004) in ESCC patients. COX regression analysis showed that N stage (P = 0.026) and FZD6 expression level (P = 0.001) were independent prognostic factors of OS for ESCC patients. Furthermore, compared with normal esophageal epithelial cell line, the up-regulation of FZD6 was detected in ESCC cell line. Knockdown of FZD6 could significantly inhibit the proliferation of ESCC cells (P < 0.001).

CONCLUSION

CDC25B, CXCL8, FZD6 and MCM4 were screened as candidate genes for prognosis assessment of patients with ESCC. The prognostic role of FZD6 in ESCC patients was confirmed in current study.

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.

Agonist-induced dimer dissociation as a macromolecular step in G protein-coupled receptor signaling

G protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors. They can exist and act as dimers, but the requirement of dimers for agonist-induced signal initiation and structural dynamics remains largely unknown. Frizzled 6 (FZD₆) is a member of Class F GPCRs, which bind WNT proteins to initiate signaling. Here, we show that FZD₆ dimerizes and that the dimer interface of FZD₆ is formed by the transmembrane α-helices four and five. Most importantly, we present the agonist-induced dissociation/re-association of a GPCR dimer through the use of live cell imaging techniques. Further analysis of a dimerization-impaired FZD₆ mutant indicates that dimer dissociation is an integral part of FZD₆ signaling to extracellular signal-regulated kinases1/2. The discovery of agonist-dependent dynamics of dimers as an intrinsic process of receptor activation extends our understanding of Class F and other dimerizing GPCRs, offering novel targets for dimer-interfering small molecules.

Frizzled 6 (FZD₆) is a G protein-coupled receptor (GPCR) involved in several cellular processes. Here, the authors use live cell imaging and spectroscopy to show that FZD₆ forms dimers, whose association is regulated by WNT proteins and that dimer dissociation is crucial for FZD₆ signaling.

Non-canonical WNT/PCP signalling in cancer: Fzd6 takes centre stage

Frizzled receptors are the mediators of the wnt canonical and non-canonical pathways, which play fundamental roles in cell differentiation and organism development. A large body of work indicates that dysregulation of wnt signalling is a feature of oncogenic transformation, but most of the studies published so far focus on the assessment of the consequences of aberrations of the canonical pathway in human cancer. In this review, we discuss the emerging role of the wnt non-canonical pathway regulated by frizzled receptor 6 (Fzd6) in the pathogenesis of different types of human malignancies. The function played by Fzd6 in the physiology of normal and cancer cells has been highlighted in the view that an increased knowledge of the signalling pathways upstream and downstream of this receptor could ultimately result in the identification of new targets for cancer therapy.

Molecular cloning, characterization and expression analysis of Frizzled 6 in the small intestine of pigs (Sus scrofa)

Frizzled 6 (FZD6) encodes an integral membrane protein that functions in multiple signal transduction pathways, for example, as a receptor in Wnt/planar cell polarity (PCP) signaling pathway for polarized cell migration and organ morphogenesis. Mutations in FZD6 have been identified in a variety of tumors. In this study, the full-length cDNA of Sus scrofa FZD6 (Sfz6) was cloned and characterized. Nucleotide sequence analysis demonstrates that the Sfz6 gene encodes the 712 amino-acid (aa) protein with seven transmembrane domain. Tissue distribution analysis showed that Sfz6 mRNA is ubiquitously expressed in various tissues, being highest in kidney, moderate in jejunum, ileum, colon, liver, and spleen. However, FZD6 protein is highly expressed in the heart and there was no significant difference in other tissues. The relative abundance and localization of FZD6 protein in jejunum along the crypt-villus axis was determined by Western blot and immunohistochemical localization. The results show that in the jejunum, FZD6 protein is highly expressed in the villus and less in the crypt cells. Cellular proliferation and viability assays indicate that knockdown of FZD6 with small interfering RNAs (siRNA) significantly reduced the cell viability of the intestinal porcine enterocyte cells (IPEC-J2). Furthermore, qPCR and Western blot analysis revealed that expressions of ras-related C3 botulinum toxin substrate 1 (Rac1); ras homolog gene family member A (RhoA) and c-Jun N-terminal kinase 1 (JNK1), some components of PCP signaling pathway were upregulated (P < 0.05) by knockdown of FZD6 in IPEC-J2 cells. In conclusion, these results showed that FZD6 abundance in the villus was higher than that in crypt cells and knockdown of FZD6 induces PCP signal pathway components expression in IPEC-J2 cells. Our findings provide the foundation for further investigation into porcine FZD6 gene.

FZD6 expression is negatively regulated by miR-199a-5p in human colorectal cancer

Colorectal cancer (CRC), the third most common cancer worldwide, also has the highest rate of cancer-related morbidity and mortality. WNT signaling is initiated by binding of WNT to various receptors, including frizzleds (FZDs), and plays a critical role in CRC and other tumor development by regulating proliferation, differentiation, migration, apoptosis, and polarity. Among the members of the FZD family, FZD6 is broadly expressed in various tissues, and its overexpression has been reported in several cancers, suggesting an important role in cancer development. In this study, we investigated the expression of FZD6 in patients with CRC and found it to be increased in tumors, as compared to paired adjacent non-tumor tissues. Additionally, we found that FZD6 expression was negatively regulated by miR199a5p in CRC cells. These results suggest that overexpression of FZD6, mediated by reduced expression of miR-199a-5p, may play an important role in the development of CRC.

Regulatory variant in FZD6 gene contributes to nonsyndromic cleft lip and palate in an African-American family

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common birth defect affecting 135,000 newborns worldwide each year. While a multifactorial etiology has been suggested as the cause, despite decades of research, the genetic underpinnings of NSCLP remain largely unexplained. In our previous genome-wide linkage study of a large NSCLP African-American family, we identified a candidate locus at 8q21.3-24.12 (LOD = 2.98). This region contained four genes, Frizzled-6 (FZD6), Matrilin-2 (MATN2), Odd-skipped related 2 (OSR2) and Solute Carrier Family 25, Member 32 (SLC25A32). FZD6 was located under the maximum linkage peak. In this study, we sequenced the coding and noncoding regions of these genes in two affected family members, and identified a rare variant in intron 1 of FZD6 (rs138557689; c.-153 + 432A>C). The variant C allele segregated with NSCLP in this family, through affected and unaffected individuals, and was found in one other NSCLP African-American family. Functional assays showed that this allele creates an allele-specific protein-binding site and decreases promoter activity. We also observed that loss and gain of fzd6 in zebrafish contributes to craniofacial anomalies. FZD6 regulates the WNT signaling pathway, which is involved in craniofacial development, including midfacial formation and upper labial fusion. We hypothesize, therefore, that alteration in FZD6 expression contributes to NSCLP in this family by perturbing the WNT signaling pathway.

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.

The Wnt/JNK signaling target gene alcam is required for embryonic kidney development

Proper development of nephrons is essential for kidney function. β-Catenin-independent Wnt signaling through Fzd8, Inversin, Daam1, RhoA and Myosin is required for nephric tubule morphogenesis. Here, we provide a novel mechanism through which non-canonical Wnt signaling contributes to tubular development. Using Xenopus laevis as a model system, we found that the cell-adhesion molecule Alcam is required for proper nephrogenesis and functions downstream of Fzd3 during embryonic kidney development. We found alcam expression to be independent of Fzd8 or Inversin, but to be transcriptionally regulated by the β-Catenin-independent Wnt/JNK pathway involving ATF2 and Pax2 in a direct manner. These novel findings indicate that several branches of Wnt signaling are independently required for proximal tubule development. Moreover, our data indicate that regulation of morphogenesis by non-canonical Wnt ligands also involves direct transcriptional responses in addition to the effects on a post-translational level.

Genetic evidence in planar cell polarity signaling pathway in human neural tube defects

Neural tube defects (NTDs) are a group of birth anomalies having a profound physical, emotional, and financial effects on families and communities. Their etiology is complex, involving environmental and genetic factors that interact to modulate the incidence and severity of the developing phenotype. The planar cell polarity (PCP) pathway controls the process of convergent extension (CE) during gastrulation and neural tube closure and has been implicated in the pathogenesis of NTDs in animal models and human cohorts. This review summarizes the cumulative results of recent studies on PCP signaling pathway and human NTDs. These results demonstrate that PCP gene alterations contribute to the etiology of human NTDs.

Restoration of WNT4 inhibits cell growth in leukemia-derived cell lines

Background

WNT signaling pathways are significantly altered during cancer development. Vertebrates possess two classes of WNT signaling pathways: the “canonical” WNT/β-catenin signaling pathway, and the “non-canonical” pathways including WNT/Ca2⁺ and WNT/Planar cell polarity [PCP] signaling. WNT4 influences hematopoietic progenitor cell expansion and survival; however, WNT4 function in cancer development and the resulting implications for oncogenesis are poorly understood.

The aim of this study was twofold: first, to determine the expression of WNT4 in mature peripheral blood cells and diverse leukemia-derived cells including cell lines from hematopoietic neoplasms and cells from patients with leukemia; second, to identify the effect of this ligand on the proliferation and apoptosis of the blast-derived cell lines BJAB, Jurkat, CEM, K562, and HL60.

Methods

We determined WNT4 expression by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) in peripheral blood mononuclear cells (PBMCs) and T- and B-lymphocytes from healthy individuals, as well as from five leukemia-derived cell lines and blasts derived from patients with leukemia. To analyze the effect of WNT4 on cell proliferation, PBMCs and cell lines were exposed to a commercially available WNT4 recombinant human protein. Furthermore, WNT4 expression was restored in BJAB cells using an inducible lentiviral expression system. Cell viability and proliferation were measured by the addition of WST-1 to cell cultures and counting cells; in addition, the progression of the cell cycle and the amount of apoptosis were analyzed in the absence or presence of WNT4. Finally, the expression of WNT-pathway target genes was measured by qRT-PCR.

Results

WNT4 expression was severely reduced in leukemia-derived cell lines and blasts derived from patients with leukemia. The exposure of cell lines to WNT4 recombinant protein significantly inhibited cell proliferation; inducing WNT4 expression in BJAB cells corroborated this observation. Interestingly, restoration of WNT4 expression in BJAB cells increased the accumulation of cells in G1 phase, and did not induce activation of canonical WNT/β-catenin target genes.

Conclusions

Our findings suggest that the WNT4 ligand plays a role in regulating the cell growth of leukemia-derived cells by arresting cells in the G1 cell cycle phase in an FZD6-independent manner, possibly through antagonizing the canonical WNT/β-catenin signaling pathway.

Clinical significance of frizzled homolog 3 protein in colorectal cancer patients

Frizzled homolog 3 receptor was up-regulated in several gastrointestinal cancers such as esophageal and gastric cancers. Moreover, frizzled homolog 3 has recently reported to be expressed in colorectal adenoma specimens. In the present study, we investigated the clinical significance of frizzled homolog 3 protein in colorectal cancer patients. Using immunocytochemical staining, frizzled homolog 3 expression was examined in 186 colorectal cancer specimens, 79 colorectal adenoma specimens, 133 colorectal polyp specimens, 127 colorectal cancer specimens with lymph node and/or distant metastasis, 310 specimens of various non-colorectal cancer metastatic carcinomas and 40 specimens with simultaneous occurrence of colorectal cancer, colorectal adenoma and colorectal polyp. Statistical analysis was used to correlate frizzled homolog 3 protein expression to the clinicohistopathological factors, recurrence/metastasis and survival after follow-up for 42 months in colorectal cancer patients. Frizzled homolog 3 protein was expressed in 100% colorectal cancer specimens, 89% colorectal adenoma specimens, 75% colorectal polyp specimens and 69% normal colorectal epithelial tissues. Moreover, frizzled homolog 3 immunocytochemical scores were highly correlated with colorectal cancer progression. Furthermore, frizzled homolog 3 was expressed in a comparatively lower percentage of metastatic hepatocellular carcinoma and metastatic renal clear cell carcinoma with focal and very weak staining than other metastatic tumor types. On the other hand, the frizzled homolog 3 immunocytochemical scores of colorectal adenomas with synchronous colorectal carcinomas were significantly higher than those of pure colorectal adenomas. Statistical analysis showed that frizzled homolog 3 immunocytochemical scores were associated with Dukes stage and lymph node status. Finally, stratified groups of colorectal cancer patients had significant differences in their recurrence/metastasis and survival. In conclusion, the present large-scale study has clearly showed that frizzled homolog 3 protein can generate clinically important information for colorectal cancer patients.

Organ specificity of beta-carotene induced lung gene-expression changes in Bcmo1-/- mice

SCOPE

Whole genome transcriptome analysis of male and female beta-carotene 15,15'-monooxygenase knockout (Bcmo1(-/-) ) and Bcmo1(+/+) (wild-type) mice with or without 14 wk of BC supplementation was done. We previously showed that only 1.8% of the genes regulated by BC in lung were also regulated in liver and inguinal white adipose tissue (iWAT), suggesting lung specific responses. Here, we explicitly questioned the lung specificity.

METHODS AND RESULTS

We show that BC supplementation resulted in an opposite direction of gene-regulation in male compared to female Bcmo1(-/-) mice in lung, liver, and iWAT. This supports a systemic effect of BC on steroid hormone metabolism mediated responses. Lung, liver, and iWAT of female Bcmo1(-/-) mice showed an increased inflammatory response, which was counteracted by supplementation of BC. This supports a genotype dependent increased sensitivity of female mice for vitamin A deficiency. Finally, the effect of BC on Wnt signaling in male Bcmo1(-/-) mice was examined. Frizzled homolog 6 (Fzd6) downregulation was seen in all three tissues. Collagen triple helix containing 1 (Cthrc1) downregulation was seen in lung tissue only, suggesting specificity. Upregulation of genes involved in oxygen sensing was seen in lung and iWAT, while protocadherin upregulation was only seen in lung.

CONCLUSION

Our results demonstrate that effects of BC are strongly sex dependent. While effects of BC on hormone metabolism mediated responses and inflammation are systemic, effects on Wnt signaling may be lung specific.

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.

FZD6 is a novel gene for human neural tube defects

Neural tube defects (NTDs) are severe malformations of the central nervous system, affecting 1 of 1,000 live births. Mouse models were instrumental in defining the signaling pathways defective in NTDs, including the planar cell polarity (PCP), also called noncanonical Frizzled/Disheveled pathway. Based on the highly penetrant occurrence of NTDs in double Fzd3/Fzd6(-/-) mutant mice, we investigated the role of the human orthologues, FZD3 and FZD6, by resequencing a cohort of 473 NTDs patients and 639 ethnically matched controls. While we could not demonstrate a significant contribution of FZD3 gene, we identified five rare FZD6 variants that were absent in all controls and predicted to have a functional effect by computational analysis: one de novo frameshift mutation (c.1843_1844insA), three missense changes (p.Arg405Gln, p.Arg511Cys p.Arg511His), and one substitution (c.*20C>T) affecting the 3'-untranslated region (UTR) of the gene. The overall rate of predicted deleterious variants of FZD6 was 5.1-fold higher in cases compared to controls, resulting in a significantly increased NTDs mutation burden. This study demonstrates that rare nonsynonymous variants in FZD6 may contribute to NTDs in humans and enlarges the spectrum of mutations that link PCP pathway to NTDs.

Downregulation of Fzd6 and Cthrc1 and upregulation of olfactory receptors and protocadherins by dietary beta-carotene in lungs of Bcmo1-/- mice

An ongoing controversy exists on beneficial versus harmful effects of high beta-carotene (BC) intake, especially for the lung. To elucidate potential mechanisms, we studied effects of BC on lung gene expression. We used a beta-carotene 15,15'-monooxygenase 1 (Bcmo1) knockout mouse (Bcmo1(-/-)) model, unable to convert BC to retinoids, and wild-type mice (Bcmo1(+/+)) mice to dissect the effects of intact BC from effects of BC metabolites. As expected, BC supplementation resulted in a higher BC accumulation in lungs of Bcmo1(-/-) mice than in lungs of Bcmo1(+/+) mice. Whole mouse genome transcriptome analysis on lung tissue revealed that more genes were regulated in Bcmo1(-/-) mice than Bcmo1(+/+) mice upon BC supplementation. Frizzled homolog 6 (Fzd6) and collagen triple helix repeat containing 1 (Cthrc1) were significantly downregulated (fold changes -2.99 and -2.60, respectively, false discovery rate < 0.05) by BC in Bcmo1(-/-). Moreover, many olfactory receptors and many members of the protocadherin family were upregulated. Since both olfactory receptors and protocadherins have an important function in sensory nerves and Fzd6 and Cthrc1 are important in stem cell development, we hypothesize that BC might have an effect on the highly innervated pulmonary neuroendocrine cell (PNEC) cluster. PNECs are highly associated with sensory nerves and are important cells in the control of stem cells. A role for BC in the innervated PNEC cluster might be of particular importance in smoke-induced carcinogenesis since PNEC-derived lung cancer is highly associated with tobacco smoke.

Non-association between polymorphisms of the frizzled receptor genes and bone mineral density in postmenopausal Korean women

We investigated the association between single nucleotide polymorphisms (SNPs) in the frizzled (FZD) genes in the Wnt signal pathway and circulating osteoprotegerin (OPG), soluble receptor activator of NF-kappaB ligand (sRANKL) levels, bone turnover markers, and bone mineral density (BMD) in postmenopausal women. The SNPs in the FZD1, FZD5, FZD6, FZD7, and FZD9 genes were analyzed by direct sequencing in 371 postmenopausal Korean women. Levels of serum OPG, sRANKL, osteocalcin, C-telopeptide of type I collagen, calcium, parathyroid hormone and calcitonin, and BMD at the lumbar spine and femoral neck were measured. The SNPs in the FZD1, FZD5, FZD7, and FZD9 genes, and in exon 2 of the FZD6 gene were not observed. No significant differences in the adjusted BMD of lumbar spine and femoral neck and serum levels of OPG, sRANKL, and bone markers were noted among the single or haplotype genotypes of the L345M and E664A SNPs in the FZD6 gene and the distributions of these single or haplotype genotypes were not different according to the bone mass status. In conclusion, the polymorphisms of the FZD genes are not associated with BMD of the lumbar spine and femoral neck, bone turnover markers, or circulating OPG-sRANKL in Korean women.

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.

Expression of Wnt4 in human pituitary adenomas regulates activation of the beta-catenin-independent pathway

The Wnt signaling pathway has been implicated in the genesis of numerous human cancers. A member of the Wnt family of genes, Wnt4, has been known to regulate proliferation of anterior pituitary cell types in the mouse during embryonic development. In order to elucidate the roles of Wnt signaling in human pituitary adenomas, we examined the expression of Wnt4 and its putative receptor Frizzled6 (Fzd6) by immunohistochemistry in pituitary adenomas and normal pituitaries. Expression of Wnt4 was higher in growth hormone-producing adenomas (GHomas), prolactin-producing adenomas (PRLomas), and thyroid-stimulating hormone-producing adenomas (TSHomas) than in the normal pituitary. Fzd6 was widely expressed in GHomas, PRLomas, TSHomas, and gonadotropin subunit (GnSU)-positive adenomas. In normal pituitary glands, Wnt4 and Fzd6 were colocalized predominantly in follicle-stimulating hormone-, luteinizing hormone-, and alpha-subunits of glycoprotein hormone-positive cells. The canonical Wnt/beta-catenin signaling pathway was analyzed by beta-catenin immunohistochemistry. beta-Catenin was localized at the cell membrane in all pituitary adenomas, but not in the nuclei. On the other hand, Erk1/2 was highly activated in GHomas and TSHomas. These results suggested that activation of Wnt4/Fzd6 signaling through a "beta-catenin-independent" pathway played a role in proliferation and survival of the pituitary adenoma cells. Detailed involvement of transcription factors including Pit-1 remains to be further investigated.

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.

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.

Wnt-4 activates the canonical beta-catenin-mediated Wnt pathway and binds Frizzled-6 CRD: functional implications of Wnt/beta-catenin activity in kidney epithelial cells

The Wnt signaling pathway is central to the development of all animals and to cancer progression, yet largely unknown are the pairings of secreted Wnt ligands to their respective Frizzled transmembrane receptors or, in many cases, the relative contributions of canonical (beta-catenin/LEF/TCF) versus noncanonical Wnt signals. Specifically, in the kidney where Wnt-4 is essential for the mesenchymal to epithelial transition that generates the tissue's collecting tubules, the corresponding Frizzled receptor(s) and downstream signaling mechanism(s) are unclear. In this report, we addressed these issues using Madin-Darby Canine Kidney (MDCK) cells, which are competent to form tubules in vitro. Employing established reporter constructs of canonical Wnt/beta-catenin pathway activity, we have determined that MDCK cells are highly responsive to Wnt-4, -1, and -3A, but not to Wnt-5A and control conditions, precisely reflecting functional findings from Wnt-4 null kidney mesenchyme ex vivo rescue studies. We have confirmed that Wnt-4's canonical signaling activity in MDCK cells is mediated by downstream effectors of the Wnt/beta-catenin pathway using beta-Engrailed and dnTCF-4 constructs that suppress this pathway. We have further found that MDCK cells express the Frizzled-6 receptor and that Wnt-4 forms a biochemical complex with the Frizzled-6 CRD. Since Frizzled-6 did not appear to transduce Wnt-4's canonical signal, data supported recently by Golan et al., there presumably exists another as yet unknown Frizzled receptor(s) mediating Wnt-4 activation of beta-catenin/LEF/TCF. Finally, we report that canonical Wnt/beta-catenin signals cells help maintain cell growth and survival in MDCK cells but do not contribute to standard HGF-induced (nonphysiologic) tubule formation. Our results in combination with work from Xenopus laevis (not shown) lead us to believe that Wnt-4 binds both canonical and noncanonical Frizzled receptors, thereby activating Wnt signaling pathways that may each contribute to kidney tubulogenesis.

The human Frizzled 6 (HFz6) acts as a negative regulator of the canonical Wnt. beta-catenin signaling cascade

Previously we have cloned the human Frizzled 1 (HFz1) and shown that it transmits the Wnt-3a-induced canonical pathway. We also cloned the human Frizzled 6 (HFz6) and show in the present study that, as opposed to HFz1, HFz6 did not activate the canonical Wnt pathway following exposure to various Wnts, whether belonging to the Wnt-1 or to the Wnt-5a group. Moreover we show that HFz6 repressed Wnt-3a-induced canonical signaling when co-expressed with HFz1. HFz6 repressed the canonical Wnt cascade activated also by various Wnt signaling intracellular mediators such as Dishevelled-1, a stabilized beta-catenin(S33Y) mutant, and LiCl-mediated repression of glycogen synthase kinase-3beta activity. Removal of HFz6 N'- or C'-terminal sequences abolished HFz6 repressive activity. As the HFz6 repressive effect was not associated with a decrease in the level of beta-catenin, it is suggested that HFz6 does not affect beta-catenin stabilization, implying that HFz6 transmits a repressive signaling that cross-talks with and inhibits the canonical Wnt pathway downstream of beta-catenin destruction complex. HFz6 did not affect the level of nuclear T-cell factor 4 (TCF4) nor did it affect beta-catenin.TCF4 complex formation. However, electrophoretic mobility shift assays indicated that HFz6 repressed the binding of TCF/lymphoid enhancer factor transcription factors to target DNA. Moreover we present data suggesting that HFz6 activates the transforming growth factor-beta-activated kinase-NEMO-like kinase pathway that blocks TCF/lymphoid enhancer factor binding to target promoters, thereby inhibiting the ability of beta-catenin to activate transcription of Wnt target genes.

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.

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.

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.

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

The WNT receptors, encoded by the Frizzled genes, are implicated in a variety of cellular processes such as cell fate determination, cell polarity control, and malignant transformation. Human Frizzled-4 (FZD4) cDNAs have been cloned and characterized. FZD4 spans a total of 7392 nucleotides and encodes a 537-amino-acid protein with the N-terminal cysteine-rich domain, seven transmembrane domains, and the C-terminal S/T-X-V motif. The FZD4 mRNA of 7.7 kb in size were detected almost ubiquitously in normal human tissues and larger amounts in fetal kidney, adult heart, skeletal muscle, and ovary. Among cancer cell lines, the FZD4 mRNA level was higher in HeLa S3. The FZD4 gene has been mapped to human chromosome 11q14-q21. FZD4 is homologous to FZD9 and FZD10, and overall amino acid identity is as follows: FZD4 vs FZD9, 51.6%; FZD4 vs FZD10, 51.2%; FZD9 vs FZD10, 65.7%. FZD4 consists of two exons, while FZD9 and FZD10 consist of a single exon. FZD4 might belong to rather the independent FZD subfamily than the FZD9-FZD10 subfamily.

Molecular cloning of Frizzled-10, a novel member of the Frizzled gene family

The Frizzled genes encode WNT receptors. Frizzled-10 (FZD10), a novel member of the Frizzled gene family, has been cloned and characterized. Nucleotide sequence analysis showed that human FZD10 gene encodes a seven-transmembrane-receptor of 581 amino acids, with the N-terminal cysteine-rich domain and the C-terminal Ser/Thr-Xxx-Val motif. Larger amounts of FZD10 mRNA, 4.0 kb in size, were detected in the placenta and fetal kidney, followed by fetal lung and brain. In adult brain, FZD10 mRNA was abundant in the cerebellum. Among cancer cell lines, FZD10 was highly expressed in a cervical cancer cell line, HeLa S3, and moderately in a colon cancer cell line, SW480. The FZD10 gene was mapped to human chromosome 12q24.33. FZD10 shares 65.7% amino-acid identity with Frizzled-9 (FZD9). FZD10 and FZD9 constitute a subfamily among the Frizzled genes.

Molecular cloning, differential expression, and chromosomal localization of human frizzled-1, frizzled-2, and frizzled-7

cDNAs for three human Wnt receptors, Frizzled-1 (FZD1), Frizzled-2 (FZD2), and Frizzled-7 (FZD7), have now been cloned and characterized. The FZD1, FZD2, and FZD7 genes encode the 647-, 565-, and 574-amino-acid proteins, respectively. FZD1, FZD2, and FZD7 share a common structure consisting of seven transmembrane domains, a cysteine-rich domain in the N-terminal extracellular region, and the C-terminal Ser/Thr-Xxx-Val motif. Relatively large amounts of FZD 1 mRNA, 4.5 kb in size, were detected in adult heart, placenta, lung, kidney, pancreas, prostate, and ovary and in fetal lung and kidney. FZD2 mRNAs 4.0 and 2.4 kb in size were detected in adult heart, fetal brain, lung, and kidney. The level of FZD7 mRNAs 5.0 and 4.0 kb in size was high in adult skeletal muscle and fetal kidney, followed by fetal lung, adult heart, brain, and placenta. The FZD1 and FZD7 genes have been mapped to human chromosome 7q21 and 2q33, respectively.