A Van Gogh/Vangl tyrosine phosphorylation switch regulates its interaction with core Planar Cell Polarity factors Prickle and Dishevelled.

Epithelial tissues can be polarized along two axes: in addition to apical-basal polarity they are often also polarized within the plane of the epithelium, known as planar cell polarity (PCP). PCP depends upon the conserved Wnt/Frizzled (Fz) signaling factors, including Fz itself and Van Gogh (Vang/Vangl in mammals). Here, taking advantage of the complementary features of Drosophila wing and mouse skin PCP establishment, we dissect how Vang/Vangl phosphorylation on a specific conserved tyrosine residue affects its interaction with two cytoplasmic core PCP factors, Dishevelled (Dsh/Dvl1-3 in mammals) and Prickle (Pk/Pk1-3). We demonstrate that Pk and Dsh/Dvl bind to Vang/Vangl in an overlapping region centered around this tyrosine. Strikingly, Vang/Vangl phosphorylation promotes its binding to Prickle, a key effector of the Vang/Vangl complex, and inhibits its interaction with Dishevelled. Thus phosphorylation of this tyrosine appears to promote the formation of the mature Vang/Vangl-Pk complex during PCP establishment and conversely it inhibits the Vang interaction with the antagonistic effector Dishevelled. Intriguingly, the phosphorylation state of this tyrosine might thus serve as a switch between transient interactions with Dishevelled and stable formation of Vang-Pk complexes during PCP establishment.

Reversal effect of quercetin on multidrug resistance via FZD7/ß-catenin pathway in hepatocellular carcinoma cells.

BACKGROUND: Chemotherapy has been widely used to treat cancer, but the appearance of multidrug resistance (MDR) is the biggest obstacle to successful chemotherapy. One of the conventional mechanisms of MDR is overexpression of ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp/ABCB1) and multidrug resistance-associated proteins (MRPs/ABCCs) that limits the prolonged and efficient use of chemotherapeutic drugs. To enhance the chemosensitivity of tumor cells, attentions have been focused on effective MDR modulators. PURPOSE: This study aimed to investigate the reversal effect of quercetin on MDR, and explored its mechanism of action in vitro. STUDY DESIGN/METHODS: The effect and mechanism of quercetin on MDR was examined by using MTT assay, flow cytometry, real-time PCR and western blot analysis in human hepatocellular carcinoma cells. RESULTS: Our data found that the intracellular accumulation of rhodamine-123 (Rh123) and doxorubicin (ADR) were increased, the sensitivity of BEL/5-FU cells to chemotherapeutic drugs were increased, and the expressions of ABCB1, ABCC1 and ABCC2 were all down-regulated, which indicated that the functions and expressions of ABCB1, ABCC1 and ABCC2 efflux pump were inhibited by quercetin treatment. Moreover, the suppression of ABCB1, ABCC1 and ABCC2 by quercetin was dependent on the FZD7 through the Wnt/ß-catenin pathway. Further research revealed that reduction of FZD7 by RNA interference (siFZD7) enhanced the sensitivity to chemotherapeutic drugs, increased the cellular accumulation of Rh123 and ADR, and induced inhibitory effects on the expression of FZD7, ABCB1, ABCC1, ABCC2 and ß-catenin, similar to quercetin. In the meanwhile, overexpression of FZD7 showed the inversely effect on the expressions. Interesting, it was confirmed that quercetin could inhibit the expression levels of FZD7, ABCB1, ABCC1, ABCC2 and ß-catenin in BEL-7402 cells; furthermore, treatment by quercetin combined with siFZD7 in BEL/5-FU cells, the expressions of these genes were effectively decreased in comparison to quercetin combined with siRNA negative control (sncRNA). CONCLUSION: Overall, these data suggested the effectiveness of using quercetin, at least in part, via inhibiting FZD7 to combat chemoresistance and showed that quercetin could be developed into an efficient natural sensitizer for resistant human hepatocellular carcinoma.

[Effects of aqueous extracts of gecko on stemness of hepatocellular carcinoma].

To explore the effects and mechanism of aqueous extracts of gecko on cancer stem cells properties of hepatocellular carcinoma. In vitro, MTT assay was used to detect the cells growth in Huh7 and Hep3B. Spheroid-forming assay and flow cytometry were performed to observe the the stemness of Huh7 and Hep3B cells. The protein expressions of ß-catenin, CD44, c-Myc, CCND1, Sox2, Oct4, Nanog and ABCG2 were detected by Western blot. Interacting proteins were detected by co-immunoprecipitation; and a subcutaneous xenograft model was used to detect the stemness of hepatoma carcinoma cells. The results indicated that aqueous extracts of gecko induced cell growth inhibition in a dose- and time-dependent manner, with the IC50 of (0.750±0.112) g•mL⁻¹ for Huh7 and (0.454±0.039) g•mL⁻¹ for Hep3B, respectively. The number and size of tumor spheres formed by hepatoma carcinoma cells were decreased after treatment by aqueous extracts of gecko(P<0.05); the proportions of cells staining with putative markers for cancer stem cells, such as CD133 and CD44, were decreased(P<0.05). After treatment with aqueous extracts of gecko, the expression levels of ß-catenin, CD44, c-Myc, CCND1, Sox2, Oct4, Nanog and ABCG2 were decreased. Co-immunoprecipitation results showed that the aqueous extracts of gecko could inhibit the interaction between LRP6 and Frizzled6, indicating that the aqueous extracts of gecko could inhibit the proliferation of hepatoma cells, the formation of tumor spheres and the proportion of tumor stem cells, and inhibit the Wnt signaling pathway by targeting LRP6 to prevent the formation of LRP6 and Frizzled6 complexes.

[Effect of Aralia echinocaulis containing serum on Wnt/ß-catenin signaling pathway of primary osteoblast].

This paper was aimed to investigate the effect of Aralia echinocaulis containing serum on expression of ß-catenin, Wnt-1, Frizzed-2, TCF and Axin in Wnt/ß-catenin signaling pathway of primary osteoblasts. SD healthy female rats (n=80) were used to make A. echinocaulis containing serum by gastric perfusion for seven days with distilled water, A. echinocaulis decoction high dosage, middle dosage, and low dosage. In vitro, primary osteoblasts were cultured and identified. The third generation primary osteoblasts were taken and cultured for 48 h, then cells were treated with the different drug serums for 10 days and calcified nodules were counted by alizarin red staining. The cells were collected after treatment for 48 h and the expression levels of ß-catenin, Wnt-1, Frizzled-2, TCF and Axin were detected by Real-time PCR and Western blot. The results suggested that the in vitro cells were primary osteoblasts; and after treatment, various doses groups could promote the mineralization ability of primary osteoblasts, up-regulate the mRNA and protein expression levels of ß-catenin, Wnt-1, Frizzled-2, and TCF, and down-regulate the mRNA and protein expression levels of Axin. These findings indicated that A. echinocaulis containing serum can enhance the differentiation and proliferation of osteoblasts by regulating the expression levels of ß-catenin, Wnt-1, Frizzled-2, TCF and Axin in Wnt/ß-catenin signaling pathway of primary osteoblasts.

The tyrosine Y2502.39 in Frizzled 4 defines a conserved motif important for structural integrity of the receptor and recruitment of Disheveled.

Frizzleds (FZDs) are unconventional G protein-coupled receptors, which activate diverse intracellular signaling pathways via the phosphoprotein Disheveled (DVL) and heterotrimeric G proteins. The interaction interplay of FZDs with DVL and G proteins is complex, involves different regions of FZD and the potential dynamics are poorly understood. In the present study, we aimed to characterize the function of a highly conserved tyrosine (Y2502.39) in the intracellular loop 1 (IL1) of human FZD4. We have found Y2502.39 to be crucial for DVL2 interaction and DVL2 translocation to the plasma membrane. Mutant FZD4-Y2502.39F, impaired in DVL2 binding, was defective in both ß-catenin-dependent and ß-catenin-independent WNT signaling induced in Xenopus laevis embryos. The same mutant maintained interaction with the heterotrimeric G proteins Gα12 and Gα13 and was able to mediate WNT-induced G protein dissociation and G protein-dependent YAP/TAZ signaling. We conclude from modeling and dynamics simulation efforts that Y2502.39 is important for the structural integrity of the FZD-DVL, but not for the FZD-G protein interface and hypothesize that the interaction network of Y2502.39 and H3484.46 plays a role in specifying downstream signaling pathways induced by the receptor.

Celsr3 and Fzd3 Organize a Pioneer Neuron Scaffold to Steer Growing Thalamocortical Axons.

Celsr3 and Fzd3 regulate the development of reciprocal thalamocortical projections independently of their expression in cortical or thalamic neurons. To understand this cell non autonomous mechanism further, we tested whether Celsr3 and Fzd3 could act via Isl1-positive guidepost cells. Isl1-positive cells appear in the forebrain at embryonic day (E) 9.5-E10.5 and, from E12.5, they form 2 contingents in ventral telencephalon and prethalamus. In control mice, corticothalamic axons run in the ventral telencephalic corridor in close contact with Isl1-positive cells. When Celsr3 or Fzd3 is inactivated in Isl1-expressing cells, corticofugal fibers stall and loop in the ventral telencephalic corridor of high Isl1 expression, and thalamic axons fail to cross the diencephalon-telencephalon junction (DTJ). At E12.5, before thalamic and cortical axons emerge, pioneer projections from Isl1-positive cells cross the DTJ from both sides in control but not mutant embryos. These early projections appear to act like a bridge to guide later growing thalamic axons through the DTJ. Our data suggest that Celsr3 and Fzd3 orchestrate the formation of a scaffold of pioneer neurons and their axons. This scaffold extends from prethalamus to ventral telencephalon and subcortex, and steers reciprocal corticothalamic fibers.

The expression and function of Frizzled-7 in human renal cell Carcinoma

Purpose: Wnt/b-catenin has emerged as an important signal pathway in renal cell carcinoma (RCC) pathogenesis. Frizzled 7 (Fzd7) is a member of Frizzled (Fzd) receptor family which binds with Wnt ligands and transduces canonical and non-canonical pathways. However, the expression of Fzd7 in human RCC is poorly investigated. Methods: 53 RCC tissues and peri-tumor tissues were collected from the patients treated with radical nephrectomy. The expression of Fzd7 was investigated by immunohistochemical staining. Three RCC cells were transfected with Fzd7shRNA and GFPshRNA to investigate the function of Fzd7 in RCC cells. Results: The immunohistochemical analysis showed that Fzd7 protein expression level was significantly increased in RCC tissues when compared with peri-tumor tissues, which suggested that Fzd7 might be involved in the formation of tumors. However, the Fzd7 expression was not correlated with clinicopathological parameters. Three RCC cell lines: 786-O, Caki-1, and OS-RC-2 also expressed Fzd7. With Fzd7 expression being interfered by shRNA, the RCC cell proliferation was mildly decreased. Wnt3a could stimulate the RCC cells proliferation, but the stimulation was decreased when Fzd7 expression was interfered. Restoring the Fzd7 expression led to the proliferation stimulation effect of Wnt3a being restored. Conclusions: This paper suggests that Fzd7 may act as one of the molecules that take part in the course of RCC formation. Fzd7 can be activated by Wnt3a to stimulate cell proliferation (AU)

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Achyranthes bidentata polysaccharides activate the Wnt/ß-catenin signaling pathway to promote chondrocyte proliferation.

Achyranthes bidentata polysaccharides (ABPS) are the active components of Radix Achyranthis Bidentatae (AB), which has been extensively used in Traditional Chinese medicine (TCM) in the treatment of osteoarthritis (OA). Our previous study provided evidence that ABPS regulated the G1/S transition to promote chondrocyte proliferation. However, the precise mechanisms involved remain to be elucidated. In the present study, we aimed to investigate the effects of ABPS on the Wnt/ß­catenin signaling pathway in chondrocytes. Chondrocytes, obtained from the knee cartilage of Sprague-Dawley rats, were identified by type II collagen immunohistochemistry. ABPS upregulated the expression of Wnt-4, Frizzled-2, ß-catenin and cyclin D1, and downregulated the expression of glycogen synthase kinase 3ß (GSK-3ß), as shown by reverse transcription PCR (RT-PCR) and western blot analysis. Using immunofluorescence, we also found that ABPS induced ß-catenin nuclear translocation. Importantly, the expression of ß-catenin and cyclin D1 was partly inhibited by Dickkopf-1 (DKK-1), an inhibitor of the Wnt/ß-catenin signaling pathway. In addition, we found that ABPS increased the expression of type II collagen in chondrocytes. These results suggest that ABPS promote chondrocyte proliferation by activating the Wnt/ß-catenin signaling pathway.

Resveratrol attenuates hypoxia/reoxygenation­induced Ca2+ overload by inhibiting the Wnt5a/Frizzled­2 pathway in rat H9c2 cells.

Resveratrol is able to protect myocardial cells from ischemia/reperfusion­induced injury. However, the mechanism has yet to be fully elucidated. In the present study, it is reported that resveratrol has a critical role in the control of Ca2+ overload, which is the primary underlying cause of ischemia/reperfusion injury. Hypoxia/reoxygenation (H/R) treatment decreased the cell viability and increased the apoptosis of H9c2 cells, whereas the caspase­3 and intracellular Ca2+ levels were greatly elevated compared with the control group. Treatment of H9c2 cells with resveratrol (5, 15 and 30 µM) reduced caspase­3 expression and cardiomyocyte apoptosis in a dose­dependent manner, and the intracellular Ca2+ overload was also significantly decreased. Furthermore, Frizzled­2 and Wnt5a belong to the non­canonical Wnt/Ca2+ pathway, which have been demonstrated to be responsible for Ca2+ overload, and were thus detected in the present study. The results indicated that both the mRNA and protein expression levels of Frizzled­2 and Wnt5a in H/R­induced H9c2 cells were markedly increased compared with the levels found in normal cells, and treatment with resveratrol (5, 15 and 30 µM) significantly reduced the expression of Frizzled­2 and Wnt5a compared with the H/R group. The results indicated that resveratrol protected myocardial cells from H/R injury by inhibiting the Ca2+ overload through suppression of the Wnt5a/Frizzled­2 pathway.

Genetic evidence that Celsr3 and Celsr2, together with Fzd3, regulate forebrain wiring in a Vangl-independent manner.

Celsr3 and Fzd3, members of "core planar cell polarity" (PCP) genes, were shown previously to control forebrain axon guidance and wiring by acting in axons and/or guidepost cells. Here, we show that Celsr2 acts redundantly with Celsr3, and that their combined mutation mimics that of Fzd3. The phenotypes generated upon inactivation of Fzd3 in different forebrain compartments are similar to those in conditional Celsr2-3 mutants, indicating that Fzd3 and Celsr2-3 act in the same population of cells. Inactivation of Celsr2-3 or Fzd3 in thalamus does not affect forebrain wiring, and joint inactivation in cortex and thalamus adds little to cortical inactivation alone in terms of thalamocortical projections. On the other hand, joint inactivation perturbs strongly the formation of the barrel field, which is unaffected upon single cortical or thalamic inactivation, indicating a role for interactions between thalamic axons and cortical neurons in cortical arealization. Unexpectedly, forebrain wiring is normal in mice defective in Vangl1 and Vangl2, showing that, contrary to epithelial PCP, axon guidance can be Vangl independent in some contexts. Our results suggest that Celsr2-3 and Fzd3 regulate axonal navigation in the forebrain by using mechanisms different from classical epithelial PCP, and require interacting partners other than Vangl1-2 that remain to be identified.

Role of Frizzled6 in the molecular mechanism of beta-carotene action in the lung.

ß-Carotene (BC) is omnipresent in our diet, both as natural food component as well as an additive. BC and its metabolites have important biological functions. For this reason, BC is generally considered to be a health promoting compound. Two human trials, however, have described adverse effects in lung tissue, increasing the risk of lung cancer. We previously applied transcriptomic analyses in a unique animal model, beta-carotene 15,15'-monooxygenase 1 knockout (Bcmo1(-/-)) mice that are, like humans, able to accumulate intact BC. In our search to unravel the molecular action of BC in the lung, we previously identified two genes particularly strongly down-regulated by BC in lung tissue of the male Bcmo1(-/-) mice: frizzled homologue 6 (Fzd6) and collagen triple helix repeat containing 1 (Cthrc1). In the present study, our aim was to further elucidate the role of FZD6 in lung epithelial cells and to provide a mechanistic explanation for BC increased lung cancer risk in humans. We performed whole genome microarray analysis on silenced FZD6 in non-tumor human type II bronchial epithelial BEAS-2B cells using RNAi. To directly link FZD6 to BC-effects on the lung, we compared the FZD6-silenced BEAS-2B gene expression profile to the BC-dependent gene expression profile of Bcmo1(-/-) mouse lungs. A number of relevant genes were regulated in the same direction in FZD6(-) BEAS-2B and in BC-exposed lungs of Bcmo1(-/-) mice and revealed enrichment of the Gene Ontology terms "oncogenes", "cell proliferation" and "cell cycle", which suggests a mediating role of FZD6 in BC-induced uncontrolled proliferation of lung cells.

Wnt5a signaling mediates biliary differentiation of fetal hepatic stem/progenitor cells in mice.

UNLABELLED: The molecular mechanisms regulating differentiation of fetal hepatic stem/progenitor cells, called hepatoblasts, which play pivotal roles in liver development, remain obscure. Wnt signaling pathways regulate the development and differentiation of stem cells in various organs. Although a ß-catenin-independent noncanonical Wnt pathway is essential for cell adhesion and polarity, the physiological functions of noncanonical Wnt pathways in liver development are unknown. Here we describe a functional role for Wnt5a, a noncanonical Wnt ligand, in the differentiation of mouse hepatoblasts. Wnt5a was expressed in mesenchymal cells and other cells of wild-type (WT) midgestational fetal liver. We analyzed fetal liver phenotypes in Wnt5a-deficient mice using a combination of histological and molecular techniques. Expression levels of Sox9 and the number of hepatocyte nuclear factor (HNF)1ß(+) HNF4α(-) biliary precursor cells were significantly higher in Wnt5a-deficient liver relative to WT liver. In Wnt5a-deficient fetal liver, in vivo formation of primitive bile ductal structures was significantly enhanced relative to WT littermates. We also investigated the function of Wnt5a protein and downstream signaling molecules using a three-dimensional culture system that included primary hepatoblasts or a hepatic progenitor cell line. In vitro differentiation assays showed that Wnt5a retarded the formation of bile duct-like structures in hepatoblasts, leading instead to hepatic maturation of such cells. Whereas Wnt5a signaling increased steady-state levels of phosphorylated calcium/calmodulin-dependent protein kinase II (CaMKII) in fetal liver, inhibition of CaMKII activity resulted in the formation of significantly more and larger-sized bile duct-like structures in vitro compared with those in vehicle-supplemented controls. CONCLUSION: Wnt5a-mediated signaling in fetal hepatic stem/progenitor cells suppresses biliary differentiation. These findings also suggest that activation of CaMKII by Wnt5a signaling suppresses biliary differentiation. (HEPATOLOGY 2013;).

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.

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.

Complex and dynamic patterns of Wnt pathway gene expression in the developing chick forebrain.

BACKGROUND: Wnt signalling regulates multiple aspects of brain development in vertebrate embryos. A large number of Wnts are expressed in the embryonic forebrain; however, it is poorly understood which specific Wnt performs which function and how they interact. Wnts are able to activate different intracellular pathways, but which of these pathways become activated in different brain subdivisions also remains enigmatic. RESULTS: We have compiled the first comprehensive spatiotemporal atlas of Wnt pathway gene expression at critical stages of forebrain regionalisation in the chick embryo and found that most of these genes are expressed in strikingly dynamic and complex patterns. Several expression domains do not respect proposed compartment boundaries in the developing forebrain, suggesting that areal identities are more dynamic than previously thought. Using an in ovo electroporation approach, we show that Wnt4 expression in the thalamus is negatively regulated by Sonic hedgehog (Shh) signalling from the zona limitans intrathalamica (ZLI), a known organising centre of forebrain development. CONCLUSION: The forebrain is exposed to a multitude of Wnts and Wnt inhibitors that are expressed in a highly dynamic and complex fashion, precluding simple correlative conclusions about their respective functions or signalling mechanisms. In various biological systems, Wnts are antagonised by Shh signalling. By demonstrating that Wnt4 expression in the thalamus is repressed by Shh from the ZLI we reveal an additional level of interaction between these two pathways and provide an example for the cross-regulation between patterning centres during forebrain regionalisation.

A transgenic marker mouse line labels Cajal-Retzius cells from the cortical hem and thalamocortical axons.

Cajal-Retzius (CR) cells are among the earliest born cortical neurons and are required for normal cortical development in rodents and humans; however, their embryonic origin has been controversial. Recent genetic lineage studies and direct visualization of migration of CR cells have demonstrated multiple germinative sources for CR cells on the edges of the developing pallium. We generated transgenic mice using 5' untranslated regions of the Frizzled10 gene in order to mark the cortical hem (the most caudomedial edge of the telencephalic neuroepithelium) and found that these mice faithfully reproduce the previously described expression pattern of Frizzled10 mRNA in the cortical hem, dorsal thalamus and dorsal neural tube. In the cortical hem, expression of LacZ mRNA was confined to the ventricular zone and perdurance of LacZ protein served as lineage marker for CR cells derived from the hem during embryonic life. When these marker mice were crossed with FoxG1 (BF1) mutants, they confirmed the previous finding that in these mice the cortical hem is expanded leading to increased production of CR cells from the medial wall of the cortex.

An evolutionary conserved role of Wnt signaling in stem cell fate decision.

Wnt/Frizzled/ss-catenin-based signaling systems play diverse roles in metazoan development, being involved not only in the establishment of body axes in embryogenesis but also in regulating stem cell fate in mammalian post-embryonic development. We have studied the role the canonical Wnt cascade plays in stem cell fate determination in Hydractinia, a member of the ancient metazoan phylum Cnidaria, by analyzing two key molecules in this pathway, frizzled and ss-catenin, and blocking GSK-3. Generally, frizzled was expressed in cells able to divide but absent in post-mitotic, terminally differentiated cells such as nerve cells and nematocytes. Transcripts of frizzled were identified in all embryonic stages beginning with maternal transcripts in the oocyte. Following gastrulation and in the planula larva, frizzled expression concentrated in the central endodermal mass from which the first interstitial stem cells and their derivatives arise. In post-metamorphic development, high levels of frizzled transcripts were detected in interstitial stem cells. Activating downstream events of the Wnt-cascade in the post-metamorphic life phase by blocking GSK-3 with paullones induced recruitment of nematocytes and nerve cells from the pool of interstitial stem cells. Terminal differentiation was preceded by an initial burst of proliferation of frizzled-positive i-cells. In activated i-cells, ss-catenin appeared in the cytoplasm, later in the nucleus. It was subsequently again observed in the cytoplasm and eventually faded out during terminal differentiation. Our results suggest an ancient role of Wnt signaling in stem cell fate determination.

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.

Cloning, sequence analysis, and distribution of rat metallocarboxypeptidase Z.

A cDNA encoding human carboxypeptidase Z (CPZ), a novel metallocarboxypeptidase, was recently cloned (Song and Fricker, J. Biol. Chem., 272, 1054, 1997). In the present study, a cDNA encoding the rat homolog of CPZ was identified. As with the human form, rat CPZ contains an N-terminal domain of 120 amino acids that has 20% to 30% amino acid identity with the "frizzled" domain found on proteins that interact with Wnt, a protein involved in tissue polarity in early embryogenesis. Sequence analysis showed rat and human CPZ to be highly conserved within the frizzled domain (77% amino acid identity), the carboxypeptidase domain (91%), and the C-terminal 28 residues (78%). The entire rat CPZ protein has high sequence similarity with human CPZ (81% amino acid identity), moderate sequence similarity to human carboxypeptidase N (45%), human carboxypeptidase E (41%), and human carboxypeptidase M (33%), and less sequence similarity with other metallocarboxypeptidases. Northern blot analysis showed rat CPZ mRNA to be abundant in the placenta, with low to moderate levels in the brain, lung, thymus, and kidney. The BRL3A rat liver cell line and the PC12 rat adrenal cell line express high levels of CPZ mRNA. In situ hybridization analysis indicated that CPZ is expressed only in specific cell types. For example, in the brain, CPZ mRNA is present in leptomeningeal cells, but not in the majority of other cell types. This distribution in leptomeningeal cells is shared by AEBP1, a recently reported member of the metallocarboxypeptidase gene family. However, the distribution of CPZ and AEBP1 differ in pituitary and thyroid. Taken together, these studies suggest that CPZ functions in a range of cell types.