Dataset Information

A secreted splice variant of the Xenopus frizzled-4 receptor is a biphasic modulator of Wnt signalling.

ABSTRACT:

Background

Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzled-4 receptor found in humans and Xenopus, was shown to augment Wnt/?-catenin signalling, and also interacts with those Wnt ligands that act on ?-catenin-independent Wnt pathways.

Findings

Here we show that Xenopus Fz4-v1 can activate and inhibit the ?-catenin-dependent Wnt pathway. Gain-of-function experiments revealed that high Wnt/?-catenin activity is inhibited by low and high concentrations of Fz4-v1. In contrast, signals generated by low amounts of Wnt ligands were enhanced by low concentrations of Fz4-v1 but were repressed by high concentrations. This biphasic activity of Fz4-v1 was not observed in non-canonical Wnt signalling. Fz4-v1 enhanced ?-catenin-independent Wnt signalling triggered by either low or high doses of Wnt11. Antisense morpholino-mediated knock-down experiments demonstrated that in early Xenopus embryos Fz4-v1 is required for the migration of cranial neural crest cells and for the development of the dorsal fin.

Conclusions

For the first time, we show that a splice variant of the Frizzled-4 receptor modulates Wnt signalling in a dose-dependent, biphasic manner. These results also demonstrate that the cystein-rich domain (CRD), which is shared by Fz4-v1 and SFRPs, is sufficient for the biphasic activity of these secreted Wnt modulators.

SUBMITTER: Gorny AK

PROVIDER: S-EPMC4077065 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Publications

A secreted splice variant of the Xenopus frizzled-4 receptor is a biphasic modulator of Wnt signalling.

Gorny Anne-Kathrin AK Kaufmann Lilian T LT Swain Rajeeb K RK Steinbeisser Herbert H

Cell communication and signaling : CCS 20131119

<h4>Background</h4>Activation of the Wnt signalling cascade is primarily based on the interplay between Wnt ligands, their receptors and extracellular modulators. One prominent family of extracellular modulators is represented by the SFRP (secreted Frizzled-related protein) family. These proteins have significant similarity to the extracellular domain of Frizzled receptors, suggesting that they bind Wnt ligands and inhibit signalling. The SFRP-type protein Fz4-v1, a splice variant of the Frizzle ...[more]

PMID: 24252524

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Project description:BackgroundDeregulation of the Wnt/ beta-catenin signal transduction pathway has been implicated in the pathogenesis of tumours in the mammary gland, colon and other tissues. Mutations in components of this pathway result in beta-catenin stabilization and accumulation, and the aberrant modulation of beta-catenin/TCF target genes. Such alterations in the cellular transcriptional profile are believed to underlie the pathogenesis of these cancers. We have sought to identify novel target genes of this pathway in mouse mammary epithelial cells.MethodsGene expression microarray analysis of mouse mammary epithelial cells inducibly expressing a constitutively active mutant of beta-catenin was used to identify target genes of this pathway.ResultsThe differential expression in response to DeltaNbeta-catenin for five putative target genes, Autotaxin, Extracellular Matrix Protein 1 (Ecm1), CD14, Hypoxia-inducible gene 2 (Hig2) and Receptor Activity Modifying Protein 3 (RAMP3), was independently validated by northern blotting. Each of these genes encodes either a receptor or a secreted protein, modulation of which may underlie the interactions between Wnt/beta-catenin tumour cells and between the tumour and its microenvironment. One of these genes, Hig2, previously shown to be induced by both hypoxia and glucose deprivation in human cervical carcinoma cells, was strongly repressed upon DeltaNbeta-catenin induction. The predicted N-terminus of Hig2 contains a putative signal peptide suggesting it might be secreted. Consistent with this, a Hig2-EGFP fusion protein was able to enter the secretory pathway and was detected in conditioned medium. Mutation of critical residues in the putative signal sequence abolished its secretion. The expression of human HIG2 was examined in a panel of human tumours and was found to be significantly downregulated in kidney tumours compared to normal adjacent tissue.ConclusionsHIG2 represents a novel non-cell autonomous target of the Wnt pathway which is potentially involved in human cancer.

Project description:BackgroundTriple negative breast cancer (TNBC) is characterized by lack of expression of both estrogen and progesterone receptor as well as lack of overexpression or amplification of HER2. Despite an increased probability of response to chemotherapy, many patients resistant to current chemotherapy regimens suffer from a worse prognosis compared to other breast cancer subtypes. However, molecular determinants of response to chemotherapy specific to TNBC remain largely unknown. Thus, there is a high demand for biomarkers potentially stratifying triple negative breast cancer patients for neoadjuvant chemotherapies or alternative therapies.MethodsIn order to identify genes correlating with both the triple negative breast cancer subtype as well as response to neoadjuvant chemotherapy we employed publicly available gene expression profiles of patients, which had received neoadjuvant chemotherapy. Analysis of tissue microarrays as well as breast cancer cell lines revealed correlation to the triple negative breast cancer subtype. Subsequently, effects of siRNA-mediated knockdown on response to standard chemotherapeutic agents as well as radiation therapy were analyzed. Additionally, we evaluated the molecular mechanisms by which SFRP1 alters the carcinogenic properties of breast cancer cells.ResultsSFRP1 was identified as being significantly overexpressed in TNBC compared to other breast cancer subtypes. Additionally, SFRP1 expression is significantly correlated with an increased probability of positive response to neoadjuvant chemotherapy. Knockdown of SFRP1 in triple negative breast cancer cells renders the cells more resistant to standard chemotherapy. Moreover, tumorigenic properties of the cells are modified by knockdown, as shown by both migration or invasion capacity as well reduced apoptotic events. Surprisingly, we found that these effects do not rely on Wnt signaling. Furthermore, we show that pro-apoptotic as well as migratory pathways are differentially regulated after SFRP1 knockdown.ConclusionWe could firstly show that SFRP1 strongly correlates with the triple negative breast cancer subtype and secondly, that SFRP1 might be used as a marker stratifying patients to positively respond to neoadjuvant chemotherapy. The mechanisms by which tumor suppressor SFRP1 influences carcinogenic properties of cancer cells do not rely on Wnt signaling, thereby demonstrating the complexity of tumor associated signaling pathways.

Dataset Information

A secreted splice variant of the Xenopus frizzled-4 receptor is a biphasic modulator of Wnt signalling.

Background

Findings

Conclusions

Publications

A secreted splice variant of the Xenopus frizzled-4 receptor is a biphasic modulator of Wnt signalling.

Similar Datasets

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