Wnt3a promotes radioresistance via autophagy in squamous cell carcinoma of the head and neck

The canonical Wnt/β‐catenin signalling pathway and autophagy play critical roles in cancer progression. However, the role of Wnt‐mediated autophagy in cancer radioresistance remains unclear. In this study, we found that irradiation activated the Wnt/β‐catenin and autophagic signalling pathways in squamous cell carcinoma of the head and neck (SCCHN). Wnt3a is a classical ligand that activated the Wnt/β‐catenin signalling pathway, induced autophagy and decreased the sensitivity of SCCHN to irradiation both in vitro and in vivo. Further mechanistic analysis revealed that Wnt3a promoted SCCHN radioresistance via protective autophagy. Finally, expression of the Wnt3a protein was elevated in both SCCHN tissues and patients' serum. Patients showing high expression of Wnt3a displayed a worse prognosis. Taken together, our study indicates that both the canonical Wnt and autophagic signalling pathways are valuable targets for sensitizing SCCHN to irradiation.     

Mitotic and mitogenic Wnt signalling

Canonical Wnt signalling plays an important role in development, tissue homeostasis, and cancer. At the cellular level, canonical Wnt signalling acts by regulating cell fate, cell growth, and cell proliferation. With regard to proliferation, there is increasing evidence for a complex interaction between canonical Wnt signalling and the cell cycle. Mitogenic Wnt signalling regulates cell proliferation by promoting G1 phase. In mitosis, components of the Wnt signalling cascade function directly in spindle formation. Moreover, Wnt signalling is strongly activated in mitosis, suggesting that 'mitotic Wnt signalling' plays an important role to orchestrate a cell division program. Here, we review the complex interplay between Wnt signalling and the cell cycle.     

WNT secretion and signalling in human disease

Wnt signalling, a key pathway involved in various aspects of embryonic development, also underlies many human diseases, in particular, cancer. Research focused on signal transduction within signal-receiving cells led to the discovery of many Wnt pathway components, but study of the secretion of Wnt ligands themselves was neglected until recently. Attention was drawn to this highly regulated process by the association of aberrant Wnt levels with an increasing number of diseases. Studying the biogenesis and processing of active Wnt ligands will open new avenues for generating therapeutics to specifically target aberrant Wnt signalling. Here we review the proteins required for Wnt secretion and signalling at the plasma membrane, ending with a discussion on potential therapeutic approaches to treat Wnt-induced diseases.     

Wnt Pathway Activity in Breast Cancer Sub-Types and Stem-Like Cells

Introduction

Wnt signalling has been implicated in stem cell regulation however its role in breast cancer stem cell regulation remains unclear.

Methods

We used a panel of normal and breast cancer cell lines to assess Wnt pathway gene and protein expression, and for the investigation of Wnt signalling within stem cell-enriched populations, mRNA and protein expression was analysed after the selection of anoikis-resistant cells. Finally, cell lines and patient-derived samples were used to investigate Wnt pathway effects on stem cell activity in vitro.

Results

Wnt pathway signalling increased in cancer compared to normal breast and in both cell lines and patient samples, expression of Wnt pathway genes correlated with estrogen receptor (ER) expression. Furthermore, specific Wnt pathway genes were predictive for recurrence within subtypes of breast cancer. Canonical Wnt pathway genes were increased in breast cancer stem cell-enriched populations in comparison to normal breast stem cell-enriched populations. Furthermore in cell lines, the ligand Wnt3a increased whilst the inhibitor DKK1 reduced mammosphere formation with the greatest inhibitory effects observed in ER+ve breast cancer cell lines. In patient-derived metastatic breast cancer samples, only ER-ve mammospheres were responsive to the ligand Wnt3a. However, the inhibitor DKK1 efficiently inhibited both ER+ve and ER-ve breast cancer but not normal mammosphere formation, suggesting that the Wnt pathway is aberrantly activated in breast cancer mammospheres.

Conclusions

Collectively, these data highlight differential Wnt signalling in breast cancer subtypes and activity in patient-derived metastatic cancer stem-like cells indicating a potential for Wnt-targeted treatment in breast cancers.     

Cell cycle control of Wnt/β-catenin signalling by conductin/axin2 through CDC20

Wnt/β-catenin signalling regulates cell proliferation by modulating the cell cycle and is negatively regulated by conductin/axin2/axil. We show that conductin levels peak at G2/M followed by a rapid decline during return to G1. In line with this, Wnt/β-catenin target genes are low at G2/M and high at G1/S, and β-catenin phosphorylation oscillates during the cell cycle in a conductin-dependent manner. Conductin is degraded by the anaphase-promoting complex/cyclosome cofactor CDC20. Knockdown of CDC20 blocks Wnt signalling through conductin. CDC20-resistant conductin inhibits Wnt signalling and attenuates colony formation of colorectal cancer cells. We propose that CDC20-mediated degradation of conductin regulates Wnt/β-catenin signalling for maximal activity during G1/S.     

Subcellular spatial regulation of canonical Wnt signalling at the primary cilium

Mechanisms of signal transduction regulation remain a fundamental question in a variety of biological processes and diseases. Previous evidence indicates that the primary cilium can act as a signalling hub, but its exact role in many of the described pathways has remained elusive. Here, we investigate the mechanism of cilia-mediated regulation of the canonical Wnt pathway. We found that primary cilia dampen canonical Wnt signalling through a spatial mechanism involving compartmentalization of signalling components. The cilium, through regulated intraflagellar transport, diverts Jouberin (Jbn), a ciliopathy protein and context-specific Wnt pathway regulator, away from the nucleus and limits β-catenin nuclear entry. This repressive regulation does not silence the pathway, but instead maintains a discrete range of Wnt responsiveness; cells without cilia have potentiated Wnt responses, whereas cells with multiple cilia have inhibited responses. Furthermore, we show that this regulation occurs during embryonic development and is disrupted in cancer cell proliferation. Together these data explain a spatial mechanism of Wnt signalling regulation that may provide insight into ciliary regulation of other signalling pathways.     

Notch and Wnt inhibitors as potential new drugs for intestinal neoplastic disease

Colorectal cancer is a major cause of death in the western world. Recent advances in treatment comprise variations on the classical themes of surgical resection combined with chemotherapy using cytotoxic drugs and radiation therapy. Because this therapy is only moderately successful, novel approaches to the treatment of colorectal cancer are required. Our rapidly increasing knowledge of molecular signalling pathways that are deregulated in colorectal cancer might provide a platform from which to develop new rational cancer therapies. Here, we give an update on the roles of the Wnt and Notch signalling pathways in the self renewal of the intestinal epithelium and the consequences of Wnt deregulation in colorectal cancer. We focus on the potential of recently identified small-molecule inhibitors of the Wnt pathway and gamma-secretase inhibitors of the Notch pathway as novel colon cancer therapeutics.     

Down-regulation of SLC35C1 induces colon cancer through over-activating Wnt pathway

The canonical Wnt signalling pathway is a critical pathway involved in the proliferation of cells. It has been well-established that it plays the central role during colorectal carcinogenesis and development. Yet the exact molecular mechanism of how the canonical Wnt pathway is fine-tuned remains elusive. We found that SLC35C1, a GDP-fucose transporter, negatively regulates the Wnt signalling pathway. We show here that SLC35C1 is reduced in all colon cancer by both immunohistochemistry images and TCGA data, whereas β-catenin is increased. Down-regulation of SLC35C1 is also detected by real-time PCR in stage 3 and stage 4 colorectal cancer tissues. Moreover, analysing the TCGA database with cBioPortal reveals the negative correlation of SLC35C1 mRNA level to the expression of β-catenin. Reduced SLC35C1 significantly promotes cell proliferation and colony formation of HEK293 cells. Meanwhile, in HEK293 cells silencing SLC35C1 activates canonical Wnt pathway, whereas overexpressing SLC35C1 inhibits it. Consistently, the reduction of SLC35C1 in HEK293 cells also elevated the mRNA level of Wnt target genes C-myc, Axin2 and Cyclin D1, as well as the secretion of Wnt3a. In conclusion, we identified SLC35C1 as a negative regulator of the Wnt signalling pathway in colon cancer. Decreased SLC35C1 may cause over-activation of Wnt signalling in colorectal cancer.     

Wnt5a is strongly expressed at the leading edge in non-melanoma skin cancer, forming active gradients, while canonical Wnt signalling is repressed

Wnt5a is one of the so-called non-canonical Wnt ligands which do not act through β-catenin. In normal development, Wnt5a is secreted and directs the migration of target cells along concentration gradients. The effect of Wnt5a on target cells is regulated by many factors, including the expression level of inhibitors and receptors. Dysregulated Wnt5a signalling facilitates invasion of multiple tumor types into adjacent tissue. However, the expression and distribution of Wnt5a in cutaneous squamous cell carcinoma (SCC) and basal cell carcinoma (BCC), as well as the effect of Wnt5a on keratinocyte migration has not been studied in detail to date. We here report that Wnt5a is upregulated in SCC and BCC and localised to the leading edge of tumors, as well as tumor-associated fibroblasts. The Wnt5a-triggered bundling of its receptor Fzd3 provides evidence of Wnt5a concentration gradients projecting into the tumor. In vitro migration assays show that Wnt5a concentration gradients determine its effect on keratinoctye migration: While chemotactic migration is inhibited by Wnt5a present in homogenous concentrations, it is enhanced in the presence of a Wnt5a gradient. Expression profiling of the Wnt pathway shows that the upregulation of Wnt5a in SCC is coupled to repression of canonical Wnt signalling. This is confirmed by immunohistochemistry showing lack of nuclear β-catenin, as well as absent accumulation of Axin2. Since both types of Wnt signalling act mutually antogonistically at multiple levels, the concurrent repression of canonical Wnt signalling suggests hyper-active Wnt5a signal transduction. Significantly, this combination of gene dysregulation is not observed in the benign hyperproliferative inflammatory skin disease psoriasis. Collectively, our data strongly suggest that Wnt5a signalling contributes to tissue invasion by non-melanoma skin cancer.     

AGR3 promotes the stemness of colorectal cancer via modulating Wnt/β-catenin signalling

Cancer cells with stem cell properties have been acknowledged to be responsible for cancer initiation and progression. Wnt/β-catenin signalling is a major signal pathway promoting the stemness of cancer cells. Anterior gradient 3 (AGR3), a member of the protein disulfide isomerase (PDI) family, was found to be overexpressed in several cancers. However, the roles and mechanisms of AGR3 in colorectal cancer (CRC) have not been previously described. In our study, we find that AGR3 is highly expressed in CRC and associated with poor prognosis. Functional studies show that AGR3 promotes the stemness of CRC cells. Mechanically, AGR3 activates Wnt/β-catenin signalling and promotes the nuclear translocation of β-catenin to upregulate stemness related genes. Wnt/β-catenin signalling inhibition counteracts the promoting effect of AGR3 on cancer stemness. Moreover, the effect of AGR3 on Wnt/β-catenin signalling and cancer stemness depends on the presence of frizzled 4 (FZD4). Thus, our study first uncovers the stemness-promoting role and the oncogenic mechanism of AGR3 in CRC, which might provide a novel target for designing anti-CRC strategies.     

Wnk kinases are positive regulators of canonical Wnt/β-catenin signalling

Wnt/β-catenin signalling is central to development and its regulation is essential in preventing cancer. Using phosphorylation of Dishevelled as readout of pathway activation, we identified Drosophila Wnk kinase as a new regulator of canonical Wnt/β-catenin signalling. WNK kinases are known for regulating ion co-transporters associated with hypertension disorders. We demonstrate that wnk loss-of-function phenotypes resemble canonical Wnt pathway mutants, while Wnk overexpression causes gain-of-function canonical Wnt-signalling phenotypes. Importantly, knockdown of human WNK1 and WNK2 also results in decreased Wnt signalling in mammalian cell culture, suggesting that Wnk kinases have a conserved function in ensuring peak levels of canonical Wnt signalling.     

Wnt, stem cells and cancer in the intestine

The intestinal epithelium is a self-renewing tissue which represents a unique model for studying interconnected cellular processes such as proliferation, differentiation, cell migration and carcinogenesis. Although the stem cells of the intestine have not yet been physically characterized or isolated, data over the past decade have strongly implicated the Wnt/beta-catenin signalling pathway in their maintenance and progression to cancer. This review will (i) describe the distinctive features of the intestinal epithelium in relation to stem-cell function, (ii) illustrate the major genetic alterations that can lead to cancer, and (iii) show how Wnt/beta-catenin signalling controls homoeostasis in this tissue.