The opposing roles of Wnt-5a in cancer. Br J Cancer. 2009;101:209-214. [PMID: 19603030 PMCID: PMC2720208 DOI: 10.1038/sj.bjc.6605174]

ROR1 and ROR2 in Human Malignancies: Potentials for Targeted Therapy

Targeted therapies require cellular protein expression that meets specific requirements that will maximize effectiveness, minimize off-target toxicities, and provide an opportunity for a therapeutic effect. The receptor tyrosine kinase-like orphan receptors (ROR) are possible targets for therapy that may meet such requirements. RORs are transmembrane proteins that are part of the receptor tyrosine kinase (RTK) family. The RORs have been shown to play a role in tumor-like behavior, such as cell migration and cell invasiveness and are normally not expressed in normal adult tissue. As part of the large effort in target discovery, ROR proteins have recently been found to be expressed in human cancers. Their unique expression profiles may provide a novel class of therapeutic targets for small molecules against the kinase or for antibody-based therapies against these receptors. Being restricted on tumor cells and not on most normal tissues, RORs are excellent targets for the treatment of minimal residual disease, the final hurdle in the curative approach to many cancers, including solid tumors such as neuroblastoma. In this review, we summarize the biology of RORs as they relate to human cancer, and highlight the therapeutic approaches directed toward them.

Frizzled7 as an emerging target for cancer therapy

Wnt proteins are secreted glycoproteins that bind to the N-terminal extra-cellular cysteine-rich domain of the Frizzled (Fzd) receptor family. The Fzd receptors can respond to Wnt proteins in the presence of Wnt co-receptors to activate the canonical and non-canonical Wnt pathways. Recent studies indicated that, among the Fzd family, Fzd7 is the Wnt receptor most commonly upregulated in a variety of cancers including colorectal cancer, hepatocellular carcinoma and triple negative breast cancer. Fzd7 plays an important role in stem cell biology and cancer development and progression. In addition, it has been demonstrated that siRNA knockdown of Fzd7, the anti-Fzd7 antibody or the extracellular peptide of Fzd7 (soluble Fzd7 peptide) displayed anti-cancer activity in vitro and in vivo mainly due to the inhibition of the canonical Wnt signaling pathway. Furthermore, pharmacological inhibition of Fzd7 by small interfering peptides or a small molecule inhibitor suppressed β-catenin-dependent tumor cell growth. Therefore, targeted inhibition of Fzd7 represents a rational and promising new approach for cancer therapy.

Loss of Wnt5a and Ror2 protein in hepatocellular carcinoma associated with poor prognosis

AIM: To investigate the expression and clinical significance of Wnt member 5a (Wnt5a) and receptor tyrosine kinase-like orphan receptor 2 (Ror2) in hepatocellular carcinoma (HCC).

METHODS: HCC tissues obtained from 85 patients were examined the mRNA expression of Ror2 by real-time reverse transcription polymerase chain reaction and the protein expressions of Wnt5a, Ror2, β-catenin and Ki-67 via immunohistochemical staining. The correlation between protein expression and HCC patients’ clinicopathology data and prognoses were analyzed.

RESULTS: Compared to nontumorous (hepatitis or cirrhotic) tissues, Ror2 mRNA expression was clearly decreased in HCC. Ror2 and Wnt5a protein expressions in the majority of HCC patients (63% and 77%, respectively) was significantly less in tumor tissues, as compared to adjacent nontumorous tissues, and this reduction was correlated with increasing serum α-fetoprotein and tumor stage. In 68% (58/85) of the HCC cases, the expression of β-catenin in tumor tissues was either downregulated in the cellular membrane, upregulated in the cytoplasm, or both. Survival analysis indicated that Wnt5a and Ror2 protein expressions could be regarded as independent prognostic factors for HCC; HCC patients with decreased Wnt5a or Ror2 protein expression had a poorer prognosis than those with elevated Wnt5a and Ror2 expression (P = 0.016, P = 0.007, respectively).

CONCLUSION: Wnt5a and Ror2 may serve as tumor suppressor genes in the development of HCC, and may serve as clinicopathologic biomarkers for prognosis in HCC patients.

WNT5A is induced by inflammatory mediators in bone marrow stromal cells and regulates cytokine and chemokine production

WNT5A has recently been implicated in inflammatory processes, but its role as a bone marrow stromal cell (BMSC)-derived mediator of joint inflammation in arthritis is unclear. Here, we investigated whether inflammatory stimuli induce WNT5A in BMSC to control inflammatory responses. WNT5A levels were determined in human BMSC after stimulation with lipopolysaccharide (LPS) or tumor necrosis factor α (TNF-α,) and in synovial cells and tissue of patients with rheumatoid arthritis (RA) and human TNF-α transgenic (hTNFtg) mice. A microarray analysis of WNT5A-treated murine osteoblasts was performed using Affymetrix gene chips. The regulation of cytokine/chemokine expression was confirmed by qPCR, ELISA, and Luminex technology in BMSC after stimulation with WNT5A or WNT5A knockdown. Relevant signaling pathways were identified using specific inhibitors. Migration of MACS-purified T lymphocytes and monocytes was assessed using the FluoroBlok system. WNT5A expression was increased threefold in BMSC after stimulation with LPS or TNF-α. Synovial fibroblasts from patients with RA showed a twofold increase of WNT5A expression compared with control cells, and its expression was highly induced in the synovial tissue of patients with RA and hTNFtg mice. Microarray analysis of WNT5A-treated osteoblasts identified cytokines and chemokines as targets. The induction of IL-1β, IL-6, CCL2, CCL5, CXCL1, and CXCL5 by WNT5A was confirmed in BMSC and depended on the activation of the NF-κB, mitogen-activated protein (MAPK), and Akt pathways. Accordingly, knockdown of WNT5A markedly reduced the basal and LPS-induced cytokine/chemokine production. Finally, migration of monocytes and T cells toward the supernatant of WNT5A-treated BMSC was increased by 25% and 20%, respectively. This study underlines the critical role of BMSC-derived WNT5A in the regulation of inflammatory processes and suggests its participation in the pathogenesis of RA.

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.

Dysregulation of Wnt/β-catenin signaling in gastrointestinal cancers

Aberrant Wnt/β-catenin signaling is widely implicated in numerous malignancies, including cancers of the gastrointestinal tract. Dysregulation of signaling is traditionally attributed to mutations in Axin, adenomatous polyposis coli, and β-catenin that lead to constitutive hyperactivation of the pathway. However, Wnt/β-catenin signaling is also modulated through various other mechanisms in cancer, including cross talk with other altered signaling pathways. A more complex view of Wnt/β-catenin signaling and its role in gastrointestinal cancers is now emerging as divergent phenotypic outcomes are found to be dictated by temporospatial context and relative levels of pathway activation. This review summarizes the dysregulation of Wnt/β-catenin signaling in colorectal carcinoma, hepatocellular carcinoma, and pancreatic ductal adenocarcinoma, with particular emphasis on the latter two. We conclude by addressing some of the major challenges faced in attempting to target the pathway in the clinic.

Expression of WNT-5a and ROR2 correlates with disease severity in osteosarcoma

Osteosarcoma, a common malignancy primarily affecting children, generally has a poor prognosis. Novel diagnostic, prognostic and therapeutic markers are required to ameliorate the negative outcomes of this disease. We investigated two potential markers, WNT-5a and ROR2, which are hypothesized to dysregulate WNT signaling pathways to promote tumorigenesis in other types of cancer. We investigated WNT-5a and ROR2 expression using immunohistochemistry in 42 osteosarcoma and 12 osteochondroma specimens, and compared the expression of these proteins with one another as well as with clinicopathological parameters. WNT-5a was detected in 34/42 (81.0%) cases and ROR2 was detected in 31/42 (73.8%) cases, significantly higher than in osteochondroma (16.7 and 25.0%, respectively; both P<0.05). Expression of these proteins was positively correlated (r=0.552, P<0.05). Furthermore, expression of WNT-5a and ROR2 was both correlated with Enneking surgical stage and tumor metastasis (P<0.05), but not with patient gender, age or pathological type. Thus, WNT-5a and ROR2 were more highly expressed in more severe disease states, and therefore may play a coordinated role in the occurrence and progression of osteosarcoma.

A dual array-based approach to assess the abundance and posttranslational modification state of signaling proteins

A system-wide analysis of cell signaling requires detecting and quantifying many different proteins and their posttranslational modification states in the same cellular sample. Here, we present Protocols for two miniaturized, array-based methods, one of which provides detailed information on a central signaling protein and the other of which provides a broad characterization of the surrounding signaling network. We describe a bead-based array and its use in characterizing the different forms and functions of β-catenin, as well as lysate microarrays (reverse-phase protein arrays) and their use in detecting and quantifying proteins involved in the canonical and noncanonical Wnt signaling pathways. As an application of this dual approach, we characterized the state of β-catenin signaling in cell lysates and linked these molecule-specific data with pathway-wide changes in signaling. The Protocols described here provide detailed instructions for cell culture methods, bead arrays, and lysate microarrays and outline how to use these complementary approaches to obtain insight into a complex network at a systems level.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.

The Wnt secretion protein Evi/Gpr177 promotes glioma tumourigenesis

Malignant astrocytomas are highly aggressive brain tumours with poor prognosis. While a number of structural genomic changes and dysregulation of signalling pathways in gliomas have been described, the identification of biomarkers and druggable targets remains an important task for novel diagnostic and therapeutic approaches. Here, we show that the Wnt-specific secretory protein Evi (also known as GPR177/Wntless/Sprinter) is overexpressed in astrocytic gliomas. Evi/Wls is a core Wnt signalling component and a specific regulator of pan-Wnt protein secretion, affecting both canonical and non-canonical signalling. We demonstrate that its depletion in glioma and glioma-derived stem-like cells led to decreased cell proliferation and apoptosis. Furthermore, Evi/Wls silencing in glioma cells reduced cell migration and the capacity to form tumours in vivo. We further show that Evi/Wls overexpression is sufficient to promote downstream Wnt signalling. Taken together, our study identifies Evi/Wls as an essential regulator of glioma tumourigenesis, identifying a pathway-specific protein trafficking factor as an oncogene and offering novel therapeutic options to interfere with the aberrant regulation of growth factors at the site of production.

Possible involvement of Wnt11 in colorectal cancer progression

Our previous report revealed that the expression of Frizzled-7 (FZD7) in colorectal cancer (CRC) and its possible role in CRC progression. In this study we measured the expression levels of candidate FZD7 ligands, Wnt3 and Wnt11 in colon cancer cell lines (n = 7) and primary CRC tissues (n = 133) by quantitative RT-PCR. We also examined the functional effects of Wnt11 with the use of Wnt11 transfectants of colon cancer HCT-116 cells. Wnt11 transfectants showed the increased proliferation and migration/invasion activities compared to mock cells. Western blot analysis of transfectants revealed that phosphorylation of JNK and c-jun was increased after Wnt11 transfection. Wnt11 mRNA expression was significantly higher in the stage I, II, III, or IV tumor tissues than in non-tumor tissues (overall P < 0.003), while there was no significant difference in Wnt3 mRNA expression between tumor and non-tumor tissues. In addition, Wnt11 mRNA expression was significantly higher in patients with recurrence or death after surgery than in those with no recurrence (disease free) after surgery (P = 0.018). We also compared the expression levels of Wnt11 mRNA with those of FZD7 mRNA in the same CRC samples. Wnt11 mRNA expression was significantly higher in patients with higher FZD7 mRNA levels than in those with lower FZD7 mRNA levels (P = 0.0005). The expression levels of Wnt11 mRNA were correlated with those of FZD7 mRNA (P < 0.0001). These data suggest that Wnt11 may play an important role in CRC progression.

Elevated level of Wnt5a protein in localized prostate cancer tissue is associated with better outcome

BACKGROUND

Wnt5a is a non-canonical secreted glycoprotein of the Wnt family that plays an important role in cancer development and progression. Previous studies report that Wnt5a is upregulated in prostate cancer and suggested that Wnt5a affects migration and invasion of prostate tumor cell. This study aimed to evaluate the prognostic value of Wnt5a protein expression in prostate cancer tissue and its potential to predict outcome after radical prostatectomy in patients with localized prostate cancer.

METHODOLOGY AND RESULTS

Immunohistochemical analysis of a tissue microarray containing prostate specimens of 503 patients with localized prostate cancer showed significantly higher Wnt5a protein expression in cancer compared to benign cores from the same patients (p<0.0001). Patients with high expression of Wnt5a protein had significantly better outcome in terms of time to biochemical recurrence compared to patients with low expression levels (p = 0.001, 95%CI 1.361-3.570, Hazard's ratio 2.204). A combination of high Wnt5a expression with low levels of Ki-67 or androgen receptor expression had even better outcome compared to all other groups. Furthermore, we found that Wnt5a expression significantly correlated with VEGF and with Ki-67 and androgen receptor expression, although not highly significant. In vitro, we demonstrated that recombinant Wnt5a decreased invasion of 22Rv1 and DU145 cells and that siRNA knockdown of endogenous Wnt5a protein led to increased invasion of 22Rv1 and LNCaP cells.

CONCLUSION

We demonstrate that preserved overexpression of Wnt5a protein in patients with localized prostate cancer predicts a favorable outcome after surgery. This finding together with our in vitro data demonstrating the ability of Wnt5a to impair the invasive properties of prostate cancer cells, suggests a tumor suppressing effect of Wnt5a in localized prostate cancer. These results indicate that Wnt5a can be used as a predictive marker and that it also is a plausible therapeutic target for treatment of localized prostate cancer.

Separate and distinctive roles for Wnt5a in tongue, lingual tissue and taste papilla development

Although canonical Wnt signaling is known to regulate taste papilla induction and numbers, roles for noncanonical Wnt pathways in tongue and taste papilla development have not been explored. With mutant mice and whole tongue organ cultures we demonstrate that Wnt5a protein and message are within anterior tongue mesenchyme across embryo stages from the initiation of tongue formation, through papilla placode appearance and taste papilla development. The Wnt5a mutant tongue is severely shortened, with an ankyloglossia, and lingual mesenchyme is disorganized. However, fungiform papilla morphology, number and innervation are preserved, as is expression of the papilla marker, Shh. These data demonstrate that the genetic regulation for tongue size and shape can be separated from that directing lingual papilla development. Preserved number of papillae in a shortened tongue results in an increased density of fungiform papillae in the mutant tongues. In tongue organ cultures, exogenous Wnt5a profoundly suppresses papilla formation and simultaneously decreases canonical Wnt signaling as measured by the TOPGAL reporter. These findings suggest that Wnt5a antagonizes canonical Wnt signaling to dictate papilla number and spacing. In all, distinctive roles for Wnt5a in tongue size, fungiform papilla patterning and development are shown and a necessary balance between non-canonical and canonical Wnt paths in regulating tongue growth and fungiform papillae is proposed in a model, through the Ror2 receptor.

Wnt/Ca2+ signaling pathway: a brief overview

The non-canonical Wnt/Ca(2+) signaling cascade is less characterized than their canonical counterpart, the Wnt/β-catenin pathway. The non-canonical Wnt signaling pathways are diverse, defined as planer cell polarity pathway, Wnt-RAP1 signaling pathway, Wnt-Ror2 signaling pathway, Wnt-PKA pathway, Wnt-GSK3MT pathway, Wnt-aPKC pathway, Wnt-RYK pathway, Wnt-mTOR pathway, and Wnt/calcium signaling pathway. All these pathways exhibit a considerable degree of overlap between them. The Wnt/Ca(2+) signaling pathway was deciphered as a crucial mediator in development. However, now there is substantial evidence that the signaling cascade is involved in many other molecular phenomena. Many aspects of Wnt/Ca(2+) pathway are yet enigmatic. This review will give a brief overview of the fundamental and evolving concepts of the Wnt/Ca(2+) signaling pathway.

Diverse mechanisms for activation of Wnt signalling in the ovarian tumour microenvironment

Wnt signalling pathways have been shown to play key roles in both normal development and tumorigenesis. Progression of many human cancers is associated with defined mutations in Wnt pathway components that result in dysregulated β-catenin-mediated gene transcription. Although Wnt pathway mutations are rare in epithelial ovarian cancer (with the exception of the endometrioid histotype), accumulating evidence supports a role for Wnt signalling in ovarian tumorigenesis in the absence of genetic mutations. The present review summarizes evidence in support of activated Wnt signalling in ovarian tumours and discusses alternative mechanisms for Wnt pathway activation in the ovarian tumour microenvironment.

Expression profile of WNT molecules in prostate cancer and its regulation by aminobisphosphonates

Skeletal metastases represent a frequent complication in patients with advanced prostate cancer (PCa) and often require bisphosphonate treatment to limit skeletal-related events. Metastasized PCa cells disturb bone remodeling. Since the WNT signaling pathway regulates bone remodeling and has been implicated in tumor progression and osteomimicry, we analyzed the WNT profile of primary PCa tissues and PCa cell lines and assessed its regulation by bisphosphonates. Prostate tissue (n = 18) was obtained from patients with benign prostate hyperplasia (BPH) and PCa patients with different disease stages. Serum samples were collected from 62 patients. Skeletal metastases were present in 17 patients of whom 6 had been treated with zoledronic acid. The WNT profile and its regulation by bisphoshonates were analyzed in tissue RNA extracts and serum samples as well as in osteotropic (PC3) and non-osteotropic (DU145, LNCaP) PCa cell lines. Several members of the WNT pathway, including WNT5A, FZD5, and DKK1 were highly up-regulated in PCa tissue from patients with advanced PCa. Interestingly, osteotropic cells showed a distinct WNT profile compared to non-osteotropic cells. While WNT5A, FZD5, and DKK1 were highly expressed in PC3 cells, WNT1 and SFRP1 mRNA levels were higher in DU145 cells. Moreover, zoledronic acid down-regulated mRNA levels of WNT5A (-34%), FZD5 (-60%), and DKK1 (-46%) in PC3 cells. Interestingly, patients with skeletal metastases who received zoledronic acid had twofold higher DKK1 serum levels compared to bisphosphonate-naive patients. The WNT signaling pathway is up-regulated in advanced PCa, differentially expressed in osteotropic versus non-osteotropic cells, and is regulated by zoledronic acid.

Hypoxia-induced methylation of a pontin chromatin remodeling factor

Pontin is a chromatin remodeling factor that possesses both ATPase and DNA helicase activities. Although Pontin is frequently overexpressed in human cancers of various types and implicated in oncogenic functions, the upstream signaling network leading to the regulation of Pontin that in turn affects transcription of downstream target genes has not been extensively studied. Here, we identify Pontin is methylated by G9a/GLP methyltransferases in hypoxic condition and potentiates HIF-1α-mediated activation by increasing the recruitment of p300 coactivator to a subset of HIF-1α target promoters. Intriguingly, Pontin methylation results in the increased invasive and migratory properties by activating downstream target gene, Ets1. In contrast, inhibition of Pontin methylation results in the suppression of tumorigenic and metastatic properties. Together, our data provide new approaches by targeting Pontin methylation and its downstream targets for the development of therapeutic agents for human cancers.

Wnt5a suppresses epithelial ovarian cancer by promoting cellular senescence

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy in the United States. Thus, there is an urgent need to develop novel therapeutics for this disease. Cellular senescence is an important tumor suppression mechanism that has recently been suggested as a novel mechanism to target for developing cancer therapeutics. Wnt5a is a noncanonical Wnt ligand that plays a context-dependent role in human cancers. Here, we investigate the role of Wnt5a in regulating senescence of EOC cells. We show that Wnt5a is expressed at significantly lower levels in human EOC cell lines and in primary human EOCs (n = 130) compared with either normal ovarian surface epithelium (n = 31; P = 0.039) or fallopian tube epithelium (n = 28; P < 0.001). Notably, a lower level of Wnt5a expression correlates with tumor stage (P = 0.003) and predicts shorter overall survival in EOC patients (P = 0.003). Significantly, restoration of Wnt5a expression inhibits the proliferation of human EOC cells both in vitro and in vivo in an orthotopic EOC mouse model. Mechanistically, Wnt5a antagonizes canonical Wnt/β-catenin signaling and induces cellular senescence by activating the histone repressor A/promyelocytic leukemia senescence pathway. In summary, we show that loss of Wnt5a predicts poor outcome in EOC patients and Wnt5a suppresses the growth of EOC cells by triggering cellular senescence. We suggest that strategies to drive senescence in EOC cells by reconstituting Wnt5a signaling may offer an effective new strategy for EOC therapy.

Genome-wide analysis of promoter methylation associated with gene expression profile in pancreatic adenocarcinoma

PURPOSE

The goal of this study was to comprehensively identify CpG island methylation alterations between pancreatic cancers and normal pancreata and their associated gene expression alterations.

EXPERIMENTAL DESIGN

We employed methylated CpG island amplification followed by CpG island microarray, a method previously validated for its accuracy and reproducibility, to analyze the methylation profile of 27,800 CpG islands covering 21 MB of the human genome in nine pairs of pancreatic cancer versus normal pancreatic epithelial tissues and in three matched pairs of pancreatic cancer versus lymphoid tissues from the same individual.

RESULTS

This analysis identified 1,658 known loci that were commonly differentially methylated in pancreatic cancer compared with normal pancreas. By integrating the pancreatic DNA methylation status with the gene expression profiles of the same samples before and after treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, and the histone deacetylase inhibitor, trichostatin A, we identified dozens of aberrantly methylated and differentially expressed genes in pancreatic cancers including a more comprehensive list of hypermethylated and silenced genes that have not been previously described as targets for aberrant methylation in cancer.

CONCLUSION

We expected that the identification of aberrantly hypermethylated and silenced genes will have diagnostic, prognostic, and therapeutic applications.

Systematic CpG islands methylation profiling of genes in the wnt pathway in epithelial ovarian cancer identifies biomarkers of progression-free survival

PURPOSE

Wnt pathways control key biological processes that potentially impact on tumor progression and patient survival. We aimed to evaluate DNA methylation at promoter CpG islands (CGI) of Wnt pathway genes in ovarian tumors at presentation and identify biomarkers of patient progression-free survival (PFS).

EXPERIMENTAL DESIGN

Epithelial ovarian tumors (screening study n = 120, validation study n = 61), prospectively collected through a cohort study, were analyzed by differential methylation hybridization at 302 loci spanning 189 promoter CGIs at 137 genes in Wnt pathways. The association of methylation and PFS was examined by Cox proportional hazards model.

RESULTS

DNA methylation is associated with PFS at 20 of 302 loci (P < 0.05, n = 111), with 5 loci significant at false discovery rate (FDR) less than 10%. A total of 11 of 20 loci retain significance in an independent validation cohort (n = 48, P ≤ 0.05, FDR ≤ 10%), and 7 of these loci, at FZD4, DVL1, NFATC3, ROCK1, LRP5, AXIN1, and NKD1 genes, are independent from clinical parameters (adjusted P < 0.05). Increased methylation at these loci associates with increased hazard of disease progression. A multivariate Cox model incorporates only NKD1 and DVL1, identifying two groups differing in PFS [HR = 2.09; 95% CI (1.39-3.15); permutation test P < 0.005]. Methylation at DVL1 and NFATC3 show significant association with response. Consistent with their epigenetic regulation, reduced expression of FZD4, DVL1, and ROCK1 is an indicator of early-disease relapse in an independent ovarian tumor cohort (n = 311, adjusted P < 0.05).

CONCLUSION

The data highlight the importance of epigenetic regulation of multiple promoter CGIs of Wnt pathway genes in ovarian cancer and identify methylation at NKD1 and DVL1 as independent predictors of PFS.

Wnt5a as an effector of TGFβ in mammary development and cancer

Wnt5a is a member of the Wingless-related/MMTV-integration family of secreted growth factors, which are involved in a wide range of cellular processes. Wnt signaling can be broadly divided into two categories the canonical, ß-catenin-dependent pathway and the non-canonical ß-catenin-independent pathway. Wnt5a is a non-canonical signaling member of the Wnt family. Loss of Wnt5a is associated with early relapse of invasive breast cancer, increased metastasis, and poor survival in humans. It has been shown that TGF-ß directly regulates expression of Wnt5a in mammary gland and that Wnt5a mediates the effects of TGF-ß on branching during mammary gland development. Here we review the evidence suggesting Wnt5a acts as an effector of TGF-ß actions in breast cancer. It is suggested that the tumor suppressive functions of TGF-ß involve Wnt5a-mediated antagonism of Wnt/ß-catenin signaling and limiting the stem cell population. Interactions between TGF-ß and Wnt5a in metastasis appear to be more complex, and may depend on specific cues from the microenvironment as well as activation of specific intracellular signaling pathways.

Flavonoids: potential Wnt/beta-catenin signaling modulators in cancer

Flavonoids are polyphenolic compounds found throughout the plant kingdom. They occur in every organ but are usually concentrated in leaves and flowers. During the last two decades, in vitro and in vivo studies demonstrated that flavonoids have inhibitory effects on human diseases through targeting of multiple cellular signaling components. Wnt/β-catenin signaling regulates proliferation, differentiation and fate specification in developmental stages and controls tissue homeostasis in adult life. For these reasons, this pathway has received great attention in the last years as potential pathway involved in distinct Human pathologies. In this review we discuss the emerging potential mechanisms for flavonoids on Wnt/β-catenin signaling in cancer and possible investigation strategies to understand flavonoids mode of action on this signaling pathway.

MicroRNA-301 mediates proliferation and invasion in human breast cancer

Several microRNAs have been implicated in human breast cancer but none to date have been validated or utilized consistently in clinical management. MicroRNA-301 (miR-301) overexpression has been implicated as a negative prognostic indicator in lymph node negative (LNN) invasive ductal breast cancer, but its potential functional impact has not been determined. Here we report that in breast cancer cells, miR-301 attenuation decreased cell proliferation, clonogenicity, migration, invasion, tamoxifen resistance, tumor growth, and microvessel density, establishing an important oncogenic role for this gene. Algorithm-based and experimental strategies identified FOXF2, BBC3, PTEN, and COL2A1 as candidate miR-301 targets, all of which were verified as direct targets through luciferase reporter assays. We noted that miR-301 is located in an intron of the SKA2 gene which is responsible for kinetochore assembly, and both genes were found to be coexpressed in primary breast cancer samples. In summary, our findings define miR-301 as a crucial oncogene in human breast cancer that acts through multiple pathways and mechanisms to promote nodal or distant relapses.

Wnt signaling and colon carcinogenesis: beyond APC

Activation of the Wnt signaling pathway via mutation of the adenomatous polyposis coli gene (APC) is a critical event in the development of colon cancer. For colon carcinogenesis, however, constitutive signaling through the canonical Wnt pathway is not a singular event. Here we review how canonical Wnt signaling is modulated by intracellular LEF/TCF composition and location, the action of different Wnt ligands, and the secretion of Wnt inhibitory molecules. We also review the contributions of non-canonical Wnt signaling and other distinct pathways in the tumor micro environment that cross-talk to the canonical Wnt pathway and thereby influence colon cancer progression. These ‘non-APC’ aspects of Wnt signaling are considered in relation to the development of potential agents for the treatment of patients with colon cancer. Regulatory pathways that influence Wnt signaling highlight how it might be possible to design therapies that target a network of signals beyond that of APC and β-catenin.

Noncanonical Wnt signaling mediates androgen-dependent tumor growth in a mouse model of prostate cancer

Prostate cancer development is associated with hyperactive androgen signaling. However, the molecular link between androgen receptor (AR) function and humoral factors remains elusive. A prostate cancer mouse model was generated by selectively mutating the AR threonine 877 into alanine in prostatic epithelial cells through Cre-ERT2-mediated targeted somatic mutagenesis. Such AR point mutant mice (ARpe-T877A/Y) developed hypertrophic prostates with responses to both an androgen antagonist and estrogen, although no prostatic tumor was seen. In prostate cancer model transgenic mice, the onset of prostatic tumorigenesis as well as tumor growth was significantly potentiated by introduction of the AR T877A mutation into the prostate. Genetic screening of mice identified Wnt-5a as an activator. Enhanced Wnt-5a expression was detected in the malignant prostate tumors of patients, whereas in benign prostatic hyperplasia such aberrant up-regulation was not obvious. These findings suggest that a noncanonical Wnt signal stimulates development of prostatic tumors with AR hyperfunction.

Elevation of WNT5A expression in polyp formation in Lkb1+/- mice and Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare, inherited disease caused by germline mutation of the LKB1 gene. Patients with PJS develop characteristic polyps in the digestive tract and carry an elevated risk of cancers in multiple organs, including the intestinal tract. While LKB1 is capable of phosphorylating AMPK and regulates the mTOR pathway, it is also known to be a multitasking protein that can influence other cellular processes, including cell polarity. We hypothesized that there may be other biological pathways directly or indirectly affected by the loss of LKB1 in PJS and aimed to investigate this possibility through transcriptional profiling of polyps harvested from an Lkb1(+/-) mouse model of PJS and from PJS patients. We identified alterations in the mRNA level of a wide range of genes, including some that are involved in Wnt signalling (Wnt5a, Wif1, Dixdc1, Wnt11, Ccnd1, and Ccnd2), although we did not observe nuclear localization of β-catenin in over 93 human PJS intestinal polyps or in 24 gastric polyps from Lkb1(+/-) mice. Among these genes, WNT5A, a non-canonical and non-transforming Wnt, is consistently up-regulated in both Lkb1(+/-) mice and human PJS polyps at a high level. We performed in situ hybridization to further define the spatial expression pattern of WNT5A and observed a strong signal in the stroma of mouse and human polyps compared to no or very low expression in the mucosa. Our findings indicate that WNT5A plays an important role in PJS polyposis.

Identification of early molecular markers for breast cancer

Background

The ductal carcinoma in situ (DCIS) of the mammary gland represents an early, pre-invasive stage in the development of invasive breast carcinoma. Since DCIS is a curable disease, it would be highly desirable to identify molecular markers that allow early detection. Mice transgenic for the WAP-SV40 early genome region were used as a model for DCIS development. Gene expression profiling was carried out on DCIS-bearing mice and control animals. Additionally, a set of human DCIS and invasive mammary tumors were analyzed in a similar fashion. Enhanced expression of these marker genes in human and murine samples was validated by quantitative RT-PCR. Besides, marker gene expression was also validated by immunohistochemistry of human samples. Furthermore in silico analyses using an online microarray database were performed.

Results

In DCIS-mice seven genes were identified that were significantly up-regulated in DCIS: DEPDC1, NUSAP1, EXO1, RRM2, FOXM1, MUC1 and SPP1. A similar up-regulation of homologues of the murine genes was observed in human DCIS samples. Enhanced expression of these genes in DCIS and IDC (invasive ductal carcinoma) was validated by quantitative RT-PCR and immunohistochemistry.

Conclusions

By comparing murine markers for the ductal carcinoma in situ (DCIS) of the mammary gland with genes up-regulated in human DCIS-samples we were able to identify a set of genes which might allow early detection of DCIS and invasive carcinomas in the future. The similarities between gene expression in DCIS and invasive carcinomas in our data suggest that the early detection and treatment of DCIS is of utmost relevance for the survival of patients who are at high risk of developing breast carcinomas.

Wnt signaling in estrogen-induced lactotroph proliferation

Prolactinomas are the most common type of functioning pituitary adenoma in humans, but the control of lactotroph proliferation remains unclear. Here, using microarray analysis, we show that estrogen treatment increased expression of Wnt4 mRNA in adult Fischer rat pituitary tissue. Dual immunofluorescence analysis revealed that Wnt4 expression was not confined to lactotrophs, but that it was expressed in all anterior pituitary cell types. Estradiol induced proliferation in the somatolactotroph GH3 cell line, in parallel with Wnt4 mRNA and protein induction. A reporter gene assay for TCF- and LEF-dependent transcription revealed that there was no activation of the canonical Wnt pathway in GH3 cells upon stimulation with Wnt-conditioned culture medium or coexpression of constitutively active mutant β-catenin. Expression of β-catenin in both GH3 cells and normal rat anterior pituitary cells was restricted to the cell membrane and was unaltered by treatment with estradiol, with no nuclear β-catenin being detected under any of the conditions tested. We show for the first time that Wnt4 affects non-canonical signaling in the pituitary by inhibiting Ca(2+) oscillations in GH3 cells, although the downstream effects are as yet unknown. In summary, Wnt4 is expressed in the adult pituitary gland, and its expression is increased by estrogen exposure, suggesting that its involvement in adult tissue plasticity is likely to involve β-catenin-independent signaling pathways.

Expression profiling of Wnt family of genes in normal and inflammatory bowel disease primary human intestinal myofibroblasts and normal human colonic crypt epithelial cells

BACKGROUND

Wnt signaling regulates intestinal epithelial stem cell function. Wnt ligands bind Frizzled (Fz) receptors and low-density lipoprotein-receptor-related protein (LRP) 5 and 6. Secreted Frizzled-related protein (SFRP) and Dickkopf families inhibit Wnt signaling. Our aim was to study expression of Wnt family of genes in isolated intestinal myofibroblasts and crypt epithelial cells.

METHODS

Myofibroblasts were isolated from normal colonic and small intestinal mucosal samples and those affected by ulcerative colitis (UC) and Crohn's disease. Expression of the Wnt family of genes was studied by polymerase chain reaction (PCR) array. Epithelial proliferation was studied using IEC-6 cells.

RESULTS

Most of the myofibroblast isolates expressed Wnt2, Wnt5A, Wnt5B, Fzd1, Fzd2, Fzd4, Fzd6, Fzd7, Fzd8, LRP6, Dickkopf1, and SFRP1. Compared to myofibroblasts isolated from normal colonic mucosal samples, real-time reverse transcription-PCR studies (using additional isolates) showed significantly reduced expression of SFRP1 in UC myofibroblasts (3.34-fold reduction, P < 0.01). Recombinant SFRP1 inhibited proliferation of IEC-6 epithelial cells. In colonic crypt epithelial cells, expression of Wnt ligands and their inhibitors was generally either absent or very weak. By contrast, all the crypt epithelial preparations expressed Fzd1, Fzd5, Fzd7, Fzd8, and LRP6.

CONCLUSIONS

Human intestinal myofibroblasts expressed a number of Wnt ligands, their receptors, and inhibitors. In contrast, colonic crypt epithelial cells predominantly expressed Wnt receptors. Compared to myofibroblasts isolated from normal colonic mucosa, those affected by UC showed significantly reduced expression of SFRP1. Since reduced SFRP1 expression has been associated with malignancy, low myofibroblast expression of this Wnt inhibitor may be implicated in increased risk of cancer in UC.

Cigarette smoke induces C/EBP-β-mediated activation of miR-31 in normal human respiratory epithelia and lung cancer cells

BACKGROUND

Limited information is available regarding mechanisms by which miRNAs contribute to pulmonary carcinogenesis. The present study was undertaken to examine expression and function of miRNAs induced by cigarette smoke condensate (CSC) in normal human respiratory epithelia and lung cancer cells.

METHODOLOGY

Micro-array and quantitative RT-PCR (qRT-PCR) techniques were used to assess miRNA and host gene expression in cultured cells, and surgical specimens. Software-guided analysis, RNA cross-link immunoprecipitation (CLIP), 3' UTR luciferase reporter assays, qRT-PCR, focused super-arrays and western blot techniques were used to identify and confirm targets of miR-31. Chromatin immunoprecipitation (ChIP) techniques were used to evaluate histone marks and transcription factors within the LOC554202 promoter. Cell count and xenograft experiments were used to assess effects of miR-31 on proliferation and tumorigenicity of lung cancer cells.

RESULTS

CSC significantly increased miR-31 expression and activated LOC554202 in normal respiratory epithelia and lung cancer cells; miR-31 and LOC554202 expression persisted following discontinuation of CSC exposure. miR-31 and LOC554202 expression levels were significantly elevated in lung cancer specimens relative to adjacent normal lung tissues. CLIP and reporter assays demonstrated direct interaction of miR-31 with Dickkopf-1 (Dkk-1) and DACT-3. Over-expression of miR-31 markedly diminished Dkk-1 and DACT3 expression levels in normal respiratory epithelia and lung cancer cells. Knock-down of miR-31 increased Dkk-1 and DACT3 levels, and abrogated CSC-mediated decreases in Dkk-1 and DACT-3 expression. Furthermore, over-expression of miR-31 diminished SFRP1, SFRP4, and WIF-1, and increased Wnt-5a expression. CSC increased H3K4Me3, H3K9/14Ac and C/EBP-β levels within the LOC554202 promoter. Knock-down of C/EBP-β abrogated CSC-mediated activation of LOC554202. Over-expression of miR-31 significantly enhanced proliferation and tumorigenicity of lung cancer cells; knock-down of miR-31 inhibited growth of these cells.

CONCLUSIONS

Cigarette smoke induces expression of miR-31 targeting several antagonists of cancer stem cell signaling in normal respiratory epithelia and lung cancer cells. miR-31 functions as an oncomir during human pulmonary carcinogenesis.

Esophageal squamous cell dysplasia and delayed differentiation with deletion of krüppel-like factor 4 in murine esophagus

BACKGROUND & AIMS

Krüppel-like factor 4 (Klf; previously known a gut-enriched Krüppel-like factor) is a DNA-binding transcriptional regulator highly expressed in skin and gastrointestinal epithelia, specifically in regions of cellular differentiation. Homozygous null mice for Klf4 die shortly after birth from skin defects, precluding their analysis at later stages. The aim of this study was to analyze the function of Klf4 in keratinocyte biology and epithelial homeostasis in the adult by focusing on the squamous lined esophagus.

METHODS

By using the ED-L2 promoter of Epstein-Barr virus to drive Cre, we obtained tissue-specific ablation of Klf4 in the squamous epithelia of the tongue, esophagus, and forestomach.

RESULTS

Mice with loss of Klf4 in esophageal epithelia survived to adulthood, bypassing the early lethality. Tissue-specific Klf4 knockout mice had increased basal cell proliferation and a delay in cellular maturation; these mice developed epithelial hypertrophy and subsequent dysplasia by 6 months of age. Moreover, loss of Klf4 in vivo was associated with increased expression of the pro-proliferative Klf5, and Klf4 down-regulated Klf5 both transcriptionally and posttranscriptionally. By using gene expression profiling, we also showed decreased expression of critical late-stage differentiation factors and identified alterations of several genes important in cellular differentiation.

CONCLUSIONS

Klf4 is essential for squamous epithelial differentiation in vivo and interacts with Klf5 to maintain normal epithelial homeostasis.

Epigenetic repression of ROR2 has a Wnt-mediated, pro-tumourigenic role in colon cancer

Background

Wnt factors control cell differentiation through semi-independent molecular cascades known as the β-catenin-dependent (canonical) and -independent (non-canonical) Wnt signalling pathways. Genetic and epigenetic alteration of components of the canonical Wnt signalling pathway is one of the primary mechanisms underlying colon cancer. Despite increasing evidence of the role of the non-canonical pathways in tumourigenesis, however, the underlying molecular mechanisms are poorly understood.

Results

Here we report that the receptor tyrosine kinase-like orphan receptor 2 (ROR2), a transmembrane receptor for Wnt factors that activates non-canonical pathways, is frequently repressed by aberrant promoter hypermethylation in human colon cancer cell lines and primary tumours. By restoring ROR2 activity in colon cancer cells harbouring ROR2 promoter hypermethylation, we show that the role of ROR2 in colon cancer cells is mediated, at least in part, by canonical Wnt and that its epigenetic-dependent loss can be pro-tumourigenic.

Conclusions

Our data show the importance of epigenetic alterations of ROR2 in colon cancer, highlighting the close interconnection between canonical and non-canonical Wnt signalling pathways in this type of tumour.

Proteomics profiling of Madin-Darby canine kidney plasma membranes reveals Wnt-5a involvement during oncogenic H-Ras/TGF-beta-mediated epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) describes a process whereby polarized epithelial cells with restricted migration transform into elongated spindle-shaped mesenchymal cells with enhanced motility and invasiveness. Although there are some molecular markers for this process, including the down-regulation of E-cadherin, our understanding of plasma membrane (PM) and associated proteins involved in EMT is limited. To specifically explore molecular alterations occurring at the PM, we used the cationic colloidal silica isolation technique to purify PM fractions from epithelial Madin-Darby canine kidney cells during Ras/TGF-β-mediated EMT. Proteins in the isolated membrane fractions were separated by one-dimensional SDS-PAGE and subjected to nano-LC-MS/MS-based protein identification. In this study, the first membrane protein analysis of an EMT model, we identified 805 proteins and determined their differential expression using label-free spectral counting. These data reveal that Madin-Darby canine kidney cells switch from cadherin-mediated to integrin-mediated adhesion following Ras/TGF-β-mediated EMT. Thus, during the EMT process, E-cadherin, claudin 4, desmoplakin, desmoglein-2, and junctional adhesion molecule A were down-regulated, whereas integrins α6β1, α3β1, α2β1, α5β1, αVβ1, and αVβ3 along with their extracellular ligands collagens I and V and fibronectin had increased expression levels. Conspicuously, Wnt-5a expression was elevated in cells undergoing EMT, and transient Wnt-5a siRNA silencing attenuated both cell migration and invasion in these cells. Furthermore, Wnt-5a expression suppressed canonical Wnt signaling induced by Wnt-3a. Wnt-5a may act through the planar cell polarity pathway of the non-canonical Wnt signaling pathway as several of the components and modulators (Wnt-5a, -5b, frizzled 6, collagen triple helix repeat-containing protein 1, tyrosine-protein kinase 7, RhoA, Rac, and JNK) were found to be up-regulated during Ras/TGF-β-mediated EMT.

A novel role for Wnt/Ca2+ signaling in actin cytoskeleton remodeling and cell motility in prostate cancer

Wnt signaling is a critical regulatory pathway in development and disease. Very little is known about the mechanisms of Wnt signaling in prostate cancer, a leading cause of death in men. A quantitative analysis of the expression of Wnt5A protein in human tissue arrays, containing 600 prostate tissue cores, showed >50% increase in malignant compared to benign cores (p<0.0001). In a matched pair of prostate cancer and normal cell line, expression of Wnt5A protein was also increased. Calcium waves were induced in prostate cells in response to Wnt5A with a 3 fold increase in Flou-4 intensity. The activity of Ca²⁺/calmodulin dependent protein kinase (CaMKII), a transducer of the non-canonical Wnt/Ca²⁺ signaling, increased by 8 fold in cancer cells; no change was observed in β-catenin expression, known to activate the canonical Wnt/β-catenin pathway. Mining of publicly available human prostate cancer oligoarray datasets revealed that the expression of numerous genes (e.g., CCND1, CD44) under the control of β-catenin transcription is down-regulated. Confocal and quantitative electron microscopy showed that specific inhibition of CaMKII in cancer cells causes remodeling of the actin cytoskeleton, irregular wound edges and loose intercellular architecture and a 6 and 8 fold increase in the frequency and length of filopodia, respectively. Conversely, untreated normal prostate cells showed an irregular wound edge and loose intercellular architecture; incubation of normal prostate cells with recombinant Wnt5A protein induced actin remodeling with a regular wound edge and increased wound healing capacity. Live cell imaging showed that a functional consequence of CaMKII inhibition was 80% decrease in wound healing capacity and reduced cell motility in cancer cells. We propose that non-canonical Wnt/Ca²⁺ signaling via CaMKII acts as a novel regulator of structural plasticity and cell motility in prostate cancer.

Significance of Wnt-5a expression in gastric carcinoma

AIM: To detect Wnt-5a expression in gastric carcinoma (GC) and explore its role in the development and progression of GC.

METHODS: The expression of Wnt-5a mRNA in 10 fresh GC and matched tumor-adjacent tissue samples was detected by real-time reverse transcription-polymerase chain reaction (RT-PCR). The expression of Wnt-5a and β-catenin proteins in 84 GC and matched tumor-adjacent tissue samples as well as 20 normal gastric mucosa tissue samples was examined by immunohistochemistry using the streptavidin-peroxidase method.

RESULTS: Real time RT-PCR analysis showed that the relative level of Wnt-5a mRNA was significantly higher in GC than in tumor-adjacent tissue (5.919 ± 1.869 vs 1.281 ± 0.744, P < 0.05). The positive rate of Wnt-5a protein expression was also significantly higher in GC than in tumor-adjacent tissue (40.54% vs 14.29%, P < 0.05). Wnt-5a expression was significantly associated with advanced TNM stage and lymph node metastasis (both P < 0.01). The rate of aberrant β-catenin expression was significantly higher in GC than in tumor-adjacent tissue (70.23% vs 38.10%, P < 0.01). Aberrant β-catenin expression was associated with advanced tumor stage and lymph node metastasis (both P < 0.05). The expression of Wnt-5a was correlated with that of β-catenin (P < 0.01).

CONCLUSION: Wnt-5a may exert oncogenic functions in GC. Wnt-5a may be activated in the early stage of gastric tumorigenesis and be related to the poor prognosis of GC. Wnt-5a and β-catenin might play an important role in the development of GC via different signal pathways.

Tumor stroma-derived Wnt5a induces differentiation of basal cell carcinoma of Ptch-mutant mice via CaMKII

Basal cell carcinoma (BCC) is the most common skin tumor in humans. Although BCCs rarely metastasize, they can cause significant morbidity due to local aggressiveness. Approximately 20% of BCCs show signs of spontaneous regression. The understanding of molecular events mediating spontaneous regression has the potential to reduce morbidity of BCC and, potentially, other tumors, if translated into tumor therapies. We show that BCCs induced in conditional Ptch(flox/flox)ERT2(+/-) knockout mice regress with time and show a more differentiated phenotype. Differentiation is accompanied by Wnt5a expression in the tumor stroma, which is first detectable at the fully developed tumor stage. Coculture experiments revealed that Wnt5a is upregulated in tumor-adjacent macrophages by soluble signals derived from BCC cells. In turn, Wnt5a induces the expression of the differentiation marker K10 in tumor cells, which is mediated by Wnt/Ca(2+) signaling in a CaMKII-dependent manner. These data support a role of stromal Wnt5a in BCC differentiation and regression, which may have important implications for development of new treatment strategies for this tumor. Taken together, our results establish BCC as an easily accessible model of tumor regression. The regression of BCC despite sustained Hedgehog signaling activity seems to be mediated by tumor-stromal interactions via Wnt5a signaling.

RORalpha attenuates Wnt/beta-catenin signaling by PKCalpha-dependent phosphorylation in colon cancer

Wnt family members play diverse roles in development and disease. Noncanonical Wnt ligands can inhibit canonical Wnt signaling depending on the cellular context; however, the underlying mechanism of this antagonism remains poorly understood. Here we identify a specific mechanism of orphan nuclear receptor RORalpha-mediated inhibition of canonical Wnt signaling in colon cancer. Wnt5a/PKCalpha-dependent phosphorylation on serine residue 35 of RORalpha is crucial to link RORalpha to Wnt/beta-catenin signaling, which exerts inhibitory function of the expression of Wnt/beta-catenin target genes. Intriguingly, there is a significant correlation of reduction of RORalpha phosphorylation in colorectal tumor cases compared to their normal counterpart, providing the clinical relevance of the findings. Our data provide evidence for a role of RORalpha, functioning at the crossroads between the canonical and the noncanonical Wnt signaling pathways, in mediating transrepression of the Wnt/beta-catenin target genes, thereby providing new approaches for the development of therapeutic agents for human cancers.

Signalling pathways in vasculogenic mimicry

Solid tumour growth is dependent on the development of an adequate blood supply. For years, sprouting angiogenesis has been considered an exclusive mechanism of tumour vascularization. However, over the last years, several other mechanisms have been identified, including vessel-co-option, intussusception, recruitment of endothelial precursor cells (EPCs) and even mechanisms that do not involve endothelial cells, a process called vasculogenic mimicry (VM). The latter describes a mechanism by which highly aggressive tumour cells can form vessel-like structures themselves, by virtue of their high plasticity. VM has been observed in several tumour types and its occurrence is strongly associated with a poor prognosis. This review will focus on signalling molecules and cascades involved in VM. In addition, we will discuss the presence of VM in relation to ongoing cancer research. Finally, we describe the clinical significance of VM regarding anti-angiogenesis treatment modalities.

Canonical Wnt signaling is antagonized by noncanonical Wnt5a in hepatocellular carcinoma cells

BACKGROUND

beta-catenin mutations that constitutively activate the canonical Wnt signaling have been observed in a subset of hepatocellular carcinomas (HCCs). These mutations are associated with chromosomal stability, low histological grade, low tumor invasion and better patient survival. We hypothesized that canonical Wnt signaling is selectively activated in well-differentiated, but repressed in poorly differentiated HCCs. To this aim, we characterized differentiation status of HCC cell lines and compared their expression status of Wnt pathway genes, and explored their activity of canonical Wnt signaling.

RESULTS

We classified human HCC cell lines into "well-differentiated" and "poorly differentiated" subtypes, based on the expression of hepatocyte lineage, epithelial and mesenchymal markers. Poorly differentiated cell lines lost epithelial and hepatocyte lineage markers, and overexpressed mesenchymal markers. Also, they were highly motile and invasive. We compared the expression of 45 Wnt pathway genes between two subtypes. TCF1 and TCF4 factors, and LRP5 and LRP6 co-receptors were ubiquitously expressed. Likewise, six Frizzled receptors, and canonical Wnt3 ligand were expressed in both subtypes. In contrast, canonical ligand Wnt8b and noncanonical ligands Wnt4, Wnt5a, Wnt5b and Wnt7b were expressed selectively in well- and poorly differentiated cell lines, respectively. Canonical Wnt signaling activity, as tested by a TCF reporter assay was detected in 80% of well-differentiated, contrary to 14% of poorly differentiated cell lines. TCF activity generated by ectopic mutant beta-catenin was weak in poorly differentiated SNU449 cell line, suggesting a repressive mechanism. We tested Wnt5a as a candidate antagonist. It strongly inhibited canonical Wnt signaling that is activated by mutant beta-catenin in HCC cell lines.

CONCLUSION

Differential expression of Wnt ligands in HCC cells is associated with selective activation of canonical Wnt signaling in well-differentiated, and its repression in poorly differentiated cell lines. One potential mechanism of repression involved Wnt5a, acting as an antagonist of canonical Wnt signaling. Our observations support the hypothesis that Wnt pathway is selectively activated or repressed depending on differentiation status of HCC cells. We propose that canonical and noncanonical Wnt pathways have complementary roles in HCC, where the canonical signaling contributes to tumor initiation, and noncanonical signaling to tumor progression.