A Theoretical Model of the Wnt Signaling Pathway in the Epithelial Mesenchymal Transition

Abstract Background Following the formation of a primary carcinoma, neoplastic cells metastasize by undergoing the epithelial mesenchymal transition (EMT), which is triggered by cues from inflammatory and stromal cells in the microenvironment. EMT allows epithelial cells to lose their highly adhesive nature and instead adopt the spindle-like appearance, as well as the invasive and migratory behavior, of mesenchymal cells. We hypothesize that a bistable switch between the epithelial and mesenchymal phenotypes governs EMT, allowing the cell to maintain its mesenchymal phenotype even after it leaves the primary tumor microenvironment and EMT-inducing extracellular signal. Results This work presents a simple mathematical model of EMT, specifically the roles played by four key proteins in the Wnt signaling pathway: Dishevelled (Dvl), E-cadherin, β-catenin, and Slug. The model predicts that following activation of the Wnt pathway, an epithelial cell in the primary carcinoma must attain a threshold level of membrane-bound Dvl to convert to the mesenchymal-like phenotype and maintain that phenotype once it has migrated away from the primary tumor. Furthermore, sensitivity analysis of the model suggests that in both the epithelial and the mesenchymal states, the steady state behavior of E-cadherin and the transcription factor Slug are sensitive to changes in the degradation rate of Slug, while E-cadherin is also sensitive to the IC50 (half-maximal) concentration of Slug necessary to inhibit E-cadherin production. The steady state behavior of Slug exhibits sensitivity to changes in the rate at which it is induced by β-catenin upon activation of the Wnt pathway. In the presence of sufficient amount of Wnt ligand, E-cadherin levels are sensitive to the ratio of the rate of Slug activation via β-catenin to the IC50 concentration of Slug necessary to inhibit E-cadherin production. Conclusions The sensitivity of E-cadherin to the degradation rate of Slug, as well as the IC50 concentration of Slug necessary to inhibit E-cadherin production, shows how the adhesive nature of the cell depends on finely-tuned regulation of Slug. By highlighting the role of β-catenin in the activation of EMT and the relationship between E-cadherin and Slug, this model identifies critical parameters of therapeutic concern, such as the threshold level of Dvl necessary to inactivate the GSK-3β complex mediating β-catenin degradation, the rate at which β-catenin translocates to the nucleus, and the IC50 concentration of Slug needed to inhibit E-cadherin production

Alternative Splicing of Fibroblast Growth Factor Receptor IgIII Loops in Cancer

Alternative splicing of the IgIII loop of fibroblast growth factor receptors (FGFRs) 1–3 produces b- and c-variants of the receptors with distinctly different biological impact based on their distinct ligand-binding spectrum. Tissue-specific expression of these splice variants regulates interactions in embryonic development, tissue maintenance and repair, and cancer. Alterations in FGFR2 splicing are involved in epithelial mesenchymal transition that produces invasive, metastatic features during tumor progression. Recent research has elucidated regulatory factors that determine the splice choice both on the level of exogenous signaling events and on the RNA-protein interaction level. Moreover, methodology has been developed that will enable the in depth analysis of splicing events during tumorigenesis and provide further insight on the role of FGFR 1–3 IIIb and IIIc in the pathophysiology of various malignancies. This paper aims to summarize expression patterns in various tumor types and outlines possibilities for further analysis and application

Serum 25-hydroxyvitamin D concentrations in dogs with osteosarcoma do not differ from those of age- and weight-matched control dogs.

Vitamin D concentrations show an inverse correlation with incidence of certain tumors in people and dogs. Additionally, human osteosarcoma has been associated with dysregulation of vitamin D-dependent pathways. The study objective was to compare serum 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in 20 dogs with osteosarcoma to age- and weight-matched control dogs. We hypothesized that dogs with osteosarcoma would have lower serum 25-hydroxyvitamin D than control dogs. The mean 25-hydroxyvitamin D3 concentrations for dogs with osteosarcoma and matched-controls were 34.95 ng/mL and 33.85 ng/mL, respectively (P = 0.784). Based on these data, 25-hydroxyvitamin D insufficiency might not be important in the pathogenesis of canine osteosarcoma

Telomere Transcripts Target Telomerase in Human Cancer Cells

Long non-coding transcripts from telomeres, called telomeric repeat-containing RNA (TERRA), were identified as blocking telomerase activity (TA), a telomere maintenance mechanism (TMM), in tumors. We expressed recombinant TERRA transcripts in tumor cell lines with TA and with alternative lengthening of telomeres (ALT) to study effects on TMM and cell growth. Adeno- and lentivirus constructs (AV and LV) were established for transient and stable expression of approximately 130 units of telomere hexanucleotide repeats under control of cytomegalovirus (CMV) and human RNase P RNA H1 (hH1) promoters with and without polyadenylation, respectively. Six human tumor cell lines either using telomerase or ALT were infected and analyzed for TA levels. Pre-infection cells using telomerase had 1%–3% of the TERRA expression levels of ALT cells. AV and LV expression of recombinant TERRA in telomerase positive cells showed a 1.3–2.6 fold increase in TERRA levels, and a decrease in TA of 25%–58%. Dominant-negative or small hairpin RNA (shRNA) viral expression against human telomerase reverse transcriptase (hTERT) results in senescence, not induced by TERRA expression. Population doubling time, cell viability and TL (telomere length) were not impacted by ectopic TERRA expression. Clonal growth was reduced by TERRA expression in TA but not ALT cell lines. ALT cells were not affected by treatments applied. Established cell models and tools may be used to better understand the role of TERRA in the cell, especially for targeting telomerase

Ezrin and moesin expression in canine and feline osteosarcoma

Biological features of canine osteosarcomas (OS) differ markedly from those found in feline and resemble more human osteosarcomas, in particular for their high rate of metastasis and poor prognosis. Ezrin, radixin and moesin are members of the ERM protein family and link the actin cytoskeleton with the cell membrane. Ezrin and moesin have been shown to be of prognostic significance in tumor progression due to their role in the metastatic process. The objective of this study was to analyze ezrin and moesin protein expression in a series of dog (n=16) and cat (n=8) osteosarcoma samples using immunohistochemistry and western blot techniques. We found that cat OS have a higher moesin expression compared to dog OS, however, the active phosphorylated forms of moesin and ezrin Tyr353 were more abundant in the dog samples. A statistically significant difference was found for the low and high immunohistochemical scores of ezrin and pan-phosphoERM proteins between cat and dog. Although phosphoezrin Thr567 was higher in feline OS, the membranous localization in dog OS samples indicates the presence of the biologically active form. Therefore, the observed differences in phosphorylated forms of ezrin and moesin status should be further studied to demonstrate if they are relevant for different biological behavior between dog and cat OS

Heterotaxin: A TGF-β Signaling Inhibitor Identified in a Multi-Phenotype Profiling Screen in Xenopus Embryos

SummaryDisruptions of anatomical left-right asymmetry result in life-threatening heterotaxic birth defects in vital organs. We performed a small molecule screen for left-right asymmetry phenotypes in Xenopus embryos and discovered a pyridine analog, heterotaxin, which disrupts both cardiovascular and digestive organ laterality and inhibits TGF-β-dependent left-right asymmetric gene expression. Heterotaxin analogs also perturb vascular development, melanogenesis, cell migration, and adhesion, and indirectly inhibit the phosphorylation of an intracellular mediator of TGF-β signaling. This combined phenotypic profile identifies these compounds as a class of TGF-β signaling inhibitors. Notably, heterotaxin analogs also possess highly desirable antitumor properties, inhibiting epithelial-mesenchymal transition, angiogenesis, and tumor cell proliferation in mammalian systems. Our results suggest that assessing multiple organ, tissue, cellular, and molecular parameters in a whole organism context is a valuable strategy for identifying the mechanism of action of bioactive compounds