Human APC sequesters β-catenin even in the absence of GSK-3β in a Drosophila model

GC-MS Chemical Characterization and In Vitro Evaluation of Antioxidant and Toxic Effects Using Drosophila melanogaster Model of the Essential Oil of Lantana montevidensis (Spreng) Briq

Background and objectives: Natural products such as essential oils with antioxidant potential can reduce the level of oxidative stress and prevent the oxidation of biomolecules. In the present study, we investigated the antioxidant potential of Lantana montevidensis leaf essential oil (EOLM) in chemical and biological models using Drosophila melanogaster. Materials and methods: in addition, the chemical components of the oil were identified and quantified by gas chromatography coupled to mass spectrometry (GC-MS), and the percentage compositions were obtained from electronic integration measurements using flame ionization detection (FID). Results: our results demonstrated that EOLM is rich in terpenes with Germacrene-D (31.27%) and β-caryophyllene (28.15%) as the major components. EOLM (0.12-0.48 g/mL) was ineffective in scavenging DPPH radical, and chelating Fe(II), but showed reducing activity at 0.24 g/mL and 0.48 g/mL. In in vivo studies, exposure of D. melanogaster to EOLM (0.12-0.48 g/mL) for 5 h resulted in 10% mortality; no change in oxidative stress parameters such as total thiol, non-protein thiol, and malondialdehyde contents, in comparison to control (p > 0.05). Conclusions: taken together, our results indicate EOLM may not be toxic at the concentrations tested, and thus may not be suitable for the development of new botanical insecticides, such as fumigants or spray-type control agents against Drosophila melanogaster.

Proteomic analysis reveals APC-dependent post-translational modifications and identifies a novel regulator of β-catenin

Wnt signaling generates patterns in all embryos, from flies to humans, and controls cell fate, proliferation and metabolic homeostasis. Inappropriate Wnt pathway activation results in diseases, including colorectal cancer. The adenomatous polyposis coli (APC) tumor suppressor gene encodes a multifunctional protein that is an essential regulator of Wnt signaling and cytoskeletal organization. Although progress has been made in defining the role of APC in a normal cellular context, there are still significant gaps in our understanding of APC-dependent cellular function and dysfunction. We expanded the APC-associated protein network using a combination of genetics and a proteomic technique called two-dimensional difference gel electrophoresis (2D-DIGE). We show that loss of Drosophila Apc2 causes protein isoform changes reflecting misregulation of post-translational modifications (PTMs), which are not dependent on β-catenin transcriptional activity. Mass spectrometry revealed that proteins involved in metabolic and biosynthetic pathways, protein synthesis and degradation, and cell signaling are affected by Apc2 loss. We demonstrate that changes in phosphorylation partially account for the altered PTMs in APC mutants, suggesting that APC mutants affect other types of PTM. Finally, through this approach Aminopeptidase P was identified as a new regulator of β-catenin abundance in Drosophila embryos. This study provides new perspectives on the cellular effects of APC that might lead to a deeper understanding of its role in development.

Characterization of Wnt/β-catenin signaling in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and accounts for about 5% of all malignant paediatric tumours. β-Catenin, a multifunctional nuclear transcription factor in the canonical Wnt signaling pathway, is active in myogenesis and embryonal somite patterning. Dysregulation of Wnt signaling facilitates tumour invasion and metastasis. This study characterizes Wnt/β-catenin signaling and functional activity in paediatric embryonal and alveolar RMS. Immunohistochemical assessment of paraffin-embedded tissues from 44 RMS showed β-catenin expression in 26 cases with cytoplasmic/membranous expression in 9/14 cases of alveolar RMS, and 15/30 cases of embryonal RMS, whereas nuclear expression was only seen in 2 cases of embryonal RMS. The potential functional significance of β-catenin expression was tested in four RMS cell lines, two derived from embryonal (RD and RD18) RMS and two from alveolar (Rh4 and Rh30) RMS. Western blot analysis demonstrated the expression of Wnt-associated proteins including β-catenin, glycogen synthase kinase-3β, disheveled, axin-1, naked, LRP-6 and cadherins in all cell lines. Cell fractionation and immunofluorescence studies of the cell lines (after stimulation by human recombinant Wnt3a) showed reduced phosphorylation of β-catenin, stabilization of the active cytosolic form and nuclear translocation of β-catenin. Reporter gene assay demonstrated a T-cell factor/lymphoid-enhancing factor-mediated transactivation in these cells. In response to human recombinant Wnt3a, the alveolar RMS cells showed a significant decrease in proliferation rate and induction of myogenic differentiation (myogenin, MyoD1 and myf5). These data indicate that the central regulatory components of canonical Wnt/β-catenin signaling are expressed and that this pathway is functionally active in a significant subset of RMS tumours and might represent a novel therapeutic target.

Drosophila melanogaster: a model and a tool to investigate malignancy and identify new therapeutics

For decades, lower-model organisms such as Drosophila melanogaster have often provided the first glimpse into the mechanism of action of human cancer-related proteins, thus making a substantial contribution to elucidating the molecular basis of the disease. More recently, D. melanogaster strains that are engineered to recapitulate key aspects of specific types of human cancer have been paving the way for the future role of this 'workhorse' of biomedical research, helping to further investigate the process of malignancy, and serving as platforms for therapeutic drug discovery.

Upregulation of glycogen synthase kinase 3β in human colorectal adenocarcinomas correlates with accumulation of CTNNB1

INTRODUCTION

Mutations of the adenomatous polyposis coli (APC) tumor suppressor gene or the CTNNB1 protooncogene have been implicated in the initiation of most human colorectal epithelial neoplasms. Glycogen synthase kinase 3β (GSK3B) serves a critical role in regulating their functions by phosphorylating both APC and CTNNB1 to facilitate CTNNB1 degradation. The current studies were performed to investigate whether GSK3B itself is regulated during the process of colorectal tumorigenesis.

PATIENTS AND METHODS

We examined the expression of GSK3B and CTNNB1 in tissue samples from 24 human colorectal adenocarcinomas by Western immunoblotting analysis, kinase activity assays and immunohistochemistry. Normal colonic mucosa from the same colectomy specimens were used as a reference for comparison.

RESULTS

We demonstrated that GSK3B expression levels and kinase activities were markedly and significantly increased in colorectal adenocarcinomas in all 24 cases compared with paired adjacent normal-appearing colonic mucosa. These increases correlated with significantly increased expression of CTNNB1 in the same tumors. Similar results were obtained in several cultured human colon cancer cell lines, demonstrating GSK3B levels correlated with CTNNB1 expression.

CONCLUSION

Though APC and CTNNB1 regulation by GSK3B are frequently disrupted by mutations in colon cancers, our observations suggest that increased functional GSK3B might drive other growth-promoting signals in colorectal tumorigenesis.