β-catenin involvement in arsenite-induced VEGF expression in neuroblastoma SH-SY5Y cells

Life-long arsenic exposure damages the microstructure of the rat hippocampus

Epidemiological studies demonstrate that arsenic exposure is associated with cognitive dysfunction. Experimental arsenic exposure models showed learning and memory deficits and molecular changes resembling the functional and pathologic neurodegeneration features. The present work focuses on hippocampal pathological changes in Wistar rats induced by continuous arsenic exposure from in utero up to 12 months of age, evaluated by magnetic resonance imaging along with immunohistochemistry. Diffusion-weighted images revealed age-related lower fractional anisotropy and higher radial-axial and mean diffusivity at 6 and 12 months, indicating that arsenic exposure leads to hippocampal demyelination. These structural alterations were paralleled by immunohistochemical changes that showed a significant loss of myelin basic protein in CA1 and CA3 regions accompanied by increased glial fibrillary acidic protein expression at all time-points studied. Concomitantly, arsenic exposure induced an altered morphology of astrocytes at all studied ages, whereas increased synaptogenesis was only observed at two months of age. These results suggest that environmental arsenic exposure is linked to impaired hippocampal connectivity and perhaps early glial senescence, which together might resemble a premature aging phenomenon leading to cognitive deficits.

The Mechanism of Trivalent Inorganic Arsenic on HIF-1α: a Systematic Review and Meta-analysis

The purpose of our study was to investigate the role of hypoxia-inducible factor-1α (HIF-1α) in arsenic-induced carcinogenesis. We included 39 articles for meta-analysis. The results showed that low-dose exposure to arsenic (≤ 10 μmol/L) could promote the expression of phosphatidylinositol 3-kinase (PI3K) and phosphorylation-protein kinase B (p-AKT). High-dose arsenic exposure (> 10 μmol/L) promoted the expression of PI3K, HIF-1α, vascular endothelial growth factor (VEGF), and p38MAPK (P38). Acute arsenic exposure (< 24 h) promoted the expression of PI3K, HIF-1α, and VEGF. Chronic arsenic exposure (≥ 24 h) promoted the expression of PI3K, p-AKT, and P38. Moreover, for normal tissue-derived cells, arsenic could induce the increased expression of PI3K, p-AKT, HIF-1α, and VEGF. For tumor tissue-derived cells, arsenic could induce the expression of PI3K, p-AKT, and P38. We found that arsenic exposure could activate the PI3K/AKT pathway, further induce the high expression of HIF-1α, and then upregulate the levels of miRNA-21 and VEGF, promote the expression of proliferating cell nuclear antigen (PCNA), and ultimately lead to malignant cell proliferation. Our findings indicated that arsenic could increase the expression of HIF-1α by activating the PI3K/AKT pathway and eventually induce malignant cell proliferation.

Effects of Arsenic on wnt/β-catenin Signaling Pathway: A Systematic Review and Meta-analysis

We aimed to systematically evaluate the regulatory effect of arsenic on wnt/β-catenin signaling pathway and to provide theoretical basis for revealing the mechanism of the relationship between arsenic and cell proliferation. The meta-analysis was carried out using Revman5.2 and Stata13.0 to describe the differences between groups with standard mean difference. We found in normal cells that the levels of wnt3a, β-catenin, glycogen synthase kinase-3β phosphorylated at serine 9 (p-GSK-3β(Ser9)), cyclinD1, proto-oncogene c-myc, and vascular endothelial growth factor (VEGF) in the arsenic intervention group were higher than those in the control group, and the level of glycogen synthase kinase-3β (GSK-3β) was lower than that in the control group (P < 0.05, respectively). Subgroup analysis showed that for a long time period (>24 h), the level of β-catenin in the arsenic intervention group was higher than that in the control group, and the level of GSK-3β of the same long-time period (>24 h) with low-dose (≤5 μM) intervention was lower than those in the control group (P < 0.05, respectively). In cancer cells, the levels of β-catenin, cyclinD1, c-myc, and VEGF in the arsenic intervention group were lower than those in the control group, while the level of GSK-3β in the arsenic intervention group was higher than that in the control group (P < 0.05, respectively). Subgroup analysis showed that the levels of β-catenin, cyclinD1, and c-myc in the high-dose (>5 μM) arsenic intervention group were lower than those in the control group, and the levels of β-catenin and cyclinD1 in the high-dose (>5 μM) arsenic intervention group were lower than those in the low-dose (≤5 μM) arsenic intervention group (P < 0.05, respectively). In addition, the regulation of arsenic on β-catenin was dose-dependent in the range of arsenic concentration from 0 to 7.5 μM. This study revealed that arsenic could upregulate wnt/β-catenin signaling pathway in normal cells and downregulate it in cancer cells, and its effect was affected by time and dose.

Nickel induces transcriptional down-regulation of DNA repair pathways in tumorigenic and non-tumorigenic lung cells

The heavy metal nickel is a known carcinogen, and occupational exposure to nickel compounds has been implicated in human lung and nasal cancers. Unlike many other environmental carcinogens, however, nickel does not directly induce DNA mutagenesis, and the mechanism of nickel-related carcinogenesis remains incompletely understood. Cellular nickel exposure leads to signaling pathway activation, transcriptional changes and epigenetic remodeling, processes also impacted by hypoxia, which itself promotes tumor growth without causing direct DNA damage. One of the mechanisms by which hypoxia contributes to tumor growth is the generation of genomic instability via down-regulation of high-fidelity DNA repair pathways. Here, we find that nickel exposure similarly leads to down-regulation of DNA repair proteins involved in homology-dependent DNA double-strand break repair (HDR) and mismatch repair (MMR) in tumorigenic and non-tumorigenic human lung cells. Functionally, nickel induces a defect in HDR capacity, as determined by plasmid-based host cell reactivation assays, persistence of ionizing radiation-induced DNA double-strand breaks and cellular hypersensitivity to ionizing radiation. Mechanistically, we find that nickel, in contrast to the metalloid arsenic, acutely induces transcriptional repression of HDR and MMR genes as part of a global transcriptional pattern similar to that seen with hypoxia. Finally, we find that exposure to low-dose nickel reduces the activity of the MLH1 promoter, but only arsenic leads to long-term MLH1 promoter silencing. Together, our data elucidate novel mechanisms of heavy metal carcinogenesis and contribute to our understanding of the influence of the microenvironment on the regulation of DNA repair pathways.

Aberrant β-catenin expression in urothelial carcinomas in blackfoot disease-endemic areas

Arsenic is a well-known toxic element and carcinogenic agent. The aim of this study was to investigate p63, E-cadherin, and β-catenin proteins in urothelial carcinoma (UC) in both arsenic contaminated areas [so-called blackfoot disease (BFD) area] and non-BFD areas. The expressions of p63, E-cadherin, and β-catenin proteins in 20 UC cases of blackfoot disease and 22 UC cases in non-BFD areas were detected using immunohistochemical methods. The results revealed a high p63 expression in 20 (47.6%) UC cases and high E-cadherin expression in six (14.3%) UC cases. Expressions of p63 and E-cadherin showed no significant correlations with clinicopathologic parameters. However, all 20 BFD cases and 12 of 22 (54.5%) non-BFD cases showed aberrant β-catenin expression. Ten out of 22 (45.5%) non-BFD cases also had normal membranous immunoreactivity. The β-catenin staining pattern significantly differed between cases in endemic and nonendemic areas of BFD (p=0.001). Tumor sites also significantly correlated with β-catenin expression (p=0.044). In addition, membranous localization of β-catenin was lower in UC from BFD-endemic areas compared with those from non-BFD endemic areas. In conclusion, it is suggested that relocalization of β-catenin from membrane to cytoplasm may be involved in the tumorigenesis of UC from BFD-endemic areas.

Roxarsone induces angiogenesis via PI3K/Akt signaling

BACKGROUND

3-Nitro-4-hydroxy phenyl arsenic acid, roxarsone, is widely used as an organic arsenic feed additive for livestock and poultry, which may increase the level of arsenic in the environment and the risk of exposure to arsenic in human. Little information is focused on the angiogenesis roxarsone-induced and its mechanism at present. This paper aims to study the role of PI3K/Akt signaling in roxarsone-induced angiogenesis in rat vascular endothelial cells and a mouse B16-F10 melanoma xenograft model.

RESULTS

The results showed that treatment with 0.1-10.0 µmol/L roxarsone resulted in an increase in the OD rate in the MTT assay, the number of BrdU-positive cells in the proliferation assay, the migration distance in the scratch test and the number of meshes in tube formation assay. Further, treatment with 1.0 µmol/L roxarsone was associated with significantly higher phosphorylation of PI3K/Akt and expression of VEGF than the control treatment. The PI3K inhibitor was found to significantly combat the effects of 1.0 µmol/L roxarsone. Furthermore, roxarsone treatment was observed to increase the weight and volume of B16-F10 xenografts and VEGF expression and PI3K/Akt phosphorylation in a dose-dependent manner, with the 25 mg/kg dose having significant effects.

CONCLUSIONS

These results demonstrate that roxarsone has the ability to promote growth and tube formation in vascular endothelial cells and the growth of mouse B16-F10 xenografts. Further, the findings also indicate that PI3K/Akt signaling plays a regulatory role in roxarsone-induced angiogenesis in vivo and in vitro.

Arsenic inhibits stem cell differentiation by altering the interplay between the Wnt3a and Notch signaling pathways

data indicates that arsenic exposure inhibits stem cell differentiation. This study investigated whether arsenic disrupted the Wnt3a signaling pathway, critical in the formation of myotubes and neurons, during the differentiation in P19 mouse embryonic stem cells. Cells were exposed to 0, 0.1, or 0.5 μM arsenite, with or without exogenous Wnt3a, for up to 9 days of differentiation. Arsenic exposure alone inhibits the differentiation of stem cells into neurons and skeletal myotubes, and reduces the expression of both β-catenin and GSK3β mRNA to ~55% of control levels. Co-culture of the arsenic-exposed cells with exogenous Wnt3a rescues the morphological phenotype, but does not alter transcript, protein, or phosphorylation status of GSK3β or β-catenin. However, arsenic exposure maintains high levels of Hes5 and decreases the expression of MASH1 by 2.2-fold, which are anti- and pro-myogenic and neurogenic genes, respectively, in the Notch signaling pathway. While rescue with exogenous Wnt3a reduced Hes5 levels, MASH1 levels stay repressed. Thus, while Wnt3a can partially rescue the inhibition of differentiation from arsenic, it does so by also modulating Notch target genes rather than only working through the canonical Wnt signaling pathway. These results indicate that arsenic alters the interplay between multiple signaling pathways, leading to reduced stem cell differentiation.

Mechanism of Wnt/β-catenin signaling pathway in enhanced malignant phenotype of non-small cell lung cancer induced by anti-angiogenesis therapy

OBJECTIVE

To study the mechanism of Wnt/β-catenin signaling pathway in the enhanced malignant phenotype of A549 cells of human non-small cell lung cancer induced by the anti-angiogenesis therapy.

METHODS

The siRNA technique was employed to inhibit the expression of vascular endothelial growth factor (VEGF) in A549 cells and simulate the clinical course of anti-angiogenesis therapy. Real-time PCR and western blot were used to study the change in the expression of Wnt/β-catenin signaling molecules at the mRNA and protein level respectively, as well as the effect on the epithelial mesenchymal transition in A549 cells. The proliferation and invasion abilities of tumor cells were detected to discuss the mechanism of Wnt/β-catenin signaling pathway in the enhanced malignant phenotype of non-small cell lung cancer induced by the anti-angiogenesis therapy.

RESULTS

The specific siRNA could significantly inhibit the expression of VEGF in cells to simulate the anti-angiogenesis therapy. Under the action of 50 nM VEGF siRNA, the proliferation ability of A549 significantly increased (P < 0.05). After being treated with VEGF siRNA, the invasion ability of cells increased. Twenty-four hours after the transcription of 50 nM siRNA into cells, the number of cells that come through the membrane was 278.3 ± 12.9. Compared with the Ctrl siRNA group, when VEGF was inhibited, the expression of β-catenin and Cyclin D1 increased by 86% and 55% respectively. Meanwhile, the expression of E-cadherin decreased, while the one of vimentin increased.

CONCLUSIONS

siRNA can significantly inhibit the expression of VEGF. For the anti-angiogenesis therapy, the inhibited expression of VEGF can activate the Wnt/β-catenin signaling pathway to cause the epithelial mesenchymal transition and then the enhanced malignant phenotype of non-small cell lung cancer.