Proliferation and morphological transformation of BALB/3T3 cells by a prolonged treatment with sodium orthovanadate

Detection of cell carcinogenic transformation by a quadruplex DNA binding fluorescent probe

Cancer can be easily treated when found early. A probe capable of detecting cell transformation may increase the success rate of early diagnosis of cancer. In this report we have tested the ability of a fluorescent, quadruplex DNA binding probe, 3,6-bis(1-methyl-4- vinylpyridinium) carbazole diiodide (BMVC), to detect cell transformation in vitro. BMVC was applied to living cells in several different models of cell transformation, and the fluorescence signals of BMVC were measured. The degrees of cell transformation in these models were characterized by alterations in cellular morphological phenotype and subcellular organization. When BMVC probes were applied, the number of BMVC-positive cells increased in accordance with the degree of transformation. BMVC was capable of significantly detecting formation of foci, increased cellular motility, cell proliferation, cell apoptosis, anchorage-independent growth, and increased invasiveness of transformed cells. These results demonstrate the ability of BMVC probes to detect cell transformation and indicate that BMVC is of promise for use as a probe in early cancer detection.

Literature review of the role of hydroxyl radicals in chemically-induced mutagenicity and carcinogenicity for the risk assessment of a disinfection system utilizing photolysis of hydrogen peroxide

We have developed a new disinfection system for oral hygiene, proving that hydroxyl radicals generated by the photolysis of 1 M hydrogen peroxide could effectively kill oral pathogenic microorganisms. Prior to any clinical testing, the safety of the system especially in terms of the risk of carcinogenicity is examined by reviewing the literature. Previous studies have investigated indirectly the kinds of reactive oxygen species involved in some sort of chemically-induced mutagenicity in vitro by using reactive oxygen species scavengers, suggesting the possible involvement of hydroxyl radicals. Similarly, possible involvement of hydroxyl radicals in some sort of chemically-induced carcinogenicity has been proposed. Notably, it is suggested that the hydroxyl radical can play a role in heavy metal-induced carcinogenicity that requires chronic exposure to the carcinogen. In these cases, hydroxyl radicals produced by Fenton-like reactions may be involved in the carcinogenicity. Meanwhile, potential advantages have been reported on the use of the hydroxyl radical, being included in host immune defense by polymorphonuclear leukocytes, and medical applications such as for cancer treatment and antibiotics. From these, we conclude that there would seem to be little to no risk in using the hydroxyl radical as a disinfectant for short-term treatment of the oral cavity.

Activation of aPKC is required for vanadate-induced phosphorylation of protein kinase B (Akt), but not p70S6k in mouse epidermal JB6 cells

Vanadium is a metal widely distributed in the environment. Although vanadate-containing compounds exert potent toxic effects on a wide variety of biological systems, the mechanisms by which vanadate mediates adverse effects are not well understood. The present study investigated the vanadate-induced phosphorylation of Akt and p70S6K, two kinases known to be vital for cell survival, growth, transformation, and transition of the cell cycle in mammals. Exposure of mouse epidermal JB6 cells to vanadium led to phosphorylation of Akt and p70S6K in a time- and dose-dependent manner. Vanadium exposure also caused translocation of atypical isoforms of PKC (lambda, zeta) from the cytosol to the membrane, but had no effect on PKCalpha translocation, suggesting that the atypical PKCs (aPKC) were specifically involved in vanadium-induced cellular response. Importantly, overexpression of a dominant negative mutant PKClambda blocked Akt phosphorylation at Ser473 and Thr308, whereas it did not inhibit p70S6k phosphorylation at Thr389 and Thr421/Ser424, suggesting that aPKC activation is specifically involved in vanadium-induced activation of Akt, but not in activation of p70S6k. Furthermore, vanadium-induced p70S6k phosphorylation at Thr389 and Thr421/Ser424 and Akt phosphorylation at Thr308 occurred through a PI-3K-dependent pathway because a PI-3K dominant negative mutant inhibited induction as compared with vector control cells. These results indicate that there was a differential role of aPKC in vanadate-induced phosphorylation of Akt and p70S6k, suggesting that signal transduction pathways leading to the activation of Akt and p70S6k were different.

Vanadate-induced expression of hypoxia-inducible factor 1 alpha and vascular endothelial growth factor through phosphatidylinositol 3-kinase/Akt pathway and reactive oxygen species

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic helix-loop-helix transcription factor composed of HIF-1 alpha and HIF-1 beta/aryl hydrocarbon nuclear translocator subunits. HIF-1 expression is induced by hypoxia, growth factors, and activation of oncogenes. In response to hypoxia, HIF-1 activates the expression of many genes including vascular endothelial growth factor (VEGF) and erythropoietin. HIF-1 and VEGF play an important role in angiogenesis and tumor progression. Vanadate is widely used in industry, and is a potent inducer of tumors in humans and animals. In this study, we demonstrate that vanadate induces HIF-1 activity through the expression of HIF-1alpha but not HIF-1 beta subunit, and increases VEGF expression in DU145 human prostate carcinoma cells. We also studied the signaling pathway involved in vanadate-induced HIF-1 alpha and VEGF expression and found that phosphatidylinositol 3-kinase/Akt signaling was required for HIF-1 and VEGF expression induced by vanadate, whereas mitogen-activated protein kinase pathway was not required. We also found that reactive oxygen species (ROS) were involved in vanadate-induced expression of HIF-1 and VEGF in DU145 cells. The major species of ROS responsible for the induction of HIF-1 and VEGF expression was H(2)O(2). These results suggest that the expression of HIF-1 and VEGF induced by vanadate through PI3K/Akt may be an important signaling pathway in the vanadate-induced carcinogenesis, and ROS may play an important role.

Vanadate disrupts mammary gland development in whole organ culture

Protein tyrosine kinases and phosphatases are signaling molecules involved in all aspects of development, including proliferation, differentiation, and apoptosis. How disruption of protein tyrosine phosphatase affects mammary gland development is not entirely clear. We examined the effects of sodium vanadate, which is known to primarily inhibit tyrosine phosphatases, in mouse mammary gland development in whole organ culture. Mammary epithelial differentiation was effectively inhibited by vanadate in a dose-dependent manner as indicated by lack of epithelial alveoli compared to the contralateral non-treated gland controls. Mammary glands in the differentiation medium after four days in the presence of vanadate did not differentiate into alveoli. Instead, they exhibited prominent terminal end buds and lost the distinctive epithelial structures. The inhibitory effect of vanadate on mammary epithelial cell differentiation was irreversible after one day of treatment. Immunohistochemical staining for PCNA (Proliferating Cell Nuclear Antigen) showed that vanadate-treated glands exhibited elevated proliferation signals in the differentiation medium. Expression of beta-casein protein in the vanadate-treated glands decreased dramatically and progressively. Short-term exposure (up to 72 hours) of mammary glands to vanadate resulted in an increase in mammary epithelial cell density and loss of organization of the mammary structures. TUNEL assay of mammary glands with prolonged exposure to vanadate revealed widespread apoptosis. Furthermore, some cells were still proliferating or expressing beta-casein after prolonged exposure to vanadate. Taken together, these data indicate that vanadate treatment blocks mammary epithelial cell differentiation and promotes abnormal proliferation and apoptosis, likely through the inhibition of protein tyrosine phosphatase-mediated signaling.

Vanadium-induced nuclear factor of activated T cells activation through hydrogen peroxide

The present study investigated the role of reactive oxygen species (ROS) in activation of nuclear factor of activated T cells (NFAT), a pivotal transcription factor responsible for regulation of cytokines, by vanadium in mouse embryo fibroblast PW cells or mouse epidermal Cl 41 cells. Exposure of cells to vanadium led to the transactivation of NFAT in a time- and dose-dependent manner. Scavenging of vanadium-induced H(2)O(2) with N-acety-L-cyteine (a general antioxidant) or catalase (a specific H(2)O(2) inhibitor) or the chelation of vanadate with deferoxamine, resulted in inhibition of NFAT activation. In contrast, an increase in H(2)O(2) generation by the addition of superoxide dismutase or NADPH enhanced vanadium-induced NFAT activation. This vanadate-mediated H(2)O(2) generation was verified by both electron spin resonance and fluorescence staining assay. These results demonstrate that H(2)O(2) plays an important role in vanadium-induced NFAT transactivation in two different cell types. Furthermore, pretreatment of cells with nifedipine, a calcium channel blocker, inhibited vanadium-induced NFAT activation, whereas and ionomycin, two calcium ionophores, had synergistic effects with vanadium for NFAT induction. Incubation of cells with cyclosporin A (CsA), a pharmacological inhibitor of the phosphatase calcineurin, blocked vanadium-induced NFAT activation. All data show that vanadium induces NFAT activation not only through a calcium-dependent and CsA-sensitive pathway but also involved H(2)O(2) generation, suggesting that H(2)O(2) may be involved in activation of calcium-calcineurin pathways for NFAT activation caused by vanadium exposure.

Vanadate induces p53 transactivation through hydrogen peroxide and causes apoptosis

Vanadium is a metal widely distributed in the environment. Although vanadate-containing compounds exert potent toxic effects on a wide variety of biological systems, the mechanisms controlling vanadate-induced adverse effects remain to be elucidated. The present study investigated the vanadate-induced p53 activation and involvement of reactive oxygen species (ROS) in p53 activation as well as the role of p53 in apoptosis induction by vanadate. Exposure of mouse epidermal JB6 cells to vanadate led to transactivation of p53 activity in a time- and dose-dependent manner. It also caused mitochondrial damage, apoptosis, and generated ROS. Scavenging of vanadate-induced H(2)O(2) by N-acetyl-l-cysteine (a general antioxidant) or catalase (a specific H(2)O(2) inhibitor), or the chelation of vanadate by deferoxamine, resulted in inhibition of p53 activation and cell mitochondrial damage. In contract, an increase in H(2)O(2) generation in response to superoxide dismutase or NADPH enhanced these effects caused by vanadate. Furthermore, vanadate-induced apoptosis occurred in cells expressing wild-type p53 (p53+/+) but was very weak in p53-deficient (p53-/-) cells. These results demonstrate that vanadate induces p53 activation mainly through H(2)O(2) generation, and this activation is required for vanadate-induced apoptosis.

Vanadate-induced activation of activator protein-1: role of reactive oxygen species

The present study was undertaken to test the hypothesis that the toxicity and carcinogenicity of vanadium might arise from elevation of reactive oxygen species leading to activation of the transcription factor activator protein-1 (AP-1). The AP-1 transactivation response has been implicated as causal in transformation responses to phorbol esters and growth factors. To investigate the possible activity of vanadium in the activation of AP-1, we treated mouse epidermal JB6 P+ cells stably transfected with an AP-1 luciferase reporter plasmid with various concentrations of vanadate. This resulted in concentration-dependent transactivation of AP-1. Superoxide dismutase (SOD) and catalase inhibited AP-1 activation induced by vanadate, indicating the involvement of superoxide anion radical (O2-*), hydroxyl radical (*OH) and/or H2O2 in the mechanism of vanadate-induced AP-1 activation. However, sodium formate, a specific *OH scavenger, did not alter vanadate-induced AP-1 activation, suggesting a minimal role for the *OH radical. NADPH enhanced AP-1 activation by increasing vanadate-mediated generation of O2-*. N-acetylcysteine, a thiol-containing antioxidant, decreased activation, further showing that vanadate-induced AP-1 activation involved redox reactions. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited activation of AP-1, demonstrating that PKC is involved in the cell signal cascades leading to vanadate-induced AP-1 activation. Electron spin resonance (ESR) measurements show that JB6 P+ cells are able to reduce vanadate to generate vanadium(IV) in the presence of NADPH. Molecular oxygen was consumed during the vanadate reduction process to generate O2-* as measured by ESR spin trapping using 5,5-dimethyl-L-pyrroline N-oxide as the spin trapping agent. SOD inhibited the ESR spin adduct signal, further demonstrating the generation of O2-* in the cellular reduction of vanadate. These results provide support for a model in which vanadium, like other classes of tumor promoters, transactivates AP-1-dependent gene expression. In the case of vanadium, AP-1 transactivation is dependent on the generation of O2-* and H2O2, but not *OH.

Growth stimulation of primary B cell precursors by the anti-phosphatase Sbf1

SET binding factor 1 (Sbf1) was originally discovered by virtue of its interaction with a highly conserved motif (the SET domain) of unknown function in the protooncoprotein homolog of Drosophila trithorax, Hrx. Sbf1 shares extensive sequence similarity with myotubularin, a dual specificity phosphatase (dsPTPase) that is mutated in a subset of patients with inherited myopathies. Both Sbf1 and myotubularin interact with the SET domains of Hrx and other epigenetic regulatory proteins, but Sbf1 lacks phosphatase activity due to several evolutionarily conserved amino acid changes in its structurally preserved catalytic pocket. Thus, Sbf1 has features of an anti-phosphatase that could competitively antagonize dsPTPases; however the in vivo role for such factors remains unknown. Given its ability to physically interact with Hrx, a developmental regulator subject to translocation-induced mutations in B cell precursor leukemias, the current studies were undertaken to assess the effects of Sbf1 on lymphopoiesis. After infection with recombinant Sbf1 retroviruses, bone marrow cells were plated under Whitlock-Witte conditions for long-term culture of B lineage cells. Sbf1-expressing cells rapidly dominated the cultures resulting in clonal outgrowths of B cell progenitors that retained a dependence on their primary bone marrow-derived stroma for continuous growth in vitro. Structure/function analyses demonstrated that the SET interaction domain of Sbf1 was necessary and sufficient for growth alterations of B cell progenitors. These observations support a model in which Sbf1 functions as a SET domain-dependent positive regulator of growth-inducing kinase signaling pathways that impinge on SET domain proteins. SET domain-dsPTPase interactions appear to be critically important for regulating the growth properties of B cell progenitors.

Lack of transforming activity of fumonisin B1 in BALB/3T3 A31-1-1 mouse embryo cells

The capacity of fumonisin B1 (FB1) to induce morphological transformation of cultured mammalian cells was assessed using BALB/3T3 A31-1-1 mouse embryo cells. FB1 with 90% purity was prepared from Fusarium proliferatum grown on whole corn. Cell growth was not inhibited by 48 hr of exposure at concentrations up to 1000 micrograms/ml. Moderate inhibition was induced by 6 days of exposure. In transformation assays with a 48-hr exposure, increases in transformed foci were observed at some concentrations; however, the responses were not reproducible. Prolonged exposure for up to 4 wk at 10, 100 and 500 micrograms/ml failed to induce increases in transformed foci. Analysis of combined results showed that only the increase induced by a 48-hr exposure at 500 micrograms/ml was significant. A trend test indicated the lack of a dose response for concentrations of 10-1000 micrograms/ml. FB1 seems to lack in vitro transforming activity.

Induction of morphological transformation in BALB/3T3 mouse embryo cells by okadaic acid

Okadaic acid is produced by several types of dinoflagellates (marine plankton) and has been implicated as a causative agent of diarrhoetic shellfish poisoning. Okadaic acid, a known tumour promoter in vivo, has been shown to promote morphological transformation of carcinogen-initiated BALB/3T3 cells. This study shows that okadaic acid is capable of inducing morphological transformation of BALB/3T3 cells in the absence of an initiator.

Oxidative stress-regulated gene expression and promotion of morphological transformation induced in C3H/10T1/2 cells by ammonium metavanadate

Promoters of C3H/10T1/2 cell morphological transformation that elevate intracellular oxidant levels can be distinguished by a spectrum of induced gene expression, which includes the oxidant-responsive murine proliferin gene family. Proliferin transcripts were induced 40- to 100-fold by 20 microM ammonium metavanadate, 20-fold by 5 microM vanadium pentoxide but only three-fold by vanadium oxide sulfate. Consistent with its response to other oxidant chemicals, induction of proliferin by ammonium metavanadate was inhibited almost completely by the antioxidant N-acetylcysteine (8 mM). Ammonium metavanadate (5 microM), added as promoter in two-stage morphological transformation assays, amplified yields of Type II and Type III foci in monolayers of 20-methylcholanthrene-initiated C3H/10T1/2 cells. Ammonium metavanadate also induced formation of Type II foci in single-step transformation assays. The results suggest that pentavalent vanadium compounds could promote morphological transformation in C3H/10T1/2 cells by creating a cellular state of oxidative stress, sufficient to induce elevated expression of the proliferin gene family.

Genotoxicity of vanadium pentoxide in Chinese hamster V79 cells

Workers in many mining and manufacturing industries are potentially exposed to vanadium. Inhalation of dust containing vanadium pentoxide (V2O5), a pentavalent compound of vanadium, has been reported to cause lung diseases. Information related to the genotoxicity and potential carcinogenicity of V2O5, however, is still limited. In this study, the effect of V2O5 on mitosis, sister-chromatid exchange (SCE), micronucleus formation (MN), and gene mutation in Chinese hamster V79 cells was determined. Cells were treated with varying concentrations of V2O5 for 24 h. The results showed that no significant increases in the frequencies of SCE or gene mutation occurred in V2O5-treated cultures. However, dose-related increases were noted for micronucleated cells in cultures exposed to this compound, and the number of binucleated cells in the presence of cytochalasin B was found to decrease with increasing V2O5 concentrations. Since the micronucleated cells induced by V2O5 contained kinetochore-positive micronuclei, their induction appears to be due to damage to the spindle apparatus. These results indicate that V2O5 is cytotoxic and aneuploidogenic to V79 cells.