Serum-stimulated cell cycle progression and stress protein synthesis in C3H10T1/2 fibroblasts treated with sodium arsenite

Arsenic trioxide induces depolymerization of microtubules in an acute promyelocytic leukemia cell line

Background

Arsenic trioxide (As₂O₃) is a well-known and effective treatment that can result in clinical remission for patients diagnosed with acute promyelocytic leukemia (APL). The biologic efficacy of As₂O₃ in APL and solid tumor cells has been explained through its actions on anti-proliferation, anti-angiogenesis, and apoptotic signaling pathways. We theorize that As₂O₃ activates a pathway that disrupts microtubule dynamics forming abnormal, nonfunctioning mitotic spindles, thus preventing cellular division. In this study, we investigated how As₂O₃ induces apoptosis by causing microtubule dysfunction.

Methods

Cultured NB4 cells were treated with As₂O₃, paclitaxel, and vincristine. Flow cytometric analysis was then performed. An MTT assay was used to determine drug-mediated cytotoxicity. For tubulin polymerization assay, each polymerized or soluble tubulin was measured. Microtubule assembly-disassembly was measured using a tubulin polymerization kit. Cellular microtubules were also observed with fluorescence microscopy.

Results

As₂O₃ treatment disrupted tubulin assembly resulting in dysfunctional microtubules that cause death in APL cells. As₂O₃ markedly enhanced the amount of depolymerized microtubules. The number of microtubule posttranslational modifications on an individual tubulin decreased with As₂O₃ concentration. Immunocytochemistry revealed changes in the cellular microtubule network and formation of polymerized microtubules in As₂O₃-treated cells.

Conclusion

The microtubules alterations found with As₂O₃ treatment suggest that As₂O₃ increases the depolymerized forms of tubulin in cells and that this is potentially due to arsenite's negative effects on spindle dynamics.

PI-3K/Akt signal pathway plays a crucial role in arsenite-induced cell proliferation of human keratinocytes through induction of cyclin D1

Exposure of arsenite can induce hyperproliferation of skin cells, which is believed to play important roles in arsenite-induced carcinogenesis by affecting both promotion and progression stages. However, the signal pathways and target genes activated by arsenite exposure responsible for the proliferation remain to be defined. In the present study, we found that: (1) exposure of human keratinocytic HaCat cells to arsenite caused an increase in cell proliferation, which was significantly inhibited by pretreatment of wortmannin, a specific chemical inhibitor of PI-3K/Akt signal pathway; (2) arsenite exposure was also able to activate PI-3K/Akt signal pathway, which thereby induced the elevation of cyclin D1 expression level in both HaCat cells and human primary keratinocytes based on that inhibition of PI-3K/Akt pathway by either pretreatment of wortmannin or the transfection of their dominant mutants, significantly inhibited cyclin D1 expression upon arsenite exposure; (3) PI-3K/Akt pathway is implicated in arsenite-induced proliferation of HaCat cells through the induction of cyclin D1 because either knockdown of cyclin D1 by its siRNA or inhibition of PI-3K/Akt signal pathway by their dominant mutants markedly impaired the proliferation of HaCat cells induced by arsenite exposure. Taken together, we provide the direct evidence that PI-3K/Akt pathway plays a role in the regulation of cell proliferation through the induction of cyclin D1 in human keratinocytes upon arsenite treatment. Given the importance of aberrant cell proliferation in cell transformation, we propose that the activation of PI-3K/Akt pathway and cyclin D1 induction may be the important mediators of human skin carcinogenic effect of arsenite.

Essential roles of PI-3K/Akt/IKKbeta/NFkappaB pathway in cyclin D1 induction by arsenite in JB6 Cl41 cells

Skin is a major target of carcinogenic trivalent arsenic (arsenite, As3+). It has been thought that cell proliferation is one of the central events involved in the carcinogenic effect of arsenite. Cyclin D1, a nuclear protein playing a pivotal role in cell proliferation and cell cycle transition from G1 to S phases, has been reported to be induced in human fibroblast by arsenite via uncertain molecular mechanisms. In the present study, the potential roles of PI-3K/Akt/IKKbeta/NFkappaB signal pathway in cyclin D1 induction by arsenite were addressed in mouse epidermal Cl41 cells. We found that exposure of Cl41 cells to arsenite was able to induce cell proliferation, activate PI-3K-->Akt/p70(S6k) signal pathway and increase cyclin D1 expression at both transcription and protein levels. Pre-treatment of Cl41 cells with PI-3K inhibitor, wortmannin, significantly inhibited the phosphorylation of Akt and p70(S6k) and thereby dramatically impaired the cyclin D1 induction by arsenite, implicating the importance of the PI-3K signal pathway in the cyclin D1 induction by arsenite. Furthermore, inhibition of PI-3K/Akt by overexpression of Deltap85 or DN-Akt blocked arsenite-induced IKK phosphorylation, IkappaBalpha degradation and cyclin D1 expression, indicating that IKK/NFkappaB is the downstream transducer of arsenite-triggered PI-3K/Akt cascade. Moreover, inhibition of IKKbeta/NFkappaB signal pathway by overexpression of its dominant negative mutant, IKKbeta-KM, also significantly blocked arsenite-induced cyclin D1 expression. Overall, arsenite exposure triggered PI-3K/Akt/IKKbeta/NFkappaB signal cascade which in turn plays essential roles in inducing cyclin D1 expression.

Inhibition of bovine herpesvirus-4 replication in endothelial cells by arsenite

The effect of arsenite pretreatment on bovine herpesvirus-4 (BHV-4) replication in bovine arterial endothelial (BAE) cells was studied. BHV-4 infectivity, including IE-2 expression, DNA replication and viral yield, were significantly reduced at nontoxic concentrations of arsenite in which cellular DNA synthesis or cell viability of BAE cells were not affected under resting and confluent conditions. This effect was accompanied by the induction of heat shock protein 70 (HSP70) and an interrupted cell cycle (causing cell cultures to accumulate at the S and G2/M phases). Actinomycin D inhibited the induction of HSP70 and reduced arsenite antiviral activity. In conclusion, cellular stress response induced by arsenite in BAE cells inhibited replication of BHV-4, and probably resulted from the induction of HSP70 and interference of cell cycle progression.

Immobilization stress induces c-Fos accumulation in liver

Acute stress-induced injury in tissues has been revealed by both biochemical markers in plasma and microscopy. However, little is known of the mechanisms by which tissue integrity is restored. Recently, induction of early response genes such as c-fos has been reported in the heart and stomach of immobilized animals. Herein, we show that immobilization stress in mice increased plasma alanine aminotransferase activity, a marker of liver damage. c-Fos protein accumulation in liver was induced by stress after 20 minutes of immobilization and persisted for 3 hours. Immobilization also induced the release of epidermal growth factor (EGF) from submandibular salivary glands and a transient increase in EGF concentration in plasma. Although EGF administration induced a 2.5-fold increase in c-Fos mass in the liver of anesthetized mice, sialoadenectomy (which abolished the effect of immobilization on plasma EGF) did not affect the stress-induced rise in plasma alanine aminotransferase activity or liver c-Fos accumulation. Therefore, we conclude that immobilization stress induces c-Fos accumulation in liver and that this effect is not triggered by the increase in plasma EGF concentration.

Efficacy of a potentized homoeopathic drug (Arsenicum Album-30) in reducing genotoxic effects produced by arsenic trioxide in mice: II. Comparative efficacy of an antibiotic, actinomycin D alone and in combination with either of two microdoses

OBJECTIVE

To determine whether actinomycin-D (AMD), an antibiotic, alters the reported efficacy of a potentized homoeopathic drug, Arsenicum Album, in reducing genotoxic effects produced in arsenic-trioxide-injected mice.

DESIGN

Mice were separately injected with AMD, As2O3, and conjointly with AMD plus As2O3, AMD plus homoeopathic drug, AMD plus As2O3 plus homoepathic drug, and As2O3 plus homoeopathic drug in separate sets.

METHODS

Several standard cytogenetical endpoints were assessed at different fixation intervals by adopting conventional techniques.

RESULTS

Both Ars Alb-30 and Ars Alb-200 showed protective ability against AMD and As2O3 when injected individually, but this ability was reduced considerably in mice injected with AMD and As2O3 together. AMD itself had genotoxic effects, but also apparently reduced genotoxic effects of arsenic to some extent.

CONCLUSION

AMD reduced the protective efficacy of the homoeopathic drug against arsenic. This result suggests a mechanism of action for homoeopathy, as AMD is a known transcription-blocker.

Induction of human endothelial cell apoptosis requires both heat shock and oxidative stress responses

Endothelial cell (EC) death may play an important role in the development of increased vascular permeability and capillary leak syndrome during systemic inflammatory response syndrome. However, the mode of EC death and the mechanisms involved remain unclear. In this study we employed the proinflammatory mediators lipopolysaccharide (LPS) and tumor necrosis factor-alpha (TNF-alpha), the chemical reagent sodium arsenite, and heat shock to trigger the stress gene responses. Human ECs were used as surrogates of the microvasculature to test the hypothesis that the induction of the heat shock response and the oxidative stress response might combine to induce apoptosis rather than necrosis in human ECs. Sodium arsenite at 80-320 microM, which induced heat shock protein 72 (HSP72) expression and reactive oxygen intermediate (ROI) generation in ECs, resulted in EC apoptosis. TNF-alpha alone (5-75 ng/ml) increased EC ROI generation but did not induce EC apoptosis. Heat shock alone (42 degrees C, 45 min) or sodium arsenite (40 microM) alone, each of which induced HSP72 expression, did not result in EC apoptosis. However, the combination of TNF-alpha with heat shock or 40 microM sodium arsenite led to EC apoptosis as HSP72 expression and ROI were induced. Furthermore, sodium arsenite (80 microM) in the presence of antioxidants failed to induce EC apoptosis. Apoptotic ECs also exhibited functional disturbances as represented by the depression of intercellular adhesion molecule-1 expression as well as the disruption of EC monolayer integrity. These results indicate that the simultaneous induction of a heat shock response and an oxidative stress response is responsible for human EC apoptosis.

Heat-shock induced protein modifications and modulation of enzyme activities

Upon heat stress, the cell physiology is profoundly altered. The extent of the alterations depends on the severity of the stress and may lead to cell death. The heat shock response is an array of metabolic changes characterized by the impairment of major cellular functions and by an adaptative reprogramming of the cell metabolism. The enhanced synthesis of the HSPs is a spectacular manifestation of this reprogramming. Numerous post translational modifications of proteins occur in response to heat stress and can be related to altered cellular functions. Some proteins are heat-denatured and temporarily inactivated. Heat-denaturation is reversible, chaperones may contribute to the repair. The extent of heat-denaturation depends on the cell metabolism: (a) it is attenuated in thermotolerant cells or in cells overexpressing the appropriate chaperones (b) it is enhanced in energy-deprived cells. Covalent modifications may also rapidly alter protein function. Changes in protein glycosylation, methylation, acetylation, farnesylation, ubiquitination have been found to occur during stress. But protein phosphorylation is the most studied modification. Several protein kinase cascades are activated, among which the various mitogen activated protein kinase (MAP kinase) cascades which are also triggered by a wide range of stimuli. As a possible consequence, stress modifies the phosphorylation status and the activity of components from the transcriptional and translational apparatuses. The same kinases also target key enzymes of the cellular metabolism. Protein denaturation results in constitutive hsp titration, this titration is a signal to trigger the heat-shock gene transcription and to activate some of the protein kinase cascades.

Stathmin is a major substrate for mitogen-activated protein kinase during heat shock and chemical stress in HeLa cells

Stathmin is a ubiquitous, highly conserved 19-kDa cytoplasmic protein whose expression and phosphorylation are regulated in relation to cell proliferation, differentiation or activation, in many biological systems. In this report, we show that stathmin undergoes major phosphorylation in HeLa cells submitted to heat or chemical stress. Heat-shock-induced stathmin phosphorylation was very rapid, as maximal incorporation of phosphate was observed at 5 min. Phosphorylation of stathmin might, therefore, occur as a very early step in the intracellular response to heat shock. The sites of phosphorylation of stathmin involved during the stress response were identified as mostly Ser25 and, to a lesser extent, Ser38. These sites are both followed by a proline residue, and known to be good substrates in vitro for mitogen-activated protein kinase (MAP-kinase) and p34cdc2 kinase, respectively. In lysates from heat-shocked cells, an increased stathmin-kinase activity, distinct from the histone-H1-kinase activity, was found to phosphorylate stathmin mostly on Ser25, the main site for MAP-kinase in vitro. This stathmin-kinase coeluted quantitatively with the stress-activated MAP-kinase from an FPLC MonoQ column. Furthermore, a stathmin kinase activity was precipitated from lysates of heat-shocked HeLa cells by an anti-(MAP-kinase) serum. Together, these results indicate that the phosphorylation of stathmin by MAP-kinase is likely to be a significant component of the signalling array controlling the cellular response to stress, and they further underline the general involvement of stathmin in intracellular signalling.

Sodium arsenite induces chromosome endoreduplication and inhibits protein phosphatase activity in human fibroblasts

Arsenic, strongly associated with increased risks of human cancers, is a potent clastogen in a variety of mammalian cell systems. The effect of sodium arsenite (a trivalent arsenic compound) on chromatid separation was studied in human skin fibroblasts (HFW). Human fibroblasts were arrested in S phase by the aid of serum starvation and aphidicolin blocking and then these cells were allowed to synchronously progress into G2 phase. Treatment of the G2-enriched HFW cells with sodium arsenite (0-200 microM) resulted in arrest of cells in the G2 phase, interference with mitotic division, inhibition of spindle assembly, and induction of chromosome endoreduplication in their second mitosis. Sodium arsenite treatment also inhibited the activities of serine/threonine protein phosphatases and enhanced phosphorylation levels of a small heat shock protein (HSP27). These results suggest that sodium arsenite may mimic okadaic acid to induce chromosome endoreduplication through its inhibitory effect on protein phosphatase activity.