No abstract

Arsenic is recognized to be a nonmutagenic carcinogen because it induces DNA damage only at very high concentrations. However, many more DNA strand breaks could be detected by digesting the DNA of arsenite-treated cells with endonuclease III, formamidopyrimidine-DNA glycosylase, and proteinase K. By doing so, arsenite could be shown to induce DNA damage in human cells within a pathologically meaningful concentration range. Oxidized guanine products were detected in all arsenite-treated human cells examined. DNA-protein cross-links were also detected in arsenite-treated NB4 and HL60 cells. In human umbilical vein endothelial cells, the induction of oxidized guanine products by arsenite was sensitive to inhibitors of nitric oxide (NO) synthase but not to oxidant modulators, whereas the opposite result was obtained in vascular smooth muscle cells. On the other hand, the arsenite-induced oxidized guanine products and DNA-protein cross-links in NB4 and HL60 cells were sensitive to modulators of calcium, NO synthase, oxidant, and myeloperoxidase. Therefore, although oxidized guanine products were detected in all the human cells treated with arsenite, the pathways could be different in different cell types. Because the sensitivity and the mechanism of arsenic intoxication are cell specific, it is important that target tissues and target cells are used for investigations. It is also important that pathologically or pharmacologically meaningful concentrations of arsenic are used. This is because in most cases we are dealing with the chronic effect rather than acute toxicity.

Fascin-1, an actin-bundling protein, plays an important role in cancer cell migration and invasion; however, the underlying mechanism remains unclear. On the basis of a 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced cell migration model, it was shown that TPA increased fascin-1 mRNA and protein expression and fascin-1-dependent cell migration. TPA dose- and time-dependently increased PKCδ and STAT3α activation and GSK3β phosphorylation; up-regulated Wnt-1, β-catenin, and STAT3α expression; and increased the nuclear translocation of β-catenin and STAT3α. Rottlerin, a PKCδ inhibitor, abrogated the increases in STAT3α activation and β-catenin and fascin-1 expression. WP1066, a STAT3 inhibitor, suppressed TPA-induced STAT3α DNA binding activity and β-catenin expression. Knockdown of β-catenin attenuated TPA-induced fascin-1 and STAT3α expression as well as cell migration. In addition to MCF-7, migration of Hs578T breast cancer cells was inhibited by silencing fascin-1, β-catenin, and STAT3α expression as well. TPA also induced Wnt-1 expression and secretion, and blocking Wnt-1 signaling abrogated β-catenin induction. DHA pretreatment attenuated TPA-induced cell migration, PKCδ and STAT3α activation, GSK3β phosphorylation, and Wnt-1, β-catenin, STAT3α, and fascin-1 expression. Our results demonstrated that TPA-induced migration is likely associated with the PKCδ and Wnt-1 pathways, which lead to STAT3α activation, GSK3β inactivation, and β-catenin increase and up-regulation of fascin-1 expression. Moreover, the anti-metastatic potential of DHA is partly attributed to its suppression of TPA-activated PKCδ and Wnt-1 signaling.

The present study was designed to investigate the pathways involved in the effect of betel nut arecoline on cell viability in 3T3-L1 preadipocytes. Arecoline, but not arecaidine or guvacine, inhibited preadipocyte viability in a concentration- and time-dependent manner. Arecoline arrested preadipocyte growth in the G2/M phase of the cell cycle; decreased the total levels of cyclin-dependent kinase 1 (CDK1), p21, and p27 proteins; increased p53 and cyclin B1 protein levels; and had no effect on CDK2 protein levels. These results suggested that arecoline selectively affected a particular CDK subfamily. Arecoline inhibited AMP-activated protein kinase (AMPK) activity; conversely, the AMPK activator, AICAR, blocked the arecoline-induced inhibition of cell viability. Pre-treatment with the antioxidant, N-acetylcysteine, prevented the actions of arecoline on cell viability, G2/M growth arrest, reactive oxygen species (ROS) production, and the levels of CDK1, p21, p27, p53, cyclin B1, and phospho-AMPK proteins. These AMPK- and ROS-dependent effects of arecoline on preadipocyte growth may be related to the mechanism underlying the modulatory effect of arecoline on body weight.

We report here that sequential digestion with endonuclease III, formamidopyrimidine-DNA glycosylase, and proteinase K in Tris buffer markedly increased the sensitivity for detecting DNA damage in arsenic-treated cells. These three enzymes increased DNA strand breaks in an additive manner. By using this sequential-enzyme-digestion comet assay, we demonstrated that trivalent inorganic arsenic induced more DNA damage than monomethylarsonous acid, monomethylarsonic acid, and dimethylarsinic acid in human blood cell lines. However, trivalent inorganic arsenic was far less potent than monomethylarsonous acid in inhibiting pyruvate dehydrogenase activity. Therefore, different mechanisms are involved in inhibiting pyruvate dehydrogenase activity and inducing DNA damage. Our results also indicate while trivalent inorganic arsenic induced more endonuclease III-digestible adducts, monomethylarsonous acid and monomethylarsonic acid induced more proteinase K-digestible adducts. These results suggest there is a difference in the mechanism for inducing DNA damage between inorganic and organic methylated arsenic compounds.