Certain forms of the heavy metals arsenic and chromium are considered human carcinogens, although they are believed to act through very different mechanisms. Chromium(VI) is believed to act as a classic genotoxic and mutagenic agent, and DNANchromatin appears to be the principal target for its effects. In contrast, arsenic(lll) is considered nongenotoxic, but is able to target specific cellular proteins, principally through sulfhydryl interactions. We had previously shown that various genotoxic chemical carcinogens, including chromium(VI), preferentially altered expression of several inducible genes but had little or no effect on constitutive gene expression. We were therefore interested in whether these carcinogenic heavy metals might target specific but distinct sites within cells, leading to alterations in gene expression that might contribute to the carcinogenic process. Arsenic(lll) and chromium(V1) each significantly altered both basal and hormone-inducible expression of a model inducible gene, phosphoenolpyruvate carboxykinase (PEPCK), at nonovertly toxic doses in the chick embryo in vivo and rat hepatoma H411E cells in culture. We have recently developed two parallel cell culture approaches for examining the molecular basis for these effects. First, we are examining the effects of heavy metals on expression and activation of specific transcription factors known to be involved in regulation of susceptible inducible genes, and have recently observed significant but different effects of arsenic(lll) and chromium(Vl) on nuclear transcription factor binding. Second, we have developed cell lines with stably integrated PEPCK promoter-luciferase reporter gene constructs to examine effects of heavy metals on promoter function, and have also recently seen profound effects induced by both chromium(V1) and arsenic(lil) in this system. These model systems should enable us to be able to identify the critical cis (DNA) and trans (protein) cellular targets of heavy metal exposure leading to alterations in expression of specific susceptible genes. It is anticipated that such information will provide valuable insight into the mechanistic basis for these effects as well as provide sensitive molecular biomarkers for evaluating human exposure. Environ Health Perspect 1 06(Suppl 4):1 005-1015 (1998). http://ehpnet1.niehs.nih.gov/docs/1998/Suppl4/ 1005-1015hamilton/abstract.html

Certain forms of the heavy metals arsenic and chromium are considered human carcinogens, although they are believed to act through very different mechanisms. Chromium(VI) is believed to act as a classic and mutagenic agent, and DNA/chromatin appears to be the principal target for its effects. In contrast, arsenic(III) is considered nongenotoxic, but is able to target specific cellular proteins, principally through sulfhydryl interactions. We had previously shown that various genotoxic chemical carcinogens, including chromium (VI), preferentially altered expression of several inducible genes but had little or no effect on constitutive gene expression. We were therefore interested in whether these carcinogenic heavy metals might target specific but distinct sites within cells, leading to alterations in gene expression that might contribute to the carcinogenic process. Arsenic(III) and chromium(VI) each significantly altered both basal and hormone-inducible expression of a model inducible gene, phosphoenolpyruvate carboxykinase (PEPCK), at nonovertly toxic doses in the chick embryo in vivo and rat hepatoma H411E cells in culture. We have recently developed two parallel cell culture approaches for examining the molecular basis for these effects. First, we are examining the effects of heavy metals on expression and activation of specific transcription factors known to be involved in regulation of susceptible inducible genes, and have recently observed significant but different effects of arsenic(III) and chromium(VI) on nuclear transcription factor binding. Second, we have developed cell lines with stably integrated PEPCK promoter-luciferase reporter gene constructs to examine effects of heavy metals on promoter function, and have also recently seen profound effects induced by both chromium(VI) and arsenic(III) in this system. These model systems should enable us to be able to identify the critical cis (DNA) and trans (protein) cellular targets of heavy metal exposure leading to alterations in expression of specific susceptible genes. It is anticipated that such information will provide valuable insight into the mechanistic basis for these effects as well as provide sensitive molecular biomarkers for evaluating human exposure.

The toxic metals arsenic(III) and chromium(VI) are considered human carcinogens, although they may act through different mechanisms. We previously showed that when administered at single low, non-overtly toxic doses, chromium, arsenic, and several other chemical carcinogens preferentially alter expression of several model inducible genes in both whole-animal and cell-culture systems. In this study, we assessed whether chromium and arsenic target specific signaling pathways within cells to selectively modulate gene expression. We examined the effects of non-cytotoxic and cytotoxic doses of arsenic(III) and chromium(VI) on nuclear binding of the transcription factors AP-1, NF-kappaB, Sp1, and YB-1 in human MDA-MB-435 breast cancer and rat H4IIE hepatoma cells. These transcription factors were chosen because they may regulate many inducible genes, including those previously shown to be altered by metal treatments. We report that both arsenic and chromium significantly altered nuclear binding levels of these factors to their respective cis-acting elements. However, there were qualitative and quantitative differences in these effects that were dependent on the metal, time, dose, transcription factor, and cell line. These effects may play a significant role in metal-induced alterations in gene expression.

The toxic metals arsenic(III) and chromium(VI) are considered human carcinogens, although they may act through different mechanisms. We previously showed that when administered at single low, non-overtly toxic doses, chromium, arsenic, and several other chemical carcinogens preferentially alter expression of several model inducible genes in both whole-animal and cell-culture systems. In this study, we assessed whether chromium and arsenic target specific signaling pathways within cells to selectively modulate gene expression. We examined the effects of non-cytotoxic and cytotoxic doses of arsenic(III) and chromium(VI) on nuclear binding of the transcription factors AP-1, NF-kappaB, Sp1, and YB-1 in human MDA-MB-435 breast cancer and rat H4IIE hepatoma cells. These transcription factors were chosen because they may regulate many inducible genes, including those previously shown to be altered by metal treatments. We report that both arsenic and chromium significantly altered nuclear binding levels of these factors to their respective cis-acting elements. However, there were qualitative and quantitative differences in these effects that were dependent on the metal, time, dose, transcription factor, and cell line. These effects may play a significant role in metal-induced alterations in gene expression.