Effects of arsenic, cadmium, chromium, and lead on gene expression regulated by a battery of 13 different promoters in recombinant HepG2 cells

Citation
Db. Tully et al., Effects of arsenic, cadmium, chromium, and lead on gene expression regulated by a battery of 13 different promoters in recombinant HepG2 cells, TOX APPL PH, 168(2), 2000, pp. 79-90
Citations number
84
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
TOXICOLOGY AND APPLIED PHARMACOLOGY
ISSN journal
0041-008X → ACNP
Volume
168
Issue
2
Year of publication
2000
Pages
79 - 90
Database
ISI
SICI code
0041-008X(20001015)168:2<79:EOACCA>2.0.ZU;2-V
Abstract
Toxic metals occur naturally at low concentrations throughout the environme nt, but are found in higher concentrations at many of the hazardous waste s ites on the EPA Superfund list. As part of the Agency for Toxic Substances and Disease Registry (ATSDR) mandate to evaluate the toxicity of metals and mixtures, we chose four of the high-priority metal pollutants from ATSDR's HAZ-DAT list, including arsenic, cadmium, chromium, and lead, to test in a commercially developed assay system, CAT-Tox(L) (Xenometrix). This assay e mploys a battery of recombinant HepG2 cell lines to test the transcriptiona l activation capacity of xenobiotics in any of 13 different signal transduc tion pathways. Our specific aims were to identify metal-responsive promoter s and determine whether the pattern of gene expression changed with a mixtu re of metals. Humic acid was used in all assays as a carrier to help solubi lize the metals and, in all cases, the cells were exposed to the humic acid -metal mixture for 48 h. Humic acid alone, at 50-100 muM, showed moderate a ctivation of the XRE promoter, but little other notable activity. As(V), at doses of 50-250 muM, produced a complex profile of activity showing signif icant dose-dependent induction of the hMTIIA, GST Ya, HSP70, FOS, XRE, NF k appa BRE, GADD153, p53RE, and CRE promoters. Pb(II) showed dose-related ind uction of the GST Ya, XRE, hMTIIA, GRP78, and CYP IA1 promoters at doses in the range of 12-100 muM. Cd(II), at 1.25-15 muM, yielded significant dose- dependent induction of hMTIIA, XRE, CYP IA1, GST Ya, HSP70, NF kappa BRE, a nd FOS. Whereas Cr(III) yielded small, though significant inductions of the CRE, FOS, GADD153, and XRE promoters only at the highest dose (750 muM), C r(VI) produced significant dose-related inductions of the p53RE, FOS, NF ka ppa BRE, XRE, GADD45, HSP70, and CRE promoters at much lower doses, in the range of 5-10 muM. Assays testing serial dilutions of a mixture comprising 7.5 muM Cd(II), 750 muM Cr(III), and 100 muM Pb(II) (the combination of met als most frequently found at National Priority List sites) showed significa nt dose-dependent induction of the hMTIIA promoter, but failed to show dose -related induction of any other promoter and showed no evidence of synergis tic activation of gene expression by the metals in this mixture. Our result s thus show metal activation of gene expression through several previously unreported signal transduction pathways, including As(V) induction of GST Y a, FOS, XRE, NFkBRE, GADD153, p53RE, and CRE; Pb(II) induction of GST Ya, X RE, Cyp IA1, and GADD153; Cd(II) induction of NFkBRE, Cyp IA1, XRE, and GST Ya; and Cr(VI) induction of p53RE, XRE, GADD45, HSP70, and CRE promoters, and thus suggest new insights into the biochemical mechanisms of toxicity a nd carcinogenicity of metals. It is also an important finding that no evide nce of synergistic activity was detected with the mixture of Cd(II), Cr(III ), and Pb(II) tested in these assays.