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Microarray examination of TCDD mediated changes in gene expression in Hepa1c1c7 murine hepatoma cells. E Dere1,4, DR Boverhof1,4, LD Burgoon3,4, and TR Zacharewski1,4. 1Department of Biochemistry and Molecular Biology, 2Department of Pharmacology and Toxicology, 3Center for Integrative Toxicology, 4National Food Safety and Toxicology Center Michigan State University, East Lansing MI, USA 48824. In an effort to characterize Ah receptor (AhR)-mediated gene expression, comprehensive temporal microarray assays were performed using murine Hepa1c1c7 wild-type (WT) and aryl hydrocarbon nuclear translocator (ARNT) defective C4 mutant hepatoma cells treated with 10 nM TCDD or vehicle (DMSO) for 1, 2, 4, 8, 12, 24 or 48 hours. Gene expression profiles were monitored using custom cDNA microarrays containing 13,361 cDNA clones representing 7,810 unique genes. Statistical analysis using an empirical Bayes approach identified 411 significant changes in gene expression in WT cells at one or more time points which grouped into 5 distinct k-means clusters. In contrast, TCDD treatment had little effect in C4 cells at 1 or 24 hours. TCDD affected functional categories in WT cells included regulation of cell cycle, growth, apoptosis and oxidative stress. Computational examination within -1500 and +1500 of the transcriptional start site, the region with the highest occurrence of dioxin response elements (DREs), identified at least one putative DRE in 284 of the temporally responsive genes. Comparison of in vitro gene expression changes to responses observed in hepatic tissue of immature ovariectomized C57BL/6 mice treated with 30 µg/kg TCDD, identified 53 significant genes in common between the two data sets with the vast majority of these involved in xenobiotic metabolism. Expression profiles for most overlapping genes exhibited a comparable pattern in response to TCDD. However, there were contradictory profiles which may be a result of differing basal levels of expression in the two systems. The similarities and differences in gene expression patterns of these genes illustrate the advantages and caveats of using cultured cell lines as models of toxicity for whole tissue responses. Supported by grant ES11271. |
