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Identification of novel TCDD-regulated genes by microarray analysis
Paul R Hanlon1, Wenchao Zheng, Alex Y Ko
1Molecular and Environmental Toxicology Center, University of Wisconsin-Madison, WI 53706, USA.
Toxicology and Applied Pharmacology
|January 26, 2005
Summary
Tetrachloro-dibenzodioxin (TCDD) alters over 1000 genes in fibroblasts, impacting cell cycle and metabolism. Its effects are modulated by epidermal growth factor (EGF) and adipogenesis, but direct aryl hydrocarbon receptor (AhR) activation remains consistent.
Area of Science:
- Toxicology
- Molecular Biology
- Cell Biology
Background:
- The environmental toxicant tetrachloro-dibenzodioxin (TCDD) is known to induce significant changes in gene expression.
- Fibroblasts are multipotent cells susceptible to environmental stimuli, making them a model for studying toxicant effects.
- Understanding TCDD's impact on gene expression, particularly its interaction with growth factor signaling, is crucial for assessing its toxicological profile.
Purpose of the Study:
- To investigate the comprehensive gene expression changes induced by TCDD in C3H10T1/2 fibroblasts.
- To determine how epidermal growth factor (EGF) and adipogenic stimuli modify TCDD's effects on gene expression.
- To elucidate the relationship between direct aryl hydrocarbon receptor (AhR) activation and TCDD-induced secondary gene responses.
Main Methods:
- Exposure of C3H10T1/2 fibroblasts to TCDD for 72 hours, with or without EGF or adipogenic stimuli during the final 24 hours.
- Gene expression profiling using transcriptomic analysis to identify altered genes and pathways.
- Measurement of direct AhR activation using integrated AhR-responsive luciferase reporters.
- Quantitative analysis of specific gene induction kinetics.
Main Results:
- TCDD exposure altered over 1000 genes, including cell cycle, glycolytic, and ribosomal clusters, independent of major mitogenic signaling pathways like ERK.
- EGF and adipogenic stimuli partially attenuated TCDD-induced gene expression changes and also prevented some TCDD-induced responses.
- Direct AhR activation was consistent across quiescent, EGF-stimulated, and adipogenic conditions, with only 23 genes consistently induced by TCDD regardless of cellular state.
- Key TCDD-responsive genes identified include cytochrome P450 family members, NAD(P)H quinone reductase 1 (NQO1), alcohol dehydrogenase 3, superoxide dismutase 3, and glypican 1, with glypican 1 potentially mediating secondary effects.
Conclusions:
- TCDD profoundly impacts fibroblast gene expression, affecting multiple cellular processes.
- The cellular context, influenced by EGF or adipogenesis, modulates TCDD's secondary effects on gene expression.
- Despite varied secondary responses, direct AhR activation by TCDD is robust, suggesting a complex interplay between direct receptor activation and downstream signaling pathways.