Benzo(a)pyrene-induced de-regulation of c-Ha-ras gene expression in vascular smooth muscle cells : role of the aryl hydrocarbon receptor /
These studies were designed to elucidate the role of the aryl hydrocarbon receptor (AhR) in the de-regulation of c-Ha-ras by benzo(a)pyrene (BaP) and related oxidants. We have established a correlation between the BaP-mediated atherogenic response and the up-regulation of c-Ha-ras in vascular smooth...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=728331771&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | These studies were designed to elucidate the role of the aryl hydrocarbon receptor (AhR) in the de-regulation of c-Ha-ras by benzo(a)pyrene (BaP) and related oxidants. We have established a correlation between the BaP-mediated atherogenic response and the up-regulation of c-Ha-ras in vascular smooth muscle cells (vSMCs). This up-regulation is partly mediated by activation of cis-acting antioxidant/electrophile response elements (ARE/EpREs) that enhance c-Ha-ras in vSMCs. BaP-mediated activation of ARE/EpREs depends upon metabolism by cytochrome P450s (CyPs) to intermediates that induce oxidative stress. Mitogen-activated c-Ha-ras expression was enhanced in G₀ synchronized vSMCs challenged with BaP, BaP-3,6-quinone and H₂O₂. Inhibitors of CyP metabolism and AhR antagonists partially inhibited c-Ha-ras induction by BaP. Buthionine-S-sulfoximine increased c-Ha-ras mRNA levels, while up-regulation of antioxidant capacity by N-acetylcysteine precluded BaP-induced c-Ha-ras expression. BaP increased the formation of reactive oxygen species and depleted cellular GSH in vSMCs. However, these changes did not correlate with the early induction of c-Ha-ras. BaP did not enhance c-Ha-ras in AhR⁻/⁻ vSMCs. Constitutive and BaP-inducible CyP1B1, but not CyP1A1, expression was observed in synchronized and randomly cycling AhR⁺/⁺ and AhR⁻/⁻ vSMCs. AHH activity was up-regulated to comparable levels in AhR⁺/⁺ and AhR⁻/⁻ vSMCs challenged with BaP. This response, however, was not mediated by CyP1A1 since ethoxyresorufin-O-deethylase activity was not detected. Neither actinomycin D nor cycloheximide blocked BaP-induced AHH activity, indicating that neither increased transcription, nor de novo protein synthesis, were necessary for AHH induction. Collectively, these results suggest that c-Ha-ras activation by BaP involves a redox sensitive mechanism that is AhR-dependent. Six-week old AhR⁺/⁺, AhR⁺/⁻, and AhR⁻/⁻ C57/B16J mice were challenged with 10mg/kg BaP once a week for 20 weeks. Vascular lesions in the thoracic aorta were observed in BaP-challenged mice from all of the AhR genotypes. However, control AhR⁻/⁻ mice exhibited altered vascular morphology as well. VSMCs isolated from BaP-challenged AhR⁺/⁺ and AhR⁻/⁻ mice displayed a decreased proliferative capacity compared to controls. Naive AhR⁺/⁺ and AhR⁻/⁻ vSMCs with BaP and subsequently propagated in culture, did not result in an enhanced proliferative phenotype. However, synchronized AhR⁺/⁺ and AhR⁺/⁻ vSMCs displayed an altered proliferation response compared to controls. |
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| Item Description: | Vita. "Major Subject: Toxicology". |
| Physical Description: | xvi, 186 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 135-185). |