| Summary: | 碩士 === 國立中興大學 === 環境工程學系 === 92 === Abstract
The objective of this research is to investigate the effects of one of the persistent organic pollutants (POPs)- (2.3.7.8-tetrachlorodibenzo-p-dioxin，TCDD), in mediating the induction of imbalances in gene expression and oxidative DNA damage by 17β-estrodiol (E2) in human breast cancer cell lines, including ER(+)/MCF-7 and ER(-)/MDA-MB-231 cells. Results from this study indicated that a 2-fold increase in the number of aldehydic DNA lesions (ADL) was detected in MCF-7 cells exposed to E2 (30 M) pretreated with TCDD and Ro 41-0960, a catechol-o-methyltrasferase (COMT) inhibitor, when compared to the corresponding control (p<0.05). A 2-fold increase in the number of ADL was also detected in MDA-MB-231 cells exposed to E2 (100 μM) alone. In contrast, pretreatment with TCDD (10 nM, 72 h) inhibited the induction of ADL by E2 in MDA-MB-231 cells. In addition, a 2-fold increase in the number of ADL was detected in MDA-MB-231 cells exposed to E2 (30-100 M) pretreated with TCDD and Ro 41-0960 when compared to the corresponding control (p<0.05). Further characterization confirmed that the ADL induced by E2 in MCF-7 and MDA-MB-231 cells was predominantly putrescine-excisable ADL. This evidence indicated that TCDD was capable of modulating the disposition of estrogen to the reactive quinones and the subsequent induction of promutagenic DNA lesions in living cells. In addition, we demonstrated the depletion of NAD(P)H (35 %) in MDA-MB-231 cells exposed to E2 (1-10 nM). Pretreatment with TCDD inhibit the depletion of NAD(P)H in MDA-MB-231 cells exposed to E2. Inclusion of Ro 41-0960 in the incubates enhances the decreases in NAD(P)H levels in MDA-MB-231 cells exposed to E2 (0.1-10 nM) (p<0.001). Further investigation indicates that the E2-induced depletion of NAD(P)H in MDA-MB-231 cells was completely blocked by PARP-1〔poly(ADP-ribose)polymerase-1〕inhibitors. This evidence suggests that exposure to TCDD and the status of COMT and ER modulate the E2-induced DNA single strand breaks (SSBs) in living cells at physiologically revelent concentration (0.1-1 nM). Further, results from semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) assay indicated that TCDD and E2 induced increases (2.5 folds) in the expression of CYP1A1, CYP1B1, and hOGG1, hAPE genes (1.5 folds) in MCF-7 cells. On the other hand, E2 induced increases (1.5 folds) in the expression of CYP1A1, CYP1B1 and hOGG1, hAPE genes (2.1 and 4.9 folds) in MDA-MB-231 cells. This result suggests that exposure to TCDD and the status of ER alter gene expression in the disposition of estrogen and DNA repair. Overall, our investigation confirmed that exposure to TCDD and the status of COMT and ER modulates the formation of quinonoid derivatives of E2 and the subsequent induction of oxidative DNA lesions in human breast cancer cell lines.
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