Abstract
Alteration of benzo[a]pyrene-induced cytochrome P450 1A1 gene expression by benzo[g,h,i]perylene or 1-nitropyrene in binary mixtures of mimic environmental pollutants Benzo[a]pyrene (BaP), benzo[g,h,i]perylene (BghiP) and 1-nitropyrene (1-NP) are all widespread environmental pollutants. BaP is thought to be a probable carcinogen in human cancer. Numerous studies have shown that BaP-induced carcinogenesis in rodents can be attenuated or gained by certain chemicals. However, the detailed molecular mechanisms through which these complex mixtures alter chemical carcinogenesis caused by BaP are not completely understood. The DNA adduct formation and cytochrome P450 1A1 (CYP1A1) induction have been suggested to be the major determinant of their carcinogenic activity. Therefore, a permanent human hepatoma cell lines HepG2 was used to explore the genotoxic action of BaP in combination with either BghiP or 1-NP. Results from 32P-postlabeling assay showed that the BaP-DNA adduct levels were increased by BghiP; whereas, those were reduced by 1-NP. In addition, the data from Western blot and Northern blot analyses showed that BghiP enhanced BaP-induced CYP 1A1 protein and its mRNA levels. However, 1-NP alleviated BaP-induced CYP1A1 mRNA expression, and caused a marked decrease in the protein levels. Furthermore, gel retardation assay was performed to elucidate the involvement of BghiP in CYP1A1 gene expression. The results showed that BghiP increased nuclear accumulation of aryl hydrocarbon receptor (AhR) in cells and/or activation of AhR to a DNA-binding form. There was a concordant increase in the transcription activation of CYP1A1 gene mediating through AhR signaling pathway. These findings demonstrate that BghiP enhanced BaP-induced CYP1A1 transcription by AhR activation, and suggest that the induction mechanism of CYP1A1 contributes to the co-carcinogenic potential of BghiP in BaP-induced carcinogenesis. On the other hand, the cotreatment with BaP and 1-NP decreased the AhR binding capacity to dioxin responsive element (DRE). This confirmed that the suppression of BaP-induced CYP1A1 mRNA expression through AhR signal pathway. However, the decrease in CYP1A1 protein levels was significantly larger than that in CYP1A1 mRNA levels. This inconsistent result was confirmed by in vitro proteolysis assay. The result revealed that an enhanced degradation rate of CYP1A1 protein was observed by adding the binary mixture of BaP and 1-NP. Administrating free radical scavengers, dimethyl sulfoxide (DMSO), or antioxidant, dithiothreitol, was added in the reaction mixture protected CYP1A1 protein degradation. Moreover, in cell viability assay, we found that mass cells death was accompanied with the decrease of CYP1A1 protein by 1-NP. These findings suggest that the transcriptional suppression by 1-NP may be partly involved in the regulation of CYP1A1 protein expression; however, free radical-mediated post-translational mechanism may play a dominated role in the loss of CYP1A1 protein content. Induction of OGG1 gene expression as an exposure biomarker of cooking oil fumes and the association with tumor progression in human lung cancer The human 8-oxoguanine DNA glycosylase 1 (hOGG1) gene encodes a DNA glycosylase/AP lyase that excises 8-hydroxydeoxyguanosine (8-OHdG) from DNA. Although hOGG1 has been suggested to be a tumor suppressor gene, infrequent mutations limit its impact in the development of tumor. In addition, little is known about the role of hOGG1 mRNA expression in lung tumorigenesis. Thus, in this study, 73 lung cancer patients and 22 non-cancer control subjects were enrolled to investigate the association of hOGG1 mRNA expression with lung cancer. The results from RT-PCR showed that hOGG1 mRNA expression was detected in 17 of 73 lung cancer patients (23.3%) and in none of the non-cancer controls. The expression of hOGG1 mRNA showed a good correlation with tumor size (p=0.014), tumor stage (p=0.001), and pRB negative immunostaining (p=0.039). In addition, the survivals of patients with hOGG1 mRNA expression were shorter than those without hOGG1 mRNA, indicating that hOGG1 mRNA expression may be associated with lung tumor progression. Furthermore, the data from H1299 lung cancer cells showed that hOGG1 mRNA expression reached the peak at G1-S transition, coinciding with phosphorylation of pRB. These results suggest that up-regulation of hOGG1 transcription may act as a predictor of lung tumor progression. On the other hand, it has been proposed that hOGG1 mRNA is a biomarker of cellular oxidative stress. Thus, in this study, hOGG1 mRNA expression was determined to assess the oxidative DNA damage induced by cooking oil fumes from frying fish (COF). The data from RT-PCR showed that the expression of hOGG1 mRNA was induced by hydrogen peroxide (H2O2) and COF in human lung adenocarcinoma CL-3 cells. It is consistent with other coworkers' findings, showing that 8-OHdG levels were increased in a dose dependent manner when calf thymus DNA reacted with various concentrations of COF. Moreover, the results from a cross-sectional study showed that the hOGG1 mRNA expression frequencies of COF-exposed cooks and housewives were significantly higher than those of control subjects. These findings confirmed that expression of hOGG1 may be adequate to act as an exposure biomarker to assess the oxidative DNA damage induced by COF. This indicated that oxidative stress involved in the exposure risk of COF may play a role in lung cancer development among Chinese women.