Modulation of gene expression and DNA adduct formation in HepG2 cells by polycyclic aromatic hydrocarbons with different carcinogenic potencies

Abstract

Polycyclic aromatic hydrocarbons (PAHs) can occur in relatively high concentrations in the air, and many PAHs are known or suspected carcinogens. In order to better understand differences in carcinogenic potency between PAHs, we investigated modulation of gene expression in human HepG2 cells after 6 h incubation with varying doses of benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), fluoranthene (FA), dibenzo[a,h]anthracene (DB[a,h]A), 1-methylphenanthrene (1-MPA) or dibenzo[a,l]pyrene (DB[a,l]P), by using cDNA microarrays containing 600 toxicologically relevant genes. Furthermore, DNA adduct levels induced by the compounds were assessed with (32)P-post-labeling, and carcinogenic potency was determined by literature study. All tested PAHs, except 1-MPA, induced gene expression changes in HepG2 cells, although generally no dose-response relationship could be detected. Clustering and principal component analysis showed that gene expression changes were compound specific, since for each compound all concentrations grouped together. Furthermore, it showed that the six PAHs can be divided into three groups, first FA and 1-MPA, second B[a]P, B[b]F and DB[a,h]A, and third DB[a,l]P. This grouping corresponds with the carcinogenic potencies of the individual compounds. Many of the modulated genes are involved in biological pathways like apoptosis, cholesterol biosynthesis and fatty acid synthesis. The order of DNA adduct levels induced by the PAHs was: B[a]P >> DB[a,l]P > B[b]F > DB[a,h]A > 1-MPA >/= FA. When comparing the expression change of individual genes with DNA adduct levels, carcinogenic potency or Ah-receptor antagonicity (the last two were taken from literature), several highly correlated genes were found, of which CYP1A1, PRKCA, SLC22A3, NFKB1A, CYP1A2 and CYP2D6 correlated with all parameters. Our data indicate that discrimination of high and low carcinogenic PAHs by gene expression profiling is feasible. Also, the carcinogenic PAHs induce several pathways that were not affected by the least carcinogenic PAHs.

Dibenzanthracenes and benzochrysenes elicit both genotoxic and nongenotoxic events in rat liver ‘stem-like’ cells

“…It has been documented, to a various extent, that benzochrysenes and dibenzanthracenes form DNA adducts and are mutagenic, with BgChry being the most potent genotoxin (Lecoq et al, 1989;Nesnow et al, 1994;Giles et al, 1995Giles et al, , 1996Giles et al, , 1997Lloyd and Hanawalt, 2002). In contrast to BgChry, DBahA, despite its known mutagenicity and carcinogenicity in vivo, has been shown to form relatively low levels of DNA adducts in vitro (Binková anď Srám, 2004;Staal et al, 2006). The formation of DNA adducts by PAHs is known to increase p53 tumour suppressor expression (Ramet et al, 1995;Binková et al, 2000).…”

Gene regulation in the marine diatom Thalassiosira pseudonana upon exposure to polycyclic aromatic hydrocarbons (PAHs)

“…In the literature there is no information on the specific effects of PAHs on diatoms' lipid metabolism, but it was reported for one fungus, able to degrade PAHs, that the lipid content was decreasing upon exposure to BaP (Verdin et al, 2006). Staal et al (2006) found a down-regulation of fatty acid synthesis related genes in HepG2 cells after exposure to several higher molecular PAHs. According to our studies, it might be possible that some genes encoding proteins involved in lipid pathways were also down-regulated while lacsA was upregulated, either because it was involved in a feedback mechanism or it might show a regulatory activity.…”

c-Jun NH2-Terminal Kinase–Related Na+/H+ Exchanger Isoform 1 Activation Controls Hexokinase II Expression in Benzo(a)Pyrene-Induced Apoptosis

“…Indeed, this transporter has been associated with tumor growth and chemotherapy resistance (7,12). Moreover, it has been shown that a highly carcinogenic PAH, benzo(a)pyrene (BaP), induced NHE1 expression in HepG2 tumoral cells (13). At this stage, it was important to identify the stimuli involved in NHE1 activation during the apoptotic process elicited by PAH.…”