title: Hexachlorobenzene induces cell proliferation, and aryl hydrocarbon receptor expression (AhR) in rat liver preneoplastic foci, and in the human hepatoma cell line HepG2. AhR is a mediator of ERK1/2 signaling, and cell cycle regulation in HCB-treated HepG2 cells.
abstract: Hexachlorobenzene (HCB) is a widespread environmental pollutant, and a liver tumor promoter in rodents. Depending on the particular cell lines studied, exposure to these compounds may lead to cell proliferation, terminal differentiation, or apoptosis. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is involved in drug and xenobiotic metabolism. AhR can also modulate a variety of cellular and physiological processes that can affect cell proliferation and cell fate determination. The mechanisms by which AhR ligands, both exogenous and endogenous, affect these processes involve multiple interactions between AhR and other signaling pathways. In the present study, we examined the effect of HCB on cell proliferation and AhR expression, using an initiation-promotion hepatocarcinogenesis protocol in rat liver and in the human-derived hepatoma cell line, HepG2. Female Wistar rats were initiated with a single dose of 100 mg/kg of diethylnitrosamine (DEN) at the start of the experiment. Two weeks later, daily dosing of 100 mg/kg HCB was maintained for 10 weeks. Partial hepatectomy was performed 3 weeks after initiation. The number and area of glutathione S-transferase-P (GST-P)-positive foci, in the rat liver were used as biomarkers of liver precancerous lesions. Immunohistochemical staining showed an increase in proliferating cell nuclear antigen (PCNA)-positive cells, along with enhanced AhR protein expression in hepatocytes within GST-P-positive foci of (DEN HCB) group, when compared to DEN. In a similar manner, Western blot analysis demonstrated that HCB induced PCNA and AhR protein expression in HepG2 cells. Flow cytometry assay indicated that the cells were accumulated at S and G2/M phases of the cell cycle. HCB increased cyclin D1 protein levels and ERK1/2 phosphorylation in a dose-dependent manner. Treatment of cells with a selective MEK1 inhibitor, prevented HCB-stimulatory effect on PCNA and cyclinD1, indicating that these effects are mediated by ERK1/2. Pretreatment with an AhR antagonist, prevented HCB-induced PCNA protein levels, ERK1/2 phosphorylation and alterations in cell cycle distribution. These results demonstrate that HCB-induced HepG2 proliferation and cell cycle progression depend on ERK1/2 phosphorylation which is mediated by the AhR. Our results provide a clue to the molecular events involved in the mechanism of action of HCB-induced hepatocarcinogenesis.
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Ana Clara
authors.initials: AC
authors.lastname: de Tomaso Portaz
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Giselle Romero
authors.initials: GR
authors.lastname: Caimi
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Marcela
authors.initials: M
authors.lastname: Sánchez
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Florencia
authors.initials: F
authors.lastname: Chiappini
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Andrea S
authors.initials: AS
authors.lastname: Randi
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina. Electronic address: dianakleiman@yahoo.com.ar.
authors.forename: Diana L
authors.initials: DL
authors.lastname: Kleiman de Pisarev
authors.affiliation: Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires, CP 1121, Argentina.
authors.forename: Laura
authors.initials: L
authors.lastname: Alvarez
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D056945:Hep G2 Cells / Q000187:drug effects*; D006581:Hexachlorobenzene / Q000633:toxicity*; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D011230:Precancerous Conditions / Q000139:chemically induced*; D051381:Rats; D017208:Rats, Wistar; D018336:Receptors, Aryl Hydrocarbon / Q000096:biosynthesis* / Q000187:drug effects
chemical_list: D018336:Receptors, Aryl Hydrocarbon; D006581:Hexachlorobenzene
keywords: Aryl hydrocarbon receptor (AhR); Cell proliferation; HepG2 cells; Hexachlorobenzene; Preneoplastic foci