The Aryl Hydrocarbon Receptor Predisposes Hepatocytes to Fas-Mediated Apoptosis

Abstract

Liver homeostasis is achieved by the removal of diseased and damaged hepatocytes and their coordinated replacement to maintain a constant liver cell mass. Cirrhosis, viral hepatitis, and toxic drug effects can all trigger apoptosis in the liver as a means of removing the unwanted cells, and the Fas "death receptor" pathway comprises a major physiological mechanism by which this occurs. The susceptibility to Fas-mediated apoptosis is, in part, a function of the hepatocyte's proteome. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor known to influence apoptosis, conceivably by regulating the expression of genes involved in apoptotic signaling. In this article, we present evidence demonstrating that AhR expression and function promote apoptosis in liver cells in response to Fas stimulation. Reintroduction of the AhR into the AhR-negative BP8 hepatoma cells as well as into primary hepatocytes from AhR knockout mice increases the magnitude of cell death in response to Fas ligand. Enhanced apoptosis correlates with increased caspase activity and mitochondrial cytochrome c release but not with the expression of several Bcl-2 family proteins. In vivo studies showed that in contrast to wild-type mice, AhR knockout mice are protected from the lethal effects of the anti-Fas Jo2 antibody. Moreover, downregulation of the aryl hydrocarbon receptor nuclear translocator protein in vivo by adenovirus-mediated RNA interference to suppress AhR activity provided wild-type mice partial protection from Jo2-induced lethality.

Identification of Stanniocalcin 2 as a Novel Aryl Hydrocarbon Receptor Target Gene

“…AhR floxed and AhR CKO primary hepatocytes were isolated using a collagenase perfusion method as previously described (Park et al, 2005). Hepatocytes were plated at a density of 8.5 Â 10 4 -1.0 Â 10 5 cells/cm 2 in Williams E medium containing penicillin (100 U/ml), streptomycin (100 mg/ml), and 5% fetal bovine serum and replaced every 24 hours with fresh medium.…”

“…Generation of AdGFP (control virus) and AdrAhRFL was described previously (Elferink et al, 2001;Park et al, 2005). To generate AdCreGFP, the Cre-recombinase-expressing Ad5 vector, AdCreM2, was purchased from Microbix (Mississauga, Ontario, Canada) and amplified using human embryonic kidney 293 packaging cells.…”

A Novel Nonconsensus Xenobiotic Response Element Capable of Mediating Aryl Hydrocarbon Receptor-Dependent Gene Expression

“…Mouse primary hepatocytes were isolated by the collagenase type IV perfusion from wild-type C57BL/6 mice as described previously (Park et al, 2005). Cells (5 ϫ 10 5 ) were plated in 35-mm plates in Williams' E medium containing penicillin (100 U/ml), streptomycin (100 g/ml), insulin (5 g/ml), bovine serum albumin (1 mg/ml), and 5% fetal bovine serum.…”

Protective effects of HFE7A, mouse anti-human/mouse Fas monoclonal antibody against acute and lethal hepatic injury induced by Jo2

“…Hepatocytes are categorized as type II cells in which mitochondrial depolarization and the following cytochrome c release from depolarized mitochondria is observed in the process of apoptosis (Park et al 2005;Liu et al 1996;Luo et al 1998). To investigate mitochondrial depolarization, hepatocytes were isolated from Jo2-injected mice and the mitochondrial membrane potential was measured.…”