The Bile Acid Glycochenodeoxycholate Induces TRAIL-Receptor 2/DR5 Expression and Apoptosis

Abstract

Toxic bile salts induce hepatocyte apoptosis by both Fas-dependent and -independent mechanisms. In this study, we examined the cellular mechanisms responsible for Fas-independent, bile acid-mediated apoptosis. HuH-7 cells, which are known to be Fas deficient, were stably transfected with the sodium-dependent bile acid transporting polypeptide. The toxic bile acid glycochenodeoxycholate (GCDC)-induced apoptosis in these cells in a time- and concentration-dependent manner. Apoptosis and mitochondrial cytochrome c release were inhibited by transfection with dominant negative FADD, CrmA transfection, or treatment with the selective caspase 8 inhibitor IETD-CHO. These observations suggested the Fas-independent apoptosis was also death receptor mediated. Reverse transcriptase-polymerase chain reaction demonstrated tumor necrosis factor-R1, tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-R1/DR4, -R2/DR5, and TRAIL, but not tumor necrosis factor-alpha expression by these cells. GCDC treatment increased expression of TRAIL-R2/DR5 mRNA and protein 10-fold while expression of TRAIL-R1 was unchanged. Furthermore, aggregation of TRAIL-R2/DR5, but not TRAIL-R1/DR4 was observed following GCDC treatment of the cells. Induction of TRAIL-R2/DR5 expression and apoptosis by bile acids provides new insights into the mechanisms of hepatocyte apoptosis and the regulation of TRAIL-R2/DR5 expression.