The bile acid glycochenodeoxycholate induces TRAIL-receptor 2/DR5 expression and apoptosis

Toxic bile salts induce hepatocyte apoptosis by both Fas-dependent and -ind ependent mechanisms. In this study, we examined the cellular mechanisms res ponsible for Fas-independent, bile acid-mediated apoptosis. HuH-7 cells, wh ich are known to be Fas deficient, were stably transfected with the sodium- dependent bile acid transporting polypeptide. The toxic bile acid glycochen odeoxycholate (GCDC)-induced apoptosis in these cells in a time- and concen tration-dependent manner. Apoptosis and mitochondrial cytochrome c release were inhibited by transfection with dominant negative FADD, CrmA transfecti on, or treatment with the selective caspase 8 inhibitor IETD-CHO. These obs ervations suggested the Fas-independent apoptosis was also death receptor m ediated. Reverse transcriptase-polymerase chain reaction demonstrated tumor necrosis factor-R1, tumor necrosis factor-related apoptosis inducing ligan d (TRAIL)-R1/DR4, -R2/DR5, and TRAIL, but not tumor necrosis fator-alpha ex pression by these cells. GCDC treatment increased expression of TRAIL-R2/DR 5 mRNA and protein 10-fold while expression of TRAIL-R1 was unchanged. Furt hermore, aggregation of TRAIL-R2/DR5, but not TRAIL-R1/DR4 was observed fol lowing GCDC treatment of the cells. Induction of TRAIL-R2/DR5 expression an d apoptosis by bile acids provides new insights into the mechanisms of hepa tocyte apoptosis and the regulation of TRAIL-R2/DR5 expression.