Bile Acid Regulation of C/EBPβ, CREB, and c-Jun Function, via the Extracellular Signal-Regulated Kinase and c-Jun NH 2 -Terminal Kinase Pathways, Modulates the Apoptotic Response of Hepatocytes

Abstract

ABSTRACT Previously, we have demonstrated that deoxycholic acid (DCA)-induced signaling of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in primary hepatocytes is a protective response. In the present study, we examined the roles of the ERK and c-Jun NH 2 -terminal kinase (JNK) pathways, and downstream transcription factors, in the survival response of hepatocytes. DCA caused activation of the ERK1/2 and JNK1/2 pathways. Inhibition of either DCA-induced ERK1/2 or DCA-induced JNK1/2 signaling enhanced the apoptotic response of hepatocytes. Further analyses demonstrated that DCA-induced JNK2 signaling was cytoprotective whereas DCA-induced JNK1 signaling was cytotoxic. DCA-induced ERK1/2 activation was responsible for increased DNA binding of C/EBPβ, CREB, and c-Jun/AP-1. Inhibition of C/EBPβ, CREB, and c-Jun function promoted apoptosis following DCA treatment, and the level of apoptosis was further increased in the case of CREB and c-Jun, but not C/EBPβ, by inhibition of MEK1/2. The combined loss of CREB and c-Jun function or of C/EBPβ and c-Jun function enhanced DCA-induced apoptosis above the levels resulting from the loss of either factor individually; however, these effects were less than additive. Loss of c-Jun or CREB function correlated with increased expression of FAS death receptor and PUMA and decreased expression of c-FLIP- L and c-FLIP- S , proteins previously implicated in the modulation of the cellular apoptotic response. Collectively, these data demonstrate that multiple DCA-induced signaling pathways and transcription factors control hepatocyte survival.