Antiapoptotic Effect of c-Jun N-terminal Kinase-1 through Mcl-1 Stabilization in TNF-Induced Hepatocyte Apoptosis

Background & Aims: c-Jun N-terminal Kinase (J\NK) is a key regulator in tumor necrosis factor (TNF)mediated liver injury. However, distinct roles for JNK1 and JNK2 in hepatocyte apoptosis are still unresolved. Although myeloid cell leukemia-1 (Mcl-1) has been reported as a substrate of JNK, the role of Mcl-1 and its functional regulation by JNK in TNF-induced hepatocyte apoptosis and liver injury remain to be elucidated. Methods: TNF-induced hepatocyte apoptosis was investigated in wild-type, jnk1(-/-) and jnk2(-/-) mice in vitro and in the galactosamine/TNF (GalN/TNF) liver injury model. For further analysis, we used adenoviruses expressing wild-type Mcl-1 or its substitution mutant, and the Cre/loxP system (mcl-1(f/f)) to delete mcl-1. Results: jnk2(-/-) Hepatocytes showed increased Mcl-1 expression and were more resistant to TNF-induced apoptosis compared with wild-type or jnk1(-/-) hepatocytes. Increased Mcl-1 expression in jnk2-/- hepatocytes correlated with their JNK activity, which is mediated by residual JNK1 and higher than in wild-type or jnk1(-/-) hepatocytes. JNK activation led to phosphorylation of Mcl-1 in hepatocytes, and this increased the half-life of the Mcl-1 protein. Overexpression of Mcl-1 confirmed its antiapoptotic effect in TNF-induced hepatocyte apoptosis in vitro and in vivo. Deletion of mcl-1 in jnk2-1hepatocytes increased TNF-induced hepatocyte apoptosis both in vitro and in GalN/TNF-induced liver injury model. Conclusions: jnk(2-/-) Hepatocytes are resistant to TNF-induced apoptosis. Activated JNK1 contributes to this antiapoptotic phenotype of jnk2(-/-) hepatocytes through phosphorylation-mediated stabilization of Mcl-1.