CD95 (APO-1/Fas)-mediated apoptosis of hepatocytes plays a central role in the pathophysiology of various human liver diseases. Hepatocyte growth factor (HGF) was shown to exert antiapoptotic functions in rodent hepatocytes. We previously showed that primary human hepatocytes (PHH) are a valuable tool for the investigation of apoptotic processes in liver cells. In this study, we analyzed the influence of HGF on CD95mediated apoptosis of PHH and its molecular determinants. HGF significantly inhibited CD95-mediated apoptosis of PHH as well as cleavage of caspase-8 and poly (ADPribose)polymerase. HGF transcriptionally induced the expression of the anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1). In contrary, HGF did not alter the expression levels of Bcl-2 or Bcl-x L . HGF activated survival pathways such as the phosphatidylinositol-3 kinase (PI3K)/Akt pathway, the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase/ERK and the signal transducer and activator of transcription 3 (STAT3) pathway. Notably, HGF triggered serine 727but not tyrosine 705 -phosphorylation of STAT3. Pretreatment of PHH with the PI3K inhibitor LY294002 as well as adenoviral transduction of dominant negative Akt1 prevented HGF-mediated Mcl-1 induction and reversed the antiapoptotic effects of HGF. In conclusion, HGF confers survival of PHH by activation of the PI3K/Akt pathway. PI3K/Akt activation by HGF results in the induction of antiapoptotic proteins such as Mcl-1. Thus, application of HGF may be a therapeutic approach to prevent CD95mediated hepatocellular damage in human liver diseases. (HEPATOLOGY 2004;39:645-654.)
C D95 (APO-1/Fas) belongs to the subfamily of death receptors among the tumor necrosis factor/ nerve growth factor receptor superfamily. 1 CD95 plays an important role in liver homeostasis. 2 Hepatocytes express high amounts of CD95 and are very sensitive toward CD95 triggering. 3,4 Mice injected with agonistic anti-CD95 antibody rapidly die of liver failure. 5 CD95-mediated apoptosis is involved in a broad spectrum of human liver diseases, including acute liver failure. 6 In vivo silencing of the CD95 gene via small, interfering RNA protects mice from liver failure as well as from fibrosis in a model of autoimmune hepatitis. 7 A key event of CD95 signaling is the formation of a multimeric complex of proteins called death-inducing signaling complex (DISC). Two different pathways are described downstream of CD95. In type I cells, the death signal is propagated by a cascade that is initiated by the activation of large amounts of caspase-8 at the DISC and subsequent activation of downstream caspases. 8 In type II cells, including hepatocytes, DISC formation is weak, and the