Toxic bile salts induce rodent hepatocyte apoptosis via direct activation of Fas

Abstract

Cholestatic liver injury appears to result from the induction of hepatocyte apoptosis by toxic bile salts such as glycochenodeoxycholate (GCDC). Previous studies from this laboratory indicate that cathepsin B is a downstream effector protease during the hepatocyte apoptotic process. Because caspases can initiate apoptosis, the present studies were undertaken to determine the role of caspases in cathepsin B activation. Immunoblotting of GCDC-treated McNtcp.24 hepatoma cells demonstrated cleavage of poly(ADP-ribose) polymerase and lamin B 1 to fragments that indicate activation of effector caspases. Transfection with CrmA, an inhibitor of caspase 8, prevented GCDC-induced cathepsin B activation and apoptosis. Consistent with these results, an increase in caspase 8-like activity was observed in GCDC-treated cells. Examination of the mechanism of GCDC-induced caspase 8 activation revealed that dominant-negative FADD inhibited apoptosis and that hepatocytes isolated from Fas-deficient lymphoproliferative mice were resistant to GCDC-induced apoptosis. After GCDC treatment, immunoprecipitation experiments demonstrated Fas oligomerization, and confocal microscopy demonstrated ∆FADD-GFP (Fas-associated death domain-green fluorescent protein, aggregation in the absence of detectable Fas ligand mRNA. Collectively, these data suggest that GCDC-induced hepatocyte apoptosis involves ligand-independent oligomerization of Fas, recruitment of FADD, activation of caspase 8, and subsequent activation of effector proteases, including downstream caspases and cathepsin B.

Death receptor 4 (DR4) efficiently kills breast cancer cells irrespective of their sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)

“…Ligand-independent oligomerization was previously demonstrated for another death receptor, Fas. 30,31 For cancer gene therapy applications, strong cytotoxicity, exhibited by DR4 overexpression, required targeting. For this purpose, we used the promoter of the hTERT gene, which has been shown to be selectively active in cancer cells, [32][33][34][35] to drive DR4 expression.…”

Deoxycholate induces DNA damage and apoptosis in human colon epithelial cells expressing either mutant or wild-type p53

“…However, previous studies suggest an involvement of the Fas receptor-mediated apoptotic pathway. Exposing rat hepatocytes to bile acids resulted in ligand-independent oligomerization of plasma membranebound Fas, recruitment of FADD, activation of caspase 8 and also a cascade of downstream caspases, and finally apoptosis [43]. Thus, since the Fas signaling pathway is functional in human colon cells [44], it is conceivable that NaDOC induced apoptosis in HCT-116 and HCT-15 cells in this manner.…”

Sweroside ameliorates α-naphthylisothiocyanate-induced cholestatic liver injury in mice by regulating bile acids and suppressing pro-inflammatory responses

“…Numerous studies have suggested that the intrahepatic accumulation of bile acids may directly or indirectly cause further damage to the liver [3] . One of the hypotheses regarding the pathophysiology of cholestasis is that accumulated hepatic bile acids directly induce cell apoptosis, as supported by studies on rat hepatocytes and human hepatoma lines [4,5] . Increasing attention has been paid the physiological role of bile acids acting as pro-inflammatory signals, which may trigger hepatic CXC chemokine formation during the development of cholestatic liver injury [6,7] .…”