TNF? sensitizes hepatocytes to FasL-induced apoptosis by NF?B-mediated Fas upregulation.

ABSTRACT: Although it is well established that TNF? contributes to hepatitis, liver failure and associated hepatocarcinogenesis via the regulation of inflammation, its pro-apoptotic role in the liver has remained enigmatic. On its own, TNF? is unable to trigger apoptosis. However, when combined with the transcriptional inhibitor GaLN, it can cause hepatocyte apoptosis and liver failure in mice. Moreover, along with others, we have shown that TNF? is capable of sensitizing cells to FasL- or drug-induced cell death via c-Jun N-terminal kinase (JNK) activation and phosphorylation/activation of the BH3-only protein Bim. In this context, TNF? could exacerbate hepatocyte cell death during simultaneous inflammatory and T-cell-mediated immune responses in the liver. Here we show that TNF? sensitizes primary hepatocytes, established hepatocyte cell lines and mouse embryo fibroblasts to FasL-induced apoptosis by the transcriptional induction and higher surface expression of Fas via the NF?B pathway. Genetic deletion, diminished expression or dominant-negative inhibition of the NF?B subunit p65 resulted in lower Fas expression and inhibited TNF?-induced Fas upregulation and sensitization to FasL-induced cell death. By hydrodynamic injection of p65 shRNA into the tail vein of mice, we confirm that Fas upregulation by TNF? is also NF?B-mediated in the liver. In conclusion, TNF? sensitization of FasL-induced apoptosis in the liver proceeds via two parallel signaling pathways, activation of JNK and Bim phosphorylation and NF?B-mediated Fas upregulation.

SUBMITTER: Faletti L 

PROVIDER: S-EPMC6125596 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature