NF-κB inactivation converts a hepatocyte cell line TNF-α response from proliferation to apoptosis

Abstract

Toxins convert the hepatocellular response to tumor necrosis factor-α (TNF-α) stimulation from proliferation to cell death, suggesting that hepatotoxins somehow sensitize hepatocytes to TNF-α toxicity. Because nuclear factor-κB (NF-κB) activation confers resistance to TNF-α cytotoxicity in nonhepatic cells, the possibility that toxin-induced sensitization to TNF-α killing results from inhibition of NF-κB-dependent gene expression was examined in the RALA rat hepatocyte cell line sensitized to TNF-α cytotoxicity by actinomycin D (ActD). ActD did not affect TNF-α-induced hepatocyte NF-κB activation but decreased NF-κB-dependent gene expression. Expression of an IκB superrepressor rendered RALA hepatocytes sensitive to TNF-α-induced apoptosis in the absence of ActD. Apoptosis was blocked by caspase inhibitors, and TNF-α treatment led to activation of caspase-2, caspase-3, and caspase-8 only when NF-κB activation was blocked. Although apoptosis was blocked by the NF-κB-dependent factor nitric oxide (NO), inhibition of endogenous NO production did not sensitize cells to TNF-α-induced cytotoxicity. Thus NF-κB activation is the critical intracellular signal that determines whether TNF-α stimulates hepatocyte proliferation or apoptosis. Although exogenous NO blocks RALA hepatocyte TNF-α cytotoxicity, endogenous production of NO is not the mechanism by which NF-κB activation inhibits this death pathway.

A high-fat diet impairs liver regeneration in C57BL/6 mice through overexpression of the NF-κB inhibitor, IκBα

“…The phenotype and altered gene induction for cyclin D1 and Bcl-xL observed in HFD-fed mice may have been the result of disturbances in the regulatory mechanisms that affect cellular proliferation and survival, in which TNF-␣-regulated NF-B is essential. [10][11][12][13][14][15] Supershift EMSA experiments showed that both p50/p65 heterodimers and p50 homodimers of NF-B were present in livers from control as well as HFD-fed mice (unpublished data). In both groups, an early peak of NF-B DNA-binding activity was seen 30 minutes to 1 hour after PHx (Fig.…”

“…34 The activation of TNF-␣ as a consequence of LPS stimulation may contribute to the higher levels of apoptosis seen in steatotic livers. 14,35 Moreover, it has been shown that due to increased adiposity, mice fed an HFD have elevated levels of leptin, 36 which, besides the regulation of food intake, also has immunomodulatory functions. 37 In particular, leptin augments inflammation through an increased release of cytokines, such as TNF-␣, which is released in large quantities from tissue macrophages, including Kupffer cells in the liver.…”

“…[5][6][7][8][9] Nuclear factor-kappa B (NF-B), crucial for the priming phase of liver regeneration, has been shown to be involved in both of these processes, promoting hepatocyte proliferation and also inhibiting apoptosis of liver cells. [10][11][12][13][14][15] To study the effects of dietary-induced obesity on liver regeneration, we subjected mice fed a high-fat diet (HFD) to PHx. We found that sustained feeding of an HFD resulted in liver steatosis and considerably impaired regeneration after PHx.…”

Expression of the NF-κB Target Gene X-Ray-Inducible Immediate Early Response Factor-1 Short Enhances TNF-α-Induced Hepatocyte Apoptosis by Inhibiting Akt Activation

“…[␥-32 P]ATP was from NEN Life Science Products (Boston, MA). Adenovirus expressing the mutant I B (Ad5I B) and control adenovirus Ad5LacZ were provided as previously reported (9). Due to missense mutations at phosphorylation sites where serines 32 and 36 are replaced with alanines, the mutant I B irreversibly binds to NF-B, preventing its activation (9).…”

Irradiation leads to sensitization of hepatocytes to TNF-α-mediated apoptosis by upregulation of IκB expression

“…Gels are representative of three independent experiments from three diVerent isolations; ExCO 100-fold excess cold NF B oligonucleotide; -AB EMSA without NF B p65 supershift antibody Discussion NF B is an essential component of ionizing radiation-triggered signal transduction pathways that can lead either to cell death or survival, depending on the respective cell type (for a review see [17]), and numerous studies have demonstrated that inhibition of NF B by diVerent means increased sensitivity of cancer cells to the apoptotic action of diverse eVectors such as TNF-, chemo-or radiotherapies (for review see [18]). In both primary rat hepatocytes and a non-transformed rat hepatocyte cell line, inhibition of NF B-activity by adenoviral delivery of a I B superrepressor sensitized these cells to death from TNF- [19,20]. However, TNF-was also recently shown to sensitize for DNA-damage-induced apoptosis via an NF-kappa-B independent mechanism [21].…”