Hepatocyte IKKbeta/NF-kappaB inhibits tumor promotion and progression by preventing oxidative stress-driven STAT3 activation

IL-1β-driven neutrophilia preserves antibacterial defense in the absence of the kinase IKKβ

Transcription factor NF-κB and its activating kinase IKKβ are associated with inflammation and are believed to be critical for innate immunity. Despite the likelihood of immune suppression, pharmacological blockade of IKKβ-NF-κB has been considered as a therapeutic strategy. However, we found neutrophilia in mice with inducible deletion of IKKβ (Ikkβ(Δ) mice). These mice had hyperproliferative granulocyte-macrophage progenitors and pregranulocytes and a prolonged lifespan of mature neutrophils that correlated with the induction of genes encoding prosurvival molecules. Deletion of interleukin 1 receptor 1 (IL-1R1) in Ikkβ(Δ) mice normalized blood cellularity and prevented neutrophil-driven inflammation. However, Ikkβ(Δ)Il1r1(-/-) mice, unlike Ikkβ(Δ) mice, were highly susceptible to bacterial infection, which indicated that signaling via IKKβ-NF-κB or IL-1R1 can maintain antimicrobial defenses in each other's absence, whereas inactivation of both pathways severely compromises innate immunity.

IL-1β-driven neutrophilia preserves antibacterial defense in the absence of the kinase IKKβ

Transcription factor NF-κB and its activating kinase IKKβ are associated with inflammation and are believed to be critical for innate immunity. Despite the likelihood of immune suppression, pharmacological blockade of IKKβ-NF-κB has been considered as a therapeutic strategy. However, we found neutrophilia in mice with inducible deletion of IKKβ (Ikkβ(Δ) mice). These mice had hyperproliferative granulocyte-macrophage progenitors and pregranulocytes and a prolonged lifespan of mature neutrophils that correlated with the induction of genes encoding prosurvival molecules. Deletion of interleukin 1 receptor 1 (IL-1R1) in Ikkβ(Δ) mice normalized blood cellularity and prevented neutrophil-driven inflammation. However, Ikkβ(Δ)Il1r1(-/-) mice, unlike Ikkβ(Δ) mice, were highly susceptible to bacterial infection, which indicated that signaling via IKKβ-NF-κB or IL-1R1 can maintain antimicrobial defenses in each other's absence, whereas inactivation of both pathways severely compromises innate immunity.

NF-κB, JNK, and TLR Signaling Pathways in Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the third largest cause of cancer deaths worldwide. The role of molecular changes in HCC have been used to identify prognostic markers and chemopreventive or therapeutic targets. It seems that toll-like receptors (TLRs) as well as the nuclear factor (NF)-κB, and JNK pathways are critical regulators for the production of the cytokines associated with tumor promotion. The cross-talk between an inflammatory cell and a neoplastic cell, which is instigated by the activation of NF-κB and JNKs, is critical for tumor organization. JNKs also regulate cell proliferation and act as oncogenes, making them the main tumor-promoting protein kinases. TLRs play roles in cytokine and hepatomitogen expression mainly in myeloid cells and may promote liver tumorigenesis. A better understanding of these signaling pathways in the liver will help us understand the mechanism of hepatocarcinogenesis and provide a new therapeutic target for HCC.

Acyclic retinoid inhibits diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BLKS/J- +(db)/+Lepr(db) mice

Obesity and the related metabolic abnormalities are associated with increased risk of hepatocellular carcinoma (HCC). Malfunctioning of retinoid X receptor (RXR) α due to phosphorylation by Ras/MAPK also plays a critical role in liver carcinogenesis. In the present study, we examined the effects of acyclic retinoid (ACR), which targets RXRα, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BLKS/J- +Lepr(db)/+Lepr(db) (db/db) obese mice. Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks, after which they were fed a diet containing 0.03% or 0.06% of ACR throughout the experiment. In mice treated with either dose of ACR for 34 weeks, the development of liver cell adenomas was significantly inhibited as compared with basal diet-fed mice. ACR markedly inhibited the activation of Ras and phosphorylation of the ERK (extracellular signal-regulated kinase) and RXRα proteins in the livers of experimental mice. It also increased the expression of RAR β and p21(CIP1) mRNA while decreasing the expression of cyclin D1, c-Fos, and c-Jun mRNA in the liver, thereby restoring RXRα function. Administration of ACR improved liver steatosis and activated the AMPK protein. The serum levels of insulin decreased by ACR treatment, whereas the quantitative insulin sensitivity check index (QUICKI) values increased, indicating improved insulin sensitivity. The serum levels of TNF-α and the expression levels of TNF- α, IL-6, and IL-1 β mRNA in the livers of DEN-treated db/db mice were decreased by ACR treatment, suggesting attenuation of the chronic inflammation induced by excessive fatty deposits. ACR may be, therefore, useful in the chemoprevention of obesity-related HCC.

Apoptosis, stem cells, and tissue regeneration

Most metazoans have at least some ability to regenerate damaged cells and tissues, although the regenerative capacity varies depending on the species, organ, or developmental stage. Cell replacement and regeneration occur in two contexts: renewal of spent cells during tissue homeostasis (homeostatic growth), and in response to external injury, wounding, or amputation (epimorphic regeneration). Model organisms that display remarkable regenerative capacity include amphibians, planarians, Hydra, and the vertebrate liver. In addition, several mammalian organs--including the skin, gut, kidney, muscle, and even the human nervous system--have some ability to replace spent or damaged cells. Although the regenerative response is complex, it typically involves the induction of new cell proliferation through formation of a blastema, followed by cell specification, differentiation, and patterning. Stem cells and undifferentiated progenitor cells play an important role in both tissue homeostasis and tissue regeneration. Stem cells are typically quiescent or passing slowly through the cell cycle in adult tissues, but they can be activated in response to cell loss and wounding. A series of studies, mostly performed in Drosophila as well as in Hydra, Xenopus, and mouse, has revealed an unexpected role of apoptotic caspases in the production of mitogenic signals that stimulate the proliferation of stem and progenitor cells to aid in tissue regeneration. This Review summarizes some of the key findings and discusses links to stem cell biology and cancer.

NFκB/p53 crosstalk-a promising new therapeutic target

The transcription factors p53 and NFκB determine cellular fate and are involved in the pathogenesis of most-if not all-cancers. The crosstalk between these transcription factors becomes increasingly appreciated as an important mechanism operative during all stages of tumorigenesis, metastasis, and immunological surveillance. In this review, we summarize molecular mechanisms regulating cross-signaling between p53 and NFκB proteins and how dysregulated interactions between p53 and NFκB family members contribute to oncogenesis. We furthermore analyze how such signaling modules represent targets for the design of novel intervention strategies using established compounds and powerful combination therapies.

The unexpected role of lymphotoxin beta receptor signaling in carcinogenesis: from lymphoid tissue formation to liver and prostate cancer development

The cytokines lymphotoxin (LT) alpha, beta and their receptor (LTbetaR) belong to the tumor necrosis factor (TNF) superfamily, whose founder-TNFalpha-was initially discovered due to its tumor necrotizing activity. LTbetaR signaling serves pleiotropic functions including the control of lymphoid organ development, support of efficient immune responses against pathogens due to maintenance of intact lymphoid structures, induction of tertiary lymphoid organs, liver regeneration or control of lipid homeostasis. Signaling through LTbetaR comprises the noncanonical/canonical nuclear factor-kappaB (NF-kappaB) pathways thus inducing chemokine, cytokine or adhesion molecule expression, cell proliferation and cell survival. Blocking LTbetaR signaling or Fcgamma-receptor mediated immunoablation of LT-expressing cells was demonstrated to be beneficial in various infectious or noninfectious inflammatory or autoimmune disorders. Only recently, LTbetaR signaling was shown to initiate inflammation-induced carcinogenesis, to influence primary tumorigenesis and to control reemergence of carcinoma in various cancer models through distinct mechanisms. Indeed, LTbetaR signaling inhibition has already been used as efficient anti-inflammatory, anti-cancer therapy in some experimental models. Here, we review the pleiotropic functions attributed to LT, the effects of its deregulation and extensively discuss the recent literature on LT's link to carcinogenesis.

Hypothesis: Targeted Ikkβ deletion upregulates MIF signaling responsiveness and MHC class II expression in mouse hepatocytes

Macrophage migration inhibitory factor (MIF) is causally related to the pathogenesis of chronic liver disease but its hepatocellular mechanisms of action are largely unknown. Scattered reports in the literature hint at functional connections between the expression of MIF and major histocompatibility complex (MHC) Class II molecules. Not surprisingly, these relationships have not yet been explored in hepatocytes because MIF and MHC Class II cell surface receptors are commonly expressed by other cell types including various antigen presenting cells of the immune system. On the other hand, mounting evidence suggests that heteromeric MIF receptors share a common molecule with intracellular MHC Class II complexes, viz., CD74, which also serves as the MHC Class II chaperone; and, while it is unclear what cancer-related role(s) MHC Class II receptors might play, increasing evidence suggests that MIF and CD74 are also implicated in the biology of hepatocellular carcinoma. These reports are provocative for two reasons: firstly, Ikkβ^Δhep mice carrying hepatocyte-targeted deletions of Ikkβ, an IκB kinase complex subunit required for the activation of the transcription factor NF-κB (nuclear factor-κB), have been shown to display heightened susceptibilities to hepatotoxins and chemical hepatocarcinogens; secondly, microarray profiling observations indicate that Ikkβ^Δhep hepatocytes constitutively and “ectopically” overexpress genes, particularly CD74, CD44 (a MIF-receptor subunit) and MHC Class II I-A/E β and I-A α chains, and gene families that regulate host immune process and immune defense responses. These findings together suggest that Ikkβ^Δhep mice might express functional MIF and MHC Class II receptors, leading to increased hepatocellular sensitivity to MIF signaling as well as to the unusual property of antigen presentation; both functions might contribute to the heightened liver disease phenotypes of Ikkβ^Δhep mice. The findings raise questions about the potential existence of cohorts of human patients with genetic abnormalities of Ikkβ that might confer heightened susceptibility to liver disease including hepatocellular carcinoma.

Dietary and genetic obesity promote liver inflammation and tumorigenesis by enhancing IL-6 and TNF expression

Epidemiological studies indicate that overweight and obesity are associated with increased cancer risk. To study how obesity augments cancer risk and development, we focused on hepatocellular carcinoma (HCC), the common form of liver cancer whose occurrence and progression are the most strongly affected by obesity among all cancers. We now demonstrate that either dietary or genetic obesity is a potent bona fide liver tumor promoter in mice. Obesity-promoted HCC development was dependent on enhanced production of the tumor-promoting cytokines IL-6 and TNF, which cause hepatic inflammation and activation of the oncogenic transcription factor STAT3. The chronic inflammatory response caused by obesity and enhanced production of IL-6 and TNF may also increase the risk of other cancers.

NF-κB in liver cancer: the plot thickens

The role of the NF-κB signaling pathway in liver cancer is complex. While some evidence suggests that in the liver, like in many other organ systems, NF-κB is oncogenic, there is strong evidence showing that in certain liver cancer models NF-κB suppresses tumorigenesis. These contrasting findings cannot be dismissed on technicalities and are likely due to the complex nature of the NF-κB response. Similar contrasting findings regarding NF-κB activity are revealed in skin cancer models. Thus, it is possible that the contradictory role of NF-κB in tumorigenesis is a general phenomenon and not an oddity related solely to the liver. Further studies are indicated to decipher the underlying molecular mechanisms. Revealing these mechanisms may facilitate the identification of patient subgroups and specific situations in which NF-κB inhibition will be a preferred therapeutic option. Moreover, it is possible that specific interventions could boost the tumor suppressor functions of NF-κB in tumors that harbor mutations that render this pathway constitutively active.