Concetta Bubici

Ferritin Heavy Chain Upregulation by NF-κB Inhibits TNFα-Induced Apoptosis by Suppressing Reactive Oxygen Species

Abstract During inflammation, NF-κB transcription factors antagonize apoptosis induced by tumor necrosis factor (TNF)α. This antiapoptotic activity of NF-κB involves suppressing the accumulation of reactive oxygen species (ROS) and controlling the activation of the c-Jun N-terminal kinase (JNK) cascade. However, the mechanism(s) by which NF-κB inhibits ROS accumulation is unclear. We identify ferritin heavy chain (FHC)—the primary iron storage factor—as an essential mediator of the antioxidant and protective activities of NF-κB. FHC is induced downstream of NF-κB and is required to prevent sustained JNK activation and, thereby, apoptosis triggered by TNFα. FHC-mediated inhibition of JNK signaling depends on suppressing ROS accumulation and is achieved through iron sequestration. These findings establish a basis for the NF-κB-mediated control of ROS induction and identify a mechanism by which NF-κB suppresses proapoptotic JNK signaling. Our results suggest modulation of FHC or, more broadly, of iron metabolism as a potential approach for anti-inflammatory therapy.

Mutual cross-talk between reactive oxygen species and nuclear factor-kappa B: molecular basis and biological significance

Reactive oxygen species (ROS) are emerging as key effectors in signal transduction. This role of ROS is especially evident in the pathways leading to programmed cell death (PCD) elicited in response to certain stress stimuli and cytokines. In these pathways, cytotoxic ROS signaling appears to be mediated in part by activation of the c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) cascade. Another pathway that is under ROS-mediated control in some systems is that leading to activation of transcription factor nuclear factor-kappa B (NF-κB), which is a central regulator of immunity, inflammation and cell survival. Remarkably, new evidence has unveiled the existence of a reciprocal, negative control that NF-κB exerts on ROS and JNK activities. This NF-κB-imposed restraint on ROS and JNK signaling is crucial for antagonism of PCD elicited by the proinflammatory cytokine tumor necrosis factor (TNF)α and likely other triggers. Effectors of this antagonistic cross-talk between NF-κB and ROS/JNK pathways have recently been identified. Because of the key roles that the prosurvival function of NF-κB plays in organismal physiology and disease, gaining a further mechanistic understanding of this cross-talk and NF-κB-dependent survival may be key to developing new therapies for the treatment of widespread human illnesses, such as cancer and chronic inflammatory conditions.

Gadd45|[beta]| mediates the NF-|[kappa]|B suppression of JNK signalling by targeting MKK7/JNKK2

NF-κB/Rel transcription factors control apoptosis, also known as programmed cell death. This control is crucial for oncogenesis, cancer chemo-resistance and for antagonizing tumour necrosis factor α (TNFα)-induced killing. With regard to TNFα, the anti-apoptotic activity of NF-κB involves suppression of the c-Jun N-terminal kinase (JNK) cascade. Using an unbiased screen, we have previously identified Gadd45β/Myd118, a member of the Gadd45 family of inducible factors, as a pivotal mediator of this suppressive activity of NF-κB. However, the mechanisms by which Gadd45β inhibits JNK signalling are not understood. Here, we identify MKK7/JNKK2 — a specific and essential activator of JNK — as a target of Gadd45β, and in fact, of NF-κB itself. Gadd45β binds to MKK7 directly and blocks its catalytic activity, thereby providing a molecular link between the NF-κB and JNK pathways. Importantly, Gadd45β is required to antagonize TNFα-induced cytotoxicity, and peptides disrupting the Gadd45β/MKK7 interaction hinder the ability of Gadd45β, as well as of NF-κB, to suppress this cytotoxicity. These findings establish a basis for the NF-κB control of JNK activation and identify MKK7 as a potential target for anti-inflammatory and anti-cancer therapy.

CD95 ligand induces motility and invasiveness of apoptosis‐resistant tumor cells

The apoptosis‐inducing death receptor CD95 (APO‐1/Fas) controls the homeostasis of many tissues. Despite its apoptotic potential, most human tumors are refractory to the cytotoxic effects of CD95 ligand. We now show that CD95 stimulation of multiple apoptosis‐resistant tumor cells by CD95 ligand induces increased motility and invasiveness, a response much less efficiently triggered by TNFα or TRAIL. Three signaling pathways resulting in activation of NF‐κB, Erk1/2 and caspase‐8 were found to be important to this novel activity of CD95. Gene chip analyses of a CD95‐stimulated tumor cell line identified a number of potential survival genes and genes that are known to regulate increased motility and invasiveness of tumor cells to be induced. Among these genes, urokinase plasminogen activator was found to be required for the CD95 ligand‐induced motility and invasiveness. Our data suggest that CD95L, which is found elevated in many human cancer patients, has tumorigenic activities on human cancer cells. This could become highly relevant during chemotherapy, which can cause upregulation of CD95 ligand by both tumor and nontumor cells.

Linking JNK signaling to NF-κB: a key to survival

In addition to marshalling immune and inflammatory responses, transcription factors of the NF-κB family control cell survival. This control is crucial to a wide range of biological processes, including B and T lymphopoiesis, adaptive immunity, oncogenesis and cancer chemoresistance. During an inflammatory response, NF-κB activation antagonizes apoptosis induced by tumor necrosis factor (TNF)-α, a protective activity that involves suppression of the Jun N-terminal kinase (JNK) cascade. This suppression can involve upregulation of the Gadd45-family member Gadd45β/Myd118, which associates with the JNK kinase MKK7/JNKK2 and blocks its catalytic activity. Upregulation of XIAP, A20 and blockers of reactive oxygen species (ROS) appear to be important additional means by which NF-κB blunts JNK signaling. These recent findings might open up entirely new avenues for therapeutic intervention in chronic inflammatory diseases and certain cancers; indeed, the Gadd45β-MKK7 interaction might be a key target for such intervention.

The NF-κB-mediated control of the JNK cascade in the antagonism of programmed cell death in health and disease

NF-κB/Rel transcription factors have recently emerged as crucial regulators of cell survival. Activation of NF-κB antagonizes programmed cell death (PCD) induced by tumor necrosis factor-receptors (TNF-Rs) and several other triggers. This prosurvival activity of NF-κB participates in a wide range of biological processes, including immunity, lymphopoiesis and development. It is also crucial for pathogenesis of various cancers, chronic inflammation and certain hereditary disorders. This participation of NF-κB in survival signaling often involves an antagonism of PCD triggered by TNF-R-family receptors, and is mediated through a suppression of the formation of reactive oxygen species (ROS) and a control of sustained activation of the Jun-N-terminal kinase (JNK) cascade. Effectors of this antagonistic activity of NF-κB on this ROS/JNK pathway have been recently identified. Indeed, further delineating the mechanisms by which NF-κB promotes cell survival might hold the key to developing new highly effective therapies for treatment of widespread human diseases.

TNF-α inhibits asbestos-induced cytotoxicity via a NF-κB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis

Asbestos is the main cause of human malignant mesothelioma (MM). In vivo, macrophages phagocytize asbestos and, in response, release TNF-α and other cytokines that contribute to carcinogenesis through unknown mechanisms. In vitro, asbestos does not induce transformation of primary human mesothelial cells (HM); instead, asbestos is very cytotoxic to HM, causing extensive cell death. This finding raised an apparent paradox: How can asbestos cause MM if HM exposed to asbestos die? We found that asbestos induced the secretion of TNF-α and the expression of TNF-α receptor I in HM. Treatment of HM with TNF-α significantly reduced asbestos cytotoxicity. Through numerous technical approaches, including chemical inhibitors and small interfering RNA strategies, we demonstrate that, in HM, TNF-α activates NF-κB and that NF-κB activation leads to HM survival and resistance to the cytotoxic effects of asbestos. Our data show a critical role for TNF-α and NF-κB signaling in mediating HM responses to asbestos. TNF-α signaling through NF-κB-dependent mechanisms increases the percent of HM that survives asbestos exposure, thus increasing the pool of asbestos-damaged HM that are susceptible to malignant transformation. Cytogenetics supported this hypothesis, showing only rare, aberrant metaphases in HM exposed to asbestos and an increased mitotic rate with fewer irregular metaphases in HM exposed to both TNF-α and asbestos. Our findings provide a mechanistic rationale for the paradoxical inability of asbestos to transform HM in vitro, elucidate and underscore the role of TNF-α in asbestos pathogenesis in humans, and identify potential molecular targets for anti-MM prevention and therapy.

JNK signalling in cancer: in need of new, smarter therapeutic targets

The JNKs are master protein kinases that regulate many physiological processes, including inflammatory responses, morphogenesis, cell proliferation, differentiation, survival and death. It is increasingly apparent that persistent activation of JNKs is involved in cancer development and progression. Therefore, JNKs represent attractive targets for therapeutic intervention with small molecule kinase inhibitors. However, evidence supportive of a tumour suppressor role for the JNK proteins has also been documented. Recent studies showed that the two major JNK proteins, JNK1 and JNK2, have distinct or even opposing functions in different types of cancer. As such, close consideration of which JNK proteins are beneficial targets and, more importantly, what effect small molecule inhibitors of JNKs have on physiological processes, are essential. A number of ATP‐competitive and ATP‐non‐competitive JNK inhibitors have been developed, but have several limitations such as a lack of specificity and cellular toxicity. In this review, we summarize the accumulating evidence supporting a role for the JNK proteins in the pathogenesis of different solid and haematological malignancies, and discuss many challenges and scientific opportunities in the targeting of JNKs in cancer.

Upregulation of Twist-1 by NF-κB Blocks Cytotoxicity Induced by Chemotherapeutic Drugs

ABSTRACT NF-κB/Rel transcription factors are central to controlling programmed cell death (PCD). Activation of NF-κB blocks PCD induced by numerous triggers, including ligand engagement of tumor necrosis factor receptor (TNF-R) family receptors. The protective activity of NF-κB is also crucial for oncogenesis and cancer chemoresistance. Downstream of TNF-Rs, this activity of NF-κB has been linked to the suppression of reactive oxygen species and the c-Jun-N-terminal-kinase (JNK) cascade. The mechanism by which NF-κB inhibits PCD triggered by chemotherapeutic drugs, however, remains poorly understood. To understand this mechanism, we sought to identify unrecognized protective genes that are regulated by NF-κB. Using an unbiased screen, we identified the basic-helix-loop-helix factor Twist-1 as a new mediator of the protective function of NF-κB. Twist-1 is an evolutionarily conserved target of NF-κB, blocks PCD induced by chemotherapeutic drugs and TNF-α in NF-κB-deficient cells, and is essential to counter this PCD in cancer cells. The protective activity of Twist-1 seemingly halts PCD independently of interference with cytotoxic JNK, p53, and p19ARF signaling, suggesting that it mediates a novel protective mechanism activated by NF-κB. Indeed, our data indicate that this activity involves a control of inhibitory Bcl-2 phosphorylation. The data also suggest that Twist-1 and -2 play an important role in NF-κB-dependent chemoresistance.

NF-κB and JNK: An Intricate Affair

NF-κB/Rel transcription factors block apoptosis or programmed cell death (PCD)induced by tumor necrosis factor (TNF)α. The antiapoptotic activity of NF-κB is alsocrucial for immunity, lymphocyte development, tumorigenesis, and cancerchemoresistance. With respect to TNF?, the NF-κB-mediated suppression of apoptosisinvolves inhibition of the c-Jun-N-terminal kinase (JNK) cascade. This inhibitory activityof NF-κB depends upon transcriptional upregulation of blockers of the JNK cascade suchas the caspase inhibitor XIAP, the zinc-finger protein A20, and the inhibitor of theMKK7/JNKK2 kinase Gadd45β/Myd118. Moreover, NF-κB blunts accumulation ofreactive oxygen species (ROS) induced by TNF?, and this antioxidant effect of NF-κB isalso critical for inhibition of TNFα-induced JNK activation. Suppression of ROS by NF-κB is mediated by Ferritin heavy chain (FHC)—the primary iron-storage mechanism incells—and possibly, by the mitochondrial enzyme Mn++ superoxide dismutase (Mn-SOD). Thus, induction of FHC and Mn-SOD represents an additional, indirect means bywhich NF-κB controls proapoptotic JNK signaling. These findings identify potential newtargets for anti-inflammatory and anti-cancer therapy.