Can G. Pham

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.

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.

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.

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.

NF-kappaB meets ROS: an 'iron-ic' encounter.

1 The Ben May Institute for Cancer Research, The University of Chicago, 924 East 57th Street, Chicago, IL 60637, USA 2 Current address: Department of Experimental Medicine, The University of L’Aquila, Via Vetoio-Coppito 2, 67100 L’Aquila, Italy * Corresponding author: G Franzoso, The Ben May Institute for Cancer Research, The University of Chicago, 924 East 57th Street, Chicago, IL 60637, USA. Tel: þ 773 834 0020; Fax:þ 773 702 1576; E-mail: gfranzos@midway.uchicago.edu

NF-κB meets ROS: an ‘iron-ic’ encounter

1 The Ben May Institute for Cancer Research, The University of Chicago, 924 East 57th Street, Chicago, IL 60637, USA 2 Current address: Department of Experimental Medicine, The University of L’Aquila, Via Vetoio-Coppito 2, 67100 L’Aquila, Italy * Corresponding author: G Franzoso, The Ben May Institute for Cancer Research, The University of Chicago, 924 East 57th Street, Chicago, IL 60637, USA. Tel: þ 773 834 0020; Fax:þ 773 702 1576; E-mail: gfranzos@midway.uchicago.edu

A Method for Isolating Prosurvival Targets of NF-κB/Rel Transcription Factors

NF-KappaB/Rel transcription factors are critical regulators of immunity, inflammation, development, and cell survival. Activation of NF-KB inhibits programmed cell death (PCD) triggered by tumor necrosis factor alpha (TNFalpha) and several other stimuli. The prosurvival activity of NF-KB is also crucial to lymphopoiesis, neuroprotection, tumorigenesis, and cancer chemoresistance. The characterization of the downstream targets that mediate the prosurvival activity of NF-KB is therefore a topic of intense investigation. Early screens aimed at identifying these genes were mainly based on expression criteria and so were poised to only isolate genes already known to have protective effects. Here, we describe a new method for the identification of these genes, whereby expression libraries are screened for their ability to halt PCD in NF-KB-deficient cells. This complementation approach provides substantial advantages over other approaches, as it enables functional assessment of isolated genes without any preconceived notion about their sequence or presumed role. Expression libraries are generated from cells that are resistant to TNFalpha-induced cytotoxicity and are then enriched in prosurvival genes upon selection with TNFa in NF-kappaB/RelA-null cells, which are highly susceptible instead to this cytotoxicity. Upon enrichment, libraries are screened through a randomized two-step approach, whereby cDNAs are first tested for cytoprotective function and then for differential expression in NF-kappaB-proficient and NF-KappaB-deficient cells.

In the Crosshairs: NF-κB Targets the JNK Signaling Cascade

NF-κB/Rel transcription factors are well-known for their roles in the regulation of inflammation and immunity. NF-κB also blocks programmed cell death (PCD) or apoptosis triggered by proinflammatory cytokine, tumor necrosis factor (TNF)α. Through transcriptional induction of distinct subsets of cyto-protective target genes, NF-κB inhibits the execution of apoptosis activated by this cytokine. This protective action is mediated, in part, by factors (such as A20, GADD45β, and XIAP) that downregulate the pro-apoptotic c-Jun-N-terminal (JNK) pathway. A suppression of reactive oxygen species (ROS), which are themselves major cell death-inducing elements activated by TNFα, is an additional protective function recently ascribed to NF-κB. This function of NF-κB involves an induction of mitochondrial anti-oxidant enzyme, manganese superoxide dismutase (Mn-SOD), and a control of cellular iron availability through upregulation of Ferritin heavy chain - one of two subunits of Ferritin, the major iron storage protein complex of the cell. An emerging view of NF-κB is that, while integrated, its actions in immunity and in promoting cell survival are executed through upregulation of distinct subsets of target genes. Thus, these inducible blockers of apoptosis may provide potential new targets to inhibit specific functions of NF-κB. In the future, this might allow for a better treatment of complex human diseases involving dysregulated NF-κB activity, including chronic inflammatory conditions and cancer.