Noncanonical NF-kappaB Signaling Research Articles

Abstract 4973: Investigating the role of non-canonical NF-kappaB signaling in tumor cells and macrophages in ovarian cancer

Abstract Background: Ovarian cancer is the most lethal gynecologic malignancy, with a 5-year survival rate of less than 50%. To have a major impact on improving clinical outcomes, a better understanding of the progression of disease and identification of truly novel treatment strategies is critical. Canonical nuclear factor-kappaB (NF-κB) signaling has been extensively studied in preclinical ovarian cancer models; however, systemic NF-κB inhibitors have had disappointing results in early clinical trials. Whether the alternative, non-canonical NF-κB signaling pathway (nc-NF-κB) represents a distinct and improved target for therapy in ovarian cancer is unknown. Here, we aim to investigate the role played by nc-NF-κB signaling both in malignant epithelial cells and in macrophages, a key immune cell component in the tumor microenvironment. Repolarizing tumor-associated macrophages (TAMs) away from pro-tumor M2-like functions towards an anti-tumor M1-like phenotype is a critical priority in macrophage-directed therapies. Methods: In ovarian cancer cell lines, mouse ovarian TAMs cultured ex vivo, and immortalized bone marrow-derived macrophages (BMDMs), nuclear levels of p52 were measured by western blot as a read-out of active nc-NF-κB signaling. Effects of macrophage polarization on nc-NF-κB signaling were determined in unpolarized (M0), M1 polarized (LPS/IFNγ treated) or M2 polarized (IL-4 treated) BMDMs. Finally, effects of inhibiting nc-NF-κB using a specific peptide inhibitor of p52 nuclear import (SN52) on cancer cell growth and macrophage phenotype were determined in sulforhodamine B growth assays and by western blot analysis of PCNA (proliferation marker) and arginase-1 (M2 macrophage marker). Results: We observed high levels of p52 expression in the majority of ovarian cancer cell lines, and in our cultured macrophage models. The functional relevance of these observations was confirmed by experiments showing reduced growth in ovarian cancer cells treated with SN52 and reduced expression of arginase-1 in SN52-treated macrophages. We saw similar results in breast cancer cells and mouse mammary TAMs, showing that nc-NF-κB signaling may also have pro-tumor effects in other cancer types. Complementary studies showed that M2 polarized macrophages expressed markedly higher levels of nuclear p52 than observed in M0 or M1 cells. Based on these promising results, experiments (i) using transgenic mice to allow targeted, inducible activation of nc-NF-κB in macrophages during ovarian cancer progression and (ii) testing the therapeutic effects of SN52 in these cancer models are underway. Conclusions: Although further studies are required to establish the translational relevance of our findings, we hope to identify non-canonical NF-κB signaling as a new therapeutic target in malignant epithelium and macrophages in ovarian cancer and potentially other cancer types. Citation Format: Andrew J. Wilson, Dominique Parker, Robert Cheng, Todd Giorgio, Marta Crispens, Fiona Yull. Investigating the role of non-canonical NF-kappaB signaling in tumor cells and macrophages in ovarian cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4973.

Abstract 2728: Modulation of NFkappaB signaling influences tumor associated macrophage phenotypes in murine models of breast cancer

Abstract Tumor associated macrophages (TAMs) often exist in high densities in breast tumors and are associated with adverse clinical outcomes. TAM repolarization as a strategy to shift the breast cancer microenvironment from immunosuppressive to immunostimulatory is an active area of research. The canonical and non-canonical NfkappaB (NFkB) signaling pathways represent potential points of intervention to influence TAM phenotypes. We have found that upregulation of the canonical NFkB signaling pathway specifically in macrophages can be used to repolarize TAMs toward an M1, anti-tumor phenotype. Using our doxycycline inducible mouse model termed IKFM, we are exploring the effects of macrophage specific upregulation of NFkB signaling on different stages of tumor growth and metastasis. In studies using the IKFM mouse model, we found that doxycycline-induced NFkB activation in macrophages in established orthotopic mammary tumors has therapeutic effects on tumor outcomes. Compared to control mice, we found that IKFM mice have reduced tumor burden in the lung, indicating prevention of metastasis. Ongoing studies are focused on understanding how macrophage specific activation of NFkB influences the metastatic niches of lung and bone; two of the most common sites of breast cancer metastasis. To move our findings towards clinical translation, we have developed an M2-macrophage targeted nanoparticle that activates NFkB signaling by delivering an siRNA against IkappaBalpha, an inhibitor of the pathway. The M2 targeted nanoparticle is currently being tested in murine models of breast cancer metastasis to both lung and bone to translate our findings from the IKFM mouse model to a pharmacological manipulation. Citation Format: Kennady K. Bullock, Dominique Parker, Evan B. Glass, Alyssa Hoover, Alyssa Merkel, Richard Maynard, Andrew Wilson, Todd Giorgio, Julie A. Rhoades, Fiona E. Yull. Modulation of NFkappaB signaling influences tumor associated macrophage phenotypes in murine models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2728.

Abstract A15: Noncanonical NF-kappaB signaling is associated with poor ovarian cancer prognosis

Abstract Objective: Mediated by a family of transcription factors, the canonical and noncanonical nuclear factor-kappaB (NF-kB) signaling pathways have key roles in inflammation, innate immunity, and cancer development and progression. As prior ovarian cancer studies have evaluated only canonical NF-kB transcription factors in relation to survival, this study was undertaken to evaluate both canonical and noncanonical NF-kB pathway components in tumor samples from epithelial ovarian cancer cases from the Vanderbilt Tissue Repository for Ovarian Cancer (TROC). Methods: We abstracted clinical data from electronic medical records and assayed p65 (representing the canonical NF-kB pathway) and p52 (representing the noncanonical NF-kB pathway) by immunohistochemistry for 197 TROC samples. Nuclear and cytoplasmic staining in tumor cells was semiquantified by H-scores and dichotomized at median values. Associations with progression-free survival (PFS) and overall survival (OS) were quantified by hazard ratios (HR) and 95% confidence intervals (CI) using Cox proportional-hazards regression. Results: Median cytoplasmic and nuclear p65 and p52 H-scores were significantly higher among high-grade and serous cases; median p52 H-scores were also significantly higher among late-stage cases and patients treated with chemotherapy (all Wilcoxon rank sum p<0.05). In unadjusted regression models, higher nuclear p65 and higher nuclear p52 were associated with approximately 40% and 70% shorter PFS and OS, respectively, but these associations were attenuated by adjustment for age, stage, tumor type, race, chemotherapy, and residual disease. In multivariable adjusted models, higher cytoplasmic p52 was associated with more than 50% shorter PFS (HR 1.68, 95% CI 1.18-2.39) and OS (HR 1.53, 95% CI 1.06-2.21). Furthermore, when cytoplasmic and nuclear staining were combined, and mutually adjusted models included both p52 and p65, only p52 remained associated with worse PFS (HR 1.57, 95% CI 1.10-2.37) and OS (HR 1.51, 95% CI 1.05-2.15). Conclusions: This is the first study to demonstrate that p52, representing noncanonical NF-kB signaling, may be an independent prognostic factor for epithelial ovarian cancer. Approaches to inhibit noncanonical NF-kB signaling should be explored as novel therapies for ovarian cancer are needed. Citation Format: Demetra Hufnagel, Andrew J. Wilson, Jamie Saxon, Dineo Khabele, Timothy Blackwell, Marta A. Crispens, Fiona Yull, Alicia Beeghly-Fadiel. Noncanonical NF-kappaB signaling is associated with poor ovarian cancer prognosis [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A15.

Abstract 1573: Non-canonical NF-kappaB signaling in the tumor microenvironment in relation to ovarian cancer survival

Abstract Introduction: Despite advances in treatment, ovarian cancer associated mortality has not substantially improved over the last 50 years. Understanding mechanisms that underlie disease progression is crucial to the development of new treatments for ovarian cancer. Mediated by a family of transcription factors, the canonical and non-canonical nuclear factor-kappaB signaling pathways have known roles in cell proliferation, as well as immune, inflammatory, and neoplastic processes. Non-canonical NF-kappaB signaling requires processing of a cytoplasmic p100/RelB dimer to a mature p52/RelB complex, capable of nuclear translocation to activate transcription of target genes. Prior studies on canonical NF-kappaB expression and ovarian cancer survival have been inconsistent, but no studies to date have evaluated the role of non-canonical NF-kappaB transcription factors. Methods: We conducted immunohistochemical staining for p52, a component of the non-canonical NF-kappaB signaling pathway, on a clinically annotated tissue microarray of ovarian tumors collected from 1994-2004 at the Vanderbilt University Medical Center. Nuclear and cytoplasmic p52 staining in tumors was semi-quantified by H-score and expression was dichotomized at median values. Associations with progression-free survival (PFS) and overall survival (OS) were quantified by hazard ratios (HR) and 95% confidence intervals (CI) using Cox proportional-hazards regression. Results: Among 194 ovarian cancer cases, p52 expression was predominantly cytoplasmic, with a relatively smaller proportion of tumor cells showing nuclear staining (median H-scores: 135.6 vs. 1.0). Cytoplasmic and nuclear p52 H-scores were significantly higher among high grade, advanced stage, and serous tumors (all Wilcoxon rank sum p<0.01). Kaplan-Meier survival analysis showed that cases with high nuclear p52 expression had significantly shorter time to disease progression (5-year PFS high vs. low: 72% vs. 17%, log-rank p<0.001). In regression models that included adjustment for age, stage, grade, and histologic subtype, high nuclear p52 was associated with a more than two-fold shorter PFS (HR 2.30, 95% CI 1.44-4.67). Significance of this finding was unaltered by additional adjustment for race, debulking, and platinum sensitivity (HR 2.26, 95% CI 1.15-4.45). In contrast, significant associations between high nuclear p52 and worse OS, and all associations for cytoplasmic p52 staining were attenuated after adjustment for clinical covariates. Conclusions: This is the first study to demonstrate that nuclear p52, representing active non-canonical NF-kappaB signaling, may be an independent prognostic factor for epithelial ovarian cancer. Thus, interventions that inhibit non-canonical NF-kappaB signaling should be explored as novel therapies to limit ovarian cancer progression. Citation Format: Demetra Hufnagel, Andrew J. Wilson, Jamie Saxon, Timothy Blackwell, Dineo Khabele, Marta A. Crispens, Alicia Beeghly-Fadiel, Fiona Yull. Non-canonical NF-kappaB signaling in the tumor microenvironment in relation to ovarian cancer survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1573.

The lymphotoxin β receptor is a potential therapeutic target in renal inflammation.

Accumulation of inflammatory cells in different renal compartments is a hallmark of progressive kidney diseases including glomerulonephritis (GN). Lymphotoxin β receptor (LTβR) signaling is crucial for the formation of lymphoid tissue, and inhibition of LTβR signaling has ameliorated several non-renal inflammatory models. Therefore, we tested whether LTβR signaling could also have a role in renal injury. Renal biopsies from patients with GN were found to express both LTα and LTβ ligands, as well as LTβR. The LTβR protein and mRNA were localized to tubular epithelial cells, parietal epithelial cells, crescents, and cells of the glomerular tuft, whereas LTβ was found on lymphocytes and tubular epithelial cells. Human tubular epithelial cells, mesangial cells, and mouse parietal epithelial cells expressed both LTα and LTβ mRNA upon stimulation with TNF in vitro. Several chemokine mRNAs and proteins were expressed in response to LTβR signaling. Importantly, in a murine lupus model, LTβR blockade improved renal function without the reduction of serum autoantibody titers or glomerular immune complex deposition. Thus, a preclinical mouse model and human studies strongly suggest that LTβR signaling is involved in renal injury and may be a suitable therapeutic target in renal diseases.

Mechanism Study of Matrix Metalloproteinase 13 Effects on Osteoclast Activation and Lytic Bone Lesions in Multiple Myeloma

Background: We have recently shown that Matrix metalloproteinase-13 (MMP-13) is highly expressed in human multiple myeloma (MM) cells and MMP-13 increases osteoclast (OCL) fusion and bone resorption independently of its metalloproteinase activity. In a mouse model of MM bone disease, knockdown (KD) of MMP-13 in MM cells inhibited development of bone lytic lesions, suggesting that MMP-13 is a potential therapeutic target for the treatment of MM bone disease (MMBD). However, the effects of MMP-13 on the MM bone marrow (BM) niche and underlying mechanism by which MMP-13 induces OCL fusion remains undefined.Methods and Results: To delineate the effects of MMP-13 on MM BM microenvironment, we investigated the effects of MMP-13 on cell proliferation and differentiation of pre-OCL, pre-osteoblast and MM cells. WT or Mmp-13-/- mouse CD11b+ BM cells were cultured with or without MMP-13 for 3 days and pre-OCL proliferation was evaluated by WST-1 assay. Neither MMP-13 treatment nor Mmp-13 deficiency affected pre-OCL proliferation, indicating MMP-13 induces OCL activation rather by promoting cell fusion than by affecting cell proliferation. To test the effects of MMP-13 on osteoblast (OB) differentiation and mineralization, mouse pre-OB cell line MC3T3-E1 and primary pre-OB cells from WT or Mmp-13-/- mice BM were cultured with or without MMP-13 for 7-14d. Neither exogenous MMP-13 nor Mmp-13 knockout affected OB differentiation or mineralization in vitro. Consistent with the in vitro observation, our Rag2-/- mouse 5TGM1 MMBD model provided in vivo evidence that knockdown of MMP-13 in MM cells does not affect MM induced OB inhibition or impairment of bone formation. Further, the effects of MMP-13 on MM cell proliferation were also assessed both in vitro and in vivo. Treatment of human MM cell lines RPMI-8266, OPM2 and MM.1S, as well as mouse MM cell line 5TGM1 with MMP-13 for up to 3 days did not induce in vitro cell proliferation. Similarly, MM cell sensitivity against anti-MM agents bortezomib and pomalidomide was not affected by MMP-13 in vitro. But, MMP-13 KD in mouse 5TGM1 MM cell line caused significantly less in vivo tumor burden in Rag2-/- intratibial MMBD model compared to 5TGM1 empty vector control cells, which we speculate occurs as a consequence of effects secondary to decreased OCL activation within the bone microenvironment following MMP-13 silencing.Our previous experiments showed that MMP-13 induces OCL fusion independent of its enzymatic activity, however the underlying mechanism is unknown. To further analyze the mechanism of action immunofluorescence staining and cell fraction-immunoblotting assay demonstrated that extracellular MMP-13 undergoes cell surface binding and subsequent active intracellular translocation into the perinuclear area, further supporting the enzymatic activity independent mechanism of MMP-13 on OCL induction. Furthermore, analysis of MMP-13-induced signaling pathways mediating osteoclastogenesis revealed that MMP-13 activates multiple cell signaling pathways including MAPK, PI3K and NF-kappaB independent of its enzymatic activity. Interestingly, the noncanonical NF-kappaB pathway is selectively activated by either MMP-13 WT or an E223A catalytically-inactive mutant, but not any by any other MMPs or MMP-13 truncated non-functional mutants, indicating that signaling through the noncanonical NF-kappaB pathway in OCL is specific for MMP-13 and may play a role in MMP-13-driven OCL fusion. Further studies are underway to screen for MMP-13 receptors and binding partners in an effort to delineate the processes underlying MMP-13 signaling.Conclusion: Our results demonstrate that MM produced MMP-13 induces OCL activation and bone resorption without affecting OB inhibition and bone formation impairment as well as anti-neoplastic response of MM cells. MMP-13 silencing in MM protects bone structure, and inhibits MM progression in vivo, which may be secondary to decreased OCL activation. MMP-13 specifically acts on OCL fusion. Signaling study showed noncanonical NF-kappaB signaling is selectively activated by MMP-13 independently of its enzymatic activity, and may be critical for MMP-13-induced OCL fusion and activation. Further screening the potential cellular receptor and intracellular transportation mechanism of MMP-13 in OCL is ongoing. DisclosuresRoodman:Amgen: Consultancy; Eli Lilly: Research Funding. Lentzsch:Axiom: Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees.

Abstract B36: NF-kappaB-dependent and -independent roles for NIK in regulating GBM cell invasion

Abstract The aggressive invasion of GBM cells into healthy brain tissue is a major factor contributing to the therapy resistance and poor prognosis of this malignancy. Our recent results demonstrated that the alternative, or noncanonical, NF-kappaB signaling pathway, predominates in the aggressive mesenchymal subtype of GBM. Additionally, NF-kappaB-inducing kinase (NIK), a key upstream activator of noncanonical NF-kappaB signaling, robustly promotes GBM cell invasion and pathogenesis. We demonstrate that expression of NIK is increased in response to exposure to collagen, a major extracellular matrix (ECM) protein present in GBM tumors, with NIK protein levels continuing to increase during invasion in 3D collagen matrices. Interestingly, NIK expression levels correlates with induction of membrane type-1 matrix metalloproteinase (MT1-MMP), a critical enzyme in many invasive tumors, functioning to degrade the basement membrane and ECM during cell migration and invasion. We provide evidence that NIK promotes MT1-MMP activation through increased phosphorylation at membrane protrusions and elevated enzymatic activity. Notably, the activation of MT1-MMP and the pro-invasive effects of NIK persist in the absence of the downstream NF-kappaB transcription factors RelA/p65 and RelB. Together, these data demonstrate a novel ability of NIK to promote GBM cell migration and invasion that is independent of NF-kappaB transcriptional activation functions. The results underscore the therapeutic potential of targeting noncanonical NF-kappaB signaling in these highly invasive tumors. Citation Format: Camille L. Duran, Linda Herrera de Lechuga, Dong W. Lee, Kayla J. Bayless, Raquel Sitcheran. NF-kappaB-dependent and -independent roles for NIK in regulating GBM cell invasion. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B36.

SAT0051 NF-KAPPAB inducing kinase (NIK) is a key regulator of angiogenesis: Implications for the role of non-canonical NF-KAPPAB signaling in synovial inflammation

BackgroundIn rheumatoid arthritis (RA) synovial tissue (ST), (pathological) angiogenesis can be observed already in the earliest phase of disease, which may be critical in the switch from acute to chronic...

AB0084 Non-canonical nf-kappab signaling induces a pro-angiogenic response in rheumatoid arthritis synovial fibroblasts and endothelial cells

BackgroundIn rheumatoid arthritis (RA) leukocytes migrate to the joints and gain entry into the synovial tissue through increased permeability of local endothelial cells[1]. These immune cells activate synovial fibroblasts (SF)...

TWEAK/Fn14 and Non-Canonical NF-kappaB Signaling in Kidney Disease

The incidence of acute kidney injury (AKI) and chronic kidney disease (CKD) is increasing. However, there is no effective therapy for AKI and current approaches only slow down, but do not prevent progression of CKD. TWEAK is a TNF superfamily cytokine. A solid base of preclinical data suggests a role of therapies targeting the TWEAK or its receptor Fn14 in AKI and CKD. In particular TWEAK/Fn14 targeting may preserve renal function and decrease cell death, inflammation, proteinuria, and fibrosis in mouse animal models. Furthermore there is clinical evidence for a role of TWEAK in human kidney injury including increased tissue and/or urinary levels of TWEAK and parenchymal renal cell expression of the receptor Fn14. In this regard, clinical trials of TWEAK targeting are ongoing in lupus nephritis. Nuclear factor-kappa B (NF-κB) activation plays a key role in TWEAK-elicited inflammatory responses. Activation of the non-canonical NF-κB pathway is a critical difference between TWEAK and TNF. TWEAK activation of the non-canonical NF-κB pathways promotes inflammatory responses in tubular cells. However, there is an incomplete understanding of the role of non-canonical NF-κB activation in kidney disease and on its contribution to TWEAK actions in vivo.

Comparative expression profiling of E. coli and S. aureus inoculated primary mammary gland cells sampled from cows with different genetic predispositions for somatic cell score

BackgroundDuring the past ten years many quantitative trait loci (QTL) affecting mastitis incidence and mastitis related traits like somatic cell score (SCS) were identified in cattle. However, little is known about the molecular architecture of QTL affecting mastitis susceptibility and the underlying physiological mechanisms and genes causing mastitis susceptibility. Here, a genome-wide expression analysis was conducted to analyze molecular mechanisms of mastitis susceptibility that are affected by a specific QTL for SCS on Bos taurus autosome 18 (BTA18). Thereby, some first insights were sought into the genetically determined mechanisms of mammary gland epithelial cells influencing the course of infection.MethodsPrimary bovine mammary gland epithelial cells (pbMEC) were sampled from the udder parenchyma of cows selected for high and low mastitis susceptibility by applying a marker-assisted selection strategy considering QTL and molecular marker information of a confirmed QTL for SCS in the telomeric region of BTA18. The cells were cultured and subsequently inoculated with heat-inactivated mastitis pathogens Escherichia coli and Staphylococcus aureus, respectively. After 1, 6 and 24 h, the cells were harvested and analyzed using the microarray expression chip technology to identify differences in mRNA expression profiles attributed to genetic predisposition, inoculation and cell culture.ResultsComparative analysis of co-expression profiles clearly showed a faster and stronger response after pathogen challenge in pbMEC from less susceptible animals that inherited the favorable QTL allele 'Q' than in pbMEC from more susceptible animals that inherited the unfavorable QTL allele 'q'. Furthermore, the results highlighted RELB as a functional and positional candidate gene and related non-canonical Nf-kappaB signaling as a functional mechanism affected by the QTL. However, in both groups, inoculation resulted in up-regulation of genes associated with the Ingenuity pathways 'dendritic cell maturation' and 'acute phase response signaling', whereas cell culture affected biological processes involved in 'cellular development'.ConclusionsThe results indicate that the complex expression profiling of pathogen challenged pbMEC sampled from cows inheriting alternative QTL alleles is suitable to study genetically determined molecular mechanisms of mastitis susceptibility in mammary epithelial cells in vitro and to highlight the most likely functional pathways and candidate genes underlying the QTL effect.

Activation of Noncanonical NF-κB Signaling by the Oncoprotein Tio

NF-kappaB transcription factors are key regulators of cellular proliferation and frequently contribute to oncogenesis. The herpesviral oncoprotein Tio, which promotes growth transformation of human T cells in a recombinant herpesvirus saimiri background, potently induces canonical NF-kappaB signaling through membrane recruitment of the ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Here, we show that, in addition to Tio-TRAF6 interaction, the Tio-induced canonical NF-kappaB signal requires the presence of the regulatory subunit of the inhibitor of kappaB kinase (IKK) complex, NF-kappaB essential modulator (NEMO), and the activity of its key kinase, IKKbeta, to up-regulate expression of endogenous cellular inhibitor of apoptosis 2 (cIAP2) and interleukin 8 (IL-8) proteins. Dependent on TRAF6 and NEMO, Tio enhances the expression of the noncanonical NF-kappaB proteins, p100 and RelB. Independent of TRAF6 and NEMO, Tio mediates stabilization of the noncanonical kinase, NF-kappaB-inducing kinase (NIK). Concomitantly, Tio induces efficient processing of the p100 precursor molecule to its active form, p52, as well as DNA binding of nuclear p52 and RelB. In human T cells transformed by infection with a Tio-recombinant virus, sustained expression of p100, RelB, and cIAP2 depends on IKKbeta activity, yet processing to p52 remains largely unaffected by IKKbeta inhibition. However, long term inhibition of IKKbeta disrupts the continuous growth of the transformed cells and induces cell death. Hence, the Tio oncoprotein triggers noncanonical NF-kappaB signaling through NEMO-dependent up-regulation of p100 precursor and RelB, as well as through NEMO-independent generation of p52 effector.

IL-6 Mediated Degeneration of Forebrain GABAergic Interneurons and Cognitive Impairment in Aged Mice through Activation of Neuronal NADPH Oxidase

BackgroundMultiple studies have shown that plasma levels of the pro-inflammatory cytokine interleukin-6 (IL-6) are elevated in patients with important and prevalent adverse health conditions, including atherosclerosis, diabetes, obesity, obstructive sleep apnea, hypertension, and frailty. Higher plasma levels of IL-6, in turn, increase the risk of many conditions associated with aging including age-related cognitive decline. However, the mechanisms underlying this association between IL-6 and cognitive vulnerability remain unclear.Methods and FindingsWe investigated the role of IL-6 in brain aging in young (4 mo) and aged (24 mo) wild-type C57BL6 and genetically-matched IL-6−/− mice, and determined that IL-6 was necessary and sufficient for increased neuronal expression of the superoxide-producing immune enzyme, NADPH-oxidase, and this was mediated by non-canonical NFκB signaling. Furthermore, superoxide production by NADPH-oxidase was directly responsible for age-related loss of parvalbumin (PV)-expressing GABAergic interneurons, neurons essential for normal information processing, encoding, and retrieval in hippocampus and cortex. Targeted deletion of IL-6 or elimination of superoxide by chronic treatment with a superoxide-dismutase mimetic prevented age-related loss of PV-interneurons and reversed age-related cognitive deficits on three standard tests of spatial learning and recall.ConclusionsPresent results indicate that IL-6 mediates age-related loss of critical PV-expressing GABAergic interneurons through increased neuronal NADPH-oxidase-derived superoxide production, and that rescue of these interneurons preserves cognitive performance in aging mice, suggesting that elevated peripheral IL-6 levels may be directly and mechanistically linked to long-lasting cognitive deficits in even normal older individuals. Further, because PV-interneurons are also selectively affected by commonly used anesthetic agents and drugs, our findings imply that IL-6 levels may predict adverse CNS effects in older patients exposed to these compounds through specific derangements in inhibitory interneurons, and that therapies directed at lowering IL-6 may have cognitive benefits clinically.

A Fourth IκB Protein within the NF-κB Signaling Module

Inflammatory NF-kappaB/RelA activation is mediated by the three canonical inhibitors, IkappaBalpha, -beta, and -epsilon. We report here the characterization of a fourth inhibitor, nfkappab2/p100, that forms two distinct inhibitory complexes with RelA, one of which mediates developmental NF-kappaB activation. Our genetic evidence confirms that p100 is required and sufficient as a fourth IkappaB protein for noncanonical NF-kappaB signaling downstream of NIK and IKK1. We develop a mathematical model of the four-IkappaB-containing NF-kappaB signaling module to account for NF-kappaB/RelA:p50 activation in response to inflammatory and developmental stimuli and find signaling crosstalk between them that determines gene-expression programs. Further combined computational and experimental studies reveal that mutant cells with altered balances between canonical and noncanonical IkappaB proteins may exhibit inappropriate inflammatory gene expression in response to developmental signals. Our results have important implications for physiological and pathological scenarios in which inflammatory and developmental signals converge.

Activation of NF-κB by HTLV-I and implications for cell transformation

T-cell transformation by the human T-cell leukemia virus type I (HTLV-I) involves deregulation of cellular transcription factors, including members of the NF-kappaB family. In normal T cells, NF-kappaB activation occurs transiently in response to immune stimuli, which is required for antigen-stimulated T-cell proliferation and survival. However, HTLV-I induces persistent activation of NF-kappaB, causing deregulated expression of a large array of cellular genes, which in turn contributes to the induction of T-cell transformation. The HTLV-I transforming protein Tax functions as an intracellular stimulator of IkappaB kinase (IKK), a cellular kinase mediating NF-kappaB activation by diverse stimuli. Tax physically interacts with IKK and renders this inducible kinase constitutively active. By assembling different Tax/IKK complexes, Tax targets the persistent activation of both canonical and noncanonical NF-kappaB signaling pathways. Whereas Tax plays a primary role in HTLV-I-mediated NF-kappaB activation, recent studies reveal that the IKK/NF-kappaB signaling pathway is also activated in freshly isolated adult T-cell leukemia (ATL) cells that often lack detectable Tax expression. The mechanism underlying this Tax-independent pathway of NF-kappaB activation remains poorly understood. Clarifying the precise nature and consequences of the constitutive NF-kappaB activation in ATL cells is important for developing rational therapeutic strategies for this T-cell malignancy.

Regulation of the NF-κB-inducing Kinase by Tumor Necrosis Factor Receptor-associated Factor 3-induced Degradation

The NF-kappaB family of transcription factors plays a pivotal role in regulation of diverse biological processes, including immune responses, cell growth, and apoptosis. Activation of NF-kappaB is mediated by both canonical and noncanonical signaling pathways. Although the canonical pathway has been extensively studied, the mechanism mediating the noncanonical pathway is still poorly understood. Recent studies have identified the NF-kappaB-inducing kinase (NIK) as a key component of the noncanonical pathway of NF-kappaB activation; however, how the signaling function of NIK is regulated remains unknown. We report here that one important mechanism of NIK regulation is through its dynamic interaction with the tumor necrosis factor receptor-associated factor 3 (TRAF3). TRAF3 physically associates with NIK via a specific sequence motif located in the N-terminal region of NIK; this molecular interaction appears to target NIK for degradation by the proteasome. Interestingly, induction of noncanonical NF-kappaB signaling by extracellular signals involves degradation of TRAF3 and the concomitant enhancement of NIK expression. These results suggest that induction of noncanonical NF-kappaB signaling may involve the rescue of NIK from TRAF3-mediated negative regulation.