SAMHD1 suppresses innate immune responses to viral infections and inflammatory stimuli by inhibiting the NF-κB and interferon pathways.

Sterile alpha motif and HD-domain-containing protein 1 (SAMHD1) blocks replication of retroviruses and certain DNA viruses by reducing the intracellular dNTP pool. SAMHD1 has been suggested to down-regulate IFN and inflammatory responses to viral infections, although the functions and mechanisms of SAMHD1 in modulating innate immunity remain unclear. Here, we show that SAMHD1 suppresses the innate immune responses to viral infections and inflammatory stimuli by inhibiting nuclear factor-κB (NF-κB) activation and type I interferon (IFN-I) induction. Compared with control cells, infection of SAMHD1-silenced human monocytic cells or primary macrophages with Sendai virus (SeV) or HIV-1, or treatment with inflammatory stimuli, induces significantly higher levels of NF-κB activation and IFN-I induction. Exogenous SAMHD1 expression in cells or SAMHD1 reconstitution in knockout cells suppresses NF-κB activation and IFN-I induction by SeV infection or inflammatory stimuli. Mechanistically, SAMHD1 inhibits NF-κB activation by interacting with NF-κB1/2 and reducing phosphorylation of the NF-κB inhibitory protein IκBα. SAMHD1 also interacts with the inhibitor-κB kinase ε (IKKε) and IFN regulatory factor 7 (IRF7), leading to the suppression of the IFN-I induction pathway by reducing IKKε-mediated IRF7 phosphorylation. Interactions of endogenous SAMHD1 with NF-κB and IFN-I pathway proteins were validated in human monocytic cells and primary macrophages. Comparing splenocytes from SAMHD1 knockout and heterozygous mice, we further confirmed SAMHD1-mediated suppression of NF-κB activation, suggesting an evolutionarily conserved property of SAMHD1. Our findings reveal functions of SAMHD1 in down-regulating innate immune responses to viral infections and inflammatory stimuli, highlighting the importance of SAMHD1 in modulating antiviral immunity.

A selective screening platform reveals unique global expression patterns of microRNAs in a cohort of human soft-tissue sarcomas.

Sarcomas are malignant heterogenous tumors of mesenchymal derivation. Emerging data suggest that miRNA might have a causal role in sarcomagenesis. Herein, we used a selective miRNA screening platform to study the comparative global miRNA expression signatures in a cohort of human sarcomas with the caveat that comparisons between tumor and non-tumor cells were performed from the same patients using formalin-fixed paraffin-embedded tissue. Five histologic types were examined that included: myxoid liposarcoma, well-differentiated liposarcoma, dedifferentiated liposarcoma, pleomorphic rhabdomyosarcoma, and synovial sarcoma. In addition, soft-tissue lipomas and normal fat were included as a separate set of controls for the lipogenic tumors. Clustering analysis showed a distinct global difference in expression patterns between the normal and sarcoma tissues. Expression signatures in an unsupervised hierarchical clustering analysis revealed tight clustering in synovial and myxoid liposarcomas, and the least clustering was observed in the pleomorphic rhabdomyosarcoma subtype. MiR-145 showed underexpression in pleomorphic rhabdomyosarcoma, well-differentiated liposarcoma, and synovial sarcoma. Unexpectedly, we found that a set of muscle-specific microRNAs (miRNAs; myomiRs): miR-133, miR-1, and miR-206 was significantly underexpressed in well-differentiated liposarcoma and synovial sarcoma, suggesting that they may function as tumor suppressors as described in muscle-relevant rhabdomyosarcomas. In addition, a tight linear progression of miRNA expression was identified from normal fat to dedifferentiated liposarcoma. These results suggest that miRNA expression profiles could elucidate classes of miRNAs that may elicit tumor-relevant activities in specific sarcoma subtypes.

Treatment with tumor-treating fields (TTFields) suppresses intercellular tunneling nanotube formation in vitro and upregulates immuno-oncologic biomarkers in vivo in malignant mesothelioma.

Disruption of intercellular communication within tumors is emerging as a novel potential strategy for cancer-directed therapy. Tumor-Treating Fields (TTFields) therapy is a treatment modality that has itself emerged over the past decade in active clinical use for patients with glioblastoma and malignant mesothelioma, based on the principle of using low-intensity alternating electric fields to disrupt microtubules in cancer cells undergoing mitosis. There is a need to identify other cellular and molecular effects of this treatment approach that could explain reported increased overall survival when TTFields are added to standard systemic agents. Tunneling nanotube (TNTs) are cell-contact-dependent filamentous-actin-based cellular protrusions that can connect two or more cells at long-range. They are upregulated in cancer, facilitating cell growth, differentiation, and in the case of invasive cancer phenotypes, a more chemoresistant phenotype. To determine whether TNTs present a potential therapeutic target for TTFields, we applied TTFields to malignant pleural mesothelioma (MPM) cells forming TNTs in vitro. TTFields at 1.0 V/cm significantly suppressed TNT formation in biphasic subtype MPM, but not sarcomatoid MPM, independent of effects on cell number. TTFields did not significantly affect function of TNTs assessed by measuring intercellular transport of mitochondrial cargo via intact TNTs. We further leveraged a spatial transcriptomic approach to characterize TTFields-induced changes to molecular profiles in vivo using an animal model of MPM. We discovered TTFields induced upregulation of immuno-oncologic biomarkers with simultaneous downregulation of pathways associated with cell hyperproliferation, invasion, and other critical regulators of oncogenic growth. Several molecular classes and pathways coincide with markers that we and others have found to be differentially expressed in cancer cell TNTs, including MPM specifically. We visualized short TNTs in the dense stromatous tumor material selected as regions of interest for spatial genomic assessment. Superimposing these regions of interest from spatial genomics over the plane of TNT clusters imaged in intact tissue is a new method that we designate Spatial Profiling of Tunneling nanoTubes (SPOTT). In sum, these results position TNTs as potential therapeutic targets for TTFields-directed cancer treatment strategies. We also identified the ability of TTFields to remodel the tumor microenvironment landscape at the molecular level, thereby presenting a potential novel strategy for converting tumors at the cellular level from 'cold' to 'hot' for potential response to immunotherapeutic drugs.

DUX4, a candidate gene for facioscapulohumeral muscular dystrophy, causes p53-dependent myopathy in vivo.

OBJECTIVE: Facioscapulohumeral muscular dystrophy (FSHD) is associated with D4Z4 repeat contraction on human chromosome 4q35. This genetic lesion does not result in complete loss or mutation of any gene. Consequently, the pathogenic mechanisms underlying FSHD have been difficult to discern. In leading FSHD pathogenesis models, D4Z4 contractions are proposed to cause epigenetic changes, which ultimately increase expression of genes with myopathic potential. Although no gene has been conclusively linked to FSHD development, recent evidence supports a role for the D4Z4-encoded DUX4 gene in FSHD. In this study, our objective was to test the in vivo myopathic potential of DUX4. METHODS: We delivered DUX4 to zebrafish and mouse muscle by transposon-mediated transgenesis and adeno-associated viral vectors, respectively. RESULTS: Overexpression of DUX4, which encodes a transcription factor, caused abnormalities associated with muscular dystrophy in zebrafish and mice. This toxicity required DNA binding, because a DUX4 DNA binding domain mutant produced no abnormalities. Importantly, we found the myopathic effects of DUX4 were p53 dependent, as p53 inhibition mitigated DUX4 toxicity in vitro, and muscles from p53 null mice were resistant to DUX4-induced damage. INTERPRETATION: Our work demonstrates the myopathic potential of DUX4 in animal muscle. Considering previous studies showed DUX4 was elevated in FSHD patient muscles, our data support the hypothesis that DUX4 overexpression contributes to FSHD development. Moreover, we provide a p53-dependent mechanism for DUX4 toxicity that is consistent with previous studies showing p53 pathway activation in FSHD muscles. Our work justifies further investigation of DUX4 and the p53 pathway in FSHD pathogenesis.

Tunneling Nanotubes between Cells Migrating in ECM Mimicking Fibrous Environments.

Tunneling nanotubes (TNTs) comprise a unique class of actin-rich nanoscale membranous protrusions. They enable long-distance intercellular communication and may play an integral role in tumor formation, progression, and drug resistance. TNTs are three-dimensional, but nearly all studies have investigated them using two-dimensional cell culture models. Here, we applied a unique 3D culture platform consisting of crosshatched and aligned fibers to fabricate synthetic suspended scaffolds that mimic the native fibrillar architecture of tumoral extracellular matrix (ECM) to characterize TNT formation and function in its native state. TNTs are upregulated in malignant mesothelioma; we used this model to analyze the biophysical properties of TNTs in this 3D setting, including cell migration in relation to TNT dynamics, rate of TNT-mediated intercellular transport of cargo, and conformation of TNT-forming cells. We found that highly migratory elongated cells on aligned fibers formed significantly longer but fewer TNTs than uniformly spread cells on crossing fibers. We developed new quantitative metrics for the classification of TNT morphologies based on shape and cytoskeletal content using confocal microscopy. In sum, our strategy for culturing cells in ECM-mimicking bioengineered scaffolds provides a new approach for accurate biophysical and biologic assessment of TNT formation and structure in native fibrous microenvironments.

TNTdetect.AI: A Deep Learning Model for Automated Detection and Counting of Tunneling Nanotubes in Microscopy Images.

BACKGROUND: Tunneling nanotubes (TNTs) are cellular structures connecting cell membranes and mediating intercellular communication. TNTs are manually identified and counted by a trained investigator; however, this process is time-intensive. We therefore sought to develop an automated approach for quantitative analysis of TNTs. METHODS: We used a convolutional neural network (U-Net) deep learning model to segment phase contrast microscopy images of both cancer and non-cancer cells. Our method was composed of preprocessing and model development. We developed a new preprocessing method to label TNTs on a pixel-wise basis. Two sequential models were employed to detect TNTs. First, we identified the regions of images with TNTs by implementing a classification algorithm. Second, we fed parts of the image classified as TNT-containing into a modified U-Net model to estimate TNTs on a pixel-wise basis. RESULTS: The algorithm detected 49.9% of human expert-identified TNTs, counted TNTs, and calculated the number of TNTs per cell, or TNT-to-cell ratio (TCR); it detected TNTs that were not originally detected by the experts. The model had 0.41 precision, 0.26 recall, and 0.32 f-1 score on a test dataset. The predicted and true TCRs were not significantly different across the training and test datasets (p = 0.78). CONCLUSIONS: Our automated approach labeled and detected TNTs and cells imaged in culture, resulting in comparable TCRs to those determined by human experts. Future studies will aim to improve on the accuracy, precision, and recall of the algorithm.

Quantitative biophysical metrics for rapid evaluation of ovarian cancer metastatic potential.

Ovarian cancer is routinely diagnosed long after the disease has metastasized through the fibrous submesothelium. Despite extensive research in the field linking ovarian cancer progression to increasingly poor prognosis, there are currently no validated cellular markers or hallmarks of ovarian cancer that can predict metastatic potential. To discern disease progression across a syngeneic mouse ovarian cancer progression model, here we fabricated extracellular matrix mimicking suspended fiber networks: cross-hatches of mismatch diameters for studying protrusion dynamics, aligned same diameter networks of varying interfiber spacing for studying migration, and aligned nanonets for measuring cell forces. We found that migration correlated with disease while a force-disease biphasic relationship exhibited F-actin stress fiber network dependence. However, unique to suspended fibers, coiling occurring at the tips of protrusions and not the length or breadth of protrusions displayed the strongest correlation with metastatic potential. To confirm that our findings were more broadly applicable beyond the mouse model, we repeated our studies in human ovarian cancer cell lines and found that the biophysical trends were consistent with our mouse model results. Altogether, we report complementary high throughput and high content biophysical metrics capable of identifying ovarian cancer metastatic potential on a timescale of hours.

Molecular alterations associated with improved outcome in patients with glioblastoma treated with Tumor-Treating Fields.

Background: The genomic and overall biologic landscape of glioblastoma (GB) has become clearer over the past 2 decades, as predictive and prognostic biomarkers of both de novo and transformed forms of GB have been identified. The oral chemotherapeutic agent temozolomide (TMZ) has been integral to standard-of-care treatment for nearly 2 decades. More recently, the use of non-pharmacologic interventions, such as application of alternating electric fields, called Tumor-Treating Fields (TTFields), has emerged as a complementary treatment option that increases overall survival (OS) in patients with newly diagnosed GB. The genomic factors associated with improved or lack of response to TTFields are unknown. Methods: We performed comprehensive genomic analysis of GB tumors resected from 55 patients who went on to receive treatment using TTFields, and compared results to 57 patients who received standard treatment without TTFields. Results: We found that molecular driver alterations in NF1, and wild-type PIK3CA and epidermal growth factor receptor (EGFR), were associated with increased benefit from TTFields as measured by progression-free survival (PFS) and OS. There were no differences when stratified by TP53 status. When NF1, PIK3CA, and EGFR status were combined as a Molecular Survival Score, the combination of the 3 factors significantly correlated with improved OS and PFS in TTFields-treated patients compared to patients not treated with TTFields. Conclusions: These results shed light on potential driver and passenger mutations in GB that can be validated as predictive biomarkers of response to TTFields treatment, and provide an objective and testable genomic-based approach to assessing response.

RelA/p65 functions to maintain cellular senescence by regulating genomic stability and DNA repair.

Nuclear factor (NF)-kappaB is a positive regulator of tumour development and progression, but how it functions in normal cells leading to oncogenesis is not clear. As cellular senescence has proven to be an intrinsic tumour suppressor mechanism that cells must overcome to establish deregulated growth, we used primary fibroblasts to follow NF-kappaB function in cells transitioning from senescence to subsequent immortalization. Our findings show that RelA/p65(-/-) murine fibroblasts immortalize at considerably faster rates than RelA/p65(+/+) cells. The ability of RelA/p65(-/-) fibroblasts to escape senescence earlier is due to their genomic instability, characterized by high frequencies of DNA mutations, gene deletions and gross chromosomal translocations. This increase in genomic instability is closely related to a compromised DNA repair that occurs in both murine RelA/p65(-/-) fibroblasts and tissues. Significantly, these results can also be duplicated in human fibroblasts lacking NF-kappaB. Altogether, our findings present a fresh perspective on the role of NF-kappaB as a tumour suppressor, which acts in pre-neoplastic cells to maintain cellular senescence by promoting DNA repair and genomic stability.

Modeling Human Cancer-induced Cachexia.

Cachexia is a wasting syndrome characterized by pronounced skeletal muscle loss. In cancer, cachexia is associated with increased morbidity and mortality and decreased treatment tolerance. Although advances have been made in understanding the mechanisms of cachexia, translating these advances to the clinic has been challenging. One reason for this shortcoming may be the current animal models, which fail to fully recapitulate the etiology of human cancer-induced tissue wasting. Because pancreatic ductal adenocarcinoma (PDA) presents with a high incidence of cachexia, we engineered a mouse model of PDA that we named KPP. KPP mice, similar to PDA patients, progressively lose skeletal and adipose mass as a consequence of their tumors. In addition, KPP muscles exhibit a similar gene ontology as cachectic patients. We envision that the KPP model will be a useful resource for advancing our mechanistic understanding and ability to treat cancer cachexia.

Epstein-Barr virus-encoded dUTPase enhances proinflammatory cytokine production by macrophages in contact with endothelial cells: evidence for depression-induced atherosclerotic risk.

Increased levels of proinflammatory cytokines, TNF-alpha and IL-6, predict mortality and morbidity. In cardiovascular disease patients, they are observed in atherosclerotic lesions and serum. Factors behind the increased levels of these cytokines are multifaceted and may include latent herpesviruses, such as Epstein-Barr virus (EBV) that can be reactivated by stress. Previously, we showed that the EBV-encoded deoxyuridine triphosphate nucleotidohydrolase (dUTPase), a protein synthesized in the early phase of virus replication, can induce human monocytes/macrophages to produce TNF-alpha and IL-6. In this study, we modeled the interactions that take place between macrophages and endothelial cells in vivo using human umbilical vein endothelial cells (HUVEC). HUVEC were stimulated by soluble factors induced by EBV dUTPase-treated monocyte-derived macrophages (MDM) that resulted in the upregulation of VCAM-1 and ICAM-1. These changes were related to MDM production of TNF-alpha following the activation of NF-kappaB. In a previous study, chronically stressed dementia caregivers had elevations in plasma IL-6 levels, a risk for cardiovascular disease. We found a relationship between plasma IL-6 levels and neutralizing antibody titers to EBV dUTPase suggesting that one source of the plasma IL-6 observed in our previous study could be related to the effect of EBV-encoded dUTPase on macrophages. The results suggest that EBV-encoded dUTPase can enhance production of proinflammatory cytokines by monocytes/macrophages in contact with endothelial cells of blood vessels, and may play a role in cardiovascular pathology and chronic inflammation.

RelA/p65 regulation of IkappaBbeta.

IkappaB inhibitor proteins are the primary regulators of NF-kappaB. In contrast to the defined regulatory interplay between NF-kappaB and IkappaBalpha, much less is known regarding the regulation of IkappaBbeta by NF-kappaB. Here, we describe in detail the regulation of IkappaBbeta by RelA/p65. Using p65(-/-) fibroblasts, we show that IkappaBbeta is profoundly reduced in these cells, but not in other NF-kappaB subunit knockouts. This regulation prevails during embryonic and postnatal development in a tissue-specific manner. Significantly, in both p65(-/-) cells and tissues, IkappaBalpha is also reduced, but not nearly to the same extent as IkappaBbeta, thus highlighting the degree to which IkappaBbeta is dependent on p65. This dependence is based on the ability of p65 to stabilize IkappaBbeta protein from the 26S proteasome, a process mediated in large part through the p65 carboxyl terminus. Furthermore, IkappaBbeta was found to exist in both a basally phosphorylated and a hyperphosphorylated form. While the hyperphosphorylated form is less abundant, it is also more stable and less dependent on p65 and its carboxyl domain. Finally, we show that in p65(-/-) fibroblasts, expression of a proteolysis-resistant form of IkappaBbeta, but not IkappaBalpha, causes a severe growth defect associated with apoptosis. Based on these findings, we propose that tight control of IkappaBbeta protein by p65 is necessary for the maintenance of cellular homeostasis.

Classical NF-κB Metabolically Reprograms Sarcoma Cells Through Regulation of Hexokinase 2.

BACKGROUND: Metabolic reprogramming has emerged as a cancer hallmark, and one of the well-known cancer-associated metabolic alterations is the increase in the rate of glycolysis. Recent reports have shown that both the classical and alternative signaling pathways of nuclear factor κB (NF-κB) play important roles in controlling the metabolic profiles of normal cells and cancer cells. However, how these signaling pathways affect the metabolism of sarcomas, specifically rhabdomyosarcoma (RMS) and osteosarcoma (OS), has not been characterized. METHODS: Classical NF-κB activity was inhibited through overexpression of the IκBα super repressor of NF-κB in RMS and OS cells. Global gene expression analysis was performed using Affymetrix GeneChip Human Transcriptome Array 2.0, and data were interpreted using gene set enrichment analysis. Seahorse Bioscience XFe24 was used to analyze oxygen consumption rate as a measure of aerobic respiration. RESULTS: Inhibition of classical NF-κB activity in sarcoma cell lines restored alternative signaling as well as an increased oxidative respiratory metabolic phenotype in vitro. In addition, microarray analysis indicated that inhibition of NF-κB in sarcoma cells reduced glycolysis. We showed that a glycolytic gene, hexokinase (HK) 2, is a direct NF-κB transcriptional target. Knockdown of HK2 shifted the metabolic profile in sarcoma cells away from aerobic glycolysis, and re-expression of HK2 rescued the metabolic shift induced by inhibition of NF-κB activity in OS cells. CONCLUSION: These findings suggest that classical signaling of NF-κB plays a crucial role in the metabolic profile of pediatric sarcomas potentially through the regulation of HK2.

Cancer cachexia is regulated by selective targeting of skeletal muscle gene products.

Cachexia is a syndrome characterized by wasting of skeletal muscle and contributes to nearly one-third of all cancer deaths. Cytokines and tumor factors mediate wasting by suppressing muscle gene products, but exactly which products are targeted by these cachectic factors is not well understood. Because of their functional relevance to muscle architecture, such targets are presumed to represent myofibrillar proteins, but whether these proteins are regulated in a general or a selective manner is also unclear. Here we demonstrate, using in vitro and in vivo models of muscle wasting, that cachectic factors are remarkably selective in targeting myosin heavy chain. In myotubes and mouse muscles, TNF-alpha plus IFN-gamma strongly reduced myosin expression through an RNA-dependent mechanism. Likewise, colon-26 tumors in mice caused the selective reduction of this myofibrillar protein, and this reduction correlated with wasting. Under these conditions, however, loss of myosin was associated with the ubiquitin-dependent proteasome pathway, which suggests that mechanisms used to regulate the expression of muscle proteins may be cachectic factor specific. These results shed new light on cancer cachexia by revealing that wasting does not result from a general downregulation of muscle proteins but rather is highly selective as to which proteins are targeted during the wasting state.

NFκB signaling in alveolar rhabdomyosarcoma.

Alveolar rhabdomyosarcoma (aRMS) is a pediatric soft tissue cancer commonly associated with a chromosomal translocation that leads to the expression of a Pax3:Foxo1 or Pax7:Foxo1 fusion protein, the developmental underpinnings of which may give clues to its therapeutic approaches. In aRMS, the NFκB-YY1-miR-29 regulatory circuit is dysregulated, resulting in repression of miR-29 and loss of the associated tumor suppressor activity. To further elucidate the role of NFκB in aRMS, we first tested 55 unique sarcoma cell lines and primary cell cultures in a large-scale chemical screen targeting diverse molecular pathways. We found that pharmacological inhibition of NFκB activity resulted in decreased cell proliferation of many of the aRMS tumor cultures. Surprisingly, mice that were orthotopically allografted with aRMS tumor cells exhibited no difference in tumor growth when administered an NFκB inhibitor, compared to control. Furthermore, inhibition of NFκB by genetically ablating its activating kinase inhibitor, IKKß, by conditional deletion in a mouse model harboring the Pax3:Foxo1 chimeric oncogene failed to abrogate spontaneous tumor growth. Genetically engineered mice with conditionally deleted IKKß exhibited a paradoxical decrease in tumor latency compared with those with active NFκB. However, using a synthetic-lethal approach, primary cell cultures derived from tumors with inactivated NFκB showed sensitivity to the BCL-2 inhibitor navitoclax. When used in combination with an NFκB inhibitor, navitoclax was synergistic in decreasing the growth of both human and IKKß wild-type mouse aRMS cells, indicating that inactivation of NFκB alone may not be sufficient for reducing tumor growth, but, when combined with another targeted therapeutic, may be clinically beneficial.

NF-κB regulates GDF-15 to suppress macrophage surveillance during early tumor development.

Macrophages are attracted to developing tumors and can participate in immune surveillance to eliminate neoplastic cells. In response, neoplastic cells utilize NF-κB to suppress this killing activity, but the mechanisms underlying their self-protection remain unclear. Here, we report that this dynamic interaction between tumor cells and macrophages is integrally linked by a soluble factor identified as growth and differentiation factor 15 (GDF-15). In vitro, tumor-derived GDF-15 signals in macrophages to suppress their proapoptotic activity by inhibiting TNF and nitric oxide (NO) production. In vivo, depletion of GDF-15 in Ras-driven tumor xenografts and in an orthotopic model of pancreatic cancer delayed tumor development. This delay correlated with increased infiltrating antitumor macrophages. Further, production of GDF-15 is directly regulated by NF-κB, and the colocalization of activated NF-κB and GDF-15 in epithelial ducts of human pancreatic adenocarcinoma supports the importance of this observation. Mechanistically, we found that GDF-15 suppresses macrophage activity by inhibiting TGF-ß-activated kinase (TAK1) signaling to NF-κB, thereby blocking synthesis of TNF and NO. Based on these results, we propose that the NF-κB/GDF-15 regulatory axis is important for tumor cells in evading macrophage immune surveillance during the early stages of tumorigenesis.

MyoD Regulates Skeletal Muscle Oxidative Metabolism Cooperatively with Alternative NF-κB.

MyoD is a key regulator of skeletal myogenesis that directs contractile protein synthesis, but whether this transcription factor also regulates skeletal muscle metabolism has not been explored. In a genome-wide ChIP-seq analysis of skeletal muscle cells, we unexpectedly observed that MyoD directly binds to numerous metabolic genes, including those associated with mitochondrial biogenesis, fatty acid oxidation, and the electron transport chain. Results in cultured cells and adult skeletal muscle confirmed that MyoD regulates oxidative metabolism through multiple transcriptional targets, including PGC-1ß, a master regulator of mitochondrial biogenesis. We find that PGC-1ß expression is cooperatively regulated by MyoD and the alternative NF-κB signaling pathway. Bioinformatics evidence suggests that this cooperativity between MyoD and NF-κB extends to other metabolic genes as well. Together, these data identify MyoD as a regulator of the metabolic capacity of mature skeletal muscle to ensure that sufficient energy is available to support muscle contraction.

Serine/Threonine Kinase MLK4 Determines Mesenchymal Identity in Glioma Stem Cells in an NF-κB-dependent Manner.

Activation of nuclear factor κB (NF-κB) induces mesenchymal (MES) transdifferentiation and radioresistance in glioma stem cells (GSCs), but molecular mechanisms for NF-κB activation in GSCs are currently unknown. Here, we report that mixed lineage kinase 4 (MLK4) is overexpressed in MES but not proneural (PN) GSCs. Silencing MLK4 suppresses self-renewal, motility, tumorigenesis, and radioresistance of MES GSCs via a loss of the MES signature. MLK4 binds and phosphorylates the NF-κB regulator IKKα, leading to activation of NF-κB signaling in GSCs. MLK4 expression is inversely correlated with patient prognosis in MES, but not PN high-grade gliomas. Collectively, our results uncover MLK4 as an upstream regulator of NF-κB signaling and a potential molecular target for the MES subtype of glioblastomas.

Microglia induce motor neuron death via the classical NF-κB pathway in amyotrophic lateral sclerosis.

Neuroinflammation is one of the most striking hallmarks of amyotrophic lateral sclerosis (ALS). Nuclear factor-kappa B (NF-κB), a master regulator of inflammation, is upregulated in spinal cords of ALS patients and SOD1-G93A mice. In this study, we show that selective NF-κB inhibition in ALS astrocytes is not sufficient to rescue motor neuron (MN) death. However, the localization of NF-κB activity and subsequent deletion of NF-κB signaling in microglia rescued MNs from microglial-mediated death in vitro and extended survival in ALS mice by impairing proinflammatory microglial activation. Conversely, constitutive activation of NF-κB selectively in wild-type microglia induced gliosis and MN death in vitro and in vivo. Taken together, these data provide a mechanism by which microglia induce MN death in ALS and suggest a novel therapeutic target that can be modulated to slow the progression of ALS and possibly other neurodegenerative diseases by which microglial activation plays a role.

miR-29 acts as a decoy in sarcomas to protect the tumor suppressor A20 mRNA from degradation by HuR.

In sarcoma, the activity of NF-κB (nuclear factor κB) reduces the abundance of the microRNA (miRNA) miR-29. The tumor suppressor A20 [also known as TNFAIP3 (tumor necrosis factor-α-induced protein 3)] inhibits an upstream activator of NF-κB and is often mutated in lymphomas. In a panel of human sarcoma cell lines, we found that the activation of NF-κB was increased and, although the abundance of A20 protein and mRNA was decreased, the gene encoding A20 was rarely mutated. The 3' untranslated region (UTR) of A20 mRNA has conserved binding sites for both of the miRNAs miR-29 and miR-125. Whereas the expression of miR-125 was increased in human sarcoma tissue, that of miR-29 was decreased in most samples. Overexpression of miR-125 decreased the abundance of A20 mRNA, whereas reconstituting miR-29 in sarcoma cell lines increased the abundance of A20 mRNA and protein. By interacting directly with the RNA binding protein HuR (human antigen R; also known as ELAVL1), miR-29 prevented HuR from binding to the A20 3'UTR and recruiting the RNA degradation complex RISC (RNA-induced silencing complex), suggesting that miR-29 can act as a decoy for HuR, thus protecting A20 transcripts. Decreased miR-29 and A20 abundance in sarcomas correlated with increased activity of NF-κB and decreased expression of genes associated with differentiation. Together, the findings reveal a unique role of miR-29 and suggest that its absence may contribute to sarcoma tumorigenesis.