Regulation of FOXO1 by TAK1-Nemo-like kinase pathway

Atypical MAPKs in cancer

Impaired kinase signalling leads to various diseases, including cancer. At the same time, kinases make up the majority of the druggable genome and targeting kinase activity has proven to be a successful first-line therapy for many cancers. Among the best-studied kinases are the mitogen-activated protein kinases (MAPKs), which regulate cell proliferation, differentiation, motility, and survival. However, the MAPK family also contains the atypical members ERK3 (MAPK6), ERK4 (MAPK4), ERK7/ERK8 (MAPK15), and NLK that are functionally and structurally different from their conventional family members and have long been neglected. Nevertheless, in recent years, important roles in carcinogenesis, actin cytoskeleton regulation and the immune system have been discovered, underlining the physiological importance of atypical MAPKs and the need to better understand their functions. This review highlights the distinctive features of the atypical MAPKs and summarizes the evidence on their regulation, physiological roles, and potential targeting strategies for cancer therapies.

Nemo-like kinase blocks myeloid differentiation by targeting tumor suppressor C/EBPα in AML

CCAAT/enhancer-binding protein α (C/EBPα), a key myeloid transcription factor, drives myeloid differentiation from blast cells by regulating the expression of granulocyte colony stimulating factor receptor and C/EBPε as required for promoting granulocyte differentiation. Here, we show that serine/threonine-protein kinase NLK, also known as Nemo-like kinase, physically associates with C/EBPα and phosphorylates it at multiple sites, including Ser21, Thr226, Thr230 and S234, leading to its ubiquitin-mediated degradation. Individual phospho-point mutants of C/EBPα could be phosphorylated by NLK, but a mutant with all phosphorylatable residues replaced by alanine resisted phosphorylation and degradation by NLK, as did the single point mutants. Furthermore, although ectopic expression of NLK enhanced phosphorylation of C/EBPα levels, it markedly inhibited total C/EBPα protein levels. Conversely, NLK depletion inhibited endogenous C/EBPα phosphorylation but enhanced its total protein levels in several acute myeloid leukemia (AML) cell lines and in peripheral blood mononuclear cells isolated from number of AML patient samples. Importantly, NLK depletion in peripheral blood mononuclear cells from primary AML patients not only restored C/EBPα protein levels, but also induced myeloid differentiation, suggesting that NLK could be therapeutically targeted to restore C/EBPα to resolve differentiation arrest in AML.

Activation of nemo-like kinase in diamond blackfan anemia suppresses early erythropoiesis by preventing mitochondrial biogenesis

Diamond Blackfan Anemia (DBA) is a rare macrocytic red blood cell aplasia that usually presents within the first year of life. The vast majority of patients carry a mutation in one of approximately 20 genes that results in ribosomal insufficiency with the most significant clinical manifestations being anemia and a predisposition to cancers. Nemo-like Kinase (NLK) is hyperactivated in the erythroid progenitors of DBA patients and inhibition of this kinase improves erythropoiesis, but how NLK contributes to the pathogenesis of the disease is unknown. Here we report that activated NLK suppresses the critical upregulation of mitochondrial biogenesis required in early erythropoiesis. During normal erythropoiesis, mTORC1 facilitates the translational upregulation of Transcription factor A, mitochondrial (TFAM), and Prohibin 2 (PHB2) to increase mitochondrial biogenesis. In our models of DBA, active NLK phosphorylates the regulatory component of mTORC1, thereby suppressing mTORC1 activity and preventing mTORC1-mediated TFAM and PHB2 upregulation and subsequent mitochondrial biogenesis. Improvement of erythropoiesis that accompanies NLK inhibition is negated when TFAM and PHB2 upregulation is prevented. These data demonstrate that a significant contribution of NLK on the pathogenesis of DBA is through loss of mitochondrial biogenesis.

Unravelling the therapeutic potential of forkhead box proteins in breast cancer: An update (Review)

Breast cancer, a prominent cause of mortality among women, develops from abnormal growth of breast tissue, thereby rendering it one of the most commonly detected cancers in the female population. Although numerous treatment strategies are available for breast cancer, discordance in terms of effective treatment and response still exists. Recently, the potential of signaling pathways and transcription factors has gained substantial attention in the cancer community; therefore, understanding their role will assist researchers in comprehending the onset and advancement of breast cancer. Forkhead box (FOX) proteins, which are important transcription factors, are considered crucial regulators of various cellular activities, including cell division and proliferation. The present study explored several subclasses of FOX proteins and their possible role in breast carcinogenesis, followed by the interaction between microRNA (miRNA) and FOX proteins. This interaction is implicated in promoting cell infiltration into surrounding tissues, ultimately leading to metastasis. The various roles that FOX proteins play in breast cancer development, their intricate relationships with miRNA, and their involvement in therapeutic resistance highlight the complexity of breast cancer dynamics. Therefore, recognizing the progress and challenges in current treatments is crucial because, despite advancements, persistent disparities in treatment effectiveness underscore the need for ongoing research, with future studies emphasizing the necessity for targeted strategies that account for the multifaceted aspects of breast cancer.

Mechanistic regulation of FOXO transcription factors in the nucleus

FOXO proteins represent evolutionarily conserved transcription factors (TFs) that play critical roles in responding to various physiological signals or pathological stimuli, either through transcription-dependent or -independent mechanisms. Dysfunction of these proteins have been implicated in numerous diseases, including cancer. Although the regulation of FOXO TFs shuttling between the cytoplasm and the nucleus has been extensively studied and reviewed, there's still a lack of a comprehensive review focusing on the intricate interactions between FOXO, DNA, and cofactors in the regulation of gene expression. In this review, we aim to summarize recent advances and provide a detailed understanding of the mechanism underlying FOXO proteins binding to target DNA. Additionally, we will discuss the challenges associated with pharmacological approaches in modulating FOXO function, and explore the dynamic association between TF, DNA, and RNA on chromatin. This review will contribute to a better understanding of mechanistic regulations of eukaryotic TFs within the nucleus.

A kinome screen reveals that Nemo-like kinase is a key suppressor of hepatic gluconeogenesis

Antihyperglycemic therapy is an important priority for the treatment of type 2 diabetes (T2D). Excessive hepatic glucose production (HGP) is a major cause of fasting hyperglycemia. Therefore, a better understanding of its regulation would be important to develop effective antihyperglycemic therapies. Using a gluconeogenesis-targeted kinome screening approach combined with transcriptome analyses, we uncovered Nemo-like kinase (NLK) as a potent suppressor of HGP. Mechanistically, NLK phosphorylates and promotes nuclear export of CRTC2 and FOXO1, two key regulators of hepatic gluconeogenesis, resulting in the proteasome-dependent degradation of the former and the inhibition of the self-transcriptional activity and expression of the latter. Importantly, the expression of NLK is downregulated in the liver of individuals with diabetes and in diabetic rodent models and restoring NLK expression in the mouse model ameliorates hyperglycemia. Therefore, our findings uncover NLK as a critical player in the gluconeogenic regulatory network and as a potential therapeutic target for T2D.

Forkhead Box Protein O1: Functional Diversity and Post-Translational Modification, a New Therapeutic Target?

Forkhead box protein O1 (FoXO1) is a transcription factor involved in the regulation of a wide variety of physiological process including glucose metabolism, lipogenesis, bone mass, apoptosis, and autophagy. FoXO1 dysfunction is involved in the pathophysiology of various diseases including metabolic diseases, atherosclerosis, and tumors. FoXO1 activity is regulated in response to different physiological or pathogenic conditions by changes in protein expression and post-translational modifications. Various modifications cooperate to regulate FoXO1 activity and FoXO1 target gene transcription. In this review, we summarize how different post-translational modifications regulate FoXO1 physiological function, which may provide new insights for drug design and development.

Adenosine A2A receptor signaling promotes FoxO associated autophagy in chondrocytes

Autophagy, a homeostatic pathway upregulated during cellular stress, is decreased in osteoarthritic chondrocytes and this reduction in autophagy is thought to contribute to the development and progression of osteoarthritis (OA). The adenosine A2A receptor (A2AR) is a potent anti-inflammatory receptor and deficiency of this receptor leads to the development of OA in mice. Moreover, treatment using liposomally conjugated adenosine or a specific A2AR agonist improved joint scores significantly in both rats with post-traumatic OA (PTOA) and mice subjected to a high fat diet obesity induced OA. Importantly, A2AR ligation is beneficial for mitochondrial health and metabolism in vitro in primary and the TC28a2 human cell line. An additional set of metabolic, stress-responsive, and homeostatic mediators include the Forkhead box O transcription factors (FoxOs). Data has shown that mouse FoxO knockouts develop early OA with reduced cartilage autophagy, indicating that FoxO-induced homeostasis is important for articular cartilage. Given the apparent similarities between A2AR and FoxO signaling, we tested the hypothesis that A2AR stimulation improves cartilage function through activation of the FoxO proteins leading to increased autophagy in chondrocytes. We analyzed the signaling pathway in the human TC28a2 cell line and corroborated these findings in vivo in a metabolically relevant obesity-induced OA mouse model. We found that A2AR stimulation increases activation and nuclear localization of FoxO1 and FoxO3, promotes an increase in autophagic flux, improves metabolic function in chondrocytes, and reduces markers of apoptosis in vitro and reduced apoptosis by TUNEL assay in vivo. A2AR ligation additionally enhances in vivo activation of FoxO1 and FoxO3 with evidence of enhanced autophagic flux upon injection of the liposome-associated A2AR agonist in a mouse obesity-induced OA model. These findings offer further evidence that A2AR may be an excellent target for promoting chondrocyte and cartilage homeostasis.

Persulfidation of transcription factor FOXO1 at cysteine 457: A novel mechanism by which H2S inhibits vascular smooth muscle cell proliferation

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FOXO1 is involved in the inhibitory effect of H₂S on vascular smooth muscle cell proliferation.

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H₂S inhibits vascular smooth muscle cell proliferation by maintaining FOXO1 activity.

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H₂S preserves FOXO1 activity by persulfidation.

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H₂S persulfidates FOXO1 at Cys457 and subsequently prevents FOXO1 phosphorylation at Ser256.

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The results provide new ideas for therapeutic strategies for anti-vascular remodeling.

Introduction

The proliferation of vascular smooth muscle cells (VSMCs) is an important physiological and pathological basis for many cardiovascular diseases. Endogenous hydrogen sulfide (H₂S), the third gasotransmitter, is found to preserve vascular structure by inhibiting VSMC proliferation. However, the mechanism by which H₂S suppresses VSMC proliferation has not been fully clear.

Objectives

This study aimed to explore whether H₂S persulfidates the transcription factor FOXO1 to inhibit VSMC proliferation.

Methods

After the proliferation of VSMC A7r5 cells was induced by endothelin-1 (ET-1), FOXO1 phosphorylation and proliferating cell nuclear antigen (PCNA) expression were detected by Western blotting, the degree of FOXO1 nuclear exclusion and PCNA fluorescent signals in the nucleus were detected by immunofluorescence, and the persulfidation of FOXO1 was measured through a biotin switch assay.

Results

The results showed that ET-1 stimulation increased cell proliferation, FOXO1 phosphorylation and FOXO1 nuclear exclusion to the cytoplasm in the cells. However, pretreatment with NaHS, an H₂S donor, successfully abolished the ET-1-induced increases in the VSMC proliferation, FOXO1 phosphorylation, and FOXO1 nuclear exclusion to the cytoplasm. Mechanistically, H₂S persulfidated the FOXO1 protein in A7r5 and 293T cells, and the thiol reductant DTT reversed this effect. Furthermore, the C457S mutation of FOXO1 abolished the H₂S-induced persulfidation of FOXO1 in the cells and the subsequent inhibitory effects on FOXO1 phosphorylation at Ser256, FOXO1 nuclear exclusion to the cytoplasm and cell proliferation.

Conclusion

Thus, our findings demonstrated that H₂S might inhibit VSMC proliferation by persulfidating FOXO1 at Cys457 and subsequently preventing FOXO1 phosphorylation at Ser256.

FOXO transcription factor family in cancer and metastasis

Forkhead box O (FOXO) transcription factors regulate diverse biological processes, affecting development, metabolism, stem cell maintenance and longevity. They have also been increasingly recognised as tumour suppressors through their ability to regulate genes essential for cell proliferation, cell death, senescence, angiogenesis, cell migration and metastasis. Mechanistically, FOXO proteins serve as key connection points to allow diverse proliferative, nutrient and stress signals to converge and integrate with distinct gene networks to control cell fate, metabolism and cancer development. In consequence, deregulation of FOXO expression and function can promote genetic disorders, metabolic diseases, deregulated ageing and cancer. Metastasis is the process by which cancer cells spread from the primary tumour often via the bloodstream or the lymphatic system and is the major cause of cancer death. The regulation and deregulation of FOXO transcription factors occur predominantly at the post-transcriptional and post-translational levels mediated by regulatory non-coding RNAs, their interactions with other protein partners and co-factors and a combination of post-translational modifications (PTMs), including phosphorylation, acetylation, methylation and ubiquitination. This review discusses the role and regulation of FOXO proteins in tumour initiation and progression, with a particular emphasis on cancer metastasis. An understanding of how signalling networks integrate with the FOXO transcription factors to modulate their developmental, metabolic and tumour-suppressive functions in normal tissues and in cancer will offer a new perspective on tumorigenesis and metastasis, and open up therapeutic opportunities for malignant diseases.

Strategies to Enhance Logic Modeling-Based Cell Line-Specific Drug Synergy Prediction

Discrete dynamical modeling shows promise in prioritizing drug combinations for screening efforts by reducing the experimental workload inherent to the vast numbers of possible drug combinations. We have investigated approaches to predict combination responses across different cancer cell lines using logic models generated from one generic prior-knowledge network representing 144 nodes covering major cancer signaling pathways. Cell-line specific models were configured to agree with baseline activity data from each unperturbed cell line. Testing against experimental data demonstrated a high number of true positive and true negative predictions, including also cell-specific responses. We demonstrate the possible enhancement of predictive capability of models by curation of literature knowledge further detailing subtle biologically founded signaling mechanisms in the model topology. In silico model analysis pinpointed a subset of network nodes highly influencing model predictions. Our results indicate that the performance of logic models can be improved by focusing on high-influence node protein activity data for model configuration and that these nodes accommodate high information flow in the regulatory network.

Diamond Blackfan anemia is mediated by hyperactive Nemo-like kinase

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome associated with ribosomal gene mutations that lead to ribosomal insufficiency. DBA is characterized by anemia, congenital anomalies, and cancer predisposition. Treatment for DBA is associated with significant morbidity. Here, we report the identification of Nemo-like kinase (NLK) as a potential target for DBA therapy. To identify new DBA targets, we screen for small molecules that increase erythroid expansion in mouse models of DBA. This screen identified a compound that inhibits NLK. Chemical and genetic inhibition of NLK increases erythroid expansion in mouse and human progenitors, including bone marrow cells from DBA patients. In DBA models and patient samples, aberrant NLK activation is initiated at the Megakaryocyte/Erythroid Progenitor (MEP) stage of differentiation and is not observed in non-erythroid hematopoietic lineages or healthy erythroblasts. We propose that NLK mediates aberrant erythropoiesis in DBA and is a potential target for therapy.

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome that is associated with anemia. Here, the authors examine the role of Nemo-like kinase (NLK) in erythroid cells in the pathogenesis of DBA and as a potential target for therapy.

Knockdown of Nemo‑like kinase promotes metastasis in non‑small‑cell lung cancer

The evolutionarily conserved serine/threonine kinase Nemo-like kinase (NLK) serves an important role in cell proliferation, migration, invasion and apoptosis by regulating transcription factors among various cancers. In the present study, the function of NLK in human non-small cell lung cancer (NSCLC) was investigated. Immunohistochemical analysis and western blotting demonstrated that NLK expression was significantly reduced in NSCLC tissues compared with corresponding peritumoral tissues. Statistical analysis revealed that decreased NLK expression was associated with the presence of primary tumors, tumor node metastasis (TNM) staging, differentiation, lymph node metastasis, and E-cadherin and vimentin expression. Univariate analysis indicated that NLK expression, differentiation, lymph node metastasis, TNM stage, and E-cadherin and vimentin expression affected the prognosis of NSCLC. Cox regression analyses revealed NLK expression and TNM as independent factors that affected prognosis. Kaplan-Meier survival analysis revealed that patients with NSCLC and low NLK expression had relatively shorter durations of overall survival. In vitro, NLK overexpression inhibited A549 ncell migration and invasion as determined by wound healing and Transwell migration assays, respectively. Additionally, immunofluorescence staining indicated that downregulation of NLK expression could induce epithelial-mesenchymal transition in NSCLC. NLK knockdown significantly decreased the expression of the epithelial marker E-cadherin, and markedly increased that of β-catenin and the mesenchymal marker vimentin. Furthermore, NLK was reported to directly interact with β-catenin as determined by a co-immunoprecipitation assay. Collectively, the results of the present study indicated that decreased NLK expression could promote tumor metastasis in NSCLC.

Phosphorylation of MAVS/VISA by Nemo-like kinase (NLK) for degradation regulates the antiviral innate immune response

MAVS is essential for antiviral immunity, but the molecular mechanisms responsible for its tight regulation remain poorly understood. Here, we show that NLK inhibits the antiviral immune response during viral infection by targeting MAVS for degradation. NLK depletion promotes virus-induced antiviral cytokine production and decreases viral replication, which is potently rescued by the reintroduction of NLK. Moreover, the depletion of NLK promotes antiviral effects and increases the survival times of mice after infection with VSV. NLK interacts with and phosphorylates MAVS at multiple sites on mitochondria or peroxisomes, thereby inducing the degradation of MAVS and subsequent inactivation of IRF3. Most importantly, a peptide derived from MAVS promotes viral-induced IFN-β production and antagonizes viral replication in vitro and in vivo. These findings provide direct insights into the molecular mechanisms by which phosphorylation of MAVS regulates its degradation and influences its activation and identify an important peptide target for propagating antiviral responses.

Streptococcus gordonii programs epithelial cells to resist ZEB2 induction by Porphyromonas gingivalis

The polymicrobial microbiome of the oral cavity is a direct precursor of periodontal diseases, and changes in microhabitat or shifts in microbial composition may also be linked to oral squamous cell carcinoma. Dysbiotic oral epithelial responses provoked by individual organisms, and which underlie these diseases, are widely studied. However, organisms may influence community partner species through manipulation of epithelial cell responses, an aspect of the host microbiome interaction that is poorly understood. We report here that Porphyromonas gingivalis, a keystone periodontal pathogen, can up-regulate expression of ZEB2, a transcription factor which controls epithelial-mesenchymal transition and inflammatory responses. ZEB2 regulation by P. gingivalis was mediated through pathways involving β-catenin and FOXO1. Among the community partners of P. gingivalis, Streptococcus gordonii was capable of antagonizing ZEB2 expression. Mechanistically, S. gordonii suppressed FOXO1 by activating the TAK1-NLK negative regulatory pathway, even in the presence of P. gingivalis Collectively, these results establish S. gordonii as homeostatic commensal, capable of mitigating the activity of a more pathogenic organism through modulation of host signaling.

Regulation of FOXO Factors in Mammalian Cells

Forkhead box O (FOXO) transcription factors are central regulators of cellular homeostasis. FOXOs respond to a wide range of external stimuli, including growth factor signaling, oxidative stress, genotoxic stress, and nutrient deprivation. These signaling inputs regulate FOXOs through a number of posttranslational modifications, including phosphorylation, acetylation, ubiquitination, and methylation. Covalent modifications can affect localization, DNA binding, and interactions with other cofactors in the cell. FOXOs integrate the various modifications to regulate cell type-specific gene expression programs that are essential for metabolic homeostasis, redox balance, and the stress response. Together, these functions are critical for coordinating a response to environmental fluctuations in order to maintain cellular homeostasis during development and to support healthy aging.

In vitro NLK Kinase Assay

This protocol provides step by step instructions to perform an in vitro kinase assay for nemo-like kinase. In addition, this protocol also describes an efficient method using mild lysis buffer for expression and purification of Glutathione S-transferase (GST) fusion proteins.

The protein kinase MBK-1 contributes to lifespan extension in daf-2 mutant and germline-deficient Caenorhabditis elegans

In Caenorhabditis elegans, reduction of insulin/IGF-1 like signaling and loss of germline stem cells both increase lifespan by activating the conserved transcription factor DAF-16 (FOXO). While the mechanisms that regulate DAF-16 nuclear localization in response to insulin/IGF-1 like signaling are well characterized, the molecular pathways that act in parallel to regulate DAF-16 transcriptional activity, and the pathways that couple DAF-16 activity to germline status, are not fully understood at present. Here, we report that inactivation of MBK-1, the C. elegans ortholog of the human FOXO1-kinase DYRK1A substantially shortens the prolonged lifespan of daf-2 and glp-1 mutant animals while decreasing wild-type lifespan to a lesser extent. On the other hand, lifespan-reduction by mutation of the MBK-1-related kinase HPK-1 was not preferential for long-lived mutants. Interestingly, mbk-1 loss still allowed for DAF-16 nuclear accumulation but reduced expression of certain DAF-16 target genes in germline-less, but not in daf-2 mutant animals. These findings indicate that mbk-1 and daf-16 functionally interact in the germline- but not in the daf-2 pathway. Together, our data suggest mbk-1 as a novel regulator of C. elegans longevity upon both, germline ablation and DAF-2 inhibition, and provide evidence for mbk-1 regulating DAF-16 activity in germline-deficient animals.

Phosphorylation by NLK inhibits YAP-14-3-3-interactions and induces its nuclear localization

Hippo signaling controls organ size by regulating cell proliferation and apoptosis. Yes-associated protein (YAP) is a key downstream effector of Hippo signaling, and LATS-mediated phosphorylation of YAP at Ser127 inhibits its nuclear localization and transcriptional activity. Here, we report that Nemo-like kinase (NLK) phosphorylates YAP at Ser128 both in vitro and in vivo, which blocks interaction with 14-3-3 and enhances its nuclear localization. Depletion of NLK increases YAP phosphorylation at Ser127 and reduces YAP-mediated reporter activity. These results suggest that YAP phosphorylation at Ser128 and at Ser127 may be mutually exclusive. We also find that with the increase in cell density, nuclear localization and the level of NLK are reduced, resulting in reduction in YAP phosphorylation at Ser128. Furthermore, knockdown of Nemo (the Drosophila NLK) in fruit fly wing imaginal discs results in reduced expression of the Yorkie (the Drosophila YAP) target genes expanded and DIAP1, while Nemo overexpression reciprocally increased the expression. Overall, our data suggest that NLK/Nemo acts as an endogenous regulator of Hippo signaling by controlling nuclear localization and activity of YAP/Yorkie.

NLK-mediated phosphorylation of HDAC1 negatively regulates Wnt signaling

Primary embryonic fibroblast cells isolated from NLK-deficient mice proliferate faster and have a shorter cell cycle than wild-type cells. Nemo-like kinase and HDAC1 together negatively regulate Wnt signaling via Tcf/Lef transcription repression and prevent aberrant proliferation of fibroblast cells.

The Wnt signaling pathway is essential in regulating various cellular processes. Different mechanisms of inhibition for Wnt signaling have been proposed. Besides β-catenin degradation through the proteasome, nemo-like kinase (NLK) is another molecule that is known to negatively regulate Wnt signaling. However, the mechanism by which NLK mediates the inhibition of Wnt signaling was not known. In the present study, we used primary embryonic fibroblast cells isolated from NLK-deficient mice and showed that these cells proliferate faster and have a shorter cell cycle than wild-type cells. In NLK-knockout cells, we observed sustained interaction between Lef1 and β-catenin, leading to elevated luciferase reporter of β-catenin/Lef1–mediated transcriptional activation. The mechanism for the reduced β-catenin/Lef1 promoter activation was explained by phosphorylation of HDAC1 at serine 421 via NLK. The phosphorylation of HDAC1 was achieved only in the presence of wild-type NLK because a catalytically inactive mutant of NLK was unable to phosphorylate HDAC1 and reduced the luciferase reporter of β-catenin/Lef1–mediated transcriptional activation. This result suggests that NLK and HDAC1 together negatively regulate Wnt signaling, which is vital in preventing aberrant proliferation of nontransformed primary fibroblast cells.

Nemo-Like Kinase (NLK) Is a Pathological Signaling Effector in the Mouse Heart

Nemo-like kinase (NLK) is an evolutionary conserved serine/threonine protein kinase implicated in development, proliferation and apoptosis regulation. Here we identified NLK as a gene product induced in the hearts of mice subjected to pressure overload or myocardial infarction injury, suggesting a potential regulatory role with pathological stimulation to this organ. To examine the potential functional consequences of increased NLK levels, cardiac-specific transgenic mice with inducible expression of this gene product were generated, as well as cardiac-specific Nlk gene-deleted mice. NLK transgenic mice demonstrated baseline cardiac hypertrophy, dilation, interstitial fibrosis, apoptosis and progression towards heart failure in response to two surgery-induced cardiac disease models. In contrast, cardiac-specific deletion of Nlk from the heart, achieved by crossing a Nlk-loxP allele containing mouse with either a mouse containing a β-myosin heavy chain promoter driven Cre transgene or a tamoxifen inducible α-myosin heavy chain promoter containing transgene driving a MerCreMer cDNA, protected the mice from cardiac dysfunction following pathological stimuli. Mechanistically, NLK interacted with multiple proteins including the transcription factor Stat1, which was significantly increased in the hearts of NLK transgenic mice. These results indicate that NLK is a pathological effector in the heart.

NLK functions to maintain proliferation and stemness of NSCLC and is a target of metformin

Objective

Nemo-like kinase (NLK) is an evolutionarily conserved serine/threonine kinase that regulates the activity of a wide range of signal transduction pathways. Metformin, an oral antidiabetic drug, is used for cancer prevention. However, the significance and underlying mechanism of NLK and metformin in oncogenesis has not been fully elucidated. Here, we investigate a novel role of NLK and metformin in human non-small cell lung cancer (NSCLC).

Materials and methods

NLK expression was analyzed in 121 NSCLCs and 92 normal lung tissue samples from benign pulmonary disease. Lentivirus vectors with NLK-shRNA were used to examine the effect of NLK on cell proliferation and tumorigenesis in vitro. Then, tumor xenograft mouse models revealed that NLK knockdown cells had a reduced ability for tumor formation compared with the control group in vivo. Multiple cell cycle regulator expression patterns induced by NLK silencing were examined by western blots in A549 cells. We also employed metformin to study its anti-cancer effects and mechanisms. Cancer stem cell property was checked by tumor sphere formation and markers including CD133, Nanog, c-Myc, and TLF4.

Results

Immunohistochemical (IHC) analysis revealed that NLK expression was up-regulated in NSCLC cases (p < 0.001) and correlated with tumor T stage (p < 0.05). Silencing of NLK suppressed cell proliferation and tumorigenicity significantly in vitro and in vivo, which might be modulated by JUN family proteins. Furthermore, metformin selectively inhibits NLK expression and proliferation in NSCLC cells, but not immortalized noncancerous lung bronchial epithelial cells. In addition, both NLK knockdown and metformin treatment reduced the tumor sphere formation capacity and percentage of CD133+ cells. Accordingly, the expression level of stem cell markers (Nanog, c-Myc, and TLF4) were decreased significantly.

Conclusion

NLK is critical for cancer cell cycle progression, and tumorigenesis in NSCLC, NLK knockdown, and metformin treatment inhibit cancer cell proliferation and stemness. Metformin inhibits NLK expression and might be a potential treatment strategy for NSCLC.

Discovery of Drug Synergies in Gastric Cancer Cells Predicted by Logical Modeling

Discovery of efficient anti-cancer drug combinations is a major challenge, since experimental testing of all possible combinations is clearly impossible. Recent efforts to computationally predict drug combination responses retain this experimental search space, as model definitions typically rely on extensive drug perturbation data. We developed a dynamical model representing a cell fate decision network in the AGS gastric cancer cell line, relying on background knowledge extracted from literature and databases. We defined a set of logical equations recapitulating AGS data observed in cells in their baseline proliferative state. Using the modeling software GINsim, model reduction and simulation compression techniques were applied to cope with the vast state space of large logical models and enable simulations of pairwise applications of specific signaling inhibitory chemical substances. Our simulations predicted synergistic growth inhibitory action of five combinations from a total of 21 possible pairs. Four of the predicted synergies were confirmed in AGS cell growth real-time assays, including known effects of combined MEK-AKT or MEK-PI3K inhibitions, along with novel synergistic effects of combined TAK1-AKT or TAK1-PI3K inhibitions. Our strategy reduces the dependence on a priori drug perturbation experimentation for well-characterized signaling networks, by demonstrating that a model predictive of combinatorial drug effects can be inferred from background knowledge on unperturbed and proliferating cancer cells. Our modeling approach can thus contribute to preclinical discovery of efficient anticancer drug combinations, and thereby to development of strategies to tailor treatment to individual cancer patients.

Redox regulation of FoxO transcription factors

Transcription factors of the forkhead box, class O (FoxO) family are important regulators of the cellular stress response and promote the cellular antioxidant defense. On one hand, FoxOs stimulate the transcription of genes coding for antioxidant proteins located in different subcellular compartments, such as in mitochondria (i.e. superoxide dismutase-2, peroxiredoxins 3 and 5) and peroxisomes (catalase), as well as for antioxidant proteins found extracellularly in plasma (e.g., selenoprotein P and ceruloplasmin). On the other hand, reactive oxygen species (ROS) as well as other stressful stimuli that elicit the formation of ROS, may modulate FoxO activity at multiple levels, including posttranslational modifications of FoxOs (such as phosphorylation and acetylation), interaction with coregulators, alterations in FoxO subcellular localization, protein synthesis and stability. Moreover, transcriptional and posttranscriptional control of the expression of genes coding for FoxOs is sensitive to ROS. Here, we review these aspects of FoxO biology focusing on redox regulation of FoxO signaling, and with emphasis on the interplay between ROS and FoxOs under various physiological and pathophysiological conditions. Of particular interest are the dual role played by FoxOs in cancer development and their key role in whole body nutrient homeostasis, modulating metabolic adaptations and/or disturbances in response to low vs. high nutrient intake. Examples discussed here include calorie restriction and starvation as well as adipogenesis, obesity and type 2 diabetes.

Stabilization of ATF5 by TAK1-Nemo-like kinase critically regulates the interleukin-1β-stimulated C/EBP signaling pathway

Interleukin-1β (IL-1β) is a key proinflammatory cytokine that initiates several signaling cascades, including those involving CCAAT/enhancer binding proteins (C/EBPs). The mechanism by which IL-1β propagates a signal that activates C/EBP has remained elusive. Nemo-like kinase (NLK) is a mitogen-activated protein kinase (MAPK)-like kinase associated with many pathways and phenotypes that are not yet well understood. Using a luciferase reporter screen, we found that IL-1β-induced C/EBP activation was positively regulated by NLK. Overexpression of NLK activated C/EBP and potentiated IL-1β-triggered C/EBP activation, whereas knockdown or knockout of NLK had the opposite effect. NLK interacted with activating transcription factor 5 (ATF5) and inhibited the proteasome-dependent degradation of ATF5 in a kinase-independent manner. Consistently, NLK deficiency resulted in decreased levels of ATF5. NLK cooperated with ATF5 to activate C/EBP, whereas NLK could not activate C/EBP upon knockdown of ATF5. Moreover, TAK1, a downstream effector of IL-1β that acts upstream of NLK, mimicked the ability of NLK to stabilize ATF5 and activate C/EBP. Thus, our findings reveal the TAK1-NLK pathway as a novel regulator of basal or IL-1β-triggered C/EBP activation though stabilization of ATF5.

Gene networks of fully connected triads with complete auto-activation enable multistability and stepwise stochastic transitions

Fully-connected triads (FCTs), such as the Oct4-Sox2-Nanog triad, have been implicated as recurring transcriptional motifs embedded within the regulatory networks that specify and maintain cellular states. To explore the possible connections between FCT topologies and cell fate determinations, we employed computational network screening to search all possible FCT topologies for multistability, a dynamic property that allows the rise of alternate regulatory states from the same transcriptional network. The search yielded a hierarchy of FCTs with various potentials for multistability, including several topologies capable of reaching eight distinct stable states. Our analyses suggested that complete auto-activation is an effective indicator for multistability, and, when gene expression noise was incorporated into the model, the networks were able to transit multiple states spontaneously. Different levels of stochasticity were found to either induce or disrupt random state transitioning with some transitions requiring layovers at one or more intermediate states. Using this framework we simulated a simplified model of induced pluripotency by including constitutive overexpression terms. The corresponding FCT showed random state transitioning from a terminal state to the pluripotent state, with the temporal distribution of this transition matching published experimental data. This work establishes a potential theoretical framework for understanding cell fate determinations by connecting conserved regulatory modules with network dynamics. Our results could also be employed experimentally, using established developmental transcription factors as seeds, to locate cell lineage specification networks by using auto-activation as a cipher.

Association of nuclear-localized Nemo-like kinase with heat-shock protein 27 inhibits apoptosis in human breast cancer cells

Nemo-like kinase (NLK), a proline-directed serine/threonine kinase regulated by phosphorylation, can be localized in the cytosol or in the nucleus. Whether the localization of NLK can affect cell survival or cell apoptosis is yet to be disclosed. In the present study we found that NLK was mainly localized in the nuclei of breast cancer cells, in contrast to a cytosolic localization in non-cancerous breast epithelial cells. The nuclear localization of NLK was mediated through direct interaction with Heat shock protein 27 (HSP27) which further protected cancer cells from apoptosis. The present study provides evidence of a novel mechanism by which HSP27 recognizes NLK in the breast cancer cells and prevents NLK-mediated cell apoptosis.

Forkhead box(O) in control of reactive oxygen species and genomic stability to ensure healthy lifespan

SIGNIFICANCE

Transcription factors of the Forkhead box O class (FOXOs) are associated with lifespan and play a role in age-related diseases. FOXOs, therefore, serve as a paradigm for developing an understanding as to how age-related diseases, such as cancer and diabetes interconnect with lifespan. Understanding the regulatory inputs on FOXO may reveal how changes in these regulatory signaling pathways affect disease and lifespan.

RECENT ADVANCES

Numerous regulators of FOXO have now been described and a clear and evolutionary conserved role has emerged for phosphoinositide-3 kinase/protein kinase B (also known as c-Akt or AKT) signaling and c-jun N-terminal kinase signaling. Analysis of FOXO function in the context of these signaling pathways has shown the importance of FOXO-mediated transcriptional regulation on cell cycle progression and other cell fates, such as cell metabolism, stress resistance, and apoptosis in mediating disease and lifespan.

CRITICAL ISSUES

Persistent DNA damage is also tightly linked to disease and aging; yet, data on a possible link between DNA damage and FOXO have been limited. Here, we discuss possible connections between FOXO and the DNA damage response in the context of the broader role of connecting lifespan and disease.

FUTURE DIRECTIONS

Understanding the role of lifespan in diseases onset may provide unique and generic possibilities to intervene in disease processes to ensure a healthy lifespan.

The mERG1a channel modulates skeletal muscle MuRF1, but not MAFbx, expression

INTRODUCTION

We investigated the mechanism by which the MERG1a K+ channel increases ubiquitin proteasome proteolysis (UPP).

METHODS

Hindlimb suspension and electro-transfer of Merg1a cDNA into mouse gastrocnemius muscles induced atrophy.

RESULTS

Atrophic gastrocnemius muscles of hindlimb-suspended mice express Merg1a, Murf1, and Mafbx genes. Electrotransfer of Merg1a significantly decreases muscle fiber size (12.6%) and increases UPP E3 ligase Murf1 mRNA (2.1-fold) and protein (23.7%), but does not affect Mafbx E3 ligase expression. Neither Merg1a-induced decreased fiber size nor Merg1a-induced increased Murf1 expression is curtailed significantly by coexpression of inactive HR-Foxo3a, a gene encoding a transcription factor known to induce Mafbx expression.

CONCLUSIONS

The MERG1a K+ channel significantly increases expression of Murf1, but not Mafbx. We explored this expression pattern by expressing inactive Foxo3a and showing that it is not involved in MERG1a-mediated expression of Murf1. These findings suggest that MERG1a may not modulate Murf1 expression through the AKT/FOXO pathway.

Nemo-like kinase associated with proliferation and apoptosis by c-Myb degradation in breast cancer

Nemo-like kinase (NLK), a mediator of the Wnt signaling pathway, binds directly to c-Myb, leading to its phosphorylation, ubiquitination and proteasome-dependent degradation. NLK was significantly downregulated in the breast cancer tissues compared to corresponding normal tissues. NLK expression was negatively correlated with c-Myb expression. NLK suppressed proliferation, induced apoptosis and mediated c-Myb degradation in MCF-7 cells via a mechanism that seems to involve c-myc and Bcl2. These findings might provide a novel target for therapeutic intervention in patients with breast cancer.

NLK is a novel therapeutic target for PTEN deficient tumour cells

PTEN (Phosphatase and tensin homolog) is a tumour suppressor gene commonly defective in human cancer, and is thus a potentially important therapeutic target. Targeting tumour suppressor loss-of-function is possible by exploiting the genetic concept of synthetic lethality (SL). By combining the use of isogenic models of PTEN deficiency with high-throughput RNA interference (RNAi) screening, we have identified Nemo-Like Kinase (NLK) inhibition as being synthetically lethal with PTEN deficiency. This SL is likely mediated by the transcription factor FOXO1 (Forkhead box O1), an NLK substrate, as the selectivity of NLK gene silencing for PTEN deficient cells can be reversed by FOXO1 knockdown. In addition, we provide evidence that PTEN defective cells targeted by NLK gene depletion undergo senescence, suggesting that NLK function is critical for the continued proliferation of PTEN deficient cells. Taken together, these data provide new insight into the potential of targeting of NLK to treat a range of tumourigenic conditions characterised by PTEN deficiency.

TAK1 inhibition for treatment of cerebral ischemia

TGFβ-activated kinase 1 (TAK1), a MAP3 kinase, is involved in at least five signaling cascades that modulate ischemic brain damage. Inhibition of TAK1 may therefore be an efficient way to interfere with multiple mechanisms in ischemic stroke. Indeed, a recent publication in Experimental Neurology confirmed that TAK1 inhibition by 5Z-7-oxozeaenol is neuroprotective. The beneficial effect of 5Z-7-oxozeaenol was associated with a reduced activation of Jun kinase that leads to inflammation and apoptosis. Recently, other TAK1 inhibitors were developed suggesting that TAK1 may prove as an efficient therapeutic target for neurodegenerative diseases if safety issues are not limiting.

Nemo-like kinase, a multifaceted cell signaling regulator

Nemo-like kinase (NLK) is an evolutionarily conserved MAP kinase-related kinase. Although NLK was originally identified as a Drosophila gene affecting cell movement during eye development, recent studies show that NLK also contributes to cell proliferation, differentiation, and morphological changes during early embryogenesis and nervous system development in vertebrates. In addition, NLK has been reported to be involved in the development of several human cancers. NLK is able to play a role in multiple processes due to its capacity to regulate a diverse array of signaling pathways, including the Wnt/β-catenin, Activin, IL-6, and Notch signaling pathways. Although the molecular mechanisms that regulate NLK activity remain unclear, our recent research has presented a new model for NLK activation. Here, we summarize the current understanding of the function and regulation of NLK and discuss the aspects of NLK regulation that remain to be resolved.

Dual functions of DP1 promote biphasic Wnt-on and Wnt-off states during anteroposterior neural patterning

DP1, a dimerization partner protein of the transcription factor E2F, is known to inhibit Wnt/β-catenin signalling along with E2F, although the function of DP1 itself was not well characterized. Here, we present a novel dual regulatory mechanism of Wnt/β-catenin signalling by DP1 independent from E2F. DP1 negatively regulates Wnt/β-catenin signalling by inhibiting Dvl-Axin interaction and by enhancing poly-ubiquitination of β-catenin. In contrast, DP1 positively modulates the signalling upon Wnt stimulation, via increasing cytosolic β-catenin and antagonizing the kinase activity of NLK. In Xenopus embryos, DP1 exerts both positive and negative roles in Wnt/β-catenin signalling during anteroposterior neural patterning. From subcellular localization analyses, we suggest that the dual roles of DP1 in Wnt/β-catenin signalling are endowed by differential nucleocytoplasmic localizations. We propose that these dual functions of DP1 can promote and stabilize biphasic Wnt-on and Wnt-off states in response to a gradual gradient of Wnt/β-catenin signalling to determine differential cell fates.

RNAi screening identifies TAK1 as a potential target for the enhanced efficacy of topoisomerase inhibitors

In an effort to develop strategies that improve the efficacy of existing anticancer agents, we have conducted a siRNA-based RNAi screen to identify genes that, when targeted by siRNA, improve the activity of the topoisomerase I (Top1) poison camptothecin (CPT). Screening was conducted using a set of siRNAs corresponding to over 400 apoptosisrelated genes in MDA-MB-231 breast cancer cells. During the course of these studies, we identified the silencing of MAP3K7 as a significant enhancer of CPT activity. Follow-up analysis of caspase activity and caspase-dependent phosphorylation of histone H2AX demonstrated that the silencing of MAP3K7 enhanced CPT-associated apoptosis. Silencing MAP3K7 also sensitized cells to additional compounds, including CPT clinical analogs. This activity was not restricted to MDA-MB-231 cells, as the silencing of MAP3K7 also sensitized the breast cancer cell line MDA-MB-468 and HCT-116 colon cancer cells. However, MAP3K7 silencing did not affect compound activity in the comparatively normal mammary epithelial cell line MCF10A, as well as some additional tumorigenic lines. MAP3K7 encodes the TAK1 kinase, an enzyme that is central to the regulation of many processes associated with the growth of cancer cells (e.g. NF- κB, JNK, and p38 signaling). An analysis of TAK1 signaling pathway members revealed that the silencing of TAB2 also sensitizes MDA-MB-231 and HCT-116 cells towards CPT. These findings may offer avenues towards lowering the effective doses of Top1 inhibitors in cancer cells and, in doing so, broaden their application.

Oxidative stress-dependent regulation of Forkhead box O4 activity by nemo-like kinase

Forkhead box O (FOXO) transcription factors are involved in various cellular processes, including cell proliferation, stress resistance, metabolism, and longevity. Regulation of FOXO transcriptional activity occurs mainly through a variety of post-translational modifications, including phosphorylation, acetylation, and ubiquitination. Here we describe nemo-like kinase (NLK) as a novel regulator of FOXOs. NLK binds to and phosphorylates FOXO1, FOXO3a, and FOXO4 on multiple residues. NLK acts as a negative regulator of FOXO transcriptional activity. For FOXO4 we show that NLK-mediated loss of FOXO4 activity co-occurs with inhibition of FOXO4 monoubiquitination. Previously, we have shown that oxidative stress-induced monoubiquitination of FOXO4 stimulates its transactivation, which leads to activation of an antioxidant defensive program. Conversely, NLK-dependent inhibition of FOXO4 activity can provide a means to downregulate this defensive program, when oxidative stress reaches a level beyond which repair is no longer feasible and cells need to undergo apoptosis.

Homodimerization of Nemo-like kinase is essential for activation and nuclear localization

NLK is an evolutionarily conserved protein kinase that phosphorylates several transcription factors. However, the molecular mechanisms that regulate NLK activity have been poorly understood. This study shows that homodimerization of NLK is required for its activation and nuclear localization.

Nemo-like kinase (NLK) is an evolutionarily conserved protein kinase that phosphorylates several transcription factors. However, the molecular mechanisms that regulate NLK activity have been poorly understood. Here we show that homodimerization of NLK is required for its activation and nuclear localization. Biochemical analysis revealed that NLK is activated through intermolecular autophosphorylation of NLK dimers at Thr-286. Mutation of NLK at Cys-425, which corresponds to the defect in the Caenorhabditis elegans NLK homologue lit-1, prevented NLK dimerization, rendering NLK defective in both nuclear localization and kinase activity. By contrast, the external addition of nerve growth factor, which has been previously identified as an NLK activator, induced dimerization and Thr-286 autophosphorylation of endogenous NLK proteins. In addition, both dimerization and Thr-286 phosphorylation of NLK were found to be essential for induction of neurite-like cellular processes by NLK. The present findings suggest that dimerization is an initial key event required for the functional activation of NLK.

Isolation of putative FOXO1 genomic elements using an improved in vitro technique to isolate genomic regulatory sequences

The regulation of gene expression drives many biological processes and alterations in normal regulation are integral in the development of the diseased state. Therefore, the ability to screen genomic DNA for direct targets of DNA binding proteins (DNA-BP) would provide valuable information about the mechanisms underlying these processes. At present chromatin immunoprecipitation (ChIP) and its variants are the primary methods for identifying regulatory elements. However, some DNA-BPs, such as the winged-helix transcription factor FOXO1, are difficult to ChIP thereby detracting from the use of this technique as a nonbiased screen to isolate regulatory sequences. In this report we use an improved in vitro method to Pull Out Regulatory Elements (PORE), which uses purified protein with a stable genomic library to isolate regulatory elements directly bound by a DNA-BP, to identify putative FOXO1 genomic regulatory sequences. We first validate this technique using two known DNA-BP (FOXO1 and Pax3) by demonstrating their ability to bind and amplify identified promoter elements when present in a genomic DNA context or when present in the context of our stable genomic library. Subsequent use of this technique with FOXO1 isolated regulatory elements associated with several genes known to be regulated in a FOXO1-dependent manner and multiple genes whose biological functions are consistent with the known biological functions of FOXO1 proving that the in vitro PORE is a valuable and easy to use alternative to ChIP for the isolation of genomic regulatory elements.

TAK1 suppresses a NEMO-dependent but NF-kappaB-independent pathway to liver cancer

The MAP3-kinase TGF-beta-activated kinase 1 (TAK1) critically modulates innate and adaptive immune responses and connects cytokine stimulation with activation of inflammatory signaling pathways. Here, we report that conditional ablation of TAK1 in liver parenchymal cells (hepatocytes and cholangiocytes) causes hepatocyte dysplasia and early-onset hepatocarcinogenesis, coinciding with biliary ductopenia and cholestasis. TAK1-mediated cancer suppression is exerted through activating NF-kappaB in response to tumor necrosis factor (TNF) and through preventing Caspase-3-dependent hepatocyte and cholangiocyte apoptosis. Moreover, TAK1 suppresses a procarcinogenic and pronecrotic pathway, which depends on NF-kappaB-independent functions of the I kappaB-kinase (IKK)-subunit NF-kappaB essential modulator (NEMO). Therefore, TAK1 serves as a gatekeeper for a protumorigenic, NF-kappaB-independent function of NEMO in parenchymal liver cells.