Discovery of potent and selective covalent inhibitors of JNK

Wnt Signaling Drives Prostate Cancer Bone Metastatic Tropism and Invasion

Wnt signaling has been implicated as a driver of prostate cancer-related osteoblast differentiation, and previous studies have linked modifications in Wnt function with the induction of tumor metastasis. A unique aspect of prostate cancer bone metastases in mouse models is their relative predilection to the hindlimb (femur) compared to the forelimb (humerus). Comparative gene expression profiling was performed within the humerus and femur from non-tumor-bearing mice to evaluate differences in the microenvironments of these locations. This revealed the relative overexpression of the Wnt signaling inhibitors WIF1 and SOST in the humerus compared to the femur, with increased WNT5A expression in femur bone marrow, suggesting a coordinated upregulation of Wnt signals within the femur compared to the humerus. Conditioned medium (CM) from bone marrow stromal cells (HS-5 cells) was used to mimic the bone marrow microenvironment, which strongly promoted prostate cancer cell invasion (3.3-fold increase in PC3 cells, P < .05; 7-fold increase in LNCaP cells, P < .05). WNT5A shRNA knockdown within the CM-producing HS-5 cells significantly decreased PC3 (56%, P < .05) and LNCaP (60%, P < .05) cell invasion. Similarly, preincubation of CM with WIF1 significantly blocked LNCaP cell invasion (40%, P < .05). shRNA-mediated knockdown of the Wnt receptors FZD4 and FZD8 also strongly inhibited tumor cell invasion (60% inhibition shFZD4, P < .05; 63% shFZD8, P < .05). Furthermore, small molecule inhibition of JNK, which is an important component of the noncanonical Wnt signaling pathway, significantly inhibited CM-mediated tumor invasion. Overall, this study reveals a role for Wnt signaling as a driver of prostate cancer bone metastatic tropism and invasion.

A post-transcriptional program of chemoresistance by AU-rich elements and TTP in quiescent leukemic cells

BACKGROUND

Quiescence (G0) is a transient, cell cycle-arrested state. By entering G0, cancer cells survive unfavorable conditions such as chemotherapy and cause relapse. While G0 cells have been studied at the transcriptome level, how post-transcriptional regulation contributes to their chemoresistance remains unknown.

RESULTS

We induce chemoresistant and G0 leukemic cells by serum starvation or chemotherapy treatment. To study post-transcriptional regulation in G0 leukemic cells, we systematically analyzed their transcriptome, translatome, and proteome. We find that our resistant G0 cells recapitulate gene expression profiles of in vivo chemoresistant leukemic and G0 models. In G0 cells, canonical translation initiation is inhibited; yet we find that inflammatory genes are highly translated, indicating alternative post-transcriptional regulation. Importantly, AU-rich elements (AREs) are significantly enriched in the upregulated G0 translatome and transcriptome. Mechanistically, we find the stress-responsive p38 MAPK-MK2 signaling pathway stabilizes ARE mRNAs by phosphorylation and inactivation of mRNA decay factor, Tristetraprolin (TTP) in G0. This permits expression of ARE mRNAs that promote chemoresistance. Conversely, inhibition of TTP phosphorylation by p38 MAPK inhibitors and non-phosphorylatable TTP mutant decreases ARE-bearing TNFα and DUSP1 mRNAs and sensitizes leukemic cells to chemotherapy. Furthermore, co-inhibiting p38 MAPK and TNFα prior to or along with chemotherapy substantially reduces chemoresistance in primary leukemic cells ex vivo and in vivo.

CONCLUSIONS

These studies uncover post-transcriptional regulation underlying chemoresistance in leukemia. Our data reveal the p38 MAPK-MK2-TTP axis as a key regulator of expression of ARE-bearing mRNAs that promote chemoresistance. By disrupting this pathway, we develop an effective combination therapy against chemosurvival.

Selective inhibitors for JNK signalling: a potential targeted therapy in cancer

c-Jun N-terminal kinase (JNK) signalling regulates both cancer cell apoptosis and survival. Emerging evidence show that JNK promoted tumour progression is involved in various cancers, that include human pancreatic-, lung-, and breast cancer. The pro-survival JNK oncoprotein functions in a cell context- and cell type-specific manner to affect signal pathways that modulate tumour initiation, proliferation, and migration. JNK is therefore considered a potential oncogenic target for cancer therapy. Currently, designing effective and specific JNK inhibitors is an active area in the cancer treatment. Some ATP-competitive inhibitors of JNK, such as SP600125 and AS601245, are widely used in vitro; however, this type of inhibitor lacks specificity as they indiscriminately inhibit phosphorylation of all JNK substrates. Moreover, JNK has at least three isoforms with different functions in cancer development and identifying specific selective inhibitors is crucial for the development of targeted therapy in cancer. Some selective inhibitors of JNK are identified; however, their clinical studies in cancer are relatively less conducted. In this review, we first summarised the function of JNK signalling in cancer progression; there is a focus on the discussion of the novel selective JNK inhibitors as potential targeting therapy in cancer. Finally, we have offered a future perspective of the selective JNK inhibitors in the context of cancer therapies. We hope this review will help to further understand the role of JNK in cancer progression and provide insight into the design of novel selective JNK inhibitors in cancer treatment.

Mitogen-Activated Protein Kinase Inhibitors and T-Cell-Dependent Immunotherapy in Cancer

Mitogen-activated protein kinase (MAPK) signaling networks serve to regulate a wide range of physiologic and cancer-associated cell processes. For instance, a variety of oncogenic mutations often lead to hyperactivation of MAPK signaling, thereby enhancing tumor cell proliferation and disease progression. As such, several components of the MAPK signaling network have been proposed as viable targets for cancer therapy. However, the contributions of MAPK signaling extend well beyond the tumor cells, and several MAPK effectors have been identified as key mediators of the tumor microenvironment (TME), particularly with respect to the local immune infiltrate. In fact, a blockade of various MAPK signals has been suggested to fundamentally alter the interaction between tumor cells and T lymphocytes and have been suggested a potential adjuvant to immune checkpoint inhibition in the clinic. Therefore, in this review article, we discuss the various mechanisms through which MAPK family members contribute to T-cell biology, as well as circumstances in which MAPK inhibition may potentiate or limit cancer immunotherapy.

Integrative discovery of treatments for high-risk neuroblastoma

Despite advances in the molecular exploration of paediatric cancers, approximately 50% of children with high-risk neuroblastoma lack effective treatment. To identify therapeutic options for this group of high-risk patients, we combine predictive data mining with experimental evaluation in patient-derived xenograft cells. Our proposed algorithm, TargetTranslator, integrates data from tumour biobanks, pharmacological databases, and cellular networks to predict how targeted interventions affect mRNA signatures associated with high patient risk or disease processes. We find more than 80 targets to be associated with neuroblastoma risk and differentiation signatures. Selected targets are evaluated in cell lines derived from high-risk patients to demonstrate reversal of risk signatures and malignant phenotypes. Using neuroblastoma xenograft models, we establish CNR2 and MAPK8 as promising candidates for the treatment of high-risk neuroblastoma. We expect that our method, available as a public tool (targettranslator.org), will enhance and expedite the discovery of risk-associated targets for paediatric and adult cancers.

We lack effective treatment for half of children with high-risk neuroblastoma. Here, the authors introduce an algorithm that can predict the effect of interventions on gene expression signatures associated with high disease processes and risk, and identify and validate promising drug targets.

Advances in covalent kinase inhibitors

This comprehensive review details recent advances, challenges and innovations in covalent kinase inhibition within a 10 year period (2007–2018).

Current Advances in the Synthesis and Biological Evaluation of Pharmacologically Relevant 1,2,4,5-Tetrasubstituted-1H-Imidazole Derivatives

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In recent years, the synthesis and evaluation of the biological properties of 1,2,4,5-tetrasubstituted-1H-imidazole derivatives have been the subject of a large number of studies by academia and industry. In these studies it has been shown that this large and highly differentiated class of heteroarene derivatives includes high valuable compounds having important biological and pharmacological properties such as antibacterial, antifungal, anthelmintic, anti-inflammatory, anticancer, antiviral, antihypertensive, cholesterol-lowering, antifibrotic, antiuricemic, antidiabetic, antileishmanial and antiulcer activities.

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The present review with 411 references, in which we focused on the literature data published mainly from 2011 to 2017, aims to update the readers on the recent developments on the synthesis and biological evaluation of pharmacologically relevant 1,2,4,5-tetrasubstituted-1H-imidazole derivatives with an emphasis on their different molecular targets and their potential use as drugs to treat various types of diseases. Reference was also made to substantial literature data acquired before 2011 in this burgeoning research area.

Structure-Based Design of Selective, Covalent G Protein-Coupled Receptor Kinase 5 Inhibitors

The ability of G protein-coupled receptor (GPCR) kinases (GRKs) to regulate desensitization of GPCRs has made GRK2 and GRK5 attractive targets for treating heart failure and other diseases such as cancer. Although advances have been made toward developing inhibitors that are selective for GRK2, there have been far fewer reports of GRK5 selective compounds. Herein, we describe the development of GRK5 subfamily selective inhibitors, 5 and 16d that covalently interact with a nonconserved cysteine (Cys474) unique to this subfamily. Compounds 5 and 16d feature a highly amenable pyrrolopyrimidine scaffold that affords high nanomolar to low micromolar activity that can be easily modified with Michael acceptors with various reactivities and geometries. Our work thereby establishes a new pathway toward further development of subfamily selective GRK inhibitors and establishes Cys474 as a new and useful covalent handle in GRK5 drug discovery.

Metabolic Modifier Screen Reveals Secondary Targets of Protein Kinase Inhibitors within Nucleotide Metabolism

Biosynthesis of the pyrimidine nucleotide uridine monophosphate (UMP) is essential for cell proliferation and is achieved by the activity of convergent de novo and salvage metabolic pathways. Here we report the development and application of a cell-based metabolic modifier screening platform that leverages the redundancy in pyrimidine metabolism for the discovery of selective UMP biosynthesis modulators. In evaluating a library of protein kinase inhibitors, we identified multiple compounds that possess nucleotide metabolism modifying activity. The JNK inhibitor JNK-IN-8 was found to potently inhibit nucleoside transport and engage ENT1. The PDK1 inhibitor OSU-03012 (also known as AR-12) and the RAF inhibitor TAK-632 were shown to inhibit the therapeutically relevant de novo pathway enzyme DHODH and their affinities were unambiguously confirmed through in vitro assays and co-crystallization with human DHODH.

Reactive oxygen species (ROS) generation is stimulated by κ opioid receptor activation through phosphorylated c-Jun N-terminal kinase and inhibited by p38 mitogen-activated protein kinase (MAPK) activation

Activation of the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase (JNK) by the Gi/o protein-coupled κ opioid receptor (KOR), μ opioid, and D2 dopamine receptors stimulates peroxiredoxin 6 (PRDX6)-mediated production of reactive oxygen species (ROS). ROS production by KOR-inactivating antagonists norbinaltorphimine (norBNI) and JDTic blocks Gαi protein activation, but the signaling mechanisms and consequences of JNK activation by KOR agonists remain uncharacterized. Binding of arrestins to KOR causes desensitization of G protein signaling and acts as a scaffold to initiate MAPK activation. Here, we found that the KOR agonists U50,488 and dynorphin B stimulated biphasic JNK activation with an early arrestin-independent phase, requiring the small G protein RAC family small GTPase 1 (RAC1) and protein kinase C (PKC), and a later arrestin-scaffolded phase, requiring RAC1 and Ras homolog family member (RHO) kinase. JNK activation by U50,488 and dynorphin B also stimulated PRDX6-dependent ROS production but with an inverted U-shaped dose-response relationship. KOR agonist-induced ROS generation resulted from the early arrestin-independent phase of JNK activation, and this ROS response was suppressed by arrestin-dependent activation of the MAPK p38. The apparent balance between p38 MAPK and JNK/ROS signaling has important physiological implications for understanding of dynorphin activities during the stress response. To visualize these activities, we monitored KOR agonist-mediated activation of ROS in transfected live cells by two fluorescent sensors, CellROX Green and HyPerRed. These findings establish an important aspect of opioid receptor signaling and suggest that ROS induction may be part of the physiological response to KOR activation.

JNK-IN-8, a c-Jun N-terminal kinase inhibitor, improves functional recovery through suppressing neuroinflammation in ischemic stroke

C‐Jun N‐terminal kinase (JNK) is a pivotal MAPK (mitogen‐activated protein kinase), which activated by ischemia brain injury and plays a fairly crucial function in cerebral ischemic injury. Emerging studies demonstrated that JNK‐IN‐8 (a JNK inhibitor with high specificity) regulates traumatic brain injury through controlling neuronal apoptosis and inflammation. However, the function of JNK‐IN‐8 in ischemic stroke and the mechanisms underlying of JNK‐IN‐8 about neuroprotection are not well understood. In this work, male rats were treated with JNK‐IN‐8 after transient middle cerebral artery occlusion, and then the modified improved neurological function score (mNSS), the foot‐fault test (FFT), interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) levels were assessed. We found that JNK‐IN‐8‐treated rats with MCAO exerted an observable melioration in space learning as tested by the improved mNSS, and showed sensorimotor functional recovery as measured by the FFT. JNK‐IN‐8 also played anti‐inflammatory roles as indicated through decreased activation of microglia and decreased IL‐6, IL‐1β, and TNF‐α expression. Furthermore, JNK‐IN‐8 suppressed the activation of JNK and nuclear factor‐κB (NF‐κB) signaling as indicated by the decreased level of phosphorylated‐JNK and p65. All data demonstrate that JNK‐IN‐8 inhibits neuroinflammation and improved neurological function by inhibiting JNK/NF‐κB and is a promising agent for the prevention of ischemic brain injury.

Cytokine production in myelofibrosis exhibits differential responsiveness to JAK-STAT, MAP kinase, and NFκB signaling

The distinct clinical features of myelofibrosis (MF) have been attributed in part to dysregulated inflammatory cytokine production. Circulating cytokine levels are elevated in MF patients; a subset of which have been shown to be poor prognostic indicators. In this study, cytokine overproduction was examined in MF patient plasma and in MF blood cells ex vivo using mass cytometry. Plasma cytokines measured following treatment with ruxolitinib remained markedly abnormal, indicating that aberrant cytokine production persists despite therapeutic JAK2 inhibition. In MF patient samples, 14/15 cytokines measured by mass cytometry were found to be constitutively overproduced, with the principal cellular source for most cytokines being monocytes, implicating a non-cell-autonomous role for monocyte-derived cytokines impacting disease-propagating stem/progenitor cells in MF. The majority of cytokines elevated in MF exhibited ex vivo hypersensitivity to thrombopoietin (TPO), toll-like receptor (TLR) ligands, and/or tumor necrosis factor (TNF). A subset of this group (including TNF, IL-6, IL-8, IL-10) was minimally sensitive to ruxolitinib. All TPO/TLR/TNF-sensitive cytokines, however, were sensitive to pharmacologic inhibition of NFκB and/or MAP kinase signaling. These results indicate that NFκB and MAP kinase signaling maintain cytokine overproduction in MF, and that inhibition of these pathways may provide optimal control of inflammatory pathophysiology in MF.

JNK2 Is Required for the Tumorigenic Properties of Melanoma Cells

Overexpression and activation of c-Jun N-terminal kinases (JNKs) have been observed in multiple cancer cell lines and tumor samples. Various JNK isoforms have been reported to promote lung and liver cancer, as well as keratinocyte transformation, suggesting an important role of JNK signaling in promoting tumor development. However, there are three JNK isoforms, and it is unclear how each individual isoform, especially the ubiquitously expressed JNK1 and JNK2, functions in melanoma. Our previous study found that C116S mutations in both JNK1 and JNK2 rendered them insensitive to the covalent pan-JNK inhibitor JNK-IN-8 while retaining kinase activity. To delineate the specific roles of JNK1 and JNK2 in melanoma cell proliferation and invasiveness, we expressed the wild type (WT) and C116S mutants in melanoma cell lines and used JNK-IN-8 to enable chemical-genetic dissection of JNK1 and JNK2 activity. We found that the JNK2^C116S allele consistently enhanced colony proliferation and cell invasiveness in the presence of JNK-IN-8. When cells individually expressing WT or C116S JNK1/2 were subcutaneously implanted into immunodeficient mice, we again found that bypass of JNK-IN-8-mediated inhibition of JNK signaling by expression of JNK2^C116S specifically resulted in enhanced tumor growth in vivo. In addition, we observed a high level of JNK pathway activation in some human BRAF inhibitor (BRAFi) resistant melanoma cell lines relative to their BRAFi sensitive isogenic counterparts. JNK-IN-8 significantly enhanced the response to dabrafenib in resistant cells overexpressing JNK1^WT, JNK2^WT, and JNK1^C116S but had no effect on cells expressing JNK2^C116S, suggesting that JNK2 signaling is also crucial for BRAFi resistance in a subset of melanomas. Collectively, our data show that JNK2 activity is specifically required for melanoma cell proliferation, invasiveness, and BRAFi resistance and that this activity is most important in the context of JNK1 suppression, thus providing a compelling rationale for the development of JNK2 selective inhibitors as a potential therapy for the treatment of melanoma.

Kinase Atlas: Druggability Analysis of Potential Allosteric Sites in Kinases

The inhibition of kinases has been pursued by the pharmaceutical industry for over 20 years. While the locations of the sites that bind type II and III inhibitors at or near the adenosine 5'-triphosphate binding sites are well defined, the literature describes 10 different regions that were reported as regulatory hot spots in some kinases and thus are potential target sites for type IV inhibitors. Kinase Atlas is a systematic collection of binding hot spots located at the above ten sites in 4910 structures of 376 distinct kinases available in the Protein Data Bank. The hot spots are identified by FTMap, a computational analogue of experimental fragment screening. Users of Kinase Atlas ( https://kinase-atlas.bu.edu ) may view summarized results for all structures of a particular kinase, such as which binding sites are present and how druggable they are, or they may view hot spot information for a particular kinase structure of interest.

Drugging K-RasG12C through covalent inhibitors: Mission possible?

Ras, whose mutants are present in approximately 30% of human tumours, is one of the most important oncogenes. Drugging Ras is thus regarded as the quest for the Holy Grail in cancer therapeutics development. Despite more than three decades of efforts, drug discovery targeting Ras constantly fails, rendering Ras undruggable, due to its smooth surface and picomolar affinity towards guanosine substrates. The most frequently mutated isoform of Ras is K-Ras, accounting for >85% of Ras-driven cancers, and one majority of them is the G12C mutation. Recent advances in structural biology shed light on drugging Ras, and one of the cutting-edge breakthroughs is the design of covalent G12C-specific inhibitors targeting the mutated cysteine. This type of inhibitor can be classified into substrate-competitive orthosteric inhibitors and non-competitive allosteric inhibitors. They display improved selectivity and enhanced potency due to their G12-specific and irreversible covalent binding nature. Thus, they represent a new hope for revolutionizing the conventional characterization of Ras as "undruggable" and pave a promising avenue for further drug discovery. Here, we provide comprehensive structural and medicinal chemical insights into K-Ras covalent inhibitors specific for the G12C mutant. We first present an in-depth analysis of the conformations of the inhibitor binding pockets. Then, all the latest covalent ligands selectively inhibiting K-Ras^G12C are reviewed. Finally, we examine the current challenges faced by this new class of anti-Ras inhibitors.

Leveraging Compound Promiscuity to Identify Targetable Cysteines within the Kinome

Covalent kinase inhibitors, which typically target cysteine residues, represent an important class of clinically relevant compounds. Approximately 215 kinases are known to have potentially targetable cysteines distributed across 18 spatially distinct locations proximal to the ATP-binding pocket. However, only 40 kinases have been covalently targeted, with certain cysteine sites being the primary focus. To address this disparity, we have developed a strategy that combines the use of a multi-targeted acrylamide-modified inhibitor, SM1-71, with a suite of complementary chemoproteomic and cellular approaches to identify additional targetable cysteines. Using this single multi-targeted compound, we successfully identified 23 kinases that are amenable to covalent inhibition including MKNK2, MAP2K1/2/3/4/6/7, GAK, AAK1, BMP2K, MAP3K7, MAPKAPK5, GSK3A/B, MAPK1/3, SRC, YES1, FGFR1, ZAK (MLTK), MAP3K1, LIMK1, and RSK2. The identification of nine of these kinases previously not targeted by a covalent inhibitor increases the number of targetable kinases and highlights opportunities for covalent kinase inhibitor development.

Opportunities and challenges for the development of covalent chemical immunomodulators

Compounds that react irreversibly with cysteines have reemerged as potent and selective tools for altering protein function, serving as chemical probes and even clinically approved drugs. The exquisite sensitivity of human immune cell signaling pathways to oxidative stress indicates the likely, yet still underexploited, general utility of covalent probes for selective chemical immunomodulation. Here, we provide an overview of immunomodulatory cysteines, including identification of electrophilic compounds available to label these residues. We focus our discussion on three protein classes essential for cell signaling, which span the 'druggability' spectrum from amenable to chemical probes (kinases), somewhat druggable (proteases), to inaccessible (phosphatases). Using existing inhibitors as a guide, we identify general strategies to guide the development of covalent probes for selected undruggable classes of proteins and propose the application of such compounds to alter immune cell functions.

Network pharmacology-based identifcation of potential targets of the flower of Trollius chinensis Bunge acting on anti-inflammatory effectss

The flower of Trollius chinensis Bunge was widely used for the treatment of inflammation-related diseases in traditional Chinese medicine (TCM). In order to clarify the anti-inflammatory mechanism of this Chinese herbs, a comprehensive network pharmacology strategy that consists of three sequential modules (pharmacophore matching, enrichment analysis and molecular docking.) was carried out. As a result, Apoptosis signal-regulating kinase 1 (ASK1), Janus kinase 1 (JAK1), c-Jun N-terminal kinases (JNKs), transforming protein p21 (HRas) and mitogen-activated protein kinase 14 (p38α) that related to the anti-inflammatory effect were filtered out. In further molecular dynamics (MD) simulation, the conformation of CID21578038 and CID20055288 were found stable in the protein ASK1 and JNKs respectively. The current investigation revealed that two effective compounds in the flower of Trollius chinensis Bunge played a crucial role in the process of inflammation by targeting ASK1 and JNKs, the comprehensive strategy can serve as a universal method to guide in illuminating the mechanism of the prescription of traditional Chinese medicine by identifying the pathways or targets.

Synthesis and structure activity relationships of a series of 4-amino-1H-pyrazoles as covalent inhibitors of CDK14

The TAIRE family of kinases are an understudied branch of the CDK kinase family, that have been implicated in a number of cancers. This manuscript describes the design, synthesis and SAR of covalent CDK14 inhibitors, culminating in identification of FMF-04-159-2, a potent, covalent CDK14 inhibitor with a TAIRE kinase biased selectivity profile.

Rapid Covalent-Probe Discovery by Electrophile-Fragment Screening

Covalent probes can display unmatched potency, selectivity, and duration of action; however, their discovery is challenging. In principle, fragments that can irreversibly bind their target can overcome the low affinity that limits reversible fragment screening, but such electrophilic fragments were considered nonselective and were rarely screened. We hypothesized that mild electrophiles might overcome the selectivity challenge and constructed a library of 993 mildly electrophilic fragments. We characterized this library by a new high-throughput thiol-reactivity assay and screened them against 10 cysteine-containing proteins. Highly reactive and promiscuous fragments were rare and could be easily eliminated. In contrast, we found hits for most targets. Combining our approach with high-throughput crystallography allowed rapid progression to potent and selective probes for two enzymes, the deubiquitinase OTUB2 and the pyrophosphatase NUDT7. No inhibitors were previously known for either. This study highlights the potential of electrophile-fragment screening as a practical and efficient tool for covalent-ligand discovery.

Genome-scale screens identify JNK-JUN signaling as a barrier for pluripotency exit and endoderm differentiation

Human embryonic and induced pluripotent stem cells (hESCs/hiPSCs) hold great promise for cell-based therapies and drug discovery. However, homogeneous differentiation remains a major challenge, highlighting the need for understanding developmental mechanisms. We performed genome-scale CRISPR screens to uncover regulators of definitive endoderm (DE) differentiation, which unexpectedly uncovered five JNK/JUN family genes as key barriers of DE differentiation. The JNK/JUN pathway does not act through directly inhibiting the DE enhancers. Instead JUN co-occupies ESC enhancers with OCT4, NANOG and SMAD2/3, and specifically inhibits the exit from the pluripotent state by impeding the decommissioning of ESC enhancers and inhibiting the reconfiguration of SMAD2/3 chromatin binding from ESC to DE enhancers. Therefore, the JNK/JUN pathway safeguards pluripotency from precocious DE differentiation. Direct pharmacological inhibition of JNK significantly improves the efficiencies of generating DE and DE-derived pancreatic and lung progenitor cells, highlighting the potential of harnessing the knowledge from developmental studies for regenerative medicine.

Triggering MSR1 promotes JNK-mediated inflammation in IL-4-activated macrophages

Alternatively activated M2 macrophages play an important role in maintenance of tissue homeostasis by scavenging dead cells, cell debris and lipoprotein aggregates via phagocytosis. Using proteomics, we investigated how alternative activation, driven by IL‐4, modulated the phagosomal proteome to control macrophage function. Our data indicate that alternative activation enhances homeostatic functions such as proteolysis, lipolysis and nutrient transport. Intriguingly, we identified the enhanced recruitment of the TAK1/MKK7/JNK signalling complex to phagosomes of IL‐4‐activated macrophages. The recruitment of this signalling complex was mediated through K63 polyubiquitylation of the macrophage scavenger receptor 1 (MSR1). Triggering of MSR1 in IL‐4‐activated macrophages leads to enhanced JNK activation, thereby promoting a phenotypic switch from an anti‐inflammatory to a pro‐inflammatory state, which was abolished upon MSR1 deletion or JNK inhibition. Moreover, MSR1 K63 polyubiquitylation correlated with the activation of JNK signalling in ovarian cancer tissue from human patients, suggesting that it may be relevant for macrophage phenotypic shift in vivo. Altogether, we identified that MSR1 signals through JNK via K63 polyubiquitylation and provides evidence for the receptor's involvement in macrophage polarization.

Discovery of Covalent CDK14 Inhibitors with Pan-TAIRE Family Specificity

Cyclin-dependent kinase 14 (CDK14) and other TAIRE family kinases (CDKs 15-18) are proteins that lack functional annotation but are frequent off-targets of clinical kinase inhibitors. In this study we develop and characterize FMF-04-159-2, a tool compound that specifically targets CDK14 covalently and possesses a TAIRE kinase-biased selectivity profile. This tool compound and its reversible analog were used to characterize the cellular consequences of covalent CDK14 inhibition, including an unbiased investigation using phospho-proteomics. To reduce confounding off-target activity, washout conditions were used to deconvolute CDK14-specific effects. This investigation suggested that CDK14 plays a supporting role in cell-cycle regulation, particularly mitotic progression, and identified putative CDK14 substrates. Together, these results represent an important step forward in understanding the cellular consequences of inhibiting CDK14 kinase activity.

Development of a Selective CDK7 Covalent Inhibitor Reveals Predominant Cell-Cycle Phenotype

Cyclin-dependent kinase 7 (CDK7) regulates both cell cycle and transcription, but its precise role remains elusive. We previously described THZ1, a CDK7 inhibitor, which dramatically inhibits superenhancer-associated gene expression. However, potent CDK12/13 off-target activity obscured CDK7s contribution to this phenotype. Here, we describe the discovery of a highly selective covalent CDK7 inhibitor. YKL-5-124 causes arrest at the G₁/S transition and inhibition of E2F-driven gene expression; these effects are rescued by a CDK7 mutant unable to covalently engage YKL-5-124, demonstrating on-target specificity. Unlike THZ1, treatment with YKL-5-124 resulted in no change to RNA polymerase II C-terminal domain phosphorylation; however, inhibition could be reconstituted by combining YKL-5-124 and THZ531, a selective CDK12/13 inhibitor, revealing potential redundancies in CDK control of gene transcription. These findings highlight the importance of CDK7/12/13 polypharmacology for anti-cancer activity of THZ1 and posit that selective inhibition of CDK7 may be useful for treatment of cancers marked by E2F misregulation.

MiR-15/16 mediate crosstalk between the MAPK and Wnt/β-catenin pathways during hepatocyte differentiation from amniotic epithelial cells

MiR-15/16 play an important role in liver development and hepatocyte differentiation, but the mechanisms by which these miRNAs regulate their targets and downstream genes to influence cell fate are poorly understood. In this study, we showed up-regulation of miR-15/16 during HGF- and FGF4-induced hepatocyte differentiation from amniotic epithelial cells (AECs). To elucidate the role of miR-15/16 and their targets in hepatocyte differentiation, we investigated the roles of miR-15/16 in both the MAPK and Wnt/β-catenin pathways, which were predicted to be involved in miR-15/16 signaling. Our results demonstrated that the transcription of miR-15/16 was enhanced by c-Fos, c-Jun, and CREB, important elements of the MAPK pathway, and miR-15/16 in turn directly targeted adenomatous polyposis coli (APC) protein, a major member of the β-catenin degradation complex. MiR-15/16 destroyed these degradation complexes to activate β-catenin, and the activated β-catenin combined with LEF/TCF7L1 to form a transcriptional complex that enhanced transcription of hepatocyte nuclear factor 4 alpha (HNF4α). HNF4α also bound the promoter region of miR-15/16 and promoted its transcription, thereby forming a regulatory circuit to promote the differentiation of AECs into hepatocytes. Endogenous miRNAs are, therefore, involved in hepatocyte differentiation from AECs and should be considered during the development of an effective hepatocyte transplant therapy for liver damage.

Live-cell imaging and profiling of c-Jun N-terminal kinases using covalent inhibitor-derived probes

c-Jun N-terminal kinases (JNKs) are involved in critical cellular functions. Herein, small-molecule JNK-targeting probes are reported based on a covalent inhibitor. Together with newly developed two-photon fluorescence Turn-ON reporters and chemoproteomic studies, we showed that some probes may be suitable for live-cell imaging and profiling of JNKs.

Targeting JNK pathway promotes human hematopoietic stem cell expansion

The limited number of human hematopoietic stem cells (HSCs) has restrained their widespread clinical application. Despite great efforts in recent years, the in vitro expansion of HSCs remains a challenge due to incomplete understanding of the signaling networks underlying HSC self-renewal. Here, we show that culturing human cord blood (CB) CD34⁺ cells with JNK-IN-8, an inhibitor of the JNK signaling pathway, can enhance the self-renewal of HSCs with a 3.88-fold increase in cell number. These cultured CD34⁺ cells repopulated recipient mice for 21 weeks and can form secondary engraftment that lasted for more than 21 weeks. Knockdown of c-Jun, a major downstream target in the JNK pathway, promoted the expansion of hematopoietic stem and progenitor cells (HSPCs). Our findings demonstrate a critical role of the JNK pathway in regulating HSC expansion, provide new insights into HSC self-renewal mechanism, and may lead to improved clinical application of HSCs.

The transcriptional coactivator WBP2 primes triple-negative breast cancer cells for responses to Wnt signaling via the JNK/Jun kinase pathway

The transcriptional coactivator WW domain-binding protein 2 (WBP2) is an emerging oncogene and serves as a node between the signaling protein Wnt and other signaling molecules and pathways, including epidermal growth factor receptor, estrogen receptor/progesterone receptor, and the Hippo pathway. The upstream regulation of WBP2 is well-studied, but its downstream activity remains unclear. Here, we elucidated WBP2's role in triple-negative breast cancer (TNBC), in which Wnt signaling is predominantly activated. Using RNAi coupled with RNA-Seq and MS analyses to identify Wnt/WBP2- and WBP2-dependent targets in MDA-MB-231 TNBC cells, we found that WBP2 is required for the expression of a core set of genes in Wnt signaling. These included AXIN2, which was essential for Wnt/WBP2-mediated breast cancer growth and migration. WBP2 also regulated a much larger set of genes and proteins independently of Wnt, revealing that WBP2 primes cells to Wnt activity by up-regulating G protein pathway suppressor 1 (GPS1) and TRAF2- and NCK-interacting kinase (TNIK). GPS1 activated the c-Jun N-terminal kinase (JNK)/Jun pathway, resulting in a positive feedback loop with TNIK that mediated Wnt-induced AXIN2 expression. WBP2 promoted TNBC growth by integrating JNK with Wnt signaling, and its expression profoundly influenced the sensitivity of TNBC to JNK/TNIK inhibitors. In conclusion, WBP2 links JNK to Wnt signaling in TNBC. GPS1 and TNIK are constituents of a WBP2-initiated cascade that primes responses to Wnt ligands and are also important for TNBC biology. We propose that WBP2 is a potential drug target for JNK/TNIK-based precision medicine for managing TNBC.

Inhibition of JNK signaling in the Asian malaria vector Anopheles stephensi extends mosquito longevity and improves resistance to Plasmodium falciparum infection

Malaria is a global health concern caused by infection with Plasmodium parasites. With rising insecticide and drug resistance, there is a critical need to develop novel control strategies, including strategies to block parasite sporogony in key mosquito vector species. MAPK signaling pathways regulated by extracellular signal-regulated kinases (ERKs) and the stress-activated protein kinases (SAPKs) c-Jun N-terminal kinases (JNKs) and p38 MAPKs are highly conserved across eukaryotes, including mosquito vectors of the human malaria parasite Plasmodium falciparum. Some of these pathways in mosquitoes have been investigated in detail, but the mechanisms of integration of parasite development and mosquito fitness by JNK signaling have not been elucidated. To this end, we engineered midgut-specific overexpression of MAPK phosphatase 4 (MKP4), which targets the SAPKs, and used two potent and specific JNK small molecule inhibitors (SMIs) to assess the effects of JNK signaling manipulations on Anopheles stephensi fecundity, lifespan, intermediary metabolism, and P. falciparum development. MKP4 overexpression and SMI treatment reduced the proportion of P. falciparum-infected mosquitoes and decreased oocyst loads relative to controls. SMI-treated mosquitoes exhibited no difference in lifespan compared to controls, whereas genetically manipulated mosquitoes exhibited extended longevity. Metabolomics analyses of SMI-treated mosquitoes revealed insights into putative resistance mechanisms and the physiology behind lifespan extension, suggesting for the first time that P. falciparum-induced JNK signaling reduces mosquito longevity and increases susceptibility to infection, in contrast to previously published reports, likely via a critical interplay between the invertebrate host and parasite for nutrients that play essential roles during sporogonic development.

Malaria is a global health concern caused by infection with Plasmodium parasites. With rising insecticide and drug resistance, there is a critical need to develop novel control strategies. One strategy is to develop a Plasmodium-resistant mosquito through the manipulation of key signaling pathways and processes in the mosquito midgut, a critical tissue for parasite development. MAPK signaling pathways are highly conserved among eukaryotes and regulate development of the human malaria parasite Plasmodium falciparum in the mosquito vector. Here, we investigated how manipulation of Anopheles stephensi JNK signaling affects development of P. falciparum and key mosquito life history traits. We used multiple, complementary approaches to demonstrate that malaria parasite infection activates mosquito JNK signaling for its own benefit at a cost to host lifespan. Notably, these combined effects derive from networked signaling with other transduction pathways and alterations to intermediary metabolism in the mosquito host.

c-Jun N-terminal kinase (JNK)-mediated phosphorylation of SARM1 regulates NAD+ cleavage activity to inhibit mitochondrial respiration

Mitochondrial dysfunction is a key pathological feature of many different types of neurodegenerative disease. Sterile alpha and Toll/interleukin receptor motif-containing protein 1 (SARM1) has been attracting much attention as an important molecule for inducing axonal degeneration and neuronal cell death by causing loss of NAD (NADH). However, it has remained unclear what exactly regulates the SARM1 activity. Here, we report that NAD⁺ cleavage activity of SARM1 is regulated by its own phosphorylation at serine 548. The phosphorylation of SARM1 was mediated by c-jun N-terminal kinase (JNK) under oxidative stress conditions, resulting in inhibition of mitochondrial respiration concomitant with enhanced activity of NAD⁺ cleavage. Nonphosphorylatable mutation of Ser-548 or treatment with a JNK inhibitor decreased SARM1 activity. Furthermore, neuronal cells derived from a familial Parkinson's disease (PD) patient showed a congenitally increased level of SARM1 phosphorylation compared with that in neuronal cells from a healthy person and were highly sensitive to oxidative stress. These results indicate that JNK-mediated phosphorylation of SARM1 at Ser-548 is a regulator of SARM1 leading to inhibition of mitochondrial respiration. These findings suggest that an abnormal regulation of SARM1 phosphorylation is involved in the pathogenesis of Parkinson's disease and possibly other neurodegenerative diseases.

Transforming growth factor-β downregulates sGC subunit expression in pulmonary artery smooth muscle cells via MEK and ERK signaling

TGFβ activation during newborn lung injury decreases the expression of pulmonary artery smooth muscle cell (PASMC)-soluble guanylate cyclase (sGC), a critical mediator of nitric oxide signaling. Using a rat PASMC line (CS54 cells), we determined how TGFβ downregulates sGC expression. We found that TGFβ decreases sGC expression through stimulating its type I receptor; TGFβ type I receptor (TGFβR1) inhibitors prevented TGFβ-1-mediated decrease in sGCα1 subunit mRNA levels in the cells. However, TGFβR1-Smad mechanisms do not regulate sGC; effective knockdown of Smad2 and Smad3 expression and function did not protect sGCα1 mRNA levels during TGFβ-1 exposure. A targeted small-molecule kinase inhibitor screen suggested that MEK signaling regulates sGC expression in TGFβ-stimulated PASMC. TGFβ activates PASMC MEK/ERK signaling; CS54 cell treatment with TGFβ-1 increased MEK and ERK phosphorylation in a biphasic, time- and dose-dependent manner. Moreover, MEK/ERK activity appears to be required for TGFβ-mediated sGC expression inhibition in PASMC; MEK and ERK inhibitors protected sGCα1 mRNA expression in TGFβ-1-treated CS54 cells. Nuclear ERK activity is sufficient for sGC regulation; heterologous expression of a nucleus-retained, constitutively active ERK2-MEK1 fusion protein decreased CS54 cell sGCα1 mRNA levels. The in vivo relevance of this TGFβ-MEK/ERK-sGC downregulation pathway is suggested by the detection of ERK activation and sGCα1 protein expression downregulation in TGFβ-associated mouse pup hyperoxic lung injury, and the determination that ERK decreases sGCα1 protein expression in TGFβ-1-treated primary PASMC obtained from mouse pups. These studies identify MEK/ERK signaling as an important pathway by which TGFβ regulates sGC expression in PASMC.

Covalent inhibitors of EGFR family protein kinases induce degradation of human Tribbles 2 (TRIB2) pseudokinase in cancer cells

A major challenge associated with biochemical and cellular analysis of pseudokinases is a lack of target-validated small-molecule compounds with which to probe function. Tribbles 2 (TRIB2) is a cancer-associated pseudokinase with a diverse interactome, including the canonical AKT signaling module. There is substantial evidence that human TRIB2 promotes survival and drug resistance in solid tumors and blood cancers and therefore is of interest as a therapeutic target. The unusual TRIB2 pseudokinase domain contains a unique cysteine-rich C-helix and interacts with a conserved peptide motif in its own carboxyl-terminal tail, which also supports its interaction with E3 ubiquitin ligases. We found that TRIB2 is a target of previously described small-molecule protein kinase inhibitors, which were originally designed to inhibit the canonical kinase domains of epidermal growth factor receptor tyrosine kinase family members. Using a thermal shift assay, we discovered TRIB2-binding compounds within the Published Kinase Inhibitor Set (PKIS) and used a drug repurposing approach to classify compounds that either stabilized or destabilized TRIB2 in vitro. TRIB2 destabilizing agents, including the covalent drug afatinib, led to rapid TRIB2 degradation in human AML cancer cells, eliciting tractable effects on signaling and survival. Our data reveal new drug leads for the development of TRIB2-degrading compounds, which will also be invaluable for unraveling the cellular mechanisms of TRIB2-based signaling. Our study highlights that small molecule-induced protein down-regulation through drug "off-targets" might be relevant for other inhibitors that serendipitously target pseudokinases.

H2O2 oxidation of cysteine residues in c-Jun N-terminal kinase 2 (JNK2) contributes to redox regulation in human articular chondrocytes

Reactive oxygen species (ROS), in particular H₂O₂, regulate intracellular signaling through reversible oxidation of reactive protein thiols present in a number of kinases and phosphatases. H₂O₂ has been shown to regulate mitogen-activated protein kinase (MAPK) signaling depending on the cellular context. We report here that in human articular chondrocytes, the MAPK family member c-Jun N-terminal kinase 2 (JNK2) is activated by fibronectin fragments and low physiological levels of H₂O₂ and inhibited by oxidation due to elevated levels of H₂O₂ The kinase activity of affinity-purified, phosphorylated JNK2 from cultured chondrocytes was reversibly inhibited by 5-20 μm H₂O₂ Using dimedone-based chemical probes that react specifically with sulfenylated cysteines (RSOH), we identified Cys-222 in JNK2, a residue not conserved in JNK1 or JNK3, as a redox-reactive site. MS analysis of human recombinant JNK2 also detected further oxidation at Cys-222 and other cysteines to sulfinic (RSO₂H) or sulfonic (RSO₃H) acid. H₂O₂ treatment of JNK2 resulted in detectable levels of peptides containing intramolecular disulfides between Cys-222 and either Cys-213 or Cys-177, without evidence of dimer formation. Substitution of Cys-222 to alanine rendered JNK2 insensitive to H₂O₂ inhibition, unlike C177A and C213A variants. Two other JNK2 variants, C116A and C163A, were also resistant to oxidative inhibition. Cumulatively, these findings indicate differential regulation of JNK2 signaling dependent on H₂O₂ levels and point to key cysteine residues regulating JNK2 activity. As levels of intracellular H₂O₂ rise, a switch occurs from activation to inhibition of JNK2 activity, linking JNK2 regulation to the redox status of the cell.

Role of the MAPK/cJun NH2-terminal kinase signaling pathway in starvation-induced autophagy

Autophagy is required for cellular homeostasis and can determine cell viability in response to stress. It is established that MTOR is a master regulator of starvation-induced macroautophagy/autophagy, but recent studies have also implicated an essential role for the MAPK8/cJun NH₂-terminal kinase 1 signal transduction pathway. We found that MAPK8/JNK1 and MAPK9/JNK2 were not required for autophagy caused by starvation or MTOR inhibition in murine fibroblasts and epithelial cells. These data demonstrate that MAPK8/9 has no required role in starvation-induced autophagy. We conclude that the role of MAPK8/9 in autophagy may be context-dependent and more complex than previously considered.

Abbreviations: AKT: thymoma viral proto-oncogene;ALB: albumin; ATG4: autophagy related 4; BCL2: B cell leukemia/lymphoma 2; BECN1: beclin 1, autophagy related; BNIP3: BCL2/adenovirus E1B interacting protein 3; CQ: chloroquine diphosphate; DMEM: Dulbecco’s modified Eagle’s medium; EDTA: ethylenediaminetetraacetic acid; EBSS: Earle’s balanced salt solution; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HRAS: Harvey rat sarcoma virus oncogene; IgG: Immunoglobulin G; MAPK3/ERK1: mitogen-activated protein kinase 3; MAPK8/JNK1: mitogen-activated protein kinase 8; MAPK9/JNK2: mitogen-activated protein kinase 9; MAPK10/JNK3: mitogen-activated protein kinase 10; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MEFs: mouse embryonic fibroblasts; MTOR: mechanistic target of rapamycin kinase; RPS6KB1/p70: ribosomal protein S6 kinase, polypeptide 1; PPARA: peroxisome proliferator activated receptor alpha; SEM: standard error of the mean; SQSTM1/p62: sequestosome 1; TORC1: target of rapamycin complex 1; TORC2: target of rapamycin complex 2; TRP53: transforming related protein 53; TUBA: tubulin alpha; UV: ultraviolet; WT: wild-type

Identification of lead anti-human cytomegalovirus compounds targeting MAP4K4 via machine learning analysis of kinase inhibitor screening data

Chemogenomic approaches involving highly annotated compound sets and cell based high throughput screening are emerging as a means to identify novel drug targets. We have previously screened a collection of highly characterized kinase inhibitors (Khan et al., Journal of General Virology, 2016) to identify compounds that increase or decrease expression of a human cytomegalovirus (HCMV) protein in infected cells. To identify potential novel anti-HCMV drug targets we used a machine learning approach to relate our phenotypic data from the aforementioned screen to kinase inhibition profiling of compounds used in this screen. Several of the potential targets had no previously reported role in HCMV replication. We focused on one potential anti-HCMV target, MAPK4K, and identified lead compounds inhibiting MAP4K4 that have anti-HCMV activity with little cellular cytotoxicity. We found that treatment of HCMV infected cells with inhibitors of MAP4K4, or an siRNA that inhibited MAP4K4 production, reduced HCMV replication and impaired detection of IE2-60, a viral protein necessary for efficient HCMV replication. Our findings demonstrate the potential of this machine learning approach to identify novel anti-viral drug targets, which can inform the discovery of novel anti-viral lead compounds.

RIP2 Gates TRAF6 Interaction with Death Receptor p75NTR to Regulate Cerebellar Granule Neuron Survival

Cerebellar granule neurons (CGNs) undergo programmed cell death during the first postnatal week of mouse development, coincident with sustained expression of the death receptor p75NTR. Although ablation of p75NTR does not affect CGN cell death, deletion of the downstream effector RIP2 significantly increases CGN apoptosis, resulting in reduced adult CGN number and impaired behaviors associated with cerebellar function. Remarkably, CGN death is restored to basal levels when p75NTR is deleted in RIP2-deficient mice. We find that RIP2 gates the signaling output of p75NTR by competing with TRAF6 for binding to the receptor intracellular domain. In CGNs lacking RIP2, more TRAF6 is associated with p75NTR, leading to increased JNK-dependent apoptosis. In agreement with this, pharmacological inhibition or genetic ablation of TRAF6 restores cell death levels in CGNs lacking RIP2. These results reveal an unexpected mechanism controlling CGN number and highlight how competitive interactions govern the logic of death receptor function.

BCL2 inhibitor ABT-199 and JNK inhibitor SP600125 exhibit synergistic cytotoxicity against imatinib-resistant Ph+ ALL cells

Imatinib (IMT), a specific tyrosine kinase inhibitor (TKI), has drastically changed the treatment strategy for Ph+ ALL (Philadelphia chromosome-positive acute lymphoblastic leukemia). However, TKI resistance remains a serious problem for patient prognosis. Here, a Ph+ ALL cell line NphA2 and the IMT-resistant subline NphA2/STIR were analyzed to identify a potential novel treatment strategy. We also examined other Ph+ ALL cells, MR87 and its IMT-resistant subline, MR87/STIR. IMT induced apoptosis of NphA2 and MR87 but had no effect on resistant sublines. Increased phosphorylated ERK and BCL2, but not BCL-XL, were observed in NphA2/STIR compared with NphA2. NphA2/STIR but not NphA2 was moderately sensitive to U0126, an ERK inhibitor. Interestingly, SP600125, a JNK inhibitor, was potent in cell growth inhibition and apoptosis induction of both parental and IMT-resistant NphA2 and MR87 cells. Moreover, NphA2 and MR87 and their IMT-resistant sublines were sensitive to ABT-199, a specific BCL2 inhibitor. The combination of SP600125 and ABT-199 synergistically suppressed both parental and IMT-resistant cells, including one with T315I mutation, suggesting that Ph+ ALL exhibits high sensitivity to ABT-199 and SP600125 regardless of TKI resistance. This combination might be a possible therapeutic strategy for Ph+ ALL in the future.

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SP600125 JNK inhibitor is cytotoxic against imatinib-resistant Ph+ ALL cells.

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BCl2 inhibitor ABT 199 exhibits cytotoxicity against imatinib-resistant Ph+ ALL.

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SP600125 and ABT199 are synergistic in imatinib-resistant Ph+ ALL with T315I.

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Some leukemia cells are sensitive to MCL1 inhibitor maritoclax but not to ABT-199.

JNK Promotes Epithelial Cell Anoikis by Transcriptional and Post-translational Regulation of BH3-Only Proteins

Developmental morphogenesis, tissue injury, and oncogenic transformation can cause the detachment of epithelial cells. These cells are eliminated by a specialized form of apoptosis (anoikis). While the processes that contribute to this form of cell death have been studied, the underlying mechanisms remain unclear. Here, we tested the role of the cJUN NH₂-terminal kinase (JNK) signaling pathway using murine models with compound JNK deficiency in mammary and kidney epithelial cells. These studies demonstrated that JNK is required for efficient anoikis in vitro and in vivo. Moreover, JNK-promoted anoikis required pro-apoptotic members of the BCL2 family of proteins. We show that JNK acts through a BAK/BAX-dependent apoptotic pathway by increasing BIM expression and phosphorylating BMF, leading to death of detached epithelial cells.

Activation of AMPK inhibits inflammatory response during hypoxia and reoxygenation through modulating JNK-mediated NF-κB pathway

BACKGROUND

AMP-activated Protein Kinase (AMPK) is a stress-activated kinase that protects against cardiomyocyte injury during ischemia and reperfusion. c-Jun N-terminal kinase (JNK), a mitogen activated protein kinase, is activated by ischemia and reperfusion. NF-κB is an important transcription factor involved in ischemia and reperfusion injury.

METHODS AND RESULTS

The intrinsic activation of AMPK attenuates the inflammation which occurred during ischemia/reperfusion through the modulation of the JNK mediated NF-κB signaling pathway. Rat cardiac myoblast H9c2 cells were subjected to hypoxia and/or reoxygenation to investigate the signal transduction that occurred during myocardial ischemia/reperfusion. Mitochondrial function was measured by the Seahorse XF24 V7 PS system. Hypoxia treatment triggered AMPK activation in H9c2 cells in a time dependent manner. The inhibition of hypoxic AMPK activation through a pharmacological approach (Compound C) or siRNA knockdown of AMPK α catalytic subunits caused dramatic augmentation in JNK activation, inflammatory NF-κB phosphorylation, and apoptosis during hypoxia and reoxygenation. Inhibition of AMPK activation significantly impaired mitochondrial function and increased the generation of reactive oxygen species (ROS) during hypoxia and reoxygenation. In contrast, pharmacological activation of AMPK by metformin significantly inhibited mitochondrial permeability transition pore (mPTP) opening and ROS generation. Moreover, AMPK activation significantly attenuated the JNK-NF-κB signaling cascade and inhibited mRNA and protein levels of pro-inflammatory cytokines, such as TNF-α and IL-6, during hyopoxia/reoxygenation in H9c2 cells. Intriguingly, both pharmacologic inhibition of JNK by JNK-IN-8 and siRNA knockdown of JNK signaling pathway attenuated NF-κB phosphorylation and apoptosis but did not affect AMPK activation in response to hypoxia and reoxygenation.

CONCLUSIONS

AMPK activation modulates JNK-NF-κB signaling cascade during hypoxia and reoxygenation stress conditions. Cardiac AMPK activation plays a critical role in maintaining mitochondrial function and inhibiting the inflammatory response caused by ischemic insults.

Matrix stiffness-upregulated LOXL2 promotes fibronectin production, MMP9 and CXCL12 expression and BMDCs recruitment to assist pre-metastatic niche formation

BACKGROUND

Higher matrix stiffness affects biological behavior of tumor cells, regulates tumor-associated gene/miRNA expression and stemness characteristic, and contributes to tumor invasion and metastasis. However, the linkage between higher matrix stiffness and pre-metastatic niche in hepatocellular carcinoma (HCC) is still largely unknown.

METHODS

We comparatively analyzed the expressions of LOX family members in HCC cells grown on different stiffness substrates, and speculated that the secreted LOXL2 may mediate the linkage between higher matrix stiffness and pre-metastatic niche. Subsequently, we investigated the underlying molecular mechanism by which matrix stiffness induced LOXL2 expression in HCC cells, and explored the effects of LOXL2 on pre-metastatic niche formation, such as BMCs recruitment, fibronectin production, MMPs and CXCL12 expression, cell adhesion, etc. RESULTS: Higher matrix stiffness significantly upregulated LOXL2 expression in HCC cells, and activated JNK/c-JUN signaling pathway. Knockdown of integrin β1 and α5 suppressed LOXL2 expression and reversed the activation of above signaling pathway. Additionally, JNK inhibitor attenuated the expressions of p-JNK, p-c-JUN, c-JUN and LOXL2, and shRNA-c-JUN also decreased LOXL2 expression. CM-LV-LOXL2-OE and rhLOXL2 upregulated MMP9 expression and fibronectin production obviously in lung fibroblasts. Moreover, activation of Akt pathway contributed to LOXL2-induced fibronectin upregulation. LOXL2 in CM as chemoattractant increased motility and invasion of BMCs, implicating a significant role of LOXL2 in BMCs recruitment. Except that, CM-LV-LOXL2-OE as chemoattractant also increased the number of migrated HCC cells, and improved chemokine CXCL12 expression in lung fibroblasts. The number of HCC cells adhered to surface of lung fibroblasts treated with CM-LV-LOXL2-OE was remarkably higher than that of the control cells. These results indicated that the secreted LOXL2 facilitated the motility of HCC cells and strengthened CTCs settlement on the remodeled matrix "soil".

CONCLUSION

Integrin β1/α5/JNK/c-JUN signaling pathway participates in higher matrix stiffness-induced LOXL2 upregulation in HCC cells. The secreted LOXL2 promotes fibronectin production, MMP9 and CXCL12 expression and BMDCs recruitment to assist pre-metastatic niche formation.

Mycophenolate Mofetil induces c-Jun-N-terminal kinase expression in 22Rv1 cells: an impact on androgen receptor signaling

Mycophenolate Mofetil (MYC) is a transplant drug used to prevent rejection in heart and kidneys transplant patients. Inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in de novo synthesis of guanosine nucleotides, was considered as a primary target for MYC. Recently, we described that MYC was activates aryl hydrocarbon receptor and it antagonizes glucocorticoid receptor. Here we describe an androgen receptor (AR) as another off-target for MYC.

We found that MYC increased basal and dihydrotestosterone (DHT)-inducible AR-dependent luciferase activity in AIZ-AR cells. In the same manner it induced or augmented mRNA level of KLK3 (prostate specific antigen; PSA) in 22Rv1 cells. Herein it displayed a hormetic effect on proliferation activity, since it significantly stimulated proliferation in lower concentrations but inhibited in higher (>1 µg/ml) concentrations in the presence of DHT. In contrast, MYC suppressed DHT-inducible KLK3 mRNA expression and cell proliferation in androgen-dependent LNCaP cells. MYC augmented DHT-inducible nuclear translocation of AR and increased the expression of MAPK8/9 (JNK46/54) resulting in the drop of their phosphorylation status. Moreover, MYC sensitized DHT-treated 22Rv1 cells to JNK-IN-8 mediated growth inhibition with the drop of IC₅₀ from 1425 nM to 84 nM within 24 hrs. In conclusion, we suggest that, castrate-resistant prostate cancers progression might be retarded with the combination of MYC and chemical JNK inhibitors, involving AR-dependent mechanism.

STAT3 activation by E6 is essential for the differentiation-dependent HPV18 life cycle

Human papillomaviruses (HPV) activate a number of host factors to control their differentiation-dependent life cycles. The transcription factor signal transducer and activator of transcription (STAT)-3 is important for cell cycle progression and cell survival in response to cytokines and growth factors. STAT3 requires phosphorylation on Ser727, in addition to phosphorylation on Tyr705 to be transcriptionally active. In this study, we show that STAT3 is essential for the HPV life cycle in undifferentiated and differentiated keratinocytes. Primary human keratinocytes containing high-risk HPV18 genomes display enhanced STAT3 phosphorylation compared to normal keratinocytes. Expression of the E6 oncoprotein is sufficient to induce the dual phosphorylation of STAT3 at Ser727 and Tyr705 by a mechanism requiring Janus kinases and members of the MAPK family. E6-mediated activation of STAT3 induces the transcription of STAT3 responsive genes including cyclin D1 and Bcl-xL. Silencing of STAT3 protein expression by siRNA or inhibition of STAT3 activation by small molecule inhibitors, or by expression of dominant negative STAT3 phosphorylation site mutants, results in blockade of cell cycle progression. Loss of active STAT3 impairs HPV gene expression and prevents episome maintenance in undifferentiated keratinocytes and upon differentiation, lack of active STAT3 abolishes virus genome amplification and late gene expression. Organotypic raft cultures of HPV18 containing keratinocytes expressing a phosphorylation site STAT3 mutant display a profound reduction in suprabasal hyperplasia, which correlates with a loss of cyclin B1 expression and increased differentiation. Finally, increased STAT3 expression and phosphorylation is observed in HPV positive cervical disease biopsies compared to control samples, highlighting a role for STAT3 activation in cervical carcinogenesis. In summary, our data provides evidence of a critical role for STAT3 in the HPV18 life cycle.