Mediator cyclin-dependent kinases upregulate transcription of inflammatory genes in cooperation with NF-κB and C/EBPβ on stimulation of Toll-like receptor 9

Bromo-substituted indirubins for inhibition of protein kinase-mediated signalling involved in inflammatory mediator release in human monocytes

Targeting protein kinases that regulate signalling pathways in inflammation is an effective pharmacological approach to alleviate uncontrolled inflammatory diseases. In this context, the natural product indirubin and its 6-bromo-substituted analogue 6-bromoindirubin-3 -glycerol-oxime ether (6BIGOE; 1) were identified as potent inhibitors of glycogen synthase kinase-3β (GSK-3β). These inhibitors suppress the release of pro-inflammatory cytokines and prostaglandins (PG) from human monocytes. However, indirubin derivatives target several protein kinases such as cyclin-dependent kinases (CDKs) which has been a major concern for their application in inflammation therapy. Here, we report on a library of 13 5-bromo-substituted indirubin derivatives that have been designed to improve potency and target selectivity. Side-by-side comparison of reference compound 1 (6BIGOE) with 5-bromo derivatives revealed its isomer 2 (5BIGOE), as the most potent derivative able to supress pro-inflammatory cytokine and PG release in lipopolysaccharide-stimulated human monocytes. Analysis of protein kinase inhibition in intact monocytes, supported by our in silico findings, proposed higher selectivity of 1 for GSK-3β inhibition with lesser potency against CDKs 8 and 9. In contrast, 2 supressed the activity of these CDKs with higher effectiveness than GSK-3β, representing additional targets of indirubins within the inflammatory response. Encapsulation of 1 and 2 into polymer-based nanoparticles (NP) improved their pharmacological potential. In conclusion, the 5- and 6-brominated indirubins 1 and 2 as dual GSK-3β and CDK8/9 inhibitors represent a novel concept for intervention with inflammatory disorders.

Mediator kinase inhibition suppresses hyperactive interferon signaling in Down syndrome

Hyperactive interferon (IFN) signaling is a hallmark of Down syndrome (DS), a condition caused by trisomy 21 (T21); strategies that normalize IFN signaling could benefit this population. Mediator-associated kinases CDK8 and CDK19 drive inflammatory responses through incompletely understood mechanisms. Using sibling-matched cell lines with/without T21, we investigated Mediator kinase function in the context of hyperactive IFN in DS over a 45min - 24h timeframe. Activation of IFN-response genes was suppressed in cells treated with the CDK8/CDK19 inhibitor cortistatin A (CA), and this occurred through rapid suppression of IFN-responsive transcription factor activity. Moreover, we discovered that CDK8/CDK19 affect splicing, a novel means by which Mediator kinases control gene expression. To further probe Mediator kinase function, we completed cytokine screens and untargeted metabolomics experiments. Cytokines are master regulators of inflammatory responses; by screening 105 different cytokine proteins, we show that Mediator kinases help drive IFN-dependent cytokine responses at least in part through transcriptional regulation of cytokine genes and receptors. Metabolomics revealed that Mediator kinase inhibition altered core metabolic pathways, including broad up-regulation of anti-inflammatory lipid mediators, whose levels were elevated during hyperactive IFN signaling. A subset of these lipid mediators (e.g. oleamide, desmosterol) serve as ligands for nuclear receptors PPAR and LXR, and activation of these receptors occurred specifically during hyperactive IFN signaling in CA-treated cells, revealing a mechanistic link between Mediator kinase activity and nuclear receptor function. Collectively, our results identify new mechanisms by which CDK8/CDK19 regulate gene expression, and establish that Mediator kinase inhibition antagonizes IFN signaling through transcriptional, metabolic, and cytokine responses, with implications for DS and other chronic inflammatory conditions.

Unveiling the impact of CDK8 on tumor progression: mechanisms and therapeutic strategies

CDK8 is an important member of the cyclin-dependent kinase family associated with transcription and acts as a key "molecular switch" in the Mediator complex. CDK8 regulates gene expression by phosphorylating transcription factors and can control the transcription process through Mediator complex. Previous studies confirmed that CDK8 is an important oncogenic factor, making it a potential tumor biomarker and a promising target for tumor therapy. However, CDK8 has also been confirmed to be a tumor suppressor, indicating that it not only promotes the development of tumors but may also be involved in tumor suppression. Therefore, the dual role of CDK8 in the process of tumor development is worth further exploration and summary. This comprehensive review delves into the intricate involvement of CDK8 in transcription-related processes, as well as its role in signaling pathways related to tumorigenesis, with a focus on its critical part in driving cancer progression.

Inhibition of Cyclin-Dependent Kinases 8/19 Restricts Bacterial and Virus-Induced Inflammatory Responses in Monocytes

Hyperactivation of the immune system remains a dramatic, life-threatening complication of viral and bacterial infections, particularly during pneumonia. Therapeutic approaches to counteract local and systemic outbreaks of cytokine storm and to prevent tissue damage remain limited. Cyclin-dependent kinases 8 and 19 (CDK8/19) potentiate transcriptional responses to the altered microenvironment, but CDK8/19 potential in immunoregulation is not fully understood. In the present study, we investigated how a selective CDK8/19 inhibitor, Senexin B, impacts the immunogenic profiles of monocytic cells stimulated using influenza virus H1N1 or bacterial lipopolysaccharides. Senexin B was able to prevent the induction of gene expression of proinflammatory cytokines in THP1 and U937 cell lines and in human peripheral blood-derived mononuclear cells. Moreover, Senexin B substantially reduced functional manifestations of inflammation, including clustering and chemokine-dependent migration of THP1 monocytes and human pulmonary fibroblasts (HPF).

Design, synthesis, and biological evaluation of indolin-2-one derivatives as novel cyclin-dependent protein kinase 8 (CDK8) inhibitors

Cyclin-dependent protein kinase 8 (CDK8) plays important roles in regulating fibrotic growth factors and inflammatory signaling pathways. Long-term chronic inflammation of the lungs can lead to idiopathic pulmonary fibrosis (IPF). Abnormal alveolar epithelial regeneration leads to the release of various fibrotic growth factors and the activation of inflammatory cells. CDK8 regulates profibrotic cytokines broadly implicated in the pathogenesis of fibrosis. Therefore, inhibition of CDK8 is considered a promising strategy for treating IPF. Here, CDK8 inhibitors were designed and optimized using a fragment-based drug design strategy. Testing results revealed that 71% of the synthesized compounds inhibited CDK8 activity better than the original compound E966-0530. Of these compounds, compound 4k exhibited the strongest CDK8 enzyme-inhibiting activity (IC₅₀ =129 nM). Notably, it displayed a 13-fold increase in potency when compared to E966-0530. Experiments on toxicity and inhibition of epithelial-mesenchymal transition (EMT) protein expressions showed that compound 4k can inhibit EMT protein expressions, but with no significant cytotoxicity for alveolar epithelial cells. Compound 4k showed a potent inhibitory effect in cell migration assays. Furthermore, compound 4k significantly inhibited the phosphorylation of p-Smad3 and RNA Pol II, which are critical mediators in the fibrotic response signaling pathway. Compound 4k remarkably reduced TGF-β1-induced oxidative stress. The above results reveal optimized CDK8 inhibitors with potential use for IPF therapeutic treatment.

TNF-α Induced Myotube Atrophy in C2C12 Cell Line Uncovers Putative Inflammatory-Related lncRNAs Mediating Muscle Wasting

Background: Muscle atrophy is a complex catabolic condition developing under different inflammatory-related systemic diseases resulting in wasting of muscle tissue. While the knowledge of the molecular background of muscle atrophy has developed in recent years, how the atrophic conditions affect the long non-coding RNA (lncRNAs) machinery and the exact participation of the latter in the mediation of muscle loss are still unknown. The purpose of the study was to assess how inflammatory condition developing under the tumor necrosis factor alpha (TNF-α) treatment affects the lncRNAs’ expression in a mouse skeletal muscle cell line. Materials and method: A C2C12 mouse myoblast cell line was treated with TNF-α to develop atrophy, and inflammatory-related lncRNAs mediating muscle loss were identified. Bioinformatics was used to validate and analyze the discovered lncRNAs. The differences in their expression under different TNF-α concentrations and treatment times were investigated. Results: Five lncRNAs were identified in a discovery set as atrophy related and then validated. Three lncRNAs, Gm4117, Ccdc41os1, and 5830418P13Rik, were selected as being significant for inflammatory-related myotube atrophy. Dynamics changes in the expression of lncRNAs depended on both TNF-α concentration and treatment time. Bioinformatics analysis revealed the mRNA and miRNA target for selected lncRNAs and their putative involvement in the molecular processes related to muscle atrophy. Conclusions: The inflammatory condition developing in the myotube under the TNF-α treatment affects the alteration of lncRNAs’ expression pattern. Experimental and bioinformatics testing suggested the prospective role of lncRNAs in the mediation of muscle loss under an inflammatory state.

The emerging roles of the CDK/cyclin complexes in antiviral innate immunity

More than 20 members of the human Cyclin-dependent kinases (CDKs) family share the feature of being activated by cyclins. CDKs have been involved in diverse biological processes, such as cell cycle, transcription, DNA damage response, and apoptosis. If CDKs are not properly regulated, they can cause diseases like cancer. CDKs are Ser/Thr kinases that work with cyclins to control cell cycle progression. Various CDK-cyclin complexes phosphorylate particular target proteins and drive different cell cycle stages. Accumulating evidence demonstrated that CDKs play an essential role in the cell cycle; however, their roles in antiviral innate immunity are just emerging. This minireview summarizes how CDKs play their roles in antiviral innate immunity. Our goal is to draw attention to the involvement of CDKs in antiviral innate immunity, whether as separate entities or as components of CDK/cyclin complexes that have gotten less attention in the past. This article is protected by copyright. All rights reserved.

Hypoxic stress suppresses lung tumor-secreted exosomal miR101 to activate macrophages and induce inflammation

Hypoxia promotes inflammation in the tumor microenvironment. Although hypoxia-inducible factor 1α (HIF1α) is a master modulator of the response to hypoxia, the exact mechanisms through which HIF1α regulates the induction of inflammation remain largely unclear. Using The Cancer Genome Atlas Lung Squamous Cell Carcinoma (TCGA-LUSC) database, we divided patients with LUSC into two groups based on low or high HIF1α expression. After analyzing the differentially expressed genes in these two groups, we found that HIF1α was positively correlated with interleukin 1A (IL1A) and IL6 expression. Our in vitro study showed that hypoxic stress did not induce IL1A or IL6 expression in tumor cells or macrophages but dramatically enhanced their expression when co-cultured with tumor cells. We then investigated the effect of tumor-derived exosomes on macrophages. Our data suggested that the changes in miR101 in the tumor-derived exosomes played an important role in IL1A and IL6 expression in macrophages, although the hypoxic stress did not change the total amount of exosome secretion. The expression of miR101 in exosomes was suppressed by hypoxic stress, since depletion of HIF1α in tumor cells recovered the miR101 expression in both tumor cells and exosomes. In vitro, miRNA101 overexpression or uptake enriched exosomes by macrophages suppressed their reprogramming into a pro-inflammatory state by targeting CDK8. Injection of miR101 into xenografted tumors resulted in the suppression of tumor growth and macrophage tumor infiltration in vivo. Collectively, this study suggests that the HIF1α-dependent suppression of exosome miR101 from hypoxic tumor cells activates macrophages to induce inflammation in the tumor microenvironment.

Angel or Devil ? - CDK8 as the new drug target

Cyclin-dependent kinase 8 (CDK8) plays an momentous role in transcription regulation by forming kinase module or transcription factor phosphorylation. A large number of evidences have identified CDK8 as an important factor in cancer occurrence and development. In addition, CDK8 also participates in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis, and drug resistance. Therefore, CDK8 is regarded as a promising target for cancer therapy. Most studies in recent years supported the role of CDK8 as a carcinogen, however, under certain conditions, CDK8 exists as a tumor suppressor. The functional diversity of CDK8 and its exceptional role in different types of cancer have aroused great interest from scientists but even more controversy during the discovery of CDK8 inhibitors. In addition, CDK8 appears to be an effective target for inflammation diseases and immune system disorders. Therefore, we summarized the research results of CDK8, involving physiological/pathogenic mechanisms and the development status of compounds targeting CDK8, provide a reference for the feasibility evaluation of CDK8 as a therapeutic target, and guidance for researchers who are involved in this field for the first time.

Transcriptional cyclin-dependent kinases as the mediators of inflammation-a review

Cyclin-dependent kinases (CDKs) belong to the serine/threonine kinase family, and their unique interactions with a variety of cyclin complexes influence its catalytic activity to ensure unimpaired cell cycle progression. In addition to their cell cycle regulatory roles, it is becoming increasingly clear that the CDKs can have multiple functional roles like transcription, epigenetic regulation, metabolism, stem cell self-renewal, neuronal functions, and in spermatogenesis. Further in addition, recent reports suggest that CDKs have a remarkable regulatory role in influencing the pro-inflammatory functions of various cytokines during the clinical inflammatory responses. CDKs initiate the inflammatory responses by triggering the activity of prominent pro-inflammatory transcription factors such as nuclear factor kappa B (NF-kB), signal transducer and activator of transcription 3 (STAT3), and activator protein 1 (AP-1). The transcriptional CDKs (tCDKs) is crucial for organizing various transcription events and associated processes such as RNA capping, splicing, 3' end formation, and chromatin remodeling. Although the in-depth mechanism of certain mammalian CDKs is explored with respect to inflammation, the role of other tCDKs or any synergistic play among the members still remains unexplored. Until today, there is only supportive and palliative care available most of the inflammatory disorders, and thus it is the right time to explore novel pharmacological targets. In this regard, we focus on the pathophysiological role of CDK7, CDK8 and CDK9 and their impact on the development of inflammatory disorders within the mammals. Additionally, we discuss the potential trends of having tCDKs as a therapeutic target for fine-tuning inflammatory disorders.

CDK8-Novel Therapeutic Opportunities

Improvements in cancer therapy frequently stem from the development of new small-molecule inhibitors, paralleled by the identification of biomarkers that can predict the treatment response. Recent evidence supports the idea that cyclin-dependent kinase 8 (CDK8) may represent a potential drug target for breast and prostate cancer, although no CDK8 inhibitors have entered the clinics. As the available inhibitors have been recently reviewed, we focus on the biological functions of CDK8 and provide an overview of the complexity of CDK8-dependent signaling throughout evolution and CDK8-dependent effects that may open novel treatment avenues.

Human granulosa cells function as innate immune cells executing an inflammatory reaction during ovulation: a microarray analysis

Ovulation has been compared to a local inflammatory reaction. We performed an in silico study on a unique, PCR validated, transcriptome microarray study to evaluate if known inflammatory mechanisms operate during ovulation. The granulosa cells were obtained in paired samples at two different time points during ovulation (just before and 36 hours after ovulation induction) from nine women receiving fertility treatment. A total of 259 genes related to inflammation became significantly upregulated during ovulation (2-80 fold, p<0.05), while specific leukocyte markers were absent. The genes and pathway analysis indicated NF-KB-, MAPK- and JAK/STAT signalling (p<1.0E-10) as the major pathways involved in danger recognition and cytokine signalling to initiate inflammation. Upregulated genes further encoded enzymes in eicosanoid production, chemo-attractants, coagulation factors, cell proliferation factors involved in tissue repair, and anti-inflammatory factors to resolve the inflammation again. We conclude that granulosa cells, without involvement from the innate immune system, can orchestrate ovulation as a complete sterile inflammatory reaction.

Molecular and in vivo Functions of the CDK8 and CDK19 Kinase Modules

CDK8 and its paralog, CDK19, collectively termed ‘Mediator Kinase,’ are cyclin-dependent kinases that have been implicated as key rheostats in cellular homeostasis and developmental programming. CDK8 and CDK19 are incorporated, in a mutually exclusive manner, as part of a 4-protein complex called the Mediator kinase module. This module reversibly associates with the Mediator, a 26 subunit protein complex that regulates RNA Polymerase II mediated gene expression. As part of this complex, the Mediator kinases have been implicated in diverse process such as developmental signaling, metabolic homeostasis and in innate immunity. In recent years, dysregulation of Mediator kinase module proteins, including CDK8/19, has been implicated in the development of different human diseases, and in particular cancer. This has led to intense efforts to understand how CDK8/19 regulate diverse biological outputs and develop Mediator kinase inhibitors that can be exploited therapeutically. Herein, we review both context and function of the Mediator kinases at a molecular, cellular and animal level. In so doing, we illuminate emerging concepts underpinning Mediator kinase biology and highlight certain aspects that remain unsolved.

Structure and Functions of the Mediator Complex

Mediator is a key factor in the regulation of expression of RNA polymerase II-transcribed genes. Recent studies have shown that Mediator acts as a coordinator of transcription activation and participates in maintaining chromatin architecture in the cell nucleus. In this review, we present current concepts on the structure and functions of Mediator.

CDK8/19 Mediator kinases potentiate induction of transcription by NFκB

The nuclear factor-κB (NFκB) family of transcription factors has been implicated in inflammatory disorders, viral infections, and cancer. Most of the drugs that inhibit NFκB show significant side effects, possibly due to sustained NFκB suppression. Drugs affecting induced, but not basal, NFκB activity may have the potential to provide therapeutic benefit without associated toxicity. NFκB activation by stress-inducible cell cycle inhibitor p21 was shown to be mediated by a p21-stimulated transcription-regulating kinase CDK8. CDK8 and its paralog CDK19, associated with the transcriptional Mediator complex, act as coregulators of several transcription factors implicated in cancer; CDK8/19 inhibitors are entering clinical development. Here we show that CDK8/19 inhibition by different small-molecule kinase inhibitors or shRNAs suppresses the elongation of NFκB-induced transcription when such transcription is activated by p21-independent canonical inducers, such as TNFα. On NFκB activation, CDK8/19 are corecruited with NFκB to the promoters of the responsive genes. Inhibition of CDK8/19 kinase activity suppresses the RNA polymerase II C-terminal domain phosphorylation required for transcriptional elongation, in a gene-specific manner. Genes coregulated by CDK8/19 and NFκB include IL8, CXCL1, and CXCL2, which encode tumor-promoting proinflammatory cytokines. Although it suppressed newly induced NFκB-driven transcription, CDK8/19 inhibition in most cases had no effect on the basal expression of NFκB-regulated genes or promoters; the same selective regulation of newly induced transcription was observed with other transcription signals potentiated by CDK8/19. This selective role of CDK8/19 identifies these kinases as mediators of transcriptional reprogramming, a key aspect of development and differentiation as well as pathological processes.

Small-molecule studies identify CDK8 as a regulator of IL-10 in myeloid cells

Enhancing production of the anti-inflammatory cytokine interleukin-10 (IL-10) is a promising strategy to suppress pathogenic inflammation. To identify new mechanisms regulating IL-10 production, we conducted a phenotypic screen for small molecules that enhance IL-10 secretion from activated dendritic cells. Mechanism-of-action studies using a prioritized hit from the screen, BRD6989, identified the Mediator-associated kinase CDK8, and its paralog CDK19, as negative regulators of IL-10 production during innate immune activation. The ability of BRD6989 to upregulate IL-10 is recapitulated by multiple, structurally differentiated CDK8 and CDK19 inhibitors and requires an intact cyclin C-CDK8 complex. Using a highly parallel pathway reporter assay, we identified a role for enhanced AP-1 activity in IL-10 potentiation following CDK8 and CDK19 inhibition, an effect associated with reduced phosphorylation of a negative regulatory site on c-Jun. These findings identify a function for CDK8 and CDK19 in regulating innate immune activation and suggest that these kinases may warrant consideration as therapeutic targets for inflammatory disorders.