Mitogen-activated protein kinase p38 controls the expression and posttranslational modification of tristetraprolin, a regulator of tumor necrosis factor alpha mRNA stability

Accelerated Bone Healing via Electrical Stimulation

Piezoelectric effect produces an electrical signal when stress is applied to the bone. When the integrity of the bone is destroyed, the biopotential within the defect site is reduced and several physiological responses are initiated to facilitate healing. During the healing of the bone defect, the bioelectric potential returns to normal levels. Treatment of fractures that exceed innate regenerative capacity or exhibit delayed healing requires surgical intervention for bone reconstruction. For bone defects that cannot heal on their own, exogenous electric fields are used to assist in treatment. This paper reviews the effects of exogenous electrical stimulation on bone healing, including osteogenesis, angiogenesis, reduction in inflammation and effects on the peripheral nervous system. This paper also reviews novel electrical stimulation methods, such as small power supplies and nanogenerators, that have emerged in recent years. Finally, the challenges and future trends of using electrical stimulation therapy for accelerating bone healing are discussed.

Dynamical and combinatorial coding by MAPK p38 and NFκB in the inflammatory response of macrophages

Macrophages sense pathogens and orchestrate specific immune responses. Stimulus specificity is thought to be achieved through combinatorial and dynamical coding by signaling pathways. While NFκB dynamics are known to encode stimulus information, dynamical coding in other signaling pathways and their combinatorial coordination remain unclear. Here, we established live-cell microscopy to investigate how NFκB and p38 dynamics interface in stimulated macrophages. Information theory and machine learning revealed that p38 dynamics distinguish cytokine TNF from pathogen-associated molecular patterns and high doses from low, but contributed little to information-rich NFκB dynamics when both pathways are considered. This suggests that immune response genes benefit from decoding immune signaling dynamics or combinatorics, but not both. We found that the heterogeneity of the two pathways is surprisingly uncorrelated. Mathematical modeling revealed potential sources of uncorrelated heterogeneity in the branched pathway network topology and predicted it to drive gene expression variability. Indeed, genes dependent on both p38 and NFκB showed high scRNAseq variability and bimodality. These results identify combinatorial signaling as a mechanism to restrict NFκB-AND-p38-responsive inflammatory cytokine expression to few cells.

Post-transcriptional regulation of BIRC5/survivin expression and induction of apoptosis in breast cancer cells by tristetraprolin

Inhibition of apoptosis is one of the hallmarks of cancer and is a target of various therapeutic interventions. BIRC5 is an inhibitor of apoptosis that is aberrantly expressed in cancer leading to sustained growth of tumours. Post-transcriptional control mechanisms involving RNA-binding proteins and AU-rich elements (AREs) are fundamental to many cellular processes and changes in the expression or function of these proteins can promote an aberrant and pathological phenotype. BIRC5 mRNA has an ARE in its 3' UTR making it a candidate for regulation by the RNA binding proteins tristetraprolin (TTP) and HuR (ELAVL1). In this study, we investigated the binding of TTP and HuR by RNA-immunoprecipitation assays and found that these proteins were associated with BIRC5 mRNA to varying extents. Consequently, BIRC5 expression decreased when TTP was overexpressed and apoptosis was induced. In the absence of TTP, BIRC5 mRNA was stabilized, protein expression increased and the number of apoptotic cells declined. As an ARE-mRNA stabilizing protein, recombinant HuR led to upregulation of BIRC5 expression, whereas HuR silencing was concomitant with downregulation of BIRC5 mRNA and protein and increased cell death. Survival analyses demonstrated that increased TTP and low BIRC5 expression predicted an overall better prognosis compared to dysregulated TTP and high BIRC5. Thus, the results present a novel target of ARE-mediated post-transcriptional regulation.

Epstein-Barr virus infectious particles initiate B cell transformation and modulate cytokine response

IMPORTANCE

The Epstein-Barr virus efficiently infects and transforms B lymphocytes. During this process, infectious viral particles transport the viral genome to the nucleus of target cells. We show here that these complex viral structures serve additional crucial roles by activating transcription of the transforming genes encoded by the virus. We show that components of the infectious particle sequentially activate proinflammatory B lymphocyte signaling pathways that, in turn, activate viral gene expression but also cause cytokine release. However, virus infection activates expression of ZFP36L1, an RNA-binding stress protein that limits the length and the intensity of the cytokine response. Thus, the infectious particles can activate viral gene expression and initiate cellular transformation at the price of a limited immune response.

Externalized histones fuel pulmonary fibrosis via a platelet-macrophage circuit of TGFβ1 and IL-27

Externalized histones erupt from the nucleus as extracellular traps, are associated with several acute and chronic lung disorders, but their implications in the molecular pathogenesis of interstitial lung disease are incompletely defined. To investigate the role and molecular mechanisms of externalized histones within the immunologic networks of pulmonary fibrosis, we studied externalized histones in human and animal bronchoalveolar lavage (BAL) samples of lung fibrosis. Neutralizing anti-histone antibodies were administered in bleomycin-induced fibrosis of C57BL/6 J mice, and subsequent studies used conditional/constitutive knockout mouse strains for TGFβ and IL-27 signaling along with isolated platelets and cultured macrophages. We found that externalized histones (citH3) were significantly (P < 0.01) increased in cell-free BAL fluids of patients with idiopathic pulmonary fibrosis (IPF; n = 29) as compared to healthy controls (n = 10). The pulmonary sources of externalized histones were Ly6G+CD11b+ neutrophils and nonhematopoietic cells after bleomycin in mice. Neutralizing monoclonal anti-histone H2A/H4 antibodies reduced the pulmonary collagen accumulation and hydroxyproline concentration. Histones activated platelets to release TGFβ1, which signaled through the TGFbRI/TGFbRII receptor complex on LysM+ cells to antagonize macrophage-derived IL-27 production. TGFβ1 evoked multiple downstream mechanisms in macrophages, including p38 MAPK, tristetraprolin, IL-10, and binding of SMAD3 to the IL-27 promotor regions. IL-27RA-deficient mice displayed more severe collagen depositions suggesting that intact IL-27 signaling limits fibrosis. In conclusion, externalized histones inactivate a safety switch of antifibrotic, macrophage-derived IL-27 by boosting platelet-derived TGFβ1. Externalized histones are accessible to neutralizing antibodies for improving the severity of experimental pulmonary fibrosis.

A Wnt-induced lncRNA-DGCR5 splicing switch drives tumor-promoting inflammation in esophageal squamous cell carcinoma

Alternative splicing (AS) is a critical mechanism for the aberrant biogenesis of long non-coding RNA (lncRNA). Although the role of Wnt signaling in AS has been implicated, it remains unclear how it mediates lncRNA splicing during cancer progression. Herein, we identify that Wnt3a induces a splicing switch of lncRNA-DGCR5 to generate a short variant (DGCR5-S) that correlates with poor prognosis in esophageal squamous cell carcinoma (ESCC). Upon Wnt3a stimulation, active nuclear β-catenin acts as a co-factor of FUS to facilitate the spliceosome assembly and the generation of DGCR5-S. DGCR5-S inhibits TTP's anti-inflammatory activity by protecting it from PP2A-mediated dephosphorylation, thus fostering tumor-promoting inflammation. Importantly, synthetic splice-switching oligonucleotides (SSOs) disrupt the splicing switch of DGCR5 and potently suppress ESCC tumor growth. These findings uncover the mechanism for Wnt signaling in lncRNA splicing and suggest that the DGCR5 splicing switch may be a targetable vulnerability in ESCC.

Self-delivering mRNA inhibitors of MK2 improve outcomes after spinal cord injury

Functional recovery and tissue damage after spinal cord injury (SCI) are influenced by secondary damage mechanisms, including inflammation. The inflammatory response after SCI relies on a variety of cell types with both protective and cytotoxic functions. The macrophage derived MAPK-activated protein kinase 2 has been described as a critical regulator of inflammation with detrimental function after SCI. Targeted modification of inflammatory effector molecules after SCI faces challenges of optimal timing, dosage and location of administration. Modified RNA inhibitors, FANA antisense oligonucleotides, are promising inhibitors due to their stability, local penetration of cells and high efficacy in targeted suppression. Here, we describe the use of anti- MAPK-activated protein kinase 2 FANA antisense oligonucleotides in a mouse model of contusional SCI. The most efficient inhibitor was selected with in vitro and in vivo techniques and then applied via intrathecal injections after SCI. This treatment resulted in improved gait applying DigiGait assessments and tissue preservation, indicating the usefulness of the target and inhibition approach.

The nexus between RNA-binding proteins and their effectors

RNA-binding proteins (RBPs) regulate essentially every event in the lifetime of an RNA molecule, from its production to its destruction. Whereas much has been learned about RNA sequence specificity and general functions of individual RBPs, the ways in which numerous RBPs instruct a much smaller number of effector molecules, that is, the core engines of RNA processing, as to where, when and how to act remain largely speculative. Here, we survey the known modes of communication between RBPs and their effectors with a particular focus on converging RBP-effector interactions and their roles in reducing the complexity of RNA networks. We discern the emerging unifying principles and discuss their utility in our understanding of RBP function, regulation of biological processes and contribution to human disease.

Circular RNA as biomarkers for acute ischemic stroke: A systematic review and meta-analysis

BACKGROUND

Rapid diagnosis of acute ischemic stroke (AIS) patients is still challenging, and reliable biomarkers are needed. Noncoding RNAs are important for many physiological activities, among which circular RNAs (circRNAs) have been proven to be more tissue-specific and conservative. Many recent studies found the potential of circRNAs as biomarkers for many diseases, including cardiovascular diseases, cancers, and ischemic stroke. This systemic review and meta-analysis aimed to identify circRNAs as potential biomarkers for AIS.

METHODS

This study has been prospectively registered in PROSPERO (Registration No. 11 CRD42021288033). Published literature comparing circRNA expression profiles between AIS and non-AIS in human and animal models were retrieved from the articles published by January 2023 in major databases. We descriptively summarized the included studies, conducted meta-analysis under a random effects model, and did bioinformatics analysis including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis.

RESULTS

Totally 23 studies were included, reporting 18 distinctive upregulated and 20 distinctive downregulated circRNAs. Diagnostic meta-analysis indicated discriminative ability of the circRNAs. Furthermore, circRNA HECTD1, circRNA DLGAP4, circRNA CDC14A, circRNA SCMH1, and circRNA TLK1 were reported with the same regulation trend in more than one study (animal studies included). GO and KEGG enrichment analyses indicated that the target genes of these five circRNAs were enriched in regulating cell proliferation, apoptosis, and oxidative stress.

CONCLUSIONS

This study demonstrates that circRNAs (circRNA HECTD1, circRNA DLGAP4, circRNA CDC14A, circRNA SCMH1, and circRNA TLK1) generally are promising as potential biomarkers for AIS. However, due to the limited number of studies, diagnostic value of individual circRNA could not be validated. More in vitro and in vivo functional studies are needed.

Innate immune sensing of pathogens and its post-transcriptional regulations by RNA-binding proteins

Innate immunity is one of the most ancient and conserved aspect of the immune system. It is responsible for an anti-infective response and has been intrinsically linked to the generation of inflammation. While the inflammatory response entails signaling to the adaptive immune system, it can be self-perpetuating and over-exaggerated, resulting in deleterious consequences, including cytokine storm, sepsis, and the development of inflammatory and autoimmune diseases. Cytokines are the defining features of the immune system. They are critical to mediation of inflammation and host immune defense, and are tightly regulated at several levels, including transcriptional and post-transcriptional levels. Recently, the role of post-transcriptional regulation in fine-tuning cytokine expression has become more appreciated. This interest has advanced our understanding of how various mechanisms are integrated and regulated to determine the amount of cytokine production in cells during inflammatory responses. Here, we would like to review how innate immunity recognizes and responds to pathogens by pattern-recognition receptors, and the molecular mechanisms regulating inflammatory responses, with a focus on the post-transcriptional regulations of inflammatory mediators by RNA-binding proteins, especially Regnase-1. Finally, we will discuss the regulatory mechanisms of Regnase-1 and highlight therapeutic strategies based on targeting Regnase-1 activity and its turnover as potential treatment options for chronic and autoimmune diseases.

Clinical implications of tristetraprolin (TTP) modulation in the treatment of inflammatory diseases

Abnormal regulation of pro-inflammatory cytokine and chemokine mediators can contribute to the excess inflammation characteristic of many autoimmune diseases, such as rheumatoid arthritis, psoriasis, Crohn's disease, type 1 diabetes, and many others. The tristetraprolin (TTP) family consists of a small group of related RNA-binding proteins that bind to preferred AU-rich binding sites within the 3'-untranslated regions of specific mRNAs to promote mRNA deadenylation and decay. TTP deficient mice develop a severe systemic inflammatory syndrome consisting of arthritis, myeloid hyperplasia, dermatitis, autoimmunity and cachexia, due at least in part to the excess accumulation of proinflammatory chemokine and cytokine mRNAs and their encoded proteins. To investigate the possibility that increased TTP expression or activity might have a beneficial effect on inflammatory diseases, at least two mouse models have been developed that provide proof of principle that increasing TTP activity can promote the decay of pro-inflammatory and other relevant transcripts, and decrease the severity of mouse models of inflammatory disease. Animal studies of this type are summarized here, and we briefly review the prospects for harnessing these insights for the development of TTP-based anti-inflammatory treatments in humans.

Regulation of CCR4-NOT complex deadenylase activity and cellular responses by MK2-dependent phosphorylation of CNOT2

CCR4-NOT complex-mediated mRNA deadenylation serves critical functions in multiple biological processes, yet how this activity is regulated is not fully understood. Here, we show that osmotic stress induces MAPKAPK-2 (MK2)-mediated phosphorylation of CNOT2. Programmed cell death is greatly enhanced by osmotic stress in CNOT2-depleted cells, indicating that CNOT2 is responsible for stress resistance of cells. Although wild-type (WT) and non-phosphorylatable CNOT2 mutants reverse this sensitivity, a phosphomimetic form of CNOT2, in which serine at the phosphorylation site is replaced with glutamate, does not have this function. We also show that mRNAs have elongated poly(A) tails in CNOT2-depleted cells and that introduction of CNOT2 WT or a non-phosphorylatable mutant, but not phosphomimetic CNOT2, renders their poly(A) tail lengths comparable to those in control HeLa cells. Consistent with this, the CCR4-NOT complex containing phosphomimetic CNOT2 exhibits less deadenylase activity than that containing CNOT2 WT. These data suggest that CCR4-NOT complex deadenylase activity is regulated by post-translational modification, yielding dynamic control of mRNA deadenylation.

Capacitive electrical stimulation of a conducting polymeric thin film induces human mesenchymal stem cell osteogenesis

Electroactive materials based on conductive polymers are promising options for tissue engineering and regenerative medicine applications. In the present work, the conducting copolymers of poly (3,4-ethylenedioxythiophene) and poly (d, l-lactic acid) (PEDOT-co-PDLLA) with PEDOT:PDLLA molar ratios of 1:50, 1:25, and 1:5 were synthesized and compared to the insulating macromonomer of EDOT-PDLLA as an experimental control. Bone marrow-derived human mesenchymal stem cells (hMSC-BM) were cultured on the copolymers and the macromonomer thin films inside a bioreactor that induced a capacitive electrical stimulation (CES) with an electric field of 100 mV/mm for 2 h per day for 21 days. Under CES, the copolymers exhibited good cell viability and promoted the differentiation from hMSC-BM to osteogenic lineages, revealed by higher mineralization mainly when the contents of conducting segments of PEDOT (i.e., copolymer with 1:25 and 1:5 PEDOT:PDLLA ratios) were increased. The results indicate that the intrinsic electrical conductivity of the substrates is an important key point for the effectiveness of the electric field generated by the CES, intending to promote the differentiation effect for bone cells.

Mitogen-activated protein kinase-activated protein kinase-2 (MK2) and its role in cell survival, inflammatory signaling, and migration in promoting cancer

Cancer and the immune system share an intimate relationship. Chronic inflammation increases the risk of cancer occurrence and can also drive inflammatory mediators into the tumor microenvironment enhancing tumor growth and survival. The p38 MAPK pathway is activated both acutely and chronically by stress, inflammatory chemokines, chronic inflammatory conditions, and cancer. These properties have led to extensive efforts to find effective drugs targeting p38, which have been unsuccessful. The immediate downstream serine/threonine kinase and substrate of p38 MAPK, mitogen-activated-protein-kinase-activated-protein-kinase-2 (MK2) protects cells against stressors by regulating the DNA damage response, transcription, protein and messenger RNA stability, and motility. The phosphorylation of downstream substrates by MK2 increases inflammatory cytokine production, drives an immune response, and contributes to wound healing. By binding directly to p38 MAPK, MK2 is responsible for the export of p38 MAPK from the nucleus which gives MK2 properties that make it unique among the large number of p38 MAPK substrates. Many of the substrates of both p38 MAPK and MK2 are separated between the cytosol and nucleus and interfering with MK2 and altering this intracellular translocation has implications for the actions of both p38 MAPK and MK2. The inhibition of MK2 has shown promise in combination with both chemotherapy and radiotherapy as a method for controlling cancer growth and metastasis in a variety of cancers. Whereas the current data are encouraging the field requires the development of selective and well tolerated drugs to target MK2 and a better understanding of its effects for effective clinical use.

Post-transcriptional screen of cancer amplified genes identifies ERBB2/Her2 signaling as AU-rich mRNA stability-promoting pathway

Amplification of specific cancer genes leads to their over-expression contributing to tumor growth, spread, and drug resistance. Little is known about the ability of these amplified oncogenes to augment the expression of cancer genes through post-transcriptional control. The AU-rich elements (ARE)-mediated mRNA decay is compromised for many key cancer genes leading to their increased abundance and effects. Here, we performed a post-transcriptional screen for frequently amplified cancer genes demonstrating that ERBB2/Her2 overexpression was able to augment the post-transcriptional effects. The ERBB1/2 inhibitor, lapatinib, led to the reversal of the aberrant ARE-mediated process in ERBB2-amplified breast cancer cells. The intersection of overexpressed genes associated with ERBB2 amplification in TCGA datasets with ARE database (ARED) identified ERBB2-associated gene cluster. Many of these genes were over-expressed in the ERBB2-positive SKBR3 cells compared to MCF10A normal-like cells, and were under-expressed due to ERBB2 siRNA treatment. Lapatinib accelerated the ARE-mRNA decay for several ERBB2-regulated genes. The ERBB2 inhibitor decreased both the abundance and stability of the phosphorylated inactive form of the mRNA decay-promoting protein, tristetraprolin (ZFP36/TTP). The ERBB2 siRNA was also able to reduce the phosphorylated ZFP36/TTP form. In contrast, ectopic expression of ERBB2 in MCF10A or HEK293 cells led to increased abundance of the phosphorylated ZFP36/TTP. The effect of ERBB2 on TTP phosphorylation appeared to be mediated via the MAPK-MK2 pathway. Screening for the impact of other amplified cancer genes in HEK293 cells also demonstrated that EGFR, AKT2, CCND1, CCNE1, SKP2, and FGFR3 caused both increased abundance of phosphorylated ZFP36/TTP and ARE-post-transcriptional reporter activity. Thus, specific amplified oncogenes dysregulate post-transcriptional ARE-mediated effects, and targeting the ARE-mediated pathway itself may provide alternative therapeutic approaches.

Stimulus-specific responses in innate immunity: Multilayered regulatory circuits

Immune sentinel cells initiate immune responses to pathogens and tissue injury and are capable of producing highly stimulus-specific responses. Insight into the mechanisms underlying such specificity has come from the identification of regulatory factors and biochemical pathways, as well as the definition of signaling circuits that enable combinatorial and temporal coding of information. Here, we review the multi-layered molecular mechanisms that underlie stimulus-specific gene expression in macrophages. We categorize components of inflammatory and anti-pathogenic signaling pathways into five layers of regulatory control and discuss unifying mechanisms determining signaling characteristics at each layer. In this context, we review mechanisms that enable combinatorial and temporal encoding of information, identify recurring regulatory motifs and principles, and present strategies for integrating experimental and computational approaches toward the understanding of signaling specificity in innate immunity.

Understanding Abnormal c-JNK/p38MAPK Signaling Overactivation Involved in the Progression of Multiple Sclerosis: Possible Therapeutic Targets and Impact on Neurodegenerative Diseases

Demyelination, immune dysregulation, and neuroinflammation are the most common triggers of motor neuron disorders such as multiple sclerosis (MS). MS is a chronic demyelinating neurodegenerative disease of the central nervous system caused by abnormal immune activation, which causes myelin sheath damage. Cell signal transduction pathways are required for a variety of physiological and pathological processes in the brain. When these signaling systems become overactive, they can lead to disease progression. In various physiological conditions, abnormal mitogen-activated protein kinase (MAPK) activation is associated with several physiological dysfunctions that cause neurodegeneration. Previous research indicates that c-JNK and p38MAPK signaling play critical roles in neuronal growth and differentiation. c-JNK/p38MAPK is a member of the MAPK family, which regulates metabolic pathways, cell proliferation, differentiation, and apoptosis that control certain neurological activities. During brain injuries, c-JNK/p38MAPK also affects neuronal elastic properties, nerve growth, and cognitive processing. This review systematically linked abnormal c-JNK/p38MAPK signaling activation to multiple neuropathological pathways in MS and related neurological dysfunctions. MS progression is linked to genetic defects, oligodendrocyte destruction, glial overactivation, and immune dysregulation. We concluded that inhibiting both the c-JNK/p38MAPK signaling pathways can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of MS and influence other neurological disorders. As a result, the potential benefits of c-JNK/p38MAPK downregulation for the development of disease-modifying treatment interventions in the future could include MS prevention and related neurocomplications.

Kinome inhibition reveals a role for polo-like kinase 1 in targeting post-transcriptional control in cancer

Dysfunctions in post-transcriptional control are observed in cancer and chronic inflammatory diseases. Here, we employed a kinome inhibitor library (n = 378) in a reporter system selective for 3'-untranslated region-AU-rich elements (ARE). Fifteen inhibitors reduced the ARE-reporter activity; among the targets is the polo-like kinase 1 (PLK1). RNA-seq experiments demonstrated that the PLK1 inhibitor, volasertib, reduces the expression of cytokine and cell growth ARE mRNAs. PLK1 inhibition caused accelerated mRNA decay in cancer cells and was associated with reduced phosphorylation and stability of the mRNA decay-promoting protein, tristetraprolin (ZFP36/TTP). Ectopic expression of PLK1 increased abundance and stability of high molecular weight of ZFP36/TTP likely of the phosphorylated form. PLK1 effect was associated with the MAPK-MK2 pathway, a major regulator of ARE-mRNA stability, as evident from MK2 inhibition, in vitro phosphorylation, and knockout experiments. Mutational analysis demonstrates that TTP serine 186 is a target for PLK1 effect. Treatment of mice with the PLK1 inhibitor reduced both ZFP36/TTP phosphorylation in xenograft tumor tissues, and the tumor size. In cancer patients' tissues, PLK1/ARE-regulated gene cluster was overexpressed in solid tumors and associated with poor survival. The data showed that PLK1-mediated post-transcriptional aberration could be a therapeutic target.

Targeting Tristetraprolin Expression or Functional Activity Regulates Inflammatory Response Induced by MSU Crystals

The RNA-binding protein tristetraprolin (TTP) is an anti-inflammatory factor that prompts the mRNA decay of target mRNAs and is involved in inflammatory diseases such as rheumatoid arthritis (RA). TTP is regulated by phosphorylation, and protein phosphatase 2A (PP2A) can dephosphorylate TTP to activate its mRNA-degrading function. Some small molecules can enhance PP2A activation. Short interfering RNA (siRNA) targeting TTP expression or PP2A agonist (Arctigenin) was administered to monosodium urate (MSU) crystal-induced J774A.1 cells, and the expression of inflammatory related genes was detected by RT-PCR and Western blot assays. The effects of Arctigenin in mouse models of acute inflammation induced by MSU crystals, including peritonitis and arthritis, were evaluated. The data indicated that TTP expression levels and endogenous PP2A activity were increased in MSU-crystal treated J774A.1 cells. TTP knockdown exacerbated inflammation-related genes expression and NLRP3 inflammasome activation. However, PP2A agonist treatment (Arctigenin) suppressed MSU crystal-induced inflammation in J774A.1 cells. Arctigenin also relieved mitochondrial reactive oxygen species (mtROS) production and improved lysosomal membrane permeability in MSU crystal-treated J774A.1 cells. Moreover, TTP knockdown reversed the anti-inflammatory and antioxidant effects of Arctigenin. Oral administration of Arctigenin significantly alleviated foot pad swelling, the number of inflammatory cells in peritoneal lavage fluids and the production of IL-1β in the mouse model of inflammation induced by MSU crystals. Collectively, these data imply that targeting TTP expression or functional activity may provide a potential therapeutic strategy for inflammation caused by MSU crystals.

p38 MAPK Activity Is Required to Prevent Hyperactivation of NLRP3 Inflammasome

Inflammation contributes to the pathogenesis and morbidity of wide spectrum of human diseases. The inflammatory response must be actively controlled to prevent bystander damage to tissues. Yet, the mechanisms controlling excessive inflammatory responses are poorly understood. NLRP3 inflammasome plays an important role in innate immune response to cellular infection or stress. Its activation must be tightly regulated because uncontrolled inflammasome activation is associated with a number of human diseases. p38 MAPK signaling plays an essential role in the regulation of inflammation. The role of p38 MAPK in inflammatory response associated with the expression of proinflammatory molecules is known. However, the anti-inflammatory functions of p38 MAPK are largely unknown. In this study, we show that pharmacologic inhibition or genetic deficiency of p38 MAPK leads to hyperactivation of NLRP3 inflammasome, resulting in enhanced Caspase 1 activation and IL-1β and IL-18 production. The deficiency of p38 MAPK activity induced an increase of cytosolic Ca²⁺ and excessive mitochondrial Ca²⁺ uptake, leading to exacerbation of mitochondrial damage, which was associated with hyperactivation of NLRP3 inflammasome. In addition, mice with deficiency of p38 MAPK in granulocytes had evidence of in vivo hyperactivation of NLRP3 inflammasome and were more susceptible to LPS-induced sepsis compared with wild-type mice. Our results suggest that p38 MAPK negatively regulates NLRP3 inflammasome through control of Ca²⁺ mobilization. Hyperactivity of inflammasome in p38-deficient mice causes lung inflammation and increased susceptibility to septic shock.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the MK2 Inhibitor ATI-450 in Healthy Subjects: A Placebo-Controlled, Randomized Phase 1 Study

Purpose

ATI-450 is an oral, small-molecule inhibitor of the p38α mitogen-activated protein kinase (MAPK)/MAPK-activated protein kinase 2 (MK2) inflammatory signaling pathway. This phase 1, single and multiple ascending dose (SAD, MAD) study evaluated ATI-450 safety, tolerability, pharmacokinetics, and pharmacodynamics.

Patients and Methods

Healthy adults were randomly assigned to SAD (10, 30, 50, 100 mg; n=24) and MAD (10, 30, 50 mg twice daily [BID] for 7 days; n=24) cohorts of ATI-450 or placebo (n=14). Safety and tolerability were evaluated through clinical and laboratory assessments. Pharmacokinetic parameters were evaluated in plasma samples; pharmacodynamic assessments included quantification of cytokine levels (tumor necrosis factor α [TNF-α], interleukin [IL]-1β, IL-6, IL-8) and phosphorylation of the MK2 downstream substrate, heat shock protein 27 (p-HSP27).

Results

The most common adverse events were headache (10/48, 20.8%), dizziness (6/48, 12.5%), upper respiratory tract infection (3/48, 6.3%), and constipation (3/48, 6.3%). Pharmacokinetics were dose-proportional, with a terminal half-life of 9‒12 hours in the MAD cohorts on day 7. Dose- and concentration-dependent inhibition of ex vivo stimulated cytokines and target biomarker was observed. On day 7, patients in the 50 mg BID dose cohort recorded mean trough drug levels that were 1.4, 2.2, 2.3, and 2.4 times greater than the IC₈₀ for TNF-α, IL-1β, IL-8, and p-HSP27, respectively. Mean C_max was 3.5, 5.4, 5.6, and 6.0 times greater than the IC₈₀ for TNF-α, IL-1β, IL-8, and p-HSP27, respectively. IL-6 inhibition >50% was noted for part of the dosing interval.

Conclusion

ATI-450 was well tolerated at the doses investigated, exhibited dose- and time-independent (ie, linear) pharmacokinetics, and dose-related pharmacodynamic effects. These results support further study of ATI-450 in immunoinflammatory diseases in phase 2 trials.

Tristetraprolin: A cytosolic regulator of mRNA turnover moonlighting as transcriptional corepressor of gene expression

Tristetraprolin (TTP) is a nucleocytoplasmic 326 amino acid protein whose sequence is characterized by possessing two CCCH-type zinc finger domains. In the cytoplasm TTP function is to promote the degradation of mRNAs that contain adenylate/uridylate-rich elements (AREs). Mechanistically, TTP promotes the recruitment of poly(A)-specific deadenylases and exoribonucleases. By reducing the half-life of about 10% of all the transcripts in the cell TTP has been shown to participate in multiple cell processes that include regulation of gene expression, cell proliferation, metabolic homeostasis and control of inflammation and immune responses. However, beyond its role in mRNA decay, in the cell nucleus TTP acts as a transcriptional coregulator by interacting with chromatin modifying enzymes. TTP has been shown to repress the transactivation of NF-κB and estrogen receptor suggesting the possibility that it participates in the transcriptional regulation of hundreds of genes in human cells and its possible involvement in breast cancer progression. In this review, we discuss the cytoplasmic and nuclear functions of TTP and the effect of the dysregulation of its protein levels in the development of human diseases. We suggest that TTP be classified as a moonlighting tumor supressor protein that regulates gene expression through two different mechanims; the decay of ARE-mRNAs and a transcriptional coregulatory function.

TTP-mediated regulation of mRNA stability in immune cells contributes to adaptive immunity, immune tolerance and clinical applications

Dendritic cells (DCs) form a sentinel network to induce protective immunity against pathogens or self-tolerance. mRNA stability is an important part of the post-transcriptional regulation (PTR) that controls the maturation and function of DCs. In this review, we summarize the effects of TTP-mediated regulation of mRNA stability in DCs, focusing on DC maturation and antigen presentation, T cell activation and differentiation, immune tolerance and inflammation. We also discuss the potential DC-based immune treatment for HIV⁺ patients through regulation of mRNA stability. This review proposes the regulation of mRNA stability as a novel immune therapy for various inflammatory diseases, such as arthritis and dermatitis.

Centrosome Dynamics and Its Role in Inflammatory Response and Metastatic Process

Metastasis is a process by which cancer cells escape from the location of the primary tumor invading normal tissues at distant organs. Chromosomal instability (CIN) is a hallmark of human cancer, associated with metastasis and therapeutic resistance. The centrosome plays a major role in organizing the microtubule cytoskeleton in animal cells regulating cellular architecture and cell division. Loss of centrosome integrity activates the p38-p53-p21 pathway, which results in cell-cycle arrest or senescence and acts as a cell-cycle checkpoint pathway. Structural and numerical centrosome abnormalities can lead to aneuploidy and CIN. New findings derived from studies on cancer and rare genetic disorders suggest that centrosome dysfunction alters the cellular microenvironment through Rho GTPases, p38, and JNK (c-Jun N-terminal Kinase)-dependent signaling in a way that is favorable for pro-invasive secretory phenotypes and aneuploidy tolerance. We here review recent data on how centrosomes act as complex molecular platforms for Rho GTPases and p38 MAPK (Mitogen activated kinase) signaling at the crossroads of CIN, cytoskeleton remodeling, and immune evasion via both cell-autonomous and non-autonomous mechanisms.

Role of Tristetraprolin in the Resolution of Inflammation

Simple Summary

Chronic inflammatory diseases account for up to 60% of deaths worldwide and, thus, are considered a great threat for human health by the World Health Organization. Nevertheless, acute inflammatory reactions are an integral part of the host defense against invading pathogens or injuries. To avoid excessive damage due to the persistence of a highly reactive environment, inflammations need to resolve in a coordinate and timely manner, ensuring for the immunological normalization of the affected tissues. Since post-transcriptional regulatory mechanisms are essential for effective resolution, the present review discusses the key role of the RNA-binding and post-transcriptional regulatory protein tristetraprolin in establishing resolution of inflammation.

Abstract

Inflammation is a crucial part of immune responses towards invading pathogens or tissue damage. While inflammatory reactions are aimed at removing the triggering stimulus, it is important that these processes are terminated in a coordinate manner to prevent excessive tissue damage due to the highly reactive inflammatory environment. Initiation of inflammatory responses was proposed to be regulated predominantly at a transcriptional level, whereas post-transcriptional modes of regulation appear to be crucial for resolution of inflammation. The RNA-binding protein tristetraprolin (TTP) interacts with AU-rich elements in the 3′ untranslated region of mRNAs, recruits deadenylase complexes and thereby facilitates degradation of its targets. As TTP regulates the mRNA stability of numerous inflammatory mediators, it was put forward as a crucial post-transcriptional regulator of inflammation. Here, we summarize the current understanding of the function of TTP with a specific focus on its role in adding to resolution of inflammation.

Cataloguing the phosphorylation sites of tristetraprolin (TTP): Functional implications for inflammatory diseases

Tristetraprolin (TTP) is a destabilizing mRNA binding protein known to regulate gene expression of a wide variety of targets, including those that control inflammation. TTP expression, regulation and function is controlled by phosphorylation. While the importance of key serine (S) sites (S⁵² and S¹⁷⁸ in mice and S¹⁸⁶ in humans) has been recognized, other sites on the hyperphosphorylated TTP protein have more recently emerged as playing an important role in regulating cellular signalling and downstream functions of TTP. In order to propel investigation of TTP and fully exploit its potential as a drug target in inflammatory disease, this review will catalogue TTP phosphorylation sites in both the murine and human TTP protein, the known and unknown roles and functions of these sites, the kinases and phosphatases that act upon TTP and overview methodological approaches to increase our knowledge of this important protein regulated by phosphorylation.

Dexamethasone and p38 MAPK inhibition of cytokine production from human lung fibroblasts

Lung fibroblasts are involved in airway inflammation and remodelling in COPD. We report an investigation of the effects of combining a p38 MAPK inhibitor with a corticosteroid on cytokine production by a human lung fibroblast cell line and primary fibroblasts obtained from human lung tissue. Our main interest was to determine whether additive or synergistic anti‐inflammatory effects would be observed. We observed inhibition of IL‐6 and CXCL8 secretion from both lung fibroblast models by dexamethasone (maximal inhibition 40–90%) and the p38 MAPK inhibitor BIRB (maximal inhibition 30–60%), used alone and evidence of increased anti‐inflammatory effects when used in combination. This combination effect was more apparent for TNF‐a stimulated cytokine production (maximal inhibition increased by 10–20%). Interaction ratio analysis showed this enhanced effect to be additive rather than synergistic interaction. Similar results were obtained using both fibroblast cell culture models. Combining a p38 MAPK to corticosteroids may help reduce fibroblast mediated inflammation in COPD.

Cross-talk between CD38 and TTP Is Essential for Resolution of Inflammation during Microbial Sepsis

The resolution phase of acute inflammation is essential for tissue homeostasis, yet the underlying mechanisms remain unclear. We demonstrate that resolution of inflammation involves interactions between CD38 and tristetraprolin (TTP). During the onset of acute inflammation, CD38 levels are increased, leading to the production of Ca²⁺-signaling messengers, nicotinic acid adenine dinucleotide phosphate (NAADP), ADP ribose (ADPR), and cyclic ADPR (cADPR) from NAD(P)⁺. To initiate the onset of resolution, TTP expression is increased by the second messengers, NAADP and cADPR, which downregulate CD38 expression. The activation of TTP by Sirt1-dependent deacetylation, in response to increased NAD⁺ levels, suppresses the acute inflammatory response and decreases Rheb expression, inhibits mTORC1, and induces autophagolysosomes for bacterial clearance. TTP may represent a mechanistic target of anti-inflammatory agents, such as carbon monoxide. TTP mediates crosstalk between acute inflammation and autophagic clearance of bacteria from damaged tissue in the resolution of inflammation during sepsis.

Tristetraprolin Overexpression in Non-hematopoietic Cells Protects Against Acute Lung Injury in Mice

Tristetraprolin (TTP) is a mRNA binding protein that binds to adenylate-uridylate-rich elements within the 3′ untranslated regions of certain transcripts, such as tumor necrosis factor (Tnf) mRNA, and increases their rate of decay. Modulation of TTP expression is implicated in inflammation; however, its role in acute lung inflammation remains unknown. Accordingly, we tested the role of TTP in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. LPS-challenged TTP-knockout (TTP^KO) mice, as well as myeloid cell-specific TTP-deficient (TTP^myeKO) mice, exhibited significant increases in lung injury, although these responses were more robust in the TTP^KO. Mice with systemic overexpression of TTP (TTP^ΔARE) were protected from ALI, as indicated by significantly reduced neutrophilic infiltration, reduced levels of neutrophil chemoattractants, and histological parameters of ALI. Interestingly, while irradiated wild-type (WT) mice reconstituted with TTP^KO hematopoietic progenitor cells (HPCs) showed exaggerated ALI, their reconstitution with the TTP^ΔARE HPCs mitigated ALI. The reconstitution of irradiated TTP^ΔARE mice with HPCs from either WT or TTP^ΔARE donors conferred significant protection against ALI. In contrast, irradiated TTP^ΔARE mice reconstituted with TTP^KO HPCs had exaggerated ALI, but the response was milder as compared to WT recipients that received TTP^KO HPCs. Finally, the reconstitution of irradiated TTP^KO recipient mice with TTP^ΔARE HPCs did not confer any protection to the TTP^KO mice. These data together suggest that non-HPCs-specific overexpression of TTP within the lungs protects against ALI via downregulation of neutrophil chemoattractants and reduction in neutrophilic infiltration.

RNA Recognition and Immunity-Innate Immune Sensing and Its Posttranscriptional Regulation Mechanisms

RNA acts as an immunostimulatory molecule in the innate immune system to activate nucleic acid sensors. It functions as an intermediate, conveying genetic information to control inflammatory responses. A key mechanism for RNA sensing is discriminating self from non-self nucleic acids to initiate antiviral responses reliably, including the expression of type I interferon (IFN) and IFN-stimulated genes. Another important aspect of the RNA-mediated inflammatory response is posttranscriptional regulation of gene expression, where RNA-binding proteins (RBPs) have essential roles in various RNA metabolisms, including splicing, nuclear export, modification, and translation and mRNA degradation. Recent evidence suggests that the control of mRNA stability is closely involved in signal transduction and orchestrates immune responses. In this study, we review the current understanding of how RNA is sensed by host RNA sensing machinery and discuss self/non-self-discrimination in innate immunity focusing on mammalian species. Finally, we discuss how posttranscriptional regulation by RBPs shape immune reactions.

Tropisetron ameliorates cyclophosphamide-induced hemorrhagic cystitis in rats

Hemorrhagic cystitis is one of the most important complications of cyclophosphamide, a drug widely used in cancer chemotherapy and bone marrow transplantation. 5-HT₃ antagonists are anti-emetic agents and have been shown to have notable anti-inflammatory and antioxidant properties. This study was designed to investigate the possible protective effects of tropisetron against cyclophosphamide-induced hemorrhagic cystitis in rats. Hemorrhagic cystitis was induced in female rats by cyclophosphamide (270 mg/kg). Tropisetron (2.5, 5 and 7.5 mg/kg), granisetron (2.5 and 5 mg/kg), and ondansetron (5 mg/kg) were injected 15 min before, 4 and 8 h after cyclophosphamide. To evaluate the role of alpha7 nicotinic acetylcholine receptor (α7nAChR), its antagonist, methyllycaconitine (5 mg/kg) was administered 30 min before tropisetron. After 24 h, animals were killed under anesthesia. Macroscopic and histological changes were evaluated. Malondialdehyde (MDA), glutathione (GSH) and Evans blue were measured spectrophotometrically. Furthermore, the protein levels of p38 mitogen-activated protein kinases (P38 MAPK), p-P38, signal transducer and activator of transcription 3 (STAT3), p-STAT3 and Poly (ADP-ribose) polymerase (PARP) were determined using Western blot. Cyclophosphamide administration significantly induced histopathological damages and increased MDA, p-p38/p38, p-STAT3/STAT3, and PARP levels compared with the saline group. Tropisetron treatment diminished histopathological injuries as well as MDA level, and STAT3 activity compared to cyclophosphamide treated rats. Co-administration of methyllycaconitine with tropisetron, partially or completely reversed the protective effects of tropisetron. Our results showed that prophylactic administration of tropisetron markedly ameliorated the cyclophosphamide-induced bladder hemorrhage and inflammation in rats. These effects of tropisetron were α7nAChR dependent.

Post-Transcriptional Inflammatory Response to Intracellular Bacterial c-di-AMP

Cyclic-di-AMP (c-di-AMP) is a bacterial second messenger that is produced by intracellular bacterial pathogens in mammalian host macrophages. Previous reports have shown that c-di-AMP is recognized by intracellular pattern recognition receptors of the innate immune system and stimulate type I interferon response. Here we report that the response to c-di-AMP includes a post-transcriptional component that is involved in the induction of additional inflammatory cytokines including IL-6, CXCL2, CCL3, and CCL4. Their mRNAs contain AU-rich elements (AREs) in their 3' UTR that promote decay and repress translation. We show that c-di-AMP leads to the phosphorylation of p38 MAPK as well as the induction of the ARE-binding protein TTP, both of which are components of a signaling pathway that modulate the expression of ARE-containing mRNAs at the post-transcriptional level. Pharmacological inhibition of p38 reduces the c-di-AMP-dependent release of induced cytokines, while TTP knockdown increases their release and mRNA stability. C-di-AMP can specifically increase the expression of a nano-Luciferase reporter that contains AREs. We propose a non-canonical intracellular mode of activation of the p38 MAPK pathway with the subsequent enhancement in the expression of inflammatory cytokines. C-di-AMP is widely distributed in bacteria, including infectious intracellular pathogens; hence, understanding of its post-transcriptional gene regulatory effect on the host response may provide novel approaches for therapy.

MAP kinase phosphatase-1, a gatekeeper of the acute innate immune response

Mitogen-activated protein kinase (MAPK)^§ cascades are crucial signaling pathways in the regulation of the host immune response to infection. MAPK phosphatase (MKP)-1, an archetypal member of the MKP family, plays a pivotal role in the down-regulation of p38 and JNK. Studies using cultured macrophages have demonstrated a pivotal role of MKP-1 in the restraint of the biosynthesis of both pro-inflammatory and anti-inflammatory cytokines as well as chemokines. Using MKP-1 knockout mice, several groups have not only confirmed the critical importance of MKP-1 in the regulation of the cytokine synthesis in vivo during the acute host response to bacterial infections, but also revealed novel functions of MKP-1 in maintaining bactericidal functions and host metabolic activities. RNA-seq analyses on livers of septic mice infected with E. coli have revealed that MKP-1 deficiency caused substantial perturbation in the expression of over 5000 genes, an impressive >20% of the entire murine genome. Among the genes whose expression are dramatically affected by MKP-1 deficiency are those encoding metabolic regulators and acute phase response proteins. These studies demonstrate that MKP-1 is an essential gate-keeper of the acute innate immune response, facilitating pathogen killing and regulating the metabolic response during pathogenic infection. In this review article, we will summarize the studies on the function of MKP-1 during acute innate immune response in the regulation of inflammation, metabolism, and acute phase response. We will also discuss the role of MKP-1 in the actions of numerous immunomodulatory agents.

Arid5a Regulation and the Roles of Arid5a in the Inflammatory Response and Disease

Abnormal gene expression patterns underlie many diseases that represent major public health concerns and robust therapeutic challenges. Posttranscriptional gene regulation by RNA-binding proteins (RBPs) is well-recognized, and the biological functions of RBPs have been implicated in many diseases, such as autoimmune diseases, inflammatory diseases, and cancer. However, a complete understanding of the regulation mediated by several RBPs is lacking. During the past few years, a novel role of AT-rich interactive domain-containing protein 5a (Arid5a) as an RBP is being investigated in the field of immunology owing to binding of Arid5a protein to the 3' untranslated region (UTR) of Il-6 mRNA. Indeed, Arid5a is a dynamic molecule because upon inflammation, it translocates to the cytoplasm and stabilizes a variety of inflammatory mRNA transcripts, including Il-6, Stat3, Ox40, T-bet, and IL-17-induced targets, and contributes to the inflammatory response and a variety of diseases. TLR4-activated NF-κB and MAPK pathways are involved in regulating Arid5a expression from synthesis to degradation, and even a slight alteration in these pathways can lead to intense production of inflammatory molecules, such as IL-6, which may further contribute to the development of inflammatory diseases such as sepsis and experimental autoimmune encephalomyelitis. This review highlights the regulation of the Arid5a expression and function. Additionally, recent findings on Arid5a are discussed to further our understanding of this molecule, which may be a promising therapeutic target for inflammatory diseases.

Role of tristetraprolin phosphorylation in paediatric patients with inflammatory bowel disease

BACKGROUND

Intestinal inflammation and epithelial injury are the leading actors of inflammatory bowel disease (IBD), causing an excessive pro-inflammatory cytokines expression. Tristetraprolin (TTP), an mRNA binding protein, plays a role in regulating the inflammatory factors, recognizing specific sequences on the 3’ untranslated region of cytokine mRNAs. TTP activity depends on its phosphorylation state: the unphosphorylated TTP degrades pro-inflammatory cytokine mRNAs; on the contrary, the phosphorylated TTP fails to destabilize mRNAs furthering their expression. The phospho-TTP forms a complex with the chaperone protein 14-3-3. This binding could be one of the factors that promote intestinal inflammation as a cause of disease progression.

AIM

To assess if TTP phosphorylation has a role in paediatric IBD.

METHODS

The study was carried out on a cohort of paediatric IBD patients. For each patient enrolled, a specimen of inflamed and non-inflamed colonic mucosa was collected. Furthermore, the experiments were conducted on macrophages differentiated from blood samples of the same patients. Macrophages from healthy donors’ blood were used as controls. Co-immunoprecipitation assay and immunoblotting analyses were performed to observe the formation of the phospho-TTP/14-3-3 complex. In the same samples TNF-α expression was also evaluated as major factor of the pro-inflammatory activity.

RESULTS

In this work we studied indirectly the phosphorylation of TTP through the binding with the chaperone protein 14-3-3. In inflamed and non-inflamed colon mucosa of IBD paediatric patients immunoblot assay demonstrated a higher expression of the TTP in inflamed samples respect to the non-inflamed; the co-immunoprecipitated 14-3-3 protein showed the same trend of expression. In the TNF-α gene expression analysis higher levels of the cytokine in inflamed tissues compared to controls were evident. The same experiments were conducted on macrophages from IBD paediatric patients and healthy controls. The immunoblot results demonstrated a high expression of both TTP and co-immunoprecipitated 14-4-3 protein in IBD-derived macrophages in comparison to healthy donors. TNF-α protein levels from macrophages lysates showed the same trend of expression in favour of IBD paediatric patients compared to healthy controls.

CONCLUSION

In this work, for the first time, we describe a relation between phospho-TTP/14-3-3 complex and IBD. Indeed, a higher expression of TTP/14-3-3 was recorded in IBD samples in comparison to controls.

Fragile X-related protein 1 (FXR1) regulates cyclooxygenase-2 (COX-2) expression at the maternal-fetal interface

Cyclooxygenase-2 (COX-2) is regulated post-transcriptionally by the AU-rich element (ARE) in the 3'-untranslated region (UTR) of its mRNA. However, the mechanism of COX-2 induction in infertility has not been thoroughly elucidated to date. The aim of this study was to examine the association between COX-2 and fragile X-related protein 1 (FXR1) in trophoblasts. Using quantitative reverse transcription polymerase chain reaction, our results showed that FXR1 mRNA expression levels were significantly decreased in trophoblasts from recurrent miscarriage patients compared with healthy controls; conversely, COX-2 mRNA expression levels were increased in patient samples. We also observed that FXR1 was highly expressed in human placental villi during early pregnancy. Furthermore, we used western blotting and immunofluorescence to analyse the expression levels of FXR1 and COX-2 in HTR-8 cells that were treated with tumour necrosis factor α; we observed that the expression of COX-2 was clearly increased in HTR-8 cells treated with FXR1 small interfering RNA, whereas the expression of COX-2 was effectively decreased in HTR-8 cells with FXR1 overexpressed via a plasmid. Importantly, bioinformatics analysis identified FXR1 binding sites in the 3'-UTR region of COX-2 and firefly luciferase reporter assay analysis verified that FXR1 binds directly to the 3'-UTR region of COX-2. ELISA assays showed that overexpression of FXR1 enhanced vascular endothelial growth factor-A and interleukin-8 expression in HTR-8 cells, whereas conversely, knockdown of FXR1 effectively repressed these effects. In conclusion, the results of this study indicate that FXR1 is a novel COX-2 regulatory factor.

The Role of TTP Phosphorylation in the Regulation of Inflammatory Cytokine Production by MK2/3

Tristetraprolin (TTP) is an RNA-binding protein and an essential factor of posttranscriptional repression of cytokine biosynthesis in macrophages. Its activity is temporally inhibited by LPS-induced p38^MAPK/MAPKAPK2/3-mediated phosphorylation, leading to a rapid increase in cytokine expression. We compared TTP expression and cytokine production in mouse bone marrow-derived macrophages of different genotypes: wild type, MAPKAP kinase 2 (MK2) deletion (MK2 knockout [KO]), MK2/3 double deletion (MK2/3 double KO [DKO]), TTP-S52A-S178A (TTPaa) knock-in, as well as combined MK2 KO/TTPaa and MK2/3 DKO/TTPaa. The comparisons reveal that MK2/3 are the only LPS-induced kinases for S52 and S178 of TTP and the role of MK2 and MK3 in the regulation of TNF biosynthesis is not restricted to phosphorylation of TTP at S52/S178 but includes independent processes, which could involve other TTP phosphorylations (such as S316) or other substrates of MK2/3 or p38^MAPK Furthermore, we found differences in the dependence of various cytokines on the cooperation between MK2/3 deletion and TTP mutation ex vivo. In the cecal ligation and puncture model of systemic inflammation, a dramatic decrease of cytokine production in MK2/3 DKO, TTPaa, and DKO/TTPaa mice compared with wild-type animals is observed, thus confirming the role of the MK2/3/TTP signaling axis in cytokine production also in vivo. These findings improve our understanding of this signaling axis and could be of future relevance in the treatment of inflammation.

Protein phosphatase 2A as a therapeutic target in inflammation and neurodegeneration

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric enzyme that catalyzes the selective removal of phosphate groups from protein serine and threonine residues. Emerging evidence suggests that it functions as a tumor suppressor by constraining phosphorylation-dependent signalling pathways that regulate cellular transformation and metastasis. Therefore, PP2A-activating drugs (PADs) are being actively sought and investigated as potential novel anti-cancer treatments. Here we explore the concept that PP2A also constrains inflammatory responses through its inhibitory effects on various signalling pathways, suggesting that PADs may be effective in the treatment of inflammation-mediated pathologies.

Anti-Inflammatory Compounds from Atractylodes macrocephala

In relation to anti-inflammatory agents from medicinal plants, we have isolated three compounds from Atractylodes macrocephala; 1, 2-[(2E)-3,7-dimethyl-2,6-octadienyl]-6-methyl-2, 5-cyclohexadiene-1, 4-dione; 2, 1-acetoxy-tetradeca-6E,12E-diene-8, 10-diyne-3-ol; 3, 1,3-diacetoxy-tetradeca-6E, 12E-diene-8, 10-diyne. Compounds 1–3 showed concentration-dependent inhibitory effects on production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. Western blotting and RT-PCR analyses demonstrated that compounds 1–3 suppressed the protein and mRNA levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Furthermore, compounds 1–3 inhibited transcriptional activity of nuclear factor-κB (NF-κB) and nuclear translocation of NF-κB in LPS-activated RAW 264.7 cells. The most active compound among them, compound 1, could reduce the mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and suppress the phosphorylation of MAPK including p38, JNK, and ERK1/2. Taken together, these results suggest that compounds 1–3 from A. macrocephala can be therapeutic candidates to treat inflammatory diseases.

Intestinal Microbiota Mediates the Susceptibility to Polymicrobial Sepsis-Induced Liver Injury by Granisetron Generation in Mice

Sepsis-induced liver injury is recognized as a key problem in intensive care units. The gut microbiota has been touted as an important mediator of liver disease development; however, the precise roles of gut microbiota in regulating sepsis-induced liver injury are unknown. Here, we aimed to investigate the role of the gut microbiota in sepsis-induced liver injury and the underlying mechanism. Cecal ligation and puncture (CLP) was used to induce polymicrobial sepsis and related liver injury. Fecal microbiota transplantation (FMT) was used to validate the roles of gut microbiota in these pathologies. Metabolomics analysis was performed to characterize the metabolic profile differences between sepsis-resistant (Res; survived to 7 days after CLP) and sepsis-sensitive (Sen; moribund before or approximately 24 hours after CLP) mice. Mice gavaged with feces from Sen mice displayed more-severe liver damage than did mice gavaged with feces from Res mice. The gut microbial metabolic profile between Sen and Res mice was different. In particular, the microbiota from Res mice generated more granisetron, a 5-hydroxytryptamine 3 (5-HT₃ ) receptor antagonist, than the microbiota from Sen mice. Granisetron protected mice against CLP-induced death and liver injury. Moreover, proinflammatory cytokine expression by macrophages after lipopolysaccharide (LPS) challenge was markedly reduced in the presence of granisetron. Both treatment with granisetron and genetic knockdown of the 5-HT_3A receptor in cells suppressed nuclear factor kappa B (NF-кB) transactivation and phosphorylated p38 (p-p38) accumulation in macrophages. Gut microbial granisetron levels showed a significantly negative correlation with plasma alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels in septic patients. Conclusion: Our study indicated that gut microbiota plays a key role in the sensitization of sepsis-induced liver injury and associates granisetron as a hepatoprotective compound during sepsis development.

MAPKAPK2: the master regulator of RNA-binding proteins modulates transcript stability and tumor progression

The p38 mitogen-activated protein kinase (p38MAPK) pathway has been implicated in a variety of pathological conditions including inflammation and metastasis. Post-transcriptional regulation of genes harboring adenine/uridine-rich elements (AREs) in their 3'-untranslated region (3'-UTR) is controlled by MAPK-activated protein kinase 2 (MAPKAPK2 or MK2), a downstream substrate of the p38MAPK. In response to diverse extracellular stimuli, MK2 influences crucial signaling events, regulates inflammatory cytokines, transcript stability and critical cellular processes. Expression of genes involved in these vital cellular cascades is controlled by subtle interactions in underlying molecular networks and post-transcriptional gene regulation that determines transcript fate in association with RNA-binding proteins (RBPs). Several RBPs associate with the 3'-UTRs of the target transcripts and regulate their expression via modulation of transcript stability. Although MK2 regulates important cellular phenomenon, yet its biological significance in tumor progression has not been well elucidated till date. In this review, we have highlighted in detail the importance of MK2 as the master regulator of RBPs and its role in the regulation of transcript stability, tumor progression, as well as the possibility of use of MK2 as a therapeutic target in tumor management.

Tristetraprolin attenuates brain edema in a rat model of cerebral hemorrhage

OBJECTIVES

We evaluated the protective effects of protein phosphatase 2A (PP2A)/tristetraprolin (TTP) against brain edema in a rat model of cerebral hemorrhage, bleeding in the brain that occurs in tissues and ventricles. TTP is a well-known mRNA-binding protein and essential regulatory molecule for gene expression.

METHODS

Cerebral hemorrhage was induced in male albino rats divided into four homogeneous groups: normal control (I), control (II), PP2A siRNA (III), and scrambled siRNA (IV). Neurological scores, caspase-3 mRNA and protein expression, PP2A and TTP protein expression, apoptosis, and water content in the brain were determined.

RESULTS

The neurological score decreased substantially to 8.2 in rats in which cerebral hemorrhage was induced and was further reduced to 7.4 and 7.7 in groups III and IV, respectively. Caspase-3 expression increased significantly by 90% in group II and by 26.9% in group III. Apoptosis increased by 26.1% in rats in which cerebral hemorrhage was induced and increased considerably by 35.3% and 33.4% in groups III and IV, respectively. PP2A and TTP protein expression increased significantly by 87% and 59%, as compared to their respective sham controls. However, PP2A and TTP siRNA treatment reduced the protein expression of PP2A and TTP in groups III and IV. The water content in the brain increased significantly by 77.4% in rats in which cerebral hemorrhage was induced (group II), as compared to the sham group. The water content in the brain increased by 84.1% and 78.7% in groups III and IV, respectively.

CONCLUSION

Taken together, these data indicate that TTP has a protective role against brain edema by reducing inflammation, apoptosis, and water content in the brain at 48 hr after cerebral hemorrhage. Our findings may be useful for developing important approaches to treating brain injury.

RNA-Binding Proteins in the Control of LPS-Induced Macrophage Response

Innate immune response is triggered by pathogen components, like lipopolysaccharides (LPS) of gram-negative bacteria. LPS initiates Toll-like receptor 4 (TLR4) signaling, which involves mitogen activated protein kinases (MAPK) and nuclear factor kappa B (NFκB) in different pathway branches and ultimately induces inflammatory cytokine and chemokine expression, macrophage migration and phagocytosis. Timely gene transcription and post-transcriptional control of gene expression confer the adequate synthesis of signaling molecules. As trans-acting factors RNA binding proteins (RBPs) contribute significantly to the surveillance of gene expression. RBPs are involved in the regulation of mRNA processing, localization, stability and translation. Thereby they enable rapid cellular responses to inflammatory mediators and facilitate a coordinated systemic immune response. Specific RBP binding to conserved sequence motifs in their target mRNAs is mediated by RNA binding domains, like Zink-finger domains, RNA recognition motifs (RRM), and hnRNP K homology domains (KH), often arranged in modular arrays. In this review, we focus on RBPs Tristetraprolin (TTP), human antigen R (HUR), T-cell intracellular antigen 1 related protein (TIAR), and heterogeneous ribonuclear protein K (hnRNP K) in LPS induced macrophages as primary responding immune cells. We discuss recent experiments employing RNA immunoprecipitation and microarray analysis (RIP-Chip) and newly developed individual-nucleotide resolution crosslinking and immunoprecipitation (iCLIP), photoactivatable ribonucleoside-enhanced crosslinking (PAR-iCLIP) and RNA sequencing techniques (RNA-Seq). The global mRNA interaction profile analysis of TTP, HUR, TIAR, and hnRNP K exhibited valuable information about the post-transcriptional control of inflammation related gene expression with a broad impact on intracellular signaling and temporal cytokine expression.

Bi-phased regulation of the post-transcriptional inflammatory response by Tristetraprolin levels

AU-rich elements (AREs) are cis-acting instability and translation inhibition elements that are present in the 3ʹUTR of most inducible inflammatory mRNAs such as TNF and Cxcl2. mRNAs that contain AREs are, by default, repressed and only transiently expressed in response to stimuli. They are targeted by the inducible RNA-binding protein Tristetraprolin (TTP) which blocks their translation and facilitates their decay, thereby contributing to the quick termination of their expression. The exogenous over-expression of TTP in HEK293 cells can unexpectedly lead to the upregulation and extended expression of a nanoLuciferase reporter that contains the ARE of TNF. Here we show that, a moderate downregulation of the highly expressed endogenous TTP after LPS induction by siRNA in macrophages can lead to a reduction in the release of TNF and Cxcl2. We propose that, in contrast to their canonical function, very high levels of induced TTP at the onset of the inflammatory response can enhance the expression of ARE-mRNAs at the post-transcriptional level, independently of phosphorylation status. As the inflammatory response progresses, TTP levels diminish but they continuously regain their ability to reduce the expression of ARE-mRNAs to reach a turning point of ‘optimal TTP level’ with a maximum ability to repress ARE-mRNA expression. Below this level, a further reduction in TTP levels now leads to the loss of canonical-TTP function resulting in increased ARE-mRNA expression. These novel findings should contribute to the understanding of feedback loops that control the kinetics of the inflammatory response.

Molecular characterization of p38 MAPK from blunt snout bream (Megalobrama amblycephala) and its expression after ammonia stress, and lipopolysaccharide and bacterial challenge

p38 mitogen-activated protein kinase (MAPK) is an important protein which plays a key role in regulating the innate immunity, so exploring its molecular characterization is helpful in understanding the resistance against microbial infections in cultured fish. Here, a full-length cDNA of p38 MAPK was cloned from liver of blunt snout bream (Megalobrama amblycephala) which covered 2419 bp with an open reading frame of 1086 bp encoding 361 amino acids. p38 MAPK contained the characteristic structures of Thr-Gly-Tyr (TGY) motif and substrate binding site Ala-Thr-Arg-Trp (ATRW), which are conserved in MAPK family. To investigate p38 MAPK functions, two in vivo experiments were carried out to examine its expression following ammonia exposure and bacterial challenge. Also, an in vitro experiment was conducted to assess the role of p38 MAPK in inflammation of primary hepatocytes induced by lipopolysaccharide (LPS). The results showed the ubiquitous expression of p38 MAPK in all the tested tissues with varying levels. p38 MAPK mRNA expression was significantly up-regulated by ammonia stress and Aeromonas hydrophila challenge, and altered in a time-dependent manner. Moreover, the results indicated that the inflammatory response induced by LPS in hepatocytes is p38 MAPK dependent as knockdown of p38 MAPK using siRNA technology depressed the expression of IL-1β and IL-6. The findings in this study showed that p38 MAPK has anti-stress property, and plays key role in protection against bacterial infection and inflammation in blunt snout bream.

Recent advances in the role of RNA-binding protein, tristetraprolin, in arthritis

The expression levels of cytokines and chemokines are strictly regulated at transcriptional and post-transcriptional levels. These small proteins are closely related to inflammatory diseases such as rheumatoid arthritis (RA). The purpose of this review is to highlight the potential utilization of tristetraprolin (TTP) as a therapeutic target in treating RA. TTP is the most notable and well-characterized RNA-binding protein that destabilizes mRNA of pro-inflammatory cytokines. TTP is thought to play an important role in RA because its target mRNA includes a lot of inflammatory cytokines such as TNFα. Post-translational modifications, especially phosphorylation, seem to be critical for the anti-inflammatory effects of TTP. Importantly, various mouse models, many of which are consistent with in vitro studies, are now available to elicit a more detailed understanding of the pathogenic role of TTP. The results of these multidisciplinary studies indicate that it is possible to improve inflammation by controlling TTP activity. Through this review, I propose that the use of recently developed mouse models and establishment of clever designs to target TTP will greatly contribute to future drug development to treat RA.