The non-classical MAP kinase ERK3 controls T cell activation

Atypical MAPKs in cancer

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

A review of non-classical MAPK family member, MAPK4: A pivotal player in cancer development and therapeutic intervention

Mitogen-Activated Protein Kinases (MAPKs) are serine/threonine protein kinases that play a crucial role in transmitting extracellular signals to the intracellular environment, influencing a wide range of cellular processes including proliferation, differentiation, apoptosis, metabolic activities, immune function and stress response. MAPK4, a non-classical MAPK, is frequently overexpressed in various malignancies, including prostate, breast, cervix, thyroid, and gliomas. It orchestrates cell proliferation, migration, and apoptosis via the AKT/mTOR and/or PDK1 signaling pathways, thus facilitating tumor cell growth. Furthermore, MAPK4 expression is closely associated with the effectiveness of specific inhibitors like PI3K and PARP1, and also correlate with the survival rates of cancer patients. Increasing evidence highlights MAPK4's involvement in the tumor microenvironment, modulating immune response and inflammation-related diseases. This review comprehensively explores the structure, function, and oncogenic role of MAPK4, providing a deeper understanding of its activation and mechanisms of action in tumorigenesis, which might be helpful for the development of innovative therapeutic strategies for cancer management.

Role of the Atypical MAPK ERK3 in Cancer Growth and Progression

Extracellular signal-regulated kinase 3 (ERK3) is an atypical mitogen-activated protein kinase (MAPK) whose structural and regulatory features are distinct from those of conventional MAPKs, such as ERK1/2. Since its identification in 1991, the regulation, substrates and functions of ERK3 have remained largely unknown. However, recent years have witnessed a wealth of new findings about ERK3 signaling. Several important biological functions for ERK3 have been revealed, including its role in neuronal morphogenesis, inflammation, metabolism, endothelial cell tube formation and epithelial architecture. In addition, ERK3 has been recently shown to play important roles in cancer cell proliferation, migration, invasion and chemoresistance in multiple types of cancers. Furthermore, accumulating studies have uncovered various molecular mechanisms by which the expression level, protein stability and activity of ERK3 are regulated. In particular, several post-translational modifications (PTMs), including ubiquitination, hydroxylation and phosphorylation, have been shown to regulate the stability and activity of ERK3 protein. In this review, we discuss recent findings regarding biochemical and cellular functions of ERK3, with a main focus on its roles in cancers, as well as the molecular mechanisms of regulating its expression and activity.

Triazole-fused pyrimidines in target-based anticancer drug discovery

In recent decades, the development of targeted drugs has featured prominently in the treatment of cancer, which is among the major causes of mortality globally. Triazole-fused pyrimidines, a widely-used class of heterocycles in medicinal chemistry, have attracted considerable interest as potential anticancer agents that target various cancer-associated targets in recent years, demonstrating them as valuable templates for discovering novel anticancer candidates. The current review concentrates on the latest advancements of triazole-pyrimidines as target-based anticancer agents, including works published between 2007 and the present (2007-2022). The structure-activity relationships (SARs) and multiple pathways are also reviewed to shed light on the development of more effective and biotargeted anticancer candidates.

Identification of Crucial Hub Genes and Differential T Cell Infiltration in Idiopathic Pulmonary Arterial Hypertension Using Bioinformatics Strategies

Background: Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disease. Growing evidence indicated that IPAH is a chronic immune disease. This study explored the molecular mechanisms and T cell infiltration of IPAH using integrated bioinformatics methods.

Methods: Gene expression profiles of dataset GSE113439 were downloaded from the Gene Expression Omnibus and analyzed using R. Protein-protein interaction (PPI) network and gene set enrichment analysis (GSEA) were established by NetworkAnalyst. Gene Ontology enrichment analysis was performed using ClueGO. Transcription factors of differentially expressed genes (DEGs) were estimated using iRegulon. Transcription factors and selected hub genes were verified by real-time polymerase chain reaction (qPCR) in the lung tissues of rats with pulmonary artery hypertension. The least absolute shrinkage and selection operator regression model and the area under the receiver operating characteristic curve (AUC) were applied jointly to identify the crucial hub genes. Moreover, immune infiltration in IPAH was calculated using ImmuCellAI, and the correlation between key hub genes and immune cells was analyzed using R.

Results: A total of 512 DEGs were screened, and ten hub genes and three transcription factors were filtered by the DEG PPI network. The DEGs were mainly enriched in mitotic nuclear division, chromosome organization, and nucleocytoplasmic transport. The ten hub genes and three transcription factors were confirmed by qPCR. Moreover, MAPK6 was identified as the most potent biomarker with an AUC of 100%, and ImmuCellAI immune infiltration analysis showed that a higher proportion of CD4-naive T cells and central memory T cells (Tcm) was apparent in the IPAH group, whereas the proportions of cytotoxic T cells (Tc), exhausted T cells (Tex), type 17 T helper cells, effector memory T cells, natural killer T cells (NKT), natural killer cells, gamma-delta T cells, and CD8 T cells were lower. Finally, MAPK6 was positively correlated with Tex and Tcm, and negatively correlated with Tc and NKT.

Conclusion:MAPK6 was identified as a crucial hub gene to discriminate IPAH from the normal group. Dysregulated immune reactions were identified in the lung tissue of patients with IPAH.

LAMB1 Is Related to the T Stage and Indicates Poor Prognosis in Gastric Cancer

BACKGROUND AND OBJECTIVE

Gastric cancer (GC) is a common tumor malignancy with high incidence and poor prognosis. Laminin is an indispensable component of basement membrane and extracellular matrix, which is responsible for bridging the internal and external environment of cells and transmitting signals. This study mainly explored the association of the LAMB1 expression with clinicopathological characteristics and prognosis in gastric cancer.

METHODS

The expression data and clinical information of gastric cancer patients were downloaded from The Cancer Genome Atlas (TCGA) and Asian Cancer Research Group (ACRG). And we analyzed the relationship between LAMB1 expression and clinical characteristics through R. CIBERSORTx was used to calculate the absolute score of immune cells in gastric tumor tissues. Then COX proportional hazard models and Kaplan-Meier curves were performed to evaluate the role of LAMB1 and its influence on prognosis in gastric cancer patients. Finally, GO and KEGG analysis were applied for LAMB1-related genes in gastric cancer, and PPI network was constructed in Cytoscape software.

RESULTS

In the TCGA cohort, patients with gastric cancer frequently generated LAMB1 gene copy number variation, but had little effect on mRNA expression. Both in the TCGA and ACRG cohorts, the mRNA expression of LAMB1 in gastric cancer tissues was higher than it in normal tissues. All patients were divided into high expression group and low expression group according to the median expression level of LAMB1. The elevated expression group obviously had more advanced cases and higher infiltration levels of M2 macrophages. COX proportional hazard models and Kaplan-Meier curves revealed that patients with enhanced expression of LAMB1 have a worse prognosis. GO/KEGG analysis showed that LAMB1-related genes were enriched in PI3K-Akt signaling pathway, focal adhesion, ECM-receptor interaction, etc.

CONCLUSIONS

The high expression of LAMB1 in gastric cancer is related to the poor prognosis of patients, and it may be related to microenvironmental changes in tumors.

The C-Terminus Tail Regulates ERK3 Kinase Activity and Its Ability in Promoting Cancer Cell Migration and Invasion

Extracellular signal-regulated kinase 3 (ERK3) is an atypical member of the mitogen-activated protein kinase (MAPK) family. It harbors a kinase domain in the N-terminus and a long C-terminus extension. The C-terminus extension comprises a conserved in ERK3 and ERK4 (C34) region and a unique C-terminus tail, which was shown to be required for the interaction of ERK3 with the cytoskeletal protein septin 7. Recent studies have elucidated the role of ERK3 signaling in promoting the motility and invasiveness of cancer cells. However, little is known about the intramolecular regulation of the enzymatic activity and cellular functions of ERK3. In this study, we investigated the role of the elongated C-terminus extension in regulating ERK3 kinase activity and its ability to promote cancer cell migration and invasion. Our study revealed that the deletion of the C-terminus tail greatly diminishes the ability of ERK3 to promote the migration and invasion of lung cancer cells. We identified two molecular mechanisms underlying this effect. Firstly, the deletion of the C-terminus tail decreases the kinase activity of ERK3 towards substrates, including the oncogenic protein steroid receptor co-activator 3 (SRC-3), an important downstream target for ERK3 signaling in cancer. Secondly, in line with the previous finding that the C-terminus tail mediates the interaction of ERK3 with septin 7, we found that the depletion of septin 7 abolished the ability of ERK3 to promote migration, indicating that septin 7 acts as a downstream effector for ERK3-induced cancer cell migration. Taken together, the findings of this study advance our understanding of the molecular regulation of ERK3 signaling by unraveling the role of the C-terminus tail in regulating ERK3 kinase activity and functions in cancer cells. These findings provide useful insights for the development of therapeutic agents targeting ERK3 signaling in cancer.

BTLA suppress acute rejection via regulating TCR downstream signals and cytokines production in kidney transplantation and prolonged allografts survival

Acute rejection is a major risk for renal transplant failure. During this adverse process, activated T cells are considered the main effectors. Recently, B and T lymphocyte attenuator (BTLA), a member of the CD28 family receptor, was reported to be a novel inhibitory regulator of T cell activation in heart and pancreatic allograft rejection. Due to the similarity of acute rejection pathways among different organs, we hypothesized that BTLA might play a role in acute rejection of kidney transplant. In renal transplant patients, we observed that BTLA expression was significantly decreased in peripheral CD3+ T lymphocytes of biopsy-proven acute rejection (BPAR) recipients compared with control patients with stable transplanted kidney functions. Remarkably, overexpression of BTLA in the rat model was found to significantly inhibit the process of acute rejection, regulate the postoperative immune status, and prolong allograft survival. BTLA overexpression significantly suppressed IL-2 and IFN-γ production and increased IL-4 and IL-10 production both in vivo and in vitro. Moreover, vital factors in T-cell signaling pathways, including mitogen-associated protein kinases (MAPK), nuclear factor-kappa B (NF-κB) and nuclear factor of activated T cells (NFAT), were also significantly repressed by BTLA overexpression. Therefore, BTLA can suppress acute rejection and regulate allogeneic responses of kidney transplant by regulating TCR downstream signals and inflammatory cytokines production to improve allografts outcomes.

Germ Line Deletion Reveals a Nonessential Role of Atypical Mitogen-Activated Protein Kinase 6/Extracellular Signal-Regulated Kinase 3

Mitogen-activated protein kinase 6/extracellular signal-regulated kinase 3 (MAPK6/ERK3) is an atypical member of the MAPKs. An essential role has been suggested by the perinatal lethal phenotype of ERK3 knockout mice carrying a lacZ insertion in exon 2 due to pulmonary dysfunction and by defects in function, activation, and positive selection of T cells. To study the role of ERK3 in vivo, we generated mice carrying a conditional Erk3 allele with exon 3 flanked by loxP sites. Loss of ERK3 protein was validated after deletion of Erk3 in the female germ line using zona pellucida 3 (Zp3)-cre and a clear reduction of the protein kinase MK5 is detected, providing the first evidence for the existence of the ERK3/MK5 signaling complex in vivo In contrast to the previously reported Erk3 knockout phenotype, these mice are viable and fertile and do not display pulmonary hypoplasia, acute respiratory failure, abnormal T-cell development, reduction of thymocyte numbers, or altered T-cell selection. Hence, ERK3 is dispensable for pulmonary and T-cell functions. The perinatal lethality and lung and T-cell defects of the previous ERK3 knockout mice are likely due to ERK3-unrelated effects of the inserted lacZ-neomycin resistance cassette. The knockout mouse of the closely related atypical MAPK ERK4/MAPK4 is also normal, suggesting redundant functions of both protein kinases.

Activation loop phosphorylation of ERK3 is important for its kinase activity and ability to promote lung cancer cell invasiveness

ERK3 is an atypical mitogen-activated protein kinase (MAPK) that has recently gained interest for its role in promoting cancer cell migration and invasion. However, the molecular regulation of ERK3 functions in cancer cells is largely unknown. ERK3 has a single phospho-acceptor site (Ser¹⁸⁹) in its activation motif rather than the TXY conserved in conventional MAPKs such as ERK1/2. Although dual phosphorylation of the TXY motif is known to be critical for the activation of conventional MAPKs, the role of Ser¹⁸⁹ phosphorylation in ERK3 activity and its function in cancer cells remain elusive. In this study, we revealed that activation loop phosphorylation is important for ERK3 in promoting cancer cell invasiveness, as the S189A mutation greatly decreased the ability of ERK3 to promote migration and invasion of lung cancer cells. Interestingly, a catalytically inactive ERK3 mutant was still capable of increasing migration and invasion, although to a lesser extent compared with WT ERK3, suggesting that ERK3 promotes cancer cell invasiveness by both kinase-dependent and kinase-independent mechanisms. To elucidate how the S189A mutation reduces the invasiveness-promoting ability of ERK3, we tested its effect on the kinase activity of ERK3 toward steroid receptor coactivator 3 (SRC3), a recently identified substrate of ERK3 critical for cancer cell invasiveness. Compared with ERK3, ERK3-S189A exhibited a dramatic decrease in kinase activity toward SRC3 and a concomitantly reduced ability to stimulate matrix metalloproteinase expression. Taken together, our study unravels the importance of Ser¹⁸⁹ phosphorylation for intramolecular regulation of ERK3 kinase activity and invasiveness-promoting ability in lung cancer cells.

Regulation of atypical MAP kinases ERK3 and ERK4 by the phosphatase DUSP2

The atypical MAP kinases ERK3 and ERK4 are activated by phosphorylation of a serine residue lying within the activation loop signature sequence S-E-G. However, the regulation of ERK3 and ERK4 phosphorylation and activity is poorly understood. Here we report that the inducible nuclear dual-specificity MAP kinase phosphatase (MKP) DUSP2, a known regulator of the ERK and p38 MAPKs, is unique amongst the MKP family in being able to bind to both ERK3 and ERK4. This interaction is mediated by a conserved common docking (CD) domain within the carboxyl-terminal domains of ERK3 and ERK4 and the conserved kinase interaction motif (KIM) located within the non-catalytic amino terminus of DUSP2. This interaction is direct and results in the dephosphorylation of ERK3 and ERK4 and the stabilization of DUSP2. In the case of ERK4 its ability to stabilize DUSP2 requires its kinase activity. Finally, we demonstrate that expression of DUSP2 inhibits ERK3 and ERK4-mediated activation of its downstream substrate MK5. We conclude that the activity of DUSP2 is not restricted to the classical MAPK pathways and that DUSP2 can also regulate the atypical ERK3/4-MK5 signalling pathway in mammalian cells.

A regulatory BMI1/let-7i/ERK3 pathway controls the motility of head and neck cancer cells

Extracellular signal‐regulated kinase 3 (ERK3) is an atypical mitogen‐activated protein kinase (MAPK), whose biological activity is tightly regulated by its cellular abundance. Recent studies have revealed that ERK3 is upregulated in multiple cancers and promotes cancer cell migration/invasion and drug resistance. Little is known, however, about how ERK3 expression level is upregulated in cancers. Here, we have identified the oncogenic polycomb group protein BMI1 as a positive regulator of ERK3 level in head and neck cancer cells. Mechanistically, BMI1 upregulates ERK3 expression by suppressing the tumor suppressive microRNA (miRNA) let‐7i, which directly targets ERK3 mRNA. ERK3 then acts as an important downstream mediator of BMI1 in promoting cancer cell migration. Importantly, ERK3 protein level is positively correlated with BMI1 level in head and neck tumor specimens of human patients. Taken together, our study revealed a molecular pathway consisting of BMI1, miRNA let‐7i, and ERK3, which controls the migration of head and neck cancer cells, and suggests that ERK3 kinase is a potential new therapeutic target in head and neck cancers, particularly those with BMI1 overexpression.

Pharmacodynamic endpoints as clinical trial objectives to answer important questions in oncology drug development

Analyzing the molecular interplay between malignancies and therapeutic agents is rarely a straightforward process, but we hope that this special issue of Seminars has highlighted the clinical value of such endeavors as well as the relevant theoretical and practical considerations. Here, we conclude with both an overview of the various high-value applications of clinical pharmacodynamics (PD) in developmental therapeutics and an outline of the framework for incorporating PD analyses into the design of clinical trials. Given the increasingly recognized importance of determining and administering the biologically effective dose (BED) and schedule of targeted agents, we explain how clinical PD biomarkers specific to the agent mechanism of action (MOA) can be used for the development of pharmacodynamics-guided biologically effective dosage regimens (PD-BEDR) to maximize the efficacy and minimize the toxicity of targeted therapies. In addition, we discuss how MOA-based PD biomarker analyses can be used both as patient selection diagnostic tools and for designing novel drug combinations targeting the specific mutational signature of a given malignancy. We also describe the role of PD analyses in clinical trials, including for MOA confirmation and dosage regimen optimization during phase 0 trials as well as for correlating molecular changes with clinical efficacy when establishing proof-of-concept in phase I/II trials. Finally, we outline the critical technological developments that are needed to enhance the quality and quantity of future clinical PD data collection, broaden the types of molecular questions that can be answered in the clinic, and, ultimately, improve patient outcomes.

Analysis of ERK3 intracellular localization: dynamic distribution during mitosis and apoptosis

Extracellular signal-regulated kinases (ERK) 1, 2 and 3 are involved in cell proliferation and differentiation, and apoptosis; although ERK1/2 have been widely studied, limited knowledge on ERK3 is available. The present work aimed at investigating ERK3 distribution during cell cycle and apoptosis in human tumor HeLa cells. The analysis performed by double immunofluorescence and immunoelectron microscopy revealed that during interphase ERK3 is mainly resident in the nucleoplasm in association with ribonuclear proteins involved in early pre-mRNA splicing, it undergoes cell cycle-dependent redistribution and, during apoptosis, it remains in the nucleus in the form of massive nuclear aggregates, then moves to the cytoplasm and is finally extruded.

Heat Shock Protein 60 in Eggs Specifically Induces Tregs and Reduces Liver Immunopathology in Mice with Schistosomiasis Japonica

Background

Parasitic helminths need to suppress the host immune system to establish chronic infections. Paradoxically, immunosuppression induced by the worm also benefits the host by limiting excessive inflammation and tissue damage, which remains the major cause leading to serious morbidity and mortality. Regulatory T cells (Tregs) are key immune regulators of this mutualism. The successive rise in Tregs during schistosome infection plays a critical role in immunoregulation. We and others previously showed that Schistosoma japonicum (S. japonicum) egg antigens (SEA) induce Tregs both in vitro and in vivo. In addition, we identified that SjHSP60 derived from SEA significantly induces Tregs in vivo and in vitro. However, the contribution of SjHSP60 in SEA to Treg induction and the related mechanisms of the Treg induction have not yet been identified.

Methodology/Principal Findings

In this study, we showed that S. japonicum stress protein HSP60 (SjHSP60) was constitutively and extensively expressed in eggs of S. japonicum. SjHSP60 specially induced Tregs in vivo and in vitro without inducing other CD4⁺ T sub-populations including Th1, Th2 and Th17 cells. Furthermore, we showed that the SjHSP60-depleted SEA almost lost the ability in vitro and displayed a significant impaired ability to induce Tregs in vivo. Finally, our study illustrated that the mechanisms of SjHSP60-mediated induction of Tregs are through both conversion of CD4⁺CD25^- T cells into CD4⁺CD25⁺Foxp3⁺ Tregs and expansion of preexisting CD4⁺CD25⁺Foxp3⁺ Tregs in a TLR4-dependent manner.

Conclusions/Significance

Collectively, our findings identify SjHSP60 as a major parasitic contributor of Treg induction in S. japonicum egg antigens, which not only contributes to the better understanding of the mechanism of immunoregulation during helminth infection, but also suggests its potential as a therapeutic target for control of immunopathology, allergic and autoimmune diseases.

The atypical MAPK ERK3 controls positive selection of thymocytes

Extracellular signal-regulated kinase 3 (ERK3 )is an atypical member of the mitogen-activated protein kinase (MAPK) family. We have previously shown that ERK3 is expressed during thymocyte differentiation and that its expression is induced in mature peripheral T cells following activation of ERK1/2 by T-cell receptor (TCR) signalling. Herein, we have investigated whether ERK3 expression is required for proper T-cell selection. Using a knock-in mouse model in which the coding sequence of ERK3 is replaced by the gene encoding for the β-galactosidase reporter, we show that ERK3 is expressed by double-positive (DP) thymocytes undergoing positive selection. In ERK3-deficient mice with a polyclonal TCR repertoire, we observe a decrease in positive selection. This reduction in positive selection was also observed when ERK3-deficient mice were backcrossed to class I- and class II-restricted TCR transgenic mice. Furthermore, the response of DP thymocytes to in vitro TCR stimulation was strongly reduced in ERK3-deficient mice. Together, these results show that ERK3 expression following TCR signalling is critical for proper thymic positive selection.

MAP Kinase Cascades in Antigen Receptor Signaling and Physiology

Mitogen-activated protein kinases (MAPKs) play roles in a cell type and context-dependent manner to convert extracellular stimuli to a variety of cellular responses, thereby directing cells to proliferation, differentiation, survival, apoptosis, and migration. Studies of genetically engineered mice or chemical inhibitors specific to each MAPK signaling pathway revealed that MAPKs have various, but non-redundant physiologically important roles among different families. MAPK cascades are obviously integrated in the B cell receptor signaling pathways as critical components to drive B cell-mediated immunity.