Mitogen-Activated Protein Kinase Phosphatases: No Longer Undruggable?

Mechanisms of pathogenicity in the hypertrophic cardiomyopathy-associated TNNI3 c.235C > T variant

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is typically manifested as a hereditary disorder, with 30 %-60 % of cases linked to cardiac sarcomere gene mutations. Despite numerous identified TNNI3 mutations associated with HCM, their severity, prevalence, and disease progression vary. The link between TNNI3 variants and phenotypes remains largely unexplored. This study aims to elucidate the impact of the TNNI3 c.235C > T mutation on HCM through clinical research and cell experiments and to explore its mechanism in HCM development.

METHODS

We screened an HCM family for pathogenic gene mutations using gene sequencing. The proband and family members were assessed through electrocardiography, echocardiography, and cardiac MRI, and a pedigree map was created for disease prediction analysis. Mutant plasmids were constructed with the TNNI3 c.235C > T mutation and transfected into the AC16 human cardiomyocyte cell line to investigate the mutation's effects.

RESULTS

The TNNI3 c.235C > T mutation was identified as the disease-causing variant in the family. This mutation led to the upregulation of hypertrophy-associated genes ANP, BNP, and MYH7, increased cardiomyocyte size, and activation of the ERK signaling pathway. Further investigations revealed that the TNNI3 c.235C > T mutation impaired mitochondrial function, disrupted cardiomyocyte metabolism, and increased cellular autophagy and apoptosis.

CONCLUSIONS

The TNNI3 c.235C > T gene mutation may be a pathogenic factor for HCM, showing heterogeneous features and clinical phenotypes. This mutation induces myocardial hypertrophy, activates the ERK signaling pathway, and exacerbates mitochondrial dysfunction, apoptosis, and autophagy in cardiomyocytes. These findings provide insights into the mechanism of HCM caused by gene mutations and may inform HCM treatment strategies.

IUPHAR Review on muscarinic M1 and M4 receptors as drug treatment targets relevant to the molecular pathology of schizophrenia

Cobenfy, a co-formulation of xanomeline and trospium, is the first drug not acting on the dopaminergic system of the CNS approved for the treatment of schizophrenia by the FDA. Xanomeline is a muscarinic M1 and M4 receptor (CHRM1 and CHRM4) agonist whilst trospium is a peripherally active CHRM antagonist that reduces the unwanted peripheral side-effects of xanomeline. Relevant to this exciting development, this review details the human CNS cholinergic systems and how those systems are affected by the molecular pathology of schizophrenia in a way suggesting activating the CHRM1 and 4 would be beneficial in treating the disorder. The CNS distribution of CHRMs is presented along with findings using CHRM knockout mice and mice treated with drugs that activate the CHRM1 and / or M4, these data explain why these CHRMs could be involved in the genesis of the symptoms of schizophrenia. Next, the process leading to the formulation of Cobenfy and the preclinical data on xanomeline are reviewed showing why Cobenfy was expected to be useful in treating schizophrenia. The pipeline of drugs targeting CHRM1 and /or M4 receptors to treat schizophrenia are discussed. Finally, the molecular pathology of two sub-groups within schizophrenia, separated based on the presence or absence of a deficit of cortical CHRM1, are reviewed to show how such approaches could identify new drug targets. In conclusion, the history of the development of Cobenfy highlights how a growing understanding the pathophysiology of schizophrenia will suggest new treatment targets for the disorder and that pharmacologists can synthesise drugs to target these sites.

Dynamic and structural insights into allosteric regulation on MKP5 a dual-specificity phosphatase

Dual-specificity mitogen-activated protein kinase (MAPK) phosphatases (MKPs) directly dephosphorylate and inactivate the MAPKs. Although the catalytic mechanism of dephosphorylation of the MAPKs by the MKPs is established, a complete molecular picture of the regulatory interplay between the MAPKs and MKPs still remains to be fully explored. Here, we sought to define the molecular mechanism of MKP5 regulation through an allosteric site within its catalytic domain. We demonstrate using crystallographic and NMR spectroscopy approaches that residue Y435 is required to maintain the structural integrity of the allosteric pocket. Along with molecular dynamics simulations, these data provide insight into how changes in the allosteric pocket propagate conformational flexibility in the surrounding loops to reorganize catalytically crucial residues in the active site. Furthermore, Y435 contributes to the interaction with p38 MAPK and JNK, thereby promoting dephosphorylation. Collectively, these results highlight the role of Y435 in the allosteric site as a novel mode of MKP5 regulation by p38 MAPK and JNK.

Therapeutic potential of targeting protein tyrosine phosphatases in liver diseases

Protein tyrosine phosphorylation is a post-translational modification that regulates protein structure to modulate demic organisms' homeostasis and function. This physiological process is regulated by two enzyme families, protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). As an important regulator of protein function, PTPs are indispensable for maintaining cell intrinsic physiology in different systems, as well as liver physiological and pathological processes. Dysregulation of PTPs has been implicated in multiple liver-related diseases, including chronic liver diseases (CLDs), hepatocellular carcinoma (HCC), and liver injury, and several PTPs are being studied as drug therapeutic targets. Therefore, given the regulatory role of PTPs in diverse liver diseases, a collated review of their function and mechanism is necessary. Moreover, based on the current research status of targeted therapy, we emphasize the inclusion of several PTP members that are clinically significant in the development and progression of liver diseases. As an emerging breakthrough direction in the treatment of liver diseases, this review summarizes the research status of PTP-targeting compounds in liver diseases to illustrate their potential in clinical treatment. Overall, this review aims to support the development of novel PTP-based treatment pathways for liver diseases.

6-Gingerol attenuates hepatic ischemia/reperfusion injury through regulating MKP5-mediated P38/JNK pathway

6-Gingerol, the main bioactive compound of ginger, has antioxidant, anti-inflammatory, anti-cancer and neuroprotective effects. However, it is unclear whether 6-Gingerol has protective effects against hepatic ischemia/reperfusion (I/R) injury. In this study, the mouse liver I/R injury model and the mouse AML12 cell hypoxia/reoxygenation (H/R) model were established by pretreatment with 6-Gingerol at different concentrations to explore the potential effects of 6-Gingerol. Serum transaminase levels, liver necrotic area, cell viability, inflammatory response, and cell apoptosis were used to assess the effect of 6-Gingerol on hepatic I/R or cell H/R injury. Quantitative polymerase chain reaction (qPCR) and Western blotting were used to detect the mRNA and protein expression. The results show that 6-Gingerol decreased serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) levels, liver necrosis, inflammatory cytokines IL-1β, IL-6, MCP-1, TNF-α expression, Ly6g+ inflammatory cell infiltration, protein phosphorylation of NF-κB signaling pathway, Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) positive cells, cell apoptosis rate, the protein expression of pro-apoptotic protein BAX and C-Caspase3, increased cell viability, and expression of anti-apoptotic protein BCL-2. Moreover, 6-Gingerol could increase the mRNA and protein expression of mitogen activated protein kinase phosphatase 5 (MKP5) and inhibit the activation of P38/JNK signaling pathway. In MKP5 knockout (KO) mice, the protective effect of 6-gingerol and the inhibition of P38/JNK pathway were significantly weakened. Therefore, our results suggest that 6-Gingerol exerts anti-inflammatory and anti-apoptotic effects to attenuate hepatic I/R injury by regulating the MKP5-mediated P38/JNK signaling pathway.

miR-147b mediated suppression of DUSP8 promotes lung cancer progression

Dual-specificity phosphatase 8 (DUSP8) plays an important role as a selective c-Jun N-terminal kinase (JNK) phosphatase in mitogen-activated protein kinase (MAPK) signaling. In this study, we found that DUSP8 is silenced by miR-147b in patients with lung adenocarcinoma (LUAD), which correlates with poor overall survival. Overexpression of DUSP8 resulted in a tumor-suppressive phenotype in vitro and in vivo experimental models, whereas silencing DUSP8 with a siRNA approach abrogated the tumor-suppressive properties. We found that miR-147b is a posttranscriptional regulator of DUSP8 that is highly expressed in patients with LUAD and is associated with lower survival. NanoString analysis revealed that the MAPK signaling pathway is mainly affected by overexpression of miR-147b, leading to increased proliferation and migration and decreased apoptosis in vitro. Moreover, induction of miR-147b promotes tumor progression in vitro and in vivo experimental models. Knockdown of miR-147b restored DUSP8, decreased tumor progression in vitro, and increased apoptosis via JNK phosphorylation. These results suggest that miR-147b plays a key role in regulating MAPK signaling in LUAD. The link between DUSP8 and miR-147b may provide novel approaches for the treatment of lung cancer.

The functions and mechanisms of post-translational modification in protein regulators of RNA methylation: Current status and future perspectives

RNA methylation, an epigenetic modification that does not alter gene sequence, may be important to diverse biological processes. Protein regulators of RNA methylation include "writers," "erasers," and "readers," which respectively deposit, remove, and recognize methylated RNA. RNA methylation, particularly N6-methyladenosine (m6A), 5-methylcytosine (m5C), N3-methylcytosine (m3C), N1-methyladenosine (m1A) and N7-methylguanosine (m7G), has been suggested as disease therapeutic targets. Despite advances in the structure and pharmacology of RNA methylation regulators that have improved drug discovery, regulating these proteins by various post-translational modifications (PTMs) has received little attention. PTM modifies protein structure and function, affecting all aspects of normal biology and pathogenesis, including immunology, cell differentiation, DNA damage repair, and tumors. It is becoming evident that RNA methylation regulators are also regulated by diverse PTMs. PTM of RNA methylation regulators induces their covalent linkage to new functional groups, hence modifying their activity and function. Mass spectrometry has identified many PTMs on protein regulators of RNA methylation. In this review, we describe the functions and PTM of protein regulators of RNA methylation and summarize the recent advances in the regulatory mode of human disease and its underlying mechanisms.

Enzyme mechanistic studies of NMA1982, a protein tyrosine phosphatase and potential virulence factor in Neisseria meningitidis

Protein phosphorylation is an integral part of many cellular processes, not only in eukaryotes but also in bacteria. The discovery of both prokaryotic protein kinases and phosphatases has created interest in generating antibacterial therapeutics that target these enzymes. NMA1982 is a putative phosphatase from Neisseria meningitidis, the causative agent of meningitis and meningococcal septicemia. The overall fold of NMA1982 closely resembles that of protein tyrosine phosphatases (PTPs). However, the hallmark C(X)5R PTP signature motif, containing the catalytic cysteine and invariant arginine, is shorter by one amino acid in NMA1982. This has cast doubt about the catalytic mechanism of NMA1982 and its assignment to the PTP superfamily. Here, we demonstrate that NMA1982 indeed employs a catalytic mechanism that is specific to PTPs. Mutagenesis experiments, transition state inhibition, pH-dependence activity, and oxidative inactivation experiments all support that NMA1982 is a genuine PTP. Importantly, we show that NMA1982 is secreted by N. meningitidis, suggesting that this protein is a potential virulence factor. Future studies will need to address whether NMA1982 is indeed essential for N. meningitidis survival and virulence. Based on its unique active site conformation, NMA1982 may become a suitable target for developing selective antibacterial drugs.

Enzyme Mechanistic Studies of NMA1982, a Protein Tyrosine Phosphatase and Potential Virulence Factor in Neisseria meningitidis

Protein phosphorylation is an integral part of many cellular processes, not only in eukaryotes but also in bacteria. The discovery of both prokaryotic protein kinases and phosphatases has created interest in generating antibacterial therapeutics that target these enzymes. NMA1982 is a putative phosphatase from Neisseria meningitidis, the causative agent of meningitis and meningococcal septicemia. The overall fold of NMA1982 closely resembles that of protein tyrosine phosphatases (PTPs). However, the hallmark C(X)5R PTP signature motif, containing the catalytic cysteine and invariant arginine, is shorter by one amino acid in NMA1982. This has cast doubt about the catalytic mechanism of NMA1982 and its assignment to the PTP superfamily. Here, we demonstrate that NMA1982 indeed employs a catalytic mechanism that is specific to PTPs. Mutagenesis experiments, transition state inhibition, pH-dependence activity, and oxidative inactivation experiments all support that NMA1982 is a genuine PTP. Importantly, we show that NMA1982 is secreted by N. meningitidis, suggesting that this protein is a potential virulence factor. Future studies will need to address whether NMA1982 is indeed essential for N. meningitidis survival and virulence. Based on its unique active site conformation, NMA1982 may become a suitable target for developing selective antibacterial drugs.

NMA1982 is a Novel Phosphatase and Potential Virulence Factor in Neisseria meningitidis

Protein phosphorylation is an integral part of many cellular processes, not only in eukaryotes but also in bacteria. The discovery of both prokaryotic protein kinases and phosphatases has created interest in generating antibacterial therapeutics that target these enzymes. NMA1982 is a putative phosphatase from Neisseria meningitidis, the causative agent of meningitis and meningococcal septicemia. The overall fold of NMA1982 closely resembles that of protein tyrosine phosphatases (PTPs). However, the hallmark C(X)5R PTP signature motif, containing the catalytic cysteine and invariant arginine, is shorter by one amino acid in NMA1982. This has cast doubt about the catalytic mechanism of NMA1982 and its assignment to the PTP superfamily. Here, we demonstrate that NMA1982 indeed employs a catalytic mechanism that is specific to PTPs. Mutagenesis experiments, transition state inhibition, pH-dependence activity, and oxidative inactivation experiments all support that NMA1982 is a genuine phosphatase. Importantly, we show that NMA1982 is secreted by N. meningitidis, suggesting that this protein is a potential virulence factor. Future studies will need to address whether NMA1982 is indeed essential for N. meningitidis survival and virulence. Based on its unique active site conformation, NMA1982 may become a suitable target for developing selective antibacterial drugs.

Biological Action of Singlet Molecular Oxygen from the Standpoint of Cell Signaling, Injury and Death

Energy transfer to ground state triplet molecular oxygen results in the generation of singlet molecular oxygen (¹O₂), which has potent oxidizing ability. Irradiation of light, notably ultraviolet A, to a photosensitizing molecule results in the generation of ¹O₂, which is thought to play a role in causing skin damage and aging. It should also be noted that ¹O₂ is a dominant tumoricidal component that is generated during the photodynamic therapy (PDT). While type II photodynamic action generates not only ¹O₂ but also other reactive species, endoperoxides release pure ¹O₂ upon mild exposure to heat and, hence, are considered to be beneficial compounds for research purposes. Concerning target molecules, ¹O₂ preferentially reacts with unsaturated fatty acids to produce lipid peroxidation. Enzymes that contain a reactive cysteine group at the catalytic center are vulnerable to ¹O₂ exposure. Guanine base in nucleic acids is also susceptible to oxidative modification, and cells carrying DNA with oxidized guanine units may experience mutations. Since ¹O₂ is produced in various physiological reactions in addition to photodynamic reactions, overcoming technical challenges related to its detection and methods used for its generation would allow its potential functions in biological systems to be better understood.

New insights into signal transduction pathways in adrenal steroidogenesis: role of mitochondrial fusion, lipid mediators, and MAPK phosphatases

Hormone-receptor signal transduction has been extensively studied in adrenal gland. Zona glomerulosa and fasciculata cells are responsible for glucocorticoid and mineralocorticoid synthesis by adrenocorticotropin (ACTH) and angiotensin II (Ang II) stimulation, respectively. Since the rate-limiting step in steroidogenesis occurs in the mitochondria, these organelles are key players in the process. The maintenance of functional mitochondria depends on mitochondrial dynamics, which involves at least two opposite events, i.e., mitochondrial fusion and fission. This review presents state-of-the-art data on the role of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2) and optic atrophy 1 (OPA1), in Ang II-stimulated steroidogenesis in adrenocortical cells. Both proteins are upregulated by Ang II, and Mfn2 is strictly necessary for adrenal steroid synthesis. The signaling cascades of steroidogenic hormones involve an increase in several lipidic metabolites such as arachidonic acid (AA). In turn, AA metabolization renders several eicosanoids released to the extracellular medium able to bind membrane receptors. This report discusses OXER1, an oxoeicosanoid receptor which has recently arisen as a novel participant in adrenocortical hormone-stimulated steroidogenesis through its activation by AA-derived 5-oxo-ETE. This work also intends to broaden knowledge of phospho/dephosphorylation relevance in adrenocortical cells, particularly MAP kinase phosphatases (MKPs) role in steroidogenesis. At least three MKPs participate in steroid production and processes such as the cellular cycle, either directly or by means of MAP kinase regulation. To sum up, this review discusses the emerging role of mitochondrial fusion proteins, OXER1 and MKPs in the regulation of steroid synthesis in adrenal cortex cells.