Structural basis for protein-protein interactions in the 14-3-3 protein family

Structural basis of ubiquitin ligase Nedd4-2 autoinhibition and regulation by calcium and 14-3-3 proteins

Nedd4-2 E3 ligase regulates Na+ homeostasis by ubiquitinating various channels and membrane transporters, including the epithelial sodium channel ENaC. In turn, Nedd4-2 dysregulation leads to various conditions, including electrolytic imbalance, respiratory distress, hypertension, and kidney diseases. However, Nedd4-2 regulation remains mostly unclear. The present study aims at elucidating Nedd4-2 regulation by structurally characterizing Nedd4-2 and its complexes using several biophysical techniques. Our cryo-EM reconstruction shows that the C2 domain blocks the E2-binding surface of the HECT domain. This blockage, ubiquitin-binding exosite masking by the WW1 domain, catalytic C922 blockage and HECT domain stabilization provide the structural basis for Nedd4-2 autoinhibition. Furthermore, Ca2+-dependent C2 membrane binding disrupts C2/HECT interactions, but not Ca2+ alone, whereas 14-3-3 protein binds to a flexible region of Nedd4-2 containing the WW2 and WW3 domains, thereby inhibiting its catalytic activity and membrane binding. Overall, our data provide key mechanistic insights into Nedd4-2 regulation toward fostering the development of strategies targeting Nedd4-2 function.

14-3-3 proteins: Regulators of cardiac excitation-contraction coupling and stress responses

14-3-3 proteins are highly conserved proteins that regulate numerous cellular processes mostly through phosphorylation-dependent protein-protein interactions. In the heart 14-3-3 proteins play critical roles in cardiac conduction pathways, excitation-contraction (EC) coupling, development and stress responses. This review summarizes the current understanding of cardiac 14-3-3 regulation and function, with particular emphasis on its role in ion channel regulation and β-adrenergic signalling. We discuss how 14-3-3 proteins act through three main mechanisms - masking, clamping, and scaffolding - to regulate target proteins, including Cx43, CaV1.2, NaV1.5, and various potassium channels. The seven mammalian 14-3-3 isoforms display distinct but overlapping functions, with tissue-specific expression patterns and isoform-specific regulation through phosphorylation and dimerization. Recent work has revealed 14-3-3's importance in cardiac development and stress responses, where it generally serves a cardioprotective role. However in some pathological contexts such as ischaemia-reperfusion injury, 14-3-3 can be detrimental. We highlight emerging themes in cardiac 14-3-3 biology, including its role in prolonging β-adrenergic signalling. Understanding the complex regulation of cardiac 14-3-3 and its numerous targets presents both opportunities and challenges for therapeutic development.

Harnessing the power of 19F NMR for characterizing dimerization and ligand binding of 14-3-3 proteins

The main role of dimeric 14-3-3 proteins is to modulate the activity of several hundred binding partners by interacting with phosphorylated residues of the partner proteins, often located in disordered regions. The inherent flexibility or large size of 14-3-3 complexes hampers their structural characterization by X-ray crystallography, cryo-electron microscopy (EM) and traditional solution nuclear magnetic resonance (NMR) spectroscopy. Here, we employ solution 1D 19F-Trp NMR spectroscopy to characterize substrate binding and dimerization of 14-3-3 proteins, focusing on 14-3-3ζ - an abundant human isoform as an example. Both conserved Trp residues are located in distinct functionally important sites - the dimeric interface and the ligand-binding groove. We substituted them by 5F-Trp, thereby introducing a convenient NMR probe. Fluorination of the two Trp did not impact the stability and interaction properties of 14-3-3ζ in a substantive manner, permitting to carry out 19F NMR experiments to assess 14-3-3's structure and behavior. Importantly, 5F-Trp228 reports on binding of substrates in the amphipathic binding groove of 14-3-3ζ and permitted to distinguish distinct recognition modes. Thus, we established that 19F NMR is a powerful approach to evaluate the binding of partner proteins to 14-3-3 and to characterize the properties of the resulting complexes.

A Personalized 14-3-3 Disease-Targeting Workflow Yields Repositioning Drug Candidates

Rare diseases typically evade the application of the standard drug discovery and development pipelines due to their understudied molecular etiology and the small market size. Herein, we report a rare disease-directed workflow that rapidly studies the molecular features of the disorder, establishes a high-throughput screening (HTS) platform, and conducts an HTS of thousands of approved drugs to identify and validate repositioning drug candidates. This study examines the pediatric neurological disorder caused by de novo mutations in YWHAG, the gene encoding the scaffolding protein 14-3-3γ, and the workflow discovers nuclear relocalization and a severe drop in 14-3-3γ binding to its phosphorylated protein partners as the key molecular features of the pathogenic hotspot YWHAG mutations. We further established a robust in vitro HTS platform and screened ca. 3000 approved drugs to identify the repositioning drug candidates that restore the deficient 14-3-3γ-phosphotarget interactions. Our workflow can be applied to other 14-3-3-related disorders and upscaled for many other rare diseases.

The phenotypic spectrum of YWHAG-related epilepsy: From mild febrile seizures to severe developmental delay and epileptic encephalopathy

AIM

To explore the phenotypic spectrum and refine the genotype-phenotype correlation of YWHAG-related epilepsy.

METHOD

This study used a retrospective cohort design to evaluate the clinical data of 15 patients with epilepsy and YWHAG variants in our Chinese cohort (nine males, six females; median age: 6 years 4 months; range: 1 year 6 months-12 years 8 months) and 40 patients with epilepsy with YWHAG variants from published studies (21 males, 19 females; median age: 10 years; range: 3 years-67 years).

RESULTS

In our cohort, seven variants were de novo and five were new. Seizure onset for 14 of 15 patients occurred within the first 2 years of life. Nine of 15 patients had a history of febrile seizures. Seizure types included generalized tonic-clonic seizures (GTCS) and myoclonic seizures. Developmental delay was present in 11 of 15 patients. Three patients were diagnosed with febrile seizures plus, one was diagnosed with myoclonic epilepsy in infancy, one had infantile epileptic spasm syndrome, and 10 had developmental and epileptic encephalopathy that could not be further classified into a specific epilepsy syndrome. Seizures were controlled in 7 of 15 patients; most were treated with valproate and levetiracetam. Collectively, in our cohort and from published studies, most variants (38 of 55, 69.1%) were located in the highly conserved triad (HCT) domain of Arg132-Arg57-Tyr133. Mild phenotypes were more frequently observed in patients with variants located outside the HCT domain, with a significant difference of 70.6% versus 27.0% (p < 0.01).

INTERPRETATION

Most patients with YWHAG variants were diagnosed during infancy. The most common seizure types were GTCS and myoclonic seizures. The phenotypic spectrum of epilepsy ranged from mild febrile seizures to severe developmental delay and epileptic encephalopathy. Most variants were localized in the HCT domain; variants residing outside the HCT domain were correlated with milder phenotypes.

Cold Atmospheric Plasma Jet Promotes Wound Healing Through CK2-Coordinated PI3K/AKT and MAPK Signaling Pathways

The promising role of cold atmospheric plasma jet (CAPJ) treatment in promoting wound healing has been widely documented in therapeutic implications. However, the fact that not all subjects respond equally to CAPJ necessitates the investigation of the underlying cellular mechanisms, which have been rarely understood so far. Given that wound healing is a complex and prolonged process, post plasma-activated medium (PAM) treated keratinocytes were collected at two time points, 2 h (receiving) and 24 h (recovery), for (phospho)proteomic analysis to systematically dissect the molecular basis of CAPJ-promoted wound healing. The receiving (phospho)proteomics datasets, referred to the time point of 2 h, revealed an apparent increase in the phosphorylation of CK2 and its-mediated PI3K/AKT and MAPK signaling pathways, accompanied by a prompted downstream physiological response of cell migration. Additionally, incorporating the network analysis of predicted kinases and their direct interactors, we reiterated that CAPJ influenced cell growth and migration, thereby paving the way for its role in subsequent wound healing processes. Further determining the proteome profiles at recovery phase, which is the time point of 24 h, displayed a totally different view from the receiving proteome which had almost no change. The upregulation of ROBOs/SLITs expression and vesicle trafficking and fusion-related proteins, along with the abundant presence of 14-3-3 family proteins, indicated that the persistent effect of PAM on the wound healing process could potentially promote keratinocyte-fibroblast cross talk and stimulate extracellular matrix synthesis upon epithelialization. Consistent with proteome patterns, CAPJ-treated wound tissues indeed showed a denser and well-organized extracellular matrix architecture, implying hastened epithelialization during wound healing. Collectively, we delineated the molecular basis of CAPJ-accelerated wound healing at early and late responses, providing valuable insights for treatment selection and the development of therapeutic strategies to achieve better outcomes.

Dynamic interactions of dimeric hub proteins underlie their diverse functions and structures: A comparative analysis of 14-3-3 and LC8

Hub proteins interact with a host of client proteins and regulate multiple cellular functions. Dynamic hubs have a single binding interface for one client at a time resulting in competition among clients with the highest affinity. Dynamic dimeric hubs with two identical sites bind either two different client proteins or two chains of the same client to form homogenous complexes and could also form heterogeneous mixtures of interconverting complexes. Here, we review the interactions of the dimeric hubs 14-3-3 and LC8. 14-3-3 is a phosphoserine/threonine binding protein involved in structuring client proteins and regulating their phosphorylation. LC8 is involved in promoting the dimerization of client peptides and the rigidification of their disordered regions. Both 14-3-3 and LC8 are essential genes, with 14-3-3 playing a crucial role in apoptosis and cell cycle regulation, while LC8 is critical for the assembly of proteins involved in transport, DNA repair, and transcription. Interestingly, both protein dimers can dissociate by phosphorylation, which results in their interactome-wide changes. Their interactions are also regulated by the phosphorylation of their clients. Both form heterogeneous complexes with various functions including phase separation, signaling, and viral hijacking where they restrict the conformational heterogeneity of their dimeric clients that bind nucleic acids. This comparative analysis highlights the importance of dynamic protein-protein interactions in the diversity of functions of 14-3-3 and LC8 and how small differences in structures of interfaces explain why 14-3-3 is primarily involved in the regulation of phosphorylation states while LC8 is primarily involved in the regulation of assembly of large dynamic complexes.

Characterization of multiple binding sites on microtubule associated protein 2c recognized by dimeric and monomeric 14-3-3ζ

Microtubule associated protein 2 (MAP2) interacts with the regulatory protein 14-3-3ζ in a cAMP-dependent protein kinase (PKA) phosphorylation dependent manner. Using selective phosphorylation, calorimetry, nuclear magnetic resonance, chemical crosslinking, and X-ray crystallography, we characterized interactions of 14-3-3ζ with various binding regions of MAP2c. Although PKA phosphorylation increases the affinity of MAP2c for 14-3-3ζ in the proline rich region and C-terminal domain, unphosphorylated MAP2c also binds the dimeric 14-3-3ζ via its microtubule binding domain and variable central domain. Monomerization of 14-3-3ζ leads to the loss of affinity for the unphosphorylated residues. In neuroblastoma cell extract, MAP2c is heavily phosphorylated by PKA and the proline kinase ERK2. Although 14-3-3ζ dimer or monomer do not interact with the residues phosphorylated by ERK2, ERK2 phosphorylation of MAP2c in the C-terminal domain reduces the binding of MAP2c to both oligomeric variants of 14-3-3ζ.

Deciphering opening mechanisms of 14-3-3 proteins

The 14-3-3 proteins are a highly conserved family of regulatory molecules that play crucial roles in various cellular processes. They are known for their ability to bind to phosphorylated serine and threonine residues on target proteins, which allows them to modulate their activity, localization, and stability. In mammals, there are seven known paralogs of 14-3-3 proteins, designated as β, ε, ζ, η, σ, τ, and γ. Each paralog has distinct biological functions and tissue distributions, which allow a diverse range of regulatory roles in cellular processes. The conformational plasticity of 14-3-3s regulates their interaction with protein partners but has not yet been thoroughly characterized. We investigated this topic by classical molecular dynamics simulations and observed how the γ, ε, and ζ paralogs exhibit different opening rates. A PCA analysis identified the main modes of these opening-conformational variations. Using correlation-based tools and simulations with single amino acid substitutions, we have recognized how the amphipathic 14-3-3 groove opening is triggered by a distally located aliphatic-π interaction. The identified residues form a partially conserved small cavity between helices H6, H7, and H8, representing a potential paralog-specific drug site.

Genome-wide identification and comparative evolution of 14-3-3 gene family members in five Brassicaceae species

BACKGROUND

The 14-3-3 proteins are highly conserved regulatory eukaryotic proteins, which are crucial in growth, development, and stress responses. However, systematic characterization of the 14-3-3 gene family in Brassicaceae species and their evolutionary relationships have not been comprehensively reported.

RESULTS

This study conducted genome-wide identification, structural characteristics, and comparative evolutionary analysis of 14-3-3 gene family members in Arabidopsis thaliana, A. lyrata, A. pumila, Camelina sativa, and Brassica oleracea using comparative genomics. Overall, a total of 108 14-3-3 genes, which were phylogenetically classified into ε and non-ε groups were identified in the five species, with the non-ε members exhibiting more similar exon-intron structures and conserved motif patterns. Collinearity analysis revealed that the Brassicaceae 14-3-3 gene family members underwent varying degrees of expansion following whole-genome duplication (WGD) events. Notably, the number of 14-3-3 gene family members between A. lyrata and A. thaliana remained similar despite the former having approximately 1.66-fold larger genome size. In contrast, the number of 14-3-3 gene family members in A. pumila and C. sativa increased in proportionately to their genome size, while gene members in the more distantly related species to A. thaliana, B. oleracea, showed irregular expansion patterns. Selection pressure analysis revealed that 14-3-3 homologs in all the five species underwent purifying selection, with the group ε members experiencing relatively weaker purifying selection. Cloning of ApGRF6-2 gene from A. pumila indicated that the ApGRF6-2 protein was localized in the cell membrane and cytoplasm, while ectopic overexpression of ApGRF6-2 in A. thaliana could promote early flowering by upregulating the expression of floral meristem identity genes.

CONCLUSION

This study provides a comprehensive and systematic identification of the 14-3-3 gene family members in five Brassicaceae species using updated genome sequences, and the results could form a basis for further validation of functional and molecular mechanisms of 14-3-3 genes in plant growth, development, abiotic stress responses, as well as flowering regulation.

Underlying features for the enhanced electrostatic strength of the extremophilic malate dehydrogenase interface salt-bridge compared to the mesophilic one

Malate dehydrogenase (MDH) exists in multimeric form in normal and extreme solvent conditions where residues of the interface are involved in specific interactions. The interface salt-bridge (ISB) and its microenvironment (ME) residues may have a crucial role in the stability and specificity of the interface. To gain insight into this, we have analyzed 218 ISBs from 42 interfaces of 15 crystal structures along with their sequences. Comparative analyses demonstrate that the ISB strength is ∼30 times greater in extremophilic cases than that of the normal one. To this end, the interface residue propensity, ISB design and pair selection, and ME-residue's types, i.e., type-I and type-II, are seen to be intrinsically involved. Although Type-I is a common type, Type-II appears to be extremophile-specific, where the net ME-residue count is much lower with an excessive net ME-energy contribution, which seems to be a novel interface compaction strategy. Furthermore, the interface strength can be enhanced by selecting the desired mutant from the net-energy profile of all possible mutations of an unfavorable ME-residue. The study that applies to other similar systems finds applications in protein-protein interaction and protein engineering.

Biochemical signatures strongly demarcate phylogenetic groups of plant 14-3-3 isoforms

Interaction of dimeric 14-3-3 proteins with phosphotargets regulates various physiological processes in plants, from flowering to transpiration and salt tolerance. Several genes express distinct 14-3-3 "isoforms," particularly numerous in plants, but these are unevenly studied even in model species. Here we systematically investigated twelve 14-3-3 isoforms from Arabidopsis thaliana. While all these proteins can homodimerize, four isoforms representing a supposedly more ancestral, epsilon phylogenetic group (iota, mu, omicron, epsilon), but not their eight non-epsilon counterparts (omega, phi, chi, psi, upsilon, nu, kappa, lambda), exhibit concentration-dependent monomerization, and pronounced surface hydrophobicity at physiologically relevant protein concentrations and under crowding conditions typical for the cell. We show that dramatically lowered thermodynamic stabilities entail aggregation of the epsilon group isoforms at near-physiological temperatures and accelerate their proteolytic degradation in vitro and in plant cell lysates. Mutations in 14-3-3 iota, inspired by structural analysis, helped us rescue non-epsilon behavior and pinpoint key positions responsible for the epsilon/non-epsilon demarcation. Combining two major demarcating positions (namely, 27th and 51st in omega) and differences in biochemical properties, we developed an epsilon/non-epsilon demarcation criterion that classified 89% of available 14-3-3 sequences from Dicots, Monocots, Gymnosperms, Ferns, and Lycophytes with 99.7% accuracy, and reliably predicted biochemical properties of a given 14-3-3 isoform, which we experimentally verified for distant 14-3-3 isoforms from Selaginella moellendorffii. The proven occurrence of isoforms of both groups in primitive plants refines the traditional phylogenetic, solely sequence-based analysis and provides intriguing insights into the evolutionary history of the epsilon phylogenetic group.

Proximity-enhanced cysteine-histidine crosslinking for elucidating intrinsically disordered and other protein complexes

Disordered proteins and domains are ubiquitous throughout the proteome of human cell types, yet the biomolecular sciences lack effective tool compounds and chemical strategies to study this class of proteins. In this context, we introduce a novel covalent tool compound approach that combines proximity-enhanced crosslinking with histidine trapping. Utilizing a maleimide-cyclohexenone crosslinker for efficient cysteine-histidine crosslinking, we elucidated the mechanism of this dual-reactive tool compound class. This tool compound concept was then applied to profile the full-length complex of 14-3-3 and hyperphosphorylated Tau (hpTau), relevant to Alzheimer's. This approach identified a cryptic binding interaction between 14-3-3 and hpTau via its phosphorylated Ser356, overlooked by the majority of 14-3-3/Tau literature. Utilizing a mutational study and an equilibrium model, this cryptic binding interaction is revealed to play a prominent biomolecular role at cellularly relevant concentrations. This finding necessitates a re-evaluation of the mechanism of the 14-3-3/Tau interaction. The histidine-trap crosslinker approach reported here not only advances our understanding of the 14-3-3/Tau interaction but also demonstrates the potential of dual-covalent tool compounds in studying complex interactions involving IDPs and IDDs.

Recent Developments in 14-3-3 Stabilizers for Regulating Protein-Protein Interactions: An Update

14-3-3 proteins play a crucial role in the regulation of protein-protein interactions, impacting various cellular processes and disease mechanisms. Recent advancements have led to the development of stabilizers that enhance the binding of 14-3-3 proteins to clients, presenting promising therapeutic potentials. This perspective provides an updated overview of the latest developments in the field of 14-3-3 stabilizers, with a focus on their design, synthesis, and biological evaluation. We discuss the structural basis for the interaction between 14-3-3 proteins and their ligands, highlighting key modifications that enhance binding affinity and selectivity. Additionally, we explore the therapeutic applications of 14-3-3 stabilizers across major therapeutic areas such as cancer, metabolic disorders, and neurodegenerative diseases. By summarizing recent research findings and technological advancements, this perspective aims to shed light on the current state of 14-3-3 stabilizer developments and outline future directions for optimizing these compounds as effective therapeutic agents.

The β2 adrenergic receptor cross-linked interactome identifies 14-3-3 proteins as regulating the availability of signaling-competent receptors

The emerging picture of G protein-coupled receptor function suggests that the global signaling response is an integrated sum of a multitude of individual receptor responses, each regulated by their local protein environment. The β2 adrenergic receptor (B2AR) has long served as an example receptor in the development of this model. However, the mechanism and the identity of the protein-protein interactions that govern the availability of receptors competent for signaling remain incompletely characterized. To address this question, we characterized the interactome of agonist-stimulated B2AR in human embryonic kidney 293 cells using FLAG coimmunoprecipitation coupled to stable isotope labeling by amino acids in cell culture and mass spectrometry. Our B2AR cross-linked interactome identified 190 high-confidence proteins, including almost all known interacting proteins and 6 out of 7 isoforms of the 14-3-3 family of scaffolding proteins. Inhibiting 14-3-3 proteins with the peptide difopein enhanced isoproterenol-stimulated adrenergic signaling via cAMP approximately 3-fold and increased both miniGs and arrestin recruitment to B2AR more than 2-fold each, without noticeably changing EC50 with respect to cAMP signaling or effector recruitment upon stimulation. Our results show that 14-3-3 proteins negatively regulate downstream signaling by inhibiting access of B2AR to effector proteins. We propose that 14-3-3 proteins maintain a dynamic pool of B2AR that has reduced signaling efficacy in response to acute agonist stimulation, limiting the number of signaling-competent receptors at the plasma membrane. SIGNIFICANCE STATEMENT: This study presents a new interactome of the agonist-stimulated β2 adrenergic receptor, a paradigmatic G protein-coupled receptor that is both a model system for members of this class and an important signaling protein in respiratory, cardiovascular, and metabolic regulation. We identify 14-3-3 proteins as responsible for restricting β2 adrenergic receptor access to signaling effectors and maintaining a receptor population that is insensitive to acute stimulation by agonists.

The Big, Mysterious World of Plant 14-3-3 Proteins

14-3-3 is a family of small regulatory proteins found exclusively in eukaryotic organisms. They selectively bind to phosphorylated molecules of partner proteins and regulate their functions. 14-3-3 proteins were first characterized in the mammalian brain approximately 60 years ago and then found in plants, 30 years later. The multifunctionality of 14-3-3 proteins is exemplified by their involvement in coordination of protein kinase cascades in animal brain and regulation of flowering, growth, metabolism, and immunity in plants. Despite extensive studies of this diverse and complex world of plant 14-3-3 proteins, our understanding of functions of these enigmatic molecules is fragmentary and unsystematic. The results of studies are often contradictory and many questions remain unanswered, including biochemical properties of 14-3-3 isoforms, structure of protein-protein complexes, and direct mechanisms by which 14-3-3 proteins influence the functions of their partners in plants. Although many plant genes coding for 14-3-3 proteins have been identified, the isoforms for in vivo and in vitro studies are often selected at random. This rather limited approach is partly due to an exceptionally large number and variety of 14-3-3 homologs in plants and erroneous a priori assumptions on the equivalence of certain isoforms. The accumulated results provide an extensive but rather fragmentary picture, which poses serious challenges for making global generalizations. This review is aimed to demonstrate the diversity and scope of studies of the functions of plant 14-3-3 proteins, as well as to identify areas that require further systematic investigation and close scientific attention.

New insights into protein-protein interaction modulators in drug discovery and therapeutic advance

Protein-protein interactions (PPIs) are fundamental to cellular signaling and transduction which marks them as attractive therapeutic drug development targets. What were once considered to be undruggable targets have become increasingly feasible due to the progress that has been made over the last two decades and the rapid technological advances. This work explores the influence of technological innovations on PPI research and development. Additionally, the diverse strategies for discovering, modulating, and characterizing PPIs and their corresponding modulators are examined with the aim of presenting a streamlined pipeline for advancing PPI-targeted therapeutics. By showcasing carefully selected case studies in PPI modulator discovery and development, we aim to illustrate the efficacy of various strategies for identifying, optimizing, and overcoming challenges associated with PPI modulator design. The valuable lessons and insights gained from the identification, optimization, and approval of PPI modulators are discussed with the aim of demonstrating that PPI modulators have transitioned beyond early-stage drug discovery and now represent a prime opportunity with significant potential. The selected examples of PPI modulators encompass those developed for cancer, inflammation and immunomodulation, as well as antiviral applications. This perspective aims to establish a foundation for the effective targeting and modulation of PPIs using PPI modulators and pave the way for future drug development.

14-3-3 protein and its isoforms: A common diagnostic marker for Alzheimer's disease, Parkinson's disease and glaucomatous neurodegeneration

There is a molecular coupling between neurodegenerative diseases, including glaucomatous neurodegeneration (GN), Alzheimer's disease (AD), and Parkinson's disease (PD). Many cells in the eye and the brain have the right amount of 14-3-3 proteins (14-3-3 s) and their isoforms, such as β, ε, γ, η, θ, π, and γ. These cells include keratocytes, endothelial cells, corneal epithelial cells, and primary conjunctival epithelial cells. 14-3-3 s regulate autophagy and mitophagy, help break down built-up proteins, and connect to other proteins to safeguard against neurodegeneration in AD, PD, GN, and glioblastoma. By interacting with these proteins, 14-3-3 s stop Bad and Bax proteins from entering mitochondria and make them less effective. These interactions inhibit neuronal apoptosis. They play many important roles in managing the breakdown of lysosomal proteins, tau, and Aβ, which is why the 14-3-3 s could be used as therapeutic targets in AD. Furthermore, researchers have discovered 14-3-3 s in Lewy bodies, which are associated with various proteins like LRRK2, ASN, and Parkin, all of which play a role in developing Parkinson's disease (PD). The 14-3-3 s influence the premature aging and natural wrinkles of human skin. Studies have shown that lowering 14-3-3 s in the brain can lead to an increase in cell-death proteins like BAX and ERK, which in turn causes excitotoxicity-induced neurodegeneration. This review aimed to clarify the role of 14-3-3 s in the neuropathology of AD, PD, and GN, as well as potential diagnostic markers for improving neuronal survival and repair.

14-3-3 binding maintains the Parkinson's associated kinase LRRK2 in an inactive state

Leucine-rich repeat kinase 2 (LRRK2) is a central player in cellular signaling and a significant contributor to Parkinson's disease (PD) pathogenesis. 14-3-3 proteins are essential regulators of LRRK2, modulating its activity. Here, we present the cryo- electron microscopy structure of the LRRK2:14-3-3 2 autoinhibitory complex, showing that a 14-3-3 dimer stabilizes an autoinhibited LRRK2 monomer by binding to key phosphorylation sites and the COR-A and COR-B subdomains within the Roc-COR GTPase domain of LRRK2. This interaction locks LRRK2 in an inactive conformation, restricting LRR domain mobility and preventing dimerization and oligomer formation. Our mutagenesis studies reveal that PD-associated mutations at the COR:14-3-3 interface and within the GTPase domain reduce 14-3-3 binding, diminishing its inhibitory effect on LRRK2. These findings provide a structural basis for understanding how LRRK2 likely remains dormant within cells, illuminate aspects of critical PD biomarkers, and suggest therapeutic strategies to enhance LRRK2-14-3-3 interactions to treat PD and related disorders.

14-3-3 phosphorylation inhibits 14-3-3θ's ability to regulate LRRK2 kinase activity and toxicity

LRRK2 mutations are among the most common genetic causes for Parkinson's disease (PD), and toxicity is associated with increased kinase activity. 14-3-3 proteins are key interactors that regulate LRRK2 kinase activity. Phosphorylation of the 14-3-3θ isoform at S232 is dramatically increased in human PD brains. Here we investigate the impact of 14-3-3θ phosphorylation on its ability to regulate LRRK2 kinase activity. Both wildtype and the non-phosphorylatable S232A 14-3-3θ mutant reduced the kinase activity of wildtype and G2019S LRRK2, whereas the phosphomimetic S232D 14-3-3θ mutant had minimal effects on LRRK2 kinase activity, as determined by measuring autophosphorylation at S1292 and T1503 and Rab10 phosphorylation. However, wildtype and both 14-3-3θ mutants similarly reduced the kinase activity of the R1441G LRRK2 mutant. 14-3-3θ phosphorylation did not promote global dissociation with LRRK2, as determined by co-immunoprecipitation and proximal ligation assays. 14-3-3s interact with LRRK2 at several phosphorylated serine/threonine sites, including T2524 in the C-terminal helix, which can fold back to regulate the kinase domain. Interaction between 14-3-3θ and phosphorylated T2524 LRRK2 was important for 14-3-3θ's ability to regulate kinase activity, as wildtype and S232A 14-3-3θ failed to reduce the kinase activity of G2019S/T2524A LRRK2. Finally, we found that the S232D mutation failed to protect against G2019S LRRK2-induced neurite shortening in primary cultures, while the S232A mutation was protective. We conclude that 14-3-3θ phosphorylation destabilizes the interaction of 14-3-3θ with LRRK2 at T2524, which consequently promotes LRRK2 kinase activity and toxicity.

Mechanistic Insights into the Function of 14-3-3 Proteins as Negative Regulators of Brassinosteroid Signaling in Arabidopsis

Brassinosteroids (BRs) are vital plant steroid hormones sensed at the cell surface by a membrane signaling complex comprising the receptor kinase BRI1 and a SERK family co-receptor kinase. Activation of this complex lead to dissociation of the inhibitor protein BKI1 from the receptor and to differential phosphorylation of BZR1/BES1 transcription factors by the glycogen synthase kinase 3 protein BIN2. Many phosphoproteins of the BR signaling pathway, including BRI1, SERKs, BKI1 and BZR1/BES1 can associate with 14-3-3 proteins. In this study, we use quantitative ligand binding assays to define the minimal 14-3-3 binding sites in the N-terminal lobe of the BRI1 kinase domain, in BKI1, and in BZR1 from Arabidopsis thaliana. All three motifs require to be phosphorylated to specifically bind 14-3-3s with mid- to low-micromolar affinity. BR signaling components display minimal isoform preference within the 14-3-3 non-ε subgroup. 14-3-3λ and 14-3-3 ω isoform complex crystal structures reveal that BKI1 and BZR1 bind as canonical type II 14-3-3 linear motifs. Disruption of key amino acids in the phosphopeptide binding site through mutation impairs the interaction of 14-3-3λ with all three linear motifs. Notably, quadruple loss-of-function mutants from the non-ε group exhibit gain-of-function BR signaling phenotypes, suggesting a role for 14-3-3 proteins as overall negative regulators of the BR pathway. Collectively, our work provides further mechanistic and genetic evidence for the regulatory role of 14-3-3 proteins at various stages of the BR signaling cascade.

Versatility of 14-3-3 proteins and their roles in bone and joint-related diseases

Bone and joint-related diseases, including osteoarthritis (OA), rheumatoid arthritis (RA), and bone tumors, pose significant health challenges due to their debilitating effects on the musculoskeletal system. 14-3-3 proteins, a family of conserved regulatory molecules, play a critical role in the pathology of these diseases. This review discusses the intricate structure and multifunctionality of 14-3-3 proteins, their regulation of signaling pathways, and their interactions with other proteins. We underscore the significance of 14-3-3 proteins in the regulation of osteoblasts, osteoclasts, chondrocytes, and bone remodeling, all key factors in the maintenance and dysfunction of bone and joint systems. Specific focus is directed toward elucidating the contribution of 14-3-3 proteins in the pathology of OA, RA, and bone malignancies, where dysregulated 14-3-3-mediated signaling cascades have been implicated in the disease processes. This review illuminates how the perturbation of 14-3-3 protein interactions can lead to the pathological manifestations observed in these disorders, including joint destruction and osteolytic activity. We highlight cutting-edge research that positions 14-3-3 proteins as potential biomarkers for disease progression and as innovative therapeutic targets, offering new avenues for disease intervention and management.

LPA3 agonist-producing Bacillus velezensis ADS024 is efficacious in multiple neuroinflammatory disease models

Neuroinflammation is a common component of neurological disorders. In the gut-brain-immune axis, bacteria and their metabolites are now thought to play a role in the modulation of the nervous and immune systems which may impact neuroinflammation. In this respect, commensal bacteria of humans have recently been shown to produce metabolites that mimic endogenous G-protein coupled receptor (GPCR) ligands. To date, it has not been established whether plant commensal bacteria, which may be ingested by animals including humans, can impact the gut-brain-immune axis via GPCR agonism. We screened an isopropanol (IPA) extract of the plant commensal Bacillus velezensis ADS024, a non-engrafting live biotherapeutic product (LBP) with anti-inflammatory properties isolated from human feces, against a panel of 168 GPCRs and identified strong agonism of the lysophosphatidic acid (LPA) receptor LPA3. The ADS024 IPA extracted material (ADS024-IPA) did not agonize LPA2, and only very weakly agonized LPA1. The agonism of LPA3 was inhibited by the reversible LPA1/3 antagonist Ki16425. ADS024-IPA signaled downstream of LPA3 through G-protein-induced calcium release, recruitment of β-arrestin, and recruitment of the neurodegeneration-associated proteins 14-3-3γ, ε and ζ but did not recruit the β isoform. Since LPA3 agonism was previously indirectly implicated in the reduction of pathology in models of Parkinson's disease (PD) and multiple sclerosis (MS) by use of the nonselective antagonist Ki16425, and since we identified an LPA3-specific agonist within ADS024, we sought to examine whether LPA3 might indeed be part of a broad underlying mechanism to control neuroinflammation. We tested oral treatment of ADS024 in multiple models of neuroinflammatory diseases using three models of PD, two models of MS, and a model each of amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and chemo-induced peripheral neuropathy (CIPN). ADS024 treatment improved model-specific functional effects including improvements in motor movement, breathing and swallowing, and allodynia suggesting that ADS024 treatment impacted a universal underlying neuroinflammatory mechanism regardless of the initiating cause of disease. We used the MOG-EAE mouse model to examine early events after disease initiation and found that ADS024 attenuated the increase in circulating lymphocytes and changes in neutrophil subtypes, and ADS024 attenuated the early loss of cell-surface LPA3 receptor expression on circulating white blood cells. ADS024 efficacy was partially inhibited by Ki16425 in vivo suggesting LPA3 may be part of its mechanism. Altogether, these data suggest that ADS024 and its LPA3 agonism activity should be investigated further as a possible treatment for diseases with a neuroinflammatory component.

Fragment-Based Interrogation of the 14-3-3/TAZ Protein-Protein Interaction

The identification of chemical starting points for the development of molecular glues is challenging. Here, we employed fragment screening and identified an allosteric stabilizer of the complex between 14-3-3 and a TAZ-derived peptide. The fragment binds preferentially to the 14-3-3/TAZ peptide complex and shows moderate stabilization in differential scanning fluorimetry and microscale thermophoresis. The binding site of the fragment was predicted by molecular dynamics calculations to be distant from the 14-3-3/TAZ peptide interface, located between helices 8 and 9 of the 14-3-3 protein. This site was confirmed by nuclear magnetic resonance and X-ray protein crystallography, revealing the first example of an allosteric stabilizer for 14-3-3 protein-protein interactions.

Look for the Scaffold: Multifaceted Regulation of Enzyme Activity by 14-3-3 Proteins

Enzyme activity is regulated by several mechanisms, including phosphorylation. Phosphorylation is a key signal transduction process in all eukaryotic cells and is thus crucial for virtually all cellular processes. In addition to its direct effect on protein structure, phosphorylation also affects protein-protein interactions, such as binding to scaffolding 14-3-3 proteins, which selectively recognize phosphorylated motifs. These interactions then modulate the catalytic activity, cellular localisation and interactions of phosphorylated enzymes through different mechanisms. The aim of this mini-review is to highlight several examples of 14-3-3 protein-dependent mechanisms of enzyme regulation previously studied in our laboratory over the past decade. More specifically, we address here the regulation of the human enzymes ubiquitin ligase Nedd4-2, procaspase-2, calcium-calmodulin dependent kinases CaMKK1/2, and death-associated protein kinase 2 (DAPK2) and yeast neutral trehalase Nth1.

Dissecting structure and function of the monovalent cation/H+ antiporters Mdm38 and Ylh47 in Saccharomyces cerevisiae

Saccharomyces cerevisiae Mdm38 and Ylh47 are homologs of the Ca2+/H+ antiporter Letm1, a candidate gene for seizures associated with Wolf-Hirschhorn syndrome in humans. Mdm38 is important for K+/H+ exchange across the inner mitochondrial membrane and contributes to membrane potential formation and mitochondrial protein translation. Ylh47 also localizes to the inner mitochondrial membrane. However, knowledge of the structures and detailed transport activities of Mdm38 and Ylh47 is limited. In this study, we conducted characterization of the ion transport activities and related structural properties of Mdm38 and Ylh47. Growth tests using Na+/H+ antiporter-deficient Escherichia coli strain TO114 showed that Mdm38 and Ylh47 had Na+ efflux activity. Measurement of transport activity across E. coli-inverted membranes showed that Mdm38 and Ylh47 had K+/H+, Na+/H+, and Li+/H+ antiport activity, but unlike Letm1, they lacked Ca2+/H+ antiport activity. Deletion of the ribosome-binding domain resulted in decreased Na+ efflux activity in Mdm38. Structural models of Mdm38 and Ylh47 identified a highly conserved glutamic acid in the pore-forming membrane-spanning region. Replacement of this glutamic acid with alanine, a non-polar amino acid, significantly impaired the ability of Mdm38 and Ylh47 to complement the salt sensitivity of E. coli TO114. These findings not only provide important insights into the structure and function of the Letm1-Mdm38-Ylh47 antiporter family but by revealing their distinctive properties also shed light on the physiological roles of these transporters in yeast and animals.

IMPORTANCE

The inner membrane of mitochondria contains numerous ion transporters, including those facilitating H+ transport by the electron transport chain and ATP synthase to maintain membrane potential. Letm1 in the inner membrane of mitochondria in animals functions as a Ca2+/H+ antiporter. However, this study reveals that homologous antiporters in mitochondria of yeast, Mdm38 and Ylh47, do not transport Ca2+ but instead are selective for K+ and Na+. Additionally, the identification of conserved amino acids crucial for antiporter activity further expanded our understanding of the structure and function of the Letm1-Mdm38-Ylh47 antiporter family.

Elucidating the Molecular Basis of 14-3-3 Interaction with α-Synuclein: Insights from Molecular Dynamics Simulations and the Design of a Novel Protein-Protein Interaction Inhibitor

Parkinson's disease is a widespread age-related neurodegenerative disorder characterized by the loss of dopaminergic neurons in the midbrain along with the appearance of protein aggregates, termed as "Lewy bodies" in the surviving neuronal cells. The components of Lewy bodies include proteins such as α-synuclein, 14-3-3, Parkin, and LRRK2, along with other cellular organelles, which, in their native state, perform a plethora of vital biological functions within the human biome. Formation of these aggregates renders these components inactive, thereby interfering with homeostasis. In this regard, the current study attempts to investigate the complexation behavior of all human-based 14-3-3 isoforms with α-synuclein via a combination of classical and enhanced sampling techniques and thereby determine the causality of these protein-protein interactions. The study indicated that upon complexation, the aggregation propensity of both 14-3-3 and α-synuclein increases, and this increment is propelled by the interfacial residues on either protein. Furthermore, mutagenesis studies revealed that Lys214 of 14-3-3 (henceforth termed K214A) is crucial for the formation of this binary complex. Principal component analysis combined with clustering studies unveiled the stability of these complexes in terms of their conformational distribution across the entire MD trajectory. For K214A, these clustered states were sparsely located, thereby making the transitions between them slightly difficult. Dynamic cross-correlation maps (DCCM) revealed the role of residues in the range 80-130 of 14-3-3 having a potential allosteric role in driving this complexation process. Finally, a novel peptide-based supramolecular inhibitor was designed, which exhibited higher proficiency in limiting the 14-3-3/α-synuclein interaction compared to the previous inhibitor model. It was also revealed that the presence of this inhibitor induces structural rigidity in α-synuclein, making changes in its conformations extremely difficult, as observed through Umbrella Sampling studies. Based on available information, the current study provides an insight into the molecular-level understanding of protein-protein interactions underlying Parkinson's disease and adds on to the methods of devising novel therapeutic approaches to treat the same.

14-3-3 Family of Proteins: Biological Implications, Molecular Interactions, and Potential Intervention in Cancer, Virus and Neurodegeneration Disorders

The 14-3-3 family of proteins are highly conserved acidic eukaryotic proteins (25-32 kDa) abundantly present in the body. Through numerous binding partners, the 14-3-3 is responsible for many essential cellular pathways, such as cell cycle regulation and gene transcription control. Hence, its dysregulation has been linked to the onset of critical illnesses such as cancers, neurodegenerative diseases and viral infections. Interestingly, explorative studies have revealed an inverse correlation of 14-3-3 protein in cancer and neurodegenerative diseases, and the direct manipulation of 14-3-3 by virus to enhance infection capacity has dramatically extended its significance. Of these, COVID-19 has been linked to the 14-3-3 proteins by the interference of the SARS-CoV-2 nucleocapsid (N) protein during virion assembly. Given its predisposition towards multiple essential host signalling pathways, it is vital to understand the holistic interactions between the 14-3-3 protein to unravel its potential therapeutic unit in the future. As such, the general structure and properties of the 14-3-3 family of proteins, as well as their known biological functions and implications in cancer, neurodegeneration, and viruses, were covered in this review. Furthermore, the potential therapeutic target of 14-3-3 proteins in the associated diseases was discussed.

Discovery of a Plant 14-3-3 Inhibitor Possessing Isoform Selectivity and In Planta Activity

Synthetic modulators of plant 14-3-3s are promising chemical tools both for understanding the 14-3-3-related signaling pathways and controlling plant physiology. Herein, we describe a novel small-molecule inhibitor for 14-3-3 proteins of Arabidopsis thaliana. The inhibitor was identified from unexpected products in a stock solution in dimethyl sulfoxide (DMSO) of an in-house chemical library. Mass spectroscopy, mutant-based analyses, fluorescence polarization assays, and thermal shift assays revealed that the inhibitor covalently binds to an allosteric site of 14-3-3 with isoform selectivity. Moreover, infiltration of the inhibitor to Arabidopsis leaves suppressed the stomatal aperture. The inhibitor should provide new insight into the design of potent and isoform-selective 14-3-3 modulators.

Human parainfluenza virus type 2 V protein inhibits mitochondrial apoptosis pathway through two ways

Paramyxoviruses are reported to block apoptosis for their replication, but the mechanisms remain unclear. Furthermore, regulation of mitochondrial apoptosis by paramyxoviruses has been hardly reported. We investigated whether and how human parainfluenza virus type 2 (hPIV-2) counteracts apoptosis. Infection of recombinant hPIV-2 carrying mutated V protein showed higher caspase 3/7 activity and higher cytochrome c release from mitochondria than wild type hPIV-2 infection. This indicates that V protein controls mitochondrial apoptosis pathway. hPIV-2 V protein interacted with Bad, an apoptotic promoting protein, and this interaction inhibited the binding of Bad to Bcl-XL. V protein also bound to 14-3-3ε, which was essential for inhibition of 14-3-3ε cleavage. Our data collectively suggest that hPIV-2 V protein has two means of preventing mitochondrial apoptosis pathway: the inhibition of Bad-Bcl-XL interaction and the suppression of 14-3-3ε cleavage. This is the first report of the mechanisms behind how paramyxoviruses modulate mitochondrial apoptosis pathways.

Temporal regulation of MDA5 inactivation by Caspase-3 dependent cleavage of 14-3-3η

The kinetics of type I interferon (IFN) induction versus the virus replication compete, and the result of the competition determines the outcome of the infection. Chaperone proteins that involved in promoting the activation kinetics of PRRs rapidly trigger antiviral innate immunity. We have previously shown that prior to the interaction with MAVS to induce type I IFN, 14-3-3η facilitates the oligomerization and intracellular redistribution of activated MDA5. Here we report that the cleavage of 14-3-3η upon MDA5 activation, and we identified Caspase-3 activated by MDA5-dependent signaling was essential to produce sub-14-3-3η lacking the C-terminal helix (αI) and tail. The cleaved form of 14-3-3η (sub-14-3-3η) could strongly interact with MDA5 but could not support MDA5-dependent type I IFN induction, indicating the opposite functions between the full-length 14-3-3η and sub-14-3-3η. During human coronavirus or enterovirus infections, the accumulation of sub-14-3-3η was observed along with the activation of Caspase-3, suggesting that RNA viruses may antagonize 14-3-3η by promoting the formation of sub-14-3-3η to impair antiviral innate immunity. In conclusion, sub-14-3-3η, which could not promote MDA5 activation, may serve as a negative feedback to return to homeostasis to prevent excessive type I IFN production and unnecessary inflammation.

Hiding in plain sight: Complex interaction patterns between Tau and 14-3-3ζ protein variants

Tau protein is an intrinsically disordered protein that plays a key role in Alzheimer's disease (AD). In brains of AD patients, Tau occurs abnormally phosphorylated and aggregated in neurofibrillary tangles (NFTs). Together with Tau, 14-3-3 proteins - abundant cytosolic dimeric proteins - were found colocalized in the NFTs. However, so far, the molecular mechanism of the process leading to pathological changes in Tau structure as well as the direct involvement of 14-3-3 proteins are not well understood. Here, we aimed to reveal the effects of phosphorylation by protein kinase A (PKA) on Tau structural preferences and provide better insight into the interaction between Tau and 14-3-3 proteins. We also addressed the impact of monomerization-inducing phosphorylation of 14-3-3 at S58 on the binding to Tau protein. Using multidimensional nuclear magnetic resonance spectroscopy (NMR), chemical cross-linking analyzed by mass spectrometry (MS) and PAGE, we unveiled differences in their binding affinity, stoichiometry, and interfaces with single-residue resolution. We revealed that the interaction between 14-3-3 and Tau proteins is mediated not only via the 14-3-3 amphipathic binding grooves, but also via less specific interactions with 14-3-3 protein surface and, in the case of monomeric 14-3-3, also partially via the exposed dimeric interface. In addition, the hyperphosphorylation of Tau changes its affinity to 14-3-3 proteins. In conclusion, we propose quite complex interaction mode between the Tau and 14-3-3 proteins.

Clinical and molecular characterization of patients with YWHAG-related epilepsy

OBJECTIVE

YWHAG variant alleles have been associated with a rare disease trait whose clinical synopsis includes an early onset epileptic encephalopathy with predominantly myoclonic seizures, developmental delay/intellectual disability, and facial dysmorphisms. Through description of a large cohort, which doubles the number of reported patients, we further delineate the spectrum of YWHAG-related epilepsy.

METHODS

We included in this study 24 patients, 21 new and three previously described, with pathogenic/likely pathogenic variants in YWHAG. We extended the analysis of clinical, electroencephalographic, brain magnetic resonance imaging, and molecular genetic information to 24 previously published patients.

RESULTS

The phenotypic spectrum of YWHAG-related disorders ranges from mild developmental delay to developmental and epileptic encephalopathy (DEE). Epilepsy onset is in the first 2 years of life. Seizure freedom can be achieved in half of the patients (13/24, 54%). Intellectual disability (23/24, 96%), behavioral disorders (18/24, 75%), neurological signs (13/24, 54%), and dysmorphisms (6/24, 25%) are common. A genotype-phenotype correlation emerged, as DEE is more represented in patients with missense variants located in the ligand-binding domain than in those with truncating or missense variants in other domains (90% vs. 19%, p < .001).

SIGNIFICANCE

This study suggests that pathogenic YWHAG variants cause a wide range of clinical presentations with variable severity, ranging from mild developmental delay to DEE. In this allelic series, a genotype-phenotype correlation begins to emerge, potentially providing prognostic information for clinical management and genetic counseling.

Recent advances in understanding the role of two mitogen-activated protein kinase cascades in plant immunity

The mitogen-activated protein kinase (MAPK/MPK) cascade is an important intercellular signaling module that regulates plant growth, development, reproduction, and responses to biotic and abiotic stresses. A MAPK cascade usually consists of a MAPK kinase kinase (MAPKKK/MEKK), a MAPK kinase (MAPKK/MKK/MEK), and a MAPK. The well-characterized MAPK cascades in plant immunity to date are the MEKK1-MKK1/2-MPK4 cascade and the MAPKKK3/4/5-MKK4/5-MPK3/6 cascade. Recently, major breakthroughs have been made in understanding the molecular mechanisms associated with the regulation of immune signaling by both of these MAPK cascades. In this review, we highlight the most recent advances in understanding the role of both MAPK cascades in activating plant defense and in suppressing or fine-tuning immune signaling. We also discuss the molecular mechanisms by which plants stabilize and maintain the activation of MAPK cascades during immune signaling. Based on this review, we reveal the complexity and importance of the MEKK1-MKK1/2-MPK4 cascade and the MAPKKK3/4/5-MKK4/5-MPK3/6 cascade, which are tightly controlled by their interacting partners or substrates, in plant immunity.

Role of two modules controlling the interaction between SKAP1 and SRC kinases comparison with SKAP2 architecture and consequences for evolution

SRC kinase associated phosphoprotein 1 (SKAP1), an adaptor for protein assembly, plays an important role in the immune system such as stabilizing immune synapses. Understanding how these functions are controlled at the level of the protein-protein interactions is necessary to describe these processes and to develop therapeutics. Here, we dissected the SKAP1 modular organization to recognize SRC kinases and compared it to that of its paralog SRC kinase associated phosphoprotein 2 (SKAP2). Different conserved motifs common to either both proteins or specific to SKAP2 were found using this comparison. Two modules harboring different binding properties between SKAP1 and SKAP2 were identified: one composed of two conserved motifs located in the second interdomain interacting at least with the SH2 domain of SRC kinases and a second one composed of the DIM domain modulated by the SH3 domain and the activation of SRC kinases. This work suggests a convergent evolution of the binding properties of some SRC kinases interacting specifically with either SKAP1 or SKAP2.

The dispensability of 14-3-3 proteins for the regulation of human cardiac sodium channel Nav1.5

BACKGROUND

14-3-3 proteins are ubiquitous proteins that play a role in cardiac physiology (e.g., metabolism, development, and cell cycle). Furthermore, 14-3-3 proteins were proposed to regulate the electrical function of the heart by interacting with several cardiac ion channels, including the voltage-gated sodium channel Nav1.5. Given the many cardiac arrhythmias associated with Nav1.5 dysfunction, understanding its regulation by the protein partners is crucial.

AIMS

In this study, we aimed to investigate the role of 14-3-3 proteins in the regulation of the human cardiac sodium channel Nav1.5.

METHODS AND RESULTS

Amongst the seven 14-3-3 isoforms, only 14-3-3η (encoded by YWHAH gene) weakly co-immunoprecipitated with Nav1.5 when heterologously co-expressed in tsA201 cells. Total and cell surface expression of Nav1.5 was however not modified by 14-3-3η overexpression or inhibition with difopein, and 14-3-3η did not affect physical interaction between Nav1.5 α-α subunits. The current-voltage relationship and the amplitude of Nav1.5-mediated sodium peak current density were also not changed.

CONCLUSIONS

Our findings illustrate that the direct implication of 14-3-3 proteins in regulating Nav1.5 is not evident in a transformed human kidney cell line tsA201.

Arnicolide C Suppresses Tumor Progression by Targeting 14-3-3θ in Breast Cancer

Background: Arnicolide C, which is isolated from Centipeda minima, has excellent antitumor effects. However, the potential impacts and related mechanisms of action of arnicolide C in breast cancer remain unknown. Methods: The viability of breast cancer cells was measured using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and colony formation assays. For analysis of apoptosis and the cell cycle, flow cytometry was used. A molecular docking approach was used to explore the possible targets of arnicolide C. Western blot analysis was used to detect changes in the expression of 14-3-3θ and proteins in related pathways after arnicolide C treatment in breast cancer cells. The anti-breast cancer effect of arnicolide C in vivo was evaluated by establishing cell-derived xenograft (CDX) and patient-derived xenograft (PDX) models. Results: Arnicolide C inhibited proliferation, increased apoptosis, and induced G1 arrest. In particular, molecular docking analysis indicated that arnicolide C binds to 14-3-3θ. Arnicolide C reduced 14-3-3θ expression and inhibited its downstream signaling pathways linked to cell proliferation. Similar results were obtained in the CDX and PDX models. Conclusion: Arnicolide C can have an anti-breast cancer effect both in vitro and in vivo and can induce cell cycle arrest and increase apoptosis in vitro. The molecular mechanism may be related to the effect of arnicolide C on the expression level of 14-3-3θ. However, the specific mechanism through which arnicolide C affects 14-3-3θ protein expression still needs to be determined.

14-3-3 proteins-a moonlight protein complex with therapeutic potential in neurological disorder: in-depth review with Alzheimer's disease

Alzheimer's disease (AD) affects millions of people worldwide and is a gradually worsening neurodegenerative condition. The accumulation of abnormal proteins, such as tau and beta-amyloid, in the brain is a hallmark of AD pathology. 14-3-3 proteins have been implicated in AD pathology in several ways. One proposed mechanism is that 14-3-3 proteins interact with tau protein and modulate its phosphorylation, aggregation, and toxicity. Tau is a protein associated with microtubules, playing a role in maintaining the structural integrity of neuronal cytoskeleton. However, in the context of Alzheimer's disease (AD), an abnormal increase in its phosphorylation occurs. This leads to the aggregation of tau into neurofibrillary tangles, which is a distinctive feature of this condition. Studies have shown that 14-3-3 proteins can bind to phosphorylated tau and regulate its function and stability. In addition, 14-3-3 proteins have been shown to interact with beta-amyloid (Aβ), the primary component of amyloid plaques in AD. 14-3-3 proteins can regulate the clearance of Aβ through the lysosomal degradation pathway by interacting with the lysosomal membrane protein LAMP2A. Dysfunction of lysosomal degradation pathway is thought to contribute to the accumulation of Aβ in the brain and the progression of AD. Furthermore, 14-3-3 proteins have been found to be downregulated in the brains of AD patients, suggesting that their dysregulation may contribute to AD pathology. For example, decreased levels of 14-3-3 proteins in cerebrospinal fluid have been suggested as a biomarker for AD. Overall, these findings suggest that 14-3-3 proteins may play an important role in AD pathology and may represent a potential therapeutic target for the disease. However, further research is needed to fully understand the mechanisms underlying the involvement of 14-3-3 proteins in AD and to explore their potential as a therapeutic target.

Characterizing the protein-protein interaction between MDM2 and 14-3-3σ; proof of concept for small molecule stabilization

Mouse Double Minute 2 (MDM2) is a key negative regulator of the tumor suppressor protein p53. MDM2 overexpression occurs in many types of cancer and results in the suppression of WT p53. The 14-3-3 family of adaptor proteins are known to bind MDM2 and the 14-3-3σ isoform controls MDM2 cellular localization and stability to inhibit its activity. Therefore, small molecule stabilization of the 14-3-3σ/MDM2 protein-protein interaction (PPI) is a potential therapeutic strategy for the treatment of cancer. Here, we provide a detailed biophysical and structural characterization of the phosphorylation-dependent interaction between 14-3-3σ and peptides that mimic the 14-3-3 binding motifs within MDM2. The data show that di-phosphorylation of MDM2 at S166 and S186 is essential for high affinity 14-3-3 binding and that the binary complex formed involves one MDM2 di-phosphorylated peptide bound to a dimer of 14-3-3σ. However, the two phosphorylation sites do not simultaneously interact so as to bridge the 14-3-3 dimer in a 'multivalent' fashion. Instead, the two phosphorylated MDM2 motifs 'rock' between the two binding grooves of the dimer, which is unusual in the context of 14-3-3 proteins. In addition, we show that the 14-3-3σ-MDM2 interaction is amenable to small molecule stabilization. The natural product fusicoccin A forms a ternary complex with a 14-3-3σ dimer and an MDM2 di-phosphorylated peptide resulting in the stabilization of the 14-3-3σ/MDM2 PPI. This work serves as a proof-of-concept of the drugability of the 14-3-3/MDM2 PPI and paves the way toward the development of more selective and efficacious small molecule stabilizers.

14-3-3ε: a protein with complex physiology function but promising therapeutic potential in cancer

Over the past decade, the role of the 14-3-3 protein has received increasing interest. Seven subtypes of 14-3-3 proteins exhibit high homology; however, each subtype maintains its specificity. The 14-3-3ε protein is involved in various physiological processes, including signal transduction, cell proliferation, apoptosis, autophagy, cell cycle regulation, repolarization of cardiac action, cardiac development, intracellular electrolyte homeostasis, neurodevelopment, and innate immunity. It also plays a significant role in the development and progression of various diseases, such as cardiovascular diseases, inflammatory diseases, neurodegenerative disorders, and cancer. These immense and various involvements of 14-3-3ε in diverse processes makes it a promising target for drug development. Although extensive research has been conducted on 14-3-3 dimers, studies on 14-3-3 monomers are limited. This review aimed to provide an overview of recent reports on the molecular mechanisms involved in the regulation of binding partners by 14-3-3ε, focusing on issues that could help advance the frontiers of this field. Video Abstract.

Target Identification of a Class of Pyrazolone Protein Aggregation Inhibitor Therapeutics for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with no cure, and current treatment options are very limited. Previously, we performed a high-throughput screen to identify small molecules that inhibit protein aggregation caused by a mutation in the gene that encodes superoxide dismutase 1 (SOD1), which is responsible for about 25% of familial ALS. This resulted in three hit series of compounds that were optimized over several years to give three compounds that were highly active in a mutant SOD1 ALS model. Here we identify the target of two of the active compounds (6 and 7) with the use of photoaffinity labeling, chemical biology reporters, affinity purification, proteomic analysis, and fluorescent/cellular thermal shift assays. Evidence is provided to demonstrate that these two pyrazolone compounds directly interact with 14-3-3-E and 14-3-3-Q isoforms, which have chaperone activity and are known to interact with mutant SOD1G93A aggregates and become insoluble in the subcellular JUNQ compartment, leading to apoptosis. Because protein aggregation is the hallmark of all neurodegenerative diseases, knowledge of the target compounds that inhibit protein aggregation allows for the design of more effective molecules for the treatment of ALS and possibly other neurodegenerative diseases.

The yeast 14-3-3 proteins Bmh1 and Bmh2 regulate key signaling pathways

Cell signaling regulates several physiological processes by receiving, processing, and transmitting signals between the extracellular and intracellular environments. In signal transduction, phosphorylation is a crucial effector as the most common posttranslational modification. Selectively recognizing specific phosphorylated motifs of target proteins and modulating their functions through binding interactions, the yeast 14-3-3 proteins Bmh1 and Bmh2 are involved in catabolite repression, carbon metabolism, endocytosis, and mitochondrial retrograde signaling, among other key cellular processes. These conserved scaffolding molecules also mediate crosstalk between ubiquitination and phosphorylation, the spatiotemporal control of meiosis, and the activity of ion transporters Trk1 and Nha1. In humans, deregulation of analogous processes triggers the development of serious diseases, such as diabetes, cancer, viral infections, microbial conditions and neuronal and age-related diseases. Accordingly, the aim of this review article is to provide a brief overview of the latest findings on the functions of yeast 14-3-3 proteins, focusing on their role in modulating the aforementioned processes.

Optimizing Phosphopeptide Structures That Target 14-3-3ε in Cutaneous Squamous Cell Carcinoma

14-3-3ε is involved in various types of malignancies by increasing cell proliferation, promoting cell invasion, or inhibiting apoptosis. In cutaneous squamous cell carcinoma (cSCC), 14-3-3ε is overexpressed and mislocalized from the nucleus to the cytoplasm where it interacts with the cell division cycle 25 A (CDC25A) and suppresses apoptosis. Hence, inhibition of the 14-3-3ε-CDC25A interaction is an attractive target for promoting apoptosis in cSCC. In this work, we optimized the structure of our previously designed inhibitor of the 14-3-3ε-CDC25A interaction, pT, a phosphopeptide fragment corresponding to one of the two binding regions of CDC25A to 14-3-3ε. Starting from pT, we developed peptide analogs that bind 14-3-3ε with nanomolar affinities. Peptide analogs were designed by shortening the pT peptide and introducing modifications at position 510 of the pT(502-510) analog. Both molecular dynamics (MD) simulations and biophysical methods were used to determine peptide binding to 14-3-3ε. Shortening the pT peptide from 14 to 9 amino acid residues resulted in a peptide (pT(502-510)) that binds 14-3-3ε with a KD value of 45.2 nM. Gly to Phe substitution in position 510 of pT(502-510) led to further improvement in affinity (KD: 22.0 nM) of the peptide for 14-3-3ε. Our results suggest that the designed peptide analogs are potential candidates for inhibiting 14-3-3ε-CDC25A interactions in cSCC cells and thus inducing their apoptosis.

Rastonia solanacearum type Ⅲ effectors target host 14-3-3 proteins to suppress plant immunity

14-3-3 proteins play important roles in plant metabolism and stress response. Tomato 14-3-3 proteins, SlTFT4 and SlTFT7, serve as hubs of plant immunity and are targeted by some pathogen effectors. Ralstonia solanacearum with more than 70 type Ⅲ effectors (T3Es) is one of the most destructive plant pathogens. However, little is known on whether R. solanacearum T3Es target SlTFT4 and SlTFT7 and hence interfere with plant immunity. We first detected the associations of SlTFT4/SlTFT7 with R. solanacearum T3Es by luciferase complementation assay, and then confirmed the interactions by yeast two-hybrid approach. We demonstrated that 22 Ralstonia T3Es were associated with both SlTFT4 and SlTFT7, and five among them suppressed the hypersensitive response induced by MAPKKKα, a protein kinase which associated with SlTFT4/SlTFT7. We further demonstrated that suppression of MAPKKKα-induced HR and plant basal defense by the T3E RipAC depend on its association with 14-3-3 proteins. Our findings firstly demonstrate that R. solanacearum T3Es can manipulate plant immunity by targeting 14-3-3 proteins, SlTFT4 and SlTFT7, providing new insights into plant-R. solanacearum interactions.

Formation of amyloid fibrils by the regulatory 14-3-3ζ protein

The 14-3-3 proteins are a highly conserved adaptor protein family with multi-layer functions, abundantly expressed in the brain. The 14-3-3 proteins modulate phosphorylation, regulate enzymatic activity and can act as chaperones. Most importantly, they play an important role in various neurodegenerative disorders due to their vast interaction partners. Particularly, the 14-3-3ζ isoform is known to co-localize in aggregation tangles in both Alzheimer's and Parkinson's diseases as a result of protein-protein interactions. These abnormal clumps consist of amyloid fibrils, insoluble aggregates, mainly formed by the amyloid-β, tau and α-synuclein proteins. However, the molecular basis of if and how 14-3-3ζ can aggregate into amyloid fibrils is unknown. In this study, we describe the formation of amyloid fibrils by 14-3-3ζ using a comprehensive approach that combines bioinformatic tools, amyloid-specific dye binding, secondary structure analysis and atomic force microscopy. The results presented herein characterize the amyloidogenic properties of 14-3-3ζ and imply that the well-folded protein undergoes aggregation to β-sheet-rich amyloid fibrils.

Voltage sensors of a Na+ channel dissociate from the pore domain and form inter-channel dimers in the resting state

Understanding voltage-gated sodium (Nav) channels is significant since they generate action potential. Nav channels consist of a pore domain (PD) and a voltage sensor domain (VSD). All resolved Nav structures in different gating states have VSDs that tightly interact with PDs; however, it is unclear whether VSDs attach to PDs during gating under physiological conditions. Here, we reconstituted three different voltage-dependent NavAb, which is cloned from Arcobacter butzleri, into a lipid membrane and observed their structural dynamics by high-speed atomic force microscopy on a sub-second timescale in the steady state. Surprisingly, VSDs dissociated from PDs in the mutant in the resting state and further dimerized to form cross-links between channels. This dimerization would occur at a realistic channel density, offering a potential explanation for the facilitation of positive cooperativity of channel activity in the rising phase of the action potential.

A high-throughput screening approach to discover potential colorectal cancer chemotherapeutics: Repurposing drugs to disrupt 14-3-3 protein-BAD interactions

Inducing apoptosis in different types of cancer cells is an effective therapeutic strategy. However, the success of existing chemotherapeutics can be compromised by tumor cell resistance and systemic off-target effects. Therefore, the discovery of pro-apoptotic compounds with minimal systemic side-effects is crucial. 14-3-3 proteins are molecular scaffolds that serve as important regulators of cell survival. Our previous study demonstrated that 14-3-3ζ can sequester BAD, a pro-apoptotic member of the BCL-2 protein family, in the cytoplasm and prevent its translocation to mitochondria to inhibit the induction of apoptosis. Despite being a critical mechanism of cell survival, it is unclear whether disrupting 14-3-3 protein:BAD interactions could be harnessed as a chemotherapeutic approach. Herein, we established a BRET-based high-throughput drug screening approach (Z'-score= 0.52) capable of identifying molecules that can disrupt 14-3-3ζ:BAD interactions. An FDA-approved drug library containing 1971 compounds was used for screening, and the capacity of identified hits to induce cell death was examined in NIH3T3-fibroblasts and colorectal cancer cell lines, HT-29 and Caco-2. Our in vitro results suggest that terfenadine, penfluridol, and lomitapide could be potentially repurposed for treating colorectal cancer. Moreover, our screening method demonstrates the feasibility of identifying pro-apoptotic agents that can be applied towards conditions where aberrant cell growth or function are key determinants of disease pathogenesis.

PADI6: What we know about the elusive fifth member of the peptidyl arginine deiminase family

Peptidyl arginine deiminase 6 (PADI6) is a maternal factor that is vital for early embryonic development. Deletion and mutations of its encoding gene in female mice or women lead to early embryonic developmental arrest, female infertility, maternal imprinting defects and hyperproliferation of the trophoblast. PADI6 is the fifth and least well-characterized member of the peptidyl arginine deiminases (PADIs), which catalyse the post-translational conversion of arginine to citrulline. It is less conserved than the other PADIs, and currently has no reported catalytic activity. While there are many suggested functions of PADI6 in the early mouse embryo, including in embryonic genome activation, cytoplasmic lattice formation, maternal mRNA and ribosome regulation, and organelle distribution, the molecular mechanisms of its function remain unknown. In this review, we discuss what is known about the function of PADI6 and highlight key outstanding questions that must be answered if we are to understand the crucial role it plays in early embryo development and female fertility. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

YWHAG Deficiency Disrupts the EMT-Associated Network to Induce Oxidative Cell Death and Prevent Metastasis

Metastasis involves epithelial-to-mesenchymal transition (EMT), a process that is regulated by complex gene networks, where their deliberate disruption may yield a promising outcome. However, little is known about mechanisms that coordinate these metastasis-associated networks. To address this gap, hub genes with broad engagement across various human cancers by analyzing the transcriptomes of different cancer cell types undergoing EMT are identified. The oncogenic signaling adaptor protein tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein gamma (YWHAG) is ranked top for its clinical relevance and impact. The cellular kinome and transcriptome data are surveyed to construct the regulome of YWHAG, revealing stress responses and metabolic processes during cancer EMT. It is demonstrated that a YWHAG-dependent cytoprotective mechanism in the regulome is embedded in EMT-associated networks to protect cancer cells from oxidative catastrophe through enhanced autophagy during EMT. YWHAG deficiency results in a rapid accumulation of reactive oxygen species (ROS), delayed EMT, and cell death. Tumor allografts show that metastasis potential and overall survival time are correlated with the YWHAG expression level of cancer cell lines. Metastasized tumors have higher expression of YWHAG and autophagy-related genes than primary tumors. Silencing YWHAG diminishes primary tumor volumes, prevents metastasis, and prolongs the median survival period of the mice.