Transgenic Mouse Proteomics Identifies New 14-3-3-associated Proteins Involved in Cytoskeletal Rearrangements and Cell Signaling

The role of the adenylate kinase 5 gene in various diseases and cancer

Adenylate kinases (AKs) are important enzymes involved in cellular energy metabolism. Among AKs, AK5 (adenylate kinase 5), a cytosolic protein, is emerging as a significant contributor to various diseases and cellular processes. This comprehensive review integrates findings from various research groups on AK5 since its discovery, shedding light on its multifaceted roles in nucleotide metabolism, energy regulation, and cellular differentiation. We investigate its implications in a spectrum of diseases, including autoimmune encephalitis, epilepsy, neurodegenerative disorders such as Alzheimer's and Parkinson's, diabetes, lower extremity arterial disease, celiac disease, and various cancers. Notably, AK5's expression levels and methylation status have been associated with cancer progression and patient outcomes, indicating its potential as a prognostic indicator. Furthermore, AK5 is implicated in regulating cellular processes in breast cancer, gastric cancer, colorectal carcinoma, prostate cancer, and colon adenocarcinoma, suggesting its relevance across different cancer types. However, a limitation lies in the need for more robust clinical validation and a deeper understanding of AK5's precise mechanisms in disease pathogenesis, despite its association with various pathophysiological conditions. Nonetheless, AK5 holds promise as a therapeutic target, with emerging evidence suggesting its potential in therapy development.

The characterization of protein lactylation in relation to cardiac metabolic reprogramming in neonatal mouse hearts

In mammals, the neonatal heart can regenerate upon injury within a short time after birth, while adults lose this ability. Metabolic reprogramming has been demonstrated to be critical for cardiomyocyte proliferation in the neonatal heart. Here, we reveal that cardiac metabolic reprogramming could be regulated by altering global protein lactylation. By performing 4D label-free proteomics and lysine lactylation (Kla) omics analyses in mouse hearts at postnatal days 1, 5, and 7, 2297 Kla sites from 980 proteins are identified, among which 1262 Kla sites from 409 proteins are quantified. Functional clustering analysis reveals that the proteins with altered Kla sites are mainly involved in metabolic processes. The expression and Kla levels of proteins in glycolysis show a positive correlation while a negative correlation in fatty acid oxidation. Furthermore, we verify the Kla levels of several differentially modified proteins, including ACAT1, ACADL, ACADVL, PFKM, PKM, and NPM1. Overall, our study reports a comprehensive Kla map in the neonatal mouse heart, which will help to understand the regulatory network of metabolic reprogramming and cardiac regeneration.

A splice site variant in MADD affects hormone expression in pancreatic β cells and pituitary gonadotropes

MAPK activating death domain (MADD) is a multifunctional protein regulating small GTPases RAB3 and RAB27, MAPK signaling, and cell survival. Polymorphisms in the MADD locus are associated with glycemic traits, but patients with biallelic variants in MADD manifest a complex syndrome affecting nervous, endocrine, exocrine, and hematological systems. We identified a homozygous splice site variant in MADD in 2 siblings with developmental delay, diabetes, congenital hypogonadotropic hypogonadism, and growth hormone deficiency. This variant led to skipping of exon 30 and in-frame deletion of 36 amino acids. To elucidate how this mutation causes pleiotropic endocrine phenotypes, we generated relevant cellular models with deletion of MADD exon 30 (dex30). We observed reduced numbers of β cells, decreased insulin content, and increased proinsulin-to-insulin ratio in dex30 human embryonic stem cell-derived pancreatic islets. Concordantly, dex30 led to decreased insulin expression in human β cell line EndoC-βH1. Furthermore, dex30 resulted in decreased luteinizing hormone expression in mouse pituitary gonadotrope cell line LβT2 but did not affect ontogeny of stem cell-derived GnRH neurons. Protein-protein interactions of wild-type and dex30 MADD revealed changes affecting multiple signaling pathways, while the GDP/GTP exchange activity of dex30 MADD remained intact. Our results suggest MADD-specific processes regulate hormone expression in pancreatic β cells and pituitary gonadotropes.

GRF2 Is Crucial for Cone Photoreceptor Viability and Ribbon Synapse Formation in the Mouse Retina

Using constitutive GRF1/2 knockout mice, we showed previously that GRF2 is a key regulator of nuclear migration in retinal cone photoreceptors. To evaluate the functional relevance of that cellular process for two putative targets of the GEF activity of GRF2 (RAC1 and CDC42), here we compared the structural and functional retinal phenotypes resulting from conditional targeting of RAC1 or CDC42 in the cone photoreceptors of constitutive GRF2KO and GRF2WT mice. We observed that single RAC1 disruption did not cause any obvious morphological or physiological changes in the retinas of GRF2WT mice, and did not modify either the phenotypic alterations previously described in the retinal photoreceptor layer of GRF2KO mice. In contrast, the single ablation of CDC42 in the cone photoreceptors of GRF2WT mice resulted in clear alterations of nuclear movement that, unlike those of the GRF2KO retinas, were not accompanied by electrophysiological defects or slow, progressive cone cell degeneration. On the other hand, the concomitant disruption of GRF2 and CDC42 in the cone photoreceptors resulted, somewhat surprisingly, in a normalized pattern of nuclear positioning/movement, similar to that physiologically observed in GRF2WT mice, along with worsened patterns of electrophysiological responses and faster rates of cell death/disappearance than those previously recorded in single GRF2KO cone cells. Interestingly, the increased rates of cone cell apoptosis/death observed in single GRF2KO and double-knockout GRF2KO/CDC42KO retinas correlated with the electron microscopic detection of significant ultrastructural alterations (flattening) of their retinal ribbon synapses that were not otherwise observed at all in single-knockout CDC42KO retinas. Our observations identify GRF2 and CDC42 (but not RAC1) as key regulators of retinal processes controlling cone photoreceptor nuclear positioning and survival, and support the notion of GRF2 loss-of-function mutations as potential drivers of cone retinal dystrophies.

Proteomics Identifies Circulating TIMP-1 as a Prognostic Biomarker for Diffuse Large B-Cell Lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease, although disease stratification using in-depth plasma proteomics has not been performed to date. By measuring more than 1000 proteins in the plasma of 147 DLBCL patients using data-independent acquisition mass spectrometry and antibody array, DLBCL patients were classified into four proteomic subtypes (PS-I-IV). Patients with the PS-IV subtype and worst prognosis had increased levels of proteins involved in inflammation, including a high expression of metalloproteinase inhibitor-1 (TIMP-1) that was associated with poor survival across two validation cohorts (n = 180). Notably, the combination of TIMP-1 with the international prognostic index (IPI) identified 64.00% to 88.24% of relapsed and 65.00% to 80.49% of deceased patients in the discovery and two validation cohorts, which represents a 24.00% to 41.67% and 20.00% to 31.70% improvement compared to the IPI score alone, respectively. Taken together, we demonstrate that DLBCL heterogeneity is reflected in the plasma proteome and that TIMP-1, together with the IPI, could improve the prognostic stratification of patients.

IFNα primes cancer cells for Fusicoccin-induced cell death via 14-3-3 PPI stabilization

The natural product family of the fusicoccanes (FCs) has been shown to display anti-cancer activity, especially when combined with established therapeutic agents. FCs stabilize 14-3-3 protein-protein interactions (PPIs). Here, we tested combinations of a small library of FCs with interferon α (IFNα) on different cancer cell lines and report a proteomics approach to identify the specific 14-3-3 PPIs that are induced by IFNα and stabilized by FCs in OVCAR-3 cells. Among the identified 14-3-3 target proteins are THEMIS2, receptor interacting protein kinase 2 (RIPK2), EIF2AK2, and several members of the LDB1 complex. Biophysical and structural biology studies confirm these 14-3-3 PPIs as physical targets of FC stabilization, and transcriptome as well as pathway analyses suggest possible explanations for the observed synergistic effect of IFNα/FC treatment on cancer cells. This study elucidates the polypharmacological effects of FCs in cancer cells and identifies potential targets from the vast interactome of 14-3-3s for therapeutic intervention in oncology.

ZNF330/NOA36 interacts with HSPA1 and HSPA8 and modulates cell cycle and proliferation in response to heat shock in HEK293 cells

BACKGROUND

The human genome contains nearly 20.000 protein-coding genes, but there are still more than 6,000 proteins poorly characterized. Among them, ZNF330/NOA36 stand out because it is a highly evolutionarily conserved nucleolar zinc-finger protein found in the genome of ancient animal phyla like sponges or cnidarians, up to humans. Firstly described as a human autoantigen, NOA36 is expressed in all tissues and human cell lines, and it has been related to apoptosis in human cells as well as in muscle morphogenesis and hematopoiesis in Drosophila. Nevertheless, further research is required to better understand the roles of this highly conserved protein.

RESULTS

Here, we have investigated possible interactors of human ZNF330/NOA36 through affinity-purification mass spectrometry (AP-MS). Among them, NOA36 interaction with HSPA1 and HSPA8 heat shock proteins was disclosed and further validated by co-immunoprecipitation. Also, "Enhancer of Rudimentary Homolog" (ERH), a protein involved in cell cycle regulation, was detected in the AP-MS approach. Furthermore, we developed a NOA36 knockout cell line using CRISPR/Cas9n in HEK293, and we found that the cell cycle profile was modified, and proliferation decreased after heat shock in the knocked-out cells. These differences were not due to a different expression of the HSPs genes detected in the AP-MS after inducing stress.

CONCLUSIONS

Our results indicate that NOA36 is necessary for proliferation recovery in response to thermal stress to achieve a regular cell cycle profile, likely by interaction with HSPA1 and HSPA8. Further studies would be required to disclose the relevance of NOA36-EHR interaction in this context.

MARK3 kinase: Regulation and physiologic roles

Microtubule affinity-regulating kinase 3 (MARK3), a member of the MARK family, regulates several essential pathways, including the cell cycle, ciliated cell differentiation, and osteoclast differentiation. It is important to understand the control of their activities as MARK3 contains an N-terminal serine/threonine kinase domain, ubiquitin-associated domain, and C-terminal kinase-associated domain, which perform multiple regulatory functions. These functions include post-translational modification (e.g., phosphorylation) and interaction with scaffolding and other proteins. Differences in the amino acid sequence and domain position result in different three-dimensional protein structures and affect the function of MARK3, which distinguish it from the other MARK family members. Recent data indicate a potential role of MARK3 in several pathological conditions, including congenital blepharophimosis syndrome, osteoporosis, and tumorigenesis. The present review focuses on the physiological and pathological role of MARK3, its regulation, and recent developments in the small molecule inhibitors of the MARK3 signalling cascade.

The Integration of Proteome-Wide PTM Data with Protein Structural and Sequence Features Identifies Phosphorylations that Mediate 14-3-3 Interactions

14-3-3s are abundant proteins that regulate essentially all aspects of cell biology, including cell cycle, motility, metabolism, and cell death. 14-3-3s work by docking to phosphorylated Ser/Thr residues on a large network of client proteins and modulating client protein function in a variety of ways. In recent years, aided by improvements in proteomics, the discovery of 14-3-3 client proteins has far outpaced our ability to understand the biological impact of individual 14-3-3 interactions. The rate-limiting step in this process is often the identification of the individual phospho-serines/threonines that mediate 14-3-3 binding, which are difficult to distinguish from other phospho-sites by sequence alone. Furthermore, trial-and-error molecular approaches to identify these phosphorylations are costly and can take months or years to identify even a single 14-3-3 docking site phosphorylation. To help overcome this challenge, we used machine learning to analyze predictive features of 14-3-3 binding sites. We found that accounting for intrinsic protein disorder and the unbiased mass spectrometry identification rate of a given phosphorylation significantly improves the identification of 14-3-3 docking site phosphorylations across the proteome. We incorporated these features, coupled with consensus sequence prediction, into a publicly available web app, called "14-3-3 site-finder". We demonstrate the strength of this approach through its ability to identify 14-3-3 binding sites that do not conform to the loose consensus sequence of 14-3-3 docking phosphorylations, which we validate with 14-3-3 client proteins, including TNK1, CHEK1, MAPK7, and others. In addition, by using this approach, we identify a phosphorylation on A-kinase anchor protein-13 (AKAP13) at Ser2467 that dominantly controls its interaction with 14-3-3.

Crystallographic mining of ASK1 regulators to unravel the intricate PPI interfaces for the discovery of small molecule

Protein seldom performs biological activities in isolation. Understanding the protein–protein interactions’ physical rewiring in response to pathological conditions or pathogen infection can help advance our comprehension of disease etiology, progression, and pathogenesis, which allow us to explore the alternate route to control the regulation of key target interactions, timely and effectively. Nonalcoholic steatohepatitis (NASH) is now a global public health problem exacerbated due to the lack of appropriate treatments. The most advanced anti-NASH lead compound (selonsertib) is withdrawn, though it is able to inhibit its target Apoptosis signal-regulating kinase 1 (ASK1) completely, indicating the necessity to explore alternate routes rather than complete inhibition. Understanding the interaction fingerprints of endogenous regulators at the molecular level that underpin disease formation and progression may spur the rationale of designing therapeutic strategies. Based on our analysis and thorough literature survey of the various key regulators and PTMs, the current review emphasizes PPI-based drug discovery’s relevance for NASH conditions. The lack of structural detail (interface sites) of ASK1 and its regulators makes it challenging to characterize the PPI interfaces. This review summarizes key regulators interaction fingerprinting of ASK1, which can be explored further to restore the homeostasis from its hyperactive states for therapeutics intervention against NASH.

Rho-Rho-Kinase Regulates Ras-ERK Signaling Through SynGAP1 for Dendritic Spine Morphology

The structural plasticity of dendritic spines plays a critical role in NMDA-induced long-term potentiation (LTP) in the brain. The small GTPases RhoA and Ras are considered key regulators of spine morphology and enlargement. However, the regulatory interaction between RhoA and Ras underlying NMDA-induced spine enlargement is largely unknown. In this study, we found that Rho-kinase/ROCK, an effector of RhoA, phosphorylated SynGAP1 (a synaptic Ras-GTPase activating protein) at Ser842 and increased its interaction with 14-3-3ζ, thereby activating Ras-ERK signaling in a reconstitution system in HeLa cells. We also found that the stimulation of NMDA receptor by glycine treatment for LTP induction stimulated SynGAP1 phosphorylation, Ras-ERK activation, spine enlargement and SynGAP1 delocalization from the spines in striatal neurons, and these effects were prevented by Rho-kinase inhibition. Rho-kinase-mediated phosphorylation of SynGAP1 appeared to increase its dissociation from PSD95, a postsynaptic scaffolding protein located at postsynaptic density, by forming a complex with 14-3-3ζ. These results suggest that Rho-kinase phosphorylates SynGAP1 at Ser842, thereby activating the Ras-ERK pathway for NMDA-induced morphological changes in dendritic spines.

The Homer1 family of proteins at the crossroad of dopamine-glutamate signaling: An emerging molecular "Lego" in the pathophysiology of psychiatric disorders. A systematic review and translational insight

Once considered only scaffolding proteins at glutamatergic postsynaptic density (PSD), Homer1 proteins are increasingly emerging as multimodal adaptors that integrate different signal transduction pathways within PSD, involved in motor and cognitive functions, with putative implications in psychiatric disorders. Regulation of type I metabotropic glutamate receptor trafficking, modulation of calcium signaling, tuning of long-term potentiation, organization of dendritic spines' growth, as well as meta- and homeostatic plasticity control are only a few of the multiple endocellular and synaptic functions that have been linked to Homer1. Findings from preclinical studies, as well as genetic studies conducted in humans, suggest that both constitutive (Homer1b/c) and inducible (Homer1a) isoforms of Homer1 play a role in the neurobiology of several psychiatric disorders, including psychosis, mood disorders, neurodevelopmental disorders, and addiction. On this background, Homer1 has been proposed as a putative novel target in psychopharmacological treatments. The aim of this review is to summarize and systematize the growing body of evidence on Homer proteins, highlighting the role of Homer1 in the pathophysiology and therapy of mental diseases.

The Human Myelin Proteome and Sub-Metalloproteome Interaction Map: Relevance to Myelin-Related Neurological Diseases

Myelin in humans is composed of about 80% lipids and 20% protein. Initially, myelin protein composition was considered low, but various recent proteome analyses have identified additional myelin proteins. Although, the myelin proteome is qualitatively and quantitatively identified through complementary proteomic approaches, the corresponding Protein–Protein Interaction (PPI) network of myelin is not yet available. In the present work, the PPI network was constructed based on available experimentally supported protein interactions of myelin in PPI databases. The network comprised 2017 PPIs between 567 myelin proteins. Interestingly, structure-based in silico analysis revealed that 20% of the myelin proteins that are interconnected in the proposed PPI network are metal-binding proteins/enzymes that construct the main sub-PPI network of myelin proteome. Finally, the PPI networks of the myelin proteome and sub-metalloproteome were analyzed ontologically to identify the biochemical processes of the myelin proteins and the interconnectivity of myelin-associated diseases in the interactomes. The presented PPI dataset could provide a useful resource to the scientific community to further our understanding of human myelin biology and serve as a basis for future studies of myelin-related neurological diseases and particular autoimmune diseases such as multiple sclerosis where myelin epitopes are implicated.

14-3-3ζ constrains insulin secretion by regulating mitochondrial function in pancreatic β-cells

While critical for neurotransmitter synthesis, 14-3-3 proteins are often assumed to have redundant functions due to their ubiquitous expression, but despite this assumption, various 14-3-3 isoforms have been implicated in regulating metabolism. We previously reported contributions of 14-3-3ζ in β cell function, but these studies were performed in tumor-derived MIN6 cells and systemic KO mice. To further characterize the regulatory roles of 14-3-3ζ in β cell function, we generated β cell–specific 14-3-3ζ–KO mice. Although no effects on β cell mass were detected, potentiated glucose-stimulated insulin secretion (GSIS), mitochondrial function, and ATP synthesis were observed. Deletion of 14-3-3ζ also altered the β cell transcriptome, as genes associated with mitochondrial respiration and oxidative phosphorylation were upregulated. Acute 14-3-3 protein inhibition in mouse and human islets recapitulated the enhancements in GSIS and mitochondrial function, suggesting that 14-3-3ζ is the critical isoform in β cells. In dysfunctional db/db islets and human islets from type 2 diabetic donors, expression of Ywhaz/YWHAZ, the gene encoding 14-3-3ζ, was inversely associated with insulin secretion, and pan–14-3-3 protein inhibition led to enhanced GSIS and mitochondrial function. Taken together, this study demonstrates important regulatory functions of 14-3-3ζ in the regulation of β cell function and provides a deeper understanding of how insulin secretion is controlled in β cells.

The 14-3-3 Protein Family and Schizophrenia

Schizophrenia is a debilitating mental disorder that affects approximately 1% of the world population, yet the disorder is not very well understood. The genetics of schizophrenia is very heterogenous, making it hard to pinpoint specific alterations that may cause the disorder. However, there is growing evidence from human studies suggesting a link between alterations in the 14-3-3 family and schizophrenia. The 14-3-3 proteins are abundantly expressed in the brain and are involved in many important cellular processes. Knockout of 14-3-3 proteins in mice has been shown to cause molecular, structural, and behavioral alterations associated with schizophrenia. Thus, 14-3-3 animal models allow for further exploration of the relationship between 14-3-3 and schizophrenia as well as the study of schizophrenia pathology. This review considers evidence from both human and animal model studies that implicate the 14-3-3 family in schizophrenia. In addition, possible mechanisms by which alterations in 14-3-3 proteins may contribute to schizophrenia-like phenotypes such as dopaminergic, glutamatergic, and cytoskeletal dysregulations are discussed.

Metastasising Fibroblasts Show an HDAC6-Dependent Increase in Migration Speed and Loss of Directionality Linked to Major Changes in the Vimentin Interactome

Metastasising cells express the intermediate filament protein vimentin, which is used to diagnose invasive tumours in the clinic. We aimed to clarify how vimentin regulates the motility of metastasising fibroblasts. STED super-resolution microscopy, live-cell imaging and quantitative proteomics revealed that oncogene-expressing and metastasising fibroblasts show a less-elongated cell shape, reduced cell spreading, increased cell migration speed, reduced directionality, and stronger coupling between these migration parameters compared to normal control cells. In total, we identified and compared 555 proteins in the vimentin interactome. In metastasising cells, the levels of keratin 18 and Rab5C were increased, while those of actin and collagen were decreased. Inhibition of HDAC6 reversed the shape, spreading and migration phenotypes of metastasising cells back to normal. Inhibition of HDAC6 also decreased the levels of talin 1, tropomyosin, Rab GDI β, collagen and emilin 1 in the vimentin interactome, and partially reversed the nanoscale vimentin organisation in oncogene-expressing cells. These findings describe the changes in the vimentin interactome and nanoscale distribution that accompany the defective cell shape, spreading and migration of metastasising cells. These results support the hypothesis that oncogenes can act through HDAC6 to regulate the vimentin binding of the cytoskeletal and cell-extracellular matrix adhesion components that contribute to the defective motility of metastasising cells.

14-3-3 protein regulation of excitation-contraction coupling

14-3-3 proteins (14-3-3 s) are a family of highly conserved proteins that regulate many cellular processes in eukaryotes by interacting with a diverse array of client proteins. The 14-3-3 proteins have been implicated in several disease states and previous reviews have condensed the literature with respect to their structure, function, and the regulation of different cellular processes. This review focuses on the growing body of literature exploring the important role 14-3-3 proteins appear to play in regulating the biochemical and biophysical events associated with excitation-contraction coupling (ECC) in muscle. It presents both a timely and unique analysis that seeks to unite studies emphasizing the identification and diversity of 14-3-3 protein function and client protein interactions, as modulators of muscle contraction. It also highlights ideas within these two well-established but intersecting fields that support further investigation with respect to the mechanistic actions of 14-3-3 proteins in the modulation of force generation in muscle.

Non-microtubule tubulin-based backbone and subordinate components of postsynaptic density lattices

This study proposes a postsynaptic density (PSD) lattice model comprising a non-microtubule tubulin-based backbone structure and its associated proteins, including various PSD scaffold/adaptor proteins and other PSD proteins.

A purification protocol was developed to identify and analyze the component proteins of a postsynaptic density (PSD) lattice, a core structure of the PSD of excitatory synapses in the central nervous system. “Enriched”- and “lean”-type PSD lattices were purified by synaptic plasma membrane treatment to identify the protein components by comprehensive shotgun mass spectrometry and group them into minimum essential cytoskeleton (MEC) and non-MEC components. Tubulin was found to be a major component of the MEC, with non-microtubule tubulin widely distributed on the purified PSD lattice. The presence of tubulin in and around PSDs was verified by post-embedding immunogold labeling EM of cerebral cortex. Non-MEC proteins included various typical scaffold/adaptor PSD proteins and other class PSD proteins. Thus, this study provides a new PSD lattice model consisting of non-microtubule tubulin-based backbone and various non-MEC proteins. Our findings suggest that tubulin is a key component constructing the backbone and that the associated components are essential for the versatile functions of the PSD.

The origins and genetic interactions of KRAS mutations are allele- and tissue-specific

Mutational activation of KRAS promotes the initiation and progression of cancers, especially in the colorectum, pancreas, lung, and blood plasma, with varying prevalence of specific activating missense mutations. Although epidemiological studies connect specific alleles to clinical outcomes, the mechanisms underlying the distinct clinical characteristics of mutant KRAS alleles are unclear. Here, we analyze 13,492 samples from these four tumor types to examine allele- and tissue-specific genetic properties associated with oncogenic KRAS mutations. The prevalence of known mutagenic mechanisms partially explains the observed spectrum of KRAS activating mutations. However, there are substantial differences between the observed and predicted frequencies for many alleles, suggesting that biological selection underlies the tissue-specific frequencies of mutant alleles. Consistent with experimental studies that have identified distinct signaling properties associated with each mutant form of KRAS, our genetic analysis reveals that each KRAS allele is associated with a distinct tissue-specific comutation network. Moreover, we identify tissue-specific genetic dependencies associated with specific mutant KRAS alleles. Overall, this analysis demonstrates that the genetic interactions of oncogenic KRAS mutations are allele- and tissue-specific, underscoring the complexity that drives their clinical consequences.

14-3-3ζ mediates an alternative, non-thermogenic mechanism in male mice to reduce heat loss and improve cold tolerance

Objective

Adaptive thermogenesis, which is partly mediated by sympathetic input on brown adipose tissue (BAT), is a mechanism of heat production that confers protection against prolonged cold exposure. Various endogenous stimuli, for example, norepinephrine and FGF-21, can also promote the conversion of inguinal white adipocytes to beige adipocytes, which may represent a secondary cell type that contributes to adaptive thermogenesis. We previously identified an essential role of the molecular scaffold 14-3-3ζ in adipogenesis, but one of the earliest, identified functions of 14-3-3ζ is its regulatory effects on the activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of norepinephrine. Herein, we examined whether 14-3-3ζ could influence adaptive thermogenesis via actions on BAT activation or the beiging of white adipocytes.

Methods

Transgenic mice over-expressing a TAP-tagged human 14-3-3ζ molecule or heterozygous mice without one allele of Ywhaz, the gene encoding 14-3-3ζ, were used to explore the contribution of 14-3-3ζ to acute (3 h) and prolonged (3 days) cold (4 °C) exposure. Metabolic caging experiments, PET-CT imaging, and laser Doppler imaging were used to determine the effect of 14-3-3ζ over-expression on thermogenic and vasoconstrictive mechanisms in response to cold.

Results

Transgenic over-expression of 14-3-3ζ (TAP) in male mice significantly improved tolerance to acute and prolonged cold. In response to cold, body temperatures in TAP mice did not decrease to the same extent when compared to wildtype (WT) mice, and this was associated with increased UCP1 expression in beige inguinal white tissue (iWAT) and BAT. Of note was the paradoxical finding that cold-induced changes in body temperatures of TAP mice were associated with significantly decreased energy expenditure. The marked improvements in tolerance to prolonged cold were not due to changes in sensitivity to β-adrenergic stimulation or BAT or iWAT oxidative metabolism; instead, over-expression of 14-3-3ζ significantly decreased thermal conductance and heat loss in mice via increased peripheral vasoconstriction.

Conclusions

Despite being associated with elevations in cold-induced UCP1 expression in brown or beige adipocytes, these findings suggest that 14-3-3ζ regulates an alternative, non-thermogenic mechanism via vasoconstriction to minimize heat loss during cold exposure.

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14-3-3ζ over-expression in male mice improves tolerance to acute and prolonged cold.

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Increasing 14-3-3ζ expression promotes beiging of inguinal white adipose tissue.

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Cold-induced changes in body temperature can be dissociated from energy expenditure.

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14-3-3ζ-dependent decreases in heat loss are associated with vasoconstriction.

Reducing 14-3-3ζ expression influences adipocyte maturity and impairs function

One of the primary metabolic functions of a mature adipocyte is to supply energy via lipolysis, or the catabolism of stored lipids. Adipose triacylglycerol lipase (ATGL) and hormone-sensitive lipase (HSL) are critical lipolytic enzymes, and their phosphorylation generates phospho-binding sites for 14-3-3 proteins, a ubiquitously expressed family of molecular scaffolds. Although we previously identified essential roles of the 14-3-3ζ isoform in murine adipogenesis, the presence of 14-3-3 protein binding sites on ATGL and HSL suggests that 14-3-3ζ could also influence mature adipocyte processes like lipolysis. Here we demonstrate that 14-3-3ζ is necessary for lipolysis in male mice and fully differentiated 3T3-L1 adipocytes, as depletion of 14-3-3ζ significantly impaired glycerol and free fatty acid (FFA) release. Unexpectedly, reducing 14-3-3ζ expression was found to significantly impact adipocyte maturity, as observed by reduced abundance of peroxisome proliferator-activated receptor (PPAR)γ2 protein and expression of mature adipocyte genes and those associated with de novo triglyceride synthesis and lipolysis. The impact of 14-3-3ζ depletion on adipocyte maturity was further examined with untargeted lipidomics, which revealed that reductions in 14-3-3ζ abundance promoted the acquisition of a lipidomic signature that resembled undifferentiated preadipocytes. Collectively, these findings reveal a novel aspect of 14-3-3ζ in adipocytes, as reducing 14-3-3ζ was found to have a negative effect on adipocyte maturity and adipocyte-specific processes like lipolysis.

AMPK phosphorylation of the β1Pix exchange factor regulates the assembly and function of an ENaC inhibitory complex in kidney epithelial cells

The metabolic sensor AMP-activated protein kinase (AMPK) inhibits the epithelial Na⁺ channel (ENaC), a key regulator of salt reabsorption by the kidney and thus total body volume and blood pressure. Recent studies have suggested that AMPK promotes the association of p21-activated kinase-interacting exchange factor-β₁ β₁Pix, 14-3-3 proteins, and the ubiquitin ligase neural precursor cell expressed developmentally downregulated protein (Nedd)4-2 into a complex that inhibits ENaC by enhancing Nedd4-2 binding to ENaC and ENaC degradation. Functional β₁Pix is required for ENaC inhibition by AMPK and promotes Nedd4-2 phosphorylation and stability in mouse kidney cortical collecting duct cells. Here, we report that AMPK directly phosphorylates β₁Pix in vitro. Among several AMPK phosphorylation sites on β₁Pix detected by mass spectrometry, Ser⁷¹ was validated as functionally significant. Compared with wild-type β₁Pix, overexpression of a phosphorylation-deficient β₁Pix-S71A mutant attenuated ENaC inhibition and the AMPK-activated interaction of both β₁Pix and Nedd4-2 to 14-3-3 proteins in cortical collecting duct cells. Similarly, overexpression of a β₁Pix-Δ602-611 deletion tract mutant unable to bind 14-3-3 proteins decreased the interaction between Nedd4-2 and 14-3-3 proteins, suggesting that 14-3-3 binding to β₁Pix is critical for the formation of a β₁Pix/Nedd4-2/14-3-3 complex. With expression of a general peptide inhibitor of 14-3-3-target protein interactions (R18), binding of both β₁Pix and Nedd4-2 to 14-3-3 proteins was reduced, and AMPK-dependent ENaC inhibition was also attenuated. Altogether, our results demonstrate the importance of AMPK-mediated phosphorylation of β₁Pix at Ser⁷¹, which promotes 14-3-3 interactions with β₁Pix and Nedd4-2 to form a tripartite ENaC inhibitory complex, in the mechanism of ENaC regulation by AMPK.

Phosphorylation of human AQP2 and its role in trafficking

Human Aquaporin 2 (AQP2) is a membrane-bound water channel found in the kidney collecting duct whose regulation by trafficking plays a key role in regulating urine volume. AQP2 trafficking is tightly controlled by the pituitary hormone arginine vasopressin (AVP), which stimulates translocation of AQP2 residing in storage vesicles to the apical membrane. The AVP-dependent translocation of AQP2 to and from the apical membrane is controlled by multiple phosphorylation sites in the AQP2 C-terminus, the phosphorylation of which alters its affinity to proteins within the cellular membrane protein trafficking machinery. The aim of this chapter is to provide a summary of what is currently known about AVP-mediated AQP2 trafficking, dissecting the roles of individual phosphorylation sites, kinases and phosphatases and interacting proteins. From this, the picture of an immensely complex process emerges, of which many structural and molecular details remains to be elucidated.

EhP3, a homolog of 14-3-3 family of protein participates in actin reorganization and phagocytosis in Entamoeba histolytica

The highly conserved proteins of the 14-3-3 family are universal adaptors known to regulate an enormous range of cellular processes in eukaryotes. However, their biological functions remain largely uncharacterized in pathogenic protists comprising of several 14-3-3 protein isoforms. In this study, we report the role of 14-3-3 in coordinating cytoskeletal dynamics during phagocytosis in a professional phagocytic protist Entamoeba histolytica, the etiological agent of human amebiasis. There are three isoforms of 14-3-3 protein in amoeba and here we have investigated Eh14-3-3 Protein 3 (EhP3). Live and fixed cell imaging studies revealed the presence of this protein throughout the parasite phagocytosis process, with high rate of accumulation at the phagocytic cups and closed phagosomes. Conditional suppression of EhP3 expression caused significant defects in phagocytosis accompanied by extensive diminution of F-actin at the site of cup formation. Downregulated cells also exhibited defective recruitment of an F-actin stabilizing protein, EhCoactosin at the phagocytic cups. In addition, mass spectrometry based analysis further revealed a large group of EhP3-associated proteins, many of these proteins are known to regulate cytoskeletal architecture in E histolytica. The dynamics of these proteins may also be controlled by EhP3. Taken together, our findings strongly suggest that EhP3 is a novel and a key regulatory element of actin dynamics and phagocytosis in E. histolytica.

Phagocytosis of host cells is central to pathogenesis of protist parasite Entamoeba histolytica, the etiological agent of human amebiasis. It is a complex and multistep process that requires dynamic remodelling of the actin cytoskeleton by a large number of scaffolding, signaling and actin-binding proteins (ABPs). Although several parasite ligands such as EhC2PK, EhCaBP1, EhCaBP3, EhAK1, Arp2/3 complex and EhCoactosin that participate in the phagocytic machinery have been identified, the mechanistic insights to their regulation process remain largely elusive. We have in this study identified and characterized the important role of scaffolding protein EhP3 in modulating cytoskeletal dynamics and regulating phagocytosis in E. histolytica. Expression knockdown, imaging and interaction studies suggest that EhP3 function as an adaptor molecule that controls the localization of an F-actin stabilizing protein EhCoactosin and thus the dynamics of F-actin rearrangement during phagocytosis. EhP3 also interact with other actin dynamics regulating proteins that may in coordination regulate cytoskeletal dynamics and thereby phagocytosis in Entamoeba.

14-3-3 gene family in spotted sea bass (Lateolabrax maculatus): Genome-wide identification, phylogenetic analysis and expression profiles after salinity stress

The tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation (14-3-3) proteins are a group of highly conserved homologous and heterologous proteins involved in a wild range of physiological processes, including the regulation of many molecular phenomena under different environmental salinities. In this study, we identified eleven 14-3-3 genes from the spotted sea bass (Lateolabrax maculatus) genome and transcriptomic databases and verified their identities by conducting phylogenetic, syntenic and gene structure analyses. The spotted sea bass 14-3-3 genes are highly conserved based on sequence alignment, conserved domains and motifs, and tertiary structural feature. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of 14-3-3 genes in gill of spotted sea bass under normal physiological conditions indicated that the expression level of 14-3-3 zeta was the highest among tested genes, followed by 14-3-3 theta. Furthermore, expression profiles of 14-3-3 genes in gill tissue (in vivo and in vitro) indicated that the 14-3-3 zeta and 14-3-3 theta genes were significantly induced by different environmental salinities in spotted sea bass, suggesting their potential involvement in response to salinity challenge. Our findings may lay the foundation for future functional studies on the 14-3-3 gene family in euryhaline teleosts.

Clinical significance of detecting HLA-DR, 14-3-3η protein and d-dimer in the diagnosis of rheumatoid arthritis

AIM

To investigate the clinical significance of detecting several biomarkers collectively in the diagnosis of rheumatoid arthritis (RA).

METHODS

128 RA patients, 174 non-RA patients and 80 healthy controls were enrolled. HLA-DR4 and HLA-DR53 were detected by the PCR-SSP method, 14-3-3η protein, anti-CCP and anti-Sa were detected by ELISA and DD was detected by latex immunoturbidimetric assay.

RESULTS

The positive rates of HLA-DR4, HLA-DR53, 14-3-3η protein, anti-CCP and anti-Sa were obviously higher in the RA group (43.8, 38.3, 51.6, 80 and 40.6%, respectively); anti-CCP was of highest sensitivity (79.68%), highest specificity (97.5%) and Youden index (0.77). The AUC of 14-3-3η protein, DD, anti-CCP, anti-Sa were 0.813, 0.859, 0.930, 0.861, respectively.

CONCLUSION

All biomarkers were strongly correlated risk factors for RA; the combination of multiple biomarkers might be of help for diagnostic and therapeutic strategies in RA of recent onset.

β1Pix exchange factor stabilizes the ubiquitin ligase Nedd4-2 and plays a critical role in ENaC regulation by AMPK in kidney epithelial cells

Our previous work has established that the metabolic sensor AMP-activated protein kinase (AMPK) inhibits the epithelial Na⁺ channel (ENaC) by promoting its binding to neural precursor cell-expressed, developmentally down-regulated 4-2, E3 ubiquitin protein ligase (Nedd4-2). Here, using MS analysis and in vitro phosphorylation, we show that AMPK phosphorylates Nedd4-2 at the Ser-444 (Xenopus Nedd4-2) site critical for Nedd4-2 stability. We further demonstrate that the Pak-interacting exchange factor β₁Pix is required for AMPK-mediated inhibition of ENaC-dependent currents in both CHO and murine kidney cortical collecting duct (CCD) cells. Short hairpin RNA-mediated knockdown of β₁Pix expression in CCD cells attenuated the inhibitory effect of AMPK activators on ENaC currents. Moreover, overexpression of a β₁Pix dimerization-deficient mutant unable to bind 14-3-3 proteins (Δ602-611) increased ENaC currents in CCD cells, whereas overexpression of WT β₁Pix had the opposite effect. Using additional immunoblotting and co-immunoprecipitation experiments, we found that treatment with AMPK activators promoted the binding of β₁Pix to 14-3-3 proteins in CCD cells. However, the association between Nedd4-2 and 14-3-3 proteins was not consistently affected by AMPK activation, β₁Pix knockdown, or overexpression of WT β₁Pix or the β₁Pix-Δ602-611 mutant. Moreover, we found that β₁Pix is important for phosphorylation of the aforementioned Nedd4-2 site critical for its stability. Overall, these findings elucidate novel molecular mechanisms by which AMPK regulates ENaC. Specifically, they indicate that AMPK promotes the assembly of β₁Pix, 14-3-3 proteins, and Nedd4-2 into a complex that inhibits ENaC by enhancing Nedd4-2 binding to ENaC and its degradation.

14-3-3 Proteins in Glutamatergic Synapses

The 14-3-3 proteins are a family of proteins that are highly expressed in the brain and particularly enriched at synapses. Evidence accumulated in the last two decades has implicated 14-3-3 proteins as an important regulator of synaptic transmission and plasticity. Here, we will review previous and more recent research that has helped us understand the roles of 14-3-3 proteins at glutamatergic synapses. A key challenge for the future is to delineate the 14-3-3-dependent molecular pathways involved in regulating synaptic functions.

Mapping protein interactions of sodium channel NaV1.7 using epitope-tagged gene-targeted mice

The voltage-gated sodium channel NaV1.7 plays a critical role in pain pathways. We generated an epitope-tagged NaV1.7 mouse that showed normal pain behaviours to identify channel-interacting proteins. Analysis of NaV1.7 complexes affinity-purified under native conditions by mass spectrometry revealed 267 proteins associated with Nav1.7 in vivo The sodium channel β3 (Scn3b), rather than the β1 subunit, complexes with Nav1.7, and we demonstrate an interaction between collapsing-response mediator protein (Crmp2) and Nav1.7, through which the analgesic drug lacosamide regulates Nav1.7 current density. Novel NaV1.7 protein interactors including membrane-trafficking protein synaptotagmin-2 (Syt2), L-type amino acid transporter 1 (Lat1) and transmembrane P24-trafficking protein 10 (Tmed10) together with Scn3b and Crmp2 were validated by co-immunoprecipitation (Co-IP) from sensory neuron extract. Nav1.7, known to regulate opioid receptor efficacy, interacts with the G protein-regulated inducer of neurite outgrowth (Gprin1), an opioid receptor-binding protein, demonstrating a physical and functional link between Nav1.7 and opioid signalling. Further information on physiological interactions provided with this normal epitope-tagged mouse should provide useful insights into the many functions now associated with the NaV1.7 channel.

14-3-3ζ loss leads to neonatal lethality by microRNA-126 downregulation-mediated developmental defects in lung vasculature

Background

The 14-3-3 family of proteins have been reported to play an important role in development in various mouse models, but the context specific developmental functions of 14-3-3ζ remain to be determined. In this study, we identified a context specific developmental function of 14-3-3ζ.

Results

Targeted deletion of 14-3-3ζ in the C57Bl/6J murine genetic background led to neonatal lethality due to respiratory distress and could be rescued by out-breeding to the CD-1 or backcrossing to the FVB/NJ congenic background. Histological analysis of lung sections from 18.5 days post coitum embryos (dpc) showed that 14-3-3ζ−/− lung development is arrested at the pseudoglandular stage and exhibits vascular defects. The expression of miR-126, an endothelial-specific miRNA known to regulate lung vascular integrity was down-regulated in the lungs of the 14-3-3ζ−/− embryos in the C57Bl/6J background as compared to their wild-type counterparts. Loss of 14-3-3ζ in endothelial cells inhibited the angiogenic capability of the endothelial cells as determined by both trans-well migration assays and tube formation assays and these defects could be rescued by re-expressing miR-126. Mechanistically, loss of 14-3-3ζ led to reduced Erk1/2 phosphorylation resulting in attenuated binding of the transcription factor Ets2 on the miR-126 promoter which ultimately reduced expression of miR-126.

Conclusion

Our data demonstrates that miR-126 is an important angiogenesis regulator that functions downstream of 14-3-3ζ and downregulation of miR-126 plays a critical role in 14-3-3ζ-loss induced defects in lung vasculature in the C57Bl/6J genetic background.

Electronic supplementary material

The online version of this article (10.1186/s13578-017-0186-y) contains supplementary material, which is available to authorized users.

piRNAs and Their Functions in the Brain

Piwi-interacting RNAs (piRNAs) are the non-coding RNAs with 24-32 nucleotides (nt). They exhibit stark differences in length, expression pattern, abundance, and genomic organization when compared to micro-RNAs (miRNAs). There are hundreds of thousands unique piRNA sequences in each species. Numerous piRNAs have been identified and deposited in public databases. Since the piRNAs were originally discovered and well-studied in the germline, a few other studies have reported the presence of piRNAs in somatic cells including neurons. This paper reviewed the common features, biogenesis, functions, and distributions of piRNAs and summarized their specific functions in the brain. This review may provide new insights and research direction for brain disorders.

Expanding functions of GIT Arf GTPase-activating proteins, PIX Rho guanine nucleotide exchange factors and GIT-PIX complexes

The GIT proteins, GIT1 and GIT2, are GTPase-activating proteins (inactivators) for the ADP-ribosylation factor (Arf) small GTP-binding proteins, and function to limit the activity of Arf proteins. The PIX proteins, α-PIX and β-PIX (also known as ARHGEF6 and ARHGEF7, respectively), are guanine nucleotide exchange factors (activators) for the Rho family small GTP-binding protein family members Rac1 and Cdc42. Through their multi-domain structures, GIT and PIX proteins can also function as signaling scaffolds by binding to numerous protein partners. Importantly, the constitutive association of GIT and PIX proteins into oligomeric GIT-PIX complexes allows these two proteins to function together as subunits of a larger structure that coordinates two distinct small GTP-binding protein pathways and serves as multivalent scaffold for the partners of both constituent subunits. Studies have revealed the involvement of GIT and PIX proteins, and of the GIT-PIX complex, in numerous fundamental cellular processes through a wide variety of mechanisms, pathways and signaling partners. In this Commentary, we discuss recent findings in key physiological systems that exemplify current understanding of the function of this important regulatory complex. Further, we draw attention to gaps in crucial information that remain to be filled to allow a better understanding of the many roles of the GIT-PIX complex in health and disease.

Proteome Analysis of Drosophila Mutants Identifies a Regulatory Role for 14-3-3ε in Metabolic Pathways

The evolutionary conserved family of 14-3-3 proteins appears to have a role in integrating numerous intracellular pathways, including signal transduction, intracellular trafficking, and metabolism. However, little is known about how this interactive network might be affected by the direct abrogation of 14-3-3 function. The loss of Drosophila 14-3-3ε resulted in reduced survival of mutants during larval-to-adult transition, which is known to depend on an energy supply coming from the histolysis of fat body tissue. Here we report a differential proteomic analysis of larval fat body tissue at the onset of larval-to-adult transition, with the loss of 14-3-3ε resulting in the altered abundance of 16 proteins. These included proteins linked to protein biosynthesis, glycolysis, tricarboxylic acid cycle, and lipid metabolic pathways. The ecdysone receptor (EcR), which is responsible for initiating the larval-to-adult transition, colocalized with 14-3-3ε in wild-type fat body tissues. The altered protein abundance in 14-3-3ε mutant fat body tissue was associated with transcriptional deregulation of alcohol dehydrogenase, fat body protein 1, and lamin genes, which are known targets of the EcR. This study indicates that 14-3-3ε has a critical role in cellular metabolism involving either molecular crosstalk with the EcR or direct interaction with metabolic proteins.

Glutamate Receptor Interacting Protein 1 Mediates Platelet Adhesion and Thrombus Formation

Thrombosis-associated pathologies, such as myocardial infarction and stroke, are major causes of morbidity and mortality worldwide. Because platelets are necessary for hemostasis and thrombosis, platelet directed therapies must balance inhibiting platelet function with bleeding risk. Glutamate receptor interacting protein 1 (GRIP1) is a large scaffolding protein that localizes and organizes interacting proteins in other cells, such as neurons. We have investigated the role of GRIP1 in platelet function to determine its role as a molecular scaffold in thrombus formation. Platelet-specific GRIP1^-/- mice were used to determine the role of GRIP1 in platelets. GRIP1^-/- mice had normal platelet counts, but a prolonged bleeding time and delayed thrombus formation in a FeCl₃-induced vessel injury model. In vitro stimulation of WT and GRIP1^-/- platelets with multiple agonists showed no difference in platelet activation. However, in vivo platelet rolling velocity after endothelial stimulation was significantly greater in GRIP1^-/- platelets compared to WT platelets, indicating a potential platelet adhesion defect. Mass spectrometry analysis of GRIP1 platelet immunoprecipitation revealed enrichment of GRIP1 binding to GPIb-IX complex proteins. Western blots confirmed the mass spectrometry findings that GRIP1 interacts with GPIbα, GPIbβ, and 14-3-3. Additionally, in resting GRIP1^-/- platelets, GPIbα and 14-3-3 have increased interaction compared to WT platelets. GRIP1 interactions with the GPIb-IX binding complex are necessary for normal platelet adhesion to a stimulated endothelium.

Altered Mitochondria, Protein Synthesis Machinery, and Purine Metabolism Are Molecular Contributors to the Pathogenesis of Creutzfeldt-Jakob Disease

Neuron loss, synaptic decline, and spongiform change are the hallmarks of sporadic Creutzfeldt-Jakob disease (sCJD), and may be related to deficiencies in mitochondria, energy metabolism, and protein synthesis. To investigate these relationships, we determined the expression levels of genes encoding subunits of the 5 protein complexes of the electron transport chain, proteins involved in energy metabolism, nucleolar and ribosomal proteins, and enzymes of purine metabolism in frontal cortex samples from 15 cases of sCJD MM1 and age-matched controls. We also assessed the protein expression levels of subunits of the respiratory chain, initiation and elongation translation factors of protein synthesis, and localization of selected mitochondrial components. We identified marked, generalized alterations of mRNA and protein expression of most subunits of all 5 mitochondrial respiratory chain complexes in sCJD cases. Expression of molecules involved in protein synthesis and purine metabolism were also altered in sCJD. These findings point to altered mRNA and protein expression of components of mitochondria, protein synthesis machinery, and purine metabolism as components of the pathogenesis of CJD.

In Vivo Interaction Proteomics in Caenorhabditis elegans Embryos Provides New Insights into P Granule Dynamics

Studying protein interactions in whole organisms is fundamental to understanding development. Here, we combine in vivo expressed GFP-tagged proteins with quantitative proteomics to identify protein-protein interactions of selected key proteins involved in early C. elegans embryogenesis. Co-affinity purification of interaction partners for eight bait proteins resulted in a pilot in vivo interaction map of proteins with a focus on early development. Our network reflects known biology and is highly enriched in functionally relevant interactions. To demonstrate the utility of the map, we looked for new regulators of P granule dynamics and found that GEI-12, a novel binding partner of the DYRK family kinase MBK-2, is a key regulator of P granule formation and germline maintenance. Our data corroborate a recently proposed model in which the phosphorylation state of GEI-12 controls P granule dynamics. In addition, we find that GEI-12 also induces granule formation in mammalian cells, suggesting a common regulatory mechanism in worms and humans. Our results show that in vivo interaction proteomics provides unique insights into animal development.

Hemotin, a Regulator of Phagocytosis Encoded by a Small ORF and Conserved across Metazoans

Translation of hundreds of small ORFs (smORFs) of less than 100 amino acids has recently been revealed in vertebrates and Drosophila. Some of these peptides have essential and conserved cellular functions. In Drosophila, we have predicted a particular smORF class encoding ~80 aa hydrophobic peptides, which may function in membranes and cell organelles. Here, we characterise hemotin, a gene encoding an 88aa transmembrane smORF peptide localised to early endosomes in Drosophila macrophages. hemotin regulates endosomal maturation during phagocytosis by repressing the cooperation of 14-3-3ζ with specific phosphatidylinositol (PI) enzymes. hemotin mutants accumulate undigested phagocytic material inside enlarged endo-lysosomes and as a result, hemotin mutants have reduced ability to fight bacteria, and hence, have severely reduced life span and resistance to infections. We identify Stannin, a peptide involved in organometallic toxicity, as the Hemotin functional homologue in vertebrates, showing that this novel regulator of phagocytic processing is widely conserved, emphasizing the significance of smORF peptides in cell biology and disease.

SORLA regulates calpain-dependent degradation of synapsin

INTRODUCTION

Sorting-related receptor with A-type repeats (SORLA) is an intracellular sorting receptor in neurons and a major risk factor for Alzheimer disease.

METHODS

Here, we performed global proteome analyses in the brain of SORLA-deficient mice followed by biochemical and histopathologic studies to identify novel neuronal pathways affected by receptor dysfunction.

RESULTS

We demonstrate that the lack of SORLA results in accumulation of phosphorylated synapsins in cortex and hippocampus. We propose an underlying molecular mechanism by demonstrating that SORLA interacts with phosphorylated synapsins through 14-3-3 adaptor proteins to deliver synapsins to calpain-mediated proteolytic degradation.

DISCUSSION

Our results suggest a novel function for SORLA which is in control of synapsin degradation, potentially impacting on synaptic vesicle endocytosis and/or exocytosis.

Inositol 1,4,5-trisphosphate receptors and their protein partners as signalling hubs

Inositol 1,4,5‐trisphosphate receptors (IP₃Rs) are expressed in nearly all animal cells, where they mediate the release of Ca²⁺ from intracellular stores. The complex spatial and temporal organization of the ensuing intracellular Ca²⁺ signals allows selective regulation of diverse physiological responses. Interactions of IP₃Rs with other proteins contribute to the specificity and speed of Ca²⁺ signalling pathways, and to their capacity to integrate information from other signalling pathways. In this review, we provide a comprehensive survey of the proteins proposed to interact with IP₃Rs and the functional effects that these interactions produce. Interacting proteins can determine the activity of IP₃Rs, facilitate their regulation by multiple signalling pathways and direct the Ca²⁺ that they release to specific targets. We suggest that IP₃Rs function as signalling hubs through which diverse inputs are processed and then emerge as cytosolic Ca²⁺ signals.

Co-immunoprecipitation with Tau Isoform-specific Antibodies Reveals Distinct Protein Interactions and Highlights a Putative Role for 2N Tau in Disease

Alternative splicing generates multiple isoforms of the microtubule-associated protein Tau, but little is known about their specific function. In the adult mouse brain, three Tau isoforms are expressed that contain either 0, 1, or 2 N-terminal inserts (0N, 1N, and 2N). We generated Tau isoform-specific antibodies and performed co-immunoprecipitations followed by tandem mass tag multiplexed quantitative mass spectrometry. We identified novel Tau-interacting proteins of which one-half comprised membrane-bound proteins, localized to the plasma membrane, mitochondria, and other organelles. Tau was also found to interact with proteins involved in presynaptic signal transduction. MetaCore analysis revealed one major Tau interaction cluster that contained 33 Tau pulldown proteins. To explore the pathways in which these proteins are involved, we conducted an ingenuity pathway analysis that revealed two significant overlapping pathways, “cell-to-cell signaling and interaction” and “neurological disease.” The functional enrichment tool DAVID showed that in particular the 2N Tau-interacting proteins were specifically associated with neurological disease. Finally, for a subset of Tau interactions (apolipoprotein A1 (apoA1), apoE, mitochondrial creatine kinase U-type, β-synuclein, synaptogyrin-3, synaptophysin, syntaxin 1B, synaptotagmin, and synapsin 1), we performed reverse co-immunoprecipitations, confirming the preferential interaction of specific isoforms. For example, apoA1 displayed a 5-fold preference for the interaction with 2N, whereas β-synuclein showed preference for 0N. Remarkably, a reverse immunoprecipitation with apoA1 detected only the 2N isoform. This highlights distinct protein interactions of the different Tau isoforms, suggesting that they execute different functions in brain tissue.

Regulation of the Water Channel Aquaporin-2 via 14-3-3θ and -ζ

The 14-3-3 family of proteins are multifunctional proteins that interact with many of their cellular targets in a phosphorylation-dependent manner. Here, we determined that 14-3-3 proteins interact with phosphorylated forms of the water channel aquaporin-2 (AQP2) and modulate its function. With the exception of σ, all 14-3-3 isoforms were abundantly expressed in mouse kidney and mouse kidney collecting duct cells (mpkCCD14). Long-term treatment of mpkCCD14 cells with the type 2 vasopressin receptor agonist dDAVP increased mRNA and protein levels of AQP2 alongside 14-3-3β and -ζ, whereas levels of 14-3-3η and -θ were decreased. Co-immunoprecipitation (co-IP) studies in mpkCCD14 cells uncovered an AQP2/14-3-3 interaction that was modulated by acute dDAVP treatment. Additional co-IP studies in HEK293 cells determined that AQP2 interacts selectively with 14-3-3ζ and -θ. Use of phosphatase inhibitors in mpkCCD14 cells, co-IP with phosphorylation deficient forms of AQP2 expressed in HEK293 cells, or surface plasmon resonance studies determined that the AQP2/14-3-3 interaction was modulated by phosphorylation of AQP2 at various sites in its carboxyl terminus, with Ser-256 phosphorylation critical for the interactions. shRNA-mediated knockdown of 14-3-3ζ in mpkCCD14 cells resulted in increased AQP2 ubiquitylation, decreased AQP2 protein half-life, and reduced AQP2 levels. In contrast, knockdown of 14-3-3θ resulted in increased AQP2 half-life and increased AQP2 levels. In conclusion, this study demonstrates phosphorylation-dependent interactions of AQP2 with 14-3-3θ and -ζ. These interactions play divergent roles in modulating AQP2 trafficking, phosphorylation, ubiquitylation, and degradation.

Cyclic Nucleotide-dependent Protein Kinases Target ARHGAP17 and ARHGEF6 Complexes in Platelets

Endothelial cells release prostacyclin (PGI2) and nitric oxide (NO) to inhibit platelet functions. PGI2 and NO effects are mediated by cyclic nucleotides, cAMP- and cGMP-dependent protein kinases (PKA, PKG), and largely unknown PKA and PKG substrate proteins. The small G-protein Rac1 plays a key role in platelets and was suggested to be a target of cyclic nucleotide signaling. We confirm that PKA and PKG activation reduces Rac1-GTP levels. Screening for potential mediators of this effect resulted in the identification of the Rac1-specific GTPase-activating protein ARHGAP17 and the guanine nucleotide exchange factor ARHGEF6 as new PKA and PKG substrates in platelets. We mapped the PKA/PKG phosphorylation sites to serine 702 on ARHGAP17 using Phos-tag gels and to serine 684 on ARHGEF6. We show that ARHGAP17 binds to the actin-regulating CIP4 protein in platelets and that Ser-702 phosphorylation interferes with this interaction. Reduced CIP4 binding results in enhanced inhibition of cell migration by ARHGAP17. Furthermore, we show that ARHGEF6 is constitutively linked to GIT1, a GAP of Arf family small G proteins, and that ARHGEF6 phosphorylation enables binding of the 14-3-3 adaptor protein to the ARHGEF6/GIT1 complex. PKA and PKG induced rearrangement of ARHGAP17- and ARHGEF6-associated protein complexes might contribute to Rac1 regulation and platelet inhibition.

14-3-3ζ coordinates adipogenesis of visceral fat

The proteins that coordinate complex adipogenic transcriptional networks are poorly understood. 14-3-3ζ is a molecular adaptor protein that regulates insulin signalling and transcription factor networks. Here we report that 14-3-3ζ-knockout mice are strikingly lean from birth with specific reductions in visceral fat depots. Conversely, transgenic 14-3-3ζ overexpression potentiates obesity, without exacerbating metabolic complications. Only the 14-3-3ζ isoform is essential for adipogenesis based on isoform-specific RNAi. Mechanistic studies show that 14-3-3ζ depletion promotes autophagy-dependent degradation of C/EBP-δ, preventing induction of the master adipogenic factors, Pparγ and C/EBP-α. Transcriptomic data indicate that 14-3-3ζ acts upstream of hedgehog signalling-dependent upregulation of Cdkn1b/p27(Kip1). Indeed, concomitant knockdown of p27(Kip1) or Gli3 rescues the early block in adipogenesis induced by 14-3-3ζ knockdown in vitro. Adipocyte precursors in 14-3-3ζKO embryos also appear to have greater Gli3 and p27(Kip1) abundance. Together, our in vivo and in vitro findings demonstrate that 14-3-3ζ is a critical upstream driver of adipogenesis.

14-3-3ζ deficient mice in the BALB/c background display behavioural and anatomical defects associated with neurodevelopmental disorders

Sequencing and expression analyses implicate 14-3-3ζ as a genetic risk factor for neurodevelopmental disorders such as schizophrenia and autism. In support of this notion, we recently found that 14-3-3ζ^−/− mice in the Sv/129 background display schizophrenia-like defects. As epistatic interactions play a significant role in disease pathogenesis we generated a new congenic strain in the BALB/c background to determine the impact of genetic interactions on the 14-3-3ζ^−/− phenotype. In addition to replicating defects such as aberrant mossy fibre connectivity and impaired spatial memory, our analysis of 14-3-3ζ^−/− BALB/c mice identified enlarged lateral ventricles, reduced synaptic density and ectopically positioned pyramidal neurons in all subfields of the hippocampus. In contrast to our previous analyses, 14-3-3ζ^−/− BALB/c mice lacked locomotor hyperactivity that was underscored by normal levels of the dopamine transporter (DAT) and dopamine signalling. Taken together, our results demonstrate that dysfunction of 14-3-3ζ gives rise to many of the pathological hallmarks associated with the human condition. 14-3-3ζ-deficient BALB/c mice therefore provide a novel model to address the underlying biology of structural defects affecting the hippocampus and ventricle, and cognitive defects such as hippocampal-dependent learning and memory.

Computational Inferences of the Functions of Alternative/Noncanonical Splice Isoforms Specific to HER2+/ER-/PR- Breast Cancers, a Chromosome 17 C-HPP Study

This study was conducted as a part of the Chromosome-Centric Human Proteome Project (C-HPP) of the Human Proteome Organization. The main objective is to identify and evaluate functionality of a set of specific noncanonical isoforms expressed in HER2-neu positive, estrogen receptor negative (ER-), and progesterone receptor negative (PR-) breast cancers (HER2+/ER-/PR- BC), an aggressive subtype of breast cancers that cause significant morbidity and mortality. We identified 11 alternative splice isoforms that were differentially expressed in HER2+/ER-/PR- BC compared to normal mammary, triple negative breast cancer and triple positive breast cancer tissues (HER2+/ER+/PR+). We used a stringent criterion that differentially expressed noncanonical isoforms (adjusted p value < 0.05) and have to be expressed in all replicates of HER2+/ER-/PR- BC samples, and the trend in differential expression (up or down) is the same in all comparisons. Of the 11 protein isoforms, six were overexpressed in HER2+/ER-/PR- BC. We explored possible functional roles of these six proteins using several complementary computational tools. Biological processes including cell cycle events and glycolysis were linked to four of these proteins. For example, glycolysis was the top ranking functional process for DMXL2 isoform 3, with a fold change of 27 compared to just two for the canonical protein. No previous reports link DMXL2 with any metabolic processes; the canonical protein is known to participate in signaling pathways. Our results clearly indicate distinct functions for the six overexpressed alternative splice isoforms, and these functions could be specific to HER2+/ER-/PR- tumor progression. Further detailed analysis is warranted as these proteins could be explored as potential biomarkers and therapeutic targets for HER2+/ER-/PR- BC patients.