Search Results (365)

Abscisic acid (ABA) is a major phytohormone regulating plant growth and stress responses. Subclass III SnRK2 kinases and clade A type 2C protein phosphatases (PP2Cs) are core components of ABA signaling. Despite advances from phosphoproteomics, major gaps remain, particularly in mapping PP2C dephosphorylation targets and SnRK2-dependent phosphorylation dynamics under non-stress conditions. Here, we performed large-scale LC–MS/MS phosphoproteomic analyses using the subclass III SnRK2 triple mutant srk2dei and the constitutively active PP2C mutant abi1–1C, with and without ABA treatment in Arabidopsis thaliana. We identified 2757 and 2886 differentially regulated phosphopeptides in srk2dei and abi1–1C, respectively. Beyond known ABA signaling components, these datasets revealed numerous previously uncharacterized candidate proteins involved in metabolism, membrane transport, transcription, and cytoskeletal regulation. Integrative analysis uncovered a core set of candidate proteins oppositely regulated by SnRK2-mediated phosphorylation and ABI1-mediated dephosphorylation, defining a coordinated hierarchical network. These results indicate that the SnRK2–PP2C module functions not only in stress-induced ABA responses but also as a central regulator of phosphorylation homeostasis under basal conditions. This study provides a systematic framework for the global SnRK2–PP2C phosphorylation network and reframes ABA signaling as a dynamic homeostatic system. Full article

Background: Excessive abdominal fat deposition is a major challenge in the chicken farming industry, making it essential to elucidate the molecular mechanisms underlying chicken adipogenesis. Nuclear Respiratory Factor 1 (NRF1) has been reported to suppress chicken adipogenesis by downregulating peroxisome proliferator-activated receptor gamma (PPARγ) expression. Protein Phosphatase 1 Catalytic Subunit Gamma (PPP1CC) is a multifunctional phosphatase involved in various biological processes; however, its role in chicken adipogenesis remains unclear. Objective: This study aimed to investigate the functional role and underlying mechanism of PPP1CC in chicken preadipocyte differentiation. Methods: Co-immunoprecipitation (Co-IP) and immunofluorescence assays were performed to determine the interaction between PPP1CC and NRF1 in DF1 cells. Bioinformatic analysis predicted potential NRF1 dephosphorylation sites targeted by PPP1CC, based on which NRF1 mutants mimicking dephosphorylation were constructed. Phos-tag SDS-PAGE combined with Western blot analysis were used to verify PPP1CC-mediated dephosphorylation of wild-type NRF1. Dual-luciferase reporter assays were used to evaluate the effect of PPP1CC-mediated dephosphorylation on NRF1-regulated PPARγ P1 promoter transcriptional activity. ChIP-qPCR was employed to assess the occupancy of NRF1 to the PPARγ P1 promoter upon PPP1CC overexpression. The effect of PPP1CC overexpression was assessed on preadipocyte differentiation using Oil Red O staining and marker gene expression analysis. Results: PPP1CC interacted with NRF1 in both the cytoplasm and nucleus of DF1 cells. Overexpression of PPP1CC significantly promoted NRF1 dephosphorylation during oleic acid-induced preadipocyte differentiation and increased endogenous NRF1 expression. Moreover, dual-luciferase assays showed that while PPP1CC strengthened the inhibitory effect of wild-type NRF1 on PPARγ P1 promoter transcriptional activity, it exerted no additional suppression on the already low activity mediated by the dephosphorylation-mimicking NRF1 mutants. Consistently, ChIP-qPCR results demonstrated that PPP1CC overexpression enhanced the occupancy of NRF1 to the PPARγ P1 promoter. Functional assays revealed that PPP1CC overexpression significantly inhibited chicken preadipocyte differentiation. Conclusions: PPP1CC interacts with NRF1 and promotes its dephosphorylation, enhancing NRF1-mediated suppression of PPARγ transcription and ultimately inhibiting chicken preadipocyte differentiation. These results identify the PPP1CC–NRF1–PPARγ regulatory axis and provide a potential molecular target for controlling fat deposition in broiler chickens. Full article

Rho GTPases are a group of guanosine triphosphate (GTP)-binding proteins with a relative molecular weight of about 20–30 kD, and 22 different Rho GTPases have been identified in mammalian cells, among which RhoA, Rac1 and Cdc42 are the most well-studied. Rho-associated coiled coil forming protein kinase (ROCK) is the most well-researched downstream effector of Rho GTPases. The Rho/ROCK signaling pathway widely participates in the reorganization of the cytoskeleton through cascade phosphorylation/dephosphorylation reactions and modulates cellular biological behaviors including cell adhesion, migration and phenotypic transformation. Abnormal activation of the Rho/ROCK signaling pathway is closely associated with the occurrence and progression of acute kidney injury, diabetic nephropathy, hypertension-related nephropathy and chronic allograft nephropathy, which contributes to podocyte injury, renal tubular epithelial-to-mesenchymal transition (EMT), mesangial cell proliferation and inflammatory infiltration in the kidney. This review focuses on the research progress and regulatory mechanisms of the Rho/ROCK signaling pathway in the above four major kidney diseases and discusses the therapeutic potential of targeting this pathway for kidney disease treatment, aiming to provide new insights for elucidating the pathogenesis of kidney diseases and developing novel therapeutic strategies. Full article

Fibrosis appears to be an out-of-control wound-healing response that drives a progressive formation of scar tissue in an organ. A key profibrotic cytokine, transforming growth factor beta-1 (TGF-β1), upregulates levels of the extracellular sialidase neuraminidase 3 (NEU3), and NEU3 in turn can activate latent TGF-β1 to release active TGF-β1 from the sequestering latency-associated peptide (LAP). In the mouse bleomycin model of pulmonary fibrosis, NEU3 is both necessary and sufficient for pulmonary fibrosis. In this report, we find that NEU3 protein levels increase both intracellularly and extracellularly in cultures of human lung fibroblasts within 5 min of TGF-β1 exposure. This effect is driven by an increase in translation and is independent of new transcription, supporting a model where TGF-β1 causes a pool of weakly translated NEU3 mRNA to increase translation. By participating in the feedback loop, latent TGF-β1 makes cells more sensitive to TGF-β1. LAP also stimulates NEU3 expression and acts synergistically with TGF-β1 to upregulate NEU3. The positive feedback loop is blocked by NEU3 inhibitors. The RNA helicase DEAD-box helicase 3 (DDX3) mediates NEU3 translation, and the DDX3 inhibitor RK-33 blocks the rapid upregulation of NEU3 by TGF-β1 and LAP. Exposure of cells to TGF-β1 but not LAP induces dephosphorylation of DDX3 within two minutes, suggesting that the mechanisms used by TGF-β1 and LAP to activate DDX3 to increase NEU3 levels may differ. Together, these results suggest that a rapid positive feedback loop involving TGF-β1, LAP, and NEU3 helps drive fibrosis. Full article

Protein phosphorylation and dephosphorylation reactions of intracellular molecules catalyzed by enzymes such as kinases and phosphatases are essential reactions in a lot of cellular functions such as intracellular signal transduction in living systems. The design and synthesis of artificial enzyme mimics are important research topics in bioorganic and bioinorganic chemistry. In this paper, we report on the construction of artificial phosphatases via the supramolecular self-assembly of compounds such as an amphiphilic bis(Zn²⁺-cyclen) (cyclen = 1,4,7,10-tetraazacyclododecane) complex, barbital derivatives modified with benzocrown ethers and boronophenyl groups, and a copper(II) ion in a two-phase solvent system. We have developed a hypothesis whereby a mono(4-nitrophenyl)phosphate (MNP) substrate coordinates to the Cu₂(µ-OH)₂ core in supramolecular complexes and is activated either by Lewis acidic units such as alkali metal (Li⁺, Na⁺ and K⁺)-benzocrown ether complexes or by boronophenyl moieties. The findings suggest that supramolecular phosphatase functionalized with a benzo-12-crown-4-Li⁺ complex shows a higher level of activity in the MNP hydrolysis of a two-phase solvent system compared with that of our previous supramolecular phosphatases in terms of hydrolysis activity and catalytic turnover. Full article

Chronic exposure to the cyanotoxin microcystin-LR is an emerging environmental driver of non-alcoholic fatty liver disease (NAFLD); however, the initiating molecular events at sub-lethal, environmentally relevant concentrations remain elusive. Current safety guidelines focus primarily on acute injury, potentially overlooking silent metabolic disruption. The present study investigates the early metabolic toxicity of chronic low-dose microcystin-LR (10 µg/L) in a 7-week rat model, specifically focusing on pre-symptomatic perturbations in lipid homeostasis. By integrating biochemical profiling with multivariate systems toxicology (LASSO and PLS-DA), we identified a specific phenotype of “Silent Hepatic Total Cholesterol Accumulation” (T-CHOL +16%, p = 0.01) occurring in the absence of systemic dyslipidemia or overt liver injury. Mechanistic analysis revealed a specific dual failure of cholesterol homeostasis, characterized by the paradoxical upregulation of the influx transporter Ldlr (LASSO coef +0.661) and the suppression of the efflux transporter Abcg1 (PLS1 loading −0.358). Crucially, Ldlr upregulation occurred despite the concomitant transcriptional downregulation of Srebp2 (Spearman ρ = −0.585), indicating a regulatory uncoupling mechanism. We propose that microcystin-LR-induced protein phosphatase 2A (PP2A) inhibition likely drives this uncoupling via a post-transcriptional override—possibly involving ERK/RSK-mediated Ldlr mRNA stabilization. Concurrently, this inhibition appears to block LXR-mediated Abcg1 expression through sustained AMPK hyperactivation resulting from the loss of dephosphorylation. These findings indicate liver-specific cholesterol accumulation as the critical first step of environmental NAFLD pathogenesis, suggesting that current WHO guidelines (1 µg/L) may require re-evaluation regarding metabolic safety. We propose the hepatic Ldlr/Abcg1 ratio as a potential early biomarker for revised risk assessment. Full article

Obesity is a major risk factor for heart failure and atrial fibrillation. This study investigated the effects of diet-induced obesity on the molecular and cellular mechanisms of cardiomyocyte contractility in the left and right atria (LA and RA). Female Wistar rats were fed a Western diet (WD) for 18 weeks. Sarcomere dynamics and calcium transients were measured in unloaded cardiomyocytes. Actin–myosin interactions and contractile protein phosphorylation were assessed via an in vitro motility assay and phosphoprotein-specific gel electrophoresis. WD-fed rats developed obesity, hypertension, and metabolic alterations in the absence of echocardiographic or histological evidence of cardiac remodeling or systolic dysfunction. In LA cardiomyocytes, contractile dysfunction was indicated by increased calcium transient amplitude coupled with reduced shortening amplitude and relengthening velocity. This functional impairment correlated with a slowed myosin cross-bridge cycle and dephosphorylation of cMyBP-C. In contrast, RA cardiomyocytes displayed only molecular changes in response to obesity, including altered phosphorylation of most sarcomeric proteins and a decelerated cross-bridge cycle, but showed no evident contractile dysfunction. Thus, an 18-week WD reflects the early stages of contractile impairment, where functional deficits are specific to the LA, while RA alterations are confined to the molecular level. Full article

Banana (Musa spp.) is a typical climacteric fruit. Xyloglucan endotransglucosylase/hydrolase (XTH) is a key factor regulating plant cell wall dynamic remodeling and participates in fruit ripening. To clarify the core physiological traits of banana ripening, four ripening stages of banana cultivar (Musa AAA ‘Minai No. 1’) fruits in the fully green stage (S1), green-yellow stage (S2), fully yellow stage (S3), and yellow with brown spots stage (S4) were used in this study’s experimental materials, to examine dynamic changes in key physiological–biochemical properties. The results showed that fruit firmness decreased continuously, starch content first increased then decreased, and soluble protein and total soluble solids (TSS) accumulated gradually during the ripening stages of banana fruits. Transcriptome analysis of the four stages found that there were 14,315 differentially expressed genes (DEGs) in S1 versus S4, the GO enrichment pathway is enriched in “protein dephosphorylation”, and the KEGG enrichment pathway is enriched in the “Protein processing in endoplasmic reticulum” and “Ubiquitin mediated proteolysis” pathways. The fruit ripening process involves the processing of numerous proteins. The heatmap revealed that MaXTH32.5 was significantly up-regulated during banana ripening and the result of RT-qPCR is consistent with the transcriptome data. A total of 989 XTH members across 16 Musa varieties of the XTH gene family were further identified. Among them, MaXTH32.5 localized at the chloroplast, and transient overexpression of MaXTH32.5 significantly reduced banana fruit firmness and may be involved in regulating ripening in banana fruits. This study indicated that the differential expression of XTH gene family members may regulate ripening-related processes in banana and MaXTH32.5 as a key candidate, providing insights into banana ripening mechanisms and a foundation for subsequent Musa XTH research. Full article

The deep fascia, traditionally regarded as a passive structural tissue, is now recognized as a metabolically and biologically active structure where biochemical signals and biomechanical forces interact to influence proprioception, pain, force transmission, and adaptation to mechanical load. In this study, the convergence point between Angiotensin II (Ang II) signaling via its receptor, Angiotensin type 1 receptor (AT1R), and the mechanosensor Yes-associated protein (YAP) was investigated in human fascial fibroblasts. The presence of angiotensin II (Ang II) receptors was confirmed in fibroblasts from the deep fascia, with the AT1 receptor being the most prevalent subtype. Short-term exposure to Ang II (15–30 min) caused YAP dephosphorylation and its translocation to the nucleus, indicating YAP activation. Notably, prolonged Ang II treatment (7 days) significantly increased the expression of fibrosis-related genes, including collagen types I and III (COL1A1, COL3A1), and hyaluronan binding protein 2 (HABP2). This gene expression was decreased by pretreatment with the AT1R antagonist irbesartan or the YAP inhibitor verteporfin. Additionally, Ang II promoted fibroblast proliferation/migration, key features of fibrotic progression, through AT1R-dependent pathways. These findings show that Ang II acts as both a biochemical and biomechanical signal in the deep fascia, activating YAP signaling and promoting fibrotic remodeling. Our results uncover a new Ang II–YAP pathway in fascial fibroblasts, offering potential targets for therapy in fibrosis and related conditions involving the deep fascia. Full article

Glucocorticoid therapy, using agents like dexamethasone (Dexa), often leads to muscle atrophy by increasing protein degradation via the ubiquitin–proteasome system while suppressing protein synthesis. Stigmasterol, a phytosterol with known bioactivities, has an unexplored role in muscle atrophy. This study investigated stigmasterol’s protective effects against Dexa-induced muscle atrophy and its impact on the FoxO3 and mTORC1 signaling pathways. Differentiated C2C12 myotubes were treated with Dexa (50 µM) ± stigmasterol (10 µM), and the morphology, viability, and protein levels in the FoxO3/MuRF1/MAFbx catabolic and mTOR/p70S6K/4E-BP1 anabolic signaling pathways were assessed. C57BL/6 mice received Dexa (20 mg/kg/day i.p.) ± stigmasterol (3 mg/kg/day oral) for 21 days, and the body/muscle mass, bone mineral density (BMD), fiber cross-sectional area (CSA), and muscle protein expression were measured. Stigmasterol (10 µM) was non-toxic and attenuated Dexa-induced reductions in myotube diameter and fusion in vitro, concurrent with suppressing Dexa-induced upregulation of FoxO3/MuRF1/MAFbx proteins and preventing the Dexa-induced dephosphorylation of mTOR/p70S6K/4E-BP1 proteins. In vivo, stigmasterol mitigated Dexa-induced losses in body weight, muscle mass, BMD, and fiber CSA. This protection was associated with attenuated upregulation of FoxO3 and MAFbx proteins in muscle tissue. Stigmasterol protected against Dexa-induced muscle atrophy in vitro and in vivo via modulation of the FoxO3–MAFbx catabolic pathway. These findings suggest stigmasterol inhibits excessive glucocorticoid-induced muscle protein breakdown. It therefore warrants further investigation as a potential therapeutic agent for glucocorticoid myopathy. Full article

Lipid metabolism plays a significant role in the regulation of various critical pathways within cells, where enhanced lipid metabolism is a hallmark of cancer cell metabolism. The Hippo signalling pathway poses as an important signalling pathway that governs tissue growth control and tumorigenesis. The effector of the Hippo signalling pathway, Yes-associated protein (YAP), serves as a central regulator for this growth control. Once a tissue develops to its correct size, YAP is phosphorylated and inactivated within the cytoplasm by the activation of the Hippo pathway, where its inactivation results in YAP nucleus translocation. This allows its dephosphorylation, modulating various cellular behaviours such as cellular proliferation and the inhibition of apoptosis. Moreover, it has been established that YAP is positively regulated by the extracellular matrix (ECM). The interplay between the Hippo signalling pathway, the ECM, and lipid metabolism, however, is not entirely clear. Thus, this study illustrates a novel link between the Hippo signalling pathway, the ECM, and lipid metabolism. Furthermore, the project identifies a novel ECM complex which is dependent upon lipids and regulates YAP in a positive manner. Full article

JC virus (JCV) replicates within the nuclei of glial cells in the human brain and causes progressive multifocal leukoencephalopathy. JCV possesses a small, circular, double-stranded DNA genome, divided into early and late protein-coding regions. The non-coding control region (NCCR) functions bidirectionally for both early and late genes, and the agnogene is located downstream of TCR and upstream of three capsid proteins in the late region. Previously, in cell culture systems, we demonstrated that these capsid proteins accumulate in intranuclear domains known as promyelocytic leukemia nuclear bodies (PML-NBs), where they assemble into virus-like particles (VLPs). To investigate the agnogene’s function, VLPs were formed in its presence or absence, and differential gene expression was analyzed using microarray technology. The results revealed altered expression of histone-modifying enzymes, including methyltransferases (EHMT1, PRMT7) and demethylases (KDM2B, KDM5C, KDM6B), as well as various kinases and phosphatases. Notably, CTDP1, which dephosphorylates the C-terminal domain of an RNA polymerase II subunit, was also differentially expressed. The changes were predominant in the presence of the agnogene. These findings indicate that the agnogene and/or its protein product likely influence epigenetic regulation associated with PML-NBs, which may influence cell cycle control. Consistently, in human brain tissue, JCV-infected glial cells displayed maintenance of a diploid chromosomal complement, likely through G2 arrest. The precise mechanism of this, however, remains to be elucidated. Full article

Stress granules (SGs) are dynamic membrane-less structures assembled in response to stress. The formation of stress granules in plants is poorly understood, especially the mechanism of mRNA recruitment. The problem of the specificity of mRNA interaction with stress granule proteins is unexplored. Oligouridylate binding protein 1B (UBP1B) is considered as the core element of plant SGs. In this study, we expressed the AtUBP1b protein from Arabidopsis thaliana in E. coli cells. Mass spectroscopic analysis showed that the AtUBP1b protein expressed in E. coli cells is phosphorylated at serine, threonine, and tyrosine residues. We also performed a de novo phosphorylation reaction in wheat germ extracts with the addition of radioactively labeled phosphorus and showed AtUBP1b phosphorylation in plant extracts. We hypothesized that phosphorylation or dephosphorylation of AtUBP1b in plant cells is a signal for protein binding to RNA. The purified protein was tested for its ability to bind to mRNA in vitro. In gel-shifting assays we demonstrated that AtUBP1b protein binds specifically to 5′-untranslated regions (5′UTR) of mRNA. When AtUBP1b was added to a cell-free wheat germ translation system, it exerted different effects on protein synthesis. We showed that AtUBP1b had a significant inhibitory effect on the expression of mRNAs containing 5′UTRs that were shown to bind to the protein in the gel-shifting reaction. Full article

The ultimate function of a protein is a summation of the activities of all its modules or domains. A major mechanism for regulating protein activity, besides modulation of its levels through translation or degradation, is covalent post-translational modification (PTM) of these modules, including phosphorylation and dephosphorylation of tyrosine, threonine, and/or serine residues. Phosphorylation is a fast, reversible, and highly specific mode of regulating protein function. Unlike proteins that are marked with other PTMs, phosphorylated proteins orchestrate an extensive network of protein interactions because of their ability to bind many protein partners. Protein phosphorylation is crucial for many cellular processes—signaling, transcription, and metabolism—because it precisely controls these processes in time and space. In this review, we will focus on signaling coordinated by tyrosine phosphorylation–dephosphorylation, specifically structural insights that govern the mechanism of recognition of phosphotyrosine (pY)-containing ligands by Src homology 2 (SH2) domains. We update the approaches used to target the SH2 domains and techniques applied in drug discovery, highlighting inhibitors that have reached clinical development. Full article

Cancer represents a leading cause of mortality globally, with its complex biological nature posing significant challenges for treatment. Central to cancer progression are molecular pathways that govern cellular function, among which protein phosphatase 2A (PP2A) plays a vital role. As a serine/threonine phosphatase, PP2A maintains cellular homeostasis by dephosphorylating a broad range of protein substrates and has emerged as a key tumor suppressor. However, PP2A activity can be physiologically inhibited by endogenous regulators such as the SE Translocation (SET) protein. Overexpression of SET has been associated with the loss of PP2A function, promoting hallmark features of cancer. Interestingly, targeting the PP2A/SET interaction has shown therapeutic potential. Indeed, inhibiting SET to reactivate PP2A may restore cellular regulation, induce apoptosis in tumor cells, and attenuate cancer progression. Research efforts have explored compounds such as the endogenous D-erythro-C18-ceramide and the drug fingolimod (FTY720), both known for their ability to reactivate PP2A. In this work, PP2A/SET complex models were generated through a computational approach and, using molecular docking, the interaction of potential SET inhibitors from a library of 26 alkoxy phenyl 1-propan-one derivatives (APPDs) was characterized. Additionally, absorption, distribution, metabolism, and excretion (ADME) predictions were performed to assess pharmacokinetic properties and therapeutic potential. Eventually, the predicted binding affinities were then correlated with biological data to assess the reliability of the models. These findings provide valuable insights into molecule–receptor interactions and lay the groundwork for developing inhibitors with encouraging therapeutic implications. Full article