Cellular Signal Transduction Mechanisms Research Articles

Targeting New Functions and Applications of Bacterial Two-Component Systems.

Two-component signal transduction systems (TCSs) are regulatory systems widely distributed in eubacteria, archaea, and a few eukaryotic organisms, but not in mammalian cells. A typical TCS consists of a histidine kinase and a response regulator protein. Functional and mechanistic studies on different TCSs have greatly advanced the understanding of cellular phosphotransfer signal transduction mechanisms. In this concept paper, we focus on the His-Asp phosphotransfer mechanism, the ATP synthesis function, antimicrobial drug design, cellular biosensors design, and protein allostery mechanisms based on recent TCS investigations to inspire new applications and future research perspectives.

Sir Michael John Berridge. 22 October 1938—13 February 2020

Sir Michael Berridge was a giant in the fields of physiology and biochemistry who, by his discovery in 1983 of inositol 1,4,5-trisphosphate (IP 3 ) as the ubiquitous intracellular messenger releasing Ca 2+ from intracellular stores, revolutionized our concepts of signal transduction mechanisms. Mike, as he was universally known, discovered one of the most important regulatory mechanisms in animal cells, involved in the control of virtually all bodily functions, including secretion, contraction and memory. Mike, working at the Department of Zoology at the University of Cambridge, personally identified IP 3 as one of the two initial products of hormone- or neurotransmitter-elicited inositol phospholipid breakdown and then, in collaboration with the research group led by Irene Schulz at the Max Planck Institute for Biophysics in Frankfurt, demonstrated directly the Ca 2+ -releasing effect of IP 3 in pancreatic acinar cells. Subsequently, in collaborations with research groups in Switzerland and the USA, Mike confirmed the Ca 2 + -releasing action of IP 3 in insulin-secreting cells, hepatocytes and photoreceptors. The IP 3 –Ca 2 + -releasing pathway became accepted amazingly quickly as one of the key elements of cellular signal transduction mechanisms and is now featured in virtually all textbooks of physiology and biochemistry. Mike was also a great synthesizer, who created an entirely new field, namely calcium signalling. Through his numerous, highly cited review articles, and his insightful keynote lectures at the most important biomedical congresses, he dominated this large and increasingly important research field for more than 30 years following his momentous 1983 discovery.

MUC1 and MUC16: critical for immune modulation in cancer therapeutics.

The Mucin (MUC) family, a range of highly glycosylated macromolecules, is ubiquitously expressed in mammalian epithelial cells. Such molecules are pivotal in establishing protective mucosal barriers, serving as defenses against pathogenic assaults. Intriguingly, the aberrant expression of specific MUC proteins, notably Mucin 1 (MUC1) and Mucin 16 (MUC16), within tumor cells, is intimately associated with oncogenesis, proliferation, and metastasis. This association involves various mechanisms, including cellular proliferation, viability, apoptosis resistance, chemotherapeutic resilience, metabolic shifts, and immune surveillance evasion. Due to their distinctive biological roles and structural features in oncology, MUC proteins have attracted considerable attention as prospective targets and biomarkers in cancer therapy. The current review offers an exhaustive exploration of the roles of MUC1 and MUC16 in the context of cancer biomarkers, elucidating their critical contributions to the mechanisms of cellular signal transduction, regulation of immune responses, and the modulation of the tumor microenvironment. Additionally, the article evaluates the latest advances in therapeutic strategies targeting these mucins, focusing on innovations in immunotherapies and targeted drugs, aiming to enhance customization and accuracy in cancer treatments.

Single-cell and bulk transcriptomics reveals M2d macrophages as a potential therapeutic strategy for mucosal healing in ulcerative colitis.

Mucosal healing is essential for treating ulcerative colitis (UC), which results from imbalanced macrophage polarization and dysregulated inflammatory responses. However, the mechanisms of cellular communication and signal transduction that regulate mucosal healing among macrophage subtypes require further investigation. We use bulk and single-cell RNA sequencing analysis to reveal that macrophage subtypes vary in different UC states. At the same time, chemokine and angiogenesis signaling is strongly associated with M2 macrophage's infiltrated proportion. To get more insight into subtypes of macrophages in mucosal healing, we divided macrophages into M1, M2b, and M2d macrophages. Based on the differentially expressed genes (DEGs) between M2d and M1 macrophages, KEGG and GO analysis highlights M2d macrophages' ability to alleviate inflammation and promote epithelial healing. Trajectory analysis revealed opposite differentiation of macrophage subsets between UC and healthy groups, with M1 and M2d macrophages coexisting in the same differentiation branch under UC conditions. Along the pseudotime axis, CCL3 and VEGFA expression increased in UC, while IL10RA remained stable in UC but increased in healthy controls. CellChat identified CCL3-CCR1 has strong communication between M1 and M2d macrophages, while the IL10 signaling pathway is activated explicitly in M2d macrophages to mitigate inflammation and promote epithelial healing. We also speculate that high levels of VEGFA activate endothelial cells expressing VEGFR and worsen inflammation. To conclude, we suggested IL10 and VEGF signaling in M2d macrophages as potential therapeutic targets for mucosal healing. However, it is necessary to establish reliable methods for isolating and purifying M2d macrophages before these targets can be effectively utilized.

Exploring Effect of P53 Signal Transduction on MMS by Use of Premature Termination Codon Strategy

Cellular signal transductions via protein-protein interactions are regulated by gene expression at the levels of transcription, translation and the post-translational modification. It is of important to dissect how cellular signal transductions are controlling cell cycles, growth, differentiation and apoptosis at the level of each gene expression. Current approaches to controlling cellular signal transduction are focused on modulating transcription, and these methods cannot precisely modulate cellular protein expression. Recently, we constructed a H1299 stable cell line harboring a p53R213X-GFP gene (i.e., H1299p53R213X), where the expression of the full-length p53 protein was silenced by a designed p53 premature termination codon (PTC) at the amino acid position of 213. We found that geneticin G418 was an efficient inducer for reading through PTC (Zhou et. al., ChemistrySelect, 3, 2018). In this work, we converted this PTC concept into an efficient strategy to modulate cellular protein translation and explored how p53 signaling enhanced the efficiency of anti-tumor agent, MMS. Our data indicated that the cell viability, cell cycle arrest and apoptosis of H1299p53R213X could be tuned and dissected, as the full-length p53 protein was controllably expressed by G418 induction in a dose-dependent manner. These phenomena became more significant when the H1299p53R213X cells were pre-treated with 200 μM of MMS. Therefore, our work not only provides a new strategy to explore cellular signal transduction mechanisms, but also provides a tool to investigate the correlation between p53 signaling transduction and anti-tumor drugs.

Mechanism of HMGB1\u2013RAGE in Kawasaki disease with coronary artery injury

BackgroundKawasaki disease (KD) is a common, yet unknown etiology disease in Asian countries, which causes acquired heart disease in childhood. It is characterized by an inflammatory acute febrile vasculitis of medium-sized arteries, particularly the coronary arteries. High-mobility group box-1 protein (HMGB1) is a non-histone chromosomal-binding protein present in the nucleus of eukaryotic cells, which contains 215 amino acid residues. Although the cellular signal transduction mechanisms of HMGB1 are currently unclear, the important role of the receptor for advanced glycation end-products (RAGE), the main receptor for HMGB1 has been reported in detail. The purpose of our study was to verify the mechanism and clinical significance of HMGB1-RAGE in coronary artery injury of Kawasaki disease.Methods52 blood samples of patients in KD were collected, and the coronary artery Z score was calculated according to the echocardiographic results. The Z score ≥ 2.0 was classified as coronary artery lesions (CAL); otherwise, it was no-coronary artery lesions (NCAL). In addition, the fever group and control group were set. Among them, the fever group were children with fever due to respiratory tract infection at the same time period as KD (heat peak ≥ 38.5 ℃). The normal group were children at a routine physical examination in the outpatient clinic of Nantong University and the physical examination center of the child care insurance, and there were no infectious diseases and heart diseases. The serum levels of HMGB1, RAGE, and NF-κB in each group were detected by ELISA. The animal model of KD was established using the New Zealand young rabbits. We used RT-qPCR/H&E staining/immunohistochemistry/ELISA and western blot to detect the level of HMGB1/RAGE and NF-κB.ResultsIn this study, we found that the HMGB1/RAGE/NF-κB axis was elevated in the serum of children with KD. In addition, an animal model of KD was subsequently prepared to examine the pathological changes of the coronary arteries. We found that the serum levels of HMGB1/RAGE/NF-κB in rabbits with KD were significantly higher than those of the control group. Moreover, the lumen diameter of the coronary artery was slightly enlarged, and the wall of the tube became thinner and deformed. In addition, the HMGB1/RAGE/NF-κB levels in the coronary artery were higher in the rabbits with KD in the acute phase.ConclusionsOn the whole, the findings of this study demonstrate that the expression of HMGB1/RAGE/NF-κB is altered at different stages of KD, suggesting that the HMGB1/RAGE/NF-κB signaling pathway plays an important role in vascular injury in KD. The results of this study may have important implications for the early warning of coronary artery lesions in KD.

Is Thiol-Disulphide Homeostasis an Indicative Marker in Prediction of Metastasis in Lung Cancer Patients.

Thiol/disulfide (SH/SS) homeostasis plays an essential and dynamic role in our body and in various cellular activities and pathways such as cell death, regulation of enzyme activities, mechanisms of transcription and cellular signal transduction. Lung cancer is the most commonly seen cancer type in the adult population. Therefore, prediction of metastases gains importance in this population. We included 150 patients with lung cancer who attended Kirikkale University Medical Faculty Hospital between June 2017 and June 2018. Our purpose was to evaluate whether metastases can be predicted in lung cancer patients by testing SH/SS homeostasis as a novel and easily applicable biochemical test. The mean age of the patients was 63.8 ± 8.1 (41 - 71) years. Advanced stage lung cancer, adenocarcinoma, squamous-cell and small cell lung cancers, and other types were detected in 54.7%, 42.7%, 41.3%, 13.3%, and 2.7% of the patients, respectively. SS values of the patients with advanced stage lung cancer were higher than in patients with early stage lung cancer (p < 0.001). It was determined that the patients with advanced stage lung cancer had statistically significantly higher mean values of SS, SS/SH (%), and SS/total SH (%) than patients with early stage lung cancer and that a statistically significantly lower mean value of SH/total SH (%) was found in advanced stage compared with early stage lung cancer patients. No statistically significant difference was found between the patient groups with advanced and early stage lung cancer regarding mean values of native SH and total SH levels. It can be concluded that SH/SS parameters may vary in advanced and early stage lung cancer patients; however, further studies should be conducted with SH/SS parameters in order to use them as indicators of cancer severity in lung cancer patients.

Modular Thermal Control of Protein Dimerization.

Protein-protein interactions and protein localization are essential mechanisms of cellular signal transduction. The ability to externally control such interactions using chemical and optogenetic methods has facilitated biological research and provided components for the engineering of cell-based therapies and materials. However, chemical and optical methods are limited in their ability to provide spatiotemporal specificity in light-scattering tissues. To overcome these limitations, we present "thermomers", modular protein dimerization domains controlled with temperature-a form of energy that can be delivered to cells both globally and locally in a wide variety of in vitro and in vivo contexts. Thermomers are based on a sharply thermolabile coiled-coil protein, which we engineered to heterodimerize at a tunable transition temperature within the biocompatible range of 37-42 °C. When fused to other proteins, thermomers can reversibly control their association, as demonstrated via membrane localization in mammalian cells. This technology enables remote control of intracellular protein-protein interactions with a form of energy that can be delivered with spatiotemporal precision in a wide range of biological, therapeutic, and living material scenarios.

Simultaneous Quantification of Protein Expression and Modifications by Top-down Targeted Proteomics: A Case of the Sarcomeric Subproteome

Determining changes in protein expression and post-translational modifications (PTMs) is crucial for elucidating cellular signal transduction and disease mechanisms. Conventional antibody-based approaches have inherent problems such as the limited availability of high-quality antibodies and batch-to-batch variation. Top-down mass spectrometry (MS)-based proteomics has emerged as the most powerful method for characterization and quantification of protein modifications. Nevertheless, robust methods to simultaneously determine changes in protein expression and PTMs remain lacking. Herein, we have developed a straightforward and robust top-down liquid chromatography (LC)/MS-based targeted proteomics platform for simultaneous quantification of protein expression and PTMs with high throughput and high reproducibility. We employed this method to analyze the sarcomeric subproteome from various muscle types of different species, which successfully revealed skeletal muscle heterogeneity and cardiac developmental changes in sarcomeric protein isoform expression and PTMs. As demonstrated, this targeted top-down proteomics platform offers an excellent 'antibody-independent' alternative for the accurate quantification of sarcomeric protein expression and PTMs concurrently in complex mixtures, which is generally applicable to different species and various tissue types.

Intermolecular Acyl-Transfer Reactions in Molecular Crystals

It is far more difficult to recognize and predict the chemical reactions that a molecule of an organic compound can undergo in crystalline (solid) state as compared to the solution state (the "organic functional group" approach), since the published data on solid-state structure-reactivity investigations and correlations are scant. The discovery of the first intermolecular acyl-transfer reaction in molecular crystals of racemic 2,4-di- O-benzoyl- myo-inositol-1,3,5-orthoformate (DiBz) during our attempts to develop methods for the synthesis of phosphoinositols, motivated us to find other molecular crystals capable of supporting similar reactions. Small changes to the molecular structure of DiBz yielded analogues with different crystal structures which showed varying degrees of acyl transfer reactivity as compared to the crystals of DiBz. A systematic investigation of the structures, polymorphism, cocrystallization behavior, and the corresponding reactivity of these crystals allowed us to correlate the acyl transfer reactivity with their structures and inherent noncovalent interactions and provided crucial insights into the mechanism of these reactions. Polymorphs or cocrystals of these compounds exhibited dissimilar reactivities due to differences in the molecular conformation and/or arrangements in their crystals. The knowledge of phase transitions between polymorphs enabled us to control and tune the reactivity in the solid state. We could identify three conditions essential for intermolecular acyl transfer: (i) favorable relative geometry of the electrophile (ester C═O) and the nucleophile (OH), (ii) noncovalent interactions (C-H···π) between the reacting molecules which help in maintaining the facility and specificity of the reaction, and (iii) the presence of channels in the lattice which enable propagation of the reaction in the crystal. Based on this supramolecular structure-reactivity correlation, we identified other molecular crystals (composed of molecules of widely different molecular structure from that of DiBz) from a survey of the Cambridge Structural Database (CSD) and predicted their acyl transfer reactivity. The increased availability of user-friendly modern X-ray diffractometers and related software has enabled efficient collection, analysis and interpretation of single crystal X-ray diffraction data, essential for such studies. The rapidly expanding CSD facilitates the identification of crystals with similar structures and reactivity patterns. In a wider perspective, facile reactions in molecular crystals fascinate chemists because these reactions usually exhibit unique product selectivity and have the potential to be developed as sustainable green reactions. We are optimistic that similar approaches for the study of other group transfer reactions in molecular crystals would augment and widen the scope of chemical reactions in molecular crystals in particular and the solid state in general. The ability to predict the reactivity of molecules in their crystals could find applications in organic synthesis, material science and industry. Realization of the involvement of inositol derivatives in cellular processes led to the discovery of cellular signal transduction mechanisms. The ability of inositol derivatives to support facile acyl-transfer reactions in the crystalline state might well have opened a new avenue for research in the area of organic solid-state reactions.

An Integrated Double-Filtration Microfluidic Device for Detection of Extracellular Vesicles from Urine for Bladder Cancer Diagnosis.

Extracellular vesicles (EVs) are present in a variety of bodily fluids and they play an important role in cellular communications and signal transduction mechanisms. Studies have shown that the number of EVs and EV-associated biomarkers (i.e., proteins, nucleic acids and lipids) can be used to aid clinical diagnosis. Although ultracentrifugation is commonly used for EV isolation, it is not practical for clinical settings. Here, we developed an integrated double-filtration device that isolated and enriched EVs from urine, and subsequently detected/quantified EVs from urine via microchip ELISA. Results showed that the concentration of EVs was significantly elevated compared to healthy controls. Receiver operating characteristic analysis demonstrated that this integrated EV quantification device had a sensitivity of 81.3% at a specificity of 90% (16 bladder cancer patients and eight healthy controls). Thus, this integrated device shows great potential to supplement urine cytology for diagnosis of bladder cancer in point-of-care (POC) settings.

Interstitial cells of Cajal integrate excitatory and inhibitory neurotransmission with intestinal slow-wave activity

The enteric nervous system contains excitatory and inhibitory neurons, which control contraction and relaxation of smooth muscle cells as well as gastrointestinal motor activity. Little is known about the exact cellular mechanisms of neuronal signal transduction to smooth muscle cells in the gut. Here we generate a c-Kit(CreERT2) knock-in allele to target a distinct population of pacemaker cells called interstitial cells of Cajal. By genetic loss-of-function studies, we show that interstitial cells of Cajal, which generate spontaneous electrical slow waves and thus rhythmic contractions of the smooth musculature, are essential for transmission of signals from enteric neurons to gastrointestinal smooth muscle cells. Interstitial cells of Cajal, therefore, integrate excitatory and inhibitory neurotransmission with slow-wave activity to orchestrate peristaltic motor activity of the gut. Impairment of the function of interstitial cells of Cajal causes severe gastrointestinal motor disorders. The results of our study show at the genetic level that these disorders are not only due to loss of slow-wave activity but also due to disturbed neurotransmission.

Modeling the Mitogen Activated Protein (MAP)-Kinase Pathway Using Ordinary Differential Equations

Mitogen Activated Protein (MAP) Kinase pathway is central to comprehend the key cellular signal transduction mechanisms in animal physiology, including human beings. Modeling MAP Kinase pathway has two main applications: deciphering a transient response of three main components (MAPKKK, MAPKK and MAPK) to regulate signaling and utilizing the models to make it behave as a potential drug target. The current study develops a mathematical representation for this transient cell-signaling pathway, based on a simple modular approach to structure and model a three-tier cascade. Based on assumptions from existing literature, ordinary differential equations have been formulated to express the concentrations of MAPKKK, MAPKK and MAPK as a function of time. Finally, the transient responses of the deduced concentrations of these components are analyzed to understand the pathway behavior and some interesting results are obtained by analyzing the temporal evolutions of the concentrations of the six components involved in the pathway. We conclude that the transient behaviour of MAPKKK can be captured with first order ordinary differential equations. Some anomalous behavior is observed in case of MAPKK and MAPK. In this perspective, future work can be designed to regulate the MAP Kinase signaling by taking Michaeli-Menten kinetics into consideration and make complex models to get more accurate results.

Improved genetically-encoded, FlincG-type fluorescent biosensors for neural cGMP imaging.

Genetically-encoded biosensors are powerful tools for understanding cellular signal transduction mechanisms. In aiming to investigate cGMP signaling in neurones using the EGFP-based fluorescent biosensor, FlincG (fluorescent indicator for cGMP), we encountered weak or non-existent fluorescence after attempted transfection with plasmid DNA, even in HEK293T cells. Adenoviral infection of HEK293T cells with FlincG, however, had previously proved successful. Both constructs were found to harbor a mutation in the EGFP domain and had a tail of 17 amino acids at the C-terminus that differed from the published sequence. These discrepancies were systematically examined, together with mutations found beneficial for the related GCaMP family of Ca2+ biosensors, in a HEK293T cell line stably expressing both nitric oxide (NO)-activated guanylyl cyclase and phosphodiesterase-5. Restoring the mutated amino acid improved basal fluorescence whereas additional restoration of the correct C-terminal tail resulted in poor cGMP sensing as assessed by superfusion of either 8-bromo-cGMP or NO. Ultimately, two improved FlincGs were identified: one (FlincG2) had the divergent tail and gave moderate basal fluorescence and cGMP response amplitude and the other (FlincG3) had the correct tail, a GCaMP-like mutation in the EGFP region and an N-terminal tag, and was superior in both respects. All variants tested were strongly influenced by pH over the physiological range, in common with other EGFP-based biosensors. Purified FlincG3 protein exhibited a lower cGMP affinity (0.89 μM) than reported for the original FlincG (0.17 μM) but retained rapid kinetics and a 230-fold selectivity over cAMP. Successful expression of FlincG2 or FlincG3 in differentiated N1E-115 neuroblastoma cells and in primary cultures of hippocampal and dorsal root ganglion cells commends them for real-time imaging of cGMP dynamics in neural (and other) cells, and in their subcellular specializations.

Studies on the Benefits for Human Health on Fermented Seafood and the Development of Freshness Maintenance Technique of Fish

I and my students have developed some fish sauces made from puffer, whale and sea urchin gonad as the local specialties of Shimonoseki city in west Japan. These sauces were commercialized. Antioxidant actives of these sauces were measured by using chemiluminescence, ESR (electron spin resonance), ORAC (oxygen radical absorbance capacity) and HORAC (hydroxyl radical averting capacity) methods. As the results, these sauces indicated the high antioxidant activities. Furthermore, these sauces were researched by the next-generation food functional estimation method, i.e., the new simultaneous measurement method using cellular signal transduction mechanisms. This method means the simultaneous measurement of chemiluminescence and fluorescence by LED light indicating superoxide anion radical generation and intracellular calcium ion concentration, respectively, of neutrophil-like HL60 culture cells. It was found that some sauces indicated the anti-inflammatory activity in addition to antioxidant activity. On the other hand, I and co-researchers investigated the supply of high quality frozen raw fish by a quick freezing method using alcohol brine. The whole body of Japanese horse mackerel was used. Alcohol brine freezing at -25°C was compared with air freezing at -20°C. Quality of fish meat was analyzed using K value as an indicator of freshness by HPLC, pH, TBARS value as an indicator of lipid oxidation, remaining ethanol by GC/MS and sensory test. As the results, it was indicated that the fish meat frozen quickly by alcohol brine method was superior to that by air freezing.

Meredys, a multi-compartment reaction-diffusion simulator using multistate realistic molecular complexes

BackgroundMost cellular signal transduction mechanisms depend on a few molecular partners whose roles depend on their position and movement in relation to the input signal. This movement can follow various rules and take place in different compartments. Additionally, the molecules can form transient complexes. Complexation and signal transduction depend on the specific states partners and complexes adopt. Several spatial simulator have been developed to date, but none are able to model reaction-diffusion of realistic multi-state transient complexes.ResultsMeredys allows for the simulation of multi-component, multi-feature state molecular species in two and three dimensions. Several compartments can be defined with different diffusion and boundary properties. The software employs a Brownian dynamics engine to simulate reaction-diffusion systems at the reactive particle level, based on compartment properties, complex structure, and hydro-dynamic radii. Zeroth-, first-, and second order reactions are supported. The molecular complexes have realistic geometries. Reactive species can contain user-defined feature states which can modify reaction rates and outcome. Models are defined in a versatile NeuroML input file. The simulation volume can be split in subvolumes to speed up run-time.ConclusionsMeredys provides a powerful and versatile way to run accurate simulations of molecular and sub-cellular systems, that complement existing multi-agent simulation systems. Meredys is a Free Software and the source code is available at http://meredys.sourceforge.net/.

Cellular signaling and factors involved in Müller cell gliosis: Neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Körperliches Training und zelluläre Anpassung des Muskels

Resistance training and to a lesser extent endurance training are capable of enhancing protein synthesis in skeletal muscle via various signaling pathways. Additionally, the expression of muscle fiber types responds to different regimes of training stimuli and immobilization as characterized by changes in myosin heavy chain isoforms (I<-->IIA<-->IIX). Eccentric resistance training has been shown to be highly efficient in inducing sarcomeric protein assembly in the longitudinal orientation of muscle cells. However, concentric contractions lead to a hypertrophic response (increased fiber diameter) in muscle which can still be activated in old age. The central signaling pathway to mediate the elevation of protein synthesis in response to training is the mTOR pathway, which is also stimulated by free amino acids. Moreover, adaptation to endurance training is mediated by the calcium-calcineurin-NFATc1 pathway which is strongly activated by the calcium transients involved in the muscle contraction process. High contraction frequency and long duration of training sessions are essential for activation and maintenance of fiber type I expression as well as for induction of transformation of type II into type I fibers. Endurance training sessions should therefore be longer than 30 min and dominated by periods of high frequency contractions. A further factor in the muscular response to training includes the recruitment and integration of satellite cells into muscle fibers. Satellite cells can respond to muscular stretch, activity and injury with increased proliferation and can later be integrated into muscle fibers. Therefore, new myonuclei are available to enhance mRNA synthesis and protein expression in muscle cells. New understanding of the cellular mechanisms of signal transduction in muscle in response to training, bed rest and ageing will help to optimize training and interventions in an ageing population.

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

Identification of protein-protein interactions is crucial for unraveling cellular processes and biochemical mechanisms of signal transduction. Here we describe, for the first time, the application of the tandem affinity purification (TAP) and LC-MS method to the characterization of protein complexes from transgenic mice. The TAP strategy developed in transgenic mice allows the emplacement of complexes in their physiological environment in contact with proteins that might only be specifically expressed in certain tissues while simultaneously ensuring the right stoichiometry of the TAP protein versus their binding partners and represents a novelty in proteomics approaches used so far. Mouse lines expressing TAP-tagged 14-3-3zeta protein were generated, and protein interactions were determined. 14-3-3 proteins are general regulators of cell signaling and represent up to 1% of the total brain protein. This study allowed the identification of almost 40 novel 14-3-3zeta-binding proteins. Biochemical and functional characterization of some of these interactions revealed new mechanisms of action of 14-3-3zeta in several signaling pathways, such as glutamate receptor signaling via binding to homer homolog 3 (Homer 3) and in cytoskeletal rearrangements and spine morphogenesis by binding and regulating the activity of the signaling complex formed by G protein-coupled receptor kinase-interactor 1 (GIT1) and p21-activated kinase-interacting exchange factor beta (betaPIX).

Computational methods in drug design: Modeling G protein-coupled receptor monomers, dimers, and oligomers

G protein-coupled receptors (GPCRs) are membrane proteins that serve as very important links through which cellular signal transduction mechanisms are activated. Many vital physiological events such as sensory perception, immune defense, cell communication, chemotaxis, and neurotransmission are mediated by GPCRs. Not surprisingly, GPCRs are major targets for drug development today. Most modeling studies in the GPCR field have focused upon the creation of a model of a single GPCR (ie, a GPCR monomer) based upon the crystal structure of the Class A GPCR, rhodopsin. However, the emerging concept of GPCR dimerization has challenged our notions of the monomeric GPCR as functional unit. Recent work has shown not only that many GPCRs exist as homo- and heterodimers but also that GPCR oligomeric assembly may have important functional roles. This review focuses first on methodology for the creation of monomeric GPCR models. Special emphasis is given to the identification of localized regions where the structure of a GPCR may diverge from that of bovine rhodopsin. The review then focuses on GPCR dimers and oligomers and the bioinformatics methods available for identifying homo- and heterodimer interfaces.