Cell Signal Transduction Processes Research Articles

High Dietary Intake of Iron Might Be Harmful to Atrial Fibrillation and Modified by Genetic Diversity: A Prospective Cohort Study.

Some studies suggest an association between iron overload and cardiovascular diseases (CVDs). However, the relationship between dietary iron intake and atrial fibrillation (AF) remains uncertain, as does the role of genetic loci on this association. The study involved 179,565 participants from UK Biobank, tracking incident atrial fibrillation (AF) cases. Iron intake was categorized into low, moderate, and high groups based on dietary surveys conducted from 2009 to 2012. The Cox regression model was used to estimate the risk of AF in relation to iron intake, assessing the hazard ratio (HR) and 95% confidence interval (95% CI). It also examined the impact of 165 AF-related and 20 iron-related genetic variants on this association. Pathway enrichment analyses were performed using Metascape and FUMA. During a median follow-up period of 11.6 years, 6693 (3.97%) incident AF cases were recorded. A total of 35,874 (20.0%) participants had high iron intake. High iron intake was associated with increased risk of AF [HR: 1.13 (95% CI: 1.05, 1.22)] in a fully adjusted model. Importantly, there were 83 SNPs (11 iron-related SNPs) that could enhance the observed associations. These genes are mainly involved in cardiac development and cell signal transduction pathways. High dietary iron intake increases the risk of atrial fibrillation, especially when iron intake exceeds 16.95 mg. The association was particularly significant among the 83 SNPs associated with AF and iron, the individuals with these risk genes. Gene enrichment analysis revealed that these genes are significantly involved in cardiac development and cell signal transduction processes.

Transcriptomic Analysis of mRNA Expression Profiles in the Microglia of Mouse Brains Infected with Rabies Viruses of Varying Virulence.

Rabies is a lethal encephalitis caused by the rabies virus (RABV) with a fatality rate near 100% after the onset of clinical symptoms in humans and animals. Microglia are resident immune cells in the central nervous system. Few studies have been conducted on the functional role of microglia in RABV infection. Here, we performed a transcriptomic analysis of mRNA expression profiles in the microglia of mouse brains intracerebrally infected with RABV. We successfully isolated single microglial cells from the mouse brains. The survival rate of dissociated microglial cells was 81.91%-96.7%, and the purity was 88.3%. Transcriptomic analysis revealed 22,079 differentially expressed mRNAs identified in the microglia of mouse brains infected with RABV strains (rRC-HL, GX074, and CVS-24) of varying virulence at 4 and 7 days post-infection (dpi) compared to the control group. The numbers of DEGs versus the control at 4 and 7 dpi in mice infected with rRC-HL, GX074, and CVS-24 were 3622 and 4590, 265 and 4901, and 4079 and 6337. The GO enrichment analysis showed that response to stress, response to external stimulus, regulation of response to stimulus, and immune system process were abundant during RABV infection. The KEGG analysis indicated that the Tlr, Tnf, RIG-I, NOD, NF-κB, MAPK, and Jak-STAT signaling pathways were involved in RABV infection at both 4 and 7 dpi. However, some phagocytosis and cell signal transduction processes, such as endocytosis, p53, phospholipase D, and oxidative phosphorylation signaling pathways, were only expressed at 7 dpi. The involvement of the Tnf and Tlr signaling pathways prompted us to construct a protein-protein interaction (PPI) network of these pathways. The PPI revealed 8 DEGs, including Mmp9, Jun, Pik3r1, and Mapk12. Notably, Il-1b interacted with Tnf and Il-6 with combined scores of 0.973 and 0.981, respectively. RABV causes significant changes in mRNA expression profiles in the microglia in mice. 22,079 differentially expressed mRNAs were identified in the microglia of mice infected with RABV strains of varying virulence at 4 and 7 dpi. The DEGs were evaluated using GO, KEGG, and PPI network analysis. Many immune pathways were up-regulated in RABV-infected groups. The findings will help elucidate the microglial molecular mechanisms of cellular metabolism dysregulated by RABV and may provide important information for investigating RABV pathogenesis and therapeutic methods.

MoRts1, a regulatory subunit of PP2A, is required for fungal development and pathogenicity of Magnaporthe oryzae

Protein phosphatase 2 A (PP2A) is a major heterotrimeric serine/threonine protein phosphatase comprised of three subunits, including structural subunits (A), regulatory subunits (B), and catalytic subunits (C). PP2A has been widely shown to involve in a series of cell signal transduction processes such as cell metabolism, cell cycle regulation, DNA replication, gene transcription and protein translation in yeast and mammalian. However, the roles of PP2A in pathogenic fungi Magnaporthe oryzae still remain unclear. We here found that MoRts1, a gene encoding B regulatory subunit of PP2A homologous to Saccharomyces cerevisiae Rts1, showed up-regulated transcription during conidia and initially infectious stage. Subcellular localization revealed that MoRts1-eGFP was localized to the cytoplasm and septum. Targeted disruption of MoRts1 leads to a reduction of mycelial growth and sporulation, as well as the defects of hydrophobicity, melanin pigmentation and cell wall integrity (CWI). The MoRts1 mutants were less pathogenic to the host plants, compared to the Ku80 strain, and the transcriptional levels of several pathogenicity-related Rho GTPase genes, including MoCdc42, MoRho2, MoRho3, MoRho4, MoRhoX and MoRac1, were significantly decreased in the MoRts1 mutants. Besides, two splicing variants of MoRts1 with unique functions of regulating the growth and pathogenicity were identified, and the B56 domain is vital for determining the sporulation and pathogenicity of M. oryzae. Furthermore, MoRts1 was identified to interact with PP2A catalytic subunit MoPPG1 in vivo in M. oryzae. In summary, our results showed that MoRts1 is an important regulator contributing to the fungal development, and pathogenicity of M. oryzae.

Protein Kinases in Hematological Disorders.

Cell signaling is an important part of the complex system of molecular communication that governs basic cellular activities and coordinates cell cycle machinery. Pathological alterations in the cellular information processing may be responsible for the diseases such as cancer. Numerous diseases may be treated effectively via the pharmacological management of cellular signaling. Protein kinases (PK) have significantly important roles in the cell signal transduction process. Protein kinases phosphorylate serine, threonine, tyrosine and histidine amino acids in a wide variety of molecular networks. Two main PK groups are distinguished; serine/threonine kinase and tyrosine kinases. MAPK (mitogen-activated protein kinases), ERK, EGFR (epidermal growth factor receptor), src, abl, FAK (focal adesion kinase), and JAK (janus family kinase) are considered as the main PK molecular networks. Protein kinases are closely related to the pathobiology of hematologic neoplastic disorders. For instance; JAKV617F point mutation-causing polycythemia vera and essential thrombocytosis occur at the position 617 in the JH2 domain of the JAK2 gene. The protein kinase inhibitor drugs targeting specific kinase molecules have already been developed and widely used in the field of Clinical Hematology. The existence of a local renin-angiotensin system (RAS) specific to the hematopoietic bone marrow (BM) microenvironment had been proposed two decades ago. Local BM RAS is important in hematopoietic stem cell biology and microenvironment. There are interactions among the local BM RAS and PK. For example, ACE2-ang(1-7)-Mas axis inhibits p38 MAPK/NF-КB signaling pathway. The Local BM RAS may have a role in the effect on PK in this biological spectrum. The aim of this review is to outline the functions of PKs in the pathobiology of hematologic neoplastic disorders.

Dampening of neurotransmitter action: molecular similarity within the melatonin structure.

Melatonin initiates physiologic and therapeutic responses in various tissues through binding to poorly defined MT receptors regulated by G-proteins and purine nucleotides. Melatonin's interaction with other G-protein regulated receptors, including those of serotonin, is unclear. This study explores the potential for the interaction of melatonin with nucleotide and receptor ligand structures. The study uses a computational program to investigate relative molecular similarity by the comparative superimposition and quantitative fitting of molecular structures to adenine and guanine nucleotide templates. A minimum energy melatonin conformer replicates the nucleotide fits of ligand structures that regulate Gαi and Gαq proteins via serotonin, dopamine, opioid, α-adrenoceptor, and muscarinic receptor classes. The same conformer also replicates the nucleotide fits of ligand structures regulating K+ and Ca2+ ion channels. The acyl-methoxy distance within the melatonin conformer matches a carbonyl-hydroxyl distance in guanine nucleotide. Molecular similarity within the melatonin and ligand structures relates to the established effects of melatonin on cell receptors regulated by purine nucleotides in cell signal transduction processes. Pharmacologic receptor promiscuity may contribute to the widespread effects of melatonin.

Loss of phospholipase C δ1 impairs keratinocyte differentiation and epidermal barrier

Phospholipase C (PLC) is a key enzyme in phosphoinositide turnover, an important signal transduction process in cells. PLC activation leads to various cellular responses through mobilization of intracellular calcium ion and protein kinase C activation. There are 13 PLC isozymes in mammals. Among them, one of PLC isozymes, PLCδ1 is abundantly expressed in differentiated layers of epidermis, suggesting that PLCδ1 plays important roles in epidermal differentiation. In this study, we examined whether loss of PLCδ1 affected differentiation of human keratinocyte. siRNA-mediated silencing of PLCδ1 revealed that PLCδ1-deficient organotypic skin culture showed decreased intensity of lypophilic dye staining in the stratum corneum. In addition, filaggrin showed broader expression in the stratum corneum of PLCδ1-deficient organotypic skin culture by immunohistochemistry. Furthermore, silencing of PLCδ1 resulted in abnormal tight junction (TJ) formation in human primary keratinocytes. Since stratum corneum lipids, filaggrin, and TJ play critical roles in formation and maintenance of the cutaneous barrier, we investigated whether loss of PLCδ1 affected barrier functions by lucifer yellow permeability assay. Lucifer yellow permeability was enhanced in PLCδ1-deficient organotypic skin culture, indicating that outside-inside barrier was impaired in PLCδ1-deficient organotypic skin culture. Taken together, our results indicate that loss of PLCδ1 disturbed keratinocyte differentiation and epidermal barrier.

CD26-mediated induction of EGR2 and IL-10 as potential regulatory mechanism for CD26 costimulatory pathway.

CD26 is associated with T cell signal transduction processes as a costimulatory molecule, and CD26(+) T cells have been suggested to be involved in the pathophysiology of diverse autoimmune diseases. Although the cellular and molecular mechanisms involved in CD26-mediated T cell activation have been extensively evaluated by our group and others, potential negative feedback mechanisms to regulate CD26-mediated activation still remain to be elucidated. In the present study, we examine the expression of inhibitory molecules induced via CD26-mediated costimulation. We show that coengagement of CD3 and CD26 induces preferential production of IL-10 in human CD4(+) T cells, mediated through NFAT and Raf-MEK-ERK pathways. A high level of early growth response 2 (EGR2) is also induced following CD26 costimulation, possibly via NFAT and AP-1-mediated signaling, and knockdown of EGR2 leads to decreased IL-10 production. Furthermore, CD3/CD26-stimulated CD4(+) T cells clearly suppress proliferative activity and effector cytokine production of bystander T cells in an IL-10-dependent manner. Taken together, our data suggest that robust CD26 costimulatory signaling induces preferential expression of EGR2 and IL-10 as a potential mechanism for regulating CD26-mediated activation.

Synthesis of [ 11C]Iressa as a new potential PET cancer imaging agent for epidermal growth factor receptor tyrosine kinase

Iressa (Gefitinib) is an orally active inhibitor of epidermal growth factor receptor tyrosine kinase (EGFR-TK) involved in cell signal transduction processes critical to proliferation, apoptosis, repair, and angiogenesis of cancer cells. [ 11C]Iressa was first designed and synthesized as a new potential positron emission tomography (PET) cancer imaging agent for EGFR-TK in 30–40% radiochemical yield with 4.0–6.0 Ci/μmol specific activity at end of bombardment (EOB).

Alterations in lens protein tyrosine phosphorylation and phosphatidylinositol 3-kinase signaling during selenite cataract formation

Purpose. Protein tyrosine phosphorylation is an important event in the cell signal transduction process. Phosphatidylinositol-3kinase (PI-3K) is an intracellular signal mediator and plays a key role in many cellular functions. In this study we have examined the changes in lens protein tyrosine phosphorylation and its impact on phosphatidylinositol 3-kinase (PI-3K) signaling during selenite cataract development. Methods. Cataract was induced in 10 days old rat pups by a single sub-cutaneous injection of sodium selenite (30µM/Kg body weight) and lenses were collected at different stages of cataract development. Immunoprecipitation and Western immunoblotting were employed to determine protein tyrosine phosphorylation, PI-3K activity and protein in lens cell extracts. Tyrosine kinase activity in lens membrane preparations was assayed in the presence of a synthetic substrate peptide and [ 32 P]ATP. Results. Protein tyrosine phosphorylation in the lens was disrupted before the onset of cataract. A decrease in tyrosine phosphorylation of lens proteins was observed within 2–3 days of selenite injection (pre-cataract stage). The effect was much more prominent with the progression of cataract. The decrease in protein tyrosine phosphorylation correlated with the decrease in tyrosine kinase activity associated with the lens membrane fraction. Stimulation of normal rat lenses in organ culture with insulin and IGF-1 caused an increase in the phosphorylation of proteins, whose tyrosine phosphorylation status appeared to be diminished during cataract development. Insulin and IGF-1 also stimulated rat lens PI-3K activity. While there was no change in total PI-3K activity during the onset of cataract, the activity of PI-3K associated with tyrosine phosphorylated proteins decreased markedly in pre-cataract lenses. Further, the ability of IGF-1 to stimulate PI-3K activity was significantly reduced in lens epithelial cells treated with selenium. Conclusions. These studies show that signaling events involving the protein tyrosine phosphorylation process and activation of PI-3K are altered during selenite cataract formation and implicate defects in signal transduction mechanisms as contributing factors in the development of cataract.

A non-linear circuit for simulating OHC of the cochlea

In the present paper, referring to known characteristics of the outer hair cells functioning in the cochlea of the inner ear, a functional model of the outer hair cells is constructed. It consists of a linear feed-forward circuit and a non-linear positive feedback circuit. The feed-forward circuit reflects the contribution of local basilar and tectorial membrane areas and passive outer hair cells’ physical parameters to the forming of low-selectivity resonance characteristics. The non-linear positive feedback circuit reflects the non-linear outer hair cell signal transduction processes and the active role of efferents from the medial superior olive in altering circuit sensitivity and selectivity. Referring to an analytical description of the circuit model and computer simulation results, an explanation is given over the biological meaning of the outer hair cells’ non-linearities in signal transduction processes and the role of the non-linearities in achieving the following: signal compression, the dependency of circuit sensitivity and frequency selectivity upon the input signal amplitude, the compatibility of high-frequency selectivity and short transient response of the biological filtering circuits.

EXPOSURE TO 50 HZ ELECTROMAGNETIC FIELDS INDUCES THE PHOSPHORYLATION AND ACTIVITY OF STRESS-ACTIVATED PROTEIN KINASE IN CULTURED CELLS

Protein phosphorylation is one of the important processes of cell signal transduction pathways. To study the effects of 50 Hz electromagnetic field (EMF) on the cell signal transduction process, the phosphorylation of stress-activated protein kinase (SAPK/JNK) extracted from Chinese hamster lung (CHL) cells exposed to 0.4 and 0.8 mT 50 Hz EMF for various durations was measured. A solid-phase kinase assay was used to measure the enzymatic activity of SAPK extracted from cells exposed to 50 Hz EMF at the same magnetic flux density and for only 15 min. The results showed that both 0.4 and 0.8 mT could induce the phosphorylation of SAPK, the phosphorylation of SAPK presented a time-dependent course, and there was a difference between the two intensities. The phosphorylated SAPK enhanced its enzymatic activity. All the data indicated that 50 Hz EMF could activate SAPK in a time- and intensity-dependent manner. The biological effects caused by 50 Hz EMF maybe related to the SAPK signal transduction pathway.

Reciprocal regulation of mammalian nitric oxide synthase and calcineurin by plant calmodulin isoforms.

Calmodulin (CaM) is the primary mediator of Ca signal transduction processes in cells. Unlike animal cells, plant cells express multiple CaM isoforms. One cloned soybean CaM isoform (SCaM-4) half-maximally activated mammalian nitric oxide synthase (NOS) at 180 nM while another (SCaM-1) served as a competitive antagonist (Ki approximately 120 nM) of this activation. The reciprocal was true for the protein phosphatase calcineurin (CaN); SCaM-1 half-maximally activated mammalian CaN at approximately 12 nM, and SCaM-4 competitively antagonized (Ki approximately 70 nM) its activation. The reciprocal enzyme activation and competitive inhibition exhibited by these plant CaM isoforms suggest that their differential expression in cells could allow selective activation of some target enzymes and the selective inhibition of others. This may allow for a branching or bifurcation in the Ca2+-CaM signal transduction pathway and to alterations in cell function.

PKC Inhibitors in the Therapy of Autoimmune Diseases

The protein kinase C ( PKC) family of isoenzymes was thought to mediate a wide range of signal transduction processes in cells. However, it is now widely accepted that its role may have been overstated. The advent of selective PKC inhibitors has led to a re-appraisal of the role this enzyme plays in these processes. This review shows how the structural lead provided by staurosporine, a non-selective protein kinase inhibitor, was used as a basis for the design of substituted bisindolylmaleimides with significantly improved selectivity for protein kinase C over cAMP-dependent protein kinase and phophorylase kinase. Evidence from studies with these inhibitors implicates PKC in inflammatory responses such as the neutrophil respiratory burst and antigen-driven T cell proliferation. Potent, orally bioavailable bisindolylmaleimide PKC inhibito_rs such as Ro 32-0432 inhibit phorbol ester -induced inflammation in rodents. These agents also selectively inhibit T cell mediated responses in animal models of arthritis and encephalomyelitis. Taken together, these results suggest that selective inhibitors of PKC may be useful in the therapy of autoimmune diseases such as rheumatoid arthritis, multiple sclerosis and psoriasis.

Theileria parvaSporozoite Entry into Bovine Lymphocytes Involves both Parasite and Host Cell Signal Transduction Processes

Theileria parvasporozoites rapidly enter bovine lymphocytes. Since lymphocytes are normally nonphagocytes sporozoite binding to the host cell surface must initiate events in the host cell, leading to the internalization of the parasite. In the present study inhibitors of various key molecules in cell signal transduction and activation pathways, in combination with a method of quantitation, have been used to examine the possible role(s) of these systems in sporozoite entry. A variety of protein kinase inhibitors caused significant inhibition of sporozoite entry. Moreover, protein kinase activities in both the sporozoite and the host cell were essential to sporozoite invasion. Down-regulation of lymphocyte protein kinase C and inhibitors of phospholipase C but not phospholipase A2 activity also blocked sporozoite entry. Parasite entry could also be blocked by inhibitors of G protein activity. Treatment of sporozoites with AIF(3–5)blocked parasite binding while treatment of host cells inhibited sporozoite internalization. Furthermore, sporozoite entry was dependent on a cholera toxin-inhibitable process(es), whereas mastroparan and pertussis toxin had no significant inhibitory effects. Collectively these results provide initial evidence for both parasite protein kinase- and G protein-dependent processes as well as the participation of a variety of host cell signal transduction pathways in the sporozoite entry process.

Regulation of Epstein-Barr virus latency by latent membrane protein 2.

Like other herpesviruses, Epstein-Barr virus persists in its host through its ability to establish a latent infection that periodically reactivates. Latent membrane protein 2A (LMP2A) regulates reactivation from latency by interfering with normal B cell signal transduction processes, and may define a new class of regulators of herpesvirus latency.

Different functional forms of G-protein βγ-subunits, βγ-I and βγ-II, in bovine brain

Heterotrimeric GTP binding regulatory proteins (G proteins) are involved in the signal transduction process in cells. We have previously demonstrated that G protein (Gi/o) in bovine brain contains two subspecies of the βγ-subunit, βγ-I and βγ-II, with distinct γ subunits, i.e., γ-I and γ-II, but identical β-subunit. We found that γ-I agreed with the γ-subunit reported elsewhere, while γ-II was a novel γ-subunit. In the present study we separated the fractions containing G-protein isoforms, Go∗, Gi1, Go and Gi2, with a Mono Q column and they were subjected to 15% polyacrylamide gel electrophoresis. All isoforms were shown to possess both γ subunits, γ-I and γ-II. The molar ratio of the two γ-subunit isoforms was one to one, based on the relative intensity of Coomassie blue-stained bands. Differences in biological activity between G proteins composed of βγ-I and βγ-II were investigated. The amount of GTPγS bound to the α-subunit was larger in αβγ-I than in αβγ-II. The pertussis toxin-catalyzed ADP-ribosylation on α-subunit was enhanced by either βγ-subunit subspecies, but the effect was larger with βγ-I than with βγ-II. From gel filtration with a Sephacryl S 300, it appeared that all α- and either βγ-subunit, i.e., βγ-I or βγ-II, formed a trimer complex. These findings suggest the possible existence of two different functional forms in each G-protein isoform depending on the βγ-subunit subspecies.

Therapeutic potential of protein kinase C inhibitors.

The serine/threonine protein kinase, protein kinase C (PKC) is a family of closely related isoforms which are physiologically activated by diacylglycerol generated by the binding of a variety of agonists to their cellular receptors. Free fatty acids may also play a role in activating PKC. The enzyme apparently mediates a wide range of signal transduction processes in cells and, therefore, inhibitors directed selectively against PKC may have wide-ranging therapeutic potential. This review highlights the evidence that inappropriate activation of PKC occurs in a number of disease states. Such evidence, however, is often seriously flawed because it relies on the use of phorbol esters, which are potent and direct PKC activators but may not mimic the physiological triggering of the enzyme in cells, or on the use of non-selective protein kinase inhibitors such as H7 and staurosporine. A new generation of bis-indolylmaleimides, derived from the lead provided by staurosporine, shows a high degree of selectivity for PKC over closely related protein kinases and such agents may provide more appropriate tools to investigate the role of PKC in cellular processes.

A novel mechanism for acetylcholine to generate diacylglycerol in brain.

The classical scheme involving inositol phospholipid breakdown by phospholipase C as the sole source of diacylglycerol (DAG) has recently been challenged by evidence that phosphatidylcholine (PC) is an alternative source. In synaptic membranes of canine cerebral cortex, cholinergic agonists caused rapid accumulation of [3H]phosphatidic acid (PA) from [3H]PC within 15 s, whereas [3H]DAG formation showed a transient lag period before becoming elevated and then exceeding the amount of [3H]PA. Additional evidence shows that DAG is produced from PC by the action of phospholipase D to yield PA, which is further dephosphorylated to DAG by PA phosphatase. Our results indicate that this muscarinic acetylcholine receptor-regulated PC phospholipase D-PA phosphatase pathway may be a novel mechanism in cell signal transduction processes for activation of protein kinase C in brain.