Showing papers in "Cell Biochemistry and Biophysics in 2005"

The role of oxidative stress in diabetic complications.

Abstract: The morbidity and mortality associated with diabetes is the result of the myriad complications related to the disease One of the most explored hypotheses to explain the onset of complications is a hyperglycemia-induced increase in oxidative stress Reactive oxygen species (ROS) are produced by oxidative phosphorylation, nicotinamide adenine dinucleotide phosphate oxidase (NADPH), xanthine oxidase, the uncoupling of lipoxygenases, cytochrome P450 monooxygenases, and glucose autoxidation Once formed, ROS deplete antioxidant defenses, rendering the affected cells and tissues more susceptible to oxidative damage Lipid, DNA, and protein are the cellular targets for oxidation, leading to changes in cellular structure and function Recent evidence suggests ROS are also important as second messengers in the regulation of intracellular signaling pathways and, ultimately, gene expression This review explores the production of ROS and the propagation and consequences of oxidative stress in diabetes

Oxidative stress in pathogenesis of chronic obstructive pulmonary disease: cellular and molecular mechanisms.

Abstract: Chronic obstructive pulmonary disease (COPD) is a slowly progressive condition characterized by airflow limitation, which is largely irreversible. Oxidative stress and inflammation are the major hallmarks of COPD. Reactive oxygen species, either directly or via the formation of lipid peroxidation products, such as 4-hydroxy-2-nonenal and F2-isoprostanes, may play a role in enhancing the inflammation through the activation and phosphorylation of mitogen-activated protein kinases (MAPKs) and redox-sensitive transcription factors such as nuclear factor-ϰB and activator protein-1 in COPD. In addition, activation of the MAPK family leads to the transactivation of transcription factors and coactivators (chromatin remodeling). This eventually results in expression of genes regulating a battery of distinct proinflammatory, antioxidant, and stress response genes. The presence of an oxidative stress has important consequences on several events of lung physiology and for the pathogenesis of COPD. These include increased sequestration of neutrophils in the pulmonary microvasculature, oxidative inactivation of antiproteases and surfactants, hypersecretion of mucus, membrane lipid peroxidation, mitochondrial respiration, alveolar epithelial injury/permeability, breakdown/remodeling of extracellular matrix, and apoptosis. Oxidative stress may have a role in the poor efficacy of corticosteroids in COPD. This review discusses cellular and molecular changes that occur in response to smoking and oxidative stress in the pathogenesis of COPD.

Mitogen-activated protein kinases in cell-cycle control.

Abstract: The mitogen-activated protein kinase (MAPK) family of kinases connects extracellular stimuli with diverse cellular responses ranging from activation or suppression of gene expression to the regulation of cell mortality, growth, and differentiation. The MAPK family has been studied extensively; however, the role of these kinases in cell growth and cell-cycle control has become increasingly complex. Patterns have begun to emerge from these studies that show the functions of MAPK subfamilies at different stages of the cell cycle. Their patterns of subcellular localization and movement during the cell cycle are subfamily-specific and have raised many questions about possible cell-cycle functions that have yet to be demonstrated. This article will compare and contrast our current understanding of the functions and localization patterns of the MAPK subfamilies (ERK, BMK, p38, and JNK) in cell-cycle control.

Molecular determinants of voltage-gated potassium currents in vascular smooth muscle.

Abstract: Voltage-gated K+ channels (Kv) play an important role in regulating contraction of vascular smooth muscle cells (VSMC) through their effects on membrane potential and on voltage-gated Ca2+ channel activity. Kv channels are tetrameric structures consisting of four identical or closely related pore-forming α subunits that may be associated with accessory subunits. More than 30 different gene products that contribute to Kv channel complexes have been identified to date, some of which are subject to alternative splicing. Consequently, there is an enormous potential diversity in the molecular composition and properties of possible Kv channel complexes. Electrophysiologic measurements of K+ currents in VSMC suggest the presence of multiple Kv channel assemblies including: (1) rapidly inactivating, 4-aminopyridine-sensitive, (2) slowly inactivating, tetraethylammonium-insensitive, and (3) noninactivating, tetraethylammonium-sensitive components. Based on electrophysiological and expression studies, it is likely that the latter two components are represented by a heteromultimeric complex of Kv1.2 with either Kv1.4 or Kv1.5 and a Kvβ1 subunit, and by at least Kv2.1, respectively. The identity of the first A-type current component, however, is not clear at this time. The relative abundance of these current components appears to vary in VSMC from different anatomical sites, from animals of different ages, and perhaps in VSMC within specific vascular segments. Expression of numerous Kv α and β subunits has been demonstrated in VSMC at both the gene and protein level. However, the number of expressed subunits appears to be much larger than the number of apparent Kv current components. It remains unclear if all of these transcripts are expressed in VSCM or in other cell types in the tissue, or if expression patterns are homogenous or heterogeneous in VSMC at a given site.

The art of arteriogenesis

Abstract: The identification of collateral artery growth (arteriogenesis) as the only mechanism to compensate for the loss of an occluded artery forced us to define the mechanisms responsible for this type of vessel growth. To achieve this, a variety of coronary as well as peripheral models of arteriogenesis have been developed. Based on these studies it is obvious that arteriogenesis obeys different mechanisms than angiogenesis, the sprouting of capillaries. Upon occlusion of an artery, the blood flow is redirected into preexisting arteriolar anastomoses that experience increased mechanical forces such as shear stress and circum ferential wall stress. The endothelium of the arteriolar connections is then activated, resulting in an increased release of monocyte-attracting proteins as well as an upregulation of adhesion molecules. Upon adherence and extravasation, monocytes promote arteriogenesis by supplying growth factors and cytokines that bind to receptors that are expressed on vascular cells within a limited time frame. Animal studies evidenced that factors, such as monocyte chemoattractant protein-1, granulocyte-monocyte colony-stimulating factor, or transforming growth factor-β1, that either attract or prolong the lifetime of monocytes efficiently enhance collateral artery growth, an effect that was seen only to a minor degree after application of a single growth factor. Bone marrow-derived stems cells and endothelial progenitor cells do not incorporate in growing arteries but, rather, function as supporting cells. Complete elucidation of the mechanisms of arteriogenesis may lead to efficacious therapies counteracting the devastating consequences of vascular occlusive diseases.

Cytoskeletal regulation of nitric oxide synthase.

Abstract: The three isoforms of nitric oxide synthase (NOS)—endothelial NOS (eNOS), inducible NOS (iNOS), and neural NOS (nNOS)—colocalize with the cytoskeleton including actin microfilaments, microtubules, and intermediate filaments directly or indirectly. These colocalizations enable optimal nitric oxide production and help NOS exert their functions. The reorganization of cytoskeletal polymerization state induced by extracellular stimuli such as shear stress, hypoxia, and drugs regulates eNOS, nNOS, and iNOS. Alterations of nitric oxide production caused by cytoskeletal reorganization play an important role in physiological and pathophysiological conditions. This review focuses on recent data regarding the regulation of NOS by the cytoskeleton at transcriptional, posttranscriptional, and posttranslational levels.

Homocysteine in microvascular endothelial cell barrier permeability

Abstract: Redox stress activates the endothelium and upregulates matrix metalloproteinases (MMPs), which degrade the matrix and lead to blood-endothelial barrier leakage. Interestingly, elevated levels of plasma homocysteine (Hcy) are associated with vascular dementia, seizure, stroke, and Alzheimer disease. Hcy competes with the γ-aminobutyric acid (GABA)-A/B receptors and behave like an excitatory neurotransmitter. GABA stimulates the inhibitory neurotransmitter GABA-A/B receptor and decreases arterial blood pressure. However, the neural mechanisms of microvascular remodeling in hyperhomocysteinemia are unclear. This review addresses the idea that Hcy induces microvascular permeability by attenuating the GABA-A/B receptors and increasing redox stress, which activates a disintegrin and metalloproteinase that suppresses tissue inhibitors of metalloproteinase. This process causes disruption of the matrix in the blood-brain barrier. Understanding the mechanism of Hcy-mediated changes in permeability of the blood-brain barrier and extracellular matrix that can alter the neuronal environment in cerebral-vascular dementia is of great importance in developing treatments for this disease.

Spin biochemistry: magnetic 24Mg-25Mg-26Mg isotope effect in mitochondrial ADP phosphorylation.

Abstract: The rates of adenosine triphosphate (ATP) production by isolated mitochondria and mitochondrial creatine kinase incubated in isotopically pure media containing, separately, (24)Mg(2+), (25)Mg(2+), and (26)Mg(2+) ions were shown to be strongly dependent on the magnesium nuclear spin and magnetic moment. The rate of adenosine 5'-diphosphate phosphorylation in mitochondria with magnetic nuclei (25)Mg is about twice higher than that with the spinless, nonmagnetic nuclei (24,26)Mg. When mitochondrial oxidative phosphorylation was selectively blocked by treatment with 1-methylnicotine amide, (25)Mg(2+) ions were shown to be nearly four times more active in mitochondrial ATP synthesis than (24,26)Mg(2+) ions. The rate of ATP production associated with creatine kinase is twice higher for (25)Mg(2+) than for (24,26)Mg and does not depend on the blockade of oxidative phosphorylation. There is no difference between (24)Mg(2+) and (26)Mg(2+) effects in both oxidative and substrate phosphorylation. These observations demonstrate that the enzymatic phosphorylation is a nuclear spin selective process controlled by magnetic isotope effect. The reaction mechanism proposed includes a participation of intermediate ion-radical pairs with Mg(+) cation as a radical partner. Therefore, the key mitochondrial phosphotransferases work as a magnesium nuclear spin mediated molecular machines.

Molecules mediating cell-ECM and cell-cell communication in human heart valves

Abstract: The specific phenotype of different tissues depends on the interactions of cells with neighboring cells and the surrounding extracellular matrix, which is mediated by cell adhesion receptors including integrins, immunoglobulin family members, syndecans, and selectins. The aim of this study was to investigate the adhesion profile of native human valve interstitial cells (ICs) in situ and in vitro by analyzing these adhesion receptors. Flow cytometry and immunocytochemistry was used to quantify the expression of the specific receptors on ICs cultured from all human cardiac valves, and immunohistochemistry were used to profile their distribution pattern in valve tissue sections. The valve leaflets and cultured ICs from all valves expressed alpha1, alpha2, alpha3, alpha4, and alpha5 integrins to varying degrees and percentages with very little expression of alpha6 and alphaV. Valve leaflet ICs from all valves, expressed predominantly beta1 integrin but no beta3 or beta4 integrin. Syndecan-1 and Syndecan-4 were not detected. Intercellular adhesion molecule-1 was weakly detected, whereas vascular adhesion molecule-1 was barely detectable and E-selectin was not detected. This study has delineated the identity of some of the integrins synthesized and expressed by human valve ICs and the specificity of adhesion molecules with which the valve ICs interact with the extracellular matrix and mediate intercellular interactions. This pattern of expression of cell surface adhesion molecules may be considered as a basis for a fingerprint on which to base future cell alternatives and would provide useful information for valve tissue engineering.

Proinflammatory cytokines upregulate mRNA expression and secretion of vascular endothelial growth factor in cultured human airway smooth muscle cells.

Abstract: Airflow obstruction in chronic airway disease is associated with airway and pulmonary vascular remodeling, of which the molecular mechanisms are poorly understood. Paracrine actions of angiogenic factors released by resident or infiltrating inflammatory cells following activation by proinflammatory cytokines in diseased airways could play a major role in the airway vascular remodeling process. Here, the proinflammatory cytokines interleukin (IL)-1β, and tumor necrosis factor (TNF)-α were investigated on cell cultures of human airway smooth muscle (ASM) for their effects on mRNA induction and protein release of the angiogenic peptide, vascular endothelial growth factor (VEGF). IL-1β (0.5 ng/mL) and TNF-α (10ng/mL) each increased VEGF mRNA (3.9 and 1.7 kb) expression in human ASM cells, reaching maximal levels between 16 and 24 and 4 and 8h, respectively. Both cytokines also induced a time-dependent release of VEGF, which was not associated with increased ASM growth. Preincubation of cells with 1μM dexamethasone abolished enhanced release of VEGF by TNF-α. The data suggest that human ASM cells express and secrete VEGF in response to proinflammatory cytokines and may participate in paracrine inflammatory mechanisms of vascular remodeling in chronic airway disease.

Mitogen-activated protein kinases (p38 and c-Jun NH2-terminal kinase) are differentially regulated during cardiac volume and pressure overload hypertrophy.

Abstract: Chronic pressure overload (PO) and volume overload (VO) result in morphologically and functionally distinct forms of myocardial hypertrophy. However, the molecular mechanism initiating these two types of hypertrophy is not yet understood. Data obtained from different cell types have indicated that the mitogen-activated protein kinases (MAPKs) comprising c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 play an important role in transmitting signals of stress stimuli to elicit the cellular response. We tested the hypothesis that early induction of MAPKs differs in two types of overload on the heart and associates with distinct expression of hypertrophic marker genes, namely ANF, α-myosin heavy chain (α-MHC), and β-MHC. In rats, VO was induced by aortocaval shunt and PO by constriction of the abdominal aorta. The PO animals were further divided into two groups depending on the severity of the constriction, mild (MPO) and severe pressure overload (SPO), having 35 and 85% aortic constriction, respectively. Early changes in MAPK activity (2–120 min and 1 to 2 d) were analyzed by the in vitro kinase assay using kinase-specific antibodies for p38, JNK, and ERK2. The change in expression of hypertrophy marker genes was examined by Northern blot analysis. In VO hypertrophy, the activity of p38 was markedly increased (10-fold), without changing the activity of ERK and JNK. However, during PO hypertrophy, the activity of JNK was significantly increased (two-to sixfold) and depended on the severity of the load. The activity of p38 was not changed in MPO hypertrophy, whereas it was slightly elevated (50%) in hearts with SPO. Similarly, ERK activity was not changed in hearts with MPO, but a transient rise in activity was observed in hearts with SPO. The expression of ANF and β-MHC genes was elevated in both PO and VO hypertrophy; however, this change was much greater in hearts subjected to PO than VO hypertrophy. α-MHC expression was downregulated in PO but remained unchanged in VO hypertrophy hearts. Thus, these results demonstrate differential activation of MAPKs in two types of cardiac hypertrophy and this, in part, may contribute to differential expression of cardiac muscle gene expression, giving rise to unique cardiac phenotype associated with different hemodynamic overloads.

The Popeye domain-containing gene family

Abstract: The Popeye domain-containing gene family has been isolated on the basis of a subtractive screen aiming at the identification of novel genes with a heart-restricted gene expression pattern. The gene family codes for membrane proteins containing three transmembrane domains. The carboxy-terminal part of the protein is localized to the cytoplasm and contains a protein domain with high sequence conservation named the Popeye domain. This domain is involved in protein homo dimerization. The gene family is expressed in heart and skeletal muscle cells as well as smooth muscle cells. In addition, Popdc genes are expressed in other cell types such as neuronal cells in restricted areas of the brain, spinal cord, and dorsal root ganglia, and in various epithelial cells. Recently, it has been proposed that Popdc proteins may function as a novel family of adhesion proteins. That the expression pattern has been conserved during evolution and is very similar in all vertebrate classes and also in basal chordates suggests that Popdc proteins play an important role in cardiac and skeletal muscle.

Protein-surface interactions: an energy-based mathematical model.

Abstract: This article describes an energy-based approach to protein adsorption, focusing on the energies involved in the interactions between a protein and a surface. Mathematical modeling and simulation based on this approach allow an improved understanding of the conditions that favor or prevent adsorption of a protein onto a surface and that can play a significant role in the design of material surfaces that interact with biological tissues according to specific needs. Biocompatibility with respect to fluids in motion, such as blood, is the main foreseeable application of our work. The considered energies are the van der Waals energy, the electrostatic energy, and the hydrophobic or hydrophilic energy. Moreover, the motion of the medium in which particles are immersed is also taken into account, considering the drag effect of the motion of the fluid on the particle, leading to a kinetic contribution to the total energy. It is shown that the adsorption behavior is not mainly determined by the van der Waals energy and by the double layer energy, but that a significant role is also played by the hydrophobic or hydrophilic energy. These results support the findings of experimental studies.

Transforming growth factor-β1 and disorders of the lung

Abstract: The transforming growth factor (TGF) superfamily encompasses about 30 members in mammals. The effect of TGF-β subfamily members is exerted and regulated via selective pathways of synthesis and signaling that involve activation of latent TGF-β, specific and high-affinity binding to cell membrane serine/threonine kinase receptors, activation of intracellular cascades that include Smad molecules and mitogen-activated protein kinases, and regulated termination of the effect by diverse mechanisms including protein degradation and transcriptional activation. Several comprehensive reviews on TGF-β biology in general and on the role of this cytokine in other diseases have been published recently. In recent years an unexpected role of TGF-β on lung homeostasis has been revealed. Here, we discuss the contribution of TGF-β to the pathogenesis of asthma and chronic obstructive pulmonary disease, two common illnesses of the lung, as well as of lymphangioleiomyomatosis, a rare disease in women. The information we collate and integrate places TGF-β at a pivotal point within complex networks that control lung physiology as well as the physiopathology of these lung diseases.

Growing applications and advancements in microarray technology and analysis tools.

Abstract: In today's field of genomics, traditional gene-by-gene approach is not adequate to meet the demand of processing information generated from mapping the complex biology of the human genome More global views of analyzing the magnitude of information are necessary, such as with microarrays Microarray technology today is rapidly uncovering broad patterns of genetic activity and showing insight into gene functions, processes, and pathways With the growing technology, imminent knowledge is being generated looking into transcriptional processes and biological mechanisms from many different organisms and phylogeny Many tools are being developed to assist with the analysis of such high-throughput data, many applications are being utilized by this technology, and the field is growing and expanding rapidly to accommodate the expanding genomics era

Exposure of human leukemic cells to direct electric current: generation of toxic compounds inducing cell death by different mechanisms.

Abstract: Treatment with direct electric current (DC) influences the growth of several cancer cells. In this work, we evaluated the effects of DC treatment on the human leukemic cell line HL60. Human cells were separately treated in the presence of the cathode or the anode or without contact with the electrodes. In all systems, DC-treated cells presented an impaired ability to proliferate. Growth inhibition was dependent on the generation of soluble products of electrolysis. Cathodic treatment of HL60 cells predominantly induced lysis, whereas treatment without contact with electrodes did not induce alterations in cell viability. In contrast, cell stimulation by the anode resulted in irreversible membrane damage, as demonstrated by trypan blue and 7-aminoactinomycin staining. Analysis of these cells by transmission electron microscopy indicated that necrosis is a major mechanism inducing cell death. In addition, apoptotic-like cells were observed under light microscopy after anodic treatment. Accordingly, DNA from anodic-treated cells presented a typical pattern of apoptosis. Apoptotic cell death was only generated after the treatment of HL60 cells in conditions in which the generation of chloride-derived compounds was favored. These results indicate that the nature of the products from cathodic or anodic reactions differently influences the mechanisms of cell death induced by DC-derived toxic compounds.

Toward a molecular understanding of the structure-function of ryanodine receptor Ca2+ release channels

Abstract: Identification of the genetic basis of human diseases linked to dysfunctional free calcium (Ca2+) signaling has triggered an explosion of interest in the functional characterization of the molecular components regulating intracellular Ca2+ homeostasis. There is a growing appreciation of the central role of intracellular ryanodine-sensitive Ca2+ release channel (RyR) regulation in skeletal and cardiac muscle pathologies, including malignant hyperthermia, heart failure, and sudden cardiac death. The use of cloned RyR isoforms and recombinant expression techniques has greatly facilitated the elucidation of the molecular basis of RyR Ca2+ release functionality. This review will focus on the recombinant techniques used in the functional characterization of recombinant RyR isoforms and the insights that these approaches have yielded in unraveling the mechanistic basis of RyR channel functionality.

Molecular dynamics simulation of a high-affinity antibody-protein complex: the binding site is a mosaic of locally flexible and preorganized rigid regions.

Abstract: One nanosecond molecular dynamic (MD) simulation of anti-hen egg white lysozyme (HEL) antibody HyHEL63 (HH63) complexed with HEL reveals rigid and flexible regions of the HH63 binding site. Fifty conformations, extracted from the MD trajectory at regular time intervals were superimposed on HH63-HEL X-ray crystal structure, and the root mean squared deviations (RMSDs) and deviations in Cα atom positions between the X-ray structure and the MD conformer were measured. Residue positions showing the large deviations in both light chain and heavy chain of the antibody were same in all the MD conformers. The residue positions showing smallest deviations were same for all the conformers in the case of light chain, whereas relatively variable in the heavy chain. Positions of large and small deviations fell in the complementarity determining regions (CDRs), for both heavy and light chains. The larger deviations were in CDR-2 of light and CDR-1 of heavy chain. Smaller deviations were in CDR-3 of light and CDR-2 and CDR-3 of heavy chains. The large and small deviating regions highlight flexible and rigid regions of HH63 binding site and suggest a mosaic binding mechanism, including both “induced fit” and preconfigured “lock-and-key” type of binding. Combined “induced fit” and “lock-and-key” binding would be a better definition for the formation of large complexes, which bury larger surface area on binding, as in the case of antibody-HEL complex. We further show that flexible regions, comprising mostly charged and polar residues, form intermolecular interactions with HEL, whereas rigid regions do not. Electrostatic complementarity between HH63 and HEL also imply optimized binding affinity. Flexible and rigid regions of a high-affinity antibody are selected during the affinity maturation of the antibody and have specific functional significance. The functional importance of local inherently flexible regions is to establish intermolecular contacts or they play a key role in molecular recognition, whereas local rigid regions provide the structural framework.

Conservation and variation of gene regulation in embryonic stem cells assessed by comparative genomics

Abstract: We have examined the gene structure and regulatory regions of octamer-binding transcription factor 3/4 (Oct 3/4), sex determining region Y box 2 (Sox2), signal transducer and activator of transcription 3 (Stat3), embryonal stem cell-specific gene 1 (ESG), nanog homeobox (Nanog), and several other genes highly expressed in embryonic stem (ES) cells across different species. Our analysis showed that ES cell-expressed Ras (ERAS) was orthologous to a human pseudogene Harvey Ras (HRASP) and that the promoter and other regulatory sequences were highly divergent. No ortholog of (ES) cell-derived homeobox containing gene (Ehox) could be identified in human, and the closest paralogs PEPP gene subfamily 1 (PEPP1), PEPP2, and extraembryonic, spermatogenesis, homeobox 1 (Esx1) were not expressed by ES cells and shared little homology. The Sox2 promoter was the most conserved across species and the Oct3/4 promoter region showed significant homology particularly in the distal enhancer active in ES cells. Analysis suggested common and divergent pathways of regulation. Conserved Oct3/4 and Sox2 co-binding domains were identified in most ES expressed genes, highlighting the importance of this transcriptional pathway. Conserved fibroblast growth factor response element sites were identified in regulatory regions, suggesting a potential parallel pathway for regulation by FGFs. A central role of Stat3 activation in self-renewal and in a regulatory feedback loop was suggested by the identification of the conserved binding sites in most pathways. Although most pathways were evolutionarily conserved, promoters and genomic structure of the leukemia inhibitory factor (LIF) pathway components were divergent, likely explaining the differential requirement of LIF for human and rodent cells. Our analysis further suggested that the Nanog regulatory pathway was relatively independent of the LIF/Oct pathway and may interact with the Nodal/transforming growth factor-β pathway. These results provide a framework for examining the current reported differences between rodent and human ES cells and define targets for future perturbation studies.

Single channel recordings from synaptosomal AMPA receptors

Abstract: Synaptic glutamate receptors play a prominent role in the excitatory neurotransmission in the vertebrate central nervous system. Although elucidation of the functional properties of glutamate receptors using electrophysiologic analyses has yielded important information, methodological and technological limitations have prevented direct measurement of single channel properties of synaptic receptors. Here, we have isolated murine mossy fiber synaptosomes and reconstituted them into small artificial lipid bilayers to characterize the single-channel properties of synaptic α amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-subtype glutamate receptors. The reconstituted synaptosomal receptors were activated by nanomolar concentrations of AMPA and blocked by a potent AMPA receptor antagonist. The synaptosomal AMPA receptors exhibited channel conductances of 14–56 pS and linear current-voltage relationship. The open and closed dwell time distributions of single channel currents were best described by three exponentials. These channels frequently exhibited burst behavior with long burst duration of approx 60 ms. Experiments with multichannel recordings revealed that steady state probabilities could not be fitted using a binomial distribution, indicating a cooperative channel gating behavior that would account for larger membrane currents. Our findings suggest that isolation, reconstitution into lipid bilayers, and subsequent single channel analysis of synaptosomal receptors is a useful method for investigation of synaptic AMPA receptors.

Acute adaptations of the coronary circulation to exercise.

Abstract: Coronary blood flow is tightly coupled to myocardial oxygen consumption to maintain a consistently high level of myocardial oxygen extraction. This tight coupling has been proposed to depend on periarteriolar, oxygen tension, signals released from cardiomyocytes (adenosine acting on KATP+ channels), and/or the endothelium (prostanoids, nitric oxide, endothelin [ET]) and autonomic influences (catecholamines), but the contribution of each of these regulatory pathways and their interactions are still incompletely understood. Until recently, experimental studies into the regulation of coronary blood flow during exercise were principally performed in the dog. We have performed several studies on the regulation of vasomotor tone in coronary resistance vessels in chronically instrumented exercising swine. These studies have shown that the coronary resistance vessels in swine lack significant α-adrenergic control, but that these vessels are subject to β-adrenergic feed-forward control during exercise, which is aided by a parasympathetic withdrawal. In addition, withdrawal of an ET-mediated vasoconstrictor influence also contributes to exercise-induced coronary vasodilation. Coronary blood flow regulation by endothelial and metabolic vasodilator pathways contributes to resting vasomotor tone regulation but does not appear to contribute to the exercise-induced coronary vasodilation. Furthermore, blockade of one vasodilator pathway is not compensated by an increased contribution of the other vasodilator mechanisms, suggesting that porcine coronary vasomotor control by endothelial and metabolic factors occurs in a linear additive rather than a nonlinear synergistic fashion.

Inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase differentially regulates contractile function in cardiac myocytes from normotensive and spontaneously hypertensive rats: role of Ca2+ regulatory proteins.

Abstract: Hypertension leads to impaired contractile function. This study examined the impact of inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) by thapsigargin or cyclopiazonic acid (CPA) on cardiac contractile function in ventricular myocytes from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Mechanical properties were examined including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90), and maximal velocity of shortening/relengthening (+/-dL/dt). Intracellular Ca2+ transients were evaluated as fura-2 fluorescent intensity (FFI), excitation-induced change in FFI (DeltaFFI = peak-basal), and fluorescence decay rate (tau). Expression of Ca2+ regulatory proteins SERCA2a, Na+-Ca2+ exchanger (NCX), and phospholamban (PLB) were assessed by reverse transcriptase polymerase chain reaction and Western blot. SHR rats exhibited elevated blood pressure. SHR myocytes displayed decreased PS +/- dL/dt, peak FFI, and DeltaFFI; shortened TPS; prolonged tau with normal TR90; and basal FFI compared with WKY myocytes. Inhibition of SERCA with thapsigargin (5 microM) or CPA (10 microM) significantly depressed PS +/- dL/dt, baseline FFI, and DeltaFFI, and prolonged TPS, TR90, and tau in WKY myocytes. However, SHR myocytes were relatively insensitive to thapsigargin or CPA with only TPS and TR90 prolonged. Both mRNA and protein expressions of NCX and PLB were significantly enhanced, whereas SERCA2a protein abundance was reduced in SHR rats compared with the WKY group. Our data suggest that inhibition of SERCA function differentially affected cardiac contractile function in ventricular myocytes from normotensive and hypertensive rats possibly through reduced SERCA2a, elevated PLB, and NCX expression under hypertension.

Kinetics of allosteric conformational transition of a macromolecule prior to ligand binding: Analysis of stopped-flow kinetic experiments

Abstract: Two fundamentally different mechanisms of ligand binding are commonly encountered in biological kinetics. One mechanism is a sequential multistep reaction in which the bimolecular binding step is followed by first-order steps. The other mechanism includes the conformational transition of the macromolecule, before the ligand binding, followed, by the ligand binding process to one of the conformational states. In stopped-flow kinetic studies, the reaction mechanism is established by examining the behavior of relaxation times and amplitudes as a function of the reactant concentrations. A major diagnostic tool for detecting the presence of a conformational equilibrium of the macromolecule, before the ligand binding, is the decreasing value of one of the reciprocal relaxation times with the increasing [ligand]. The sequential mechanism cannot generate this behavior for any of the relaxation times. Such dependence is intuitively understood on the basis of approximate expressions for the relaxation times that can be comprehensively derived, using the characteristic equation of the coefficient matrix and polynomial theory. Generally, however, the used approximations may not be fulfilled. On the other hand, the two kinetic mechanisms can always be distinguished, using the approach based on the combined application of pseudo-first-order conditions, with respect to the ligand and the macromolecule. The two experimental conditions differ profoundly in the extent of the effect of the ligand on the protein conformational equilibrium. In a large excess of the ligand, the conformational equilibrium of the macromolecule, before the ligand binding, is strongly affected by the binding process. However, in a large excess of the macromolecule, ligand binding does not perturb the internal equilibrium of the macromolecule. As a result, the normal mode, affected by the conformational transition, is absent in the observed relaxation process. In the case of a sequential mechanism, the number of relaxation times is not altered by different pseudo-first-order conditions. Thus, the approach provides a strong diagnostic criterion for detecting the presence of the conformational transition of the macromolecule and establishing the correct mechanism. Application of this approach is illustrated for the binding of 3′-O-(N-methylantraniloyl)-5′-diphosphate to the E. coli DnaC protein.

Central domain of the human cardiac muscle ryanodine receptor does not mediate interaction with FKBP12.6.

Abstract: The immunophilin, FK506-binding protein (FKBP12), is an essential component of the ryanodine receptor channel complex of skeletal muscle (RyR1) and modulates intracellular calcium signaling from the endoplasmic reticulum. The cardiac muscle RyR isoform (RyR2) specifically associates with a distinct FKBP isoform, FKBP12.6. Previous studies have led to the proposal that the central domain of RyR1 exclusively mediates the interaction with FKBP12. To characterize the topography of the FKBP12.6 binding site on the human cardiac RyR2, we have applied complementary protein-protein interaction methods using both in vivoyeast two-hybrid analysis and in vitroimmunoprecipitation experiments. Our results indicate an absence of interaction of FKBP12/12.6 with fragments containing the central domain of either RyR1, RyR2, or RyR3. Furthermore, no interaction was detected between FKBP12.6 with a series of overlapping fragments encompassing the entire RyR2, either individually or in multiple combination. We also found that a distinct, alternatively spliced variant of FKBP12.6 was unable to interact with RyR. In contrast, we successfully demonstrated a robust association between the cytoplasmic domain of transforming growth factor-beta receptor type I and both FKBP12 and FKBP12.6 in parallel positive control experiments, as well as between native RyR2 and FKBP12.6. These results suggest that the specific interaction of FKBP12.6 with RyR2, and generally of FKBPs with any RyR isoform, is not readily reconstituted by peptide fragments corresponding to central RyR domains. Further structural analysis will be necessary to unravel this intricate signaling system and the current model of FKBP12-RyR interaction via a single, central RyR epitope may therefore require revision.

5-HT induction of c-fos gene expression requires reactive oxygen species and Rac1 and Ras GTPases.

Abstract: Serotonin (5-HT) stimulates superoxide release, phosphorylation of p42/p44 mitogen-activated protein kinase (MAPK), and DNA synthesis in bovine pulmonary artery smooth muscle cells. Both p42/p44 MAPK and reactive oxygen species (ROS) generation are required for 5-HT-induced growth in SMC. Agents that block the production of ROS, or ROS scavengers, block MAPK activation by 5-HT. However, specific signal transduction by 5-HT leading to proteins that control entrance into the cell cycle are not well defined in smooth muscle cells. Here, we show by Western blot that 5-HT upregulates c-Fos, an immediate early gene product known to regulate the entrance of quiescent cells into the cell cycle. Northern blots showed that c-fos mRNA is induced by 5-HT in 30 min. This induction is blocked by PD98059, indicating that activation of MAPK is required. 5-HT-induced expression of a 350 bp c-fos promoter in a luciferase reporter is blocked by PD98059 and diphenyliodonium (DPI). The GTPases Rac1 and Ras have been implicated in growth factor-induced generation of ROS. Overexpression of either dominant negative (DN) Rac1 or DN Ras inhibited 5-HT-mediated c-fos promoter activation. 5-HT also induced expression from a truncated c-fos promoter containing an isolated serum response element. This activation was blocked by DPI and PD98059. Overexpression of activated Ras and Rac1 were additive for activation of the serum response element promoter. Regulation of cyclin D1, a protein shown to be regulated by c-fos and required for entry into the cell cycle, is upregulated by 5-HT and is blocked by DPI and PD98059. Nuclear factor-kappaB, which can also regulate cyclin D1, was not activated. We conclude that 5-HT stimulates c-fos and cyclin D1 expression through a ROS-dependent mechanism that requires Ras, Rac1, and MAPK.

Regulation of N-myristoyltransferase by novel inhibitor proteins

Abstract: N-myristoylation ensures the proper function and intracellular trafficking of proteins. Many proteins involved in a wide variety of signaling, including cellular transformation and oncogenesis, are myristoylated. The myristoylation of proteins is catalyzed by the ubiquitously distributed eukaryotic enzyme N-myristoyltransferase (NMT). Previously, we reported that NMT activity is higher in colonic epithelial neoplasms than in normal-appearing colonic tissue and that the increase in NMT activity appears at an early stage in colonic carcinogenesis. Furthermore, we observed that NMT expression is elevated in colorectal and gallbladder carcinoma. In our laboratory, an endogenous NMT inhibitor protein (NIP71) was discovered from bovine brain that inhibited NMT activity in rat colonic tumors. Very recently we have demonstrated that the protein NIP71, which is a potential inhibitor of NMT, is homologous to heat-shock cognate protein (HSC70). In addition, we have discovered that enolase is a potent inhibitor of NMT. Further work may elucidate the role of HSC70 and/or enolase in the regulation of NMT, which may lead to the development of a gene-based therapy of colorectal cancer. The interaction of oncoproteomic and oncogenomic data sets through powerful bioinformatics will yield a comprehensive database of protein properties, which will serve as an invaluable tool for cancer researchers to understand the progress of tumorigenesis.

Long QT syndrome-associated I593R mutation in HERG potassium channel activates ER stress pathways.

Abstract: Hereditary long QT syndrome is a fatal arrhythmia associated with gene mutations in potassium and sodium channels that are expressed in ventricle. By employing heterologous expression and making comparisons to cells expressing wild-type human-ether-a-go-go-related protein (HERG), a potassium channel that contributes to I(Kr) current in ventricular cardiomyocytes, we demonstrate activation of an elevated endoplasmic reticulum (ER) stress response by the mutant I593R HERG potassium channel implicated in long QT syndrome type 2. I593R HERG is trafficking-impaired and forms Triton-insoluble aggregates. Expression of I593R HERG activates the unfolded protein response pathway and, separately, NF-kappaB signaling. ATF6, the activating transcription factor of the unfolded protein response pathway, is processed into the active transcription factor in the cells expressing I593R HERG. Consistent with ATF6 activation, the ER chaperones/calcium-binding proteins Grp78, Grp94, and calreticulin are elevated in I593R HERG-expressing cells. Coexpression of I593R HERG with wild-type HERG also results in ER stress pathway activation. By eliciting downstream links in signal transduction pathways associated with ER stress, expression of mutant trafficking impaired ion channels may contribute to disease etiology mechanisms that augment those associated with attenuated ion flux.

Light-induced protein-matrix uncoupling and protein relaxation in dry samples of trehalose-coated MbCO at room temperature

Abstract: In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal side) heme pocket, experiencing averaged protein heme pocket structures, as a result of the presence of Brownian motions. At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme pocket side probing in nonaveraged structures. We revisit here the flash photolysis data by Librizzi et al. (2002) and report on new, room temperature experiments in MbCO-trehalose samples, shortly illuminated prior the laser pulse. In dry samples, pre-illumination increased the diffusion of CO from the distal to the proximal heme pocket side, which resulted in less structure than in non-pre-illuminated samples. Such an effect, which is absent in humid samples, stems from a decoupling of the protein internal degrees of freedom from those of the external water-sugar matrix. We suggest that such a decoupling can be brought about by the continuous attempts performed by the protein during pre-illumination to undergo relaxation toward the photodissociated deoxy state. This, in turn, causes a collapse in the hydrogen bond network, which connects the protein surface to the water-sugar matrix, as reported by Cottone et al. (2002) and Giuffrida et al. (2003). In the conclusion section, we discuss the possible involvement of the processes invoked to rationalize the present data, in the function of macromolecules and interactions in living cells.

TFAR19 gene changes the biophysical properties of murine erythroleukemia cells.

Abstract: TFAR19 is a novel apoptosis-related gene and can accelerate cell apoptosis in the presence of apoptosis inducements. Here, we studied the effects of TFAR19 on some biophysical properties of mouse erythroleukemia (MEL) cells and their molecular and structural basis. After transfected with TFAR19 and apoptosis inducement, MEL revealed a high cell membrane fluidity, a decrease in resynthesis of phospholipids, an increase in the proteins/nucleic acids ratio, a relatively orderly cytoskeleton network, an impaired deformability, a low integrin aM expression, and a decrease in adhesion to endothelial cells. These findings suggest the potential of TFAR19 for antitumor cell migration, and thus for antitumor gene therapy.

Osmosis and solute-solvent drag: fluid transport and fluid exchange in animals and plants.

Abstract: In 1903, George Hulett explained how solute alters water in an aqueous solution to lower the vapor pressure of its water. Hulett also explained how the same altered water causes osmosis and osmotic pressure when the solution is separated from liquid water by a membrane permeable to the water only. Hulett recognized that the solute molecules diffuse toward all boundaries of the solution containing the solute. Solute diffusion is stopped at all boundaries, at an open-unopposed surface of the solution, at a semipermeable membrane, at a container wall, or at the boundary of a solid or gaseous inclusion surrounded by solution but not dissolved in it. At each boundary of the solution, the solute molecules are reflected, they change momentum, and the change of momentum of all reflected molecules is a pressure, a solute pressure (i.e., a force on a unit area of reflecting boundary). When a boundary of the solution is open and unopposed, the solute pressure alters the internal tension in the force bonding the water in its liquid phase, namely, the hydrogen bond. All altered properties of the water in the solution are explained by the altered internal tension of the water in the solution. We acclaim Hulett's explanation of osmosis, osmotic pressure, and lowering of the vapor pressure of water in an aqueous solution. His explanation is self-evident. It is the necessary, sufficient, and inescapable explanation of all altered properties of the water in the solution relative to the same property of pure liquid water at the same externally applied pressure and the same temperature. We extend Hulett's explanation of osmosis to included the osmotic effects of solute diffusing through solvent and dragging on the solvent through which it diffuses. Therein lies the explanations of (1) the extravasation from and return of interstitial fluid to capillaries, (2) the return of luminal fluid in the proximal and distal convoluted tubules of a kidney nephron to their peritubular capillaries, (3) the return of interstitial fluid to the vasa recta, (4) return of aqueous humor to the episcleral veins, and (5) flow of phloem from source to sink in higher plants and many more examples of fluid transport and fluid exchange in animal and plant physiology. When a membrane is permeable to water only and when it separates differing aqueous solutions, the flow of water is from the solution with the lower osmotic pressure to the solution with the higher osmotic pressure. On the contrary, when no diffusion barrier separates differing parts of an aqueous solution, fluid may flow from the part with the higher osmotic pressure to the part with the lower osmotic pressure because the solute molecules diffuse toward their lower concentration and they drag on the water through which they diffuse. This latter osmotic effect (diffusing solute dragging on solvent or counterosmosis) between differing parts of a solution has long been neglected and ignored when explaining fluid fluxes in plant and animal physiology. For two solutions separated by a semipermeable membrane, osmosis is the flow of its solvent from the solution with the lower solute concentration into the solution with the higher solute concentration. For two contiguous solutions not separated by a semipermeable membrane, counterosmosis is the flow of solution with the higher solute concentration toward the solution with the lower solute concentration. Corrective treatment of medical disorders attributable to faulty distribution of body fluids (e.g., glaucoma, pulmonary edema, systemic edema) are possible with these new insights regarding fluid transport and exchange provided in this review.