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Results for “Light Signal Transduction”

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PubMed1995

Mutations in the NPH1 locus of Arabidopsis disrupt the perception of phototropic stimuli.

The phototropic response is an important component of seedling establishment in higher plants because it orients the young seedlings for maximal photosynthetic light capture. Despite their obvious importance, little is known about the mechanisms underlying the perception and transduction of the light signals that induce phototropic curvatures. Here, we report the isolation of eight mutants of Arabidopsis that lack or have severely impaired phototropic responses. These nph (for nonphototropic hypocotyl) mutants comprise four genetic loci: nph1, nph2, nph3, and nph4. Physiological and biochemical characterization of the nph1 allele series indicated that the NPH1 locus may encode the apoprotein for a dual-chromophoric or multichromophoric holoprotein photoreceptor capable of absorbing UV-A, blue, and green light and that this photoreceptor regulates all the phototropic responses of Arabidopsis. It appears that the NPH1 protein is most likely a 120-kD plasma membrane-associated phosphoprotein because all of the nph1 mutations negatively affected the abundance of this protein. In addition, the putative NPH1 photoreceptor protein is genetically and biochemically distinct from the HY4 protein, which most likely acts as a photoreceptor for blue light-mediated hypocotyl growth inhibition. Furthermore, the NPH1 and HY4 proteins are not functionally redundant because mutations in either gene alone affect only one physiological response but not the other, thus providing strong support for the hypothesis that more than one blue light photoreceptor is required for the normal growth and development of a seedling.

Arabidopsis↗

PubMed2001

Update on thiol status and supplements in physical exercise.

Strenuous physical exercise represents a condition that is often associated with increased production of reactive oxygen species in various tissues. One of the most reliable indices of exercise-induced oxidant production is tissue glutathione oxidation. In humans, exercise-induced blood glutathione oxidation is rapid and subject to control by antioxidant supplementation. The objective of this brief review is to provide an update of our current understanding of cellular thiols and thiol antioxidants. Cellular thiols are critically important in maintaining the cellular antioxidant defense network. In addition, thiols play a key role in regulating redox-sensitive signal transduction process. Lipoic acid is a highly promising thiol antioxidant supplement. Recent studies have clarified that while higher levels of oxidants may indeed inflict oxidative damage, oxidants are not necessarily deleterious. Under certain conditions oxidants may function as cellular messengers that regulate a multitude of signal transduction pathways. In light of this, the significance of oxidants in various aspects of biology needs to be revisited.

Animals↗

PubMedDate not supplied

[Phytochrome regulation of the plant phospholipase activity].

The interaction of external stimuli with receptors of plant cell surface can activate the enzymes of lipid metabolism such as phospholipases C and D. The products of the catalysis, i.e., posphoinositide metabolites, phosphatidic acid, fatty acids, etc. participate in signal transduction as secondary messengers related to numerous regulatory processes. One of the physiologically important factors of regulatory control in plants is light, which plays the crucial role in triggering the cellular signaling network. This review presents the information on phospholipid signaling in plants, which is connected with light transduction processes occurring with the involvement of the plant regulatory pigment phytochrome.

Enzyme Activation↗

PubMed2006

G-protein-coupled receptor 1, G-protein Galpha-subunit 1, and prephenate dehydratase 1 are required for blue light-induced production of phenylalanine in etiolated Arabidopsis.

Different classes of plant hormones and different wavelengths of light act through specific signal transduction mechanisms to coordinate higher plant development. A specific prephenate dehydratase protein (PD1) was discovered to have a strong interaction with the sole canonical G-protein Galpha-subunit (GPA1) in Arabidopsis (Arabidopsis thaliana). PD1 is a protein located in the cytosol, present in etiolated seedlings, with a specific role in blue light-mediated synthesis of phenylpyruvate and subsequently of phenylalanine (Phe). Insertion mutagenesis confirms that GPA1 and the sole canonical G-protein-coupled receptor (GCR1) in Arabidopsis also have a role in this blue light-mediated event. In vitro analyses indicate that the increase in PD1 activity is the direct and specific consequence of its interaction with activated GPA1. Because of their shared role in the light-mediated synthesis of phenylpyruvate and Phe, because they are iteratively interactive, and because activated GPA1 is directly responsible for the activation of PD1; GCR1, GPA1, and PD1 form all of or part of a signal transduction mechanism responsible for the light-mediated synthesis of phenylpyruvate, Phe, and those metabolites that derive from that Phe. Data are also presented to confirm that abscisic acid can act through the same pathway. An additional outcome of the work is the confirmation that phenylpyruvate acts as the intermediate in the synthesis of Phe in etiolated plants, as it commonly does in bacteria and fungi.

Amino Acid Sequence↗

PubMed2002

Phytochrome signalling modulates the SA-perceptive pathway in Arabidopsis.

The interaction of phytochrome signalling with the SA signal transduction pathway has been investigated in Arabidopsis using single and multiple mutants affected in light perception (phyA and phyB deficient) and light-signal processing (psi2, phytochrome signalling). The induction of PR1 by SA and functional analogues has been found to strictly correlate with the activity of the signalling pathway controlled by both phyA and phyB photoreceptors. In darkness as well as dim light, and independently of a carbohydrate source, SA-induced PR gene expression as well as the hypersensitive response to pathogens (HR) are strongly reduced. Moreover, the initiation of HR also exhibits a strict dependence upon both the presence and the amplitude of a phytochrome-elicited signal. The growth of an incompatible strain of bacterial a pathogen (Pseudomonas syringae pv. tomato) was enhanced in phyA-phyB and decreased in psi2 mutants. While functional chloroplasts were found necessary for the development of an HR, the induction of PRs was strictly dependent on light, but independent of functional chloroplasts. Taken together, these data demonstrate that the light-induced signalling pathway interacts with the pathogen/SA-mediated signal transduction route. These results are summarized in a formalism that allows qualitative computer simulation.

Arabidopsis↗

PubMed1996

Light-induced phase shifting of the circadian conidiation rhythm is inhibited by calmodulin antagonists in Neurospora crassa.

The effects of calmodulin antagonists and inhibitors of protein kinases and phosphatases on light-induced phase shifting were investigated in Neurospora crassa. Calmodulin antagonists, namely, trifluoperazine, chlorpromazine, and W-7, almost completely inhibited the light-induced phase shifting without having any effect on the circadian clock itself. Chlorpromazine was less effective in inhibiting the light-induced phase shifting than trifluoperazine. W-5, a dechlorinated analogue of W-7, failed to inhibit the light-induced phase shifting at the same concentration as that at which W-7 was effective. These results suggest that calmodulin is required during signal transduction from the light-perceiving system to the circadian clock in N. crassa. Inhibitors of protein phosphorylation did not inhibit the light-induced phase shifting, although these inhibitors completely inhibited mycelial growth. Trifluoperazine partially inhibited the phosphorylation of three proteins when phosphorylation was assayed in vitro.

Calmodulin↗

PubMed1994

DET1, a negative regulator of light-mediated development and gene expression in arabidopsis, encodes a novel nuclear-localized protein.

The mechanisms by which plants integrate light signals to modify endogenous developmental programs are largely unknown. One candidate for a signal transduction component that may integrate light with developmental pathways is the Arabidopsis DET1 gene product. Here we report the positional cloning of the DET1 locus and show that DET1 is a unique nuclear-localized protein. An analysis of a number of det1 mutants indicates that mutants with partial DET1 activity develop as light-grown plants in the dark. det1 null mutants share this phenotype, but also display severe defects in temporal and spatial regulation of gene expression. These results suggest that DET1 acts in the nucleus to control the cell type-specific expression of light-regulated promoters.

Amino Acid Sequence↗

PubMed2002

Cytoskeleton participation in subcellular trafficking of signal transduction proteins in rod photoreceptor cells.

Light sensitivity and adaptation, general characteristics of rod photoreceptor cell vision, allow rods to modulate their response depending on the lighting environment to which they are exposed. In dim light, rods are maximally sensitive, whereas, in bright light, rods are essentially inactive. In the retinas of dark-adapted mice, arrestin (an inhibitory protein) is located in the rod inner segment (RIS), and transducin (an activating protein) is located in the rod outer segment (ROS). In light-adapted retinas, the proteins have reciprocal localizations. In this study, our data demonstrate that the temporal and spatial changes in the subcellular localization of arrestin and beta-transducin are correlated with the amount of light to which the animals are exposed. By using the frog Xenopus laevis and immunofluorescence confocal microscopy, our results also show that in the dark-adapted retina some arrestin remains in the ROS. The data most dramatically demonstrate that this residual arrestin is highly concentrated in the connecting cilium, the axoneme, and the microtubules associated with the disc incisures. These data suggest a structure-function relationship between the light-dependent positional status of arrestin and the elements of the rod photoreceptor cytoskeleton. The massive, rapid, light-induced reciprocal changes in the subcellular concentrations of these proteins must directly affect phototransduction and appear to be a general phenomenon by which photoreceptor cells rapidly and transiently regulate the trafficking and subcellular concentration of a variety of signal transduction proteins within the RIS and ROS. Hereditary mutations in the components of the movement mechanism should lead to defects in vision and possibly blindness.

Animals↗

PubMed1991

Signal transduction in Coprinus congregatus: evidence for the involvement of G proteins in blue light photomorphogenesis.

This paper reports the presence of several G proteins and light-sensitive GTP-binding proteins in the fungus Coprinus congregatus, a filamentous eukaryote. (Mono)ADP-ribosylation experiments with crude membranes in the presence of the (poly)ADP-ribosyltransferase inhibitor, 3-amino-benzamide, resulted in the detection of a cholera toxin substrate of 52 kDa and two pertussis toxin substrates, 33 and 39 kDa. Two-dimensional polyacrylamide gel analysis of GTP-binding proteins exposed in vivo to [35S]-labeled guanosine 5'-[gamma-thio]-triphosphate in the presence or absence of light demonstrated light enhanced analog binding. These results support the concept of the involvement of G proteins in phototransduction in C. congregatus.

Cell Membrane↗

PubMed1997

Light control of plant development.

To grow and develop optimally, all organisms need to perceive and process information from both their biotic and abiotic surroundings. A particularly important environmental cue is light, to which organisms respond in many different ways. Because they are photosynthetic and non-motile, plants need to be especially plastic in response to their light environment. The diverse responses of plants to light require sophisticated sensing of its intensity, direction, duration, and wavelength. The action spectra of light responses provided assays to identify three photoreceptor systems absorbing in the red/far-red, blue/near-ultraviolet, and ultraviolet spectral ranges. Following absorption of light, photoreceptors interact with other signal transduction elements, which eventually leads to many molecular and morphological responses. While a complete signal transduction cascade is not known yet, molecular genetic studies using the model plant Arabidopsis have led to substantial progress in dissecting the signal transduction network. Important gains have been made in determining the function of the photoreceptors, the terminal response pathways, and the intervening signal transduction components.

Cryptochromes↗

PubMed2003

Cryptochrome structure and signal transduction.

Cryptochromes are photosensory receptors mediating light regulation of growth and development in plants. Since the isolation of the Arabidopsis CRY1 gene in 1993, cryptochromes have been found in every multicellular eukaryote examined. Most plant cryptochromes have a chromophore-binding domain that shares similar structure with DNA photolyase, and a carboxyl terminal extension that contains a DQXVP-acidic-STAES (DAS) domain conserved from moss, to fern, to angiosperm. In Arabidopsis, cryptochromes are nuclear proteins that mediate light control of stem elongation, leaf expansion, photoperiodic flowering, and the circadian clock. Cryptochromes may act by interacting with proteins such as phytochromes, COP1, and clock proteins, or/and chromatin and DNA. Recent studies suggest that cryptochromes undergo a blue light-dependent phosphorylation that affects the conformation, intermolecular interactions, physiological activities, and protein abundance of the photoreceptors.

Amino Acid Sequence↗

PubMed2001

Mass spectrometric characterization of proteins extracted from Jurkat T cell detergent-resistant membrane domains.

Plasma membranes of most cell types are thought to contain microdomains commonly referred to as lipid rafts, biochemically distinct from bulk plasma membrane, apparently enriched for proteins involved in signal transduction. In T cells, it is believed that lipid rafts aggregate at the site of T cell receptor engagement and act as foci for initiation of the signaling process. In order to gain insight into the possible functioning of lipid rafts, we applied microcapillary liquid chromatography electrospray ionization tandem mass spectrometry (microLC-ESI-MS/MS) methodologies to the identification of proteins which copurified with lipid rafts. Following isolation of lipid rafts as Triton-insoluble, low-density membrane fractions from Jurkat T cells, tryptic digests were generated of individual protein bands resolved electrophoretically. Alternatively, cysteine-containing peptides were isolated from total tryptic digests of unseparated lipid raft proteins following labeling with a cysteine-specific biotinylation reagent and avidin affinity purification. In both cases, protein identifications were made by comparison of tandem MS spectra generated by microLC-ESI-MS/MS to both protein and DNA sequence databases using Sequest software. Proteins identified essentially fell into two groups: cytoskeletal proteins, and proteins involved in signal transduction. These findings are discussed in the light of the current understanding of both lipid raft biology and signal transduction.

Chromatography, Ion Exchange↗

PubMed1996

Signal transduction and HIV transcriptional activation after exposure to ultraviolet light and other DNA-damaging agents.

Short wavelength (254 nm) ultraviolet light (UVC) radiation was much more potent in activating transcription of human immunodeficiency virus 1 (HIV) reporter genes stably integrated into the genomes of human and monkey cells than ionizing radiation (IR) from a 137Cs source at similarly cytotoxic doses. A similar differential was also observed when c-jun transcription levels were examined. However, these transcription levels do not correlate with activation of nuclear factor (NF)-kappa B and AP-1 measured by band-shift assays, i.e. both types of radiation produce similar increases in NF-kappa B and AP-1 activity, suggesting existence of additional levels of regulation during these responses. Because of the well-established involvement of cytoplasmic signaling pathways in the cellular response to tumor necrosis factor-alpha (TNF-alpha), UVC, and IR using other types of assays, the role of TNF-alpha in the UVC response of HIV and c-jun was investigated in our cell system. We demonstrate that UVC and TNF-alpha activate HIV gene expression in a synergistic fashion, suggesting that it is unlikely that TNF-alpha is involved in UVC activation of HIV transcription in stably transfected HeLa cells. Moreover, maximum TNF-alpha stimulation resulted in one order of magnitude lower levels of HIV expression than that observed after UVC exposure. We also observed an additive effect of UVC and TNF-alpha on c-jun steady-state mRNA levels, suggestive of a partial overlap in activation mechanism of c-jun by UVC and TNF-alpha; yet these responses are distinct to some extent. Our results indicate that the HIV, and to some extent also the c-jun, transcriptional responses to UVC are not the result of TNF-alpha stimulation and subsequent downstream cytoplasmic signaling events in HeLa cells. Additional levels of regulation that do not directly involve the NF-kappa B and AP-1 transcription factors, such as changes in chromatin structure associated with the UV repair process, may also be important for a full transcriptional response of HIV and c-jun to UVC. In addition to the new data, this report also summarizes our current views regarding UVC-induced activations of HIV gene expression in stably transfected cells.

Animals↗

PubMed2005

Dynamic hysteresis in a one-dimensional Ising model: application to allosteric proteins.

We solve exactly the problem of dynamic hysteresis for a finite one-dimensional Ising model at low temperature. We find that the area of the hysteresis loop, as the field is varied periodically, scales as the square root of the field frequency for a large range of frequencies. Below a critical frequency there is a correction to the scaling law, resulting in a linear relationship between hysteresis area and frequency. The one-dimensional Ising model provides a simplified description of switchlike behavior in allosteric proteins, such as hemoglobin. Thus our analysis predicts the switching dynamics of allosteric proteins when they are exposed to a ligand concentration which changes with time. Many allosteric proteins bind a regulator that is maintained at a nonequilibrium concentration by active signal transduction processes. In the light of our analysis, we discuss to what extent allosteric proteins can respond to changes in regulator concentration caused by an upstream signaling event, while remaining insensitive to the intrinsic nonequilibrium fluctuations in regulator level which occur in the absence of a signal.

Allosteric Regulation↗

PubMed2002

New aspects of signal transduction in the Xenopus laevis melanotrope cell.

Light and temperature stimuli act via various brain centers and neurochemical messengers on the pituitary melanotrope cells of Xenopus laevis to control distinct subcellular activities such as the biosynthesis, processing, and release of alpha-melanophore-stimulating hormone (alphaMSH). The melanotrope signal transduction involves the action of a large repertoire of neurotransmitter and neuropeptide receptors and the second messengers cAMP and Ca(2+). Here we briefly review this signaling mechanism and then present new data on two aspects of this process, viz. the presence of a stimulatory beta-adrenergic receptor acting via cAMP and the egress of cAMP from the melanotrope upon a change of alphaMSH release activity.

Animals↗

PubMed2004

Direct involvement of hydrogen peroxide in curvature of wheat coleoptile in blue-light-treated and dark-grown coleoptiles.

Blue-light-induced photomorphogenesis is the sum total of a sequence of phenomena involving absorption of light by specific receptors, generation of a signal, processing transmembrane transport of signal, and the activation of a cascade of reactions in the cell interior. Though four blue-light receptors cryptochrome1, cryptochrome2, phototropin1, and phototropin2 have been identified, the signal transduction events associated with blue-light receptor activation are not understood. In this report, we demonstrate the generation and spatiotemporal distribution of H(2)O(2) in wheat coleoptile in response to blue light. Interception of the free-radical generation pathways dithiothreitol and propyl gallate rendered wheat coleoptile tips phototropically non-responsive. Unilateral application of H(2)O(2) onto the sub-apical region of a growing coleoptile brought about curvature in dark. Blue light also caused lipid peroxidation and augmented membrane rigidity of coleoptile cell membranes. We conclude that H(2)O(2) can act as a translocating second messenger that could bring about coleoptile curvature, and the signaling events may trigger Ca(2+) signaling cascades, changes in gene expression, and protein modifications.

Cell Membrane↗

PubMed1998

[Signal transduction in photoreceptor cells].

Vertebrate photoreceptors respond to light with a brief hyperpolarization of their membrane potential. In the dark, photoreceptors are depolarized by cation influx through channels in the plasma membrane which are kept open by the second messenger cGMP. Light absorption activates an enzyme cascade that hydrolytically destroys cGMP, resulting in channel closure and hyperpolarization of the membrane. In addition, processes are initiated that allow photoreceptors to adapt their sensitivity to the ambient illumination. Although these adaptational mechanisms are less well understood, it is clear that they are strongly controlled by the intracellular Ca2+ concentration. This review describes our present knowledge about the signal transduction and its fine tuning by a complex network of Ca(2+)-mediated processes in vertebrate photoreceptors.

Animals↗

PubMed1981

The pH dependence of photosensory responses in Stentor coeruleus and model system.

1. Live Stentor coeruleus exhibits a substantially red-shifted fluorescence maximum, corresponding to the anionic species of the photoreceptor chromophore. No change was observed in either the absorption or fluorescence excitation spectrum, indicating an efficient deprotonation of the photoreceptor pigment upon excitation by light. 2 Changes in external pH exhibit a dramatic effect on the pulmonary response of Stentor. Phototaxis is specifically inhibited at pH less than 6, with loss of photosensory perception which is restored when the pH is returned to pH greater than 6. 3. Fluorescence changes of 9-aminoacridine in suspensions of live Stentor indicate the generation of a pH gradient upon irradiation with light. Both pH gradient and phototaxis were inhibited by the addition of nigericin and p-tri-fluoromethoxy carbonyl cyanide phenylhydrazone (FCCP). 4. Incorporation of the Stentor photoreceptor protein in to artificial liposomes demonstrates the ability of the system to generate pH gradients across model membranes as monitored by the quenching of 9-aminoacridine fluorescence. The effect of external pH on net proton movement in the model system is strikingly similar to the pH dependent of the liver Stentor, thus lending support for transient proton flux being an important mode of light signal processing for photosensory transduction.

Animals↗