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PubMed2001

The TNF superfamily members LIGHT and CD154 (CD40 ligand) costimulate induction of dendritic cell maturation and elicit specific CTL activity.

LIGHT is a recently identified member of the TNF superfamily that is up-regulated upon activation of T cells. Herpesvirus entry mediator, one of its receptors, is constitutively expressed on immature dendritic cells (DCs). In this report, we demonstrate that LIGHT induces partial DC maturation as demonstrated by Ag presentation and up-regulation of adhesion and costimulatory molecules. LIGHT-stimulated DCs show reduced macropinocytosis and enhanced allogeneic stimulatory capacity but fail to produce significant amounts of IL-12, IL-6, IL-1beta, or TNF-alpha compared with unstimulated DCs. However, LIGHT cooperates with CD154 (CD40 ligand) in DC maturation, with particular potentiation of allogeneic T cell proliferation and cytokine secretion of IL-12, IL-6, and TNF-alpha. Moreover, LIGHT costimulation allows DCs to prime in vitro-enhanced specific CTL responses. Our results suggest that LIGHT plays an important role in DC-mediated immune responses by regulating CD154 signals and represents a potential tool for DC-based cancer immunotherapy.

Animals↗
PubMed2005

Indole-3-butyric acid synthesis in ecotypes and mutants of Arabidopsis thaliana under different growth conditions.

Although IBA is a naturally occurring auxin, its role in plant development is still under debate. In this study a set of Arabidopsis mutants was used to analyze the biosynthesis of IBA in vitro. The mutants chosen for this study can be classified as: (1) involvement in auxin metabolism, transport or synthesis (amt1, aux1, ilr1, nit1, rib1, sur1, trp1-100); (2) other hormones possibly involved in the regulation of IBA synthesis (aba1, aba3, eto2, fae1, hls1, jar1); (3) photomorphogenesis (det1, det2, det3); and (4) root architecture (cob1, cob2, scr1). In addition, two transgenic lines overexpressing the IAA glucose synthase (iaglu) gene from maize were analyzed. The ecotypes No-0 and Wassilewskija showed the highest IBA synthetase activity under control conditions, followed by Columbia, Enkheim and Landsberg erecta. In the mutant lines IBA synthetase activity differed in most cases from the wild type, however no particular pattern of up- or down-regulation, which could be correlated to their possible function, was found. For rib1 mutant seedlings it was tested whether reduced IBA synthetase activity correlates with the endogenous IBA levels. Free IBA differed only depending on the culture conditions, but gave no clear correlation with IBA synthetase activity compared to the wild type. Since drought and osmotic stress as well as abscisic acid (ABA) application enhanced IBA synthesis in maize, it was tested whether IBA synthetase from Arabidopsis is also inducible by drought stress conditions. This was confirmed for the two ecotypes Col and Ler which showed different IBA synthetase activity when cultivated with various degrees of drought stress. IBA synthetase was also determined in photomorphogenic mutants under different light regimes. Induction of IBA synthetase in det1 and det3 plants was found under short day plus a red light pulse or in the dark, respectively. The results are discussed with respect to the functions of the mutated genes.

Arabidopsis↗
PubMed2003

Reactive oxygen species affect photomorphogenesis in Neurospora crassa.

In Neurospora crassa, several biological phenomena such as the synthesis of carotenoids in the mycelia and polarity of perithecia are regulated by light. We found that a sod-1 mutant, with a defective Cu,Zn-type superoxide dismutase (SOD), showed accelerated light-dependent induction of carotenoid accumulation in the mycelia compared with the wild type. The initial rate of light-induced carotenoid accumulation in the sod-1 mutant was faster than that in the vvd mutant known to accumulate high concentrations. This acceleration was suppressed by treatment with antioxidant reagents. Light-induced transcription of genes involved in carotenoid synthesis, al-1, -2, and -3, was sustained in the sod-1 mutant, whereas it was transient in the wild type. Moreover sod-1 was defective in terms of light-induced polarity of perithecia. By genetic analysis, the enhancement in light-inducible carotenoid synthesis in sod-1 was dependent on the wild type alleles of wc-1 and wc-2. However, the sod-1;vvd double mutant showed additive effects on the carotenoid accumulation in the mycelia. These results suggested that intracellular reactive oxygen species regulated by SOD-1 could affect the light-signal transduction pathway via WC proteins.

Antioxidants↗
PubMed1976

Effect of light and glucose on the induction of nitrate reductase and on the distribution of nitrate in etiolated barley leaves.

Barley seedlings grown in the dark with 10 mm KNO(3) have low levels of nitrate reductase activity even though large amounts of No(3) (-) accumulate in the leaves. When the leaves are excised and transferred to the light, there is an increase in nitrate reductase activity both in the presence and absence of exogenous NO(3) (-). When the leaves are transferred to a glucose solution (0.05 m) but kept in the dark, induction of nitrate reductase activity occurs only when fresh NO(3) (-) is added to the system.In dark-grown leaves, there are small traces of NO(3) (-) in a "metabolic pool." Addition of glucose does not alter this distribution. Light, on the other hand, results in an appreciable accumulation of NO(3) (-) in the metabolic pool. There is a linear correlation between nitrate reductase activity and the size of the metabolic NO(3) (-) pool. Our results thus suggest that NO(3) (-) accumulates in a storage pool when seedlings are grown in continuous darkness. The transfer of this NO(3) (-) to an active metabolic pool is mediated by light but not by glucose. We believe that this transfer of NO(3) (-) leads to the induction of nitrate reductase. When NO(3) (-) is included in the medium, both light and glucose increase its incorporation into the metabolic pool. The results suggest two mechanisms for regulating the metabolic NO(3) (-) pool: (a) a transfer from the storage pool which requires light; and (b) a transfer from the external medium which requires either glucose or light.

Journal Article↗
PubMed2003

Light and cytokinin play a co-operative role in MGDG synthesis in greening cucumber cotyledons.

The current research investigated the regulation of monogalactosyldiacylglycerol (MGDG) biosynthesis, catalyzed by MGDG synthase (MGD) (UDP-galactose:1,2-diacylglycerol 3-beta-D-galactosyltransferase; EC 2.4.1.46), during chloroplast development in cucumbers (Cucumis sativus L. cv. Aonagajibai). In etiolated seedlings, white light induced a transient increase in MGD mRNA, followed by a subsequent increase in enzyme activity. MGDG, digalactosyldiacylglycerol (DGDG), and linolenic acid (18 : 3) of both MGDG and DGDG accumulated in a light-dependent manner. Early light-dependent induction of MGD protein was also identified in isolated chloroplasts. When cotyledons were detached from seedlings, these light-induced changes diminished. However, when a synthetic cytokinin, benzyladenine, was added to the detached cotyledons, a transient increase in MGD mRNA and a linear increase in the enzyme activity were induced even in the dark. Galactolipids subsequently accumulated to some extent and 18 : 3 content also increased. MGDG fully accumulated in detached cotyledons with co-treatment of light and a cytokinin. Red light (>600 nm) and far-red light (>700 nm) both induced an increase in MGD mRNA and enzyme activity but far-red light did not induce an accumulation of MGDG. These results suggest that (1). galactolipid biosynthesis is regulated by the cooperation of light and a cytokinin; (2). the accumulation of MGDG requires cytokinin in addition to light; (3). a red light (600-700 nm) dependent factor is necessary for the maximal galactolipid accumulation in addition to increase in MGD transcript and activity.

Adenine↗
PubMed2004

Significance of the lipid phase in the dynamics and functions of the xanthophyll cycle as revealed by PsbS overexpression in tobacco and in-vitro de-epoxidation in monogalactosyldiacylglycerol micelles.

The dynamics of the xanthophyll cycle relative to non-photochemical quenching (NPQ) were examined in tobacco plants overexpressing violaxanthin de-epoxidase (VDE), PsbS and PsbS+VDE for effects on NPQ and violaxanthin (V) de-epoxidation over a range of light intensities. Induction of de-epoxidation and NPQ increased in overexpressed VDE and PsbS plants, respectively. Surprisingly, under low light, overexpressing PsbS enhanced de-epoxidation in addition to NPQ. The effect was hypothesized as due to PsbS binding zeaxanthin (Z) or inducing the binding of Z within the quenching complex, thus shifting the equilibrium toward higher de-epoxidation states. Studies in model systems show that Z can stereospecifically inhibit VDE activity against violaxanthin. This effect, observed under conditions of limiting lipid concentration, was interpreted as product feedback inhibition. These results support the hypothesis that the capacity of the thylakoid lipid phase for xanthophylls is limited and modulates xanthophyll-cycle activity, in conjunction with the release of V and binding of Z by pigment-binding proteins. These modulating factors are incorporated into a lipid-matrix model that has elements of a signal transduction system wherein the light-generated protons are the signal, VDE the signal receptor, Z the secondary messenger, the lipid phase the transduction network, and Z-binding proteins the targets.

Galactolipids↗
PubMed1995

Intracellular expression of the monoclonal anti-ras antibody Y13-259 blocks the transforming activity of ras oncogenes.

Microinjection of the anti-ras antibody Mab Y13-259 modifies ras function and can induce temporary reversion of the transformed phenotype in mutant ras-transformed cells. Intracellular production of neutralizing antibodies represents an approach to investigate the regulation of gene function. The genes coding for the heavy and light chains of Mab Y13-259 were isolated from a cDNA library. NIH3T3 cells transfected with heavy and light chain expression vectors produced functional anti-ras antibody. The production of functional antibody did not require glycosylation. To ensure that the antibody entered the cytoplasm and not the secretory pathway, the hydrophobic leader sequences of both chains were removed and replaced with synthetic initiator sequences. The modified heavy chain gene was cloned under the control of the murine sarcoma virus long terminal repeat, and the light chain gene under the control of the mouse mammary tumor virus long terminal repeat, which allows the induction of light chain expression in the presence of dexamethasone. When both heavy and light chain genes were expressed in cells with activated ras (morphologically transformed) in the presence of dexamethasone, we observed phenotypic reversion to characteristics of nontransformed cells. These experiments show that intracellular expression of antibodies can also be used as an alternative to analyze biological functions of a given protein.

3T3 Cells↗
PubMed2003

Light-regulated translation mediates gated induction of the Arabidopsis clock protein LHY.

The transcription factor LHY and the related protein CCA1 perform overlapping functions in a regulatory feedback loop that is closely associated with the circadian oscillator of Arabidopsis: Overexpression of LHY abolished function of the circadian clock in constant light, but rhythmic expression of several circadian clock-regulated transcripts was observed under light- dark cycles. These oscillations correlated with high amplitude changes in LHY protein levels, caused by light-induced translation of the LHY transcript. Increases in LHY protein levels were also observed in light-grown wild-type plants, when light signals coincided with the circadian-regulated peak of LHY transcription at dawn. Unexpectedly, translational induction coincided with acute downregulation of LHY transcript levels. We suggest that the simultaneous translational induction and transcriptional repression of LHY expression play a role to narrow the peak of LHY protein synthesis at dawn and increase the robustness and accuracy of circadian oscillations. Strong phase shifting responses to light signals were observed in plants lacking function of LHY, CCA1 or both, suggesting that light-regulated expression of these proteins does not mediate entrainment of the clock to light-dark cycles.

Arabidopsis↗
PubMed1987

Equivalence between Pfr and Cyclic AMP in the Induction of d-Usnic Acid Dehydrogenase in the Lichen Evernia prunastri.

d-Usnic acid dehydrogenase is induced in Evernia prunastri thalli by a supply of exogenous d-usnic acid in light. This effect is enhanced by red light pulses through a two step way: a very rapid increase of activity after the first 10 minutes of red light, which is not reversed by far-red light, and a slow enhancement following successive red light pulses at the beginning of each hour of incubation. The last response is completely reversed by far-red following red light. Although induction of the enzyme is not achieved in the dark, 0.1 and 0.5 millimolar cyclic AMP, or 0.1 millimolar dibutyryl cyclic AMP substitutes light action and, then, the enzyme is produced. In addition, phytochrome-far red-absorbing form-increases the amount of endogenously produced cyclic AMP and this effect is shown to be photoreversible when ethylenediaminetetraacetic acid is inhibiting adenylate cyclase.

Journal Article↗
PubMed1995

Developmental study in the circadian clock of the golden hamster: a putative role of astrocytes.

The hypothalamic suprachiasmatic nuclei (SCN) house the circadian clock in the mammalian brain. A glial fibrillary acidic protein immunoreactivity (GFAP-ir) distribution rhythm has been observed in the SCN of adult Syrian hamster. The implication of astrocytes in photic entrainment was analyzed through developmental studies of the photic pathway and of SCN astrocytes appearance. Using anterograde tracing we studied the timing of penetration of the retinohypothalamic tract (RHT) fibers into the SCN. Using c-fos induction by light we followed the maturation of RHT synapses in the SCN. When RHT terminals reach the SCN, c-fos induction can be obtained. Using GFAP immunoreactivity we demonstrated that the number of astrocytes increased in parallel with RHT development from PN5 to PN15. At PN15, a time when pups can shift from maternal to photic entrainment, RHT terminals and GFAP-ir exhibit an adult-like pattern. One demonstrated role of astrocytes is to control extracellular glutamate concentration. Glutamate is the neurotransmitter released at RHT terminals; its content fluctuates according to a circadian rhythm within the SCN. Thus the present data tend to indicate that SCN astrocytes are participating in the circadian rhythm of SCN glutamate content.

Aging↗
PubMed1978

Effect of light nitrogenase function and synthesis in Rhodopseudomonas capsulata.

The metabolic versatility of the purple nonsulfur photosynethetic bacterial permits the expression of either a phototrophic or a dark aerobic mode of growth. These organism also possess nitrogenase activity which may function under semiaerboic conditions. On the basis of these important properties, the light dependence of nitrogenase function and synthesis in Rhodopseudomonas capsulata was investigated. Nitrogenase activity was strictly dependent on light; no activity was observed in the dark, even when energy (ATP) was supplied by oxidative phosphorylation. It was concluded that the low-potential reducing agent required by the nitrogenase-catalyzed reaction could only be generated by a photochemical reaction. Nitrogenase biosynthesis was also largely dependent on light; however, a small amount of synthesis was observed in resting cells incubated in the dark. Resting cells prepared from dark-grown cultures synthesized nitrogenase at high rates upon illumination. The highest stability of nitrogenase in these resting cells was observed when suspensions were exposed to a diurnal pattern of illumination rather than continuous light. Although nitrogenase function and synthesis are closely coupled to photosynthetic activity, the biosyntheses of bacteriochorophyll and nitrogenase are independent of each other and are most probably subject to different regulatory mechanisms by light.

Anaerobiosis↗
PubMed1996

Different mechanisms are responsible for c-jun mRNA induction by cisplatin and ultraviolet light.

Ultraviolet light (UV) and different DNA-damaging agents are known to induce AP-l-transcription-factor activity. Whereas UV induction appears to be triggered by events at the cell membrane, the mechanism of AP-l activation by alkylating or platinating agents is not known. We have here examined the effect of cisplatin on AP-l activity in RPMI-8322 melanoma cells. Cisplatin was found to induce binding of nuclear proteins to TRE elements from the c-jun and collagenase-gene promoters, and was also found to induce activation of a c-jun-promoter reporter construct. Compared with stimulation by UV, cisplatin stimulation of c-jun-promoter activity was found to be less sensitive to a dominant negative mutant of Raf-I protein kinase. Furthermore, whereas UV treatment resulted in strong MAP-kinase activation, cisplatin treatment resulted only in a weak and transient increase. These data suggest that the Raf-MAPK pathway is of minor importance for the induction of c-jun-promoter activity by cisplatin. Finally, we report that cisplatin induction of c-jun in RPMI-8322 cells was blocked by herbimycin A, an inhibitor of Src-family tyrosine kinases. In contrast, UV induction of c-jun was not blocked by herbimycin A. In conclusion, our data strongly suggest that UV and cisplatin induction of c-jun mRNA in RPMI-8322 melanoma cells occur by distinct mechanisms.

Benzoquinones↗
PubMed2007

The S1YZ* metalloradical EPR signal of photosystem II contains two distinct components that advance respectively to the multiline and g = 4.1 conformations of S2.

The S2 state of the oxygen-evolving complex (OEC) of photosystem II is heterogeneous, exhibiting two main EPR spectral forms, the multiline and the g = 4.1 signal. It is not clearly established whether this heterogeneity develops during the S1 to S2 transition or is already present in the precursor states. We have compared the spectra of the S1YZ* intermediate, obtained by visible light excitation (induction of charge separation) of the S1 state at liquid He temperatures, (S1YZ*)vis, or by near-infrared (NIR) light excitation of the S2 state (utilization of the unusual property of the Mn cluster to act as an oxidant of Yz when excited by NIR), (S1YZ*)NIR. The decay kinetics of the (S1YZ*)vis spectrum at 11 K was also studied by the application of rapid-scan EPR. The two spectra share in common a signal with a characteristic feature at g = 2.035, but the (S1YZ*)vis spectrum contains in addition a fast decaying component 26 G wide. The analysis of the surface of the rapid-scan spectra yielded 270 +/- 35 and 90 +/- 15 s for the respective half-times of the two components of the (S1YZ*)vis spectrum at 11 K. (S1YZ*)vis advances efficiently to S2 when annealed at 200 K; notably the g = 2.035 signal advances to the multiline while the 26 G component advances to the g = 4.1 conformation. The "26 G" component is absent or very small, respectively, in thermophilic cyanobacteria or glycerol-containing spinach samples, in correlation to vanishing or very small amounts of the g = 4.1 component in the S2 spectrum. The results validate the assignment of S1YZ* to a true S1 to S2 intermediate and imply that the heterogeneity observed in S2 is already present in S1. Tentative valences are assigned to the individual Mn ions of the OEC in the two heterogeneous conformations of S1.

Electron Spin Resonance Spectroscopy↗
PubMed2000

Antagonistic action of low-fluence and high-irradiance modes of response of phytochrome on germination and beta-mannanase activity in Datura ferox seeds.

Seed germination is often induced by a pulse of red light perceived by phytochrome and cancelled by a subsequent pulse of far-red light. When the pulse of red light is followed by several hours of darkness, a pulse of far-red light is no longer effective and prolonged far-red is necessary to block germination. The aim was to investigate whether the red light pulse and prolonged far-red light act on the same or different processes during germination of Datura ferox seeds. Forty-five hours after the inductive red light pulse, germination could not be blocked by one pulse or six hourly pulses of far-red light, but was significantly reduced by 6 h of continuous far-red light. The pulse of red light increased embryo growth potential and the activities of beta-mannanase and beta-mannosidase extracted from the micropylar region of the endosperm. Continuous far-red light had no effect on embryo growth potential or beta-mannosidase activity, but severely reduced the activity of beta-mannanase. The effect of far-red light had the features of a high-irradiance response of phytochrome. Both germination and beta-mannanase activity were restored by a pulse of red light given after the end of the continuous far-red treatment. It is concluded that the low-fluence response and the high-irradiance response modes of phytochrome have antagonistic effects on seed germination and that the control of beta-mannanase activity is one process where this antagonism is established.

Datura stramonium↗
PubMed1974

Circadian function in the photoperiodic induction of gonadotropin secretion in the white-crowned sparrow, Zonotrichia leucophrys gambelii.

Photosensitive White-crowned Sparrows (Zonotrichia leucophrys gambelii) previously maintained on short day lengths (8-hr light; 16-hr darkness) were transferred to complete darkness. At various intervals thereafter (2-100 hr) they were exposed to a single 8-hr light period. To determine if the light period had been inductive, plasma luteinizing-hormone concentration was measured by radioimmunoassay in blood samples taken before and after the light period. Inductive light periods recurred at approximately daily intervals. The data provide further evidence for the involvement of a circadian rhythm in time measurement in the photoperiodic responses of birds.

Animals↗
PubMed1988

Autoregulation of rhodopsin synthesis in Chlamydomonas reinhardtii.

A sensitive assay for the induction of carotenoid and rhodopsin synthesis, based on the phototactic response, has been developed in a mutant of the unicellular alga Chlamydomonas reinhardtii. In the dark, the mutant fails to synthesize carotene and retinal, but it contains the apoprotein opsin. When retinal synthesis is induced by light treatment, the retinal combines with opsin to form rhodopsin, and the cells swim away from a source of light. Since the amount of light required to trigger a phototactic response is inversely proportional to the concentration of rhodopsin, the decrease in amount of light necessary to generate that response can serve as a measure of the amount of retinal synthesized in cells after induction. Using this assay, we found that (i) light induction of retinal depends linearly on light exposure and rhodopsin concentration during the exposure; (ii) the action spectrum of light induction is identical with that for phototaxis for which the receptor pigment is rhodopsin; and (iii) incubation with all-trans-7,8-dihydroretinal before light exposure shifts the action-spectrum peak for light induction 0.41 eV (-71 nm). We conclude that the photopigment for induction of retinal synthesis is a rhodopsin. The time lag required for induction of retinal synthesis and preliminary experiments with transcription or translation inhibitors suggest that alterations in gene expression could be involved in the induction process. Its control could be similar to other processes in which membrane receptors for hormones, neurotransmitters, or growth factors regulate gene expression.

Cell Movement↗
PubMed1997

Impairment of pupillary responses and optokinetic nystagmus in the mGluR6-deficient mouse.

Retinal bipolar cells receive glutamatergic transmission from photoreceptors and mediate a key process in segregating visual signals into ON-center and OFF-center pathways. The segregation of ON responses involves a G protein-coupled metabotropic glutamate receptor (mGluR). The mGluR6 subtype is expressed restrictedly at the postsynaptic site of retinal ON-bipolar cells. Ablation of mGluR6 in the ON-bipolar cells by gene targeting results in a loss of ON responses but unchanged OFF responses in visual transmission. Thus, mGluR6 is essential for inducing ON responses. The aims of this study are analyses of visual responsiveness and possible visual dysfunction in mGluR6-deficient mice. We report here that mGluR6-deficient mice have unaltered locomotor activity in a daily light-dark cycle and exhibit light-stimulated induction of Fos immunoreactivity in the suprachiasmatic nucleus. These findings indicate that mGluR6-deficient mice are capable or responding to light stimulation. The mGluR6 deficiency, however, markedly reduces the sensitivity of pupillary responses to light stimulus and severely impairs the ability to drive optokinetic nystagmus in response to visual contrasts. This study thus demonstrates that mGluR6 contributes to discrimination of visual contrasts.

Animals↗