Signal transduction controlling the blue- and red-light mediated gene expression of S-adenosylmethionine decarboxylase in Pharbitis nil

The signal transduction processes involved in the regulation of SAMDC gene expression by blue and red light were examined using pharmacological inhibitors of signalling pathways. Calcium and calmodulin positively regulated SAMDC gene expression in red light, whereas in blue light they regulated negatively. These results indicate that calcium homeostasis is involved in both red and blue light induction of SAMDC expression. Both signal transduction pathways also require new protein synthesis.     

Phototropins and neochrome1 mediate nuclear movement in the fern Adiantum capillus-veneris

In gametophytic cells (prothalli) of the fern Adiantum capillus-veneris, nuclei as well as chloroplasts change their position according to light conditions. Nuclei reside on anticlinal walls in darkness and move to periclinal or anticlinal walls under weak or strong light conditions, respectively. Here we reveal that red light-induced nuclear movement is mediated by neochrome1 (neo1), blue light-induced movement is redundantly mediated by neo1, phototropin2 (phot2) and possibly phot1, and dark positioning of both nuclei and chloroplasts is mediated by phot2. Thus, both the nuclear and chloroplast photorelocation movements share common photoreceptor systems.     

Enhancement of fibroblast collagenase-1 (MMP-1) gene expression by tumor promoter okadaic acid is mediated by stress-activated protein kinases jun N-terminal kinase and p38

Collagenase-1 (matrix metalloproteinase-1, MMP-1) is expressed by several types of cells, including fibroblasts, and apparently plays an important role in the remodeling of collagenous extracellular matrix in various physiologic and pathologic situations. Here, we have examined the molecular mechanisms of the activation of fibroblast MMP-1 gene expression by a naturally occurring non-phorbol ester type tumor promoter okadaic acid (OA), a potent inhibitor of serine/threonine protein phosphatase 2A. We show that in fibroblasts OA activates three distinct subgroups of mitogen activated protein kinases (MAPKs): extracellular signal-regulated kinase 1,2 (ERK 1,2), c-Jun N-terminal-kinase/stress-activated protein kinase (JNK/SAPK) and p38. Activation of MMP-1 promoter by OA is entirely blocked by overexpression of dual-specificity MAPK phosphatase CL100. In addition, expression of kinase-deficient forms of ERK 1,2, SAPKβ, p38, or JNK/SAPK kinase SEK1 strongly inhibited OA-elicited activation of MMP-1 promoter. OA-elicited enhancement of MMP-1 mRNA abundance was also strongly prevented by two chemical MAPK inhibitors: PD 98059, a specific inhibitor of the activation of ERK1,2 kinases MEK1,2; and SB 203580, a selective inhibitor of p38 activity. Results of this study show that MMP-1 gene expression in fibroblasts is coordinately regulated by ERK1,2, JNK/SAPK, and p38 MAPKs and suggest an important role for the stress-activated MAPKs JNK/SAPK and p38 in the activation of MMP-1 gene expression. Based on these observations, it is conceivable that specific inhibition of stress-activated MAPK pathways may serve as a novel therapeutic target for inhibiting degradation of collagenous extracellular matrix.     

Long-term blue light exposure induces RGC-5 cell death in vitro: involvement of mitochondria-dependent apoptosis,oxidative stress,and MAPK signaling pathways

The mechanism of blue light-induced retinal ganglion cell (RGC) injury is poorly understood. In this study, we established a patented light-emitting diode-based system to study the effects of long-term blue light exposure under culture conditions on RGC-5 cells. Long-term blue light exposure significantly reduced cell viability in a time-dependent manner and induced apoptosis and necrosis in RGC-5 cells. Long-term blue light exposure marked an increase in the expression of Bax and active Caspase-3 (p17), which was accompanied by Bcl-2 down-regulation, and displayed features of the mitochondria-dependent apoptosis pathway. Blue light exposure also increased the generation of reactive oxygen species (ROS), and was a strong inducer of ROS-sensitive protein nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expression. Moreover, blue light exposure constitutively activated p38 mitogen-activated protein kinases and c-Jun NH2-terminal kinase (JNK), as well as induced the phosphorylation of extracellular signal-regulated kinase in the early phase, in blue light-exposed RGC-5 cells. The protein expression of c-jun and c-fos was further enhanced after RGC-5 cells were exposed to blue light. Taken together, these findings indicated that blue light induced RGC-5 cell line death in dependence upon exposure duration. The potential mechanisms for this phenomenon might be via activated mitochondria-dependent apoptosis, increased ROS production and protein expressions of Nrf2 and HO-1, and activated JNK/p38 MAPK signaling pathways.     

Fast manipulation of cellular cAMP level by light in vivo

The flagellate Euglena gracilis contains a photoactivated adenylyl cyclase (PAC), consisting of the flavoproteins PACalpha and PACbeta. Here we report functional expression of PACs in Xenopus laevis oocytes, HEK293 cells and in Drosophila melanogaster, where neuronal expression yields light-induced changes in behavior. The activity of PACs is strongly and reversibly enhanced by blue light, providing a powerful tool for light-induced manipulation of cAMP in animal cells.     

Phytochrome A regulates the intracellular distribution of phototropin 1-green fluorescent protein in Arabidopsis thaliana

It has been known for decades that red light pretreatment has complex effects on subsequent phototropic sensitivity of etiolated seedlings. Here, we demonstrate that brief pulses of red light given 2 h prior to phototropic induction by low fluence rates of blue light prevent the blue light-induced loss of green fluorescent protein-tagged phototropin 1 (PHOT1-GFP) from the plasma membrane of cortical cells of transgenic seedlings of Arabidopsis thaliana expressing PHOT1-GFP in a phot1-5 null mutant background. This red light effect is mediated by phytochrome A and requires approximately 2 h in the dark at room temperature to go to completion. It is fully far red reversible and shows escape from photoreversibility following 30 min of subsequent darkness. Red light-induced inhibition of blue light-inducible changes in the subcellular distribution of PHOT1-GFP is only observed in rapidly elongating regions of the hypocotyl. It is absent in hook tissues and in mature cells below the elongation zone. We hypothesize that red light-induced retention of the PHOT1-GFP on the plasma membrane may account for the red light-induced increase in phototropic sensitivity to low fluence rates of blue light.     

LED Light-Induced ROS Differentially Regulates Focal Adhesion Kinase Activity in HaCaT Cell Viability

In this study, changes in cell signaling mechanisms in skin cells induced by various wavelengths and intensities of light-emitting diodes (LED) were investigated, focusing on the activity of focal adhesion kinase (FAK) in particular. We examined the effect of LED irradiation on cell survival, the generation of intracellular reactive oxygen species (ROS), and the activity of various cell-signaling proteins. Red LED light increased cell viability at all intensities, whereas strong green and blue LED light reduced cell viability, and this effect was reversed by NAC or DPI treatment. Red LED light caused an increase in ROS formation according to the increase in the intensity of the LED light, and green and blue LED lights led to sharp increases in ROS formation. In the initial reaction to LEDs, red LED light only increased the phosphorylation of FAK and extracellular-signal regulated protein kinase (ERK), whereas green and blue LED lights increased the phosphorylation of inhibitory-κB Kinase α (IKKα), c-jun N-terminal kinase (JNK), and p38. The phosphorylation of these intracellular proteins was reduced via FAK inhibitor, NAC, and DPI treatments. Even after 24 h of LED irradiation, the activity of FAK and ERK appeared in cells treated with red LED light but did not appear in cells treated with green and blue LED lights. Furthermore, the activity of caspase-3 was confirmed along with cell detachment. Therefore, our results suggest that red LED light induced mitogenic effects via low levels of ROS–FAK–ERK, while green and blue LED lights induced cytotoxic effects via cellular stress and apoptosis signaling resulting from high levels of ROS.     

Negative phototropic response of rhizoid cells in the fern Adiantum capillus-veneris

In general, phototropic responses in land plants are induced by blue light and mediated by blue light receptor phototropins. In many cryptogam plants including the fern Adiantum capillus-veneris, however, red as well as blue light effectively induces a positive phototropic response in protonemal cells. In A. capillus-veneris, the red light effect on the tropistic response is mediated by phytochrome 3 (phy3), a chimeric photoreceptor of phytochrome and full-length phototropin. Here, we report red and blue light-induced negative phototropism in A. capillus-veneris rhizoid cells. Mutants deficient for phy3 lacked red light-induced negative phototropism, indicating that under red light, phy3 mediates negative phototropism in rhizoid cells, contrasting with its role in regulating positive phototropism in protonemal cells. Mutants for phy3 were also partially deficient in rhizoid blue light-induced negative phototropism, suggesting that phy3, in conjunction with phototropins, redundantly mediates the blue light response.     

Suppressing autophagy protects photoreceptor cells from light-induced injury

Autophagy, a conserved cellular self-degradation process, not only serves to protect cells at critical times during development and nutrient stress, but also contributes to cell death. Photoreceptor cells are unique neurons which when directly exposed to the light, transduces light stimuli into visual signal. However, intense light exposure can be cytotoxic to the retina. So far, the precise mechanism underlying retina light injury remains unknown, and the effective therapy is still unavailable. Here, we found that visible light exposure activated the mitogen-activated protein kinases (MAPK) pathway and led to remarkable autophagy in photoreceptor cells (661W cells). Directly blocking autophagy with 3MA or LY294002 markedly attenuated light-induced death in 661W cells. Among the activated downstream factors of MAPK pathway, ERK, not JNK or p-38, played a critical role in light-induced death mechanism. Inhibiting the activation of ERK with its specific inhibitor PD98059 significantly suppressed light-induced autophagy and protected 661W cells from light injury. These results indicate that autophagy is an essential event in light-induced photoreceptor death and that directly blocking autophagy or suppressing autophagy by inhibiting the ERK pathway could effectively attenuates light-induced damage. These observations may have a potential application in the treatment of retinal light injury.     

The Arabidopsis blue light receptor cryptochrome 2 is a nuclear protein regulated by a blue light-dependent post-transcriptional mechanism

Cryptochrome 2 is a flavin-type blue light receptor mediating floral induction in response to photoperiod and a blue light-induced hypocotyl growth inhibition. cry2 is required for the elevated expression of the flowering-time gene CO in response to long-day photoperiods, but the molecular mechanism underlying the function of cry2 is not clear. The carboxyl domain of cry2 bears a basic bipartite nuclear localization signal, and the cry2 protein was co-fractionated with the nucleus. Analysis of transgenic plants expressing a fusion protein of CRY2 and the reporter enzyme GUS (GUS-CRY2) indicated that the GUS-CRY2 fusion protein accumulated in the nucleus of transgenic plants grown in dark or light. The C-terminal domain of cry2 that contains the basic bipartite nuclear localization signal was sufficient to confer nuclear localization of the fusion protein. Phenotypic analysis of transgenic plants expressing the fusion protein GUS-CRY2 demonstrated that GUS-CRY2 acts as a functional photoreceptor in vivo, mediating the blue light-induced inhibition of hypocotyl elongation. These results strongly suggest that cry2 is a nuclear protein. Although no obvious light regulation was found for the nuclear compartmentation of GUS-CRY2 fusion protein, the abundance of GUS-CRY2 was regulated by blue light in a way similar to that of cry2.     

Light-Regulated Gravitropism in Seedling Roots of Maize

Red light-induced changes in the gravitropism of roots of Zea mays variety Merit is a very low fluence response with a threshold of 10⁻⁹ moles per square meter and is not reversible by far red light. Blue light also affects root gravitropism but the sensitivity of roots to blue is 50 to 100 times less than to an equal fluence of red. In Z. mays Merit we conclude that phytochrome is the sole pigment associated with light-induced changes in root gravitropism.