The Effects of Melatonin on Transcriptional Profile of Unfolded Protein Response Genes Under Endoplasmic Reticulum Stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

When the load of secretory pathway is increased or folding capacity in the endoplasmic reticulum (ER) is insufficient, unfolded proteins might accumulate in ER lumen causing a phenomenon called ER stress. During ER stress, normal cell functions are suppressed and unfolded protein response (UPR) is induced. Studies in animal systems suggest that melatonin alleviates the detrimental effects of ER stress; however, there is no study in plants in this respect. Hence, in this study, we investigated the possible role of melatonin on alleviation of ER stress in model plant Arabidopsis thaliana. Tunicamycin (Tm) was used to specifically induce ER stress. Melatonin treatment (10 and 25 μM but not 1 μM) increased root growth under Tm treatment, but it did not reach control levels. ER stress induced the expressions of ER stress sensor/transducer genes, ER chaperones and folding helper genes, ER-associated degradation (ERAD) genes, and ER stress-associated apoptosis genes in roots and shoots (a total of 16 genes). Among them, the expressions of ER stress sensor/transducer bZIP17, bZIP28, IRE1A, IRE1B, ERAD-related SEL1, and apoptosis genes AGB1 were decreased back to control levels with 25 μM melatonin under ER stress in roots. Moreover, Tm?+?melatonin treatments decreased the expressions of these genes when compared to only Tm-treated plants. Downregulation of UPR components with increased concentrations of melatonin under Tm treatment demonstrated that melatonin alleviated the detrimental effects of ER stress.     

RNA-Mediated Feedback Control of Transcriptional Condensates

1. Download : Download high-res image (203KB)
2. Download : Download full-size image

     

Crystal structures of NodS N-methyltransferase from Bradyrhizobium japonicum in ligand-free form and as SAH complex

NodS is an S-adenosyl-l-methionine (SAM)-dependent N-methyltransferase that is involved in the biosynthesis of Nod factor (NF) in rhizobia, which are bacterial symbionts of legume plants. NF is a modified chitooligosaccharide (COS) signal molecule that is recognized by the legume host, where it initiates symbiotic processes leading to atmospheric nitrogen fixation. We report the crystal structure of recombinant NodS protein from Bradyrhizobium japonicum, which infects lupine and serradella legumes. Two crystal forms—ligand-free NodS and NodS in complex with S-adenosyl-l-homocysteine, which is a by-product of the methylation reaction—were obtained, and their structures were refined to resolutions of 2.43 Å and 1.85 Å, respectively. Although the overall fold (consisting of a seven-stranded β-sheet flanked by layers of helices) is similar to those of other SAM-dependent methyltransferases, NodS has specific features reflecting the unique character of its oligosaccharide substrate. In particular, the N-terminal helix and its connecting loop get ordered upon SAM binding, thereby closing the methyl donor cavity and shaping a long surface canyon that is clearly the binding site for the acceptor molecule. Comparison of the two structural forms of NodS suggests that there are also other conformational changes taking place upon the binding of the donor substrate. As an enzyme that methylates a COS substrate, NodS is the first example among all SAM-dependent methyltransferases to have its three-dimensional structure elucidated. Gaining insight about how NodS binds its donor and acceptor substrates helps to better understand the mechanism of NodS activity and the basis of its functional difference in various rhizobia.     

Stability of the saccadic oculomotor system

A variety of different types of instability has been found in the saccadic system of humans. Some of the instabilities correspond to clinical conditions, whereas others are inherent in the normal saccadic system. How can these instabilities arise within the mechanism of normal saccadic eye movements? A physiologically-based model of the saccadic system predicts that horizontal saccadic oscillations will occur with excessive mutual inhibition between the left and right burst cells and with underaction of the pause cells. The amplitudes and frequencies of the oscillations had ranges of 0–6° and 6–20 cycles per second, respectively. Application of stability analysis techniques to the model reveals that development of the oscillations can be explained by the Hopf bifurcation mechanism. Future development of this approach will involve classifying pathological instabilities of the saccadic system according to the bifurcation involved in their generation.     

Boc-lysinated-betulonic acid: a potent, anti-prostate cancer agent

Betulonic acid, derived from betulinol, a pentacyclic styrene, has shown a highly specific anti-prostate cancer activity in in vitro cell cultures. However, due to the lack of solubility of betulonic acid in aqueous medium, its potent anti-cancer activity in vivo has not been determined to the fullest extent. The present study describes the chemical synthesis of hydrophilic Boc-lysinated-betulonic acid, which has improved its solubility in an aqueous biocompatible solvent. Evaluation in cytotoxicity assays, Boc-lysinated-betulonic acid dissolved in phosphate-buffered saline (PBS) containing 22% ethanol and 4% human serum albumin, has shown 95.7% inhibition of LNCaP prostate cancer cells in culture after 72 h incubation at a concentration of 100 microM, but with little effect on normally proliferating fibroblast cells. In the in vivo assay, male athymic mice transplanted with human prostate LNCaP xenografts were injected with Boc-lysinated-betulonic acid intraperitoneally at a dose of 30 mg/kg daily for 17 days. The treated mice exhibited 92% inhibition of tumor growth as compared to controls. Histological sections of the tumors showed that Boc-lysinated-betulonic acid arrested mitosis and induced apoptosis, which was confirmed by TUNEL assay, Yo-Pro-1 staining, and the release of cleaved caspase-3 from the ex vivo in tumor culture. These studies, for the first time, demonstrate that a non-toxic hydrophilic lysinated derivative of betulonic acid and its solubility in a biocompatible aqueous medium has enhanced the bioavailability of the drug and has thus unleashed its full anti-prostate cancer activity.