Trehalose-6-phosphate synthase/phosphatase regulates cell shape and plant architecture in Arabidopsis

The vacuole occupies most of the volume of plant cells; thus, the tonoplast marker delta-tonoplast intrinsic protein-green fluorescent protein delineates cell shape, for example, in epidermis. This permits rapid identification of mutants. Using this strategy, we identified the cell shape phenotype-1 (csp-1) mutant in Arabidopsis thaliana. Beyond an absence of lobes in pavement cells, phenotypes included reduced trichome branching, altered leaf serration and stem branching, and increased stomatal density. This result from a point mutation in AtTPS6 encoding a conserved amino-terminal domain, thought to catalyze trehalose-6-phosphate synthesis and a carboxy-terminal phosphatase domain, is catalyzing a two-step conversion to trehalose. Expression of AtTPS6 in the Saccharomyces cerevisiae mutants tps1 (encoding a synthase domain) and tps2 (encoding synthase and phosphatase domains) indicates that AtTPS6 is an active trehalose synthase. AtTPS6 fully complemented defects in csp-1. Mutations in class I genes (AtTPS1-AtTPS4) indicate a role in regulating starch storage, resistance to drought, and inflorescence architecture. Class II genes (AtTPS5-AtTPS11) encode multifunctional enzymes having synthase and phosphatase activity. We show that class II AtTPS6 regulates plant architecture, shape of epidermal pavement cells, and branching of trichomes. Thus, beyond a role in development, we demonstrate that the class II gene AtTPS6 is important for controlling cellular morphogenesis.     

The Arabidopsis calcium sensor calcineurin B-like 3 inhibits the 5'-methylthioadenosine nucleosidase in a calcium-dependent manner

Calcineurin B-like (CBL) proteins represent a unique family of calcium sensors in plant cells. Sensing the calcium signals elicited by a variety of abiotic stresses, CBLs transmit the information to a group of serine/threonine protein kinases (CBL-interacting protein kinases [CIPKs]), which are currently known as the sole targets of the CBL family. Here, we report that the CBL3 member of this family has a novel interaction partner in addition to the CIPK proteins. Extensive yeast two-hybrid screenings with CBL3 as bait identified an interesting Arabidopsis (Arabidopsis thaliana) cDNA clone (named AtMTAN, for 5'-methylthioadenosine nucleosidase), which encodes a polypeptide similar to EcMTAN from Escherichia coli. Deletion analyses showed that CBL3 utilizes the different structural modules to interact with its distinct target proteins, CIPKs and AtMTAN. In vitro and in vivo analyses verified that CBL3 and AtMTAN physically associate only in the presence of Ca(2+). In addition, we empirically demonstrated that the AtMTAN protein indeed possesses the MTAN activity, which can be inhibited specifically by Ca(2+)-bound CBL3. Overall, these findings suggest that the CBL family members can relay the calcium signals in more diverse ways than previously thought. We also discuss a possible mechanism by which the CBL3-mediated calcium signaling regulates the biosynthesis of ethylene and polyamines, which are involved in plant growth and development as well as various stress responses.     

Health Risk Assessment of Lead in the Republic of Korea

The purpose of this study was to estimate the daily exposure to lead due to food ingestion, air inhalation, and soil ingestion in the Republic of Korea's general population, and to evaluate the level of risk associated with the current lead exposure level using the proportional daily dose (3–4 μg/kg body weight/day) corresponding to the Provisional Tolerable Weekly Intake (PTWI) suggested by the Joint FAO/WHO Expert Committee on Food Additives as the toxicological tolerance level. The estimation of the daily exposure to lead via three pathways including food, soil ingestion and air inhalation was conducted as a chronic exposure assessment. For the lead exposure assessment through dietary intake, 1,389 lead residue data for 45 commodities investigated by the Korea Food and Drug Administration during the period 1995–2000 were utilized (KFDA 1996, 1997, 1998). Six hundred seventy-two air monitoring data from 7 major cities during the period 1993–2000 and 4,500 soil residue data at 1,500 sites during the period 1999–2001 were considered for the lead exposure assessment involving air inhalation and soil ingestion, respectively. The total daily exposure to lead was estimated by combining dietary intake, inhaled amount and soil intake corresponding to the typical activity of the general population, which was treated as a group of adults with a body weight of 60 kg. For risk characterization, the daily exposure to lead was compared with the toxicological tolerance level. The level of risk due to lead exposure was calculated using the hazard ratio (HR). The dietary intake of lead was 9.71 × 10_?4 mg/kg/day and the total daily exposure level, including air inhalation and soil ingestion, was 9.97 × 10_?4 mg/kg/day. The exposure contributions of foods, air and soil induced from the percentage of each media to the total daily exposure were 97.4%, 2.1% and 0.5%, respectively. Of the different commodity groups, the highest contribution to the total exposure came from grain, which represented 47.7% of the total. Additional exposure to lead occurs in certain population groups due to the use of tobacco, alcoholic beverages, and the intake of other foods, all factors not considered in this study. Through the comparison of the daily exposure to lead with the tolerance level based on the PTWI, the hazard ratio was estimated as being 0.25–0.33. This value implies that no increase in blood lead level is to be expected in the general population at the current lead exposure levels.     

Expanding substrate specificity of GT-B fold glycosyltransferase via domain swapping and high-throughput screening

Glycosyltransferases (GTs) are crucial enzymes in the biosynthesis and diversification of therapeutically important natural products, and the majority of them belong to the GT-B superfamily, which is composed of separate N- and C-domains that are responsible for the recognition of the sugar acceptor and donor, respectively. In an effort to expand the substrate specificity of GT, a chimeric library with different crossover points was constructed between the N-terminal fragments of kanamycin GT (kanF) and the C-terminal fragments of vancomycin GT (gtfE) genes by incremental truncation method. A plate-based pH color assay was newly developed for the selection of functional domain-swapped GTs, and a mutant (HMT31) with a crossover point (N-kanF-669 bp and 753 bp-gtfE-C) for domain swapping was screened. The most active mutant HMT31 (50 kDa) efficiently catalyzed 2-DOS (aglycone substrate for KanF) glucosylation using dTDP-glucose (glycone substrate for GtfE) with k(cat)/K(m) of 162.8 +/- 0.1 mM(-1) min(-1). Moreover, HMT31 showed improved substrate specificity toward seven more NDP-sugars. This study presents a domain swapping method as a potential means to glycorandomization toward various syntheses of 2-DOS-based aminoglycoside derivatives.     

Cell-free synthesis of functional proteins using transcription/translation machinery entrapped in silica sol-gel matrix

Herewith we report the encapsulation of functional protein synthesis machinery in a silica sol-gel matrix. When the sol-gel reaction using alkoxysilane monomers was carried out in the presence of Escherichia coli cell extract, macromolecular protein synthesis machinery in the cell extract was successfully immobilized within a silica gel matrix, catalyzing the translation of co-immobilized DNA when supplied with small-molecular-weight substrates for protein synthesis. The efficiency of protein synthesis was affected by the pore size of the gel structure, which was controlled through the use of appropriate additives during the sol-gel reactions. To the best of our knowledge, this is the first report describing the reproduction of the entire set of complicated biological process within an inorganic gel matrix, and we expect that the developed technology will find many applications in numerous fields such as high-throughput gene expression and the development of multifunctional biosensors.     

Control of cell motility by interaction of gangliosides, tetraspanins, and epidermal growth factor receptor in A431 versus KB epidermoid tumor cells

Growth of epidermoid carcinoma cell lines, A431 and KB, has been known to be controlled by the interaction of epidermal growth factor (EGF) and its receptor (EGFR) with tyrosine kinase. Ganglioside GM3 was previously found to interact with EGFR and to inhibit EGFR tyrosine kinase. However, motility of these cells, controlled by EGFR and ganglioside, was not studied. The present study is focused on the control mechanism of the motility of these cells through interaction of ganglioside, tetraspanin (TSP), and EGFR. Key results are as follows: (i) The level of EGFR expressed in A431 cells is 6 times higher than that expressed in KB cells, and motility of A431 cells is also much higher than that of KB cells, yet growth of A431 cells is either not affected or is inhibited by EGF. In contrast, growth of KB cells is enhanced by EGF. (ii) Levels of TSPs (CD9, CD82, and CD81) expressed in A431 cells are much higher than those expressed in KB cells, and TSPs expressed in A431 cells are reduced by treatment of cells with EtDO-P4, which inhibits the synthesis of glycosphingolipids (GSLs) and gangliosides. (iii) These TSPs are co-immunoprecipitated with EGFR in both A431 and KB cells, indicating that TSPs are closely associated with EGFR. (iv) High motility of A431 cells is greatly reduced, while low motility of KB cells is not affected, by treatment of cells with EtDO-P4. These results, taken together, suggest that there is a close correlation between high motility of A431 cells and high expression of EGFR and TSPs, and between ganglioside GM3/GM2 and TSP. A similar correlation was suggested between the low motility of KB cells and low levels of EGFR and TSP. The correlation between high motility and high level of EGFR with the ganglioside–TSP complex in A431 cells is unique. This is in contrast to our previous studies that indicate that motility of many types of tumor cells is inhibited by a high level of CD9 or CD82, together with growth factor receptors and integrins.     

Alteration of Toll-like receptor 4 activation by 4-hydroxy-2-nonenal mediated by the suppression of receptor homodimerization

Toll-like receptors (TLRs) detect invading microbial pathogens and initiate immune responses as part of host defense mechanisms. They also respond to host-derived substances released from injured cells and tissues to ensure wound healing and tissue homeostasis. Dysregulation of TLRs increases the risk of chronic inflammatory diseases and immune disorders. Inflammatory events are often accompanied by oxidative stress, which generates lipid peroxidation products such as 4-hydroxy-2-nonenal (4-HNE). Therefore, we investigated if 4-HNE affects TLR activation. We found that 4-HNE blocked LPS (a TLR4 agonist)-induced activation of NFκB and IRF3 as well as expression of IFNβ, IP-10, RANTES, and TNFα. To investigate the mechanism of inhibition by 4-HNE, we examined its effects on TLR4 dimerization, one of the initial steps in TLR4 activation. 4-HNE suppressed both ligand-induced and ligand-independent receptor dimerization. The thiol donors, DTT and NAC, prevented the inhibitory effects of 4-HNE on TLR4 dimerization, and LC–MS/MS analysis showed that 4-HNE formed adducts with cysteine residues of synthetic peptides derived from TLR4. These observations suggest that the reactivity of 4-HNE with sulfhydryl moieties is implicated in the inhibition of TLR4 activation. Furthermore, inhibition of TLR4 activation by 4-HNE resulted in down-regulation of the phagocytic activity of macrophages. Collectively, these results demonstrate that 4-HNE blocks TLR4-mediated macrophage activation, gene expression, and phagocytic functions, at least partly by suppressing receptor dimerization. They further suggest that 4-HNE influences innate immune responses at sites of infection and inflammation by inhibiting TLR4 activation.     

The cryopreservation of high concentrated PBMC for dendritic cell (DC)-based cancer immunotherapy

Peripheral blood mononuclear cells (PBMC) have been accepted as a unique material for cancer immunotherapy using dendritic cells (DC) or activated lymphocytes that are being developed as an alternative or adjuvant to conventional therapies such as surgery, chemotherapy and radiation treatment. Although successful cryopreservation of large numbers of PBMC is critical for the immunotherapy, subsequent functional study of the effects of PBMC cryopreservation on differentiation into immune cells has not been well defined. In this study, over 1.0 × 10⁸ cells/ml PBMC were cryopreserved as long as 52 weeks using a controlled-rate freezer (CRF) and stored in a vapor phase of liquid nitrogen tank. The effect of PBMC cryopreservation on differentiation into DC was studied by comparing the phenotypic and functional properties of immature DC (iDC) and mature DC (mDC) derived from cryopreserved PBMC to those from fresh PBMC. The results show that cryopreservation of PBMC at a fairly high cell concentration does not significantly affect cell recovery, viability, or phenotypes of PBMC. After differentiation into DC, iDC and mDC derived from cryopreserved PBMC had their typical phenotypes and function equivalent to those derived from fresh PBMC. Therefore, the improved cryopreservation process of PBMC described in this study is available for DC-based cancer immunotherapy.     

Effects of Treadmill Exercise on Cell Proliferation and Differentiation in the Subgranular Zone of the Dentate Gyrus in a Rat Model of Type II Diabetes

In the present study, we investigated the effects of a treadmill exercise on serum glucose levels and Ki67 and doublecortin (DCX) immunoreactivity, which is a marker of cell proliferation expressed during cell cycles except G0 and early G1 and a marker of progenitors differentiating into neurons, respectively, in the subgranular zone of the dentate gyrus (SZDG) using a type II diabetic model. At 6 weeks of age, Zucker lean control (ZLC) and Zucker diabetic fatty (ZDF) rats were put on a treadmill with or without running for 1 h/day/5 consecutive days at 22 m/min for 5 weeks. Body weight was significantly increased in the control (without running)-ZDF rats compared to that in the other groups. In the control groups blood glucose levels were increased by 392.7 mg/dl in the control-ZDF rats and by 143.3 mg/dl in the control-ZLC rats. However, in the exercise groups, blood glucose levels were similar between the exercise-ZLC and ZDF rats: The blood glucose levels were 110.0 and 118.2 mg/dl, respectively. Ki67 positive nuclei were detected in the SZDG in control and exercise groups. The number of Ki67 positive nuclei was significantly high in exercise groups compared to that in the control groups. In addition, Ki67 positive cells were abundant in ZLC groups compared to those in ZDF groups. DCX-immunoreactive structures in the control-ZDF rats were lower than that in the control-ZLC rats. In the exercise groups, DCX-immunoreactive structures (somata and processes with tertiary dendrites) and DCX protein levels were markedly increased in both the exercise-ZLC and ZDF rats compared to that in the control groups. These results suggest that a treadmill exercise reduces blood glucose levels in ZDF rats and increases cell proliferation and differentiation in the SZDG in ZLC and ZDF rats compared to those in control groups.     

Comparative study on high fat diet-induced 4-hydroxy-2E-nonenal adducts in the hippocampal CA1 region of C57BL/6N and C3H/HeN mice

In the present study, we investigated the influences of a high fat diet (HD) fed for 12 weeks, on lipid peroxidation and antioxidant enzyme using 4-hydroxy-2E-nonenal (HNE)-modified proteins (HNE-mp) and Cu,Zn-superoxide dismutase (SOD1) in the hippocampal CA1 region (CA1) in C57BL/6N and C3H/HeN mice. Body weights and body weight gains were significantly higher in HD fed C57BL/6N mice than in low fat diet (LD) fed C57BL/6N and LD or HD fed C3H/HeN mice. In the HD fed C57BL/6N and C3H/HeN mice, HNE-mp immunoreactivity and protein levels were much higher than in the LD fed C57BL/6N or C3H/HeN mice. In particular, HNE-mp immunoreactivity and protein levels in HD fed C57BL/6N mice was higher than that in the HD fed C3H/HeN mice. SOD1 immunoreaction was detected in the non-pyramidal cells of C57BL/6N mice, while in the C3H/HeN mice SOD1 immunoreaction was observed in CA1 pyramidal cells. The SOD1 immunoreactivity in the LD fed C57BL/6N and C3H/HeN mice was slightly, but not significantly decreased compared to that in the HD fed C57BL/6N and C3H/HeN mice, respectively. In addition, ionized calcium-binding adapter molecule 1 (Iba-1) immunoreactive microglia in the HD fed C57BL/6N showed hypertrophy of cytoplasm, which is the characteristics of activated microglia. These results suggest that HD fed C57BL/6N mice are more susceptible to lipid peroxidation in the CA1 than in LD fed C57BL/6N and LD or HD fed C3H/HeN mice without any differences of SOD1 expression. In Koo Hwang and Il Yong Kim have contributed equally to this article.