Design of n+-base width of two-terminal-electrode vertical thyristor for cross-point memory cell without selector

The n⁺-base width of a two-terminal vertical thyristor fabricated with n⁺⁺(top-emitter)-p⁺(base)-n⁺(base)-p⁺⁺(bottom-emitter) epitaxial Si layers was designed to produce a cross-point memory cell without a selector. Both the latch-up and latch-down voltages increased linearly with the n⁺-base width, but the voltage increase slope of the latch-up was 2.6 times higher than that of the latch-down, and the memory window increased linearly with the n⁺-base width. There was an optimal n⁺-base width that satisfied cross-point memory cell operation; i.e. ∼180 nm, determined by confirming that the memory window principally determined the condition of operation as a cross-point memory cell (i.e. one half of the latch-up voltage being less than the latch-down voltage and a sufficient voltage difference existing between the latch-up and latch-down voltages). The vertical thyristor designed with the optimal n⁺-base width produced write/erase endurance cycles of ∼10⁹ by sustaining a memory margin (I _on /I _off ) of 10², and the cross-point memory cell array size of 1024 K sustained a sensing margin of 99 %, which is comparable with that of current dynamic random-access memory (DRAM). In addition, in the cross-point memory cell array, a ½ bias scheme (i.e. a memory array size of 1024 K for 0.02 W of power consumption) resulted in lower power consumption than a [Formula: see text] bias scheme (i.e. a memory array size of 256 K for 0.02 W of power consumption).

ROS1-Dependent DNA Demethylation Is Required for ABA-Inducible NIC3 Expression

DNA methylation plays an important role in diverse developmental processes in many eukaryotes, including the response to environmental stress. Abscisic acid (ABA) is a plant hormone that is up-regulated under stress. The involvement of DNA methylation in the ABA response has been reported but is poorly understood. DNA demethylation is a reverse process of DNA methylation and often induces structural changes of chromatin leading to transcriptional activation. In Arabidopsis (Arabidopsis thaliana), active DNA demethylation depends on the activity of REPRESSOR OF SILENCING 1 (ROS1), which directly excises 5-methylcytosine from DNA. Here we showed that ros1 mutants were hypersensitive to ABA during early seedling development and root elongation. Expression levels of some ABA-inducible genes were decreased in ros1 mutants, and more than 60% of their proximal regions became hypermethylated, indicating that a subset of ABA-inducible genes are under the regulation of ROS1-dependent DNA demethylation. Notable among them is NICOTINAMIDASE 3 (NIC3) that encodes an enzyme that converts nicotinamide to nicotinic acid in the NAD⁺ salvage pathway. Many enzymes in this pathway are known to be involved in stress responses. The nic3 mutants display hypersensitivity to ABA, whereas overexpression of NIC3 restores normal ABA responses. Our data suggest that NIC3 is responsive to ABA but requires ROS1-mediated DNA demethylation at the promoter as a prerequisite to transcriptional activation. These findings suggest that ROS1-induced active DNA demethylation maintains the active state of NIC3 transcription in response to ABA.

Performance of thyristor memory device formed by a wet etching process

Thyristor random access memory without a capacitor has been highlighted for its significant potential to replace current dynamic random access memory. We fabricated a two-terminal (2-T) thyristor by wet chemical etching techniques on n⁺-p-n-p⁺ silicon epitaxial layers, which have the proper thicknesses and carrier concentrations, as provided by technology computer-aided design simulation. The etched features such as etch rate, surface roughness, and morphologies, in a potassium hydroxide (KOH) and an isotropic etchant, were compared. The type of silicon etchant strongly affected the etched shapes of the side wall and therefore critically influenced the device performance with varying turn-on voltages. The turn-on voltage of thyristor fabricated with a KOH solution showed a consistent tendency of operation voltage in the range of 2.2-2.5 V regardless of the cell size, while the thyristor formulated with isotropic etchant had an operation voltage which increased from about 2.3-4.4 V as the device dimension decreased from 200 μm to 10 μm. The optimized 2-T thyristor showed a memory window of about 2 V, a nearly zero-subthreshold swing, and a current on-off ratio of about 10⁴-10⁵.

STABILIZED1 as a heat stress-specific splicing factor in Arabidopsis thaliana

To overcome high temperature stress, plants have developed transcriptional cascades which express a large amount of chaperone proteins called heat shock proteins (HSPs). In our recent publication, we reported that STABILIZED1, as an U5-snRNP-interacting protein, is involved in the splicing of heat shock factor (HSF) and HSP transcripts during high temperature stress. This indicates that not only transcriptional regulation, but also post-transcriptional regulation by STA1, is essential for the full activation of HSF-HSP cascades and for thermotolerance. Here, we observed that the splicing of HSP transcripts was induced independent of STA1 at room temperature after heat acclimation, indicating that STA1 acts as a high temperature-specific splicing factor for the splicing of HSP transcripts. Our findings suggest the molecular mechanism for how HSF and HSP transcripts are spliced well under high temperature stress that blocks the splicing of overall transcripts.

Regulatory Functions of Cellular Energy Sensor SNF1-Related Kinase1 for Leaf Senescence Delay through ETHYLENE- INSENSITIVE3 Repression

Aging of living organisms is governed by intrinsic developmental programs, of which progression is often under the regulation of their cellular energy status. For example, calorie restriction is known to slow down aging of heterotrophic organisms from yeasts to mammals. In autotrophic plants cellular energy deprivation by perturbation of photosynthesis or sugar metabolism is also shown to induce senescence delay. However, the underlying molecular and biochemical mechanisms remain elusive. Our plant cell-based functional and biochemical assays have demonstrated that SNF1-RELATED KINASE1 (SnRK1) directly interacts, phosphorylates, and destabilizes the key transcription factor ETHYLENE INSENSITIVE3 (EIN3) in senescence-promoting hormone ethylene signaling. Combining chemical manipulation and genetic validation using extended loss-of-function mutants and gain-of-function transgenic lines, we further revealed that a SnRK1 elicitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea enables to slow down senescence-associated leaf degreening through the regulation of EIN3 in Arabidopsis. Our findings enlighten that an evolutionary conserved cellular energy sensor SnRK1 plays a role in fine-tuning of organ senescence progression to avoid sudden death during the last step of leaf growth and development.

Phytohormone ethylene-responsive Arabidopsis organ growth under light is in the fine regulation of Photosystem II deficiency-inducible AKIN10 expression

For photoautotrophic plants, light-dependent photosynthesis plays an important role in organismal growth and development. Under light, Arabidopsis hypocotyl growth is promoted by the phytohormone ethylene. Despite well-characterized ethylene signaling pathways, the functions of light in the hormone-inducible growth response still remain elusive. Our cell-based functional and plant-system-based genetic analyses with biophysical and chemical tools showed that a chemical blockade of photosystem (PS) II activity affects ethylene-induced hypocotyl response under light. Interestingly, ethylene responsiveness modulates PSII activity in retrospect. The lack of ethylene responsiveness-inducible PSII inefficiency correlates with the induction of AKIN10 expression. Consistently, overexpression of AKIN10 in transgenic plants suppresses ethylene-inducible hypocotyl growth promotion under illumination as in other ethylene-insensitive mutants. Our findings provide information on how ethylene responsiveness-dependent photosynthetic activity controls evolutionarily conserved energy sensor AKIN10 that fine-tunes EIN3-mediated ethylene signaling responses in organ growth under light.

Phytohormone ethylene-responsive Arabidopsis organ growth under light is in the fine regulation of Photosystem II deficiency-inducible AKIN10 expression

For photoautotrophic plants, light-dependent photosynthesis plays an important role in organismal growth and development. Under light, Arabidopsis hypocotyl growth is promoted by the phytohormone ethylene. Despite well-characterized ethylene signaling pathways, the functions of light in the hormone-inducible growth response still remain elusive. Our cell-based functional and plant-system-based genetic analyses with biophysical and chemical tools showed that a chemical blockade of photosystem (PS) II activity affects ethylene-induced hypocotyl response under light. Interestingly, ethylene responsiveness modulates PSII activity in retrospect. The lack of ethylene responsiveness-inducible PSII inefficiency correlates with the induction of AKIN10 expression. Consistently, overexpression of AKIN10 in transgenic plants suppresses ethylene-inducible hypocotyl growth promotion under illumination as in other ethylene-insensitive mutants. Our findings provide information on how ethylene responsiveness-dependent photosynthetic activity controls evolutionarily conserved energy sensor AKIN10 that fine-tunes EIN3-mediated ethylene signaling responses in organ growth under light.

STABILIZED1 Modulates Pre-mRNA Splicing for Thermotolerance

High-temperature stress often leads to differential RNA splicing, thus accumulating different types and/or amounts of mature mRNAs in eukaryotic cells. However, regulatory mechanisms underlying plant precursor mRNA (pre-mRNA) splicing in the environmental stress conditions remain elusive. Herein, we describe that a U5-snRNP-interacting protein homolog STABILIZED1 (STA1) has pre-mRNA splicing activity for heat-inducible transcripts including HEAT STRESS TRANSCRIPTION FACTORs and various HEAT SHOCK PROTEINs for the establishment of heat stress tolerance in Arabidopsis (Arabidopsis thaliana). Our cell-based splicing reporter assay demonstrated STA1 acts on pre-mRNA splicing for specific subsets of stress-related genes. Cellular reconstitution of heat-inducible transcription cascades supported the view that STA1-dependent pre-mRNA splicing plays a role in DREB2A-dependent HSFA3 expression for heat-responsive gene expression. Further genetic analysis with a loss-of-function mutant sta1-1, STA1-expressing transgenic plants in Col background, and STA1-expressing transgenic plants in the sta1-1 background verified that STA1 is essential in expression of necessary genes including HSFA3 for two-step heat stress tolerance in plants. However, constitutive overexpression of the cDNA version of HSFA3 in the sta1-1 background is unable to execute plant heat stress tolerance in sta1-1 Consistently our global target analysis of STA1 showed that its splicing activity modulates a rather broad range of gene expression in response to heat treatment. The findings of this study reveal that heat-inducible STA1 activity for pre-mRNA splicing serves as a molecular regulatory mechanism underlying the plant stress tolerance to high-temperature stress.

MYBD employed by HY5 increases anthocyanin accumulation via repression of MYBL2 in Arabidopsis

Photomorphogenesis is an essential program in plant development. This process is effected by the balanced cooperation of many factors under light and dark conditions. In a previous study, we showed that MYB hypocotyl elongation-related (MYBH) is involved in cell elongation. To expand our understanding of MYBH function, we performed a yeast two-hybrid assay and identified an MYB-like Domain transcription factor (MYBD). In this study, we investigated the function of MYBD, which is an MYBH homolog involved in anthocyanin accumulation. MYBD expression increased in response to light or cytokinin, and MYBD enhanced anthocyanin biosynthesis via repression of MYBL2, which encodes a transcription factor that has a negative effect on this process. In addition, MYBD binding in vivo to the MYBL2 promoter and the lower level of histone H3K9 acetylation at the upstream region of MYBL2 in MYBD over-expressing plants in comparison with wild-type plants imply that MYBD represses MYBL2 expression via an epigenetic mechanism. HY5 directly binds to the MYBD promoter, which indicates that MYBD acts on HY5-downstream in light- or cytokinin-triggered signaling pathways, leading to anthocyanin accumulation. Our results suggest that, although MYBD and MYBH are homologs, they act in opposite ways during plant photomorphogenesis, and these functions should be examined in further studies.

Regulatory role of BOTRYTIS INDUCED KINASE1 in ETHYLENE INSENSITIVE3-dependent gene expression in Arabidopsis

Arabidopsis BIK1 negatively regulates EIN3-depedent gene expression as an immediate cellular response. BIK1 localizes to the plasma membrane and its autophosphorylation and kinase activity involves in EIN3 repression. BOTRYTIS INDUCED KINASE1 (BIK1) is a multifunctional receptor-like kinase that involves in ethylene-mediated plant defense signaling. The loss of function BIK1 becomes insensitive to ethylene, but it still accumulates a higher level of ETHYLENE INSENSITIVE3 (EIN3) that serves as the key transcription activator in ethylene signaling. To unequivocally elucidate BIK1 function on EIN3 regulation in ethylene signaling, we took a combined approach of transient expression assay and stable expression analysis of BIK1. In our cell-based functional assay BIK1 destabilized EIN3 and down-regulated EIN3-dependent transcription. Membrane localization and autophosphorylation of BIK1 were required for full repression of EIN3 function, but its kinase activity potential compromised such regulatory action. Consistently, the analysis of transgenic plants verified BIK1 function on EIN3 repression. Our findings have clarified that autophosphorylated BIK1 in the plasma membrane negatively regulates EIN3-dependent gene expression. Thus, ethylene insensitivity in bik1 appears to be an indirect or a feedback long-term response.

PHABULOSA controls the quiescent center-independent root meristem activities in Arabidopsis thaliana

Plant growth depends on stem cell niches in meristems. In the root apical meristem, the quiescent center (QC) cells form a niche together with the surrounding stem cells. Stem cells produce daughter cells that are displaced into a transit-amplifying (TA) domain of the root meristem. TA cells divide several times to provide cells for growth. SHORTROOT (SHR) and SCARECROW (SCR) are key regulators of the stem cell niche. Cytokinin controls TA cell activities in a dose-dependent manner. Although the regulatory programs in each compartment of the root meristem have been identified, it is still unclear how they coordinate one another. Here, we investigate how PHABULOSA (PHB), under the posttranscriptional control of SHR and SCR, regulates TA cell activities. The root meristem and growth defects in shr or scr mutants were significantly recovered in the shr phb or scr phb double mutant, respectively. This rescue in root growth occurs in the absence of a QC. Conversely, when the modified PHB, which is highly resistant to microRNA, was expressed throughout the stele of the wild-type root meristem, root growth became very similar to that observed in the shr; however, the identity of the QC was unaffected. Interestingly, a moderate increase in PHB resulted in a root meristem phenotype similar to that observed following the application of high levels of cytokinin. Our protoplast assay and transgenic approach using ARR10 suggest that the depletion of TA cells by high PHB in the stele occurs via the repression of B-ARR activities. This regulatory mechanism seems to help to maintain the cytokinin homeostasis in the meristem. Taken together, our study suggests that PHB can dynamically regulate TA cell activities in a QC-independent manner, and that the SHR-PHB pathway enables a robust root growth system by coordinating the stem cell niche and TA domain.

Plant roots are programmed to grow continuously into the soil, searching for nutrients and water. The iterative process of cell division, elongation, and differentiation contributes to root growth. The quiescent center (QC) is known to maintain the root meristem, and thus ensure root growth. In this study, we report a novel aspect of root growth regulation controlled independently of the QC by PHABULOSA (PHB). In shr mutant plants, PHB, which in the meristem is actively restricted to the central region of the stele by SHORTROOT (SHR) via miR165/6, suppresses root meristem activity leading to root growth arrest. A high concentration of PHB in the stele does this by modulating B-ARR activity through a QC-independent pathway. Accordingly, we observed a significant recovery of root meristem activity and growth in the shr phb double mutant, while the QC remained absent. However, the presence of QC may be required to sustain continuous root growth. On the basis of our results, we propose that SHR maintains root growth via two separate pathways: by modulating PHB levels in the root stele, and by maintaining the QC identity.

Functional characterization and reconstitution of ABA signaling components using transient gene expression in rice protoplasts

The core components of ABA-dependent gene expression signaling have been identified in Arabidopsis and rice. This signaling pathway consists of four major components; group A OsbZIPs, SAPKs, subclass A OsPP2Cs and OsPYL/RCARs in rice. These might be able to make thousands of combinations through interaction networks resulting in diverse signaling responses. We tried to characterize those gene functions using transient gene expression for rice protoplasts (TGERP) because it is instantaneous and convenient system. Firstly, in order to monitor the ABA signaling output, we developed reporter system named pRab16A-fLUC which consists of Rab16A promoter of rice and luciferase gene. It responses more rapidly and sensitively to ABA than pABRC3-fLUC that consists of ABRC3 of HVA1 promoter in TGERP. We screened the reporter responses for over-expression of each signaling components from group A OsbZIPs to OsPYL/RCARs with or without ABA in TGERP. OsbZIP46 induced reporter most strongly among OsbZIPs tested in the presence of ABA. SAPKs could activate the OsbZIP46 even in the ABA independence. Subclass A OsPP2C6 and -8 almost completely inhibited the OsbZIP46 activity in the different degree through the SAPK9. Lastly, OsPYL/RCAR2 and -5 rescued the OsbZIP46 activity in the presence of SAPK9 and OsPP2C6 dependent on ABA concentration and expression level. By using TGERP, we could characterize successfully the effects of ABA dependent gene expression signaling components in rice. In conclusion, TGERP represents very useful technology to study systemic functional genomics in rice or other monocots.

Regulatory functions of evolutionarily conserved AN1/A20-like Zinc finger family proteins in Arabidopsis stress responses under high temperature

AN1/A20-like Zinc finger family proteins are evolutionarily conserved regulatory components in eukaryotic signaling circuits. In Arabidopsis thaliana, the AN1/A20 Zinc finger family is encoded as 14 members in the genome and collectively referred to as stress-associated proteins (SAPs). Here we described AtSAP5 localized to the nucleus, and played a role in heat-responsive gene regulation together with MBF1c. Seedling survival assay of sap5 and mbf1c demonstrated consistent effects of AtSAP5 and MBF1C in response to two-step heat treatment, supporting their function in heat stress tolerance. Our findings yield an insight in A20/AN1-like Zinc finger protein AtSAP5 functions in plant adaptability under high temperature.

Inverse modulation of the energy sensor Snf1-related protein kinase 1 on hypoxia adaptation and salt stress tolerance in Arabidopsis thaliana

Terrestrial plants are exposed to complex stresses of high salt-induced abscisic acid (ABA) and submergence-induced hypoxia when seawater floods fields. Many studies have investigated plant responses to individual stress conditions, but not so much for coupled or sequentially imposed stresses. We examined molecular regulatory mechanisms of gene expression underlying the cellular responses involved in crosstalk between salt and hypoxia stresses. Salt/ABA- and AtMYC2-dependent induction of a synthetic ABA-responsive element and the native RD22 promoters were utilized in our cell-based functional assays. Such promoter-based reporter induction was largely inhibited by hypoxia and hypoxia-inducible AKIN10 activity. Biochemical analyses showed that AKIN10 negatively modulates AtMYC2 protein accumulation via proteasome activity upon AKIN10 kinase activity-dependent protein modification. Further genetic analysis using transgenic plants expressing AKIN10 provided evidence that AKIN10 activity undermined AtMYC2-dependent salt tolerance. Our findings unravel a novel molecular interaction between the key signalling constituents leading crosstalk between salt and hypoxia stresses in Arabidopsis thaliana under the detrimental condition of submergence in saltwater.

Novel connections and gaps in ethylene signaling from the ER membrane to the nucleus

The signaling of the plant hormone ethylene has been studied genetically, resulting in the identification of signaling components from membrane receptors to nuclear effectors. Among constituents of the hormone signaling pathway, functional links involving a putative mitogen-activated protein kinase kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) and a membrane transporter-like protein ETHYLENE INSENSITIVE2 (EIN2) have been missing for a long time. We now learn that EIN2 is cleaved and its C-terminal end moves to the nucleus upon ethylene perception at the membrane receptors, and then the C-terminal end of EIN2 in the nucleus supports EIN3-dependent ethylene-response gene expression. CTR1 kinase activity negatively controls the EIN2 cleavage process through direct phosphorylation. Despite the novel connection of CTR1 with EIN2 that explains a large portion of the missing links in ethylene signaling, our understanding still remains far from its completion. This focused review will summarize recent advances in the EIN3-dependent ethylene signaling mechanisms including CTR1-EIN2 functions with respect to EIN3 regulation and ethylene responses. This will also present several emerging issues that need to be addressed for the comprehensive understanding of signaling pathways of the invaluable plant hormone ethylene.

Phosphorylation of D-allose by hexokinase involved in regulation of OsABF1 expression for growth inhibition in Oryza sativa L

We previously reported that a rare sugar D-allose, which is the D-glucose epimer at C3, inhibits the gibberellin-dependent responses such as elongation of the second leaf sheath and induction of α-amylase in embryo-less half seeds in rice (Fukumoto et al. 2011). D-Allose suppresses expressions of gibberellin-responsive genes downstream of SLR1 protein in the gibberellin-signaling through hexokinase (HXK)-dependent pathway. In this study, we discovered that D-allose induced expression of ABA-related genes including OsNCED1-3 and OsABA8ox1-3 in rice. Interestingly, D-allose also up-regulated expression of OsABF1, encoding a conserved bZIP transcription factor in ABA signaling, in rice. The D-allose-induced expression of OsABF1 was diminished by a hexokinase inhibitor, D-mannoheptulose (MNH). Consistently, D-allose also inhibited Arabidopsis growth, but failed to trigger growth retardation in the glucose-insensitive2 (gin2) mutant, which is a loss-of-function mutant of the glucose sensor AtHXK1. D-Allose activated AtABI5 expression in transgenic gin2 over-expressing wild-type AtHXK1 but not in gin2 over-expressing the catalytic mutant AtHXK1(S177A), indicating that the D-allose phosphorylation by HXK to D-allose 6-phosphate (A6P) is the first step for the up-regulation of AtABI5 gene expression as well as D-allose-induced growth inhibition. Moreover, overexpression of OsABF1 showed increased sensitivity to D-allose in rice. These findings indicated that the phosphorylation of D-allose at C6 by hexokinase is essential and OsABF1 is involved in the signal transduction for D-allose-induced growth inhibition.

Association of CXCL1 promoter polymorphism with ischaemic stroke in Korean population

This is a pilot study analysing association of chemokine gene polymorphisms (CXCL1, rs3117604; CXCL2, rs3806792; CCL2, rs2857656 and rs3760396; CCL5, rs2107538) in Korean patients with ischemic stroke (IS) (n = 120) and age-matched controls (n = 267). The CXCL1 gene and particularly T allele of rs3117604 was associated with IS.

Cytokinins enhance sugar-induced anthocyanin biosynthesis in Arabidopsis

In higher plants, the regulation of anthocyanin synthesis by various factors including light, sugars and hormones is mediated by numerous regulatory factors acting at the transcriptional level. Here, the association between sucrose and the plant hormone, cytokinin, in the presence of light was investigated to elucidate cytokinin signaling cascades leading to the transcriptional activation of anthocyanin biosynthesis genes in Arabidopsis seedlings. We showed that cytokinin enhances anthocyanin content and transcript levels of sugar inducible structural gene UDPglucose: flavonoid 3-O-glucosyl transferase (UF3GT) and regulatory gene PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1). Genetic analysis showed that cytokinin signaling modulates sugar-induced anthocyanin biosynthesis through a two-component signaling cascade involving the type-B response regulators ARR1, ARR10 and ARR12 in a redundant manner. Genetic, physiological and molecular biological approaches demonstrated that cytokinin enhancement is partially dependent on phytochrome and cryptochrome downstream component HY5, but mainly on photosynthetic electron transport. Taken together, we suggest that cytokinin acts down-stream of the photosynthetic electron transport chain in which the plastoquinone redox poise is modulated by sugars in a photoreceptor independent manner.

Regulatory functions of SnRK1 in stress-responsive gene expression and in plant growth and development

Sucrose-nonfermentation1-related protein kinase1 (SnRK1) is an evolutionarily conserved energy sensor protein that regulates gene expression in response to energy depletion in plants. Efforts to elucidate the functions and mechanisms of this protein kinase are hampered, however, by inherent growth defects of snrk1-null mutant plants. To overcome these limitations and study SnRK1 functions in vivo, we applied a method combining transient expression in leaf mesophyll protoplasts and stable expression in transgenic plants. We found that both rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) SnRK1 activities critically influence stress-inducible gene expression and the induction of stress tolerance. Genetic, molecular, and chromatin immunoprecipitation analyses further revealed that the nuclear SnRK1 modulated target gene transcription in a submergence-dependent manner. From early seedling development through late senescence, SnRK1 activities appeared to modulate developmental processes in the plants. Our findings offer insight into the regulatory functions of plant SnRK1 in stress-responsive gene regulation and in plant growth and development throughout the life cycle.

Giant chloroplast development in ethylene response1-1 is caused by a second mutation in ACCUMULATION AND REPLICATION OF CHLOROPLAST3 in Arabidopsis

The higher plants of today array a large number of small chloroplasts in their photosynthetic cells. This array of small chloroplasts results from organelle division via prokaryotic binary fission in a eukaryotic plant cell environment. Functional abnormalities of the tightly coordinated biochemical event of chloroplast division lead to abnormal chloroplast development in plants. Here, we described an abnormal chloroplast phenotype in an ethylene insensitive ethylene response1-1 (etr1-1) of Arabidopsis thaliana. Extensive transgenic and genetic analyses revealed that this organelle abnormality was not linked to etr1-1 or ethylene signaling, but linked to a second mutation in ACCUMULATION AND REPLICATION3 (ARC3), which was further verified by genetic complementation analysis. Despite the normal expression of other plastid division-related genes, the loss of ARC3 caused the enlargement of chloroplasts as well as the diminution of a photosynthetic protein Rubisco in etr1-1. Our study has suggested that the increased size of the abnormal chloroplasts may not be able to fully compensate for the loss of a greater array of small chloroplasts in higher plants.

A rice orthologue of the ABA receptor, OsPYL/RCAR5, is a positive regulator of the ABA signal transduction pathway in seed germination and early seedling growth

Abscisic acid (ABA) is a phytohormone that positively regulates seed dormancy and stress tolerance. PYL/RCARs were identified an intracellular ABA receptors regulating ABA-dependent gene expression in Arabidopsis thaliana. However, their function in monocot species has not been characterized yet. Herein, it is demonstrated that PYL/RCAR orthologues in Oryza sativa function as a positive regulator of the ABA signal transduction pathway. Transgenic rice plants expressing OsPYL/RCAR5, a PYL/RCAR orthologue of rice, were found to be hypersensitive to ABA during seed germination and early seedling growth. A rice ABA signalling unit composed of OsPYL/RCAR5, OsPP2C30, SAPK2, and OREB1 for ABA-dependent gene regulation was further identified, via interaction assays and a transient gene expression assay. Thus, a core signalling unit for ABA-responsive gene expression modulating seed germination and early seedling growth in rice has been unravelled. This study provides substantial contributions toward understanding the ABA signal transduction pathway in rice.

Cell fate in the Arabidopsis root epidermis is determined by competition between WEREWOLF and CAPRICE

The root hair and nonhair cells in the Arabidopsis (Arabidopsis thaliana) root epidermis are specified by a suite of transcriptional regulators. Two of these are WEREWOLF (WER) and CAPRICE (CPC), which encode MYB transcription factors that are required for promoting the nonhair cell fate and the hair cell fate, respectively. However, the precise function and relationship between these transcriptional regulators have not been fully defined experimentally. Here, we examine these issues by misexpressing the WER gene using the GAL4-upstream activation sequence transactivation system. We find that WER overexpression in the Arabidopsis root tip is sufficient to cause epidermal cells to adopt the nonhair cell fate through direct induction of GLABRA2 (GL2) gene expression. We also show that GLABRA3 (GL3) and ENHANCER OF GLABRA3 (EGL3), two closely related bHLH proteins, are required for the action of the overexpressed WER and that WER interacts with these bHLHs in plant cells. Furthermore, we find that CPC suppresses the WER overexpression phenotype quantitatively. These results show that WER acts together with GL3/EGL3 to induce GL2 expression and that WER and CPC compete with one another to define cell fates in the Arabidopsis root epidermis.

Pause-and-stop: the effects of osmotic stress on cell proliferation during early leaf development in Arabidopsis and a role for ethylene signaling in cell cycle arrest

Despite its relevance for agricultural production, environmental stress-induced growth inhibition, which is responsible for significant yield reductions, is only poorly understood. Here, we investigated the molecular mechanisms underlying cell cycle inhibition in young proliferating leaves of the model plant Arabidopsis thaliana when subjected to mild osmotic stress. A detailed cellular analysis demonstrated that as soon as osmotic stress is sensed, cell cycle progression rapidly arrests, but cells are kept in a latent ambivalent state allowing a quick recovery (pause). Remarkably, cell cycle arrest coincides with an increase in 1-aminocyclopropane-1-carboxylate levels and the activation of ethylene signaling. Our work showed that ethylene acts on cell cycle progression via inhibition of cyclin-dependent kinase A activity independently of EIN3 transcriptional control. When the stress persists, cells exit the mitotic cell cycle and initiate the differentiation process (stop). This stop is reflected by early endoreduplication onset, in a process independent of ethylene. Nonetheless, the potential to partially recover the decreased cell numbers remains due to the activity of meristemoids. Together, these data present a conceptual framework to understand how environmental stress reduces plant growth.

Signaling role of fructose mediated by FINS1/FBP in Arabidopsis thaliana

Sugars are evolutionarily conserved signaling molecules that regulate the growth and development of both unicellular and multicellular organisms. As sugar-producing photosynthetic organisms, plants utilize glucose as one of their major signaling molecules. However, the details of other sugar signaling molecules and their regulatory factors have remained elusive, due to the complexity of the metabolite and hormone interactions that control physiological and developmental programs in plants. We combined information from a gain-of-function cell-based screen and a loss-of-function reverse-genetic analysis to demonstrate that fructose acts as a signaling molecule in Arabidopsis thaliana. Fructose signaling induced seedling developmental arrest and interacted with plant stress hormone signaling in a manner similar to that of glucose. For fructose signaling responses, the plant glucose sensor HEXOKINASE1 (HXK1) was dispensable, while FRUCTOSE INSENSITIVE1 (FINS1), a putative FRUCTOSE-1,6-BISPHOSPHATASE, played a crucial role. Interestingly, FINS1 function in fructose signaling appeared to be independent of its catalytic activity in sugar metabolism. Genetic analysis further indicated that FINS1-dependent fructose signaling may act downstream of the abscisic acid pathway, in spite of the fact that HXK1-dependent glucose signaling works upstream of hormone synthesis. Our findings revealed that multiple layers of controls by fructose, glucose, and abscisic acid finely tune the plant autotrophic transition and modulate early seedling establishment after seed germination.

Photosynthesis-dependent anthocyanin pigmentation in Arabidopsis

Light is the ultimate energy source for photo-autotrophs on earth. For green plants, however, it can also be toxic under certain stressful environmental conditions and at critical developmental stages. Anthocyanins, a class of flavonoids, act as an effective screening mechanism that allows plant survival and proliferation under occasional periods of harmful irradiation through modulation of light absorption. Apart from light-sensing through photoreceptors such as phytochrome and cryptochrome, plants use the photosynthetic electron transfer (PET) chain to integrate light information. The redox status of the plastoquinone (PQ) pool of the PET chain regulates anthocyanin biosynthesis genes, together with the plant hormone ethylene and plant hormone-like sugars. A complex signaling apparatus in acyanic cells appears to transduce information to cyanic cells to regulate anthocyanin production through an intercellular signaling pathway that remains largely uncharacterized. This review will highlight recent advances in this field and their implications for the regulation of anthocyanin pigmentation.

Ethylene suppression of sugar-induced anthocyanin pigmentation in Arabidopsis

Anthocyanin accumulation is regulated negatively by ethylene signaling and positively by sugar and light signaling. However, the antagonistic interactions underlying these signalings remain to be elucidated fully. We show that ethylene inhibits anthocyanin accumulation induced by sucrose (Suc) and light by suppressing the expression of transcription factors that positively regulate anthocyanin biosynthesis, including GLABRA3, TRANSPARENT TESTA8, and PRODUCTION OF ANTHOCYANIN PIGMENT1, while stimulating the concomitant expression of the negative R3-MYB regulator MYBL2. Genetic analyses show that the ethylene-mediated suppression of anthocyanin accumulation is dependent upon ethylene signaling components responsible for the triple response. Furthermore, these positive and negative signaling pathways appear to be under photosynthetic control. Suc and light induction of anthocyanin accumulation was almost fully inhibited in wild-type Arabidopsis (Arabidopsis thaliana) ecotype Columbia and ethylene (ethylene response1 [etr1-1]) and light (long hypocotyl1 [hy1], cryptochrome1/2, and hy5) signaling mutants treated with the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The transcript level of the sugar transporter gene SUC1 was enhanced in ecotype Columbia treated with the ethylene-binding inhibitor silver and in etr1-1, ethylene insensitive2 (ein2-1), and ein3 ein3-like1 mutants. In contrast, 3-(3,4-dichlorophenyl)-1,1-dimethylurea treatment reduced SUC1 expression, which indicates strongly that SUC1 represents an integrator for signals provided by sugar, light, and ethylene. SUC1 mutations lowered accumulations of anthocyanin pigment, soluble sugar content, and ethylene production in response to Suc and light signals. These data demonstrate that the suppression of SUC1 expression by ethylene inhibits Suc-induced anthocyanin accumulation in the presence of light and, hence, fine-tunes anthocyanin homeostasis.

The DOF transcription factor Dof5.1 influences leaf axial patterning by promoting Revoluta transcription in Arabidopsis

Dof proteins are transcription factors that have a conserved single zinc finger DNA-binding domain. In this study, we isolated an activation tagging mutant Dof5.1-D exhibiting an upward-curling leaf phenotype due to enhanced expression of the REV gene that is required for establishing adaxial-abaxial polarity. Dof5.1-D plants also had reduced transcript levels for IAA6 and IAA19 genes, indicating an altered auxin biosynthesis in Dof5.1-D. An electrophoretic mobility shift assay using the Dof5.1 DNA-binding motif and the REV promoter region indicated that the DNA-binding domain of Dof5.1 binds to a TAAAGT motif located in the 5'-distal promoter region of the REV promoter. Further, transient and chromatin immunoprecipitation assays verified binding activity of the Dof5.1 DNA-binding motif with the REV promoter. Consistent with binding assays, constitutive over-expression of the Dof5.1 DNA-binding domain in wild-type plants caused a downward-curling phenotype, whereas crossing Dof5.1-D to a rev mutant reverted the upward-curling phenotype of the Dof5.1-D mutant leaf to the wild-type. These results suggest that the Dof5.1 protein directly binds to the REV promoter and thereby regulates adaxial-abaxial polarity.

Emerging connections in the ethylene signaling network

The gaseous plant hormone ethylene acts as a pivotal mediator to respond to and coordinate internal and external cues in modulating plant growth dynamics and developmental programs. Genetic analysis of Arabidopsis thaliana has been used to identify key components and to build a linear ethylene-signaling pathway from the receptors through to the nuclear transcription factors. Studies applying integrative approaches have revealed new regulators, molecular connections and mechanisms in ethylene signaling and unexpected links to other plant hormones. Here, we review and discuss recent discoveries about the functional mode of ethylene receptor complexes, dual mitogen-activated protein kinase cascade signaling, stability control of the master nuclear transcription activator ETHYLENE INSENSITIVE 3 (EIN3), and the contextual relationships between ethylene and other plant hormones, such as auxin and gibberellins, in organ-specific growth regulation.

MAPK signaling in plant hormone ethylene signal transduction

The signal transduction pathway of the plant stress and defense hormone, ethylene, has been extensively elucidated using the plant genetic model Arabidopsis over the last two decades. Among others, a MAPKKK CTR1 was identified as a negative regulator that has led to the speculation of MAPK involvement in ethylene signaling. However, it remained unclear how the MAPK modules acting downstream of the receptors to mediate ethylene signaling. We have recently presented new evidence that the MKK9-MPK3/6 modules identified by combined functional genomic and genetic screens mediate ethylene signaling, which is negatively regulated by the genetically identified CTR1-dependent cascades. Our genetic studies show consistently that the MKK9-MPK3/MPK6 modules act downstream of the ethylene receptors. Biochemical and transgenic analyses further demonstrated that the positive-acting and negative-acting MAPK activities are integrated and act simultaneously to control the key transcription factor EIN3 through dual phosphorylations to regulate the EIN3 protein stability and downstream transcription cascades. This study has revealed a novel molecular mechanism that defines the specificity of complex MAPK signaling. Comprehensive elucidation of MAPK cascades and the underlying molecular mechanisms would provide more precise explanations for how plant cells utilize MAPK cascades to control specific downstream outputs in response to distinct stimuli.

Arabidopsis mesophyll protoplasts: a versatile cell system for transient gene expression analysis

The transient gene expression system using Arabidopsis mesophyll protoplasts has proven an important and versatile tool for conducting cell-based experiments using molecular, cellular, biochemical, genetic, genomic and proteomic approaches to analyze the functions of diverse signaling pathways and cellular machineries. A well-established protocol that has been extensively tested and applied in numerous experiments is presented here. The method includes protoplast isolation, PEG-calcium transfection of plasmid DNA and protoplast culture. Physiological responses and high-throughput capability enable facile and cost-effective explorations as well as hypothesis-driven tests. The protoplast isolation and DNA transfection procedures take 6-8 h, and the results can be obtained in 2-24 h. The cell system offers reliable guidelines for further comprehensive analysis of complex regulatory mechanisms in whole-plant physiology, immunity, growth and development.

Glucose signaling through nuclear hexokinase1 complex in Arabidopsis

Arabidopsis hexokinase1 (HXK1) is a glucose sensor that regulates gene expression and plant growth and development. We have previously developed a high glucose (6%) assay based on the seedling developmental arrest to isolate and characterize the glucose-insensitive (gin) mutants. The analysis of gin2 as a null HXK1 mutant has revealed that the regulatory functions of HXK1 are distinct from its conventional role in glycolysis. In the Nov 3rd issue of Cell, we presented a new insight into the mechanism of HXK1-dependent glucose signaling. By combining proteomic and binary interaction screens, we discover two HXK1 unconventional partners (HUPs). HXK1 and HUPs form a core complex in the nucleus and directly regulate glucose-responsive gene expression and plant growth. As the 6% glucose assay is complicated by additional osmotic stress and nitrate signals, we have tested the gin2 and hup mutants using the 2% glucose assay. We believe that the new and more physiological glucose assay could help us better dissect the molecular mechanisms that link glucose regulation to diverse plant signaling pathways. Further functional analysis of gin mutants and the components in the novel nuclear HXK1 complex will provide more comprehensive mechanistic understanding of glucose sensing and signaling in plants.

Regulatory functions of nuclear hexokinase1 complex in glucose signaling

Arabidopsis hexokinase1 (HXK1) is a glucose sensor that integrates nutrient and hormone signals to govern gene expression and plant growth in response to environmental cues. How the metabolic enzyme mediates glucose signaling remains a mystery. By coupling proteomic and binary-interaction screens, we discover two nuclear-specific HXK1 unconventional partners: the vacuolar H(+)-ATPase B1 (VHA-B1) and the 19S regulatory particle of proteasome subunit (RPT5B). Remarkably, vha-B1 and rpt5b mutants uniquely share a broad spectrum of glucose response defects with the HXK1 mutant gin2 (glucose-insensitive2). Genetic and chromatin immunoprecipitation analyses suggest that the nuclear HXK1 forms a glucose signaling complex core with VHA-B1 and RPT5B that directly modulates specific target gene transcription independent of glucose metabolism. The findings support a model in which conserved metabolic enzymes and proteins of well-established activities may perform previously unrecognized nuclear functions.

Arabidopsis EIN3-binding F-box 1 and 2 form ubiquitin-protein ligases that repress ethylene action and promote growth by directing EIN3 degradation

Ubiquitination of various intracellular proteins by ubiquitin-protein ligases (or E3s) plays an essential role in eukaryotic cell regulation primarily through its ability to selectively target proteins for degradation by the 26S proteasome. Skp1, Cullin, F-box (SCF) complexes are one influential E3 class that use F-box proteins to deliver targets to a core ligase activity provided by the Skp1, Cullin, and Rbx1 subunits. Almost 700 F-box proteins can be found in Arabidopsis, indicating that SCF E3s likely play a pervasive role in plant physiology and development. Here, we describe the reverse genetic analysis of two F-box proteins, EBF1 and -2, that work coordinately in SCF complexes to repress ethylene action. Mutations in either gene cause hypersensitivity to exogenous ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid. EBF1 and -2 interact directly with ethylene insensitive 3 (EIN3), a transcriptional regulator important for ethylene signaling. Levels of EIN3 are increased in mutants affecting either EBF1 or -2, suggesting that the corresponding SCF complexes work together in EIN3 breakdown. Surprisingly, double ebf1 ebf2 mutants display a substantial arrest of seedling growth and have elevated EIN3 levels, even in the absence of exogenous ethylene. Collectively, our results show that the SCF(EBF1/EBF2)-dependent ubiquitination and subsequent removal of EIN3 is critical not only for proper ethylene signaling but also for growth in plants.

Intranasal delivery of PEGylated salmon calcitonins: hypocalcemic effects in rats

To evaluate the hypocalcemic effect of polyethylene gtycol-conjugated salmon calcitonins (PEG-sCT) in rats, mono-PEGylated sCTs (mono-PEG-sCTs) and unmodified sCT were administered via the intranasal route and serum calcium levels were measured by colorimetric assay using o-cresolphthalein. Mono-PEG-sCTs were prepared with different sizes of succinimidyl succinate monomethoxy PEG molecules (PEG2K), PEG5K, PEG12K) and characterized by HPLC and MALDI-TOF mass spectrometry. Nasal instillation of mono-PEG2K-sCT at a dose of 2 IU/kg resulted in sustained reduction in serum calcium levels over 8 hr, with a maximum reduction (% maxd) of 13% after 6 hr of application. Whereas unmodified sCT showed a transient decrease in serum calcium levels with the maximum reduction (5%) observed after 30 min of administration. The overall reductions in serum calcium levels expressed as the net change in AUC relative to control in 8 hr were 11.9 +/- 0.2, 4.6 +/- 0.7, and 2.6 +/- 0.7% for mono-PEG2K-, mono-PEG5K-, and mono-PEG12K-sCT, respectively, compared to 3.2 +/- 0.6% for unmodified sCT. The relative bioavailability of nasally administered 2 IU/kg of mono-PEG2K-sCT was approximately 4-fold higher than nasally administrated unmodified sCT, and the absolute bioavailability was approximately 91% of intravenously injected sCT in 8 hr. It can be concluded that the intranasal absorption of mono-PEG-sCTs was inversely related to the molecular weights of the PEG attached. Of the PEGylated sCTs examined, mono-PEG2K-sCT showed the most pronounced hypocalcemic effect. Therefore the intranasal application would probably be an alternative route of administration for mono-PEG-sCTs in achieving sustained calcium-lowering effects.

Differential regulation of EIN3 stability by glucose and ethylene signalling in plants

Glucose is a global regulator of growth and metabolism that is evolutionarily conserved from unicellular microorganisms to multicellular animals and plants. In photosynthetic plants, glucose shows hormone-like activities and modulates many essential processes, including embryogenesis, germination, seedling development, vegetative growth, reproduction and senescence. Genetic and phenotypic analyses of Arabidopsis mutants with glucose-insensitive (gin) and glucose-oversensitive (glo) phenotypes have identified an unexpected antagonistic interaction between glucose and the plant stress hormone ethylene. The ethylene-insensitive etr1 and ein2 mutants have glo phenotypes, whereas the constitutive ethylene signalling mutant ctr1 is allelic to gin4 (refs 4, 5). The precise molecular mechanisms underlying the complex signalling network that governs plant growth and development in response to nutrients and plant hormones are mostly unknown. Here we show that glucose enhances the degradation of ETHYLENE-INSENSITIVE3 (EIN3), a key transcriptional regulator in ethylene signalling, through the plant glucose sensor hexokinase. Ethylene, by contrast, enhances the stability of EIN3. The ein3 mutant has a glo phenotype, and overexpression of EIN3 in transgenic Arabidopsis decreases glucose sensitivity.

Cloning, expression, and characterization of sorbitol transporters from developing sour cherry fruit and leaf sink tissues

The acyclic polyol sorbitol is a primary photosynthetic product and the principal photosynthetic transport substance in many economically important members of the family Rosaceace (e.g. almond [Prunus dulcis (P. Mill.) D.A. Webber], apple [Malus pumila P. Mill.], cherry [Prunus spp.], peach [Prunus persica L. Batsch], and pear [Pyrus communis]). To understand key steps in long-distance transport and particularly partitioning and accumulation of sorbitol in sink tissues, we have cloned two sorbitol transporter genes (PcSOT1 and PcSOT2) from sour cherry (Prunus cerasus) fruit tissues that accumulate large quantities of sorbitol. Sorbitol uptake activities and other characteristics were measured by heterologous expression of PcSOT1 and PcSOT2 in yeast (Saccharomyces cerevisiae). Both genes encode proton-dependent, sorbitol-specific transporters with similar affinities (K(m) sorbitol of 0.81 mM for PcSOT1 and 0.64 mM for PcSOT2). Analyses of gene expression of these transporters, however, suggest different roles during leaf and fruit development. PcSOT1 is expressed throughout fruit development, but especially when growth and sorbitol accumulation rates are highest. In leaves, PcSOT1 expression is highest in young, expanding tissues, but substantially less in mature leaves. In contrast, PcSOT2 is mainly expressed only early in fruit development and not in leaves. Compositional analyses suggest that transport mediated by PcSOT1 and PcSOT2 plays a major role in sorbitol and dry matter accumulation in sour cherry fruits. Presence of these transporters and the high fruit sorbitol concentrations suggest that there is an apoplastic step during phloem unloading and accumulation in these sink tissues. Expression of PcSOT1 in young leaves before completion of the transition from sink to source is further evidence for a role in determining sink activity.

Causes of lower respiratory infection in HIV-infected Ugandan adults who are sputum AFB smear-negative

SETTING

Mulago national referral and teaching hospital.

OBJECTIVE

To assess the etiology of lower respiratory infections in HIV-infected Ugandan adults who are sputum acid-fast bacilli (AFB) smear-negative.

DESIGN

A descriptive cross-sectional study. Participants included consecutive adult patients admitted to medical wards with respiratory symptoms of at least 3 weeks and infiltrates on chest radiograph. Those who were sputum AFB smear-negative and HIV-positive underwent bronchoscopy and bronchoalveolar lavage (BAL). BAL fluid was obtained and stained for AFB and Pneumocystis carinii, and cultured for bacteria and fungi.

RESULTS

Of 198 patients screened, 48 were sputum smear-positive for AFB. Sixty-seven were excluded for various reasons, leaving 83 patients who met the inclusion criteria and underwent bronchoscopy: 32 (38.6%) patients had P. carinii infection, 20 (24%) had pulmonary tuberculosis, nine (11%) had pulmonary Kaposi's sarcoma and pyogenic bacteria were identified in seven (8%). No aetiological diagnosis was found in 24 (30%) patients.

CONCLUSION

P. carinii and Mycobacterium tuberculosis were the commonest causes of disease among sputum AFB smear-negative, HIV-positive adults presenting to Mulago Hospital. Pulmonary Kaposi's sarcoma and pyogenic bacteria occurred with less frequency.

Bioavailability and mammary excretion of bisphenol a in Sprague-Dawley rats

This study reports the absolute oral bioavailability and mammary excretion of bisphenol A in rats. The oral bioavailability was determined after administration of relatively low iv (0.1 mg/kg) and oral (10 mg/kg) doses of bisphenol A to rats. After iv injection, serum levels of bisphenol A declined biexponentially, with the mean initial distribution and terminal elimination half-lives being 6.1 +/- 1.3 min and 52.5 +/- 2.4 min, respectively. The systemic clearance (Cls) and the steady-state volume of distribution (Vss) averaged 107.9 +/- 28.7 m/min/kg and 5.6 +/- 2.4 L/kg, respectively. Upon oral administration, the maximum serum concentration (Cmax) and the time to reach the maximum concentration (Tmax) were 14.7 +/- 10.9 ng/ml and 0.2 +/- 0.2 h, respectively. The apparent terminal elimination half-life of bisphenol A (21.3 +/- 7.4 h) after oral administration was significantly longer than that after iv injection, indicating the flip-flop of the absorption and elimination rates. The absolute oral bioavailability of bisphenol A was low (5.3 +/- 2.1%). To determine the extent of mammary excretion, bisphenol A was given by simultaneous iv bolus injection plus infusion to steady state at low, medium, and high doses. The steady-state serum levels of bisphenol A were linearly increased with higher dosing rates. The systemic clearance (mean range, 119.2-154.1 ml/min/kg) remained unaltered over the dosing rate studied. The levels of bisphenol A in milk exceeded those in serum, with the steady-state milk to serum concentration ratio being 2.4-2.7.

Potential estrogenic effects of bisphenol-A estimated by in vitro and in vivo combination assays

The potential estrogenic activities of bisphenol-A were investigated in vitro (E-screen and estrogen receptor competitive binding bioassays) and in vivo (uterotrophic assay). Uterotrophic responses were evaluated using mature ovariectomized Sprague-Dawley female rats treated subcutaneously with bisphenol A (1, 5, 10, 50, and 100 mg/kg/day), E2 (0.3 microgram/kg), and DES (0.3 microgram/kg) for 3 consecutive days. In a MCF-7 cell proliferation assay, E2 and DES used as positive estrogens induced maximum proliferation of MCF-7 cells at 1.0 nM, whereas BPA slightly induced MCF-7 cell proliferation at a higher level of 0.1 microM and maximum proliferation at 10 microM. In a competitive binding assay, E2 and DES showed inhibition of 17 beta-[3H]estradiol binding to the rat uterus ER with an IC50 of 1.0 nM and 0.5 nM, respectively. However, BPA had an IC50 of 5 microM, which was approximately 5,000 or 10,000-fold greater than the IC50 of E2 and DES. In uterotrophic assays, uterus (wet and blotted) and vagina weights were significantly increased at the dose of BPA 100 mg/kg/day in OVX Sprague-Dawley rats. These studies demonstrate that BPA exhibits weak estrogenic activity in all experimental systems, and thus its migration from epoxy resins or polycarbonate products should be controlled not to exceed a safety levels for humans.

Determination of growth hormone-releasing hexapeptide by reversed-phase high-performance liquid chromatography with electrochemical detection

A novel HPLC method with electrochemical detection is described for the determination of a growth-hormone-releasing hexapeptide (GHRP-6). HPLC conditions, such as the column, mobile phase, and oxidation potential, were optimized for sensitivity and selectivity of analysis. GHRP-6 was separated on a reversed-phase CN column with 37% acetonitrile in 100 mM phosphate buffer (pH 7.0) as the mobile phase. The optimum electrochemical oxidation signal was obtained at 0.85 V vs. Ag/AgCl in a glassy carbon working electrode due to two electroactive tryptophans and a histidine residue. Solid-phase extraction using octadecyl cartridges was optimized for sample cleanup of GHRP-6 from serum samples and the method was successfully applied over the concentration range of 5 to 100 ng/ml of analyte. reserved.

Identification of the modifying sites of mono-PEGylated salmon calcitonins by capillary electrophoresis and MALDI-TOF mass spectrometry

A capillary electrophoretic method (CE) was developed for the determination of the PEG-modification sites of three positional isomers of mono-PEG modified salmon calcitonins (mono-PEG-sCTs). Resistance to proteolytic degradation on the PEG modification sites resulted in different patterns of CE electropherograms for the tryptic digested mono-PEG-sCTs isomers, and the PEG modification sites were assigned accordingly. The PEG-modification sites were also confirmed directly by determining the molecular masses of the tryptic digested PEG-modified fragments of respective mono-PEG-sCT by the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry.

Pharmacokinetic disposition of polyethylene glycol-modified salmon calcitonins in rats

This study first reports the pharmacokinetic disposition of polyethylene glycol (PEG)-modified salmon calcitonin (sCT) based on the number of attached PEG molecules. PEG-modified sCT was prepared by covalent linkage with succinimidyl carbonate monomethoxy polyethylene glycol. Mono- and di-PEG-sCTs were separated by size exclusion and reverse phase HPLC, and radioiodinated by the chloramine-T method with Na125I. 125I-mono-PEG sCT, 125I-di-PEG-sCT and unmodified 125I-sCT were administered to rats by i.v. injection. Serial blood samples, urine and various tissue samples were taken for the determination of radioactivity. Di-PEG-sCT exhibited significantly reduced systemic clearance (2.3 vs. 11.1 ml/min/kg) and steady-state volume of distribution (229.9 vs. 603.1 ml/kg), while mono-PEG-sCT showed a prolonged elimination half-life (189.1 min vs. 59.8 min) compared with unmodified sCT. The extent of urinary excretion of the PEG-modified sCTs was higher than for the unmodified sCT, but all these chemicals were excreted in urine in small quantities (< or = 0.6%). There was a tendency toward reduced accumulation of PEGylated sCTs in tissues, with its reduction being inversely proportional to the molecular size. Accumulation of the total radioactivity of the unmodified and PEG-modified sCTs was highest in the liver, followed by kidneys, lungs, spleen, heart and thyroid. When expressed per tissue gram weight, however, the highest radioactivity was found in the kidneys. PEGylated sCTs may have greater therapeutic potential via reduced systemic clearance and prolonged elimination half-life over unmodified sCT.

Pharmacokinetic disposition and tissue distribution of bisphenol A in rats after intravenous administration

This study examined the dose-linearity pharmacokinetics of bisphenol A, a U.S. Environmental Protection Agency (EPA) classified endocrine disruptor, in rats following iv administration. Upon iv injection of 0.2, 0.5, 1, or 2 mg/kg, serum levels of bisphenol A declined biexponentially, with mean initial distribution and elimination half-life ranges of 4-8.2 min and 38.6-62.2 min, respectively. There were no significant alterations in the systemic clearance rate (mean range 90.1-123.6 ml/min/kg) and the steady-state volume of distribution (mean range 4.6-6.0 L/kg) as a function of the administered dose. In addition, the area under the serum concentration-time curve linearly rose as the dose was increased. In a second study, bisphenol A was given by simultaneous iv bolus injection plus infusion to steady state, and levels were measured in serum and various organs. When expressed in concentration terms (e.g., amount accumulated per gram organ weight), bisphenol A was found predominantly in the lung, followed by kidneys, thyroid, stomach, heart, spleen, testes, liver, and brain. Ratios of the organ to serum bisphenol A concentrations exceeded unity for all the organs examined (ratio range 2.0-5.8) except for brain (ratio 0.75). Given the high systemic clearance and short elimination half-life, bisphenol A is unlikely to accumulate significantly in the rat.

The inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in chronic myelogenous leukemic K562 cells

In this study, the downstream signaling of Bcr-Abl tyrosine kinase responsible for apoptosis resistance was investigated. DNA fragmentation, a hallmark of apoptosis, was observed after 2 days of herbimycin A treatment with a peak on 3 day. During the apoptosis induced by the treatment of herbimycin A, stress-activated protein kinase (SAPK) and p38 kinase were activated time- and dose-dependently, while extracellular signal-regulated kinase (ERK) was inhibited. However, apoptosis was induced by the treatment of PD98059, a specific inhibitor of MEK (MAPK or ERK kinase), not by the treatment of sorbitol, a strong activator of SAPK and p38 kinase. Although K562 cells were very resistant to sorbitol-induced apoptosis, DNA fragmentation was induced rapidly in Jurkat, HL-60 and U937 cells after exposure to sorbitol, despite that these apoptosis-sensitive cells have similar or lower activities of JNK/SAPK and p38 kinase compared with K562 cells after treatment of sorbitol. K562 cells had a much higher basal activity of ERK/MAPK than other apoptosis-sensitive cell lines, which were very susceptible to apoptosis induced by low dose of PD98059 compared with K562 cells. In HL-60 cells, sorbitol-induced apoptosis was prevented by the treatment of phorbol myristate 13-acetate (PMA), which activates the ERK/MAPK pathway, and this was blocked by PD98059. From these results, it could be suggested that the inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in K562 cells.

Absorption, first-pass metabolism, and disposition of itraconazole in rats

This study examined the pharmacokinetic disposition, oral absorption and hepatic extraction of itraconazole and its active metabolite, hydroxyitraconazole, in rats. After i.v. injection, serum itraconazole concentrations decreased biexponentially, with an average terminal elimination half-life, volume of distribution and systemic clearance of 4.9 h, 6.0 l/kg and 14.2 ml/min/kg, respectively. When given orally, its absorption was low, with a mean absolute bioavailability of 16.6%. The metabolite to parent drug area under the curve (AUC) ratio was higher after oral administration compared with i.v. injection (mean ratio, 2.7 vs. 0.9). The hepatic drug extraction ratio determined after femoral and portal vein administration averaged 18.5%. When hydroxyitraconazole was injected i.v., the elimination half-life, volume of distribution and systemic clearance of itraconazole averaged 10.0 h, 2.4 l/kg and 3.4 ml/min/kg, respectively. The fraction of the systemically available itraconazole that was metabolized to hydroxyitraconazole was 21.0% and 76.0% after i.v. and oral administration, respectively. In summary, this study is the first reporting the hepatic extraction of itraconazole and the i.v. disposition characteristics of hydroxyitraconazole in rats. Itraconazole is a drug with a low hepatic extraction ratio and its systemic clearance appears to be largely accounted for by hepatic metabolism.

Downregulation of JNK/SAPK activity is associated with the cross-resistance to P-glycoprotein-unrelated drugs in multidrug-resistant FM3A/M cells overexpressing P-glycoprotein

In the present study, cross-drug resistance in multidrug-resistant (MDR) cells, which overexpress P-glycoprotein (Pgp), a mdr1 gene product, against Pgp-unrelated drugs, and its relevance to c-Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK) activity were examined. The multidrug-resistant FM3A/M cells overexpressing Pgp were resistant to apoptotic cell death induced either by Pgp-related drugs including vincristine and vinblastine, which are pumped out by Pgp, or by the Pgp-unrelated drugs including 5'-fluorouracil (5-FU) and bleomycin, which are not targets for Pgp, compared with the parental FM3A cells. Verapamil reversed the resistance of FM3A/M cells to apoptosis induced by the Pgp-related drugs but not that induced by the Pgp-unrelated drugs. Interestingly, FM3A/M cells have shown significantly lower basal and drug-stimulated JNK/SAPK activities than FM3A cells. After transfection with pEBG-SEK or pEBG-SAPK constructs, FM3A/M cells recovered the basal and Pgp-unrelated drug-stimulated activities of JNK/SAPK and the susceptibility to Pgp-unrelated drug-induced apoptotic cell death comparable to those of FM3A cells. Furthermore, FM3A cells became resistant to apoptotic cell death induced by vincristine and 5-FU after transfection with pEBG-SEK(K --> R), a dominant negative inhibitory mutant of SEK. These results suggest that downregulation of JNK/SAPK activity appears to confer on Pgp-associated FM3A/M cells a cross-resistance to Pgp-unrelated drugs.

Bioavailability of itraconazole in rats and rabbits after administration of tablets containing solid dispersion particles

A tablet dosage form containing solid dispersions of itraconazole (Asd tablets) was prepared by using the spray-drying and wet granulation methods. The dissolution rate of itraconazole from Asd tablets was fast, with more than 90% released within 10 min, compared to less than 20% for a marketed product, Sporanox capsules. The oral absorption of itraconazole from Asd tablets was determined in rats and rabbits and was compared with that for Sporanox capsules. In the rat, there was no difference between the Asd tablets and Sporanox capsules in the mean area under the curve (AUC) (3089.5 +/- 4332.8 ng.hr/ml and 3653.9 +/- 2348.9 ng.hr/ml, respectively) and Cmax (295.0 +/- 344.5 and 390.5 +/- 169.4 ng/ml, respectively). Also, in the rabbit, no difference was found between the two products in the mean AUC (AUMC; 19357.9 +/- 5117.5 ng.hr/ml and 23382.2 +/- 6236.5 ng.hr/ml, respectively) and Cmax (766.4 +/- 276.5 and 1127.5 +/- 577.9 ng/ml, respectively). Despite the rapid in vitro release characteristics of itraconazole from the Asd tablets, the in vivo absorption of itraconazole was comparable to that of Sporanox capsules, with no difference in Tmax in both animal species. Serum levels of the major active metabolite hydroxyitraconazole were also measured. Itraconazole was rapidly converted to hydroxyitraconazole in both rats and rabbits, but there were species-specific differences in their pharmacokinetics. It is concluded that, in addition to drug solubility and dissolution characteristics, other formulation factors such as the physical state of the drug and the granulation process, may also need to be considered in the prediction of the in vivo absorption of itraconazole based on in vitro data.