Polyinosinic acid is a ligand for toll-like receptor 3

Innate immune responses are critical in controlling viral infections. Viral proteins and nucleic acids have been shown to be recognized by pattern recognition receptors of the Toll-like receptor (TLR) family, triggering downstream signaling cascades that lead to cellular activation and cytokine production. Viral DNA is sensed by TLR9, and TLRs 3, 7, and 8 have been implicated in innate responses to RNA viruses by virtue of their ability to sense double-stranded (ds) RNA (TLR3) or single-stranded RNA (murine TLR7 and human TLR8). Viral and synthetic dsRNAs have also been shown to be a potent adjuvant, promoting enhanced adaptive immune responses, and this property is also dependent on their recognition by TLR3. It has recently been shown that mRNA that is largely single-stranded is a ligand for TLR3. Here we have investigated the ability of single-stranded homopolymeric nucleic acids to induce innate responses by murine immune cells. We show for the first time that polyinosinic acid (poly(I)) activates B lymphocytes, dendritic cells, and macrophages and that these responses are dependent on the expression of both TLR3 and the adaptor molecule, Toll/IL-1 receptor domain-containing adaptor inducing IFN-beta (TRIF). We therefore conclude that TLR3 is able to sense both single-stranded RNA and dsRNA.     

Hydroxylated jasmonates are commonly occurring metabolites of jasmonic acid and contribute to a partial switch-off in jasmonate signaling

In potato 12-hydroxyjasmonic acid (12-OH-JA) is a tuber-inducing compound. Here, it is demonstrated that 12-OH-JA, as well as its sulfated and glucosylated derivatives, are constituents of various organs of many plant species. All accumulate differentially and usually to much higher concentrations than jasmonic acid (JA). In wounded tomato leaves, 12-OH-JA and its sulfated, as well as glucosylated, derivative accumulate after JA, and their diminished accumulation in wounded leaves of the JA-deficient mutants spr2 and acx1 and also a JA-deficient 35S::AOCantisense line suggest their JA-dependent formation. To elucidate how signaling properties of JA/JAME (jasmonic acid methyl ester) are affected by hydroxylation and sulfation, germination and root growth were recorded in the presence of the different jasmonates, indicating that 12-OH-JA and 12-hydroxyjasmonic acid sulfate (12-HSO(4)-JA) were not bioactive. Expression analyses for 29 genes showed that expression of wound-inducible genes such as those coding for PROTEINASE INHIBITOR2, POLYPHENOL OXIDASE, THREONINE DEAMINASE or ARGINASE was induced by JAME and less induced or even down-regulated by 12-OH-JA and 12-HSO(4)-JA. Almost all genes coding for enzymes in JA biosynthesis were up-regulated by JAME but down-regulated by 12-OH-JA and 12-HSO(4)-JA. The data suggest that wound-induced metabolic conversion of JA/JAME into 12-OH-JA alters expression pattern of genes including a switch off in JA signaling for a subset of genes.     

The ligand binding domain of the epidermal growth factor receptor is not required for receptor dimerization.

To examine the role of the ligand binding domain of epidermal growth factor receptor in its dimerization, we studied the dimerization of a truncated form of the receptor that resembles v-erbB in that it lacks a ligand binding domain. Receptor dimerization was determined by sedimentation analysis on sucrose density gradients at different concentrations of Triton X-100. At high concentrations of Triton X-100 (0.2%), the truncated receptor occurred as a monomer and displayed low basal autophosphorylation. By contrast, at low concentrations of Triton X-100 (0.01%), it existed as a dimer and exhibited high basal autophosphorylation. The ability of the truncated receptor to dimerize indicates that the ligand binding domain of the epidermal growth factor receptor is not required for receptor dimerization.     

Dictyostelium EB1 is a genuine centrosomal component required for proper spindle formation

EB1 proteins are ubiquitous microtubule-associated proteins involved in microtubule search and capture, regulation of microtubule dynamics, cell polarity, and chromosome stability. We have cloned a complete cDNA of Dictyostelium EB1 (DdEB1), the largest known EB1 homolog (57 kDa). Immunofluorescence analysis and expression of a green fluorescent protein-DdEB1 fusion protein revealed that DdEB1 localizes along microtubules, at microtubule tips, centrosomes, and protruding pseudopods. During mitosis, it was found at the spindle, spindle poles, and kinetochores. DdEB1 is the first EB1-homolog that is also a genuine centrosomal component, because it was localized at isolated centrosomes that are free of microtubules. Furthermore, centrosomal DdEB1 distribution was unaffected by nocodazole treatment. DdEB1 colocalized with DdCP224, the XMAP215 homolog, at microtubule tips, the centrosome, and kinetochores. Furthermore, both proteins were part of the same cytosolic protein complex, suggesting that they may act together in their functions. DdEB1 deletion mutants expressed as green fluorescent protein or maltose-binding fusion proteins indicated that microtubule binding requires homo-oligomerization, which is mediated by a coiled-coil domain. A DdEB1 null mutant was viable but retarded in prometaphase progression due to a defect in spindle formation. Because spindle elongation was normal, DdEB1 seems to be required for the initiation of the outgrowth of spindle microtubules.     

Cytoplasmic domain of human Fcalpha/mu receptor is required for ligand internalization

The Fcalpha/mu receptor (Fcα/μR), a type I transmembrane protein, is an immunoglobulin Fc receptor for both IgA and IgM. Its functions in immune defense are not clear at present. In this work, human Fcα/μR was expressed in CHO, 293T, and COS-7 cells to study its biochemical functions. Fcα/μR expressed by CHO and 293T was only in monomer form in cytoplasma and the monomeric receptor could not bind IgA or IgM. In comparison, Fcα/μR expressed by COS-7 cells had both monomer and dimer forms. The binding assay showed that Fcα/μR expressed by COS-7 cells could bind IgM strongly and IgA weakly, implying that dimeric receptor could be expressed on cell membrane and functioned. The bound IgM could be internalized and the internalization was abolished when the cytoplasmic domain of Fcα/μR was truncated. Therefore, the cytoplasmic portion of human Fcα/μR is required in the internalization.     

The biosynthesis of jasmonic acid: a physiological role for plant lipoxygenase

Linolenic acid was converted to a cyclic product, 12-oxo-phytodienoic acid, by lipoxygenase and hydroperoxide cyclase enzymes present in Vicia faba pericarp. Isotope labeling studies in which [U-14C] 12-[180] oxo-phytodienoic acid was incubated with thin sections of pericarp tissue showed that 12-oxo-phytodienoic acid is a biosynthetic precursor to jasmonic acid, a plant growth regulator which promotes senescence. Key enzymes proposed for this pathway are a reductase enzyme which reduces a double bond in the cyclopentenone ring, and beta-oxidation enzymes which remove six carbons from the carboxyl end of the molecule.     

GTR1 is a jasmonic acid and jasmonoyl-l-isoleucine transporter in Arabidopsis thaliana

Jasmonates are major plant hormones involved in wounding responses. Systemic wounding responses are induced by an electrical signal derived from damaged leaves. After the signaling, jasmonic acid (JA) and jasmonoyl-l-isoleucine (JA-Ile) are translocated from wounded to undamaged leaves, but the molecular mechanism of the transport remains unclear. Here, we found that a JA-Ile transporter, GTR1, contributed to these translocations in Arabidopsis thaliana. GTR1 was expressed in and surrounding the leaf veins both of wounded and undamaged leaves. Less accumulations and translocation of JA and JA-Ile were observed in undamaged leaves of gtr1 at 30 min after wounding. Expressions of some genes related to wound responses were induced systemically in undamaged leaves of gtr1. These results suggested that GTR1 would be involved in the translocation of JA and JA-Ile in plant and may be contributed to correct positioning of JA and JA-Ile to attenuate an excessive wound response in undamaged leaves.     

Identification of a domain of ETA receptor required for ligand binding.

Various chimeric ETA and ETB receptors were produced in CHO cells for the elucidation of a specific domain which influences the affinity of the receptor toward BQ-123, a selective ETA antagonist. Replacement of the first extracellular loop domain (B-loop) of the ETA receptor with the corresponding domain of the ETB receptor, reduced the inhibition by BQ-123 drastically, while the replacements of other extracellular domains of ETA did not. By contrast, the introduction of the B-loop of ETA in place of the corresponding domain of the ETB receptor endowed the ETB-based chimeric receptor with a sensitivity to BQ-123. These observations suggest that the B-loop domain of the ETA receptor is involved in ligand binding.     

Amalgam is a ligand for the transmembrane receptor neurotactin and is required for neurotactin-mediated cell adhesion and axon fasciculation in Drosophila

Neurotactin (NRT), a member of the cholinesterase-homologous protein family, is a heterophilic cell adhesion molecule that is required for proper axon guidance during Drosophila development. In this study, we identify amalgam (AMA), a member of the immunoglobulin superfamily, as a ligand for the NRT receptor. Using transfected Schneider 2 cells and embryonic primary cultures, we demonstrate that AMA is a secreted protein. Furthermore, AMA is necessary for NRT-expressing cells both to aggregate with themselves and to associate with embryonic primary culture cells. Aggregation assays performed with truncated NRT molecules reveal that the integrity of the cholinesterase-like extracellular domain was not required either for AMA binding or for adhesion, with only amino acids 347-482 of the extracellular domain being necessary for both activities. Moreover, the NRT cytoplasmic domain is required for NRT-mediated adhesion, although not for AMA binding. Using an ama-deficient stock, we find that ama function is not essential for viability. Pupae deficient for ama do exhibit defasciculation defects of the ocellar nerves similar to those found in nrt mutants.     

Retinoic acid receptor gamma is required for proliferation of pancreatic cancer cells

Despite the expectation that retinoic acid receptor could be the potential therapeutic targets for pancreatic cancers, there has been the lack of information about the role and the impact of retinoic acid receptor gamma (RARγ, RARG) on pancreatic cancer, unlike other two RARs. Herein, we applied TCGA and GEO database to show that the expression and prognosis of RARG is closely related to pancreatic cancer, which demonstrates that RARG is commonly overexpressed in human pancreatic cancer and is an independent diagnostic marker predicting the poor prognosis of pancreatic cancer patients. In addition, we demonstrated that the reduction in the expression of RARG in human pancreatic cancer cells dramatically suppress their proliferation and tumor growth in vivo, partially attributable to the downregulation of tumor-supporting biological processes such as cell proliferation, antiapoptosis and metabolism and the decreased expression of various oncogenes like MYC and STAT3. Mechanistically, RARG binds on the promoters of MYC, STAT3, and SLC2A1 which is distinguished from well-known conventional Retinotic acid response elements (RAREs) and that the binding is likely to be responsible for the epigenetic activation in the level of chromatin, assessed by the measurement of deposition of the gene activation marker histone H3 K27 acetylation (H3K27ac) using ChIP-qPCR. In this study, we reveal that RARG plays important role in the tumorigenesis of pancreatic cancer and represents new therapeutic targets for human pancreatic cancer.     

茉莉酸在植物抗逆性中的研究进展

茉莉酸(jasmonic acid, JA)是一种植物内源合成的脂类激素，在植物响应胁迫的调控中发挥着重要作用。本文概括了JA的生物合成与代谢途径及其调控机制；总结了JA信号的传导通路；系统归纳了JA在植物响应生物和非生物胁迫应答中的作用机制和调控网络，重点关注了最新的研究进展。此外，本文梳理了JA与其他植物激素在植物抗逆性调节过程中的信号交流。最后讨论了JA信号通路介导的植物抗逆性研究中亟待解决的问题，并展望了新的分子生物学技术在调控JA信号通路增强作物抗性中的应用前景，以期为植物的抗逆性研究和改良提供参考。     

Root-localized phytochrome chromophore synthesis is required for photoregulation of root elongation and impacts root sensitivity to jasmonic acid in Arabidopsis

Plants exhibit organ- and tissue-specific light responses. To explore the molecular basis of spatial-specific phytochrome-regulated responses, a transgenic approach for regulating the synthesis and accumulation of the phytochrome chromophore phytochromobilin (PΦB) was employed. In prior experiments, transgenic expression of the BILIVERDIN REDUCTASE (BVR) gene was used to metabolically inactivate biliverdin IXα, a key precursor in the biosynthesis of PΦB, and thereby render cells accumulating BVR phytochrome deficient. Here, we report analyses of transgenic Arabidopsis (Arabidopsis thaliana) lines with distinct patterns of BVR accumulation dependent upon constitutive or tissue-specific, promoter-driven BVR expression that have resulted in insights on a correlation between root-localized BVR accumulation and photoregulation of root elongation. Plants with BVR accumulation in roots and a PΦB-deficient elongated hypocotyl2 (hy2-1) mutant exhibit roots that are longer than those of wild-type plants under white illumination. Additional analyses of a line with root-specific BVR accumulation generated using a GAL4-dependent bipartite enhancer-trap system confirmed that PΦB or phytochromes localized in roots directly impact light-dependent root elongation under white, blue, and red illumination. Additionally, roots of plants with constitutive plastid-localized or root-specific cytosolic BVR accumulation, as well as phytochrome chromophore-deficient hy1-1 and hy2-1 mutants, exhibit reduced sensitivity to the plant hormone jasmonic acid (JA) in JA-dependent root inhibition assays, similar to the response observed for the JA-insensitive mutants jar1 and myc2. Our analyses of lines with root-localized phytochrome deficiency or root-specific phytochrome depletion have provided novel insights into the roles of root-specific PΦB, or phytochromes themselves, in the photoregulation of root development and root sensitivity to JA.     

Decorin is a novel antagonistic ligand of the Met receptor

Decorin, a member of the small leucine-rich proteoglycan gene family, impedes tumor cell growth by down-regulating the epidermal growth factor receptor. Decorin has a complex binding repertoire, thus, we predicted that decorin would modulate the bioactivity of other tyrosine kinase receptors. We discovered that decorin binds directly and with high affinity (K_d = ∼1.5 nM) to Met, the receptor for hepatocyte growth factor (HGF). Binding of decorin to Met is efficiently displaced by HGF and less efficiently by internalin B, a bacterial Met ligand. Interaction of decorin with Met induces transient receptor activation, recruitment of the E3 ubiquitin ligase c-Cbl, and rapid intracellular degradation of Met (half-life = ∼6 min). Decorin suppresses intracellular levels of β-catenin, a known downstream Met effector, and inhibits Met-mediated cell migration and growth. Thus, by antagonistically targeting multiple tyrosine kinase receptors, decorin contributes to reduction in primary tumor growth and metastastic spreading.     

4-Hydroxy-trans-2-nonenoic acid is a gamma-hydroxybutyrate receptor ligand in the cerebral cortex and hippocampus

Elevated production of 4-hydroxy-trans-2-nonenal (HNE) occurs in numerous neurological disorders involving oxidative damage. HNE is metabolized to the non-toxic 4-hydroxy-trans-2-nonenoic acid (HNEAcid) by aldehyde dehydrogenases in the rat cerebral cortex. Based upon the structural similarity of HNEAcid to ligands of the gamma-hydroxybutyrate (GHB) receptor, we hypothesized that HNEAcid is an endogenous ligand for the GHB receptor. HNEAcid displaced the specific binding of the GHB receptor ligand (3)H-NCS382 (30 nm) in membrane preparations of human frontal cerebral cortex and whole rat cerebral cortex with IC(50s) of 3.9 +/- 1.1 and 5.6 +/- 1.2 micro m, respectively. Inhibition was attenuated when the carboxyl group of HNEAcid was replaced with an aldehyde or an alcohol. HNEAcid (300 micro m) did not displace the binding of beta-adrenergic receptor and GABA(B) receptor antagonists, demonstrating the selectivity of HNEAcid for the GHB receptor. HNEAcid is formed in homogenates of human frontal cortical gray matter in an NAD(+)-dependent (V(Max), 0.71 nmol/min/mg) and NADP(+)-dependent (V(Max), 0.12 nmol/min/mg) manner. Lastly, (3)H-NCS382 binding is elevated 2.7-fold with age in the cerebral cortex of rats. Our data demonstrate that an HNE metabolite, formed in rat and human brain, is a signaling molecule analogous to other bioactive lipid peroxidation products.     

The wound response in tomato--role of jasmonic acid

Plants respond to mechanical wounding or herbivore attack with a complex scenario of sequential, antagonistic or synergistic action of different signals leading to defense gene expression. Tomato plants were used as a model system since the peptide systemin and the lipid-derived jasmonic acid (JA) were recognized as essential signals in wound-induced gene expression. In this review recent data are discussed with emphasis on wound-signaling in tomato. The following aspects are covered: (i) systemin signaling, (ii) JA biosynthesis and action, (iii) orchestration of various signals such as JA, H2O2, NO, and salicylate, (iv) local and systemic response, and (v) amplification in wound signaling. The common occurrence of JA biosynthesis and systemin generation in the vascular bundles suggest JA as the systemic signal. Grafting experiments with JA-deficient, JA-insensitive and systemin-insensitive mutants strongly support this assumption.     

Megalin is a receptor for albumin in astrocytes and is required for the synthesis of the neurotrophic factor oleic acid

We have previously shown that the uptake and transcytosis of albumin in astrocytes promote the synthesis of the neurotrophic factor oleic acid. Although the mechanism by which albumin induces oleic acid synthesis is well known, the mechanism of albumin uptake in astrocytes remains unknown. In this work, we found that astrocytes express megalin, an endocytic receptor for multiple ligands including albumin. In addition, when the activity of megalin is blocked by specific antibodies or by silencing megalin with specific siRNA, albumin binding and internalization is strongly reduced indicating that megalin is required for albumin binding and internalization in the astrocyte. Since the uptake of albumin in astrocytes aims at synthesizing the neurotrophic factor oleic acid, we tested the ability of megalin-silenced astrocytes to synthesize and release oleic acid in the presence of albumin. Our results showed that the amount of oleic acid found in the extracellular medium of megalin-silenced astrocytes was strongly reduced as compared with their controls. Together, the results of this work indicate that megalin is a receptor for albumin in astrocytes and is required for the synthesis of the neurotrophic factor oleic acid. Consequently, the possible involvement of albumin in the holoprosencephalic syndrome observed in megalin-deficient mice is suggested.