An Efficient, Simple, and Noninvasive Procedure for Genotyping Aquatic and Nonaquatic Laboratory Animals

Various animal models are indispensible in biomedical research. Increasing awareness and regulations have prompted the adaptation of more humane approaches in the use of laboratory animals. With the development of easier and faster methodologies to generate genetically altered animals, convenient and humane methods to genotype these animals are important for research involving such animals. Here, we report skin swabbing as a simple and noninvasive method for extracting genomic DNA from mice and frogs for genotyping. We show that this method is highly reliable and suitable for both immature and adult animals. Our approach allows a simpler and more humane approach for genotyping vertebrate animals.

Red fluorescent genetically encoded Ca2+ indicators for use in mitochondria and endoplasmic reticulum

Ca2+ is a key intermediary in a variety of signalling pathways and undergoes dynamic changes in its cytoplasmic concentration due to release from stores within the endoplasmic reticulum (ER) and influx from the extracellular environment. In addition to regulating cytoplasmic Ca2+ signals, these responses also affect the concentration of Ca2+ within the ER and mitochondria. Single fluorescent protein-based Ca2+ indicators, such as the GCaMP series based on GFP, are powerful tools for imaging changes in the concentration of Ca2+ associated with intracellular signalling pathways. Most GCaMP-type indicators have dissociation constants (Kd) for Ca2+ in the high nanomolar to low micromolar range and are therefore optimal for measuring cytoplasmic [Ca2+], but poorly suited for use in mitochondria and ER where [Ca2+] can reach concentrations of several hundred micromolar. We now report GCaMP-type low-affinity red fluorescent genetically encoded Ca2+ indicators for optical imaging (LAR-GECO), engineered to have Kd values of 24 μM (LAR-GECO1) and 12 μM (LAR-GECO1.2). We demonstrate that these indicators can be used to image mitochondrial and ER Ca2+ dynamics in several cell types. In addition, we perform two-colour imaging of intracellular Ca2+ dynamics in cells expressing both cytoplasmic GCaMP and ER-targeted LAR-GECO1. The development of these low-affinity intensiometric red fluorescent Ca2+ indicators enables monitoring of ER and mitochondrial Ca2+ in combination with GFP-based reporters.

Polo-like kinase 1 (PLK1) and protein phosphatase 6 (PP6) regulate DNA-dependent protein kinase catalytic subunit (DNA-PKcs) phosphorylation in mitosis

The protein kinase activity of the DNA-PKcs (DNA-dependent protein kinase catalytic subunit) and its autophosphorylation are critical for DBS (DNA double-strand break) repair via NHEJ (non-homologous end-joining). Recent studies have shown that depletion or inactivation of DNA-PKcs kinase activity also results in mitotic defects. DNA-PKcs is autophosphorylated on Ser2056, Thr2647 and Thr2609 in mitosis and phosphorylated DNA-PKcs localize to centrosomes, mitotic spindles and the midbody. DNA-PKcs also interacts with PP6 (protein phosphatase 6), and PP6 has been shown to dephosphorylate Aurora A kinase in mitosis. Here we report that DNA-PKcs is phosphorylated on Ser3205 and Thr3950 in mitosis. Phosphorylation of Thr3950 is DNA-PK-dependent, whereas phosphorylation of Ser3205 requires PLK1 (polo-like kinase 1). Moreover, PLK1 phosphorylates DNA-PKcs on Ser3205 in vitro and interacts with DNA-PKcs in mitosis. In addition, PP6 dephosphorylates DNA-PKcs at Ser3205 in mitosis and after IR (ionizing radiation). DNA-PKcs also phosphorylates Chk2 on Thr68 in mitosis and both phosphorylation of Chk2 and autophosphorylation of DNA-PKcs in mitosis occur in the apparent absence of Ku and DNA damage. Our findings provide mechanistic insight into the roles of DNA-PKcs and PP6 in mitosis and suggest that DNA-PKcs' role in mitosis may be mechanistically distinct from its well-established role in NHEJ.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.

Spontaneous cardiac calcinosis in BALB/cByJ mice

BALB/c mice are predisposed to dystrophic cardiac calcinosis-the mineralization of cardiac tissues, especially the right ventricular epicardium. In previous reports, the disease appeared in aged animals and had an unknown etiology. In the current study, we report a substrain of BALB/c mice (BALB/cByJ) that develops disease early and with high frequency. Here we analyzed hearts grossly to identify the presence and measure the severity of disease and to compare BALB/c substrains. Histologic analysis and fluorescent and immunofluorescent microscopy were used to characterize the calcinotic lesions. BALB/cByJ mice exhibited more frequent and severe calcium deposition than did BALB/c mice of other substrains (90% compared with 3% at 5 wk). At this age, lesions covered an average of 30% of the total ventricular surface area in BALB/cByJ mice, compared with less than 1% in other strains. In bone-marrow-chimeric mice, green fluorescent protein was used as a marker to show that the lesions contain an infiltration of cells of bone marrow origin. Lesion histology showed that calcium deposits were surrounded by fibrosis with interspersed immune cells. Lymphocytes, macrophages, and granulocytes were all present. Internalization of the gap-junction protein connexin 43 was observed in myocytes adjacent to lesions. In conclusion, BALB/cByJ mice exhibit more frequent and severe dystrophic cardiac calcinosis than do other BALB/c substrains. Our findings suggest that immune cells are actively recruited to lesions and that myocyte gap junctions are altered near lesions.

Intestinal peptidases form functional complexes with the neutral amino acid transporter B(0)AT1

The brush-border membrane of the small intestine and kidney proximal tubule are the major sites for the absorption and re-absorption of nutrients in the body respectively. Transport of amino acids is mediated through the action of numerous secondary active transporters. In the mouse, neutral amino acids are transported by B(0)AT1 [broad neutral ((0)) amino acid transporter 1; SLC6A19 (solute carrier family 6 member 19)] in the intestine and by B(0)AT1 and B(0)AT3 (SLC6A18) in the kidney. Immunoprecipitation and Blue native electrophoresis of intestinal brush-border membrane proteins revealed that B(0)AT1 forms complexes with two peptidases, APN (aminopeptidase N/CD13) and ACE2 (angiotensin-converting enzyme 2). Physiological characterization of B(0)AT1 expressed together with these peptidases in Xenopus laevis oocytes revealed that APN increased the substrate affinity of the transporter up to 2.5-fold and also increased its surface expression (V(max)). Peptide competition experiments, in silico modelling and site-directed mutagenesis of APN suggest that the catalytic site of the peptidase is involved in the observed changes of B(0)AT1 apparent substrate affinity, possibly by increasing the local substrate concentration. These results provide evidence for the existence of B(0)AT1-containing digestive complexes in the brush-border membrane, interacting differentially with various peptidases, and responding to the dynamic needs of nutrient absorption in the intestine and kidney.

Catalytic residues and a predicted structure of tetrahydrobiopterin-dependent alkylglycerol mono-oxygenase

Alkylglycerol mono-oxygenase (EC 1.14.16.5) forms a third, distinct, class among tetrahydrobiopterin-dependent enzymes in addition to aromatic amino acid hydroxylases and nitric oxide synthases. Its protein sequence contains the fatty acid hydroxylase motif, a signature indicative of a di-iron centre, which contains eight conserved histidine residues. Membrane enzymes containing this motif, including alkylglycerol mono-oxygenase, are especially labile and so far have not been purified to homogeneity in active form. To obtain a first insight into structure-function relationships of this enzyme, we performed site-directed mutagenesis of 26 selected amino acid residues and expressed wild-type and mutant proteins containing a C-terminal Myc tag together with fatty aldehyde dehydrogenase in Chinese-hamster ovary cells. Among all of the acidic residues within the eight-histidine motif, only mutation of Glu137 to alanine led to an 18-fold increase in the Michaelis-Menten constant for tetrahydrobiopterin, suggesting a role in tetrahydrobiopterin interaction. A ninth additional histidine residue essential for activity was also identified. Nine membrane domains were predicted by four programs: ESKW, TMHMM, MEMSAT and Phobius. Prediction of a part of the structure using the Rosetta membrane ab initio method led to a plausible suggestion for a structure of the catalytic site of alkylglycerol mono-oxygenase.

Novel plant-derived recombinant human interferons with broad spectrum antiviral activity

Type I interferons (IFNs) are potent mediators of the innate immune response to viral infection. IFNs released from infected cells bind to a receptor (IFNAR) on neighboring cells, triggering signaling cascades that limit further infection. Subtle variations in amino acids can alter IFNAR binding and signaling outcomes. We used a new gene crossbreeding method to generate hybrid, type I human IFNs with enhanced antiviral activity against four dissimilar, highly pathogenic viruses. Approximately 1400 novel IFN genes were expressed in plants, and the resultant IFN proteins were screened for antiviral activity. Comparing the gene sequences of a final set of 12 potent IFNs to those of parent genes revealed strong selection pressures at numerous amino acids. Using three-dimensional models based on a recently solved experimental structure of IFN bound to IFNAR, we show that many but not all of the amino acids that were highly selected for are predicted to improve receptor binding.

Opposite effects of HIF-1α and HIF-2α on the regulation of IL-8 expression in endothelial cells

Recently we have shown that hypoxia as well as overexpression of the stable form of hypoxia-inducible factor-1α (HIF-1α) diminished the expression of interleukin-8 (IL-8) by inhibition of the Nrf2 transcription factor in HMEC-1 cells. Because HIF isoforms may exert different effects, we aimed to examine the influence of HIF-2α on IL-8 expression in endothelial cells. In contrast to HIF-1α, overexpression of HIF-2α obtained by adenoviral transduction resulted in increased expression of IL-8 in an Nrf2-independent way. Importantly, HIF-2α augmented the activity of SP-1, a transcription factor involved in IL-8 regulation and known coactivator of c-Myc. Additionally, HIF-1 decreased, whereas HIF-2 increased, c-Myc expression, and silencing of Mxi-1, a c-Myc antagonist, restored IL-8 expression downregulated by HIF-1α or hypoxia. Accordingly, binding of c-Myc to the IL-8 promoter was abolished in hypoxia. Importantly, both severe (0.5% O(2)) and mild (5% O(2)) hypoxia diminished IL-8 expression despite the stabilization of both HIF-1 and HIF-2. This study reveals the opposite roles of HIF-1α and HIF-2α in the regulation of IL-8 expression in endothelial cells. However, despite stabilization of both isoforms in hypoxia the effect of HIF-1 is predominant, and downregulation of IL-8 expression in hypoxia is caused by attenuation of Nrf2 and c-Myc.

A role for heparan sulfate proteoglycans in Plasmodium falciparum sporozoite invasion of anopheline mosquito salivary glands

HS (heparan sulfate) has been shown to be an important mediator of Plasmodium sporozoite homing and invasion of the liver, but the role of this glycosaminoglycan in mosquito vector host-sporozoite interactions is unknown. We have biochemically characterized the function of AgOXT1 (Anopheles gambiae peptide-O-xylosyltransferase 1) and confirmed that AgOXT1 can modify peptides representing model HS and chondroitin sulfate proteoglycans in vitro. Moreover, we also demonstrated that the mosquito salivary gland basal lamina proteoglycans are modified by HS. We used RNA interference-mediated knockdown of HS biosynthesis in A. gambiae salivary glands to determine whether Plasmodium falciparum sporozoites that are released from mosquito midgut oocysts use salivary gland HS as a receptor for tissue invasion. Our results suggest that salivary gland basal lamina HS glycosaminoglycans only partially mediate midgut sporozoite invasion of this tissue, and that in the absence of HS, the presence of other surface co-receptors is sufficient to facilitate parasite entry.

Binding of the inhibitor protein IF(1) to bovine F(1)-ATPase

In the structure of bovine F(1)-ATPase inhibited with residues 1-60 of the bovine inhibitor protein IF(1), the α-helical inhibitor interacts with five of the nine subunits of F(1)-ATPase. In order to understand the contributions of individual amino acid residues to this complex binding mode, N-terminal deletions and point mutations have been introduced, and the binding properties of each mutant inhibitor protein have been examined. The N-terminal region of IF(1) destabilizes the interaction of the inhibitor with F(1)-ATPase and may assist in removing the inhibitor from its binding site when F(1)F(o)-ATPase is making ATP. Binding energy is provided by hydrophobic interactions between residues in the long α-helix of IF(1) and the C-terminal domains of the β(DP)-subunit and β(TP)-subunit and a salt bridge between residue E30 in the inhibitor and residue R408 in the C-terminal domain of the β(DP)-subunit. Several conserved charged amino acids in the long α-helix of IF(1) are also required for establishing inhibitory activity, but in the final inhibited state, they are not in contact with F(1)-ATPase and occupy aqueous cavities in F(1)-ATPase. They probably participate in the pathway from the initial interaction of the inhibitor and the enzyme to the final inhibited complex observed in the structure, in which two molecules of ATP are hydrolysed and the rotor of the enzyme turns through two 120° steps. These findings contribute to the fundamental understanding of how the inhibitor functions and to the design of new inhibitors for the systematic analysis of the catalytic cycle of the enzyme.

Catheterization of intestinal loops in ruminants does not adversely affect loop function

Catheterized intestinal loops may be a valuable model to elucidate key components of the host response to various treatments within the small intestine of ruminants. We examined whether catheterizing ileal loops in sheep affected the overall health of animals and intestinal function, whether a bacterial treatment could be introduced into the loops through the catheters, and whether broad-spectrum antibiotics could sterilize the loops. Escherichia coli cells transformed to express the GFP gene were introduced readily into the loops through the catheters, and GFP E. coli cells were localized within the injected loops. Catheterized loops, interspaces, and intact ileum exhibited no abnormalities in tissue appearance or electrical resistance. Expression of the IFNγ, IL1α, IL4, IL6, IL12p40, IL18, TGFβ1, and TNFα cytokine genes did not differ significantly among the intact ileum, catheterized loops, and interspaces, nor did the expression of the gene for inducible nitric oxide synthase. Broad-spectrum antibiotics administered during surgery did not sterilize the loops or interspaces and did not substantively change the composition of the microbiota. However, antibiotics reduced the overall number of bacterial cells within the loop and the relative abundance of community constituents. We concluded that catheterization of intestinal loops did not adversely affect health or loop function in sheep. Furthermore, allowing animals to recover fully from surgery and to clear pharmaceuticals will remove any confounding effects due to these factors, making catheterized intestinal loops a feasible model for studying host responses in ruminants.

Stem cells and cell therapy approaches in lung biology and diseases

Cell-based therapies with embryonic or adult stem cells, including induced pluripotent stem cells, have emerged as potential novel approaches for several devastating and otherwise incurable lung diseases, including emphysema, pulmonary fibrosis, pulmonary hypertension, and the acute respiratory distress syndrome. Although initial studies suggested engraftment of exogenously administered stem cells in lung, this is now generally felt to be a rare occurrence of uncertain physiologic significance. However, more recent studies have demonstrated paracrine effects of administered cells, including stimulation of angiogenesis and modulation of local inflammatory and immune responses in mouse lung disease models. Based on these studies and on safety and initial efficacy data from trials of adult stem cells in other diseases, groundbreaking clinical trials of cell-based therapy have been initiated for pulmonary hypertension and for chronic obstructive pulmonary disease. In parallel, the identity and role of endogenous lung progenitor cells in development and in repair from injury and potential contribution as lung cancer stem cells continue to be elucidated. Most recently, novel bioengineering approaches have been applied to develop functional lung tissue ex vivo. Advances in each of these areas will be described in this review with particular reference to animal models.

Guinea pig adenovirus infection does not inhibit cochlear transfection with human adenoviral vectors in a model of hearing loss

Routine surveillance of guinea pigs maintained within a barrier facility detected guinea pig adenovirus (GPAdV) in sentinel animals. These guinea pigs served as models of induced hearing loss followed by regeneration of cochlear sensory (hair) cells through transdifferentiation of nonsensory cells by using human adenoviral (hAV) gene therapy. To determine whether natural GPAdV infection affected the ability of hAV vectors to transfect inner ear cells, adult male pigmented guinea pigs (n = 7) were enrolled in this study because of their prolonged exposure to GPAdV-seropositive conspecifics. Animals were deafened chemically (n = 2), received an hAV vector carrying the gene for green fluorescent protein (hAV-GFP) surgically without prior deafening (n = 2), or were deafened chemically with subsequent surgical inoculation of hAV-GFP (n = 3). Cochleae were evaluated by using fluorescence microscopy, and GFP expression in supporting cells indicated that the hAV-GFP vector was able to transfect inner ears in GPAdV-seropositive guinea pigs that had been chemically deafened. Animals had histologic evidence of interstitial pneumonia, attributable to prior infection with GPAdV. These findings confirmed that the described guinea pigs were less robust animal models with diminished utility for the overall studies. Serology tests confirmed that 5 of 7 animals (71%) were positive for antibodies against GPAdV at necropsy, approximately 7 mo after initial detection of sentinel infection. Control animals (n = 5) were confirmed to be seronegative for GPAdV with clinically normal pulmonary tissue. This study is the first to demonstrate that natural GPAdV infection does not negatively affect transfection with hAV vectors into guinea pig inner ear cells, despite the presence of other health complications attributed to the viral infection.

Comparison of tetraploid blastocyst microinjection of outbred Crl:CD1(ICR), hybrid B6D2F1/Tac, and inbred C57BL/6NTac embryos for generation of mice derived from embryonic stem cells

Embryo electrofusion and tetraploid blastocyst microinjection is a modification of the traditional embryonic stem cell (ES cell)-based method to generate targeted mutant mice. Viability of tetraploid embryos is reportedly lower than with diploid embryos, with considerable interstrain variation. Here we assessed fetus and pup viability after ES cell microinjection of tetraploid blastocysts derived from outbred, hybrid, and inbred mice. Two-cell mouse embryos (C57BL/6NTac [B6], n = 788; B6D2F1/Tac [BDF1], n = 1871; Crl:CD1(ICR) [CD1], n = 1308) were electrofused; most resultant tetraploid blastocysts were injected with ES cells and surgically transferred into pseudopregnant recipient mice. Reproductive tracts were examined at midgestation for embryologic studies using B6 and BDF1 blastocysts; implantation sites and viable fetuses were counted. Pregnancies were carried to term for studies of targeted mutant mice using BDF1 and CD1 blastocysts, and pup yield was evaluated. Electrofusion rates of 2-cell embryos did not differ among B6, BDF1, and CD1 mice (overall mean, 92.8% +/- 5.4%). For embryologic studies, 244 B6 blastocysts were surgically transferred and 1 fetus was viable (0.41%), compared with 644 BDF1 blastocysts surgically transferred and 88 viable fetuses (13.7%). For targeted mutant mouse studies, 259 BDF1 blastocysts were surgically transferred yielding 10 pups (3.9%); 569 CD1 blastocysts yielded 44 pups (7.7%).

Phospholipase C beta3 is a key component in the Gbetagamma/PKCeta/PKD-mediated regulation of trans-Golgi network to plasma membrane transport

The requirement of DAG (diacylglycerol) to recruit PKD (protein kinase D) to the TGN (trans-Golgi network) for the targeting of transport carriers to the cell surface, has led us to a search for new components involved in this regulatory pathway. Previous findings reveal that the heterotrimeric Gbetagamma (GTP-binding protein betagamma subunits) act as PKD activators, leading to fission of transport vesicles at the TGN. We have recently shown that PKCeta (protein kinase Ceta) functions as an intermediate member in the vesicle generating pathway. DAG is capable of activating this kinase at the TGN, and at the same time is able to recruit PKD to this organelle in order to interact with PKCeta, allowing phosphorylation of PKD's activation loop. The most qualified candidates for the production of DAG at the TGN are PI-PLCs (phosphatidylinositol-specific phospholipases C), since some members of this family can be directly activated by Gbetagamma, utilizing PtdIns(4,5)P2 as a substrate, to produce the second messengers DAG and InsP3. In the present study we show that betagamma-dependent Golgi fragmentation, PKD1 activation and TGN to plasma membrane transport were affected by a specific PI-PLC inhibitor, U73122 [1-(6-{[17-3-methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-1H-pyrrole-2,5-dione]. In addition, a recently described PI-PLC activator, m-3M3FBS [2,4,6-trimethyl-N-(m-3-trifluoromethylphenyl)benzenesulfonamide], induced vesiculation of the Golgi apparatus as well as PKD1 phosphorylation at its activation loop. Finally, using siRNA (small interfering RNA) to block several PI-PLCs, we were able to identify PLCbeta3 as the sole member of this family involved in the regulation of the formation of transport carriers at the TGN. In conclusion, we demonstrate that fission of transport carriers at the TGN is dependent on PI-PLCs, specifically PLCbeta3, which is necessary to activate PKCeta and PKD in that Golgi compartment, via DAG production.

Structure and ligand-binding site characteristics of the human P2Y11 nucleotide receptor deduced from computational modelling and mutational analysis

The P2Y11-R (P2Y11 receptor) is a less explored drug target. We computed an hP2Y11-R (human P2Y11) homology model with two templates, bovine-rhodopsin (2.6 A resolution; 1 A=0.1 nm) and a hP2Y1-ATP complex model. The hP2Y11-R model was refined using molecular dynamics calculations and validated by virtual screening methods, with an enrichment factor of 5. Furthermore, mutational analyses of Arg106, Glu186, Arg268, Arg307 and Ala313 confirmed the adequacy of our hP2Y11-R model and the computed ligand recognition mode. The E186A and R268A mutants reduced the potency of ATP by one and three orders of magnitude respectively. The R106A and R307A mutants were functionally inactive. We propose that residues Arg106, Arg268, Arg307 and Glu186 are involved in ionic interactions with the phosphate moiety of ATP. Arg307 is possibly also H-bonded to N6 of ATP via the backbone carbonyl. Activity of ATP at the F109I mutant revealed that the proposed p-stacking of Phe109 with the adenine ring is a minor interaction. The mutation A313N, which is part of a hydrophobic pocket in the vicinity of the ATP C-2 position, partially explains the high activity of 2-MeS-ATP at P2Y1-R as compared with the negligible activity at the P2Y11-R. Inactivity of ATP at the Y261A mutant implies that Tyr261 acts as a molecular switch, as in other G-protein-coupled receptors. Moreover, analysis of cAMP responses seen with the mutants showed that the efficacy of coupling of the P2Y11-R with Gs is more variable than coupling with Gq. Our model also indicates that Ser206 forms an H-bond with Pgamma (the gamma-phosphate of the triphosphate chain of ATP) and Met310 interacts with the adenine moiety.

BHLH32 modulates several biochemical and morphological processes that respond to Pi starvation in Arabidopsis

P(i) (inorganic phosphate) limitation severely impairs plant growth and reduces crop yield. Hence plants have evolved several biochemical and morphological responses to P(i) starvation that both enhance uptake and conserve use. The mechanisms involved in P(i) sensing and signal transduction are not completely understood. In the present study we report that a previously uncharacterized transcription factor, BHLH32, acts as a negative regulator of a range of P(i) starvation-induced processes in Arabidopsis. In bhlh32 mutant plants in P(i)-sufficient conditions, expression of several P(i) starvation-induced genes, formation of anthocyanins, total P(i) content and root hair formation were all significantly increased compared with the wild-type. Among the genes negatively regulated by BHLH32 are those encoding PPCK (phosphoenolpyruvate carboxylase kinase), which is involved in modifying metabolism so that P(i) is spared. The present study has shown that PPCK genes are rapidly induced by P(i) starvation leading to increased phosphorylation of phosphoenolpyruvate carboxylase. Furthermore, several Arabidopsis proteins that regulate epidermal cell differentiation [TTG1 (TRANSPARENT TESTA GLABRA1), GL3 (GLABRA3) and EGL3 (ENHANCER OF GL3)] positively regulate PPCK gene expression in response to P(i) starvation. BHLH32 can physically interact with TTG1 and GL3. We propose that BHLH32 interferes with the function of TTG1-containing complexes and thereby affects several biochemical and morphological processes that respond to P(i) availability.

Phosphoethanolamine N-methyltransferase (PMT-1) catalyses the first reaction of a new pathway for phosphocholine biosynthesis in Caenorhabditis elegans

The development of nematicides targeting parasitic nematodes of animals and plants requires the identification of biochemical targets not found in host organisms. Recent studies suggest that Caenorhabditis elegans synthesizes phosphocholine through the action of PEAMT (S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferases) that convert phosphoethanolamine into phosphocholine. Here, we examine the function of a PEAMT from C. elegans (gene: pmt-1; protein: PMT-1). Our analysis shows that PMT-1 only catalyses the conversion of phosphoethanolamine into phospho-monomethylethanolamine, which is the first step in the PEAMT pathway. This is in contrast with the multifunctional PEAMT from plants and Plasmodium that perform multiple methylations in the pathway using a single enzyme. Initial velocity and product inhibition studies indicate that PMT-1 uses a random sequential kinetic mechanism and is feedback inhibited by phosphocholine. To examine the effect of abrogating PMT-1 activity in C. elegans, RNAi (RNA interference) experiments demonstrate that pmt-1 is required for worm growth and development and validate PMT-1 as a potential target for inhibition. Moreover, providing pathway metabolites downstream of PMT-1 reverses the RNAi phenotype of pmt-1. Because PMT-1 is not found in mammals, is only distantly related to the plant PEAMT and is conserved in multiple parasitic nematodes of humans, animals and crop plants, inhibitors targeting it may prove valuable in human and veterinary medicine and agriculture.

Mapping binding sites for the PDE4D5 cAMP-specific phosphodiesterase to the N- and C-domains of beta-arrestin using spot-immobilized peptide arrays

Beta2-ARs (beta2-adrenoceptors) become desensitized rapidly upon recruitment of cytosolic beta-arrestin. PDE4D5 (family 4 cAMP-specific phosphodiesterase, subfamily D, isoform 5) can be recruited in complex with beta-arrestin, whereupon it regulates PKA (cAMP-dependent protein kinase) phosphorylation of the beta2-AR. In the present study, we have used novel technology, employing a library of overlapping peptides (25-mers) immobilized on cellulose membranes that scan the entire sequence of beta-arrestin 2, to define the interaction sites on beta-arrestin 2 for binding of PDE4D5 and the cognate long isoform, PDE4D3. We have identified a binding site in the beta-arrestin 2 N-domain for the common PDE4D catalytic unit and two regions in the beta-arrestin 2 C-domain that confer specificity for PDE4D5 binding. Alanine-scanning peptide array analysis of the N-domain binding region identified severely reduced interaction with PDE4D5 upon R26A substitution, and reduced interaction upon either K18A or T20A substitution. Similar analysis of the beta-arrestin 2 C-domain identified Arg286 and Asp291, together with the Leu215-His220 region, as being important for binding PDE4D5, but not PDE4D3. Transfection with wild-type beta-arrestin 2 profoundly decreased isoprenaline-stimulated PKA phosphorylation of the beta2-AR in MEFs (mouse embryo fibroblasts) lacking both beta-arrestin 1 and beta-arrestin 2. This effect was negated using either the R26A or the R286A mutant form of beta-arrestin 2 or a mutant with substitution of an alanine cassette for Leu215-His220, which showed little or no PDE4D5 binding, but was still recruited to the beta2-AR upon isoprenaline challenge. These data show that the interaction of PDE4D5 with both the N- and C-domains of beta-arrestin 2 are essential for beta2-AR regulation.

Functional diversification of a basic helix-loop-helix protein due to alternative transcription during generation of amphidiploidy in tobacco plants

A plastid-resident basic helix-loop-helix protein, previously identified in Nicotiana tabacum and designated as NtWIN4 (N. tabacum wound-induced clone 4), has been converted from a nuclear transcription repressor into a plastid-resident regulatory factor through replacement of the DNA-binding domain with a plastid transit sequence during evolution. N. tabacum is a natural amphidiploid plant derived from Nicotiana tomentosiformis and Nicotiana sylvestris and immunoblot staining using anti-NtWIN4 antibodies identified two protein species, a 26 kDa form and a 17 kDa form, in N. sylvestris, whereas only the 17 kDa form was found in N. tabacum. The 26 kDa protein is produced when translation starts from the first AUG codon of the mRNA and is predominantly localized in the cytoplasm and nucleus, whereas the 17 kDa protein is derived from a 24 kDa precursor protein, synthesized from the second AUG codon, and localizes only to plastids. Subsequent analyses revealed that the lengths of the mRNAs vary in the two plant species. One major form lacks the first AUG, while minor populations possess variable 5'-untranslated regions prior to the first AUG codon. Translation of the two types produces the 24 kDa and 26 kDa proteins respectively. In vitro translation assays indicated that initiation frequency from the first AUG codon is higher in mRNAs from N. sylvestris than from N. tabacum. In contrast, initiation from the second AUG codon was found to be equally efficient in mRNAs from both species. These results suggest that both mRNA populations and translation efficiency changed during the amphidiploidization responsible for generation of N. tabacum. This scheme could reflect a molecular mechanism of protein evolution in plants.

Structural and biochemical characterization of human orphan DHRS10 reveals a novel cytosolic enzyme with steroid dehydrogenase activity

To this day, a significant proportion of the human genome remains devoid of functional characterization. In this study, we present evidence that the previously functionally uncharacterized product of the human DHRS10 gene is endowed with 17beta-HSD (17beta-hydroxysteroid dehydrogenase) activity. 17beta-HSD enzymes are primarily involved in the metabolism of steroids at the C-17 position and also of other substrates such as fatty acids, prostaglandins and xenobiotics. In vitro, DHRS10 converts NAD+ into NADH in the presence of oestradiol, testosterone and 5-androstene-3beta,17beta-diol. Furthermore, the product of oestradiol oxidation, oestrone, was identified in intact cells transfected with a construct plasmid encoding the DHRS10 protein. In situ fluorescence hybridization studies have revealed the cytoplasmic localization of DHRS10. Along with tissue expression data, this suggests a role for DHRS10 in the local inactivation of steroids in the central nervous system and placenta. The crystal structure of the DHRS10 apoenzyme exhibits secondary structure of the SDR (short-chain dehydrogenase/reductase) family: a Rossmann-fold with variable loops surrounding the active site. It also reveals a broad and deep active site cleft into which NAD+ and oestradiol can be docked in a catalytically competent orientation.

Cyclo-oxygenase 2 expression impairs serum-withdrawal-induced apoptosis in liver cells

We have investigated the mechanism of COX-2 (cyclo-oxygenase 2)-dependent inhibition of apoptosis in liver, a key pathway underlying proliferative actions of COX-2 in liver cancers, cirrhosis, chronic hepatitis C infection and regeneration after partial hepatectomy. Stable expression of COX-2 in CHL (Chang liver) cells induced proliferation, with an increase in the proportion of cells in S-phase, but no other significant changes in cell-cycle distribution. This was associated with a marked inhibition of the apoptotic response to serum deprivation, an effect mimicked by treating empty-vector-transfected control cells (CHL-V cells) with prostaglandin E2 and prevented in COX-2-expressing cells (CHL-C cells) treated with selective inhibitors of COX-2. Serum-deprived CHL-V cells displayed several indicators of activation of intrinsic apoptosis: caspases 9 and 3 activated within 6 h and caspase 8 within 18 h, Bax expression was induced, cytochrome c was released to the cytosol, and PARP-1 [poly(ADP-ribose) polymerase 1] cleavage was evident in nuclei. COX-2 expression blocked these events, concomitant with reduced expression of p53 and promotion of Akt phosphorylation, the latter indicating activation of survival pathways. CHL cells were resistant to stimulation of the extrinsic pathway with anti-Fas antibody. Moreover, in vivo expression of GFP (green fluorescent protein)-labelled COX-2 in mice by hydrodynamics-based transient transfection conferred resistance to caspase 3 activation and apoptosis induced by stimulation of Fas.

Directed differentiation of mouse embryonic stem cells into thyroid follicular cells

Elucidating the molecular mechanisms leading to the induction and specification of thyroid follicular cells is important for our understanding of thyroid development. To characterize the key events in this process, we previously established an experimental embryonic stem (ES) cell model system, which shows that wild-type mouse CCE ES cells can give rise to thyrocyte-like cells in vitro. We extend our analysis in this report by using a genetically manipulated ES cell line in which green fluorescent protein (GFP) cDNA is targeted to the TSH receptor (TSHR) gene, linking GFP expression to the transcription of the endogenous TSHR gene. The appearance of GFP-positive cells was dependent on the formation of embryoid bodies from undifferentiated ES cells and was greatly enhanced by TSH treatment during the first 2-4 d of differentiation. With the support of Matrigel, highly enriched ES cell-derived GFP-positive cells formed thyroid follicle-like clusters in a serum-free medium supplemented with TSH. Importantly, these clusters display the characteristics of thyroid follicular cells. Immunofluorescent studies confirmed the colocalization of TSHR with the Na+/I- symporter in the clusters and indicated that Na+/I- symporter was expressed exclusively in the plasma membrane. In addition, I- uptake activity was observed in these cells. Our results indicate that ES cells can be induced to differentiate into thyroid follicular cells, providing a powerful tool to study embryonic thyroid development and function.

Bax translocates to mitochondria of heart cells during simulated ischaemia: involvement of AMP-activated and p38 mitogen-activated protein kinases

The cytosolic protein Bax plays a key role in apoptosis by migrating to mitochondria and releasing proapoptotic proteins from the mitochondrial intermembrane space. The present study investigates the movement of Bax in isolated rat neonatal cardiomyocytes subjected to simulated ischaemia (minus glucose, plus cyanide), using green fluorescent protein-tagged Bax as a means of imaging Bax movements. Simulated ischaemia induced Bax translocation from the cytosol to mitochondria, commencing within 20 min of simulated ischaemia and progressing for several hours. Under the same conditions, there was an increase in the active, phosphorylated forms of p38 MAPK (mitogen-activated protein kinase) and AMPK (AMP-activated protein kinase). The AMPK activators AICAR (5-aminoimidazole-4-carboxamide ribonucleoside) and metformin also stimulated Bax translocation. Inhibition of p38 MAPK with SB203580 attenuated the phosphorylation of the downstream substrates, MAPK-activated protein kinases 2 and 3, but not that of the upstream MAPK kinase 3, nor of AMPK. Under all conditions (ischaemia, AICAR and metformin), SB203580 blocked Bax translocation completely. It is concluded that Bax translocation to mitochondria is an early step in ischaemia and that it occurs in response to activation of p38 MAPK downstream of AMPK.

Phospholemman inhibition of the cardiac Na+/Ca2+ exchanger. Role of phosphorylation

We have demonstrated previously that phospholemman (PLM), a 15-kDa integral sarcolemmal phosphoprotein, inhibits the cardiac Na+/Ca2+ exchanger (NCX1). In addition, protein kinase A phosphorylates serine 68, whereas protein kinase C phosphorylates both serine 63 and serine 68 of PLM. Using human embryonic kidney 293 cells that are devoid of both endogenous PLM and NCX1, we first demonstrated that the exogenous NCX1 current (I(NaCa)) was increased by phorbol 12-myristate 13-acetate (PMA) but not by forskolin. When co-expressed with NCX1, PLM resulted in: (i) decreases in I(NaCa), (ii) attenuation of the increase in I(NaCa) by PMA, and (iii) additional reduction in I(NaCa) in cells treated with forskolin. Mutating serine 63 to alanine (S63A) preserved the sensitivity of PLM to forskolin in terms of suppression of I(NaCa), whereas mutating serine 68 to alanine (S68A) abolished the inhibitory effect of PLM on I(NaCa). Mutating serine 68 to glutamic acid (phosphomimetic) resulted in additional suppression of I(NaCa) as compared with wild-type PLM. These results suggest that PLM phosphorylated at serine 68 inhibited I(NaCa). The physiological significance of inhibition of NCX1 by phosphorylated PLM was evaluated in PLM-knock-out (KO) mice. When compared with wild-type myocytes, I(NaCa) was significant larger in PLM-KO myocytes. In addition, the PMA-induced increase in I(NaCa) was significantly higher in PLM-KO myocytes. By contrast, forskolin had no effect on I(NaCa) in wild-type myocytes. We conclude that PLM, when phosphorylated at serine 68, inhibits Na+/Ca2+ exchange in the heart.

The ubiquitin-associated domain of AMPK-related kinases regulates conformation and LKB1-mediated phosphorylation and activation

Recent work indicates that the LKB1 tumour suppressor protein kinase, which is mutated in Peutz-Jeghers cancer syndrome, phosphorylates and activates a group of protein kinases that are related to AMPK (AMP-activated protein kinase). Ten of the 14 AMPK-related protein kinases activated by LKB1, including SIK (salt-induced kinase), MARK (microtubule-affinity-regulating kinase) and BRSK (brain-specific kinase) isoforms, possess a ubiquitin-associated (UBA) domain immediately C-terminal to the kinase catalytic domain. These are the only protein kinases in the human genome known to possess a UBA domain, but their roles in regulating AMPK-related kinases are unknown. We have investigated the roles that the UBA domain may play in regulating these enzymes. Limited proteolysis of MARK2 revealed that the kinase and UBA domains were contained within a fragment that was resistant to trypsin proteolysis. SAXS (small-angle X-ray scattering) analysis of inactive and active LKB1-phosphorylated MARK2 revealed that activation of MARK2 is accompanied by a significant conformational change that alters the orientation of the UBA domain with respect to the catalytic domain. Our results indicate that none of the UBA domains found in AMPK-related kinases interact with polyubiquitin or other ubiquitin-like molecules. Instead, the UBA domains appear to play an essential conformational role and are required for the LKB1-mediated phosphorylation and activation of AMPK-related kinases. This is based on the findings that mutation or removal of the UBA domains of several AMPK-related kinases, including isoforms of MARK, SIK and BRSK, markedly impaired the catalytic activity and LKB1-mediated phosphorylation of these enzymes. We also provide evidence that the UBA domains do not function as LKB1-STRAD (STE20-related adaptor)-MO25 (mouse protein 25) docking/interacting sites and that mutations in the UBA domain of SIK suppressed the ability of SIK to localize within punctate regions of the nucleus. Taken together, these findings suggest that the UBA domains of AMPK-related kinases play an important role in regulating the conformation, activation and localization of these enzymes.

C/EBPalpha and HNF6 protein complex formation stimulates HNF6-dependent transcription by CBP coactivator recruitment in HepG2 cells

We previously demonstrated that formation of complexes between the DNA-binding domains of hepatocyte nuclear factor 6 (HNF6) and forkhead box a2 (Foxa2) proteins stimulated Foxa2 transcriptional activity. Here, we used HepG2 cell cotransfection assays to demonstrate that HNF6 transcriptional activity was stimulated by CCAAT/enhancer-binding protein alpha (C/EBPalpha), but not by the related C/EBPbeta or C/EBPdelta proteins. Formation of the C/EBPalpha-HNF6 protein complex required the HNF6 cut domain and the C/EBPalpha activation domain (AD) 1/AD2 sequences. This C/EBPalpha-HNF6 transcriptional synergy required both the N-terminal HNF6 polyhistidine and serine/threonine/proline box sequences, as well as the C/EBPalpha AD1/AD2 sequences, the latter of which are known to recruit the CREB binding protein (CBP) transcriptional coactivator. Consistent with these findings, adenovirus E1A-mediated inhibition of p300/CBP histone acetyltransferase activity abrogated C/EBPalpha-HNF6 transcriptional synergy in cotransfection assays. Co-immunoprecipitation assays with liver protein extracts demonstrate an association between the HNF6 and C/EBPalpha transcription factors and the CBP coactivator protein in vivo. Furthermore, chromatin immunoprecipitation assays with hepatoma cells demonstrated that increased levels of both C/EBPalpha and HNF6 proteins were required to stimulate association of these transcription factors and the CBP coactivator protein with the endogenous mouse Foxa2 promoter region. In conclusion, formation of the C/EBPalpha-HNF6 protein complex stimulates recruitment of the CBP coactivator protein for expression of Foxa2, a transcription factor critical for regulating expression of hepatic gluconeogenic genes during fasting.

A novel ARF-binding protein (LZAP) alters ARF regulation of HDM2

The tumour suppressor ARF (alternative reading frame) is encoded by the INK4a (inhibitor of cyclin-dependent kinase 4)/ARF locus, which is frequently altered in human tumours. ARF binds MDM2 (murine double minute 2) and releases p53 from inhibition by MDM2, resulting in stabilization, accumulation and activation of p53. Recently, ARF has been found to associate with other proteins, but, to date, little is known about ARF-associated proteins that are implicated in post-translational regulation of ARF activity. Using a yeast two-hybrid screen, we have identified a novel protein, LZAP (LXXLL/leucine-zipper-containing ARF-binding protein), that interacts with endogenous ARF in mammalian cells. In the present study, we show that LZAP reversed the ability of ARF to inhibit HDM2's ubiquitin ligase activity towards p53, but simultaneously co-operated with ARF, maintaining p53 stability and increasing p53 transcriptional activity. Expression of LZAP, in addition to ARF, increased the percentage of cells in the G1 phase of the cell cycle. Expression of LZAP also caused activation of p53 and a p53-dependent G1 cell-cycle arrest in the absence of ARF. Taken together, our data suggest that LZAP can regulate ARF biochemical and biological activity. Additionally, LZAP has p53-dependent cell-cycle effects that are independent of ARF.

Intracellular colocalization and interaction of IGF-binding protein-2 with the cyclin-dependent kinase inhibitor p21CIP1/WAF1 during growth inhibition

It is presently unknown whether any member of the IGFBP (insulin-like growth factor binding protein) family directly participates in the control of cell proliferation. We have previously documented that induction of IGFBP-2 was associated with inhibition of DNA synthesis in lung alveolar epithelial cells. In the present study, we investigated the relationship between IGFBP-2 and the cell cycle inhibitor p21CIP1/WAF1 further. We used serum deprivation to inhibit the proliferation of MLE (mouse lung epithelial)-12 cells, and characterized the spatial localization of IGFBP-2. We found that growth inhibition, which was supported by the strong induction of p21CIP1/WAF1, was correlated with increased secretion of IGFBP-2 and, unexpectedly, with its increased localization in the nucleus and particularly in the cytoplasm. By coimmunoprecipitation, we discovered that IGFBP-2 is capable of binding to p21CIP1/WAF1. Interaction between these two proteins was further supported by colocalization of the proteins within growth-arrested cells, as visualized by confocal microscopy. Furthermore, this interaction increased with the duration of the stress, but was suppressed when proliferation was restimulated by the addition of serum. The recombinant expression of GFP (green fluorescent protein)-tagged IGFBP-2 in transfected MLE-12 cells demonstrated its ability to bind specifically to p21CIP1/WAF1. Taken together, these results provide a link between IGFBP-2 and p21CIP1/WAF1 in the regulation of alveolar lung cell proliferation.

FoxO6 transcriptional activity is regulated by Thr26 and Ser184, independent of nucleo-cytoplasmic shuttling

Forkhead members of the 'O' class (FoxO) are transcription factors crucial for the regulation of metabolism, cell cycle, cell death and cell survival. FoxO factors are regulated by insulin-mediated activation of PI3K (phosphoinositide 3-kinase)-PKB (protein kinase B) signalling. Activation of PI3K-PKB signalling results in the phosphorylation of FoxO factors on three conserved phosphorylation motifs, which are essential for the translocation of FoxO factors from the nucleus to the cytosol. FoxO6, however, remains mostly nuclear due to the fact that its shuttling ability is dramatically impaired. FoxO1, FoxO3 and FoxO4 all contain an N- and C-terminal PKB motif and a motif located in the forkhead domain. FoxO6 lacks the conserved C-terminal PKB motif, which is the cause of the shuttling impairment. Since FoxO6 can be considered constitutively nuclear, we investigated whether it is also a constitutively active transcription factor. Our results show that FoxO6 transcriptional activity is inhibited by growth factors, independent of shuttling, indicating that it is not constitutively active. The PKB site in the forkhead domain (Ser184) regulated the DNA binding characteristics and the N-terminal PKB site acted as a growth factor sensor. In summary, FoxO6 is not a constitutively active transcription factor and can be regulated by growth factors in a Thr26- and Ser184-dependent manner, independent of shuttling to the cytosol.

The signal peptide of the rat corticotropin-releasing factor receptor 1 promotes receptor expression but is not essential for establishing a functional receptor

Approximately 5-10% of the GPCRs (G-protein-coupled receptors) contain N-terminal signal peptides that are cleaved off during receptor insertion into the ER (endoplasmic reticulum) membrane by the signal peptidases of the ER. The reason as to why only a subset of GPCRs requires these additional signal peptides is not known. We have recently shown that the signal peptide of the human ET(B)-R (endothelin B receptor) does not influence receptor expression but is necessary for the translocation of the receptor's N-tail across the ER membrane and thus for the establishment of a functional receptor [Köchl, Alken, Rutz, Krause, Oksche, Rosenthal and Schülein (2002) J. Biol. Chem. 277, 16131-16138]. In the present study, we show that the signal peptide of the rat CRF-R1 (corticotropin-releasing factor receptor 1) has a different function: a mutant of the CRF-R1 lacking the signal peptide was functional and displayed wild-type properties with respect to ligand binding and activation of adenylate cyclase. However, immunoblot analysis and confocal laser scanning microscopy revealed that the mutant receptor was expressed at 10-fold lower levels than the wild-type receptor. Northern-blot and in vitro transcription translation analyses precluded the possibility that the reduced receptor expression is due to decreased transcription or translation levels. Thus the signal peptide of the CRF-R1 promotes an early step of receptor biogenesis, such as targeting of the nascent chain to the ER membrane and/or the gating of the protein-conducting translocon of the ER membrane.

Mirk/Dyrk1B mediates survival during the differentiation of C2C12 myoblasts

The kinase Mirk/dyrk1B is essential for the differentiation of C2C12 myoblasts. Mirk reinforces the G0/G1 arrest state in which differentiation occurs by directly phosphorylating and stabilizing p27(Kip1) and destabilizing cyclin D1. We now demonstrate that Mirk is anti-apoptotic in myoblasts. Knockdown of endogenous Mirk by RNA interference activated caspase 3 and decreased myoblast survival by 75%, whereas transient overexpression of Mirk increased cell survival. Mirk exerts its anti-apoptotic effects during muscle differentiation at least in part through effects on the cell cycle inhibitor and pro-survival molecule p21(Cip1). Overexpression and RNA interference experiments demonstrated that Mirk phosphorylates p21 within its nuclear localization domain at Ser-153 causing a portion of the typically nuclear p21 to localize in the cytoplasm. Phosphomimetic GFP-p21-S153D was pancellular in both cycling C2C12 myoblasts and NIH3T3 cells. Endogenous Mirk in myotubes and overexpressed Mirk in NIH3T3 cells were able to cause the pancellular localization of wild-type GFP-p21 but not the nonphosphorylatable mutant GFP-p21-S153A. Translocation to the cytoplasm enables p21 to block apoptosis through inhibitory interaction with pro-apoptotic molecules. Phosphomimetic p21-S153D was more effective than wild-type p21 in blocking the activation of caspase 3. Transient expression of p21-S153D also increased myoblast viability in colony forming assays, whereas the p21-S153A mutant had no effect. This Mirk-dependent change in p21 intracellular localization is a natural part of myoblast differentiation. Endogenous p21 localized exclusively to the nuclei of proliferating myoblasts but was also found in the cytoplasm of post-mitotic multinucleated myotubes and adult human skeletal myofibers.

The prototype gamma-2 herpesvirus nucleocytoplasmic shuttling protein, ORF 57, transports viral RNA through the cellular mRNA export pathway

HVS (herpesvirus saimiri) is the prototype gamma-2 herpesvirus. This is a subfamily of herpesviruses gaining importance since the identification of the first human gamma-2 herpesvirus, Kaposi's sarcoma-associated herpesvirus. The HVS ORF 57 (open reading frame 57) protein is a multifunctional transregulatory protein homologous with genes identified in all classes of herpesviruses. Recent work has demonstrated that ORF 57 has the ability to bind viral RNA, shuttles between the nucleus and cytoplasm and promotes the nuclear export of viral transcripts. In the present study, we show that ORF 57 shuttles between the nucleus and cytoplasm in a CRM-1 (chromosomal region maintenance 1)-independent manner. ORF 57 interacts with the mRNA export factor REF (RNA export factor) and two other components of the exon junction complex, Y14 and Magoh. The association of ORF 57 with REF stimulates recruitment of the cellular mRNA export factor TAP (Tip-associated protein), and HVS infection triggers the relocalization of REF and TAP from the nuclear speckles to several large clumps within the cell. Using a dominant-negative form of TAP and RNA interference to deplete TAP, we show that it is essential for bulk mRNA export in mammalian cells and is required for ORF 57-mediated viral RNA export. Furthermore, we show that the disruption of TAP reduces viral replication. These results indicate that HVS utilizes ORF 57 to recruit components of the exon junction complex and subsequently TAP to promote viral RNA export through the cellular mRNA export pathway.

Protein interaction quantified in vivo by spectrally resolved fluorescence resonance energy transfer

We describe a fluorescence resonance energy transfer (FRET)-based method for finding in living cells the fraction of a protein population (alpha(T)) forming complexes, and the average number (n) of those protein molecules in each complex. The method relies both on sensitized acceptor emission and on donor de-quenching (by photobleaching of the acceptor molecules), coupled with full spectral analysis of the differential fluorescence signature, in order to quantify the donor/acceptor energy transfer. The approach and sensitivity limits are well suited for in vivo microscopic investigations. This is demonstrated using a scanning laser confocal microscope to study complex formation of the sterile 2 alpha-factor receptor protein (Ste2p), labelled with green, cyan, and yellow fluorescent proteins (GFP, CFP, and YFP respectively), in budding yeast Saccharomyces cerevisiae. A theoretical model is presented that relates the efficiency of energy transfer in protein populations (the apparent FRET efficiency, E(app)) to the energy transferred in a single donor/acceptor pair (E, the true FRET efficiency). We determined E by using a new method that relies on E(app) measurements for two donor/acceptor pairs, Ste2p-CFP/Ste2p-YFP and Ste2p-GFP/Ste2p-YFP. From E(app) and E we determined alpha(T) approximately 1 and n approximately 2 for Ste2 proteins. Since the Ste2p complexes are formed in the absence of the ligand in our experiments, we conclude that the alpha-factor pheromone is not necessary for dimerization.

Identification of mRNA that binds to eukaryotic initiation factor 5A by affinity co-purification and differential display

Eukaryotic initiation factor 5A (eIF-5A) is the only protein in nature that contains hypusine, an unusual amino acid formed post-translationally by deoxyhypusine synthase and deoxyhypusine hydroxylase. Genetic and pharmacological evidence suggests that eIF-5A is essential for cell survival and proliferation. However, the precise function and interacting partners of eIF-5A remain unclear. We have shown previously that eIF-5A can bind to RRE (Rev-response element) and U6 RNA in vitro. Using SELEX (systematic evolution of ligands by exponential enrichment), we have also shown that eIF-5A is capable of binding to RNA in a sequence-specific manner [Xu and Chen (2001) J. Biol. Chem. 276, 2555-2561]. In the present paper, we show that the identification of mRNA species that bind to eIF-5A can be achieved by affinity co-purification and PCR differential display. Using this approach with three sets of anchoring and arbitrary primers, we have found 20 RNA sequences that co-purified specifically with eIF-5A. Five of them contained AAAUGU, the putative eIF-5A-interacting element that we identified previously using the SELEX method. Direct binding of the cloned RNA to eIF-5A could be demonstrated by electrophoretic mobility-shift assay. BLAST analysis revealed that the eIF-5A-interacting RNAs encode proteins such as ribosomal L35a, plasminogen activation inhibitor mRNA-binding protein, NADH dehydrogenase subunit and ADP-ribose pyrophosphatase. Some, however, encode hypothetical proteins. All the cloned RNAs have the potential to form extensive stem-loop structures.

Characterization of three novel members of the Arabidopsis thaliana equilibrative nucleoside transporter (ENT) family

Research on metabolism of nucleotides and their derivatives has gained increasing interest in the recent past. This includes de novo synthesis, analysis of salvage pathways, breakdown and transport of nucleotides, nucleosides and nucleobases. To perform a further step towards the analysis of nucleoside transport in Arabidopsis, we incubated leaf discs with various radioactively labelled nucleosides. Leaf cells imported labelled nucleosides and incorporated these compounds into RNA, but not into DNA. Furthermore, we report on the biochemical properties of three so far uncharacterized members of the Arabidopsis ENT (equilibrative nucleoside transporter) family (AtENT4, AtENT6 and AtENT7). After heterologous expression in yeast, all three proteins exhibited broad substrate specificity and transported the purine nucleosides adenosine and guanosine, as well as the pyrimidine nucleosides cytidine and uridine. The apparent K(m) values were in the range 3-94 microM, and transport was inhibited most strongly by deoxynucleosides, and to a smaller extent by nucleobases. Typical inhibitors of mammalian ENT proteins, such as dilazep and NBMPR (nitrobenzylmercaptopurine ribonucleoside, also known as nitrobenzylthioinosine) surprisingly exerted almost no effect on Arabidopsis ENT proteins. Transport mediated by the AtENT isoforms differed in pH-dependency, e.g. AtENT7 was not affected by changes in pH, AtENT3, 4 and 6 exhibited a less pronounced pH-dependency, and AtENT1 activity was clearly pH-dependent. Using a GFP (green fluorescent protein)-fusion protein transiently expressed in tobacco leaf protoplasts, a localization of AtENT6 in the plant plasma membrane has been revealed.

Expression of the gene for Dec2, a basic helix-loop-helix transcription factor, is regulated by a molecular clock system

Dec2, a member of the basic helix-loop-helix superfamily, is a recently confirmed regulatory protein for the clockwork system. Transcripts of Dec2, as well as those of its related gene Dec1, exhibit a striking circadian oscillation in the suprachiasmatic nucleus, and Dec2 inhibits transcription from the Per1 promoter induced by Clock/Bmal1 [Honma, Kawamoto, Takagi, Fujimoto, Sato, Noshiro, Kato and Honma (2002) Nature (London) 419, 841-844]. It is known that mammalian circadian rhythms are controlled by molecular clockwork systems based on negative-feedback loop(s), but the molecular mechanisms for the circadian regulation of Dec2 gene expression have not been clarified. We show here that transcription of the Dec2 gene is regulated by several clock molecules and a negative-feedback loop. Luciferase and gel retardation assays showed that expression of Dec2 was negatively regulated by binding of Dec2 or Dec1 to two CACGTG E-boxes in the Dec2 promoter. Forced expression of Clock/Bmal1 and Clock/Bmal2 markedly increased Dec2 mRNA levels, and up-regulated the transcription of the Dec2 gene through the CACGTG E-boxes. Like Dec, Cry and Per also suppressed Clock/Bmal-induced transcription from the Dec2 promoter. Moreover, the circadian expression of Dec2 transcripts was abolished in the kidney of Clock/Clock mutant mice. These findings suggest that the Clock/Bmal heterodimer enhances Dec2 transcription via the CACGTG E-boxes, whereas the induced transcription is suppressed by Dec2, which therefore must contribute to its own rhythmic expression. In addition, Cry and Per may also modulate Dec2 transcription.

Cyan-emitting and orange-emitting fluorescent proteins as a donor/acceptor pair for fluorescence resonance energy transfer

GFP (green fluorescent protein)-based FRET (fluorescence resonance energy transfer) technology has facilitated the exploration of the spatio-temporal patterns of cellular signalling. While most studies have used cyan- and yellow-emitting FPs (fluorescent proteins) as FRET donors and acceptors respectively, this pair of proteins suffers from problems of pH-sensitivity and bleeding between channels. In the present paper, we demonstrate the use of an alternative additional donor/acceptor pair. We have cloned two genes encoding FPs from stony corals. We isolated a cyan-emitting FP from Acropara sp., whose tentacles exhibit cyan coloration. Similar to GFP from Renilla reniformis, the cyan FP forms a tight dimeric complex. We also discovered an orange-emitting FP from Fungia concinna. As the orange FP exists in a complex oligomeric structure, we converted this protein into a monomeric form through the introduction of three amino acid substitutions, recently reported to be effective for converting DsRed into a monomer (Clontech). We used the cyan FP and monomeric orange FP as a donor/acceptor pair to monitor the activity of caspase 3 during apoptosis. Due to the close spectral overlap of the donor emission and acceptor absorption (a large Förster distance), substantial pH-resistance of the donor fluorescence quantum yield and the acceptor absorbance, as well as good separation of the donor and acceptor signals, the new pair can be used for more effective quantitative FRET imaging.

Extracellular cysteines define ectopeptidase (APN, CD13) expression and function

Alanyl aminopeptidase (APN) is a surface-bound metallopeptidase that processes the N-terminals of biologically active peptides such as enkephalins, angiotensins, neurokinins, and cytokines. It exerts profound activity on vital processes such as immune response, cellular growth, and blood pressure control. Inhibition of either APN gene expression or its enzymatic activity severely affects leukocyte growth and function. We show here that oxidoreductase-mediated modulations of the cell surface thiol status affect the enzymatic activity of APN. Additional evidence for the pivotal role of extracellular cysteines in the APN molecule was obtained when substitution of any of these six cysteines caused complete loss of surface expression and enzymatic activity. In contrast, the transmembrane Cys24 appears to have no similar function. Enzymatically inactive cysteine mutants were retained in the endoplasmic reticulum as shown by high-resolution imaging and Endoglycosidase H digestion. In the absence of any crystal-structure data, the demonstration that individual extracellular cysteines contribute to APN expression and function appears to be of particular importance. The data are the first to show thiol-dependent modulation of the activity of a typical surface-bound peptidase at the cell surface, probably reflecting a general regulating mechanism. This may relate to various disease processes such as inflammation or malignant transformation.