Enzyme-treated red rice (Oryza sativa L.) bran extracts mitigate inflammatory markers in RAW 264.7 macrophage cells and exhibit anti-inflammatory efficacy greater/comparable to ferulic acid, catechin, γ-tocopherol, and γ-oryzanol

ETHNOPHARMACOLOGICAL RELEVANCE

Rice (Oryza sativa L.), a staple food for a significant portion of the global population, has been recognized for its traditional medicinal properties for centuries. Rice bran, a by-product of rice milling, contains many bioactive compounds with potential pharmaceutical and therapeutic benefits. In recent years, research has highlighted the anti-inflammatory potential of rice bran, contributed by the bioactive components concentrated in their bran but, unfortunately, entrapped in the bran matrix, with limited bioavailability. Previous studies have reported that the enzymatic treatment of rice bran improves the bran's bioactive compound profile but did not investigate its impact on chronic conditions such as inflammation.

AIM OF THE STUDY

This study investigates the anti-inflammatory effects of endo-1,4-β-xylanase (ERB) and Viscozyme (VRB) treated red rice bran extracts against lipopolysaccharide-induced inflammation in RAW264.7 macrophages in comparison with non-enzyme-treated bran (CRB). Further established their efficacy with known anti-inflammatory compounds-ferulic acid (FA), catechin (CAT), γ-tocopherol (GTP), and γ-oryzanol (ORZ).

MATERIALS AND METHODS

The RAW 264.7 macrophage cells were pre-treated with non-toxic concentrations (10-200 μg/mL) of FA, CAT, GTP, ORZ, CRB, ERB, and VRB, followed by inflammatory stimulation with LPS for 24 h. Further, the cell supernatant and pellets were harvested to study the anti-inflammatory effects by evaluating and measuring their efficacy in inhibiting pro-inflammatory cytokines (TNF-α, IL-6, IL-10, IL-1β) and mediators (ROS, NO, PGE2, COX2, iNOS) through biochemical, ELISA, and mRNA expression studies.

RESULTS

The findings showed that both ERB and VRB effectively inhibited the production of pro-inflammatory markers (TNF-α, IL-6) and mediators (ROS, NO, PGE2) by downregulating mRNA expressions of inflammatory genes (TNF-α, IL-1β, IL-6, IL-10, COX2, iNOS) and demonstrated anti-inflammatory efficacy higher than CRB. On comparison, ERB demonstrated exceptional efficacy by causing a reduction of 48% in ROS, 20% in TNF-α, and 23% in PGE2 at 10 μg/mL, surpassing the anti-inflammatory capabilities of all the bioactive compounds, FA and ORZ, respectively. At the same time, VRB exhibited remarkable efficacy by reducing NO production by 52% at 200 μg/mL and IL-6 by 66% at 10 μg/mL, surpassing FA, CAT, ORZ, and GTP. Further, ERB downregulated the mRNA expression of IL-10 and iNOS, while VRB downregulated TNF-α, IL-1β, and COX2 expression. Both extracts equally downregulated IL-6 expression at 10 μg/mL, demonstrating the efficacy more remarkable/on par with established anti-inflammatory compounds.

CONCLUSIONS

Overall, enzyme-treated rice bran/extract, particularly ERB, possesses excellent anti-inflammatory properties, making them promising agents for alternatives to contemporary nutraceuticals/functional food against inflammatory diseases.

Green tea polyphenols inhibit TBBPA-induced lung injury via enhancing antioxidant capacity and modulating the NF-κB pathway in mice

Tetrabromobisphenol A (TBBPA) is a global pollutant. When TBBPA is absorbed by the body through various routes, it can have a wide range of harmful effects on the body. Green tea polyphenols (GTPs) can act as antioxidants, resisting the toxic effects of TBBPA on animals. The effects and mechanisms of GTP and TBBPA on oxidative stress, inflammation and apoptosis in the mouse lung are unknown. Therefore, we established in vivo and in vitro models of TBBPA exposure and GTP antagonism using C57 mice and A549 cells and examined the expression of factors related to oxidative stress, autophagy, inflammation and apoptosis. The results of the study showed that the increase in reactive oxygen species (ROS) levels after TBBPA exposure decreased the expression of autophagy-related factors Beclin1, LC3-II, ATG3, ATG5, ATG7 and ATG12 and increased the expression of p62; oxidative stress inhibits autophagy levels. The increased expression of the pro-inflammatory factors IL-1β, IL-6 and TNF-α decreased the expression of the anti-inflammatory factor IL-10 and activation of the NF-κB p65/TNF-α pathway. The increased expression of Bax, caspase-3, caspase-7 and caspase-9 and the decreased expression of Bcl-2 activate apoptosis-related pathways. The addition of GTP attenuated oxidative stress levels, restored autophagy inhibition and reduced the inflammation and apoptosis levels. Our results suggest that GTP can attenuate the toxic effects of TBBPA by modulating ROS, reducing oxidative stress levels, increasing autophagy and attenuating inflammation and apoptosis in mouse lung and A549 cells. These results provide fundamental information for exploring the antioxidant mechanism of GTP and further for studying the toxic effects of TBBPA.

Extracellular Guanosine and Guanine Nucleotides Decrease Viability of Human Breast Cancer SKBR-3 Cells

Though the physiological effects of adenosine and adenine nucleotides on purinergic receptors in cancer cells have been well studied, the influence of extracellular guanosine and guanine nucleotides on breast cancer cells remains unclear. Here, we show that extracellular guanosine and guanine nucleotides decrease the viability and proliferation of human breast cancer SKBR-3 cells. Treatment with guanosine or guanine nucleotides increased mitochondrial production of reactive oxygen species (ROS), and modified the cell cycle. Guanosine-induced cell death was suppressed by treatment with adenosine or the equilibrium nucleoside transporter (ENT) 1/2 inhibitor dipyridamole, but was not affected by adenosine receptor agonists or antagonists. These results suggest that guanosine inhibits adenosine uptake through ENT1/2, but does not antagonize adenosine receptors. In contrast, guanosine triphosphate (GTP)-induced cell death was suppressed not only by adenosine and dipyridamole, but also by the A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), suggesting that GTP-induced cell death is mediated in part by an antagonistic effect on adenosine A1 receptor. Thus, both guanosine and GTP induce apoptosis of breast cancer cells, but via at least partially different mechanisms.

LRRK2 is involved in the chemotaxis of neutrophils and differentiated HL-60 cells, and the inhibition of LRRK2 kinase activity increases fMLP-induced chemotactic activity

BACKGROUND

Neutrophils depend heavily on glycolysis for energy production under normal conditions. In contrast, neutrophils require energy supplied by mitochondrial oxidative phosphorylation (OXPHOS) during chemotaxis. However, the mechanism by which the energy supply changes from glycolysis to OXPHOS remains unknown. Leucine-rich repeat kinase 2 (LRRK2) is partially present in the outer mitochondrial membrane fraction. Lrrk2-deficient cells show mitochondrial fragmentation and reduced OXPHOS activity. We have previously reported that mitofusin (MFN) 2 is involved in chemotaxis and OXPHOS activation upon chemoattractant N-formyl-Met-Leu-Phe (fMLP) stimulation in differentiated HL-60 (dHL-60) cells. It has been previously reported that LRRK2 binds to MFN2 and partially colocalizes with MFN2 at the mitochondrial membranes. This study investigated the involvement of LRRK2 in chemotaxis and MFN2 activation in neutrophils and dHL-60 cells.

METHODS

Lrrk2 knockout neutrophils and Lrrk2 knockdown dHL-60 cells were used to examine the possible involvement of LRRK2 in chemotaxis. Lrrk2 knockdown dHL-60 cells were used a tetracycline-inducible small hairpin RNA (shRNA) system to minimize the effects of LRRK2 knockdown during cell culture. The relationship between LRRK2 and MFN2 was investigated by measuring the GTP-binding activity of MFN2 in Lrrk2 knockdown dHL-60 cells. The effects of LRRK2 kinase activity on chemotaxis were examined using the LRRK2 kinase inhibitor MLi-2.

RESULTS

fMLP-induced chemotactic activity was reduced in Lrrk2 knockout neutrophils in vitro and in vivo. Lrrk2 knockdown in dHL-60 cells expressing Lrrk2 shRNA also reduced fMLP-induced chemotactic activity. Lrrk2 knockdown dHL-60 cells showed reduced OXPHOS activity and suppressed mitochondrial morphological change, similar to Mfn2 knockdown dHL-60 cells. The amount of LRRK2 in the mitochondrial fraction and the GTP-binding activity of MFN2 increased upon fMLP stimulation, and the MFN2 GTP-binding activity was suppressed in Lrrk2 knockdown dHL-60 cells. Furthermore, the kinase activity of LRRK2 and Ser935 phosphorylation of LRRK2 were reduced upon fMLP stimulation, and LRRK2 kinase inhibition by MLi-2 increased the migration to fMLP.

CONCLUSIONS

LRRK2 is involved in neutrophil chemotaxis and the GTP-binding activity of MFN2 upon fMLP stimulation. On the other hand, the kinase activity of LRRK2 shows a negative regulatory effect on fMLP-induced chemotactic activity in dHL-60 cells. Video Abstract.

Effects of green tea polyphenols against metal-induced genotoxic damage: underlying mechanistic pathways

This review is based upon evidence from the published effects of green tea polyphenols (GTP) on genotoxic damage induced by metals with carcinogenic potential. First, the relationship between GTP and antioxidant defense system is provided. Subsequently, the processes involved in the oxidative stress generated by metals and their relationship to oxidative DNA damage is examined. The review demonstrated that GTP generally decrease oxidative DNA damage induced by exposure to metals such as arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), and lead (Pb). The pathways involved in these effects are related to: (1) direct scavenging of free radicals (FR); (2) activation of mechanisms to repair oxidative DNA damage; (3) regulation of the endogenous antioxidant system; and (4) elimination of cells with genetic damage via apoptosis. The results obtained in the studies reviewed demonstrate potential for possible use of GTP to prevent and treat oxidative damage in populations exposed to metals. Further, GTP may be considered as adjuvants to treatments for metal-associated diseases related to oxidative stress and DNA damage.

Green Tea Polyphenols Alleviate Kidney Injury Induced by Di(2-Ethylhexyl) Phthalate in Mice

INTRODUCTION

Di(2-ethylhexyl) phthalate (DEHP) is a common plasticizer. Studies have revealed that DEHP exposure can cause kidney damage. Green tea is among the most popular beverages in China. Green tea polyphenols (GTPs) have been proven to have therapeutic effects on organ damage induced by heavy metal exposure. However, few studies have reported on GTP-relieving DEHP-induced kidney damage.

METHODS

C57BL/6J male mice aged 6-8 weeks were treated with distilled water (control group), 1,500 mg/kg/d DEHP + corn oil (model group), 1,500 mg/kg/d DEHP + corn oil + 70 mg/kg GTP (treatment group), corn oil (oil group), and 70 mg/kg GTP (GTP group) by gavage for 8 weeks, respectively. The renal function of mice and renal tissue histopathology of each group were evaluated. The renal tissues of mice in the model, treatment, and control groups were analyzed using high-throughput sequencing. We calculated the differentially expressed microRNAs (miRNAs) and messenger RNAs (mRNAs) using the limma R package, the CIBERSORT algorithm was used to predict immune infiltration, the starBase database was used to screen the miRNA-mRNA regulatory axis, and immunohistochemical analyses were performed to verify protein expression.

RESULTS

GTP alleviated the deterioration of renal function, renal inflammation and fibrosis, and mitochondrial and endoplasmic reticulum lesions induced by DEHP in mice. Differential immune infiltrations of plasma, dendritic, T, and B cells were noted between the model and treatment groups. We found that three differentially expressed miRNAs (mmu-miR-383-5p, mmu-miR-152-3p, and mmu-miR-144-3p), three differentially expressed mRNAs (Ddit4, Dusp1, and Snx18), and three differentially expressed proteins (Ddit4, Dusp1, and Snx18) played crucial roles in the miRNA-mRNA-protein regulatory axes when GTPs mitigate DEHP-induced kidney damage in mice.

CONCLUSION

GTP can alleviate DEHP-induced kidney damage and regulate immune cell infiltration. We screened four important miRNA-mRNA-protein regulatory axes of GTP, mitigating DEHP-induced kidney damage in mice.

Hyperinsulinism/hyperammonemia syndrome caused by biallelic SLC25A36 mutation

Hyperinsulinism/hyperammonemia (HI/HA) syndrome has been known to be caused by dominant gain-of-function mutations in GLUD1, encoding the mitochondrial enzyme glutamate dehydrogenase. Pathogenic GLUD1 mutations enhance enzymatic activity by reducing its sensitivity to allosteric inhibition by GTP. Two recent independent studies showed that a similar HI/HA phenotype can be caused by biallelic mutations in SLC25A36, encoding pyrimidine nucleotide carrier 2 (PNC2), a mitochondrial nucleotide carrier that transports pyrimidine and guanine nucleotides across the inner mitochondrial membrane: one study reported a single case caused by a homozygous truncating mutation in SLC25A36 resulting in lack of expression of SLC25A36 in patients' fibroblasts. A second study described two siblings with a splice site mutation in SLC25A36, causing reduction of mitochondrial GTP content, putatively leading to hyperactivation of glutamate dehydrogenase. In an independent study, through combined linkage analysis and exome sequencing, we demonstrate in four individuals of two Bedouin Israeli related families the same disease-causing SLC25A36 (NM_018155.3) c.284 + 3A > T homozygous splice-site mutation found in the two siblings. We demonstrate that the mutation, while causing skipping of exon 3, does not abrogate expression of mRNA and protein of the mutant SLC25A36 in patients' blood and fibroblasts. Affected individuals had hyperinsulinism, hyperammonemia, borderline low birth weight, tonic-clonic seizures commencing around 6 months of age, yet normal intellect and no significant other morbidities. Chronic constipation, hypothyroidism, and developmental delay previously described in a single patient were not found. We thus verify that biallelic SLC25A36 mutations indeed cause HI/HA syndrome and clearly delineate the disease phenotype.

Plerixafor and resatorvid inhibit hepatitis B virus in vitro by upregulating elongation factor Tu GTP-binding domain containing 2

Background

An increase in the demand for a functional cure has accelerated research on new methods of therapy for chronic hepatitis B, which is mainly focused on restoring antiviral immunity for controlling viral infections. Previously, we had described elongation factor Tu GTP-binding domain containing 2 (EFTUD2) as an innate immune regulator and suggested that it might be an antiviral target.

Methods

In this study, we generated the Epro-LUC-HepG2 cell model for screening compounds that target EFTUD2. Plerixafor and resatorvid were screened from 261 immunity and inflammation-related compounds due to their ability to highly upregulate EFTUD2. The effects of plerixafor and resatorvid on hepatitis B virus (HBV) were examined in HepAD38 cells and HBV-infected HepG2-NTCP cells.

Results

The dual-luciferase reporter assays showed that the EFTUD2 promoter hEFTUD2pro-0.5 kb had the strongest activity. In Epro-LUC-HepG2 cells, plerixafor and resatorvid significantly upregulated the activity of the EFTUD2 promoter and the expression of the gene and protein. In HepAD38 cells and HBV-infected HepG2-NTCP cells, treatment with plerixafor and resatorvid strongly inhibited HBsAg, HBV DNA, HBV RNAs, and cccDNA in a dose-dependent manner. Furthermore, the anti-HBV effect was enhanced when entecavir was administered along with either of the previous two compounds, and the effect could be blocked by knocking down EFTUD2.

Conclusion

We established a convenient model for screening compounds that target EFTUD2 and further identified plerixafor and resatorvid as novel HBV inhibitors in vitro. Our findings provided information on the development of a new class of anti-HBV agents that act on host factors rather than viral enzymes.

How the initiating ribosome copes with ppGpp to translate mRNAs

During host colonization, bacteria use the alarmones (p)ppGpp to reshape their proteome by acting pleiotropically on DNA, RNA, and protein synthesis. Here, we elucidate how the initiating ribosome senses the cellular pool of guanosine nucleotides and regulates the progression towards protein synthesis. Our results show that the affinity of guanosine triphosphate (GTP) and the inhibitory concentration of ppGpp for the 30S-bound initiation factor IF2 vary depending on the programmed mRNA. The TufA mRNA enhanced GTP affinity for 30S complexes, resulting in improved ppGpp tolerance and allowing efficient protein synthesis. Conversely, the InfA mRNA allowed ppGpp to compete with GTP for IF2, thus stalling 30S complexes. Structural modeling and biochemical analysis of the TufA mRNA unveiled a structured enhancer of translation initiation (SETI) composed of two consecutive hairpins proximal to the translation initiation region (TIR) that largely account for ppGpp tolerance under physiological concentrations of guanosine nucleotides. Furthermore, our results show that the mechanism enhancing ppGpp tolerance is not restricted to the TufA mRNA, as similar ppGpp tolerance was found for the SETI-containing Rnr mRNA. Finally, we show that IF2 can use pppGpp to promote the formation of 30S initiation complexes (ICs), albeit requiring higher factor concentration and resulting in slower transitions to translation elongation. Altogether, our data unveil a novel regulatory mechanism at the onset of protein synthesis that tolerates physiological concentrations of ppGpp and that bacteria can exploit to modulate their proteome as a function of the nutritional shift happening during stringent response and infection.

Guanosine triphosphate can directly regulate cortisol production by activating Ca(2+)-messenger systems in bovine adrenal fasciculata cells

Adenosine triphosphate (ATP) is known to stimulate cortisol production in vitro, however, the effect of guanosine triphosphate (GTP) on cortisol production is not known. We studied the effect of GTP on cortisol production and investigated the regulation of intracellular signal transduction systems, including the cyclic AMP-dependent and Ca(2+)-messenger systems, in bovine adrenal fasciculata cells. GTP clearly induced cortisol biosynthesis but only to a level less than half the adrenocorticotropic hormone (ACTH)-induced maximum. The binding site for [γ-(35)S]-GTPγS was shown to differ completely from that for ATP and also from those for Gs and Gi, as indicated by the fact that binding was not influenced by pretreatment with cholera toxin and pertussis toxin. GTP significantly increased cytosolic calcium ([Ca(2+)]i) and inositol 1, 4, 5-triphosphate without affecting cyclic AMP formation. GTP-induced cortisol production was suppressed by H-9 and Calphostin C (specific protein kinase C inhibitors) but not by H-8 and KT5720 (specific inhibitors of cyclic AMP-dependent protein kinase), suggesting that GTP activates cortisol biosynthesis possibly via a protein kinase C-dependent pathway. Extracellular calcium may be essential for GTP activity since GTP-induced cortisol production was almost completely suppressed in its absence. In conclusion, it can be postulated that GTP-induced steroid secretion in bovine adrenal fasciculata cells is under paracrine or autocrine control.

Elevated guanosine 5'-diphosphate 3'-diphosphate level inhibits bacterial growth and interferes with FtsZ assembly

FtsZ, a protein essential for prokaryotic cell division, forms a ring structure known as the Z-ring at the division site. FtsZ has a GTP binding site and is assembled into linear structures in a GTP-dependent manner in vitro. We assessed whether guanosine 5'-diphosphate 3'-diphosphate (ppGpp), a global regulator of gene expression in starved bacteria, affects cell division in Salmonella Paratyphi A. Elevation of intracellular ppGpp levels by using the relA expression vector induced repression of bacterial growth and incorrect FtsZ assembly. We found that FtsZ forms helical structures in the presence of ppGpp by using the GTP binding site; however, ppGpp levels required to form helical structures were at least 20-fold higher than the required GTP levels in vitro. Furthermore, once formed, helical structures did not change to the straight form even after GTP addition. Our data indicate that elevation of the ppGpp level leads to inhibition of bacterial growth and interferes with FtsZ assembly.

β-D-2'-C-Methyl-2,6-diaminopurine Ribonucleoside Phosphoramidates are Potent and Selective Inhibitors of Hepatitis C Virus (HCV) and Are Bioconverted Intracellularly to Bioactive 2,6-Diaminopurine and Guanosine 5'-Triphosphate Forms

The conversion of selected β-D-2,6-diaminopurine nucleosides (DAPNs) to their phosphoramidate prodrug (PD) substantially blocks the conversion to the G-analog allowing for the generation of two bioactive nucleoside triphosphates (NTPs) in human hepatocytes. A variety of 2'-C-methyl DAPN-PDs were prepared and evaluated for inhibition of HCV viral replication in Huh-7 cells, cytotoxicity in various cell lines, and cellular pharmacology in both Huh-7 and primary human liver cells. The DAPN-PDs were pan-genotypic, effective against various HCV resistant mutants, and resistant variants could not be selected. 2'-C-Me-DAPN-TP and 2'-C-Me-GTP were chain terminators for genotype 1b HCV-pol, and single nucleotide incorporation assays revealed that 2'-C-Me-DAPN-TP was incorporated opposite U. No cytotoxicity was observed with our DAPN-PD when tested up to 50 μM. A novel, DAPN-PD, 15c, has been selected for further evaluation because of its good virologic and toxicologic profile and its ability to deliver two active metabolites, potentially simplifying HCV treatment.

Characteristics of serotonin receptors in the rat brain

Two biochemical methods are currently available for studying 5-HT receptors in the central nervous system. The first consists of measuring the specific high affinity binding of 3H-5-HT to synaptic membranes. The other derives from the discovery of an adenylate cyclase which can be activated by 5-HT in brain homogenates. Whereas the specific 3H-5-HT binding is measurable in young as well as in adult rats, the 5-HT-sensitive adenylate cyclase can be quantitatively estimated only during the first three weeks following birth. Later on, the increment of adenylate cyclase activity produced by 5-HT is too low to permit valid measurements, notably in tissues from adult rats. Studies on the effects of various agonists and antagonists demonstrated that the specific binding site characterized by a high affinity for 3H-5-HT (Kd = 1.5 nM) exhibited the expected properties of a 5-HT receptor in brain. Performing chemical lesions on serotoninergic neurons by an intracerebral injection of 5, 7-dihydroxytryptamine or the blockade of central 5-HT receptors by the peripheral administration of methiothepin resulted in a subsequent increase in the number of specific binding sites for 3H-5-HT particularly in the hippocampus (+30 to +45%). In contrast, preliminary attempts to detect any supersensitivity of the 5-HT-sensitive adenylate cyclase after selective raphe lesions were unsuccessful. Indeed, several observations strongly suggested that the high affinity binding site for 3H-5-HT did not correspond to the 5-HT receptor coupled to adenylate cyclase in synaptic membranes: 1) the apparent affinity of the 5-HT-sensitive adenylate cyclase for 5-HT was about 300 times lower (Kd = 0.5 microM) than that of the specific 3H-5-HT binding site; 2)the ontogenic evolutions of 3H-5-HT binding and 5-HT-sensitive adenylate cyclase were not parallel, notably in the hippocampus; 3) they were differently affected by several drugs. For instance, quipazine, a putative 5-HT agonist, effectively displaced 3H-5-HT from its specific binding site (Ki = 0.23 microM) whereas it did not affect 5-HT-sensitive adenylate cyclase. In conclusion, it is likely that the high affinity binding site for 3H-5-HT and the 5-HT-sensitive adenylate cyclase belong to two different postsynaptic 5-HT receptors in the rat brain.

[Mobilization of Ca2+ from intracellular stores of spermatozoa of Bos taurus depending on their functional status]

On the basis of inhibitory analysis by using a fluorescence probe chlortetracycline, calcium transduction pathway in spermatozoa of Bos taurus has been examined. Additional release of Ca2+ from intracellular stores of sperm was found after combiened action of prolactin and GTP, which took place under influence of protein kinase C inhibitor (compound Ro 31-8220); the combined effect of theophylline and GDP also stimulated additional release of Ca2+ from intracellular stores, which was missing when adding inhibitor of protein kinase A, compound H-89. Using chlortetracycline test (analysis localization of chlortetracycline fluorescence in spermatozoa), we have shown the combined action of prolactin and GTP increases the number of sperm with acrosome reaction, which is reduced after influence of Ro 31-8220; the combined effect of theophylline and GDP increases the percentage of capacitated spermatozoa, which was decreased in the presence of H-89. According with the data obtained, we propose the hypothesis that the transduction of Ca2+ between intracellular stores in bull spermatozoa stimulated by the combined action of prolactin and GTP, or theophylline and GDP, determines the functional status of the spermatozoa. Namely: the transduction of Ca2+ between intracellular stores in bull spermatozoa stimulated by the combined action of prolactin and GTP is involved in the regulation of acrosomal processes, while sperm capacitation is mediated by the transduction of calcium between intracellular stores activated by the combined influence of theophylline and GDP.

Polymorphism of FtsZ filaments on lipid surfaces: role of monomer orientation

FtsZ is a bacterial cytoskeletal protein involved in cell division. It forms a ringlike structure that attaches to the membrane to complete bacterial division. It binds and hydrolyzes GTP, assembling into polymers in a GTP-dependent manner. To test how the orientation of the monomers affects the curvature of the filaments on a surface, we performed site-directed mutagenesis on the E. coli FtsZ protein to insert cysteine residues at lateral locations to orient FtsZ on planar lipid bilayers. The E93C and S255C mutants were overproduced, purified, and found to be functionally active in solution, as well as being capable of sustaining cell division in vivo in complementation assays. Atomic force microscopy was used to observe the shape of the filament fibers formed on the surface. The FtsZ mutants were covalently linked to the lipids and could be polymerized on the bilayer surface in the presence of GTP. Unexpectedly, both mutants assembled into straight structures. E93C formed a well-defined lattice with monomers interacting at 60° and 120° angles, whereas S255C formed a more open array of straight thicker filament aggregates. These results indicate that filament curvature and bending are not fixed and that they can be modulated by the orientation of the monomers with respect to the membrane surface. As filament curvature has been associated with the force generation mechanism, these results point to a possible role of filament membrane attachment in lateral association and curvature, elements currently identified as relevant for force generation.

Oxidized LDL/CD36 interaction induces loss of cell polarity and inhibits macrophage locomotion

Cell polarization is essential for migration and the exploratory function of leukocytes. However, the mechanism by which cells maintain polarity or how cells revert to the immobilized state by gaining cellular symmetry is not clear. Previously we showed that interaction between oxidized low-density lipoprotein (oxLDL) and CD36 inhibits macrophage migration; in the current study we tested the hypothesis that oxLDL/CD36-induced inhibition of migration is the result of intracellular signals that regulate cell polarity. Live cell imaging of macrophages showed that oxLDL actuated retraction of macrophage front end lamellipodia and induced loss of cell polarity. Cd36 null and macrophages null for Vav, a guanine nucleotide exchange factor (GEF), did not show this effect. These findings were caused by Rac-mediated inhibition of nonmuscle myosin II, a cell polarity determinant. OxLDL induced dephosphorylation of myosin regulatory light chain (MRLC) by increasing the activity of Rac. Six-thioguanine triphosphate (6-thio-GTP), which inhibits Vav-mediated activation of Rac, abrogated the effect of oxLDL. Activation of the Vav-Rac-myosin II pathway by oxidant stress may induce trapping of macrophages at sites of chronic inflammation such as atherosclerotic plaque.

ppGpp inhibits peptide elongation cycle of chloroplast translation system in vitro

Chloroplasts possess common biosynthetic pathways for generating guanosine 3',5'-(bis)pyrophosphate (ppGpp) from GDP and ATP by RelA-SpoT homolog enzymes. To date, several hypothetical targets of ppGpp in chloroplasts have been suggested, but they remain largely unverified. In this study, we have investigated effects of ppGpp on translation apparatus in chloroplasts by developing in vitro protein synthesis system based on an extract of chloroplasts isolated from pea (Pisum sativum). The chloroplast extracts showed stable protein synthesis activity in vitro, and the activity was sensitive to various types of antibiotics. We have demonstrated that ppGpp inhibits the activity of chloroplast translation in dose-effective manner, as does the toxic nonhydrolyzable GTP analog guanosine 5'-(β,γ-imido)triphosphate (GDPNP). We further examined polyuridylic acid-directed polyphenylalanine synthesis as a measure of peptide elongation activity in the pea chloroplast extract. Both ppGpp and GDPNP as well as antibiotics, fusidic acid and thiostrepton, inhibited the peptide elongation cycle of the translation system, but GDP in the similar range of the tested ppGpp concentration did not affect the activity. Our results thus show that ppGpp directly affect the translation system of chloroplasts, as they do that of bacteria. We suggest that the role of the ppGpp signaling system in translation in bacteria is conserved in the translation system of chloroplasts.

[Identification of signal transduction pathway in fresh and vitrified porcine oocytes]

Signal transduction pathway under the influence of somatotropin have been identified basis on the analysis of Ca2+ release from intracellular stores of fresh and vitrified porcine oocytes using inhibitory analysis. Somatotropin and GTP individually stimulated Ca2+ release from intracellular stores. The joint action of somatotropin and GTP activated additional Ca2+ release from intracellular stores both in fresh and vitrified porcine oocytes. Treatment of the oocytes with inhibitor of protein kinase C caused no additional Ca2+ release from intracellular stores. Ca2+ release from intracellular stores stimulated by GTP was connected with phosphate hydrolysis. Moving between intracellular Ca2+ depots stimulated by GTP was not determined by phosphate hydrolysis. Inhibitor of protein kinase C and microtubules were involved in the interaction of various intracellular depots. The data obtained suggest that signal transduction pathway in porcine oocytes do not change after vitrification.

Transcriptional profile of GTP-mediated differentiation of C2C12 skeletal muscle cells

Several purine receptors have been localised on skeletal muscle membranes. Previous data support the hypothesis that extracellular guanosine 5'-triphosphate (GTP) is an important regulatory factor in the development and function of muscle tissue. We have previously described specific extracellular binding sites for GTP on the plasma membrane of mouse skeletal muscle (C2C12) cells. Extracellular GTP induces an increase in intracellular Ca(2+) concentrations that results in membrane hyperpolarisation through Ca(2+)-activated K(+) channels, as has been demonstrated by patch-clamp experiments. This GTP-evoked increase in intracellular Ca(2+) is due to release of Ca(2+) from intracellular inositol-1,4,5-trisphosphate-sensitive stores. This enhances the expression of the myosin heavy chain in these C2C12 myoblasts and commits them to fuse into multinucleated myotubes, probably via a phosphoinositide-3-kinase-dependent signal-transduction mechanism. To define the signalling of extracellular GTP as an enhancer or modulator of myogenesis, we investigated whether the gene-expression profile of differentiated C2C12 cells (4 and 24 h in culture) is affected by extracellular GTP. To investigate the nuclear activity and target genes modulated by GTP, transcriptional profile analysis and real-time PCR were used. We demonstrate that in the early stages of differentiation, GTP up-regulates genes involved in different pathways associated with myogenic processes, including cytoskeleton structure, the respiratory chain, myogenesis, chromatin reorganisation, cell adhesion, and the Jak/Stat pathway, and down-regulates the mitogen-activated protein kinase pathway. GTP also increases the expression of three genes involved in myogenesis, Pp3ca, Gsk3b, and Pax7. Our data suggests that in the myogenic C2C12 cell line, extracellular GTP acts as a differentiative factor in the induction and sustaining of myogenesis.

The translation initiation factor, PeIF5B, from Pisum sativum displays chaperone activity

We earlier documented the structural and functional characterization of PeIF5B factor from Pisum sativum that shows strong homology to the universal translation initiation factor eIF5B (Rasheedi et al., 2007, 2010 [12,13]). We now show that PeIF5B is an unusually thermo-stable protein resisting temperatures up to 95 °C. PeIF5B prevents thermal aggregation of heat labile proteins, such as citrate synthase (CS) and NdeI, under heat stress or chemical denaturation conditions and promotes their functional folding. It also prevents the aggregation of DTT induced insulin reduction. GTP appears to stimulate PeIF5B-mediated chaperone activity. In-vivo, PeIF5B over expression significantly enhances, the viability of Escherichia coli cells after heat stress (50 °C). These observations lead us to conclude that PeIF5B, in addition to its role in protein translation, has chaperone like activity and could be likely involved in protein folding and protection from stress.

The effects of P2X receptor agonists on renal sodium and water excretion in anaesthetized rats

AIM

To investigate in vivo effects of P2X receptor activation on sodium and water excretion in urine.

METHODS

The clearance experiments were carried out in anaesthetized rats during intravenous infusion (2 μmol kg(-1) + 20 nmol (kg min)(-1) , v = 40 μL min(-1)) of P2X receptors agonists: α,β-methylene ATP (α,β-meATP) and β,γ-methylene ATP (β,γ-meATP). Cortical blood flow (CBF) was estimated by laser Doppler flux during intrarenal artery infusion of β,γ-meATP (20 nmol (kg min)(-1) , v = 2 μL min(-1)). Influence of α,β-meATP and β,γ-meATP on the activity of Na-K-ATPase was investigated in isolated proximal tubules.

RESULTS

Intravenous infusion of β,γ-meATP resulted in a marked, progressively increasing diuresis and this effect was accompanied by a progressive increase in the sodium excretion rate. The glomerular filtration rate was unaffected. The effects of β,γ-meATP were abolished by P2 receptor antagonist PPADS (70 nmol (kg min)(-1)). CBF increased by 16 ± 2% during renal artery infusion of β,γ-meATP. Furthermore, α,β-meATP and β,γ-meATP increased 1.5-fold lithium clearance (C(Li)). Sodium excretion, expressed as a fraction of the distal delivery (C(Na) C(Li) (-1)), increased 1.5-fold during infusion of α,β-meATP or β,γ-meATP. Both agonists at 10(-6) (M) produced a statistical significant decrement in the ouabain-sensitive ATPase activity about 16-20% and these effects were blocked in the presence of PPADS.

CONCLUSION

Activation of P2X receptors increased renal sodium and water excretion. Mechanistically, P2X agonists increased renal perfusion and inhibited sodium reabsorption via an Na-K-ATPase-dependent mechanism.

Inhibition by purine nucleotides of the release of reactive oxygen species from muscle mitochondria: indication for a function of uncoupling proteins as superoxide anion transporters

Release of reactive oxygen species (ROS), measured as the sum of hydrogen peroxide (H₂O₂) and superoxide anion radical (O₂·⁻), from respiring rat heart and skeletal muscle mitochondria was significantly decreased by millimolar concentrations of GTP or GDP. Attempts to differentiate between the two forms of ROS showed that the release of O₂·⁻ rather than that of H₂O₂ was affected. Meanwhile, intramitochondrial ROS accumulation, measured by inactivation of aconitase, increased. These results suggest that guanine nucleotides inhibit the release of O₂·⁻ from mitochondria. As these nucleotides are known inhibitors of uncoupling proteins (UCPs), it is proposed that UCPs may function as carriers of O₂·⁻, thus enabling its removal from the matrix compartment.

Acute starvation in C57BL/6J mice increases myocardial UCP2 and UCP3 protein expression levels and decreases mitochondrial bio-energetic function

Associations between uncoupling protein (UCP) expression and functional changes in myocardial mitochondrial bio-energetics have not been well studied during periods of starvation stress. Our aim was to study the effects of acute starvation, for 24 or 48 h, on combined cardiac mitochondrial function and UCP expression in mice. Isolated heart mitochondria from female mice starved for 48 h compared to that from mice fed revealed a significantly (p < 0.05) decreased adenosine diphosphate-to-oxygen ratio, a significantly increased proton leak and an increased GTP inhibition on palmitic acid-induced state 4 oxygen consumption (p < 0.05). These bio-energetic functional changes were associated with increases in mitochondrial UCP2 and UCP3 protein expression. In conclusion, our findings suggest that increased UCP2 and UCP3 levels may contribute to decreased myocardial mitochondrial bio-energetic function due to starvation.

Antagonism of phenanthrene cytotoxicity for human embryo lung fibroblast cell line HFL-I by green tea polyphenols

Polycyclic aromatic hydrocarbons (PAHs) have been detected in some commercial teas around the world and pose a threat to tea consumers. However, green tea polyphenols (GTP) possess remarkable antioxidant and anticancer effects. In this study, the potential of GTP to block the toxicity of the model PAH phenanthrene was examined in human embryo lung fibroblast cell line HFL-I. Both GTP and phenanthrene treatment individually caused dose-dependent inhibition of cell growth. A full factorial design experiment demonstrated that the interaction of phenanthrene and GTP significantly reduced growth inhibition. Using the median effect method showed that phenanthrene and GTP were antagonistic when the inhibitory levels were less than about 50%. Apoptosis and cell cycle detection suggested that only phenanthrene affected cell cycle significantly and caused cell death; GTP lowered the mortality of HFL-I cells exposed to phenanthrene; However, GTP did not affect modulation of the cell cycle by phenanthrene.

RhoA regulates peroxisome association to microtubules and the actin cytoskeleton

The current view of peroxisome inheritance provides for the formation of new peroxisomes by both budding from the endoplasmic reticulum and autonomous division. Here we investigate peroxisome-cytoskeleton interactions and show by proteomics, biochemical and immunofluorescence analyses that actin, non-muscle myosin IIA (NMM IIA), RhoA, Rho kinase II (ROCKII) and Rab8 associate with peroxisomes. Our data provide evidence that (i) RhoA in its inactive state, maintained for example by C. botulinum toxin exoenzyme C3, dissociates from peroxisomes enabling microtubule-based peroxisomal movements and (ii) dominant-active RhoA targets to peroxisomes, uncouples the organelles from microtubules and favors Rho kinase recruitment to peroxisomes. We suggest that ROCKII activates NMM IIA mediating local peroxisomal constrictions. Although our understanding of peroxisome-cytoskeleton interactions is still incomplete, a picture is emerging demonstrating alternate RhoA-dependent association of peroxisomes to the microtubular and actin cytoskeleton. Whereas association of peroxisomes to microtubules clearly serves bidirectional, long-range saltatory movements, peroxisome-acto-myosin interactions may support biogenetic functions balancing peroxisome size, shape, number, and clustering.

Spatial regulation of membrane fusion controlled by modification of phosphoinositides

Membrane fusion plays a central role in many cell processes from vesicular transport to nuclear envelope reconstitution at mitosis but the mechanisms that underlie fusion of natural membranes are not well understood. Studies with synthetic membranes and theoretical considerations indicate that accumulation of lipids characterised by negative curvature such as diacylglycerol (DAG) facilitate fusion. However, the specific role of lipids in membrane fusion of natural membranes is not well established. Nuclear envelope (NE) assembly was used as a model for membrane fusion. A natural membrane population highly enriched in the enzyme and substrate needed to produce DAG has been isolated and is required for fusions leading to nuclear envelope formation, although it contributes only a small amount of the membrane eventually incorporated into the NE. It was postulated to initiate and regulate membrane fusion. Here we use a multidisciplinary approach including subcellular membrane purification, fluorescence spectroscopy and Förster resonance energy transfer (FRET)/two-photon fluorescence lifetime imaging microscopy (FLIM) to demonstrate that initiation of vesicle fusion arises from two unique sites where these vesicles bind to chromatin. Fusion is subsequently propagated to the endoplasmic reticulum-derived membranes that make up the bulk of the NE to ultimately enclose the chromatin. We show how initiation of multiple vesicle fusions can be controlled by localised production of DAG and propagated bidirectionally. Phospholipase C (PLCγ), GTP hydrolysis and (phosphatidylinsositol-(4,5)-bisphosphate (PtdIns(4,5)P₂) are required for the latter process. We discuss the general implications of membrane fusion regulation and spatial control utilising such a mechanism.

GTP is required for the microtubule catastrophe-inducing activity of MAP200, a tobacco homolog of XMAP215

Widely conserved among eukaryotes, the microtubule-associated protein 215 (MAP215) family enhances microtubule dynamic instability. The family member studied most extensively, Xenopus laevis XMAP215, has been reported to enhance both assembly and disassembly parameters, although the mechanism whereby one protein can exert these apparently contradictory effects has not been clarified. Here, we analyze the activity of a plant MAP215 homolog, tobacco (Nicotiana tabacum) MAP200 on microtubule behavior in vitro. We show that, like XMAP215, MAP200 promotes both assembly and disassembly parameters, including microtubule growth rate and catastrophe frequency. When MAP200 is added to tubulin and taxol, strikingly long-coiled structures form. When GDP partially replaces GTP, the increase of catastrophe frequency by MAP200 is strongly diminished, even though this replacement stimulates catastrophe in the absence of MAP200. This implies that MAP200 induces catastrophes by a specific, GTP-requiring pathway. We hypothesize that, in the presence of MAP200, a catastrophe-prone microtubule lattice forms occasionally when elongated but nonadjacent protofilaments make lateral contacts.

Sodium nitroprusside alters dark voltage and light responses in isolated retinal rods during whole-cell recording

Dark voltage and light responses of isolated retinal rods of Rana esculenta were investigated by employing the whole-cell patch-clamp technique. When the recording pipette was filled with a medium devoid of nucleotides, a spontaneous hyperpolarization of the dark voltage partly due to a diffusional loss of cGMP and its precursor GTP and a retardation in the recovery of the light responses was observed. The larger part of the retardation of the light responses was prevented by 1 mM ATP. Addition of GTP attenuated the hyperpolarization, but did not abolish it completely. When the nitric-oxide-releasing substance sodium nitroprusside plus GTP was applied, the tendency of hyperpolarization disappeared and a stable dark voltage or even a slight depolarization was measured during the whole-cell recording period. Similar results were also obtained when GTP was given in combination with either EGTA or IBMX which are both known to interfere with the cGMP regulating enzymes in retinal rods. In addition to its effects on the dark voltage, an acceleration of the recovery phase of the light responses by sodium nitroprusside was also observed. Our observations strongly suggest that sodium nitroprusside activates guanylate cyclase in photoreceptors, as it does in other tissues, but we cannot exclude with certainty an effect on the phosphodiesterase.

Evidence for a distinct ligand binding site on tubulin discovered through inhibition by GDP of paclitaxel-induced tubulin assembly in the absence of exogenous GTP

GDP inhibits paclitaxel-induced tubulin assembly without GTP when the tubulin bears GDP in the exchangeable site (E-site). Initially, we thought inhibition was mediated through the E-site, since small amounts of GTP or Mg(2+), which favors GTP binding to the E-site, reduced inhibition by GDP. We thought trace GTP released from the nonexchangeable site (N-site) by tubulin denaturation was required for polymer nucleation, but microtubule length was unaffected by GDP. Further, enhancing polymer nucleation reduced inhibition by GDP. Other mechanisms involving the E-site were eliminated experimentally. Upon finding that ATP weakly inhibited paclitaxel-induced assembly, we concluded that another ligand binding site was responsible for these inhibitory effects, and we found that GDP was not binding at the taxoid, colchicine, or vinca sites. There may therefore be a lower affinity site on tubulin to which GDP can bind distinct from the E- and N-sites, possibly on alpha-tubulin, based on molecular modeling studies.

[Effect of estradiol on Ca2+ release from intracellular stores in porcine oocytes stimulated by prolactin, theophylline, or guanosine triphosphate]

The interaction between prolactin and theophylline as well as between prolactin and guanosine triphosphate during Ca2+ release from intracellular stores of estradiol-treated porcine oocytes isolated from the ovary at the stage of follicular growth were studied using fluorescent Ca(2+)-sensitive probe chlortetracycline. In the absence of estradiol, prolactin or theophylline induced Ca2+ release from intracellular stores; however, no increase in Ca2+ release was observed after their combined action. Conversely, Ca2+ release from intracellular stores increased only after the combined exposure to prolactin and theophylline in the the presence of estradiol. In the absence of estradiol, guanosine triphosphate induced calcium release alone and together with prolactin. Protein kinase C regulated Ca2+ release from intracellular stores after the combined exposure to prolactin and theophylline only in the presence of estradiol; while the activation of protein kinase C required no estradiol during the combined exposure to prolactin and guanosine triphosphate. The data obtained indicate the effect of estradiol on Ca2+ release from intracellular stores after the combined exposure to prolactin and theophylline, while no such effect was observed after the combined exposure to prolactin and guanosine triphosphate.

Adenine nucleotides decrease the apparent Km of endogenous natriuretic peptide receptors for GTP

Natriuretic peptide receptors A (NPR-A) and B (NPR-B) mediate most effects of natriuretic peptides by synthesizing cGMP. ATP increases the activity of these receptors by an unknown mechanism. We recently reported that a nonhydrolyzable form of ATP, adenylyl imidodiphosphate (AMPPNP), stabilizes but is not required for the activation of NPR-A and NPR-B in membranes from highly overexpressing cells. Here, we repeated these studies on receptors expressed in endogenous settings. Kinetic analysis indicated that both AMPPNP and ATP dramatically decrease the apparent K(m) of both receptors for GTP but had little effect on the V(max). The EC(50) for AMPPNP decreased as substrate concentration increased whereas the magnitude of the effect was greater at lower GTP concentrations. ATP increased the activity of a mutant receptor containing glutamates substituted for all known phosphorylation sites similarly to the wild-type receptor, consistent with a phosphorylation independent mechanism. Finally, the putative ATP binding sites were investigated. Mutation of the ATP modulatory domain region had no effect, but mutation of K535A dramatically diminished ANP-dependent cyclase activity in a manner that was unresponsive to ATP. Mutation of the highly conserved 630-KSS to AAA (all alanines) resulted in an expressed receptor that had no detectable guanylyl cyclase activity. We conclude that ATP is not required for the initial activation of NPRs but does increase activity over time by reducing the apparent K(m) for GTP.

Structure of BeF3- -modified response regulator PleD: implications for diguanylate cyclase activation, catalysis, and feedback inhibition

Cyclic di-guanosine monophosphate (c-di-GMP) is a ubiquitous bacterial second messenger involved in the regulation of cell surface-associated traits and persistence. We have determined the crystal structure of PleD from Caulobacter crescentus, a response regulator with a diguanylate cyclase (DGC) domain, in its activated form. The BeF(3)(-) modification of its receiver domain causes rearrangement with respect to an adaptor domain, which, in turn, promotes dimer formation, allowing for the efficient encounter of two symmetric catalytic domains. The substrate analog GTPalphaS and two putative cations are bound to the active sites in a manner similar to adenylate cyclases, suggesting an analogous two-metal catalytic mechanism. An allosteric c-di-GMP-binding mode that crosslinks DGC and an adaptor domain had been identified before. Here, a second mode is observed that crosslinks the DGC domains within a PleD dimer. Both modes cause noncompetitive product inhibition by domain immobilization.

Coupling of M3 acetylcholine receptor to Gq16 activates a natriuretic peptide receptor guanylyl cyclase

Muscarinic activation of tracheal smooth muscle (TSM) involves a M(3)AChR/heterotrimeric-G protein/NPR-GC coupling mechanism. G protein activators Mastoparan (MAS) and Mastoparan-7 stimulated 4- and 10-fold the NPR-GC respectively, being insensitive to PTX and antibodies against Galpha(i/o) subfamily. Muscarinic and MAS stimulation of NPR-GC was blocked by antibodies against C-terminal of Galpha(q16), whose expression was confirmed by RT-PCR. However, synthetic peptides from C-terminal of Galpha(q15/16) stimulated the NPR-GC. Coupling of alpha(q16) to M(3)AChR is supported by MAS decreased [(3)H]QNB binding, being abolished after M(3)AChR-4-DAMP-alkylation. Anti-i(3)M(3)AChR antibodies blocked the muscarinic activation of NPR-GC, and synthetic peptide from i(3)M(3)AChR (M(3)P) was more potent than MAS increasing GTPgamma [(35)S] and decreasing the [(3)H]QNB activities. Coupling between NPR-GC and Galpha(q16) was evaluated by using trypsin-solubilized-fraction from TSM membranes, which displayed a MAS-sensitive-NPR-GC activity, being immunoprecipitated with anti-Galpha(q16), also showing an immunoreactive heterotrimeric-G-beta-subunit. These data support the existence of a novel transducing cascade, involving Galpha(q16)beta gamma coupling M(3)AChR to NPR-GC.

Extracellular nucleotides block bone mineralization in vitro: evidence for dual inhibitory mechanisms involving both P2Y2 receptors and pyrophosphate

Extracellular nucleotides, signaling through P2 receptors, may act as local regulators of bone cell function. We investigated the effects of nucleotide agonists [ATP, ADP, uridine triphosphate (UTP), and uridine diphosphate] and pyrophosphate (PPi, a key physiological inhibitor of mineralization) on the deposition and mineralization of collagenous matrix by primary osteoblasts derived from rat calvariae. Our results show that extracellular ATP, UTP, and PPi strongly and selectively blocked the mineralization of matrix nodules; ADP and uridine diphosphate were without effect. Significant inhibition of mineralization occurred in the presence of relatively low concentrations of ATP, UTP, or PPi (1-10 microm), without affecting production of fibrillar or soluble collagen. In cultures treated with 10 microm ATP or UTP, the expression and activity of alkaline phosphatase, which promotes mineralization by hydrolyzing PPi, was inhibited. The potent inhibitory actions of ATP and UTP on bone mineralization are consistent pharmacologically with mediation by the P2Y(2) receptor, which is strongly expressed by mature osteoblasts. In support of this notion, we found 9-17% increases in bone mineral content of hindlimbs of P2Y(2)-deficient mice. We also found that osteoblasts express ectonucleotide phosphodiesterase/pyrophosphatase-1, an ectonucleotidase that hydrolyzes nucleotide triphosphates to yield PPi, and that addition of 10 microm ATP or UTP to osteoblast cultures generated 2 microm PPi within 10 min. Thus, a component of the profound inhibitory action of ATP and UTP on bone mineralization could be mediated directly by PPi, independently of P2 receptors.

Inhibition of DNA polymerase eta by oxetanocin derivatives

DNA polymerase eta is recently found as a responsible gene product of xeroderma pigmentosum variant. Differently from other eukaryotic DNA polymerases, such as alpha, beta or gamma, eta polymerase is categorized in Y family. Specific inhibitors for DNA polymerases are useful tools to study the exact role of enzyme in the living cells, however, the inhibitor for DNA polymerase eta has not been developed. We examined the inhibitory effects of several sugar-modified nucleotide analogs on DNA polymerase eta. The arabinonucleotides (araCTP), dideoxynucleotides (ddTTP) and 3'-modified nucleotides (3'-dCTP and 3'-azidothymidine tri-phosphate) did not show any inhibitory effect on DNA polymerase eta. On the other hand, the oxetanocin derivatives those have the oxetane ring as a sugar moiety, OXT-GTP and OXT-ATP, strongly inhibited this polymerase. These results suggest that DNA polymerase eta has a unique recognition mode against the sugar moiety of nucleotide compared with other eukaryotic nucleotide polymerases.

Dynamic activity of lipid droplets: protein phosphorylation and GTP-mediated protein translocation

Lipid droplet is a cellular organelle with a neutral lipid core surrounded by a phospholipid monolayer and coated with structural as well as functional proteins. The determination of these proteins, especially their functional regulations and dynamic movement on and off droplets, holds a key to resolving the biological functions of the cellular organelle. To address this, we carried out a comprehensive proteomic study that includes a complete proteomic, a phosphoprotein proteomic, and a comparative proteomic analysis using purified lipid droplets and mass spectrometry techniques. The complete proteome identified 125 proteins of which 70 proteins had not been identified on droplets of mammalian cells previously. In phosphoprotein proteomic analysis, 7 functional lipid droplet proteins were determined to be phosphorylated, including adipose differentiation related protein (ADRP/ADFP), two Rab proteins, and four lipid metabolism enzymes, including adipose triglyceride lipase (ATGL). To understand the dynamics of lipid droplets, GTP-dependent protein recruitment was analyzed by comparative proteomics. Arf1 and some of its coatomers, three other Arfs, several other small G-proteins including 3 Rabs, and several lipid synthetic enzymes were recruited from cytosol to purified droplets. Together, the present study suggests that lipid droplet is an active and dynamic cellular organelle that governs lipid homeostasis and intracellular trafficking through protein phosphorylation as well as GTP-regulated protein translocation.

Receptor-coupling properties of the invertebrate visual guanine nucleotide binding protein iGqalpha

Invertebrate visual iG(q)alpha is homologous to mammalian mG(q)alpha in two of the three domains important for G protein interaction with receptors; the C-terminus and the linker regions that connect the helical and ras-like domains of the alpha subunit. The third receptor-interacting domain, the N-terminus, contains a six amino acid extension MTLESI in mG(q)alpha that is not present in iG(q)alpha. In co-expression studies we assessed the promiscuity and efficacy of receptor coupling to phospholipase C (PLC) by iG(q)alpha, a non-palmitoylated mutant iG(q)alpha(C3,4A), mG(q)alpha and G(15)alpha. The invertebrate G proteins and mG(q)alpha only coupled to G(q)-coupled receptors (m1 muscarinic acetylcholine receptor (mChR1), alpha(1A)-adrenergic receptor (alpha1-AR)) and not to the G(i/s)-coupled receptors (CCR1 receptor, beta2-adrenergic receptor or dopamine D1 receptor) while G(15)alpha coupled to all receptors. iG(q)alpha and iG(q)alpha(C3,4A) both had double the efficacy for PLC activation compared to the mammalian G proteins when co-expressed with mChR1 and alpha1-AR. The increased efficacy of iG(q)alpha compared to mG(q)alpha was also seen downstream of PLC with carbachol stimulation of the mitogen-activated protein kinase, ERK1/2. Addition of the MTLESI extension onto the N-terminus of iG(q)alpha decreased its efficacy by 35% whereas deletion of this sequence from mG(q)alpha increased its efficacy by 60% in the PLC and ERK1/2 assays. iG(q)alpha, iG(q)alpha(C3,4A) and mG(q)alpha all displayed similar receptor-independent AlF(4)(-)activation of PLC and guanosine triphosphate hydrolysis (GTPase) activity. iG(q)alpha, and iG(q)alpha(C3,4A) both had increased receptor-activated guanosine 5'-[gamma-[(35)S]thio]triphosphate ([(35)S]GTPgammaS) binding when compared to mG(q)alpha when co-expressed with the mChR1. These results demonstrate that G(q) protein efficacy is at least partially determined by the presence of the amino-terminal MTLESI extension. Comparison of [(35)S]GTPgammaS binding rates helps explain the increased efficacy of the invertebrate G proteins.

Modulation of a delayed-rectifier K+ current by angiotensin II in rat sympathetic neurons

It is well known that angiotensin II (Angio II) mimics most of the muscarinic-mediated excitatory actions of acetylcholine on superior cervical ganglion neurons. For instance, in addition to depolarization and stimulation of norepinephrine release, muscarinic agonists and Angio II modulate the M-type K(+) current and the N-type Ca(2+) current. We recently found that muscarinic receptors modulate the delayed rectifier current I(KV) as well. Therefore a whole cell patch-clamp experiment was carried out in rat cultured sympathetic neurons to assess whether Angio II modulates I(KV). We found that Angio II increased I(KV) by about 30% with a time constant of approximately 30 s. In comparison, inhibition of M-current was faster (tau approximately 8 s) and stronger ( approximately 61%). Modulation of I(KV) was disrupted by the AT(1) receptor-antagonist losartan but not by the AT(2)-antagonist PD123319. I(KV) enhancement was reduced by the G-protein inhibitor GDP-beta-S, whereas current modulation remained unaltered after cell treatment with pertussis toxin. The peptidergic modulation of I(KV) was severely disrupted when internal ATP was replaced by its nonhydrolyzable analogue AMP-PNP. Angio II enhanced I(KV) and further reduced the stimulatory action of a muscarinic agonist on I(KV). Likewise, the muscarinc agonist enhanced I(KV) and occluded the effect of Angio II on I(KV). We have also found that the protein kinase C activator PMA enhanced I(KV), thereby mimicking and further attenuating the action of Angio II on I(KV). These results suggest that AT(1) receptors by coupling to pertussis toxin-insensitive G proteins, stimulate an ATP-dependent and PKC-mediated pathway to modulate I(KV).

ERK1/2 inactivation and p38 MAPK-dependent caspase activation during guanosine 5'-triphosphate-mediated terminal erythroid differentiation of K562 cells

Since differentiation therapy is one of the promising strategies for treatment of leukemia, universal efforts have been focused on finding new differentiating agents. In that respect, it was recently shown that guanosine 5'-triphosphate (GTP) induced the differentiation of K562 cells, suggesting its possible efficiency in treatment of chronic myelogenous leukemia (CML). However, further investigations are required to verify this possibility. Here, the effects of GTP on activation of mitogen-activated protein kinases (MAPKs) and caspases in K562 cells were examined. Exposure of K562 cells to 100muM GTP markedly inhibited growth (4-70%) and increased percent glycophorin A positive cells after 1-6 days. GTP-induced terminal erythroid differentiation of K562 cells was accompanied with activation of three key caspases, i.e., caspase-3, -6 and -9. More detailed studies revealed that mitochondrial pathway is activated along with down-regulation of Bcl-xL and releasing of cytochrome c into cytosol. Among MAPKs, ERK1/2and p38 were modulated after GTP treatment. Western blot analyses showed that sustained phosphorylation of p38 MAPK was accompanied by a decrease in ERK1/2 activation. These modulatory effects of GTP were observed at early exposure times before the onset of differentiation (3h), and followed for 24-96h. Interestingly, inhibition of p38 MAPK pathway by SB202190 impeded GTP-mediated caspases activation and differentiation in K562 cells, suggesting that p38 MAPK may act upstream of caspases in our system. These results point to a pivotal role for p38 MAPK pathway during GTP-mediated erythroid differentiation of K562 cells and will hopefully have important impact on pharmaceutical evaluation of GTP for CML treatment in differentiation therapy approaches.

Detection of adenylyl cyclase activity using a fluorescent ATP substrate and capillary electrophoresis

A capillary electrophoresis laser-induced fluorescence (CE-LIF) assay was developed for detection of adenylyl cyclase (AC) activity using BODIPY FL ATP (BATP) as substrate. In the assay, BATP was incubated with AC and the resulting mixture of BATP and enzyme product (BODIPY cyclic AMP, BcAMP) separated in 5 min by CE-LIF. Substrate depletion and product accumulation were simultaneously monitored during the course of the reaction. The rate of product formation depended upon the presence of AC activators forskolin or Galpha(s)-GTPgammaS as evidenced by a more rapid BATP turnover to BcAMP compared to basal levels. The CE-LIF assay detected EC50 values for forskolin and Galpha(s)-GTPgammaS of 27 +/- 6 microM and 317 +/- 56 nM, respectively. These EC50 values compared well to those previously reported using [alpha-32P]ATP as substrate. When AC was concurrently activated with 2.5 microM forskolin and 25 nM Galpha(s)-GTPgammaS, the amount of BcAMP formed was 3.4 times higher than the additive amounts of each activator alone indicating a positively cooperative activation by these compounds in agreement with previous assays using radiolabeled substrate. Inhibition of AC activity was also demonstrated using the AC inhibitor 2'-(or-3')-O-(N-methylanthraniloyl) guanosine 5'-triphosphate with an IC50 of 9 +/- 6 nM. The use of a fluorescent substrate combined with CE separation has enabled development of a rapid and robust method for detection of AC activity that is an attractive alternative to the AC assay using radioactive nucleotide and column chromatography. In addition, the assay has potential for high-throughput screening of drugs that act at AC.

Enhanced cardiac allograft survival by Vav1-Rac signaling blockade in a mouse model

BACKGROUND

Vav1-Rac signaling plays a pivotal role in TCR/antigen and CD28 signals for T cell activation. However, pharmacological interference of this signaling has not been tested in the prevention of alloimmune-mediated allograft rejection. It has been demonstrated that 6-thio-GTP, a metabolite of azathioprine, specifically inhibits Vav1-Rac activity in T lymphocytes. Here we show the immunosuppressive efficacy of 6-thio-GTP in the prevention of cardiac allograft rejection.

METHODS

T cell proliferations were measured by (3)H-thymidine uptake. The immunosuppressive activities of 6-thio-GTP were tested in the cardiac allograft model of C57BL/6 (H-2(b)) to Balb/c (H-2(d)) mice.

RESULTS

6-Thio-GTP inhibited TCR/alloantigen stimulated T cell proliferation and CD28-dependent T cell survival. Administration of 6-thio-GTP (0.5 mg/kg) prolonged graft survival to 13.8+/-2.39 days compared to 8.3+/-0.48 days in PBS controls (p<0.0001). Combination of 6-thio-GTP (0.5 mg/kg) with CsA (15 mg/kg) enhanced graft survival from 15.0+/-1.61 days in CsA treated recipients to 36.8+/-2.17 days in those received 20 days of combination therapy of CsA and 6-thio-GTP (p<0.0001), or to 42.7+/-16.63 days in the group treated with 20 days of CsA and 60 days of 6-thio-GTP (p<0.0001). Lymphocytes from 6-thio-GTP treated recipients with long-term surviving grafts (>60 days) displayed reduced proliferative response to alloantigen and higher frequencies of regulatory T cells (Treg).

CONCLUSION

Vav1-Rac inhibitor 6-thio-GTP prolongs allograft survival alone or in combination with CsA by suppression of alloreactive T cell activation. Our findings suggest the therapeutic potential of pharmacological interference of Vav1-Rac signaling for transplantation.

The integrin alpha5beta1 regulates chondrocyte hypertrophic differentiation induced by GTP-bound transglutaminase 2

Soluble GTP-bound transglutaminase 2 (TG2) induces hypertrophic differentiation in chondrocyte cultures in a beta1 integrin-dependent fashion. beta1 integrin subfamily consists of 12 heterodimers with 12 different alpha subunits and a beta1 subunit. To identify the specific integrin heterodimer(s) responsible for this process, we specifically blocked individual beta1 integrins on the CH-8 immortalized human chondrocytes during hypertrophic differentiation. Blockade of alpha5beta1 inhibited matrix metalloproteinase 13 (MMP-13), type X collagen expression, alkaline phosphatase activity and matrix calcification by 30-50% associated with weak effects of anti-alpha3beta1 and -alpha4beta1. Anti-alpha1beta1, -alpha2beta1 and -alpha6beta1 had no effect. To examine whether the dominant effect of integrin alpha5beta1 was due to a direct interaction with TG2, we incubated the chondrocytic cells on plates coated with GTP-bound TG2. The immobilized GTP-bound TG2 induced hypertrophic differentiation to the same extent as the soluble GTP-bound TG2, which was also inhibited by anti-alpha5beta1. CH-8 cells grown on plates coated with GTP-bound TG2 demonstrated adherence associated with focal adhesion kinase phosphorylation. These properties were inhibited by anti-alpha5beta1. Furthermore, engagement of alpha5beta1 on CH-8 cells via anti-alpha5beta1 antibody did, in fact, induce differentiation. Although CH-8 cells adhered to GTP-free TG2 via integrin alpha5beta1, the cells failed to undergo hypertrophic differentiation. Thus, integrin alpha5beta1 is critical for the chondrocyte hypertrophic differentiation induced by GTP-bound TG2, and this induction is ligand dependent.

Intracellular calcium stores in beta-escin skinned rat and guinea-pig bladders

Intracellular Ca2+ stores in rat and guinea-pig bladders and taenia caecum were studied in beta-escin skinned smooth muscle strips. 30 min of skinning with 40 microM and 80 microM beta-escin were the best parameters found to obtain good calcium response curves (10(-7)-10(-4) M) in rat and guinea pig, respectively. Calmodulin (1 microM) increased the calcium contractions significantly. pCa 6 was used to load intracellular stores and application of carbachol (50 microM) in all tissues then only contracted the tissues in the presence of guanosine-5'-triphosphate (GTP; 100 microM). Inositol triphosphate (IP3; 50 microM), applied after pCa 6, contracted all tissues. Carbachol added after IP3 or heparin (1 mg/ml) no longer caused a contraction in any of them. In bladders, caffeine (30 mM) but not ryanodine (5 microM) prevented the subsequent carbachol contraction. A slowly rising contraction with carbachol was elicited after caffeine (30 mM) or ryanodine (5 microM) in the taenia and after ryanodine in the bladders. Caffeine (30 mM) suppressed the calcium response curves in all tissues. Procaine (30 mM) blocked the carbachol (50 microM) contractions in bladders but not in taenia. These results suggest that calcium induced calcium release (CICR) and IP3 induced calcium release (IICR) release calcium from a common store in bladder but two different compartments in taenia.

Polycystin-2 cation channel function in the human syncytiotrophoblast is regulated by microtubular structures

Polycystin-2 (PC2), encoded by PKD2, which is one of the genes whose mutations cause polycystic kidney disease, is abundantly produced in the apical domain of the syncytiotrophoblast (hST) of term human placenta. PC2, a TRP-type (TRPP2) non-selective cation channel, is present in primary cilia of renal epithelial cells, a microtubule-based ancillary structure with sensory function. The hST has abundant cytoskeletal structures, and actin filament dynamics regulate PC2 channel function in this epithelium. However, it is expected that the apical hST excludes microtubular structures. Here, we demonstrated by Western blot and immunocytochemical analyses that hST apical vesicles indeed contain microtubule structural components, including tubulin isoforms, acetylated alpha-tubulin, and the kinesin motor proteins KIF3A and KIF3B. PC2 and tubulin were substantially colocalized in hST vesicles. Treatment of hST vesicles with either the microtubular disrupter colchicine (15 microM) or the microtubular stabilizer paclitaxel (taxol, 15 microM) resulted in distinct patterns of microtubular re-organization and PC2 redistribution. We also observed that changes in microtubular dynamics regulate PC2 channel function. Addition of colchicine rapidly inhibited PC2 channel activity in lipid-bilayer reconstituted hST membranes. Addition of either tubulin and GTP, or taxol, however, stimulated PC2 channel activity in control hST membranes. Interestingly, we found that the kinesin motor protein KIF3A was capable of increasing PC2 channel activity in hST. We believe that the data are the first to provide a direct demonstration of a microtubular interaction with PC2 in the hST. This interaction thus plays an important regulatory role in the control of ion transport in the human placenta.

Metabotropic P2Y receptors inhibit P2X3 receptor-channels via G protein-dependent facilitation of their desensitization

BACKGROUND AND PURPOSE

The aim of the present study was to investigate whether the endogenous metabotropic P2Y receptors modulate ionotropic P2X(3) receptor-channels.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp experiments were carried out on HEK293 cells permanently transfected with human P2X(3) receptors (HEK293-hP2X(3) cells) and rat dorsal root ganglion (DRG) neurons.

KEY RESULTS

In both cell types, the P2Y(1,12,13) receptor agonist, ADP-beta-S, inhibited P2X(3) currents evoked by the selective agonist, alpha,beta-methylene ATP (alpha,beta-meATP). This inhibition could be markedly counteracted by replacing in the pipette solution the usual GTP with GDP-beta-S, a procedure known to block all G protein heterotrimers. P2X(3) currents evoked by ATP, activating both P2Y and P2X receptors, caused a smaller peak amplitude and desensitized faster than those currents evoked by the selective P2X(3) receptor agonist alpha,beta-meATP. In the presence of intracellular GDP-beta-S, ATP- and alpha,beta-meATP-induced currents were identical. Recovery from P2X(3) receptor desensitization induced by repetitive ATP application was slower than the recovery from alpha,beta-meATP-induced desensitization. When G proteins were blocked by intracellular GDP-beta-S, the recovery from the ATP- and alpha,beta-meATP-induced desensitization were of comparable speed.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the activation of P2Y receptors G protein-dependently facilitates the desensitization of P2X(3) receptors and suppresses the recovery from the desensitized state. Hence, the concomitant stimulation of P2X(3) and P2Y receptors of DRG neurons by ATP may result both in an algesic effect and a partly counterbalancing analgesic activity.

Mutations of Cys-17 and Ala-271 in the human histamine H2 receptor determine the species selectivity of guanidine-type agonists and increase constitutive activity

In a steady-state GTPase activity assay, N-[3-(1H-imidazol-4-yl)propyl)]guanidines and N(G)-acylated derivatives are more potent and efficacious at fusion proteins of guinea pig (gpH(2)R-G(salphaS)) than human (hH(2)R-G(salphaS)) histamine H(2) receptor, coupled to the short splice variant of G(salpha), G(salphaS). Whereas Ala-271 (hH(2)R) and Asp-271 (gpH(2)R) in transmembrane domain 7 were identified to determine the potency differences of guanidine-type agonists, the molecular basis for the efficacy differences remains to be elucidated. A homology model of the gpH(2)R suggested that an H-bond between Tyr-17 and Asp-271 stabilizes an active receptor conformation of the gpH(2)R. In the present study, we generated a mutant hH(2)R-G(salphaS) with Cys-17--> Tyr-17/Ala-271--> Asp-271 exchanges (hH(2)R-->gpH(2)R) that exhibited an enhanced level of constitutive GTPase activity and adenylyl cyclase activity compared with wild-type hH(2)R-G(salphaS) and gpH(2)R-G(salphaS). Potencies and efficacies of guanidines and N(G)-acylguanidines were increased at this mutant receptor compared with hH(2)R-G(salphaS), but they were still lower than at gpH(2)R-G(salphaS), suggesting that aside from Tyr-17 and Asp-271 additional amino acids contribute to the distinct pharmacological profiles of both species isoforms. Another hH(2)R-G(salphaS) mutant with a Cys-17--> Tyr-17 exchange showed inefficient coupling to G(salphaS) as revealed by reduced agonist-stimulated GTPase and basal adenylyl cyclase activities. Collectively, our present pharmacological study confirms the existence of an H-bond between Tyr-17 and Asp-271 favoring the stabilization of an active receptor conformation. Distinct potencies and efficacies of agonists and inverse agonists further support the concept of ligand-specific conformations in wild-type and mutant H(2)R-G(salphaS) fusion proteins.

Kinetic analysis of the interaction of tissue transglutaminase with a nonpeptidic slow-binding inhibitor

Tissue transglutaminase (TGase) is a Ca2+-dependent enzyme that catalyzes cross-linking of intracellular proteins through a mechanism that involves isopeptide bond formation between Gln and Lys residues and is allosterically regulated by GTP. TGase is thought to play a pathogenic role in neurodegenerative diseases by promoting aggregation of disease-specific proteins that accumulate as part of these disorders. Given the role that TGase plays in neurodegenerative disorders, we initiated a research program to discover inhibitors of this enzyme that might ultimately be developed into therapeutic agents. To identify such inhibitors, we screened 110,000 druglike compounds for their ability to inhibit TGase [Case, A., et al. (2005) Anal. Biochem. 338, 237-244]. In this paper, we report the kinetics of interaction of human TGase with one of the inhibitors that we identified, LDN-27219. We found that this compound is a reversible, slow-binding inhibitor that appears not to bind at the enzyme's active site but rather at the enzyme's GTP site, or a site that regulates binding of GTP. Interestingly, the potency and kinetics of inhibition are dependent on substrate structure and suggest a novel mechanism of inhibition that involves differential binding of LDN-27219 to multiple conformational states of this enzyme.

A minor role for Ca2+ sensitization in sustained contraction through activation of muscarinic receptor in circular muscle of rat distal colon

We previously demonstrated that Ca(2+) sensitization has an essential role for carbachol-induced contraction in the longitudinal muscle of the rat distal colon. In the present study, we extended these studies to clarify the role of Ca(2+) sensitization in contraction induced by the activation of muscarinic receptors in the circular muscle of the rat distal colon. Carbachol induced a rapid phasic contraction followed by a sustained contraction that was significantly lower than the phasic and was superimposed with the rhythmic contractions. The extent of increase in intracellular Ca(2+) concentration that was measured simultaneously with tension recording was dissociated from the phasic contraction, whereas it exhibited to a similar extent as sustained contraction. In alpha-toxin-permeabilized preparations, Ca(2+) induced contraction comprising a rapid phasic and a subsequent low sustained component. After Ca(2+)-induced sustained contraction reached a constant level, guanosine triphosphate (GTP) addition resulted in the enhancement of contractile force in a concentration-dependent manner. Carbachol in the presence of GTP caused a further minimal increase in tension (Ca(2+) sensitization). Chelerythrine, a protein kinase C (PKC) inhibitor, inhibited carbachol-induced Ca(2+) sensitization but not GTP-induced Ca(2+) sensitization. In contrast, Y-27632, a Rho kinase inhibitor, inhibited GTP-induced Ca(2+) sensitization but not that induced by carbachol. Phorbol 12,13-dibutyrate, a PKC activator, increased the sustained contraction. These results suggest that the activation of muscarinic receptor with carbachol induces Ca(2+) sensitization via activation of PKC, but this action is minor in the circular muscle of the rat distal colon as a result of limited coupling between muscarinic receptors and Ca(2+) sensitization via the PKC pathway.