Involvement of abnormal dystroglycan expression and matriglycan levels in cancer pathogenesis

Dystroglycan (DG) is a glycoprotein composed of two subunits that remain non-covalently bound at the plasma membrane: α-DG, which is extracellular and heavily O-mannosyl glycosylated, and β-DG, an integral transmembrane polypeptide. α-DG is involved in the maintenance of tissue integrity and function in the adult, providing an O-glycosylation-dependent link for cells to their extracellular matrix. β-DG in turn contacts the cytoskeleton via dystrophin and participates in a variety of pathways transmitting extracellular signals to the nucleus. Increasing evidence exists of a pivotal role of DG in the modulation of normal cellular proliferation. In this context, deficiencies in DG glycosylation levels, in particular those affecting the so-called matriglycan structure, have been found in an ample variety of human tumors and cancer-derived cell lines. This occurs together with an underexpression of the DAG1 mRNA and/or its α-DG (core) polypeptide product or, more frequently, with a downregulation of β-DG protein levels. These changes are in general accompanied in tumor cells by a low expression of genes involved in the last steps of the α-DG O-mannosyl glycosylation pathway, namely POMT1/2, POMGNT2, CRPPA, B4GAT1 and LARGE1/2. On the other hand, a series of other genes acting earlier in this pathway are overexpressed in tumor cells, namely DOLK, DPM1/2/3, POMGNT1, B3GALNT2, POMK and FKTN, hence exerting instead a pro-oncogenic role. Finally, downregulation of β-DG, altered β-DG processing and/or impaired β-DG nuclear levels are increasingly found in human tumors and cell lines. It follows that DG itself, particular genes/proteins involved in its glycosylation and/or their interactors in the cell could be useful as biomarkers of certain types of human cancer, and/or as molecular targets of new therapies addressing these neoplasms.

Retinal Proteomics of a Mouse Model of Dystroglycanopathies Reveals Molecular Alterations in Photoreceptors

Mutations in the POMT1 gene, encoding a protein O-mannosyltransferase essential for α-dystroglycan (α-DG) glycosylation, are frequently observed in a group of rare congenital muscular dystrophies, collectively known as dystroglycanopathies. However, it is hitherto unclear whether the effects seen in affected patients can be fully ascribed to α-DG hypoglycosylation. To study this, here we used comparative mass spectrometry-based proteomics and immunofluorescence microscopy and investigated the changes in the retina of mice in which Pomt1 is specifically knocked out in photoreceptor cells. Our results demonstrate significant proteomic changes and associated structural alteration in photoreceptor cells of Pomt1 cKO mice. In addition to the effects related to impaired α-DG O-mannosylation, we observed morphological alterations in the outer segment that are associated with dysregulation of a relatively understudied POMT1 substrate (KIAA1549), BBSome proteins, and retinal stress markers. In conclusion, our study provides new hypotheses to explain the phenotypic changes that are observed in the retina of patients with dystroglycanopathies.

Differential Effects of IGF-1R Small Molecule Tyrosine Kinase Inhibitors BMS-754807 and OSI-906 on Human Cancer Cell Lines

Simple Summary

We have tested the effects of IGF-1R tyrosine kinase inhibitors BMS-754807 (BMS) and OSI-906 (OSI) on human colon, pancreatic carcinoma cell, and glioblastoma cell lines and primary cultures. Although OSI and BMS are able to inhibit IGF-1R activity at low doses, the differential effect on cell proliferation and cell-cycle phase distribution shown by both compounds probes that many effects observed are mediated by BMS off-target interactions. Using MAPKs ELISAs and phospho-RTK array analysis, we have identified several BMS regulated putative kinases able to mediate BMS off-target effects. Interestingly, molecular docking assays suggest that BMS could affect these kinases not only by blocking their ATP-binding domain, but also by means of allosteric interactions. Since BMS has an important antineoplastic effect on these poor prognosis types of cancer, these compounds could be taken in consideration for treatment independently of IGF-1R status.

Abstract

We have determined the effects of the IGF-1R tyrosine kinase inhibitors BMS-754807 (BMS) and OSI-906 (OSI) on cell proliferation and cell-cycle phase distribution in human colon, pancreatic carcinoma, and glioblastoma cell lines and primary cultures. IGF-1R signaling was blocked by BMS and OSI at equivalent doses, although both inhibitors exhibited differential antiproliferative effects. In all pancreatic carcinoma cell lines tested, BMS exerted a strong antiproliferative effect, whereas OSI had a minimal effect. Similar results were obtained on glioblastoma primary cultures, where HGUE-GB-15, -16 and -17 displayed resistance to OSI effects, whereas they were inhibited in their proliferation by BMS. Differential effects of BMS and OSI were also observed in colon carcinoma cell lines. Both inhibitors also showed different effects on cell cycle phase distribution, BMS induced G₂/M arrest followed by cell death, while OSI induced G₁ arrest with no cell death. Both inhibitors also showed different effects on other protein kinases activities. Taken together, our results are indicative that BMS mainly acts through off-target effects exerted on other protein kinases. Given that BMS exhibits a potent antiproliferative effect, we believe that this compound could be useful for the treatment of different types of tumors independently of their IGF-1R activation status.

A role for DJ-1 against oxidative stress in the mammalian retina

We have previously reported the expression of Parkinson disease-associated genes encoding α-synuclein, parkin and UCH-L1 in the retina across mammals. DJ-1, or parkinsonism-associated deglycase, is a redox-sensitive protein with putative roles in cellular protection against oxidative stress, among a variety of functions, acting through distinct pathways and mechanisms in a wide variety of tissues. Its function in counteracting oxidative stress in the retina, as it occurs in Parkinson and other human neurodegenerative diseases, is, however, poorly understood. In the present study, we address the expression of DJ-1 in the mammalian retina and its putative neuroprotective role in this tissue in a well-known model of parkinsonism, the rotenone-treated rat. As a result, we demonstrate that the DJ1 gene is expressed at both mRNA and protein levels in the neural retina and retinal pigment epithelium (RPE) of all mammalian species studied. We also present evidence that DJ-1 functions in the retina as a sensor of cellular redox homeostasis, which reacts to oxidative stress by increasing its intracellular levels and additionally becoming oxidized. Levels of α-synuclein also became upregulated, although parkin and UCH-L1 expression remained unchanged. It is inferred that DJ-1 likely exerts in the retina a potential neuroprotective role against oxidative stress, including α-synuclein oxidation and aggregation, which should be operative under both physiological and pathological conditions.

Impairment of photoreceptor ribbon synapses in a novel Pomt1 conditional knockout mouse model of dystroglycanopathy

Hypoglycosylation of α-dystroglycan (α-DG) resulting from deficiency of protein O-mannosyltransferase 1 (POMT1) may cause severe neuromuscular dystrophies with brain and eye anomalies, named dystroglycanopathies. The retinal involvement of these disorders motivated us to generate a conditional knockout (cKO) mouse experiencing a Pomt1 intragenic deletion (exons 3-4) during the development of photoreceptors, mediated by the Cre recombinase expressed from the cone-rod homeobox (Crx) gene promoter. In this mouse, retinal α-DG was unglycosylated and incapable of binding laminin. Retinal POMT1 deficiency caused significant impairments in both electroretinographic recordings and optokinetic reflex in Pomt1 cKO mice, and immunohistochemical analyses revealed the absence of β-DG and of the α-DG-interacting protein, pikachurin, in the outer plexiform layer (OPL). At the ultrastructural level, noticeable alterations were observed in the ribbon synapses established between photoreceptors and bipolar cells. Therefore, O-mannosylation of α-DG in the retina carried out by POMT1 is crucial for the establishment of proper synapses at the OPL and transmission of visual information from cones and rods to their postsynaptic neurons.

Expression in retinal neurons of fukutin and FKRP, the protein products of two dystroglycanopathy-causative genes

Purpose

Dystroglycanopathies are a heterogeneous group of recessive neuromuscular dystrophies that affect the muscle, brain and retina, and are caused by deficiencies in the O-glycosylation of α-dystroglycan. This post-translational modification is essential for the formation and maintenance of ribbon synapses in the retina. Fukutin and fukutin-related protein (FKRP) are two glycosyltransferases whose deficiency is associated with severe dystroglycanopathies. These enzymes carry out in vitro the addition of a tandem ribitol 5-phosphate moiety to the so-called core M3 phosphotrisaccharide of α-dystroglycan. However, their expression pattern and function in the healthy mammalian retina has not so far been investigated. In this work, we have addressed the expression of the FKTN (fukutin) and FKRP genes in the retina of mammals, and characterized the distribution pattern of their protein products in the adult mouse retina and the 661W photoreceptor cell line.

Methods

By means of reverse transcription (RT)-PCR and immunoblotting, we have studied the expression at the mRNA and protein levels of the fukutin and FKRP genes in different mammalian species, from rodents to humans. Immunofluorescence confocal microscopy analyses were performed to characterize the distribution profile of their protein products in mouse retinal sections and in 661W cultured cells.

Results

Both genes were expressed at the mRNA and protein levels in the neural retina of all mammals studied. Fukutin was present in the cytoplasmic and nuclear fractions in the mouse retina and 661W cells, and accumulated in the endoplasmic reticulum. FKRP was located in the cytoplasmic fraction in the mouse retina and concentrated in the Golgi complex. However, and in contrast to retinal tissue, FKRP additionally accumulated in the nucleus of the 661W photoreceptors.

Conclusions

Our results suggest that fukutin and FKRP not only participate in the synthesis of O-mannosyl glycans added to α-dystroglycan in the endoplasmic reticulum and Golgi complex, but that they could also play a role, that remains to be established, in the nucleus of retinal neurons.

Endophytic colonization of barley (Hordeum vulgare) roots by the nematophagous fungus Pochonia chlamydosporia reveals plant growth promotion and a general defense and stress transcriptomic response

Plant crop yields are negatively conditioned by a large set of biotic and abiotic factors. An alternative to mitigate these adverse effects is the use of fungal biological control agents and endophytes. The egg-parasitic fungus Pochonia chlamydosporia has been traditionally studied because of its potential as a biological control agent of plant-parasitic nematodes. This fungus can also act as an endophyte in monocot and dicot plants, and has been shown to promote plant growth in different agronomic crops. An Affymetrix 22K Barley GeneChip was used in this work to analyze the barley root transcriptomic response to P. chlamydosporia root colonization. Functional gene ontology (GO) and gene set enrichment analyses showed that genes involved in stress response were enriched in the barley transcriptome under endophytism. An 87.5% of the probesets identified within the abiotic stress response group encoded heat shock proteins. Additionally, we found in our transcriptomic analysis an up-regulation of genes implicated in the biosynthesis of plant hormones, such as auxin, ethylene and jasmonic acid. Along with these, we detected induction of brassinosteroid insensitive 1-associated receptor kinase 1 (BR1) and other genes related to effector-triggered immunity (ETI) and pattern-triggered immunity (PTI). Our study supports at the molecular level the growth-promoting effect observed in plants endophytically colonized by P. chlamydosporia, which opens the door to further studies addressing the capacity of this fungus to mitigate the negative effects of biotic and abiotic factors on plant crops.

Oleic acid modulates mRNA expression of liver X receptor (LXR) and its target genes ABCA1 and SREBP1c in human neutrophils

PURPOSE

Regulation of liver X receptors (LXRs) is essential for cholesterol homeostasis and inflammation. The present study was conducted to determine whether oleic acid (OA) could regulate mRNA expression of LXRα and LXRα-regulated genes and to assess the potential promotion of oxidative stress by OA in neutrophils.

METHODS

Human neutrophils were treated with OA at different doses and LXR target gene expression, oxidative stress production, lipid efflux and inflammation state were analyzed.

RESULTS

We describe that mRNA synthesis of both LXRα and ABCA1 (a reverse cholesterol transporter) was induced by OA in human neutrophils. This fatty acid enhanced the effects of LXR ligands on ABCA1 and LXR expression, but it decreased the mRNA levels of sterol regulatory element-binding protein 1c (a transcription factor that regulates the synthesis of triglycerides). Although OA elicited a slight oxidative stress in the short term (15-30 min) in neutrophils, it is unlikely that this is relevant for the modulation of transcription in our experimental conditions, which involve longer incubation time (i.e., 6 h). Of physiological importance is our finding that OA depresses intracellular lipid levels and that markers of inflammation, such as ERK1/2 and p38 mitogen-activated protein kinase phosphorylation, were decreased by OA treatment. In addition, 200 μM OA reduced the migration of human neutrophils, another marker of the inflammatory state. However, OA did not affect lipid peroxidation induced by pro-oxidant agents.

CONCLUSIONS

This work presents for the first time evidence that human neutrophils are highly sensitive to OA and provides novel data in support of a protective role of this monounsaturated acid against the activation of neutrophils during inflammation.

Sequencing and functional analysis of the genome of a nematode egg-parasitic fungus, Pochonia chlamydosporia

Pochonia chlamydosporia is a worldwide-distributed soil fungus with a great capacity to infect and destroy the eggs and kill females of plant-parasitic nematodes. Additionally, it has the ability to colonize endophytically roots of economically-important crop plants, thereby promoting their growth and eliciting plant defenses. This multitrophic behavior makes P. chlamydosporia a potentially useful tool for sustainable agriculture approaches. We sequenced and assembled ∼41 Mb of P. chlamydosporia genomic DNA and predicted 12,122 gene models, of which many were homologous to genes of fungal pathogens of invertebrates and fungal plant pathogens. Predicted genes (65%) were functionally annotated according to Gene Ontology, and 16% of them found to share homology with genes in the Pathogen Host Interactions (PHI) database. The genome of this fungus is highly enriched in genes encoding hydrolytic enzymes, such as proteases, glycoside hydrolases and carbohydrate esterases. We used RNA-Seq technology in order to identify the genes expressed during endophytic behavior of P. chlamydosporia when colonizing barley roots. Functional annotation of these genes showed that hydrolytic enzymes and transporters are expressed during endophytism. This structural and functional analysis of the P. chlamydosporia genome provides a starting point for understanding the molecular mechanisms involved in the multitrophic lifestyle of this fungus. The genomic information provided here should also prove useful for enhancing the capabilities of this fungus as a biocontrol agent of plant-parasitic nematodes and as a plant growth-promoting organism.

Platelet-activating factor downregulates the expression of liver X receptor-α and its target genes in human neutrophils

Liver X receptors (LXRs) are ligand-activated members of the nuclear receptor superfamily that regulate the expression of genes involved in lipid metabolism and inflammation, although their role in inflammation and immunity is less well known. It has been reported that oxysterols/LXRs may act as anti-inflammatory molecules, although opposite actions have also been reported. In this study, we investigated the effect of platelet-activating factor (PAF), a proinflammatory molecule, on LXRα signalling in human neutrophils. We found that PAF exerted an inhibitory effect on mRNA expression of TO901317-induced LXRα, ATP-binding cassette transporter A1, ATP-binding cassette transporter G1, and sterol response element binding protein 1c. This negative action was mediated by the PAF receptor, and was dependent on the release of reactive oxygen species elicited by PAF, as it was enhanced by pro-oxidant treatment and reversed by antioxidants. Current data also support the idea that PAF induces phosphorylation of the LXRα molecule in an extracellular signal-regulated kinase 1/2-mediated fashion. These results suggest that a possible mechanism by which PAF exerts its proinflammatory effect is through the downregulation of LXRα and its related genes, which supports the notion that LXRα ligands exert a modulatory role in the neutrophil-mediated inflammatory response.

The ubiquitin-proteasome system in retinal health and disease

The ubiquitin-proteasome system (UPS) is the main intracellular pathway for modulated protein turnover, playing an important role in the maintenance of cellular homeostasis. It also exerts a protein quality control through degradation of oxidized, mutant, denatured, or misfolded proteins and is involved in many biological processes where protein level regulation is necessary. This system allows the cell to modulate its protein expression pattern in response to changing physiological conditions and provides a critical protective role in health and disease. Impairments of UPS function in the central nervous system (CNS) underlie an increasing number of genetic and idiopathic diseases, many of which affect the retina. Current knowledge on the UPS composition and function in this tissue, however, is scarce and dispersed. This review focuses on UPS elements reported in the retina, including ubiquitinating and deubiquitinating enzymes (DUBs), and alternative proteasome assemblies. Known and inferred roles of protein ubiquitination, and of the related, SUMO conjugation (SUMOylation) process, in normal retinal development and adult homeostasis are addressed, including modulation of the visual cycle and response to retinal stress and injury. Additionally, the relationship between UPS dysfunction and human neurodegenerative disorders affecting the retina, including Alzheimer's, Parkinson's, and Huntington's diseases, are dealt with, together with numerous instances of retina-specific illnesses with UPS involvement, such as retinitis pigmentosa, macular degenerations, glaucoma, diabetic retinopathy (DR), and aging-related impairments. This information, though still basic and limited, constitutes a suitable framework to be expanded in incoming years and should prove orientative toward future therapy design targeting sight-affecting diseases with a UPS underlying basis.

Transcription of liver X receptor is down-regulated by 15-deoxy-Δ(12,14)-prostaglandin J(2) through oxidative stress in human neutrophils

Liver X receptors (LXRs) are ligand-activated transcription factors of the nuclear receptor superfamily. They play important roles in controlling cholesterol homeostasis and as regulators of inflammatory gene expression and innate immunity, by blunting the induction of classical pro-inflammatory genes. However, opposite data have also been reported on the consequences of LXR activation by oxysterols, resulting in the specific production of potent pro-inflammatory cytokines and reactive oxygen species (ROS). The effect of the inflammatory state on the expression of LXRs has not been studied in human cells, and constitutes the main aim of the present work. Our data show that when human neutrophils are triggered with synthetic ligands, the synthesis of LXRα mRNA became activated together with transcription of the LXR target genes ABCA1, ABCG1 and SREBP1c. An inflammatory mediator, 15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂), hindered T0901317-promoted induction of LXRα mRNA expression together with transcription of its target genes in both neutrophils and human macrophages. This down-regulatory effect was dependent on the release of reactive oxygen species elicited by 15dPGJ₂, since it was enhanced by pro-oxidant treatment and reversed by antioxidants, and was also mediated by ERK1/2 activation. Present data also support that the 15dPGJ₂-induced serine phosphorylation of the LXRα molecule is mediated by ERK1/2. These results allow to postulate that down-regulation of LXR cellular levels by pro-inflammatory stimuli might be involved in the development of different vascular diseases, such as atherosclerosis.

Calcineurin expression and activity is regulated by the intracellular redox status and under hypertension in human neutrophils

Calcineurin (protein phosphatase 2B) (CN) comprises a family of serine/threonine phosphatases that play a pivotal role in signal transduction cascades in a variety of cells, including neutrophils. Angiotensin II (Ang II) increases both activity and de novo synthesis of CN in human neutrophils. This study focuses on the role that intracellular redox status plays in the induction of CN activity by Ang II. Both de novo synthesis of CN and activity increase promoted by Ang II were downregulated when cells were treated with L-buthionine-(S,R)-sulfoximine, an inhibitor of synthesis of the antioxidant glutathione. We have also investigated the effect of pyrrolidine dithiocarbamate and phenazine methosulfate, which are antioxidant and oxidant compounds, respectively, and concluded that the intracellular redox status of neutrophils is highly critical for Ang II-induced increase of CN expression and activity. Results obtained in neutrophils from hypertensive patients were very similar to those obtained in these cells on treatment with Ang II. We have also addressed the possible functional implication of CN activation in the development of hypertension. Present findings indicate that downregulation of hemoxygenase-1 expression in neutrophils from hypertensive subjects is likely mediated by CN, which acts by hindering translocation to the nucleus of the transcription factor NRF2. These data support and extend our previous results and those from other authors on modulation of CN expression and activity levels by the intracellular redox status.

Safranal, a saffron constituent, attenuates retinal degeneration in P23H rats

Saffron, an extract from Crocus sativus, has been largely used in traditional medicine for its antiapoptotic and anticarcinogenic properties. In this work, we investigate the effects of safranal, a component of saffron stigmas, in attenuating retinal degeneration in the P23H rat model of autosomal dominant retinitis pigmentosa. We demonstrate that administration of safranal to homozygous P23H line-3 rats preserves both photoreceptor morphology and number. Electroretinographic recordings showed higher a- and b-wave amplitudes under both photopic and scotopic conditions in safranal-treated versus non-treated animals. Furthermore, the capillary network in safranal-treated animals was preserved, unlike that found in untreated animals. Our findings indicate that dietary supplementation with safranal slows photoreceptor cell degeneration and ameliorates the loss of retinal function and vascular network disruption in P23H rats. This work also suggests that safranal could be potentially useful to retard retinal degeneration in patients with retinitis pigmentosa.

Gene cloning, molecular modeling, and phylogenetics of serine protease P32 and serine carboxypeptidase SCP1 from nematophagous fungi Pochonia rubescens and Pochonia chlamydosporia

The fungi Pochonia chlamydosporia and Pochonia rubescens are parasites of nematode eggs and thus are biocontrol agents of nematodes. Proteolytic enzymes such as the S8 proteases VCP1 and P32, secreted during the pathogenesis of nematode eggs, are major virulence factors in these fungi. Recently, expression of these enzymes and of SCP1, a new putative S10 carboxypeptidase, was detected during endophytic colonization of barley roots by these fungi. In our study, we cloned the genomic and mRNA sequences encoding P32 from P. rubescens and SCP1 from P. chlamydosporia. P32 showed a high homology with the serine proteases Pr1A from the entomopathogenic fungus Metarhizium anisopliae and VCP1 from P. chlamydosporia (86% and 76% identity, respectively). However, the catalytic pocket of P32 showed differences in the amino acids of the substrate-recognition sites compared with the catalytic pockets of Pr1A and VCP1 proteases. Phylogenetic analysis of P32 suggests a common ancestor with protease Pr1A. SCP1 displays the characteristic features of a member of the S10 family of serine proteases. Phylogenetic comparisons show that SCP1 and other carboxypeptidases from filamentous fungi have an origin different from that of yeast vacuolar serine carboxypeptidases. Understanding protease genes from nematophagous fungi is crucial for enhancing the biocontrol potential of these organisms.

Tauroursodeoxycholic acid prevents retinal degeneration in transgenic P23H rats

PURPOSE

To evaluate the preventive effect of tauroursodeoxycholic acid (TUDCA) on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP).

METHODS

P23H line-3 rats were injected with TUDCA once a week from postnatal day (P)21 to P120, in parallel with vehicle-administered controls. At P120, functional activity of the retina was evaluated by electroretinographic (ERG) recording. The effects of TUDCA on the number, morphology, integrity, and synaptic connectivity of retinal cells were characterized by immunofluorescence confocal microscopy.

RESULTS

The amplitude of ERG a- and b-waves was significantly higher in TUDCA-treated animals under both scotopic and photopic conditions than in control animals. In the central area of the retina, TUDCA-treated P23H rats showed threefold more photoreceptors than control animals. The number of TUNEL-positive cells was significantly smaller in TUDCA-treated rats, in which photoreceptor morphology was preserved. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in TUDCA-treated P23H rats. Furthermore, in TUDCA-treated rat retinas, the number of both rod bipolar and horizontal cell bodies, as well as the density of their synaptic terminals in the outer plexiform layer, was greater than in control rats.

CONCLUSIONS

TUDCA treatment was capable of preserving cone and rod structure and function, together with their contacts with their postsynaptic neurons. The neuroprotective effects of TUDCA make this compound potentially useful for delaying retinal degeneration in RP.

Expression in the mammalian retina of parkin and UCH-L1, two components of the ubiquitin-proteasome system

The ubiquitin-proteasome system (UPS) functions as a major degradation pathway for misfolded and damaged proteins with an important neuroprotective role in the CNS against a variety of cellular stresses. Parkin and ubiquitin C-terminal hydrolase L1 (UCH-L1) are two relevant components of the UPS associated with a number of neurodegenerative disorders. We here address the expression profile of parkin and UCH-L1 in the mammalian retina, with special emphasis on primates. We describe for the first time the presence of parkin in the retina of mammals, including humans. Parkin and UCH-L1 genes were expressed at the mRNA and protein levels in the retina of all species examined. The immunolocalization pattern of parkin was quite widespread, being expressed by most retinal neuronal types, including photoreceptors. UCH-L1 was localized to horizontal cells and specific subtypes of bipolar and amacrine cells, as well as to ganglion cells and their axons forming the nerve fiber layer. In rodents no UCH-L1 immunoreactivity was found in cone or rod photoreceptors, whereas this protein was present along the whole length of cones in all other mammals. Remarkably, UCH-L1 was expressed by dopaminergic amacrine cells of primates. The ample distribution of parkin and UCH-L1 in the mammalian retina, together with the crucial role played by the UPS in normal neuronal physiology in the brain, points to a participation of these two proteins in the ubiquitin-proteasomal pathway of protein degradation in most retinal cell types, where they could exert a protective function against neuronal stress.

Gradual morphogenesis of retinal neurons in the peripheral retinal margin of adult monkeys and humans

The adult mammalian retina has for long been considered to lack a neurogenerative capacity. However, retinal stem/progenitor cells, which can originate retinal neurons in vitro, have been recently reported in the ciliary body of adult mammals. Here we explored the possibility of retinal neurogenesis occurring in vivo in adult monkeys and humans. We found the presence of cells expressing molecular markers of neural and retinal progenitors in the nonlaminated retinal margin and ciliary body pars plana of mature primates. By means of immunohistochemistry and electron microscopy we also observed photoreceptors and other retinal cell types in different stages of morphological differentiation along the peripheral retinal margin. These findings allow us to extend to primates the idea of neurogenesis aimed at retinal cell turnover throughout life.

Expression of the transcription factor NFAT2 in human neutrophils: IgE-dependent, Ca2+- and calcineurin-mediated NFAT2 activation

NFAT (nuclear factors of activated T cells) proteins constitute a family of transcription factors involved in mediating signal transduction. The presence of NFAT isoforms has been described in all cell types of the immune system, with the exception of neutrophils. In the present work we report for the first time the expression in human neutrophils of NFAT2 mRNA and protein. We also report that specific antigens were able to promote NFAT2 protein translocation to the nucleus, an effect that was mimicked by the treatment of neutrophils with anti-immunoglobulin E (anti-IgE) or anti-Fcepsilon-receptor antibodies. Antigens, anti-IgE and anti-FcepsilonRs also increased Ca2+ release and the intracellular activity of calcineurin, which was able to interact physically with NFAT2, in parallel to eliciting an enhanced NFAT2 DNA-binding activity. In addition, specific chemical inhibitors of the NFAT pathway, such as cyclosporin A and VIVIT peptide, abolished antigen and anti-IgE-induced cyclooxygenase-2 (COX2) gene upregulation and prostaglandin (PGE(2)) release, suggesting that this process is through NFAT. Our results provide evidence that NFAT2 is constitutively expressed in human neutrophils, and after IgE-dependent activation operates as a transcription factor in the modulation of genes, such as COX2, during allergic inflammation.

Rac2 GTPase activation by angiotensin II is modulated by Ca2+/calcineurin and mitogen-activated protein kinases in human neutrophils

Angiotensin II (Ang II) highly stimulates superoxide anion production by neutrophils. The G-protein Rac2 modulates the activity of NADPH oxidase in response to various stimuli. Here, we describe that Ang II induced both Rac2 translocation from the cytosol to the plasma membrane and Rac2 GTP-binding activity. Furthermore, Clostridium difficile toxin A, an inhibitor of the Rho-GTPases family Rho, Rac and Cdc42, prevented Ang II-elicited O2-/ROS production, phosphorylation of the mitogen-activated protein kinases (MAPKs) p38, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase 1/2, and Rac2 activation. Rac2 GTPase inhibition by C. difficile toxin A was accompanied by a robust reduction of the cytosolic Ca(2)(+) elevation induced by Ang II in human neutrophils. Furthermore, SB203580 and PD098059 act as inhibitors of p38MAPK and ERK1/2 respectively, wortmannin, an inhibitor of phosphatidylinositol-3-kinase, and cyclosporin A, a calcineurin inhibitor, hindered both translocation of Rac2 from the cytosol to the plasma membrane and enhancement of Rac2 GTP-binding elicited by Ang II. These results provide evidence that the activation of Rac2 by Ang II is exerted through multiple signalling pathways, involving Ca(2)(+)/calcineurin and protein kinases, the elucidation of which should be insightful in the design of new therapies aimed at reversing the inflammation of vessel walls found in a number of cardiovascular diseases.

Alpha synuclein gene expression profile in the retina of vertebrates

PURPOSE

Alpha-synuclein is a Parkinson's disease-linked protein of ubiquitous expression in the central nervous system. It has a proposed role in the modulation of neurotransmission and synaptic function. This study was aimed at analyzing expression of the alpha-synuclein gene in the normal retina, and characterizing its pattern of distribution in the different retinal cell types and layers in a variety of vertebrates, ranging from fish to humans.

METHODS

Reverse transcriptase-polymerase chain reaction and immunoblotting were used to assess alpha-synuclein expression at both mRNA and protein levels. Its retinal distribution profile was characterized by immunohistochemical methods. With this purpose, retinal sections were analyzed under fluorescent confocal microscopy using specific antibodies against alpha-synuclein, alone and in double or triple combinations with a set of antibodies to molecular markers for the distinct retinal neuronal types. Also, synaptophysin was used as a marker for synaptic vesicles in the retina.

RESULTS

Alpha-synuclein mRNA and protein were expressed by both retinal pigment epithelium (RPE) and neural retinal cells. The pattern of alpha-synuclein distribution in the retina was quite consistent across all vertebrate species examined. A strong immunoreactivity was found in the outer segments (OS) of photoreceptors and in their axon terminals (cone pedicles and rod spherules) in the outer plexiform layer (OPL) of the retina. Alpha-synuclein was also present in rod and cone bipolar cells, as well as in GABAergic and glycinergic amacrines, distributing along a complex plexus throughout the inner plexiform layer (IPL). Additionally, colocalization was found between alpha-synuclein and synaptophysin at presynaptic terminals of the retina. Alpha-synuclein-positive phagosome-like structures were observed in the cytoplasm of RPE cells.

CONCLUSIONS

An involvement of alpha-synuclein can be postulated in neurotransmission at axon terminals of photoreceptors in the OPL, and at presynaptic endings of bipolar and amacrine cells in the IPL. As well, this protein could have a role in the function as well as the maintenance of photoreceptor OS. Alpha-synuclein contained in RPE cells should derive not only from protein expression by this cell type, but also from their phagocytosis of OS disc membranes.

Modulation of IgE-dependent COX-2 gene expression by reactive oxygen species in human neutrophils

Cyclooxygenase (COX) is a key enzyme in prostaglandin (PG) synthesis. Up-regulation of its COX-2 isoform is responsible for the increased PG release, taking place under inflammatory conditions, and also, is thought to be involved in allergic and inflammatory diseases. In the present work, we demonstrate that COX-2 expression becomes highly induced by anti-immunoglobulin E (IgE) antibodies and by antigens in human neutrophils from allergic patients. This induction was detected at mRNA and protein levels and was accompanied by a concomitant PGE(2) and thromboxane A(2) release. We also show evidence that inhibitors of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, such as 4-(2-aminoethyl)benzenesulphonyl fluoride and 4-hydroxy-3-methoxyaceto-phenone, completely cancelled anti-IgE-induced COX-2 protein up-regulation, suggesting that this process is mediated by reactive oxygen species (ROS) derived from NADPH oxidase activity. Moreover, the mitogen-activated protein kinases (MAPKs), p38 and extracellular signal-regulated kinase, and also, the transcription factor, nuclear factor (NF)-kappaB, are involved in the up-regulation of COX-2 expression, as specific chemical inhibitors of these two kinases, such as SB203580 and PD098059, and of the NF-kappaB pathway, such as N(alpha)-benzyloxycarbonyl-l-leucyl-l-leucyl-l-leucinal, abolished IgE-dependent COX-2 induction. Evidence is also presented, using Fe(2)(+)/Cu(2)(+) ions, that hydroxyl radicals generated from hydrogen peroxide through Fenton reactions could constitute candidate modulators able to directly trigger anti-IgE-elicited COX-2 expression through MAPK and NF-kappaB pathways. Present results underscore a new role for ROS as second messengers in the modulation of COX-2 expression by human neutrophils in allergic conditions.

Morphological impairments in retinal neurons of the scotopic visual pathway in a monkey model of Parkinson's disease

Physiological abnormalities resulting from death of dopaminergic neurons of the central nervous system in Parkinson's disease also extend to the retina, resulting in impaired visual functions. In both parkinsonian patients and animal models, low levels of dopamine and loss of dopaminergic cells in the retina have been reported. However, the morphology and connectivity of their postsynaptic neurons, the amacrine cells, have not been analyzed. Here we report, with macaques chronically treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a model of Parkinson's disease, that morphological impairments in dopaminergic retinal neurons and their plexus in the inner retina are accompanied by an immunoreactivity decrease in gamma-aminobutyric acidergic and glycinergic amacrine cells. Especially deteriorated were AII amacrine cells, the main neuronal subtype postsynaptic to dopaminergic cells, which exhibited a marked loss of lobular appendages and dendritic processes. Concomitantly, electrical synapses among AII cells, as well as chemical synapses between these and rod bipolar cells, were highly deteriorated in parkinsonian monkeys. These results highlight that the scotopic visual pathway is severely impaired in the parkinsonian condition and provide a morphological basis for a number of abnormalities found in electrophysiological and psychophysical trials in Parkinson's disease patients and animal models.

Homocysteine enhances superoxide anion release and NADPH oxidase assembly by human neutrophils. Effects on MAPK activation and neutrophil migration

Hyperhomocysteinaemia has recently been recognized as a risk factor of cardiovascular disease. However, the action mechanisms of homocysteine (Hcy) are not well understood. Given that Hcy may be involved in the recruitment of monocytes and neutrophils to the vascular wall, we have investigated the role of Hcy in essential functions of human neutrophils. We show that Hcy increased superoxide anion (O2*-) release by neutrophils to the extracellular medium, and that this effect was inhibited by superoxide dismutase and diphenyleneiodonium (DPI), an inhibitor of NADPH oxidase activity. The enzyme from rat peritoneal macrophages displayed a similar response. These effects were accompanied by a time-dependent increased translocation of p47phox and p67phox subunits of NADPH oxidase to the plasma membrane. We also show that Hcy increased intracellular H2O2 production by neutrophils, that Hcy enhanced the activation and phosphorylation of mitogen-activated protein kinases (MAPKs), specifically p38-MAPK and ERK1/2, and that the migration of neutrophils was increased by Hcy. Present results are the first evidence that Hcy enhances the oxidative stress of neutrophils, and underscore the potential role of phagocytic cells in vascular wall injury through O2*- release in hyperhomocysteinaemia conditions.

15-Deoxy-Δ12,14-prostaglandin J2 Induces Heme Oxygenase-1 Gene Expression in a Reactive Oxygen Species-dependent Manner in Human Lymphocytes

15-Deoxy-delta(12,14)-prostaglandin J(2) (15dPGJ(2) has been recently proposed as a potent anti-inflammatory agent. However, the mechanisms by which 15dPGJ(2) mediates its therapeutic effects in vivo are unclear. We demonstrate that 15dPGJ(2) at micromolar (2.5-10 microm) concentrations induces the expression of heme oxygenase-1 (HO-1), an anti-inflammatory enzyme, at both mRNA and protein levels in human lymphocytes. In contrast, troglitazone and ciglitazone, two thiazolidinediones that mimic several effects of 15dPGJ(2) through their binding to the peroxisome proliferator-activated receptor (PPAR)-gamma, did not affect HO-1 expression, and the positive effect of 15dPGJ(2) on this process was mimicked instead by other cyclopentenone prostaglandins (PG), such as PGD(2) (the precursor of 15dPGJ(2)) and PGA(1) and PGA(2) which do not interact with PPAR-gamma. Also, 15dPGJ(2) enhanced the intracellular production of reactive oxygen species (ROS) and increased xanthine oxidase activity in vitro. Inhibition of intracellular ROS production by N-acetylcysteine, TEMPO, Me(2)SO, 1,10-phenanthroline, or allopurinol resulted in a decreased 15dPGJ(2)-dependent HO-1 expression in the cells. Furthermore, buthionine sulfoximine, an inhibitor of reduced glutathione synthesis, or Fe(2+)/Cu(2+) ions enhanced the positive effect of 15dPGJ(2) on HO-1 expression. On the other hand, the inhibition of phosphatidylinositol 3-kinase or p38 mitogen-activated protein kinase, or the blockade of transcription factor NF-kappaB activation, hindered 15dPGJ(2)-elicited HO-1 expression. Collectively, the present data suggest that 15dPGJ(2) anti-inflammatory actions at pharmacological concentrations involve the induction of HO-1 gene expression through mechanisms independent of PPAR-gamma activation and dependent on ROS produced via the xanthine/xanthine oxidase system and/or through Fenton reactions. Both phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase signaling pathways also appear implicated in modulation of HO-1 expression by 15dPGJ(2).

A new role for monoamine oxidases in the modulation of macrophage-inducible nitric oxide synthase gene expression

This report focuses on the modulatory role of endogenous H(2)O(2) on lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma)-induced inducible nitric oxide synthase (NOS2) gene expression in rat peritoneal macrophages. Exogenously added H(2)O(2) was initially found to inhibit the synthesis of NOS2, which prompted us to assess the effect of the activity of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) as H(2)O(2)-forming enzymes on NOS2 gene expression. In the presence of their substrates, tyramine for MAO and benzylamine for SSAO, intracellular synthesis of H(2)O(2) took place with concomitant inhibition of LPS/IFN-gamma-induced NOS2 protein synthesis, as detected by Western blotting, flow cytometry, and immunofluorescence microscopy analyses. Pargyline and semicarbazide, specific inhibitors of MAO and SSAO, respectively, canceled this negative effect of MAO substrates on NOS2 expression. In the presence of Fe(2+) and Cu(2+) ions, inhibition of NOS2 expression was enhanced, suggesting the participation in this regulation of species derived from Fenton chemistry. In addition, the negative effect of H(2)O(2), generated by MAOs, was found to be exerted on NOS2 mRNA levels. These data offer a new insight in the control of NOS2 expression through the intracellular levels of H(2)O(2) and other reactive oxygen species (ROS). The hypothesis can be raised that the inhibition of NOS by H(2)O(2) could constitute a protective mechanism against the cytotoxic consequences of the activation of ROS-generating enzymes, thus providing a new, singular role for the MAO family of proteins.

Activation of phagocytic cell NADPH oxidase by norfloxacin: a potential mechanism to explain its bactericidal action

The mechanisms underlying the bactericidal power of fluoroquinolones against intracellular parasites in host macrophages remain poorly understood. We have analyzed the effect of norfloxacin, a fluoroquinolone antibiotic, on the production of reactive oxygen intermediates (O(2)(*-) and H(2)O(2)) and NADPH oxidase activity in mouse macrophages. The generation of anion superoxide (O(2)(*-)) was found to be significantly greater in macrophages incubated with norfloxacin than in untreated controls. This enhancing effect of norfloxacin was dose-dependent and reached maximal values within 10 min after its addition. The O(2)(*-) generated was mainly intracellular, as determined by the use of specific dyes, such as lucigenin and luminol, and able to diffuse freely through the cell membrane. Also, the production of H(2)O(2) was increased in macrophages in response to norfloxacin. The positive effect of norfloxacin was associated to an enhanced mobilization of NADPH oxidase subunits p47(phox) and p67(phox) from the cytosol to the plasma membrane in phagocytic cells. The effect of the antibiotic persisted in vivo for several hours. These data support the notion that norfloxacin inhibits mycobacterial growth within phagocytic cells by enhancing intracellular production of O(2)(*-) and other reactive oxygen species.

Two-hybrid analysis of domain interactions involving NtrB and NtrC two-component regulators

Signal transduction by two-component regulatory systems involves phosphorylation of the receiver domain of a response regulator by the transmitter domain of the cognate histidine kinase. In the NtrBC system, phosphorylation of NtrC by NtrB results in transcriptional activation of nitrogen-regulated genes. We have used the yeast two-hybrid system to probe interactions between domains of the NtrB and NtrC proteins from Klebsiella pneumoniae. We constructed fusions from each of a series of proteins or protein domains to the activation and the DNA-binding domains of GAL4 and analysed expression of GAL1:lacZ and GAL1:HIS3 reporters in yeast. The DNA-binding domain of NtrC and the so-called sensor domain of NtrB appeared to provide the major determinants for dimerization of the fusion proteins. A strong and specific interaction was also shown between NtrB and NtrC, localized to the HN region of the NtrB transmitter module and to the NtrC receiver domain, whereas other domains of these proteins do not appear to contribute to the recognition specificity. The results presented here indicate that communication between two-component partners also involves protein-protein interactions that can be detected in vivo, suggesting that the yeast two-hybrid system is a powerful genetic tool for identifying functional partners of prokaryotic signal transduction pathways.

Characterization of a new plasma membrane-associated ecto-5'-phosphodiesterase/nucleotide-pyrophosphatase from rat hepatocarcinoma AS-30D cells

We have identified in plasma membrane fractions isolated from rat hepatocarcinoma AS-30D ascites cells three glycoproteins of 125 kDa, 115 kDa and 105 kDa (gp125, gp115 and gp105) which become adenylylated using ATP as substrate, most readily in the presence of EDTA. The gp115 becomes also phosphorylated. The adenylylation of these tumor glycoproteins was much lower than that of a group of analogous adenylylatable glycoproteins (gp130, gp120-gp110 dimer and gp100) present in normal rat liver plasma membrane. The tumor glycoproteins were reversibly O-adenylylated at threonine residues, as was the case for their normal rat liver counterparts. The tumor gp115, and the gp120-gp110 dimer from normal rat liver were both isolated using either ATP-affinity chromatography and/or AMP-affinity chromatography. The gp120-gp110 dimer from normal rat liver was identified as the plasma cell differentiation antigen-1 (PC-1 protein), an ecto-5' phosphodiesterase/nucleotide-pyrophosphatase (5'-PDE/NPPase). The gp115 from tumor cells also exhibited Zn2+ stimulated 5'-PDE and NPPase activities in alkaline conditions, although it appears to be distinct from the PC-1 protein. We have determined that the gp115 is an ecto-enzyme that catalyzes the hydrolysis of extracellular ATP, since its adenylylation and phosphorylation were detected in intact cells using extracellularly added [alpha-32P]ATP or [gamma-32P]ATP, respectively, in the absence of any permeabilizing agent.

Characterization of a new plasma membrane-associated ecto-5'-phosphodiesterase/nucleotide-pyrophosphatase from rat hepatocarcinoma AS-30D cells

We have identified in plasma membrane fractions isolated from rat hepatocarcinoma AS-30D ascites cells three glycoproteins of 125 kDa, 115 kDa and 105 kDa (gp125, gp115 and gp105) which become adenylylated using ATP as substrate, most readily in the presence of EDTA. The gp115 becomes also phosphorylated. The adenylylation of these tumor glycoproteins was much lower than that of a group of analogous adenylylatable glycoproteins (gp130, gp120-gp110 dimer and gp100) present in normal rat liver plasma membrane. The tumor glycoproteins were reversibly O-adenylylated at threonine residues, as was the case for their normal rat liver counterparts. The tumor gp115, and the gp120-gp110 dimer from normal rat liver were both isolated using either ATP-affinity chromatography and/or AMP-affinity chromatography. The gp120-gp110 dimer from normal rat liver was identified as the plasma cell differentiation antigen-1 (PC-1 protein), an ecto-5' phosphodiesterase/ nucleotide-pyrophosphatase (5'-PDE/NPPase). The gp115 from tumor cells also exhibited Zn2+-stimulated 5'-PDE and NPPase activities in alkaline conditions, although it appears to be distinct from the PC-1 protein. We have determined that the gp115 is an ecto-enzyme that catalyzes the hydrolysis of extracellular ATP, since its adenylylation and phosphorylation were detected in intact cells using extracellularly added [alpha-32P]ATP or [gamma-32P]ATP, respectively, in the absence of any permeabilizing agent.

Retinoic acid stimulates HIV-1 transcription in human neuroblastoma SH-SY5Y cells

Although the brain is an important target for the human immunodeficiency virus type 1 (HIV) and viral infection causes neuronal degeneration and dementia, the mechanisms responsible for HIV transcription in neuronal cells are largely unknown. We show here that retinoic acid (RA) stimulates HIV transcription in human neuronal SH-SY5Y cells. The steroid receptor coactivator 1 (SRC-1) enhances the transcriptional response to RA, and the viral protein Tat cooperates with RA and SRC-1 to induce a strong transactivation. These results suggest that retinoid receptors could play an important role as activators of viral gene expression in the human brain.

Oxidative stress triggers STAT3 tyrosine phosphorylation and nuclear translocation in human lymphocytes

Oxidizing agents are powerful activators of factors responsible for the transcriptional activation of cytokine-encoding genes involved in tissue injury. In this study we show evidence that STAT3 is a transcription factor whose activity is modulated by H2O2 in human lymphocytes, in which endogenous catalase had previously been inhibited. H2O2-induced nuclear translocation of STAT3 to form sequence-specific DNA-bound complexes was evidenced by immunoblotting of nuclear fractions and electrophoretic mobility shift assays, and vanadate was found to strongly synergize with H2O2. Moreover, anti-STAT3 antibodies specifically precipitated a protein of 92 kDa that becomes phosphorylated on tyrosine upon lymphocyte treatment with H2O2. Phenylarsine oxide, a tyrosine phosphatase inhibitor, and genistein, a tyrosine kinase inhibitor, cooperated and cancelled, respectively, the H2O2-promoted STAT3 nuclear translocation. Evidence is also presented, using Fe2+/Cu2+ ions, that.OH generated from H2O2 through Fenton reactions could be a candidate oxygen reactive species to directly activate STAT3. Present data suggest that H2O2 and vanadate are likely to inhibit the activity of intracellular tyrosine phosphatase(s), leading to enhanced STAT3 tyrosine phosphorylation and hence its translocation to the nucleus. These results demonstrate that the DNA binding activity of STAT3 can be modulated by oxidizing agents and provide a framework to understand the effects of oxidative stress on the JAK-STAT signaling pathway.

Characterization of calcineurin in human neutrophils. Inhibitory effect of hydrogen peroxide on its enzyme activity and on NF-kappaB DNA binding

We describe here a specific calcineurin activity in neutrophil lysates, which is dependent on Ca2+, inhibited by trifluoroperazine, and insensitive to okadaic acid. Immunoblotting experiments using a specific antiserum recognized both the A and B chains of calcineurin. Neutrophils treated with cyclosporin A or FK 506 showed a dose-dependent inhibition of calcineurin activity. The effect of oxidant compounds on calcineurin activity was also investigated. Neutrophils treated with hydrogen peroxide (H2O2), where catalase was inhibited with aminotriazole, exhibited a specific inhibition of calcineurin activity. However, the addition of reducing agents to neutrophil extracts partially reversed the inhibition caused by H2O2. A similar inhibitory effect of H2O2 on calcineurin activity was observed to occur in isolated lymphocytes. This is the first demonstration that redox agents modulate calcineurin activity in a cellular system. In addition, electrophoretic mobility shift assays revealed that lipopolysaccharide-induced activation of NF-kappaB in human neutrophils is inhibited by cell pretreatment with H2O2 in a dose-dependent manner. These data indicate that calcineurin activity regulates the functional activity of lipopolysaccharide-induced NF-kappaB/Rel proteins in human neutrophils. These data indicate a role of peroxides in the modulation of calcineurin activity and that the H2O2-dependent NF-kappaB inactivation in neutrophils occurs in concert with inhibition of calcineurin.

The human epidermal growth factor receptor contains a juxtamembrane calmodulin-binding site

A ligand-insensitive form of the human epidermal growth factor receptor (EGFR) was enriched by Ca2+-dependent calmodulin-affinity chromatography purification. The basic amphiphilic segment Arg645-Arg-Arg-His-Ile-Val-Arg-Lys-Arg-Thr654-Leu-Arg-Arg-Le u-Leu-Gln 660, located within the cytoplasmic juxtamembrane domain of this receptor, was purified as a fusion protein with glutathione S-transferase and shown to bind calmodulin in a Ca2+-dependent manner. An apparent dissociation constant of 0.4 microM calmodulin (Kd'(CaM)) and an apparent affinity constant of 0.5 microM free Ca2+ (Ka'(Ca)) were measured for this binding process. Binding of calmodulin at the juxtamembrane site prevented the phosphorylation of residue Thr-654 by protein kinase C, and an apparent inhibition constant of 0.5-1 microM calmodulin (Ki'(CaM)) was determined. Conversely, phosphorylation of this site by protein kinase C prevented its subsequent interaction with calmodulin. We therefore propose that cross talk between signaling pathways mediated by calmodulin and protein kinase C occurs at the juxtamembrane domain of the EGFR. This calmodulin-binding sequence is highly conserved among protein tyrosine kinases of the vertebrate EGFR family.

Nitric oxide reversibly inhibits the epidermal growth factor receptor tyrosine kinase

Although it has been demonstrated that NO inhibits the proliferation of different cell types, the mechanisms of its anti-mitotic action are not well understood. In this work we have studied the possible interaction of NO with the epidermal growth factor receptor (EGFR), using transfected fibroblasts which overexpress the human EGFR. The NO donors S-nitroso-N-acetylpenicillamine (SNAP), 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (DEA-NO) and N-{4-[1-(3-aminopropyl)-2-hydroxy-2-nitrosohydrazino]butyl}propane -1, 3-diamine (DETA-NO) inhibited DNA synthesis of fibroblasts growing in the presence of fetal calf serum, epidermal growth factor (EGF) or EGF plus insulin, as assessed by [methyl-3H]thymidine incorporation. Neither 8-bromo-cGMP nor the cGMP-phosphodiesterase inhibitor zaprinast mimicked this effect, suggesting that NO is unlikely to inhibit cell proliferation via a cGMP-dependent pathway. SNAP, DEA-NO and DETA-NO also inhibited the transphosphorylation of the EGFR and its tyrosine kinase activity toward the exogenous substrate poly-l-(Glu-Tyr), as measured in permeabilized cells using [gamma-32P]ATP as phosphate donor. In contrast, 3-[morpholinosydnonimine hydrochloride] (SIN-1), a peroxynitrite-forming compound, did not significantly inhibit either DNA synthesis or the EGFR tyrosine kinase activity. The inhibitory action of DEA-NO on the EGFR tyrosine kinase was prevented by haemoglobin, an NO scavenger, but not by superoxide dismutase, and was reversed by dithiothreitol. The binding of EGF to its receptor was unaffected by DEA-NO. The inhibitory action of DEA-NO on the EGF-dependent transphosphorylation of the receptor was also demonstrated in intact cells by immunoblot analysis using an anti-phosphotyrosine antibody. Taken together, these results suggest that NO, but not peroxynitrite, inhibits in a reversible manner the EGFR tyrosine kinase activity by S-nitrosylation of the receptor.

Ehrlich ascites tumor cells produce a transforming growth factor-beta (TGFbeta)-like activity but lack receptors with TGFbeta-binding capacity

Ehrlich ascites tumor cells incorporate [methyl-3H]thymidine into DNA independently of exogenous growth factors or fetal calf serum. Using an acid/ethanol extraction procedure we have obtained from these tumor cells a fraction that induces both the proliferation and the formation of cell foci by Swiss 3T3 mouse fibroblasts in the presence of insulin; inhibits the proliferation of Mv1Lu mink lung epithelial cells; and stimulates the growth of NRK rat kidney fibroblasts in soft-agar in the presence of epidermal growth factor. An antibody against transforming growth factor-beta (TGFbeta) prevents both the tumor extract-induced proliferation of Swiss 3T3 fibroblasts and the tumor extract-induced proliferative arrest of Mv1Lu cells. The tumor cells secrete a TGF beta-like activity to the extracellular medium in a partially-activated form. However, authentic TGFbeta does not affect their proliferation, and no TGFbeta receptors were detected using [125I]TGFbeta as a ligand. Therefore, the absence of TGFbeta receptors with ligand-binding capacity in these tumor cells may bypass the negative control that this factor exerts on the proliferation of their normal cell counterparts.

Phosphorylation of calmodulin by permeabilized fibroblasts overexpressing the human epidermal growth factor receptor

Detergent-permeabilized EGFR-T17 fibroblasts, which overexpress the human epidermal growth factor (EGF) receptor, phosphorylate both poly-L-(glutamic acid, tyrosine) and exogenous calmodulin in an EGF-stimulated manner. Phosphorylation of calmodulin requires the presence of cationic polypeptides, such as poly-L-(lysine) or histones, which exert a biphasic effect toward calmodulin phosphorylation. Optimum cationic polypeptide/calmodulin molar ratios of 0.3 and 7 were determined for poly-L-(lysine) and histones, respectively. Maximum levels of calmodulin phosphorylation were attained in the absence of free calcium, and a strong inhibition of this process was observed at very low concentrations (Ki = 0.2 microM) of this cation. The incorporation of phosphate into calmodulin occurred predominantly on tyrosine residue(s) and was stimulated 34-fold by EGF.

General distribution of the nitrogen control gene ntcA in cyanobacteria

The ntcA gene from Synechococcus sp. strain PCC 7942 encodes a regulatory protein which is required for the expression of all of the genes known to be subject to repression by ammonium in that cyanobacterium. Homologs to ntcA have now been cloned by hybridization from the cyanobacteria Synechocystis sp. strain PCC 6803 and Anabaena sp. strain PCC 7120. Sequence analysis has shown that these ntcA genes would encode polypeptides strongly similar (77 to 79% identity) to the Synechococcus NtcA protein. Sequences hybridizing to ntcA have been detected in the genomes of nine other cyanobacteria that were tested, including strains of the genera Anabaena, Calothrix, Fischerella, Nostoc, Pseudoanabaena, Synechococcus, and Synechocystis.

Control of Nitrogenase mRNA Levels by Products of Nitrate Assimilation in the Cyanobacterium Anabaena sp. Strain PCC 7120

Nitrate inhibited nitrogenase synthesis and heterocyst development in the cyanobacterium Anabaena sp. strain PCC 7120. Inhibition of dinitrogen fixation by nitrate did not take place, however, in nitrate reductase-deficient derivatives of this strain. Hybridization of total RNA isolated from cells grown on different nitrogen sources with an internal fragment of the nifD gene showed that regulation of nitrogenase activity by nitrate is exerted through a negative control of the nitrogenase mRNA levels.