Antiproliferative effect of nitric oxide on epidermal growth factor-responsive human neuroblastoma cells

Increase of the Intracellular Zinc Concentration Leads to an Activation and Internalisation of the Epidermal Growth Factor Receptor in A549 Cells

(1) Background: Zinc is suggested to play a major role in epidermal growth factor (EGF)-induced cell regeneration and proliferation. To deepen the knowledge on the underlying mechanisms zinc’s effects on the epidermal growth factor receptor (EGFR) activation and its endocytosis was investigated in the alveolar carcinoma cell line A549. (2) Methods: An increase of intracellular zinc was generated by adding zinc extracellularly compared to the intracellular release of zinc from zinc-binding proteins by stimulation with a nitric oxide donor. Zinc-initiated EGFR phosphorylation was checked by Western blotting and receptor endocytosis assays were performed by using flow cytometry. (3) Results: Besides a dose-dependent EGFR phosphorylation, a dose- and time dependent significant receptor internalisation was initiated by both types of zinc increases. In addition, both increased intracellular zinc levels further promoted EGF-induced EGFR phosphorylation and internalisation. (4) Conclusion: This report confirms a transactivating effect of zinc on the EGFR for A549 cells and is the first describing an influence of zinc on the EGFR endocytosis. The transferability of the fine-tuning of EGFR-induced signalling by zinc needs to be verified in vivo, but the presented data underline that zinc might be helpful during treatment of disturbed regeneration and tissue repair.

Updates on Versatile Role of Putative Gasotransmitter Nitric Oxide: Culprit in Neurodegenerative Disease Pathology

Nitric oxide (NO) is a versatile gasotransmitter that contributes in a range of physiological and pathological mechanims depending on its cellular levels. An appropriate concentration of NO is essentially required for cellular physiology; however, its increased level triggers pathological mechanisms like altered cellular redox regulation, functional impairment of mitochondrion, and modifications in cellular proteins and DNA. Its increased levels also exhibit post-translational modifications in protein through S-nitrosylation of their thiol amino acids, which critically affect the cellular physiology. Along with such modifications, NO could also nitrosylate the endoplasmic reticulum (ER)-membrane located sensors of ER stress, which subsequently affect the cellular protein degradation capacity and lead to aggregation of misfolded/unfolded proteins. Since protein aggregation is one of the pathological hallmarks of neurodegenerative disease, NO should be taken into account during development of disease therapies. In this Review, we shed light on the diverse role of NO in both cellular physiology and pathology and discussed its involvement in various pathological events in the context of neurodegenerative diseases.

Molecular and Cellular Mechanisms of Sporadic Alzheimer's Disease: Studies on Rodent Models in vivo

In this review, recent data are presented on molecular and cellular mechanisms of pathogenesis of the most widespread (about 95%) sporadic forms of Alzheimer's disease obtained on in vivo rodent models. Although none of the available models can fully reproduce the human disease, several key molecular mechanisms (such as dysfunction of neurotransmitter systems, especially of the acetylcholinergic system, β-amyloid toxicity, oxidative stress, neuroinflammation, mitochondrial dysfunction, disturbances in neurotrophic systems) are confirmed with different models. Injection models, olfactory bulbectomy, and senescence accelerated OXYS rats are reviewed in detail. These three approaches to in vivo modeling of sporadic Alzheimer's disease have demonstrated a considerable similarity in molecular and cellular mechanisms of pathology development. Studies on these models provide complementary data, and each model possesses its specific advantages. A general analysis of the data reported for the three models provides a multifaceted and the currently most complete molecular picture of sporadic Alzheimer's disease. This is highly relevant also from the practical viewpoint because it creates a basis for elaboration and preclinical studies of means for treatment of this disease.

Power Frequency Magnetic Fields Affect the p38 MAPK-Mediated Regulation of NB69 Cell Proliferation Implication of Free Radicals

The proliferative response of the neuroblastoma line NB69 to a 100 µT, 50 Hz magnetic field (MF) has been shown mediated by activation of the MAPK-ERK1/2 pathway. This work investigates the MF effect on the cell cycle of NB69, the participation of p38 and c-Jun N-terminal (JNK) kinases in the field-induced proliferative response and the potential involvement of reactive oxygen species (ROS) in the activation of the MAPK-ERK1/2 and -p38 signaling pathways. NB69 cultures were exposed to the 100 µT MF, either intermittently for 24, 42 or 63 h, or continuously for periods of 15 to 120 min, in the presence or absence of p38 or JNK inhibitors: SB203580 and SP600125, respectively. Antioxidant N-acetylcysteine (NAC) was used as ROS scavenger. Field exposure induced transient activation of p38, JNK and ERK1/2. The MF proliferative effect, which was mediated by changes in the cell cycle, was blocked by the p38 inhibitor, but not by the JNK inhibitor. NAC blocked the field effects on cell proliferation and p38 activation, but not those on ERK1/2 activation. The MF-induced proliferative effects are exerted through sequential upregulation of MAPK-p38 and -ERK1/2 activation, and they are likely mediated by a ROS-dependent activation of p38.

Effects of nitric oxide modulating activities on development of enteric nervous system mediated gut motility in chick embryo model

The enteric nervous system (ENS) arises from the enteric neural crest-derived cells (ENCCs), and many molecules and biochemical processes may be involved in its development. This study examined the effects of modulating embryonic nitric oxide (NO) activity on the intestinal motility induced by ENS. One-hundred-and-twenty fertilized chicken eggs were assigned to three main groups and incubated at 37 degrees Centigrade and 60 percent humidity. The eggs were treated with NG-nitro-Larginine methyl ester (L-NAME), sodium nitroprusside (SNP), L-arginine (L-Arg) or vehicle from days 3 (1st group), 7 (2nd group) and 10 (3rd group) of incubation and continued up to day 18. On day 19, the embryos were sacrificed, the jejunal and colorectal segments were taken and the intestinal motility was assessed using isolated organ system. The intestinal motility was recorded normally and following cholinergic, adrenergic and non-adrenergic non-cholinergic (NANC) stimulations. The ENS structure was assessed by immunohistochemistry (IHC) using glial fibrillary acidic protein (GFAP). Rhythmic intestinal contractions were seen in all treatment groups, but inhibition of NO in the LNAME- treated embryos caused significant decrease (p less than 0.01) in the frequency and amplitude of the contraction. The responsiveness to adrenergic, cholinergic and NANC stimulations was also significantly decreased (p less than 0.05). The GFAP expression was significantly (p less than 0.05) reduced in the L-NAME-treated embryos. This study showed that the inhibition of NO caused a deficient development of the ENS, leading to a decrease in the frequency and amplitude of the intestinal contractions and reduced the responsiveness to adrenergic, cholinergic and NANC signalling.

sGC-cGMP signaling: target for anticancer therapy

The biologic endogenous production of cGMP was reported in the 1960s and followed by the demonstration of guanylyl cyclase activity and the isoforms of soluble and membrane-bound guanylyl cyclases. During the same period, cGMP specific phosphodiesterases also was discovered. Murad's lab established link between the endothelium derived relaxation factor (EDRF) and elevated cGMP concentration in the vascular system. October 12, 1998, the Nobel Assembly awarded the Nobel Prize in Medicine or Physiology to scientists Robert Furchgott, Louis Ignarro, and Ferid Murad for their discoveries concerning nitric oxide (NO) as a signaling molecule in the cardiovascular system. In contrast with the short research history of the enzymatic synthesis of NO, the introduction of nitrate-containing compounds for medicinal purposes marked its 150th anniversary in 1997. Glyceryl trinitrate (nitroglycerin; GTN) is the first compound of this category. Alfred Nobel (the founder of the Nobel Prize) himself had suffered from angina pectoris and was prescribed nitroglycerin for his chest pain while he refused to take due to the induction of headaches. Almost a century after its first chemical use, research in the nitric oxide and 3',5'-cyclic guanosine monophosphate (NO/cGMP) pathway has dramatically expanded and the role of NO/cGMP in physiology and pathology has been extensively studied. Soluble guanylyl cyclase (sGC) is the receptor for NO. The α1β1 heterodimer is the predominant isoform of sGC that is obligatory for catalytic activity. NO binds to the ferrous (Fe(2+)) heme at histidine 105 of the β1 subunit and leads to an increase in sGC activity and cGMP production of at least 200-fold. In this chapter, we reviewed the studies of sGC-cGMP signaling in cell proliferation; introduced our work of targeting sGC-cGMP signaling for cancer therapy; and explored the role of sGC-cGMP signaling in the chromatin-microenvironment.

Nitric oxide from inflammatory origin impairs neural stem cell proliferation by inhibiting epidermal growth factor receptor signaling

Neuroinflammation is characterized by activation of microglial cells, followed by production of nitric oxide (NO), which may have different outcomes on neurogenesis, favoring or inhibiting this process. In the present study, we investigated how the inflammatory mediator NO can affect proliferation of neural stem cells (NSCs), and explored possible mechanisms underlying this effect. We investigated which mechanisms are involved in the regulation of NSC proliferation following treatment with an inflammatory stimulus (lipopolysaccharide plus IFN-γ), using a culture system of subventricular zone (SVZ)-derived NSCs mixed with microglia cells obtained from wild-type mice (iNOS(+/+)) or from iNOS knockout mice (iNOS(-/-)). We found an impairment of NSC cell proliferation in iNOS(+/+) mixed cultures, which was not observed in iNOS(-/-) mixed cultures. Furthermore, the increased release of NO by activated iNOS(+/+) microglial cells decreased the activation of the ERK/MAPK signaling pathway, which was concomitant with an enhanced nitration of the EGF receptor. Preventing nitrogen reactive species formation with MnTBAP, a scavenger of peroxynitrite (ONOO(-)), or using the ONOO(-) degradation catalyst FeTMPyP, cell proliferation and ERK signaling were restored to basal levels in iNOS(+/+) mixed cultures. Moreover, exposure to the NO donor NOC-18 (100 μM), for 48 h, inhibited SVZ-derived NSC proliferation. Regarding the antiproliferative effect of NO, we found that NOC-18 caused the impairment of signaling through the ERK/MAPK pathway, which may be related to increased nitration of the EGF receptor in NSC. Using MnTBAP nitration was prevented, maintaining ERK signaling, rescuing NSC proliferation. We show that NO from inflammatory origin leads to a decreased function of the EGF receptor, which compromised proliferation of NSC. We also demonstrated that NO-mediated nitration of the EGF receptor caused a decrease in its phosphorylation, thus preventing regular proliferation signaling through the ERK/MAPK pathway.

Mig6 haploinsufficiency protects mice against streptozotocin-induced diabetes

AIMS/HYPOTHESIS

EGF and gastrin co-administration reverses type 1 diabetes in rodent models. However, the failure of this to translate into a clinical treatment suggests that EGF-mediated tissue repair is a complicated process and warrants further investigation. Thus, we aimed to determine whether EGF receptor (EGFR) feedback inhibition by mitogen-inducible gene 6 protein (MIG6) limits the effectiveness of EGF therapy and promotes type 1 diabetes development.

METHODS

We treated Mig6 (also known as Errfi1) haploinsufficient mice (Mig6 (+/-)) and their wild-type littermates (Mig6 (+/+)) with multiple low doses of streptozotocin (STZ), and monitored diabetes development via glucose homeostasis tests and histological analyses. We also investigated MIG6-mediated cytokine-induced desensitisation of EGFR signalling and the DNA damage repair response in 832/13 INS-1 beta cells.

RESULTS

Whereas STZ-treated Mig6 (+/+) mice became diabetic, STZ-treated Mig6 (+/-) mice remained glucose tolerant. In addition, STZ-treated Mig6 (+/-) mice exhibited preserved circulating insulin levels following a glucose challenge. As insulin sensitivity was similar between Mig6 (+/-) and Mig6 (+/+) mice, the preserved glucose tolerance in STZ-treated Mig6 (+/-) mice probably results from preserved beta cell function. This is supported by elevated Pdx1 and Irs2 mRNA levels in islets isolated from STZ-treated Mig6 (+/-) mice. Conversely, MIG6 overexpression in isolated islets compromises glucose-stimulated insulin secretion. Studies in 832/13 cells suggested that cytokine-induced MIG6 hinders EGFR activation and inhibits DNA damage repair. STZ-treated Mig6 (+/-) mice also have increased beta cell mass recovery.

CONCLUSIONS/INTERPRETATION

Reducing Mig6 expression promotes beta cell repair and abates the development of experimental diabetes, suggesting that MIG6 may be a novel therapeutic target for preserving beta cells.

Paracrine regulation of neural stem cells in the subependymal zone

Stem cells maintain their self-renewal and multipotency capacities through a self-organizing network of transcription factors and intracellular pathways activated by extracellular signaling from the microenvironment or "niche" in which they reside in vivo. In the adult mammalian brain new neurons continue to be generated throughout life of the organisms and this lifelong process of neurogenesis is supported by a reservoir of neural stem cells in the germinal regions. The discovery of adult neurogenesis in the mammalian brain has sparked great interest in defining the conditions that guide neural stem cell (NSC) maintenance and differentiation into the great variety of neuronal and glial subtypes. Here we review current knowledge regarding the paracrine regulation provided by the components of the niche and its function, focusing on the main germinal region of the adult central nervous system (CNS), the subependymal zone (SEZ).

Involvement of NOS3 in RA-Induced neural differentiation of human NT2/D1 cells

Nitric oxide (NO) plays a key role in neurogenesis as a regulator of cell proliferation and differentiation. NO is synthesized from the amino acid L-arginine by nitric oxide synthases (NOS1, NOS2, and NOS3), which are encoded by separate genes and display different tissue distributions. We used an in vitro model of RA-induced neural differentiation of NT2 cells to examine which of the three NO-synthesizing enzymes is involved in this process. The results revealed a transient induction of NOS3 (known as the constitutively expressed endothelial nitric oxide synthase; eNOS) during the time course of the RA treatment. The peak of gene expression and the nuclear presence of NOS3 protein coincided with cell cycle exit of NT2-derived neuronal precursors. The subsequent analysis of cytosine methylation and histone H3 acetylation of the human NOS3 5' regulatory sequences indicated that epigenetic modifications, especially upstream of the proximal promoter (-734 to -989, relative to exon 2 TSS at +1), were also taking place. NOS1 was expressed only in the differentiated neurons (NT2-N), whereas NOS2 was not expressed at all in this cellular model. Thus, a burst of NO production, possibly required to inhibit neural cell proliferation, was generated by the transient expression of NOS3. This pattern of gene expression, in turn, required epigenetic remodeling of its regulatory region.

L-N-iminoethyl-lysine after experimental brain trauma attenuates cellular proliferation and astrocyte differentiation

BACKGROUND

The effects, and thereby possible benefit, of inhibiting nitric oxide synthases (NOS) after brain injury are not fully understood. Nitric oxide (NO) has both neuroprotective and damaging features, and its effect on the cellular proliferation and differentiation that occurs in response to traumatic brain injury (TBI) is largely unknown. This study was undertaken to investigate the effects of the selective inducible NOS-inhibitor, L-N-iminoethyl-lysine (L-NIL), on proliferating cell populations in rat brain areas with self-renewing capacity.

METHODS

A brain contusion was produced using a weight-drop model in rats. Animals received treatment with L-NIL or saline, and were killed after 6 days. Brain sections were stained with a cell marker of proliferation, Ki67, to detect dividing cells in the hippocampus, perilesional zone and the subventricular zone (SVZ).

RESULTS

A significant decrease of proliferating cells was seen in the SVZ bilaterally in L-NIL-treated animals compared to controls. Hippocampal proliferation showed a tendency to decrease in L-NIL-treated animals that did not reach statistical significance. Perilesional proliferation was equal in the treatment group and controls. The percentage of proliferating GFAP expressing cells was, however, lower in L-NIL-treated animals. The proliferating cell populations were predominantly immunoreactive for GFAP, while a smaller population was immunoreactive for Nestin. The inhibition of inducible NOS with L-NIL attenuated the level of cellular proliferation and influenced the differentiation of astrocytes at 6 days after experimental brain contusion.

CONCLUSIONS

Our results confirmed that reactive glial cells dominated the proliferating cell population after TBI and suggested that NO-regulated mechanisms are relevant for post-traumatic cellular proliferation and differentiation, since NO inhibition decreased the number of proliferating cells in the SVZ and the proportion of proliferating cells expressing GFAP, a marker of glial proliferation.

Activation of the BRCA1/Chk1/p53/p21(Cip1/Waf1) pathway by nitric oxide and cell cycle arrest in human neuroblastoma NB69 cells

Nitric oxide (NO) works as a bi-modal effector of cell proliferation, inducing either the increase or decrease of cell growth when cells are exposed, respectively, to low or high NO concentrations. To get further insight into the action of NO, we tested the effect of short- and long-lived NO donors on the control of the cell cycle in human neuroblastoma NB69 cells. We demonstrated that long-time exposure of cells to NO not only decreased the expression and/or the phosphorylation of elements involved in the control of the G(1)/S transition, such as the transcriptional repressor pRb and cyclin D1, but also down-regulated systems controlling the S and G(2)/M phases, such as the phosphorylation of Cdk1(cdc2) and the expression of cyclins A and B1. Increasing concentrations of NO also induced a biphasic effect on the expression of cyclins D1, A and B1, while this effect was less pronounced for cyclin E expression, but the levels of mRNAs of those cyclins changed in a distinct and complex manner. NO also changed the phosphorylation pattern of cyclin E and decreased the levels of phospho-cyclins D1 and B1. Moreover, NO decreased the expression of the Cdk inhibitors p16(Ink4a) and p19(Ink4d), without affecting p27(Kip1). In contrast, NO induced a biphasic effect on p21(Cip1/Waf1) expression. The BRCA1/Chk1/p53 pathway mediated the upregulation of p21(Cip1/Waf1). We also demonstrated that the NO-mediated up-regulation of p21(Cip1/Waf1) was inversely correlated with the activation status of the p38MAPK pathway.

Restoring soluble guanylyl cyclase expression and function blocks the aggressive course of glioma

The NO and cGMP signaling pathways are of broad physiological and pathological significance. We compared the NO/soluble guanylyl cyclase (sGC)/cGMP pathway in human glioma tissues and cell lines with that of healthy control samples and demonstrated that sGC expression is significantly lower in glioma preparations. Our analysis of GEO databases (National Cancer Institute) further revealed a statistically significant reduction of sGC transcript levels in human glioma specimens. On the other hand, the expression levels of particulate (membrane) guanylyl cyclases (pGC) and cGMP-specific phosphodiesterase (PDE) were intact in the glioma cells that we have tested. Pharmacologically manipulating endogenous cGMP generation in glioma cells through either stimulating pGC by ANP/BNP, or blocking PDE by 3-isobutyl-1-methylxanthine/zaprinast caused significant inhibition of proliferation and colony formation of glioma cells. Genetically restoring sGC expression also correlated inversely with glioma cells growth. Orthotopic implantation of glioma cells transfected with an active mutant form of sGC (sGCα1β1(Cys105)) in athymic mice increased the survival time by 4-fold over the control. Histological analysis of xenografts overexpressing α1β1(Cys105) sGC revealed changes in cellular architecture that resemble the morphology of normal cells. In addition, a decrease in angiogenesis contributed to glioma inhibition by sGC/cGMP therapy. Our study proposes the new concept that suppressed expression of sGC, a key enzyme in the NO/cGMP pathway, may be associated with an aggressive course of glioma. The sGC/cGMP signaling-targeted therapy may be a favorable alternative to chemotherapy and radiotherapy for glioma and perhaps other tumors.

An early decrease in cell proliferation after pentylenetetrazole-induced seizures

There are increasing data on the influence of seizures on neurogenesis in the adult brain. However, data on cell proliferation and differentiation during the early stages of kindling are scarce. We have used pentylenetetrazole (PTZ)-induced kindling to investigate the temporal profile of cytogenesis in the germinative zones of adult rat brain. For comparison, we also used a single PTZ-induced generalized tonic-clonic seizure. During kindling development, the density of 5-bromo-2'-deoxyuridine-positive cells demonstrated similar changes in all germinative zones: a dramatic decrease after the first subthreshold PTZ injection, and a gradual increase to the control level following repeated PTZ administration. On the contrary, a single PTZ-induced generalized tonic-clonic seizure was followed by an increase in the number of proliferating cells in both the dentate gyrus and the subventricular zone. These results may indicate the existence of global mechanisms affecting cellular proliferation in adult brain during seizures. Different temporal profiles of neuronal damage and proliferation changes suggest that neurodegeneration is unlikely to be a global proliferation-regulating factor. The data may contribute to better understanding of the initial phase of kindling development and epileptogenesis.

Nitric oxide changes distinct aspects of the glycophenotype of human neuroblastoma NB69 cells

It is an open question whether the presence of nitric oxide (NO) affects the cell glycophenotype. A panel of six plant lectins was used in this study to monitor distinct aspects of cell surface glycosylation under nitrosative stress. We determined that treating human neuroblastoma NB69 cells with the long-lived NO donor 2,2'-(hydroxynitrosohydrazono)bis-ethanimine (DETA/NO) and monitoring the non-apoptotic adherent cell population significantly increases the presentation of N-glycans as detected by concanavalin A. Examining fine-structural features, bisected N-glycans and branch-end tailoring including α2,6-sialylation were found to be enhanced. Confocal fluorescence microscopy and cell permeabilization experiments pointed to a major effect of NO on the extent of cell surface N-glycan presentation. We also show that NO increases the level of protein O-GlcNAcylation, a multifunctional post-translational modification. Our results thus establish the first evidence for NO as modulator of distinct aspects of cell glycosylation.

S-Nitrosylation of the epidermal growth factor receptor: a regulatory mechanism of receptor tyrosine kinase activity

Nitric oxide (NO) donors inhibit the epidermal growth factor (EGF)-dependent auto(trans)phosphorylation of the EGF receptor (EGFR) in several cell types in which NO exerts antiproliferative effects. We demonstrate in this report that NO inhibits, whereas NO synthase inhibition potentiates, the EGFR tyrosine kinase activity in NO-producing cells, indicating that physiological concentrations of NO were able to regulate the receptor activity. Depletion of intracellular glutathione enhanced the inhibitory effect of the NO donor 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (DEA/NO) on EGFR tyrosine kinase activity, supporting the notion that such inhibition was a consequence of an S-nitrosylation reaction. Addition of DEA/NO to cell lysates resulted in the S-nitrosylation of a large number of proteins including the EGFR, as confirmed by the chemical detection of nitrosothiol groups in the immunoprecipitated receptor. We prepared a set of seven EGFR(C --> S) substitution mutants and demonstrated in transfected cells that the tyrosine kinase activity of the EGFR(C166S) mutant was completely resistant to NO, whereas the EGFR(C305S) mutant was partially resistant. In the presence of EGF, DEA/NO significantly inhibited Akt phosphorylation in cells transfected with wild-type EGFR, but not in those transfected with C166S or C305S mutants. We conclude that the EGFR can be posttranslationally regulated by reversible S-nitrosylation of C166 and C305 in living cells.

Activation of epidermal growth factor receptor and its downstream signaling pathway by nitric oxide in response to ionizing radiation

Epidermal growth factor receptor (EGFR) is activated by ionizing radiation (IR), but the molecular mechanism for this effect is unknown. We have found that intracellular generation of nitric oxide (NO) by NO synthase (NOS) is required for the rapid activation of EGFR phosphorylation by IR. Treatment of A549 lung cancer cells with IR increased NOS activity within minutes, accompanied by an increase of NO. 2-Phenyl-4,4,5,5,-tetramethylimidazolline-1-oxyl-3-oxide, an NO scavenger, and NG-monomethyl-l-arginine, an NOS inhibitor, abolished the increase in intracellular NO and activation of EGFR by IR. In addition, an NO donor alone induced EGFR phosphorylation. Transient transfection with small interfering RNA for endothelial NOS reduced IR-induced NO production and suppressed IR-induced EGFR activation. Overexpression of endothelial NOS increased IR-induced NO generation and EGFR activation. These results indicate a novel molecular mechanism for EGFR activation by IR-induced NO production via NOS.

Age-dependent effect of nitric oxide on subventricular zone and olfactory bulb neural precursor proliferation

Nitric oxide (NO) synthase (NOS) is developmentally regulated in the embryonic brain, where NO participates in cell proliferation, survival, and differentiation. In adults, NO inhibits neurogenesis under physiological conditions. This work investigates whether the NO action is preserved all along development up to adulthood or whether its effects in adults are a new feature acquired during brain maturation. The relationship between nitrergic neurons and precursors, as well as the functional consequences of pharmacological NOS inhibition, were comparatively analyzed in the subventricular zone (SVZ) and olfactory bulb (OB) of postnatal (P7) and adult (>P60) mouse brains. The SVZ was markedly reduced between P7 and adults, and, at both ages, neurons expressing neuronal NOS (nNOS) were found in its striatal limits. In postnatal mice, these nitrergic neurons contained PSA-NCAM, and their projections were scarce, whereas, in adults, mature nitrergic neurons, devoid of PSA-NCAM, presented abundant neuropil. In the OB, local proliferation almost disappeared in the transition to adulthood, and periglomerular nitrergic neurons, some of which were PSA-NCAM positive, were found in postnatal and adult mice. Administration of the NOS inhibitor L-NAME did not affect cell proliferation in the SVZ or in the OB of postnatal mice, whereas it significantly enhanced the number of mitotic cells in both regions in adults. Thus, the NO action on SVZ neurogenesis is a phenomenon that appears after the postnatal age, which is probably due to the germinal layer size reduction, allowing exposure of the NO-sensitive neural precursors to the NO produced in the SVZ-striatum limits.

Differential p38 mitogen-activated protein kinase-controlled hypophosphorylation of the retinoblastoma protein induced by nitric oxide in neuroblastoma cells

In this report we show that exogenous NO added to human neuroblastoma NB69 cells inhibits cell proliferation and downregulates the epidermal growth factor receptor (EGFR) and its downstream signaling pathways. These comprise the 3-phosphoinositide-dependent kinase 1/Akt/glycogen synthase kinase-3beta pathway, the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinases 1 and 2 pathway, and the phospholipase Cgamma pathway. In contrast, NO enhances the EGFR-controlled p38MAPK pathway. We also show that NO enhances the activation of the cAMP-responsive element binding protein, a transcription factor controlled by p38MAPK, as demonstrated using 4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole (SB202190), a p38MAPK inhibitor. These processes are accompanied by the NO-mediated hypophosphorylation of the retinoblastoma protein (pRb), preferentially at Ser795 compared to Ser780 and Ser807/811, and the downregulation of p27(KIP1), p21(CIP1/WAF1), and p16(INK4a), although NO downregulated p16(INK4a) only when the p38MAPK activity was suppressed. The p38MAPK pathway controls the phosphorylation status of pRb as SB202190 enhances the hypophosphorylation of pRb. We reverted the inhibitory action of NO on EGFR and pRb phosphorylation in living cells using cell-permeable reducing agents, which suggested that reversible S-nitrosation controls these proteins. Our results support the notion that NO negatively modulates the p38MAPK-controlled phosphorylation of pRb, inducing the subsequent arrest of the cell cycle at the G1/S transition.

Chronic inhibition of nitric oxide synthesis enhances both subventricular zone neurogenesis and olfactory learning in adult mice

The ability to generate new neurons during the course of adult life is preserved in the subventricular zone of the lateral ventricles and the dentate gyrus of the hippocampus in the mammalian brain. These two regions constitute specifically regulated neurogenic niches, and provide newborn neurons involved in olfactory and spatial learning, respectively. Nitric oxide (NO) is a negative regulator of neurogenesis in the subventricular zone, whereas its role in the dentate gyrus remains controversial. Using systemic administration of NO synthase (NOS) inhibitors to chronically inhibit NO production, we increased neural precursor proliferation in the subventricular zone as well as neurogenesis in the olfactory bulb, without modifying the number of mitotic cells or the granular cell layer thickness in the dentate gyrus. The same treatment specifically improved olfactory learning performance, whereas spatial learning and memory was unchanged, thus demonstrating that olfactory memory is closely associated with the level of ongoing neurogenesis in the subventricular zone-olfactory bulb. The anatomical specificity of the NOS inhibitor actions was not due to differences in the availability of NO, as demonstrated by immunohistochemical detection of neuronal NOS and S-nitrosylated proteins in both regions. Remarkably, the distinct NO sensitivity might result from a differential expression of epidermal growth factor receptor in precursor cells in both regions, as the proliferative effect of NOS inhibitors in the subventricular zone was restricted to the cells that expressed this receptor.

Nitric oxide decreases subventricular zone stem cell proliferation by inhibition of epidermal growth factor receptor and phosphoinositide-3-kinase/Akt pathway

Nitric oxide (NO) inhibits proliferation of subventricular zone (SVZ) neural precursor cells in adult mice in vivo under physiological conditions. The mechanisms underlying this NO effect have now been investigated using SVZ-derived neural stem cells, which generate neurospheres in vitro when stimulated by epidermal growth factor (EGF). In these cultures, NO donors decreased the number of newly formed neurospheres as well as their size, which indicates that NO was acting on the neurosphere-forming neural stem cells and the daughter neural progenitors. The effect of NO was cytostatic, not proapoptotic, and did not involve cGMP synthesis. Neurosphere cells expressed the neuronal and endothelial isoforms of NO synthase (NOS) and produced NO in culture. Inhibition of NOS activity by N(omega)-nitro-L-arginine methylester (L-NAME) promoted neurosphere formation and growth, thus revealing an autocrine/paracrine action of NO on the neural precursor cells. Both exogenous and endogenous NO impaired the EGF-induced activation of the EGF receptor (EGFR) tyrosine kinase and prevented the EGF-induced Akt phosphorylation in neurosphere cells. Inhibition of the phosphoinositide-3-kinase (PI3-K)/Akt pathway by LY294002 significantly reduced the number of newly formed neurospheres, which indicates that this is an essential pathway for neural stem cell self-renewal. Chronic administration of l-NAME to adult mice enhanced phospho-Akt staining in the SVZ and reduced nuclear p27(Kip1) in the SVZ and olfactory bulb. The inhibition of EGFR and PI3-K pathway by NO explains, at least in part, its antimitotic effect on neurosphere cells and may be a mechanism involved in the physiological role of NO as a negative regulator of SVZ neurogenesis in adult mice.

Nitric oxide and cell proliferation

Nitric oxide (NO*) has been proposed to be a physiological modulator of cell proliferation, able to promote in most cases cell cycle arrest. In this review I explore the molecular basis of this mechanism of action. The modulatory action of NO* on the intracellular concentration of cGMP and the machinery directly involved in the control of cell cycle progression, including the expression and activity of diverse cyclins and cyclin-dependent kinases, their physiological inhibitors, and the master transcriptional regulator retinoblastoma protein, will be discussed. The role of NO* in proliferation mediated by tyrosine kinase receptors such as the epidermal growth factor receptor and downstream signalling pathways will also be considered. Finally, the involvement of NO* in proliferative processes relevant for normal development will be outlined.

Proliferation of cerebellar precursor cells is negatively regulated by nitric oxide in newborn rat

The diffusible messenger, nitric oxide plays multiple roles in neuroprotection, neurodegeneration and brain plasticity. Its involvement in neurogenesis has been disputed, on the basis of results on models in vivo and in culture. We report here that pharmacological blockade of nitric oxide production in rat pups resulted, during a restricted time window of the first three postnatal days, in increased cerebellar proliferation rate, as assessed through tritiated thymidine or BrdU incorporation into DNA. This was accompanied by increased expression of Myc, a transcription factor essential for cerebellar development, and of the cell cycle regulating gene, cyclin D1. These effects were mediated downstream by the nitric oxide-dependent second messenger, cGMP. Schedules of pharmacological NO deprivation targeted to later developmental stages (from postnatal day 3 to 7), no longer increased proliferation, probably because of partial escape of the cGMP level from nitric oxide control. Though limited to a brief temporal window, the proliferative effect of neonatal nitric oxide deprivation could be traced into adulthood. Indeed, the number of BrdU-labeled surviving cells, most of which were of neuronal phenotype, was larger in the cerebellum of 60-day-old rats that had been subjected to NO deprivation during the first three postnatal days than in control rats. Experiments on cell cultures from neonatal cerebellum confirmed that nitric oxide deprivation stimulated proliferation of cerebellar precursor cells and that this effect was not additive with the proliferative action of sonic hedgehog peptide. The finding that nitric oxide deprivation during early cerebellar neurogenesis, stimulates a brief increase in cell proliferation may contribute to a better understanding of the controversial role of nitric oxide in brain development.

Regulation of Neuronal Nitric-oxide Synthase Activity by Somatostatin Analogs following SST5 Somatostatin Receptor Activation

Somatostatin receptor SST5 is an inhibitory G protein-coupled receptor that exerts a strong cytostatic effect on various cell types. We reported previously that the SST5 anti-proliferative effect results in the inhibition of mitogen-induced increases in intracellular cGMP levels and MAPK activity. This study was conducted to define the early molecular events accountable for the SST5-mediated anti-proliferative effect. Here, we demonstrate that, in Chinese hamster ovary cells expressing SST5 (CHO/SST5 cells), somatostatin inhibited cell proliferation induced by nitric oxide donors and overexpression of the neuronal nitric-oxide synthase (nNOS) protein isoform. Accordingly, nNOS activity and dimerization were strongly inhibited following SST5 activation by the somatostatin analog RC-160. In CHO/SST5 cells, nNOS was dynamically recruited by the SST5 receptor and phosphorylated at tyrosyl residues following RC-160 treatment. RC-160 induced SST5-p60(src) kinase complex formation and subsequent p60(src) kinase activation. Coexpression of an inactive p60(src) kinase mutant with SST5 blocked RC-160-induced nNOS phosphorylation and inactivation and prevented the SST5-mediated anti-proliferative effect. In CHO/SST5 cells, p60(src) kinase associated with nNOS to induce its inactivation by phosphorylation at tyrosyl residues following RC-160 treatment. Using recombinant proteins, we demonstrated that such phosphorylation prevented nNOS homodimerization. Next, surface plasmon resonance and mutation analysis revealed that p60(src) directly associated with nNOS phosphorylated Tyr604. SST5-mediated inhibition of nNOS activity was demonstrated to be essential to the RC-160 anti-proliferative effect on pancreatic endocrine tumor-derived cells. We therefore identified nNOS as a new p60(src) kinase substrate essential for SST5-mediated anti-proliferative action.

Role of intracellular Ca2+ and calmodulin/MAP kinase kinase/extracellular signal-regulated protein kinase signalling pathway in the mitogenic and antimitogenic effect of nitric oxide in glia- and neurone-derived cell lines

To elucidate the mechanism of cell growth regulation by nitric oxide (NO) and the role played in it by Ca2+, we studied the relationship among intracellular Ca2+ concentration ([Ca2+]i), mitogen-activated protein kinases [extracellular signal-regulated protein kinase (ERK)] and proliferation in cell lines exposed to different levels of NO. Data showed that NO released by low [(z)-1-[2-aminiethyl]-N-[2-ammonioethyl]amino]diazen-1-ium-1,2diolate (DETA/NO) concentrations (10 microm) determined a gradual, moderate elevation in [Ca2+]i (46.8 +/- 7.2% over controls) which paralleled activation of ERK and potentiation of cell division. Functionally blocking Ca2+ or inhibiting calmodulin or MAP kinase kinase activities prevented ERK activation and antagonized the mitogenic effect of NO. Experimental conditions favouring Ca2+ entry into cells led to increased [Ca2+]i (189.5 +/- 4.8%), ERK activation and cell division. NO potentiated the Ca2+ elevation (358 +/- 16.8%) and ERK activation leading to expression of p21Cip1 and inhibition of cell proliferation. Furthermore, functionally blocking Ca2+ down-regulated ERK activation and reversed the antiproliferative effect of NO. Both the mitogenic and antimitogenic responses induced by NO were mimicked by a cGMP analogue whereas they were completely antagonized by selective cGMP inhibitors. These results demonstrate for the first time that regulation of cell proliferation by low NO levels is cGMP dependent and occurs via the Ca2+/calmodulin/MAP kinase kinase/ERK pathway. In this effect the amplitude of Ca2+ signalling determines the specificity of the proliferative response to NO possibly by modulating the strength of ERK activation. In contrast to the low level, the high levels (50-300 microm) of DETA/NO negatively regulated cell proliferation via a Ca2+-independent mechanism.

Programmed cell death in the apical ganglion during larval metamorphosis of the marine mollusc Ilyanassa obsoleta

The apical ganglion (AG) of larval caenogastropods, such as Ilyanassa obsoleta, houses a sensory organ, contains five serotonergic neurons, innervates the muscular and ciliary components of the velum, and sends neurites into a neuropil that lies atop the cerebral commissure. During metamorphosis, the AG is lost. This loss had been postulated to occur through some form of programmed cell death (PCD), but it is possible for cells within the AG to be respecified or to migrate into adjacent ganglia. Evidence from histological sections is supported by results from a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, which indicate that cells of the AG degenerate by PCD. PCD occurs after metamorphic induction by serotonin or by inhibition of nitric oxide synthase (NOS) activity. Cellular degeneration and nuclear condensation and loss were observed within 12 h of metamorphic induction by NOS inhibition and occur before loss of the velar lobes, the ciliated tissue used for larval swimming and feeding. Velar disintegration happens more rapidly after metamorphic induction by serotonin than by 7-nitroindazole, a NOS inhibitor. Loss of the AG was complete by 72 h after induction. Spontaneous loss of the AG in older competent larvae may arise from a natural decrease in endogenous NOS activity, giving rise to the tendency of aging larvae to display spontaneous metamorphosis in culture.

Proliferation of human neuroblastomas mediated by the epidermal growth factor receptor

Neuroblastoma is a common solid tumor of childhood that is derived from the neural crest. Expression of epidermal growth factor (EGF) receptors (EGFRs) has been associated with enhanced cell growth and aggressive behavior in other tumors. Here, we examined the expression profile of EGFRs in neuroblastoma cell lines and primary tumors. We found that all 13 neuroblastoma cell lines examined expressed EGFR1 (HER1), most at readily detectable levels. Low levels of other human EGFR family receptors were also detected in almost all cell lines. All primary tumors examined expressed readily detectable levels of HER1 and HER3 and lower levels of HER2 and HER4. EGF had a significant effect on the proliferation of neuroblastoma cell lines in vitro. EGF treatment (100 ng/mL) of the cell lines SY5Y and NLF significantly increased cell number (P < 0.01). EGF stimulated more cells to enter S and G2-M phase, as suggested by flow cytometry, indicating that EGF increases cell number by increasing proliferation, with no appreciable change in apoptosis. EGF exposure resulted in receptor autophosphorylation and activation of both the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT pathways. Exposure to 0.5 micromol/L ZD1839, a HER1-specific inhibitor, caused a 40% to 50% reduction in the number of SY5Y and NLF cells grown in medium containing 10% fetal bovine serum (P < 0.01). Even at 0.01 micromol/L, ZD1839 inhibited autophosphorylation of HER1 by EGF. At 0.1 micromol/L, it also blocked phosphorylation of AKT, but not MAPK, in NLF cells. Additional studies showed that the PI3K/AKT-specific inhibitor LY294002 had a more profound effect than the MAPK-specific inhibitor U0126 in blocking EGF-induced cell proliferation. This suggests that the PI3K/AKT pathway is the main signaling pathway responsible for the proliferation effects of EGF in neuroblastomas. Our results also indicate that ZD1839 is a potent inhibitor of neuroblastoma cell proliferation; therefore, it may be a useful, biologically based therapeutic agent for these tumors.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

Role of nitric oxide in subventricular zone neurogenesis

A possible role of nitric oxide (NO) in adult neurogenesis has been suggested based on anatomical findings showing that subventricular zone (SVZ) neuroblasts are located close to NO-producing cells, and on the known antiproliferative actions of NO in many cell types. Experiments have been performed in rodents with systemic and intracerebroventricular administrations of the NO synthase (NOS) inhibitor L-NAME. NOS inhibition leads to significant increases in the number of proliferating cells in the SVZ and olfactory bulb (OB). NO exerts its cytostatic action preferentially on the cell population expressing nestin but not betaIII-tubulin, which may correspond to the type C cells described in the SVZ. The negative effect of NO on SVZ cell proliferation has also been confirmed in SVZ primary cultures. An inhibition of the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) is described as one of the molecular mechanisms responsible for the antiproliferative effect of NO in SVZ cells. Biochemical data supporting this conclusion has been obtained using the neuroblastoma cell line NB69, which endogenously expresses the EGFR. In these cells, the antimitotic action of NO occurs upon inhibition of the EGFR tyrosine phosphorylation, probably by a direct S-nitrosylation of the receptor. The latest published reports on NO and neurogenesis indicate that NO physiologically participates in the control of adult neurogenesis by modulating the proliferation and fate of the SVZ progenitor cells. These effects might be partially due to a direct inhibition of the EGFR by S-nitrosylation.

Age-Related Changes of NADPH-Diaphorase Positivity in the Rat Rostral Migratory Stream

Accumulating evidence confirms that nitric oxide (NO), a versatile diffusible signaling molecule, contributes to controling of adult neurogenesis. We have previously shown the timing of NADPH-diaphorase (NADPH-d) positivity within the rat rostral migratory stream (RMS) during the first postnatal month. The present study was designed to describe further age-related changes of NO presence in this neurogenic region. The presence of NO synthesizing cells in the RMS was shown by NADPH-d histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry. The phenotypic identity of nitrergic cells was examined by double labeling with GFAP and NeuN. Systematic qualitative and quantitative analysis of NADPH-d-positive cells was performed in the neonatal (P14), adult(5 months) and aging (20 months) rat RMS. 1. Nitrergic cells with different distribution pattern and morphological characteristics were present in the RMS at all ages examined. In neonatal animals, small, moderately stained NADPH-d-positive cells were identified in the RMS vertical arm and in the RMS elbow. In adult and aging rats a few labeled cells could be also detected in the RMS horizontal arm. NADPH-d-positive cells in adult and aging rats were characterized by long varicose processes and displayed dark labeling in comparison to the neonatal group. 2. Double immunolabeling has revealed that nNOS-immunoreactivity co-localized with that of NeuN. This indicates that nitrergic cells within the RMS are neurons. 3. Quantitative analysis showed that the number of NADPH-d-positive cells increases with advancing age. The presence of NO producing cells in the RMS of neonatal adult and aging rats indicates, that this proliferating and migratory area is under the influence of NO throughout the entire life of the animals.

Nitric oxide and adult neurogenesis in health and disease

Adult neurogenesis may be functionally important as a mechanism of brain plasticity in physiological conditions and brain repair after injury. Nitric oxide (NO), a diffusible intracellular and intercellular messenger in the mammalian nervous system, has been shown to affect adult neurogenesis in different ways. In the normal brain, NO, synthesized by the neuronal isoform of NO synthase in nitrergic neurons, is a negative regulator of precursor cell proliferation. However, after brain damage, NO overproduction in different neural and nonneural cell types promotes neurogenesis. Recently reported results on the effects of NO on new neuron generation in the adult brain are reviewed, with special attention to the proposed mechanisms of action and functional consequences in health and disease.

Synergistic antiproliferative and apoptotic effects induced by mixed epidermal growth factor receptor inhibitor ZD1839 and nitric oxide donor in human prostatic cancer cell lines

BACKGROUND

The specific inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, ZD1839 induces potent antitumoral effects on several advanced cancer types. The present study was undertaken to determine whether the combination of ZD1839 with an agent donating nitric oxide (NO(*)), sodium nitroprusside (SNP) results in a synergy of anticarcinogenic responses on metastatic prostate cancer (PC) cells.

METHODS

The antiproliferative and apoptotic/necrotic effects of ZD1839 and SNP alone or in combination were estimated on EGF- and serum-stimulated LNCaP, DU145, and PC3 cells by MTT growth tests, trypan blue dye exclusion method, and flow cytometric analyses. Moreover, the cellular ceramide levels were evaluated by the diacylglycerol kinase enzymatic method and the amounts of cytosolic cytochrome c by ELISA assays.

RESULTS

ZD1839 and SNP alone or in combination at lower concentrations induced an inhibition of EGF- and serum-stimulated growth of LNCaP, DU145, and PC3 concomitant with an arrest in the G1 phase of cellular cycle. Interestingly, the mixed ZD1839 and SNP also caused a more substantial apoptotic/necrotic death of these PC cells as compared to drugs alone. Moreover, we have observed that an inhibition of acidic sphingomyelinase, hydrogen peroxide (H(2)O(2)) accumulation and caspase cascades results in a significant reduction of apoptotic/necrotic death induced by mixed ZD1839 and SNP in EGF-stimulated PC3 cells. In addition, the combined ZD1839 plus SNP also induced a higher cellular ceramide and reactive oxygen species (ROS) production, mitochondrial transmembrane potential decrease, and cytochrome c amount released into cytosol as compared to drugs alone.

CONCLUSIONS

The simultaneous use of EGFR inhibitor and compound releasing NO(*) might lead to a synergy in the ceramide and ROS production which might cause cellular membrane damages resulting in a massive apoptotic/necrotic death of metastatic PC cells.

Role of nitric oxide in the regulation of neuronal proliferation, survival and differentiation

Nitric oxide (NO), an important cellular messenger, has been linked to both neurodegenerative and neuroprotective actions. In the present review, we focus on recent data establishing a survival and differentiation role for NO in several neural in vitro and in vivo models. Nitric oxide has been found to be essential for survival of neuronal cell lines and primary neurons in culture under various death challenges. Furthermore, its lack may aggravate some neuropathological conditions in experimental animals. Several cellular pathways and signaling systems subserving this neuroprotective role of NO are considered in the review. Survey of recent data related to the developmental role of NO mainly focus on its action as a negative regulator of neuronal precursor cells proliferation and on its role of promotion of neuronal differentiation. Discussion on discrepancies arising from the literature is focused on the Janus-faced properties of the molecule and it is proposed that most controversial results are related to the intrinsic property of NO to compensate among functionally opposed effects. As an example, the increased proliferation of neural cell precursors under conditions of NO shortage may be, later on in the development, compensated by increased elimination through programmed cell death as a consequence of the lack of the survival-promoting action of the molecule. To elucidate these complex, and possibly contrasting, effects of NO is indicated as an important task for future researches.

Nitric oxide synthesis inhibition increases proliferation of neural precursors isolated from the postnatal mouse subventricular zone

The subventricular zone (SVZ) of rodents retains the capacity to generate new neurons throughout the entire life of the animal. Neural progenitors of the SVZ survive and proliferate in vitro in the presence of epidermal growth factor (EGF). Nitric oxide (NO) has been shown to participate in neural tissue formation during development and to have antiproliferative actions, mediated in part by inhibition of the EGF receptor. Based on these findings, we have investigated the possible effects of endogenously produced and exogenously added NO on SVZ cell proliferation and differentiation. Explants were obtained from postnatal mouse SVZ and cultured in the presence of EGF. Cells migrated out of the explants and proliferated in culture, as assessed by bromodeoxyuridine (BrdU) incorporation. After 72 h in vitro, the colonies formed around the explants were constituted by cells of neuronal or glial lineages, as well as undifferentiated progenitors. Immunoreactivity for the neuronal isoform of NO synthase was observed in neuronal cells with long varicose processes. Cultures treated with the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) showed an increase in the percentage of BrdU-immunoreactive cells, whereas treatment with the NO donor diethylenetriamine-nitric oxide adduct (DETA-NO) led to a decrease in cell proliferation, without affecting apoptosis. The differentiation pattern was also altered by L-NAME treatment resulting in an enlargement of the neuronal population. The results suggest that endogenous NO may contribute to postnatal neurogenesis by modulating the proliferation and fate of SVZ progenitor cells.

Nitric oxide is a physiological inhibitor of neurogenesis in the adult mouse subventricular zone and olfactory bulb

The subventricular zone of the rodent brain retains the capacity of generating new neurons in adulthood. The newly formed neuroblasts migrate rostrally toward the olfactory bulb, where they differentiate as granular and periglomerular interneurons. The reported presence of differentiated neurons expressing the neuronal isoform of nitric oxide synthase (NOS) in the periphery of the neurogenic region and the organization of their varicose axons as a network in which the precursors are immersed raised the hypothesis that endogenous nitric oxide (NO) may participate in the control of neurogenesis in the subventricular zone. Systemic administration of the NOS inhibitors N(omega)-nitro-L-arginine methyl ester or 7-nitroindazole to adult mice produced a dose- and time-dependent increase in the number of mitotic cells in the subventricular zone, rostral migratory stream, and olfactory bulb, but not in the dentate gyrus of the hippocampus, without affecting apoptosis. In the subventricular zone, this effect was exerted selectively on a precursor subpopulation expressing nestin but not neuronal or glial cell-specific proteins. In addition, in the olfactory bulb, analysis of maturation markers in the newly generated neurons indicated that chronic NOS inhibition caused a delay in neuronal differentiation. Postmitotic cell survival and migration were not affected when NO production was impaired. Our results suggest that NO, produced by nitrergic neurons in the adult mouse subventricular zone and olfactory bulb, exerts a negative control on the size of the undifferentiated precursor pool and promotes neuronal differentiation.

Nitric oxide-induced epidermal growth factor-dependent phosphorylations in A431 tumour cells

Nitric oxide (NO*) strongly inhibits the proliferation of human A431 tumour cells. It also inhibits tyrosine phosphorylation of a 170-kDa band corresponding to the epidermal growth factor receptor (EGFR) and induces the phosphorylation at tyrosine residue(s) of a 58-kDa protein which we have denoted NOIPP-58 (nitric oxide-induced 58-kDa phosphoprotein). The NO*-induced phosphorylation of NOIPP-58 is strictly dependent on the presence of EGF. Phosphorylation of NOIPP-58 and inhibition of the phosphorylation of the band corresponding to EGFR are both cGMP-independent processes. We also demonstrate that the p38 mitogen-activated protein kinase (p38MAPK) pathway is activated by NO* in the absence and presence of EGF, whereas the activity of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and the c-Jun N-terminal kinase 1/2 (JNK1/2) pathways are not significantly affected or are slightly decreased, respectively, on addition of this agent. Moreover, we show that the p38MAPK inhibitor, SB202190, induces rapid vanadate/peroxovanadate-sensitive dephosphorylation of prephosphorylated EGFR and NOIPP-58. We propose that the dephosphorylation of both NOIPP-58 and EGFR are mediated by a p38MAPK-controlled phosphotyrosine-protein phosphatase (PYPP). Activation of the p38MAPK pathway during nitrosative stress probably prevents the operation of this PYPP, allowing NOIPP-58, and in part EGFR, to remain phosphorylated and therefore capable of generating signalling events.