Ras Guanine Nucleotide-releasing Factor Research Articles

Median Nerve Stimulation Attenuates Traumatic Brain Injury–Induced Comatose State by Regulating the Orexin-A/RasGRF1 Signaling Pathway

Despite the arousal effect of median nerve stimulation (MNS) being well documented in the clinical treatment of coma patients with traumatic brain injury (TBI), the mechanisms underlying the observed effect are still not completely understood. This study aimed to evaluate the protective effects and potential mechanism of MNS in comatose rats with TBI. A total of 60 rats were randomly divided into 5 groups: the control group, sham-stimulated group, MNS group, orexins receptor type 1 (OX1R) antagonist group, and antagonist control group. The free-fall drop method was used to establish a TBI model. After administrating MNS or OX1R antagonist, consciousness was evaluated. Protein levels in the prefrontal cortex were measured using an enzyme-linked immunosorbent assay, Western blotting, and immunofluorescence. In the MNS group, tissue damage and consciousness state was markedly improved compared with that in the sham-stimulated group. Administration of the OX1R antagonist attenuated the beneficial effects of MNS in TBI-induced comatose rats. Additionally, MNS also significantly enhanced the expression of orexin-A/OX1R and the activation of Ras guanine nucleotide-releasing factor 1 (RasGRF1). These data show that MNS exerts its wake-promoting effect by activating the OX1R-RasGRF1 pathway in TBI-induced comatose rats.

A Rational Design of α-Helix-Shaped Peptides Employing the Hydrogen-Bond Surrogate Approach: A Modulation Strategy for Ras-RasGRF1 Interaction in Neuropsychiatric Disorders.

In the last two decades, abnormal Ras (rat sarcoma protein)–ERK (extracellular signal-regulated kinase) signalling in the brain has been involved in a variety of neuropsychiatric disorders, including drug addiction, certain forms of intellectual disability, and autism spectrum disorder. Modulation of membrane-receptor-mediated Ras activation has been proposed as a potential target mechanism to attenuate ERK signalling in the brain. Previously, we showed that a cell penetrating peptide, RB3, was able to inhibit downstream signalling by preventing RasGRF1 (Ras guanine nucleotide-releasing factor 1), a neuronal specific GDP/GTP exchange factor, to bind Ras proteins, both in brain slices and in vivo, with an IC50 value in the micromolar range. The aim of this work was to mutate and improve this peptide through computer-aided techniques to increase its inhibitory activity against RasGRF1. The designed peptides were built based on the RB3 peptide structure corresponding to the α-helix of RasGRF1 responsible for Ras binding. For this purpose, the hydrogen-bond surrogate (HBS) approach was exploited to maintain the helical conformation of the designed peptides. Finally, residue scanning, MD simulations, and MM-GBSA calculations were used to identify 18 most promising α-helix-shaped peptides that will be assayed to check their potential activity against Ras-RasGRF1 and prevent downstream molecular events implicated in brain disorders.

MG132 exerts anti-viral activity against HSV-1 by overcoming virus-mediated suppression of the ERK signaling pathway

Herpes simplex virus 1 (HSV-1) causes a number of clinical manifestations including cold sores, keratitis, meningitis and encephalitis. Although current drugs are available to treat HSV-1 infection, they can cause side effects such as nephrotoxicity. Moreover, owing to the emergence of drug-resistant HSV-1 strains, new anti-HSV-1 compounds are needed. Because many viruses exploit cellular host proteases and encode their own viral proteases for survival, we investigated the inhibitory effects of a panel of protease inhibitors (TLCK, TPCK, E64, bortezomib, or MG132) on HSV-1 replication and several host cell signaling pathways. We found that HSV-1 infection suppressed c-Raf-MEK1/2-ERK1/2-p90RSK signaling in host cells, which facilitated viral replication. The mechanism by which HSV-1 inhibited ERK signaling was mediated through the polyubiquitination and proteasomal degradation of Ras-guanine nucleotide-releasing factor 2 (Ras-GRF2). Importantly, the proteasome inhibitor MG132 inhibited HSV-1 replication by reversing ERK suppression in infected cells, inhibiting lytic genes (ICP5, ICP27 and UL42) expression, and overcoming the downregulation of Ras-GRF2. These results indicate that the suppression of ERK signaling via proteasomal degradation of Ras-GRF2 is necessary for HSV-1 infection and replication. Given that ERK activation by MG132 exhibits anti-HSV-1 activity, these results suggest that the proteasome inhibitor could serve as a novel therapeutic agent against HSV-1 infection.

Calcium Signaling and Gene Expression.

Calcium signaling plays an important role in gene expression. At the transcriptional level, this may underpin mammalian neuronal synaptic plasticity. Calcium influx into the postsynaptic neuron via: N-methyl-D-aspartate (NMDA) receptors activates small GTPase Rac1 and other Rac guanine nucleotide exchange factors, and stimulates calmodulin-dependent kinase kinase (CaMKK) and CaMKI; α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors that are not impermeable to calcium ions, that is, those lacking the glutamate receptor-2 subunits, leads to activation of Ras guanine nucleotide-releasing factor proteins, which is coupled with activation of the mitogen-activated protein kinases/extracellular signal-regulated kinases signaling cascade; L-type voltage-gated calcium channels activates signaling pathways involving CaMKII, downstream responsive element antagonist modulator and distinct microdomains. Key members of these signaling cascades then translocate into the nucleus, where they alter the expression of genes involved in neuronal synaptic plasticity. At the post-transcriptional level, intracellular calcium level changes can change alternative splicing patterns; in the mammalian brain, alterations in calcium signaling via NMDA receptors is associated with exon silencing of the CI cassette of the NMDA R1 receptor (GRIN1) transcript by UAGG motifs in response to neuronal excitation. Regulation also occurs at the translational level; transglutaminase-2 (TG2) mediates calcium ion-regulated crosslinking of Y-box binding protein-1 (YB-1) translation-regulatory protein in TGFβ1-activated myofibroblasts; YB-1 binds smooth muscle α-actin mRNA and regulates its translational activity. Calcium signaling is also important in epigenetic regulation, for example in respect of changes in cytosine bases. Targeting calcium signaling may provide therapeutically useful options, for example to induce epigenetic reactivation of tumor suppressor genes in cancer patients.

The Inhibition of RasGRF2, But Not RasGRF1, Alters Cocaine Reward in Mice.

Ras/Raf/MEK/ERK (Ras-ERK) signaling has been implicated in the effects of drugs of abuse. Inhibitors of MEK1/2, the kinases upstream of ERK1/2, have been critical in defining the role of the Ras-ERK cascade in drug-dependent alterations in behavioral plasticity, but the Ras family of small GTPases has not been extensively examined in drug-related behaviors. We examined the role of Ras Guanine Nucleotide Releasing Factor 1 (RasGRF1) and 2 (RasGRF2), upstream regulators of the Ras-ERK signaling cascade, on cocaine self-administration (SA) in male mice. We first established a role for Ras-ERK signaling in cocaine SA, demonstrating that pERK1/2 is upregulated following SA in C57BL/6N mice in striatum. We then compared RasGRF1 and RasGRF2 KO mouse lines, demonstrating that cocaine SA in RasGRF2 KO mice was increased relative to WT controls, whereas RasGRF1 KO and WT mice did not differ. This effect in RasGRF2 mice is likely mediated by the Ras-ERK signaling pathway, as pERK1/2 upregulation following cocaine SA was absent in RasGRF2 KO mice. Interestingly, the lentiviral knockdown of RasGRF2 in the NAc had the opposite effect to that in RasGRF2 KO mice, reducing cocaine SA. We subsequently demonstrated that the MEK inhibitor PD325901 administered peripherally prior to cocaine SA increased cocaine intake, replicating the increase seen in RasGRF2 KO mice, whereas PD325901 administered into the NAc decreased cocaine intake, similar to the effect seen following lentiviral knockdown of RasGRF2. These data indicate a role for RasGRF2 in cocaine SA in mice that is ERK-dependent, and suggest a differential effect of global versus site-specific RasGRF2 inhibition.SIGNIFICANCE STATEMENT Exposure to drugs of abuse activates a variety of intracellular pathways, and following repeated exposure, persistent changes in these pathways contribute to drug dependence. Downstream components of the Ras-ERK signaling cascade are involved in the acute and chronic effects of drugs of abuse, but their upstream mediators have not been extensively characterized. Here we show, using a combination of molecular, pharmacological, and lentiviral techniques, that the guanine nucleotide exchange factor RasGRF2 mediates cocaine self-administration via an ERK-dependent mechanism, whereas RasGRF1 has no effect on responding for cocaine. These data indicate dissociative effects of mediators of Ras activity on cocaine reward and expand the understanding of the contribution of Ras-ERK signaling to drug-taking behavior.

Unraveling the Mechanism of Dyskinesia One Transcription Factor at a Time

L-DOPA–induced dyskinesia (LID), or abnormal involuntary movements, is a common side effect of L-DOPA therapy in patients with Parkinson’s disease. When L-DOPA is initially administered, it effectively reverses akinesia caused by the loss of dopamine. However, long-term L-DOPA administration produces a hyperkinetic effect, triggering excessive movements in human patients and in animal models. The mechanisms of LID have been under intense investigation for decades, and numerous important discoveries in the past several years established the key mechanisms of LID development. Five dopamine receptor subtypes in the striatal neurons mediate the action of dopamine produced from L-DOPA. The main subtypes, D1 and D2, are expressed on the striatonigral and striatopallidal medium spiny neurons (MSNs), respectively, with a high degree of segregation. The relative contribution of the D1-dependent and D2-dependent signaling to LID has been hotly debated. However, findings demonstrating that genetic ablation of the D1, but not the D2, receptor abrogates LID (1) strongly suggest that the aberrant signaling via the D1 receptor is the main contributor. The striking molecular feature of the dopamine-depleted striatum is the hyperresponsiveness of multiple signaling pathways to acute dopaminergic stimulation. The D1 receptor in MSNs couples to the adenylyl cyclase–stimulating Golf, and in the dopamine-depleted striatum, the cyclic adenosine monophosphate (cAMP) response to L-DOPA is augmented, resulting in the increased activity of protein kinase A (PKA) and enhanced phosphorylation of PKA substrates. One of the substrates, the dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), upon phosphorylation by PKA at Thr34, acts as an inhibitor of protein phosphatase 1, further enhancing the activity of the cAMP-PKA cascade. Sensitized DARPP-32 contributes to LID because its genetic ablation or elimination of the PKA-phosphorylated residue ameliorates LID (2,3). In addition, DARPP-32 inactivation significantly attenuates the extracellular signal-regulated kinase (ERK) superactivity in the dopamine-depleted striatum (2), suggesting that the elevated cAMP signaling is an important mediator of the ERK superactivity. The ERK pathway shows very strong dopamine depletion– induced supersensitivity. The dopamine-induced hyperactivation of the ERK response is confined to the striatonigral MSNs, or direct pathway MSNs (dMSNs) (1,3), and genetic ablation of the D1 receptor prevents the supersensitive ERK response (1), reinforcing the notion of the prime role of the D1 receptor signaling in LID. The neuron-specific Ras–guanine nucleotidereleasing factor 1 (Ras-GRF1), the upstream activator of Ras, implicated in LID could serve as the mechanistic connection between the D1 receptor signaling and activation of the ERK

P.6.c.009 The role of ras guanine nucleotide-releasing factor 1 (ras-GRF1) in cocaine self-administration

P.6.c.009 The role of ras guanine nucleotide-releasing factor 1 (ras-GRF1) in cocaine self-administration

Derangement of Ras-Guanine Nucleotide-Releasing Factor 1 (Ras-GRF1) and Extracellular Signal-Regulated Kinase (ERK) Dependent Striatal Plasticity in L-DOPA-Induced Dyskinesia

BackgroundBidirectional long-term plasticity at the corticostriatal synapse has been proposed as a central cellular mechanism governing dopamine-mediated behavioral adaptations in the basal ganglia system. Balanced activity of medium spiny neurons (MSNs) in the direct and the indirect pathways is essential for normal striatal function. This balance is disrupted in Parkinson’s disease and in l-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia (LID), a common motor complication of current pharmacotherapy of Parkinson’s disease. MethodsElectrophysiological recordings were performed in mouse cortico-striatal slice preparation. Synaptic plasticity, such as long-term potentiation (LTP) and depotentiation, was investigated. Specific pharmacological inhibitors or genetic manipulations were used to modulate the Ras-extracellular signal-regulated kinase (Ras-ERK) pathway, a signal transduction cascade implicated in behavioral plasticity, and synaptic activity in different subpopulations of striatal neurons was measured. ResultsWe found that the Ras-ERK pathway, is not only essential for long-term potentiation induced with a high frequency stimulation protocol (HFS-LTP) in the dorsal striatum, but also for its reversal, synaptic depotentiation. Ablation of Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a neuronal activator of Ras proteins, causes a specific loss of HFS-LTP in the medium spiny neurons in the direct pathway without affecting LTP in the indirect pathway. Analysis of LTP in animals with unilateral 6-hydroxydopamine lesions (6-OHDA) rendered dyskinetic with chronic L-DOPA treatment reveals a complex, Ras-GRF1 and pathway-independent, apparently stochastic involvement of ERK. ConclusionsThese data not only demonstrate a central role for Ras-ERK signaling in striatal LTP, depotentiation, and LTP restored after L-DOPA treatment but also disclose multifaceted synaptic adaptations occurring in response to dopaminergic denervation and pulsatile administration of L-DOPA.

P.2.019 The role of Ras guanine nucleotide-releasing factor 1 in cocaine self-administration

P.2.019 The role of Ras guanine nucleotide-releasing factor 1 in cocaine self-administration

Acquisition of Contextual Discrimination Involves the Appearance of a RAS-GRF1/p38 Mitogen-activated Protein (MAP) Kinase-mediated Signaling Pathway That Promotes Long Term Potentiation (LTP)

RAS-GRF1 is a guanine nucleotide exchange factor with the ability to activate RAS and RAC GTPases in response to elevated calcium levels. We previously showed that beginning at 1 month of age, RAS-GRF1 mediates NMDA-type glutamate receptor (NMDAR)-induction of long term depression in the CA1 region of the hippocampus of mice. Here we show that beginning at 2 months of age, when mice first acquire the ability to discriminate between closely related contexts, RAS-GRF1 begins to contribute to the induction of long term potentiation (LTP) in the CA1 hippocampus by mediating the action of calcium-permeable, AMPA-type glutamate receptors (CP-AMPARs). Surprisingly, LTP induction by CP-AMPARs through RAS-GRF1 occurs via activation of p38 MAP kinase rather than ERK MAP kinase, which has more frequently been linked to LTP. Moreover, contextual discrimination is blocked by knockdown of Ras-Grf1 expression specifically in the CA1 hippocampus, infusion of a p38 MAP kinase inhibitor into the CA1 hippocampus, or the injection of an inhibitor of CP-AMPARs. These findings implicate the CA1 hippocampus in the developmentally dependent capacity to distinguish closely related contexts through the appearance of a novel LTP-supporting signaling pathway.

Decreased expression of Ras-GRF1 in the brain tissue of the intractable epilepsy patients and experimental rats

Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) is present mainly at synaptosome and its expression after birth increases in parallel with the development of neuronal circuitry. Evidences suggested that Ras-GRF1 could mediate forms of synaptic plasticity and might participate in the regulation of neuronal excitability and neurite outgrowth though various signal transduction pathway. The aim of this study was to measure Ras-GRF1 expression in brain tissue of patients with drug-refractory temporal lobe epilepsy (TLE) and lithium chloride-pilocarprine kindled rats using double-label immunofluorescence, immunohistochemistry and Western blotting and to discuss the possible role of Ras-GRF1 in TLE. We randomly selected 30 temporal neocortices tissues from patients with TLE and 9 histologically normal temporal neocortices samples from controls. Meanwhile, we investigated the distribution and level of Ras-GRF1 protein expression during the different phases (the acute period, the latent period and the chronic phase) in the epileptic and control rats. Ras-GRF1 was mainly expressed in the plasma membrane and dendrite of neurons, but it was not co-expressed with GFAP-positive astrocytes in the brain tissue of patients and epileptic rats. Compared with controls, Ras-GRF1 expression was significantly decreased in TLE patients. Ras-GRF1 expression in epileptic rats was already reduced at 1 day post-seizures, then gradually decreased during the latent period and reached a minimum level during the chronic phase. These results demonstrated that the decreased expression of Ras-GRF1 could be involved in the pathogenesis of human TLE.

N-Methyl-d-aspartate Receptor Mechanosensitivity Is Governed by C Terminus of NR2B Subunit

N-methyl-D-aspartate receptors (NMDARs), critical mediators of both physiologic and pathologic neurological signaling, have previously been shown to be sensitive to mechanical stretch through the loss of its native Mg(2+) block. However, the regulation of this mechanosensitivity has yet to be further explored. Furthermore, as it has become apparent that NMDAR-mediated signaling is dependent on specific NMDAR subtypes, as governed by the identity of the NR2 subunit, a crucial unanswered question is the role of subunit composition in observed NMDAR mechanosensitivity. Here, we used a recombinant system to assess the mechanosensitivity of specific subtypes and demonstrate that the mechanosensitive property is uniquely governed by the NR2B subunit. NR1/NR2B NMDARs displayed significant stretch sensitivity, whereas NR1/NR2A NMDARs did not respond to stretch. Furthermore, NR2B mechanosensitivity was regulated by PKC activity, because PKC inhibition reduced stretch responses in transfected HEK 293 cells and primary cortical neurons. Finally, using NR2B point mutations, we identified a PKC phosphorylation site, Ser-1323 on NR2B, as a unique critical regulator of stretch sensitivity. These data suggest that the selective mechanosensitivity of NR2B can significantly impact neuronal response to traumatic brain injury and illustrate that the mechanical tone of the neuron can be dynamically regulated by PKC activity.

NeuroNEXT: New Neuroscience Network Aims to Speed Up Phase 2 Trials

“One important question is whether drugs acting on mTORC1 signaling might have the same anti-dyskinetic effect of rapamycin without causing immune suppression,” he said. “Another question is whether rapamycin or analogues to it can counteract dyskinesia once it has been established. In our initial study, we only showed that the development of dyskinesia is reduced when you give rapamycin at the same time you begin L-DOPA therapy.” Whereas the drugs already in clinical trials for dyskinesia act upon neurotransmitter receptors, all three of the approaches presented at the symposium target defects occurring within the striatal neurons themselves, Dr. Fisone said. “This concept of targeting intracellular signalling molecules is already being used in the treatment of cancer, but it has lagged behind in the treatment of disorders of the nervous system,” he said. “We think that acting at the level of intracellular signaling represents an alternative treatment approach for neuropsychiatric and neurodegenerative disorders.” • REFERENCES: • Ahmed MR, Berthet A, Bychkov E, et al. Lentiviral overexpression of GRK6 alleviates L-DOPA–induced dyskinesia in experimental Parkinson’s disease. Science Translat Med 2010; 2 (28): 1-9. • Fasano S, Bezard E, D’Antoni A, et al. Inhibition of Ras-guanine nucleotide-releasing factor 1 (RasGRF1) signaling in the striatum reverts motor symptoms associated with L-DOPA–induced dyskinesia. Proc Natl Acad Sci 2010; 107 (50): 21824-29. • Santini E, Heiman M, Greengard P, et al. Inhibition of mTOR signaling in Parkinson’s disease prevents L-DOPA induced dyskinesia. Science Signaling 2009; 2 (80): 1-10. DR. GILBERTO FISONE: “This concept of targeting intracellular signaling molecules is already being used in the treatment of cancer, but it has lagged behind in the treatment of disorders of the nervous system. We think that acting at the level of intracellular signaling represents an alternative treatment approach for neuropsychiatric and neurodegenerative disorders.” Dyskinesia Continued from page 22 If you’ve ever played a role in conducting a federally funded clinical trial, you know that one of the biggest challenges often isn’t the science — it’s the paperwork. Moving a phase 2 exploratory clinical trial forward so that it can answer the necessary questions about a new therapy and — hopefully — lead to testing that therapy in a larger phase 3 trial, nearly always involves cumbersome approval processes that are exponentially multiplied by the number of sites involved in the trial. Have 10 trial sites? That requires 10 institutional review boards (IRBs) and 10 contracts with the NIH that need to be reviewed and reapproved annually. “I have a trial with over 60 sites,” said Merit Cudkowicz, MD, the Julieanne Dorn Professor of Neurology at Harvard Medical School and director of the Neurology Clinical Trials Unit at Massachusetts General Hospital. “It can often take the entire year to get that trial’s contract renegotiated at all 60 sites. And then the next year you have to amend it and do it all over again.” In an effort to turn the cumbersome elephant of today’s phase 2 neuroscience trials into a sleek and effi cient cheetah, the NINDS has recently announced the establishment of an innovative new trials network: NeuroNEXT, a Network for Excellence in Neuroscience Clinical Trials. NINDS will invest more than $84 million over the next seven years in supporting the NeuroNEXT infrastructure, which brings together a group of 25 neuroscience clinical trials sites plus one coordinating center (Massachusetts General) and one data center (the University of Iowa). The aim: to facilitate the rapid, effi cient advancement of phase 2 exploratory trials in neuroscience.

Inhibition of Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) signaling in the striatum reverts motor symptoms associated with l -dopa–induced dyskinesia

L-dopa-induced dyskinesia (LID) is a common debilitating complication of dopamine replacement therapy in Parkinson's disease. Recent evidence suggests that LID may be linked causally to a hyperactivation of the Ras-ERK signaling cascade in the basal ganglia. We set out to determine whether specific targeting of Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a brain-specific activator of the Ras-ERK pathway, may provide a therapy for LID. On the rodent abnormal involuntary movements scale, Ras-GRF1-deficient mice were significantly resistant to the development of dyskinesia during chronic L-dopa treatment. Furthermore, in a nonhuman primate model of LID, lentiviral vectors expressing dominant negative forms of Ras-GRF1 caused a dramatic reversion of dyskinesia severity leaving intact the therapeutic effect of L-dopa. These data reveal the central role of Ras-GRF1 in governing striatal adaptations to dopamine replacement therapy and validate a viable treatment for LID based on intracellular signaling modulation.

Amphetamine alters Ras-guanine nucleotide-releasing factor expression in the rat striatum in vivo

Ras-guanine nucleotide-releasing factors (Ras-GRFs) are densely expressed in neurons of the mammalian brain. As a Ras-specific activator predominantly concentrated at synaptic sites, Ras-GRFs activate the Ras-mitogen-activated protein kinase (Ras-MAPK) cascade in response to changing synaptic inputs, thereby modifying a variety of cellular and synaptic activities. While the Ras-MAPK cascade in the limbic reward circuit is well-known to be sensitive to dopamine inputs, the sensitivity of its upstream activator (Ras-GRFs) to dopamine remains to be investigated. In this study, the response of Ras-GRFs in their protein expression to dopamine stimulation was evaluated in the rat striatum in vivo. A single systemic injection of the psychostimulant amphetamine produced an increase in Ras-GRF1 protein levels in both the dorsal (caudoputamen) and ventral (nucleus accumbens) striatum. The increase in Ras-GRF1 proteins was dose-dependent. The reliable increase was seen 2.5 h after drug injection and returned to normal levels by 6 h. In contrast to Ras-GRF1, protein levels of Ras-GRF2 in the striatum were not altered by amphetamine. In addition to the striatum, the medial prefrontal cortex is another forebrain site where amphetamine induced a parallel increase in Ras-GRF1 but not Ras-GRF2. No significant change in Ras-GRF1/2 proteins was observed in the hippocampus. These data demonstrate that Ras-GRF1 is a susceptible and selective target of amphetamine in striatal and cortical neurons. Its protein expression is subject to the modulation by acute exposure of amphetamine.

Ras-Guanine Nucleotide-Releasing Factor 1 (Ras-GRF1) Controls Activation of Extracellular Signal-Regulated Kinase (ERK) Signaling in the Striatum and Long-Term Behavioral Responses to Cocaine

Ras-extracellular signal-regulated kinase (Ras-ERK) signaling is central to the molecular machinery underlying cognitive functions. In the striatum, ERK1/2 kinases are co-activated by glutamate and dopamine D1/5 receptors, but the mechanisms providing such signaling integration are still unknown. The Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a neuronal specific activator of Ras-ERK signaling, is a likely candidate for coupling these neurotransmitter signals to ERK kinases in the striatonigral medium spiny neurons (MSN) and for modulating behavioral responses to drug abuse such as cocaine. We used genetically modified mouse mutants for Ras-GRF1 as a source of primary MSN cultures and organotypic slices, to perform both immunoblot and immunofluorescence studies in response to glutamate and dopamine receptor agonists. Mice were also subjected to behavioral and immunohistochemical investigations upon treatment with cocaine. Phosphorylation of ERK1/2 in response to glutamate, dopamine D1 agonist, or both stimuli simultaneously is impaired in Ras-GRF1-deficient striatal cells and organotypic slices of the striatonigral MSN compartment. Consistently, behavioral responses to cocaine are also affected in mice deficient for Ras-GRF1 or overexpressing it. Both locomotor sensitization and conditioned place preference are significantly attenuated in Ras-GRF1-deficient mice, whereas a robust facilitation is observed in overexpressing transgenic animals. Finally, we found corresponding changes in ERK1/2 activation and in accumulation of FosB/DeltaFosB, a well-characterized marker for long-term responses to cocaine, in MSN from these animals. These results strongly implicate Ras-GRF1 in the integration of the two main neurotransmitter inputs to the striatum and in the maladaptive modulation of striatal networks in response to cocaine.

Differences in flexibility underlie functional differences in the Ras activators son of sevenless and Ras guanine nucleotide releasing factor 1.

The Ras-specific nucleotide exchange factor Son of sevenless (Sos) is inactive without Ras bound to a distal allosteric site. In contrast, the catalytic domain of Ras guanine nucleotide releasing factor 1 (RasGRF1) is active intrinsically. By substituting residues from RasGRF1 into Sos, we have generated mutants of Sos with basal activity, partially relieved of their dependence on allosteric activation. We have performed molecular dynamics simulations showing how Ras binding to the allosteric site leads to a bias toward the active conformation of Sos. The trajectories show that Sos fluctuates between active and inactive conformations in the absence of Ras and that the activating mutations favor conformations of Sos that are more permissive to Ras binding at the catalytic site. In contrast, unliganded RasGRF1 fluctuates primarily among active conformations. Our results support the premise that the catalytic domain of Sos has evolved an allosteric activation mechanism that extends beyond the simple process of membrane recruitment.

The Ras guanine nucleotide exchange factor RasGRF1 promotes matrix metalloproteinase-3 production in rheumatoid arthritis synovial tissue

IntroductionFibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA) patients share many similarities with transformed cancer cells, including spontaneous production of matrix metalloproteinases (MMPs). Altered or chronic activation of proto-oncogenic Ras family GTPases is thought to contribute to inflammation and joint destruction in RA, and abrogation of Ras family signaling is therapeutic in animal models of RA. Recently, expression and post-translational modification of Ras guanine nucleotide releasing factor 1 (RasGRF1) was found to contribute to spontaneous MMP production in melanoma cancer cells. Here, we examine the potential relationship between RasGRF1 expression and MMP production in RA, reactive arthritis, and inflammatory osteoarthritis synovial tissue and FLS.MethodsExpression of RasGRF1, MMP-1, MMP-3, and IL-6 was detected in synovial tissue by immunohistochemistry and stained sections were evaluated by digital image analysis. Expression of RasGRF1 in FLS and synovial tissue was also assessed by immunoblotting. Double staining was performed to detect proteins in specific cell populations, and cells producing MMP-1 and MMP-3. RasGRF1 expression was manipulated in RA FLS by cDNA transfection and gene silencing, and effects on MMP-1, TIMP-1, MMP-3, IL-6, and IL-8 production measured by ELISA.ResultsExpression of RasGRF1 was significantly enhanced in RA synovial tissue, and detected in FLS and synovial macrophages in situ. In cultured FLS and synovial biopsies, RasGRF1 was detected by immunoblotting as a truncated fragment lacking its negative regulatory domain. Production of MMP-1 and MMP-3 in RA but not non-RA synovial tissue positively correlated with expression of RasGRF1 and co-localized in cells expressing RasGRF1. RasGRF1 overexpression in FLS induced production of MMP-3, and RasGRF1 silencing inhibited spontaneous MMP-3 production.ConclusionsEnhanced expression and post-translational modification of RasGRF1 contributes to MMP-3 production in RA synovial tissue and the semi-transformed phenotype of RA FLS.

Discovery of Epigenetically Silenced Genes by Methylated DNA Immunoprecipitation in Colon Cancer Cells

CpG island promoter hypermethylation of tumor suppressor genes is a common hallmark of human cancer, and new large-scale epigenomic technologies might be useful in our attempts to define the complete DNA hypermethylome of tumor cells. Here, we report a functional search for hypermethylated CpG islands using the colorectal cancer cell line HCT-116, in which two major DNA methyltransferases, DNMT1 and DNMT3b, have been genetically disrupted (DKO cells). Using methylated DNA immunoprecipitation methodology in conjunction with promoter microarray analyses, we found that DKO cells experience a significant loss of hypermethylated CpG islands. Further characterization of these candidate sequences shows CpG island promoter hypermethylation and silencing of genes with potentially important roles in tumorigenesis, such as the Ras guanine nucleotide-releasing factor (RASGRF2), the apoptosis-associated basic helix-loop transcription factor (BHLHB9), and the homeobox gene (HOXD1). Hypermethylation of these genes occurs in premalignant lesions and accumulates during tumorigenesis. Thus, our results show the usefulness of DNMT genetic disruption strategies combined with methylated DNA immunoprecipitation in searching for unknown hypermethylated candidate genes in human cancer that might aid our understanding of the biology of the disease and be of potential translational use.

Cocaine increases Ras-guanine nucleotide-releasing factor 1 protein expression in the rat striatum in vivo

Psychostimulants activate the Ras-mitogen-activated protein kinase (Ras-MAPK) cascade in the limbic reward circuit and thereby trigger a transcription-dependent mechanism underlying enduring synaptic plasticity related to addictive properties of drugs of abuse. The Ras-specific activator, Ras-guanine nucleotide-releasing factor (Ras-GRF), is predominantly expressed at synapses and is thought to actively regulate Ras-MAPK responses to changing synaptic signals. In this study, a possible influence of cocaine on Ras-GRF gene expression at the protein level in the rat striatum was investigated in vivo. A single systemic injection of cocaine induced an increase in Ras-GRF1 protein levels in both the dorsal (caudoputamen) and ventral (nucleus accumbens) striatum. The increase in Ras-GRF1 proteins was dose-dependent and was a delayed and transient event. In contrast to Ras-GRF1, a closely related Ras-GRF2 showed no change in its protein abundance following cocaine administration. These data identify the Ras activator, Ras-GRF1, although not Ras-GRF2, as a susceptible target to cocaine stimulation in striatal neurons.