Young-Don Lee

Ajou University, Sŏul, Seoul, South Korea

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Publications (25)78.57 Total impact

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    ABSTRACT: Stroke is one of the common causes of death and disability. Despite extensive efforts in stroke research, therapeutic options for improving the functional recovery remain limited in clinical practice. Experimental stroke models using genetically modified mice could aid in unraveling the complex pathophysiology triggered by ischemic brain injury. Here, we optimized the procedure for generating mouse stroke model using an intraluminal suture in the middle cerebral artery and verified the blockage of blood flow using indocyanine green coupled with near infra-red radiation. The first week after the ischemic injury was critical for survivability. The survival rate of 11% in mice without any treatment but increased to 60% on administering prophylactic antibiotics. During this period, mice showed severe functional impairment but recovered spontaneously starting from the second week onward. Among the various behavioral tests, the pole tests and neurological severity score tests remained reliable up to 4 weeks after ischemia, whereas the rotarod and corner tests became less sensitive for assessing the severity of ischemic injury with time. Further, loss of body weight was also observed for up 4 weeks after ischemia induction. In conclusion, we have developed an improved approach which allows us to investigate the role of the cell death-related genes in the disease progression using genetically modified mice and to evaluate the modes of action of candidate drugs.
    Experimental neurobiology. 03/2014; 23(1):104-14.
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    ABSTRACT: The Cre/LoxP system is a well-established approach to spatially and temporally control genetic inactivation. The calcium/calmodulin-dependent protein kinase II alpha subunit (CaMKIIα) promoter limits expression to specific regions of the forebrain and thus has been utilized for the brain-specific inactivation of the genes. Here, we show that CaMKIIα-Cre can be utilized for simultaneous inactivation of genes in the adult brain and in male germ cells. Double transgenic Rosa26(+/stop-lacZ)::CaMKIIα-Cre(+/Cre) mice generated by crossing CaMKIIα-Cre(+/Cre) mice with floxed ROSA26 lacZ reporter (Rosa26(+/stop-lacZ)) mice exhibited lacZ expression in the brain and testis. When these mice were mated to wild-type females, about 27% of the offspring were whole body blue by X-gal staining without inheriting the Cre transgene. These results indicate that recombination can occur in the germ cells of male Rosa26(+/stop-lacZ)::CaMKIIα-Cre(+/Cre) mice. Similarly, when double transgenic Gnao(+/f)::CaMKIIα-Cre(+/Cre) mice carrying a floxed Go-alpha gene (Gnao(f/f)) were backcrossed to wild-type females, approximately 22% of the offspring carried the disrupted allele (Gnao(Δ)) without inheriting the Cre transgene. The Gnao(Δ/Δ) mice closely resembled conventional Go-alpha knockout mice (Gnao(-/-)) with respect to impairment of their behavior. Thus, we conclude that CaMKIIα-Cre mice afford recombination for both tissue- and time-controlled inactivation of floxed target genes in the brain and for their permanent disruption. This work also emphasizes that extra caution should be exercised in utilizing CaMKIIα-Cre mice as breeding pairs.
    Experimental & molecular medicine. 01/2014; 46:e93.
  • Neurobiology of Disease 10/2013; 58(C):249-257. · 5.62 Impact Factor
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    ABSTRACT: Transplantation of mesenchymal stem cells (MSCs) has been shown to enhance the recovery of brain functions following ischemic injury. Although immune modulation has been suggested to be one of the mechanisms, the molecular mechanisms underlying improved recovery has not been clearly identified. Here, we report that MSCs secrete transforming growth factor-beta (TGF-β) to suppress immune propagation in the ischemic rat brain. Ischemic stroke caused global death of resident cells in the infarcted area, elevated the monocyte chemoattractant protein-1 (MCP-1) level, and evoked massive infiltration of circulating CD68+ immune cells through the impaired blood brain barrier. Transplantation of MSCs at day 3 post-ischemia blocked the subsequent upregulation of MCP-1 in the ischemic area and the infiltration of additional CD68+ immune cells. MSC-conditioned media decreased the migration and MCP-1 production of freshly isolated immune cells in vitro, and this effect was blocked by an inhibitor of TGF-β signaling or an anti-TGF-β neutralizing antibody. Finally, transplantation of TGF-β1-silenced MSCs failed to attenuate the infiltration of CD68+ cells into the ischemic brain, and was associated with only minor improvements in motor function. These results indicate that TGF-β is key to the ability of MSCs to beneficially attenuate immune reactions in the ischemic brain. Our findings offer insight into the interactions between allogeneic MSCs and the host immune system, reinforcing the prospective clinical value of using MSCs in the treatment of neurological disorders involving inflammation-mediated secondary damage.
    Neurobiology of Disease 06/2013; · 5.62 Impact Factor
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    ABSTRACT: Human mesenchymal stem cells (MSCs) have emerged as attractive cellular vehicles to deliver therapeutic genes for ex-vivo therapy of diverse diseases; this is, in part, because they have the capability to migrate into tumor or lesion sites. Previously, we showed that MSCs could be utilized to deliver a bacterial cytosine deaminase (CD) suicide gene to brain tumors. Here we assessed whether transduction with a retroviral vector encoding CD gene altered the stem cell property of MSCs. MSCs were transduced at passage 1 and cultivated up to passage 11. We found that proliferation and differentiation potentials, chromosomal stability and surface antigenicity of MSCs were not altered by retroviral transduction. The results indicate that retroviral vectors can be safely utilized for delivery of suicide genes to MSCs for ex-vivo therapy. We also found that a single retroviral transduction was sufficient for sustainable expression up to passage 10. The persistent expression of the transduced gene indicates that transduced MSCs provide a tractable and manageable approach for potential use in allogeneic transplantation.
    Experimental & molecular medicine. 01/2013; 45:e10.
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is characterized by progressive dysfunction and degeneration of motor neurons in the central nervous system (CNS). In the absence of effective drug treatments for ALS, stem-cell treatment has emerged as a candidate therapy for this disease. To date, however, there is no consensus protocol that stipulates stem cell types, transplantation timing, or frequency. Using an ALS mouse model carrying a high copy-number of a mutant human superoxide dismutase-1 (SOD1)(G93A) transgene, we investigated the effect of neural induction on the innate therapeutic potential of mesenchymal stem cells (MSCs) in relation to preclinical transplantation parameters. In our study, the expression of monocyte chemoattractant protein-1 (MCP-1) was elevated in the ALS mouse spinal cord. Neural induction of MSCs with neurogenin1 (Ngn1) upregulated the expression level of the MCP-1 receptor, CCR2 and enhanced the migration activity toward MCP-1 in vitro. Ngn1- expressing MSCs (MSCs-Ngn1) showed a corresponding increase in tropism to the CNS after systemic transplantation in ALS mice. Notably, MSCs-Ngn1 delayed disease onset if transplanted during pre-onset ages, whereas unprocessed MSCs failed to do so. If transplanted near the onset ages, a single treatment with MSCs-Ngn1 was sufficient to enhance motor functions during the symptomatic period (15-17 weeks), whereas unprocessed MSCs required repeated transplantation to achieve similar levels of motor function improvement. Our data indicate that systemically transplanted MSCs-Ngn1 can migrate to the CNS and exert beneficial effects on host neural cells for an extended period of time through paracrine functions, suggesting a potential benefit of neural induction of transplanted MSCs in long-term treatment of ALS.
    Cell Transplantation 04/2012; · 4.42 Impact Factor
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    ABSTRACT: CREB mediates the transcriptional effects of glucose and incretin hormones in insulin-target cells and insulin-producing β-cells. Although the inhibition of CREB activity is known to decrease the β-cell mass, it is still unknown what factors inversely alter the CREB signaling pathway in β-cells. Here, we show that β-cell dysfunctions occurring in chronic hyperglycemia are not caused by simple inhibition of CREB activity but rather by the persistent activation of CREB due to decreases in protein phophatase PP2A. When freshly isolated rat pancreatic islets were chronically exposed to 25 mM (high) glucose, the PP2A activity was reduced with a concomitant increase in active pCREB. Brief challenges with 15 mM glucose or 30 µM forskolin after 2 hour fasting further increased the level of pCREB and consequently induced the persistent expression of ICER. The excessively produced ICER was sufficient to repress the transcription of NeuroD, insulin, and SUR1 genes. In contrast, when islets were grown in 5 mM (low) glucose, CREB was transiently activated in response to glucose or forskolin stimuli. Thus, ICER expression was transient and insufficient to repress those target genes. Importantly, overexpression of PP2A reversed the adverse effects of chronic hyperglycemia and successfully restored the transient activation of CREB and ICER. Conversely, depletion of PP2A with siRNA was sufficient to disrupt the negative feedback regulation of CREB and induce hyperglycemic phenotypes even under low glucose conditions. Our findings suggest that the failure of the negative feedback regulation of CREB is the primary cause for β-cell dysfunctions under conditions of pathogenic hyperglycemia, and PP2A can be a novel target for future therapies aiming to protect β-cells mass in the late transitional phase of non-insulin dependent type 2 diabetes (NIDDM).
    PLoS ONE 01/2012; 7(4):e34860. · 3.53 Impact Factor
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    ABSTRACT: Suicide genes have recently emerged as an attractive alternative therapy for the treatment of various types of intractable cancers. The efficacy of suicide gene therapy relies on efficient gene delivery to target tissues and the localized concentration of final gene products. Here, we showed a potential ex vivo therapy that used mesenchymal stem cells (MSCs) as cellular vehicles to deliver a bacterial suicide gene, cytosine deaminase (CD) to brain tumors. MSCs were engineered to produce CD enzymes at various levels using different promoters. When co-cultured, CD-expressing MSCs had a bystander, anti-cancer effect on neighboring C6 glioma cells in proportion to the levels of CD enzymes that could convert a nontoxic prodrug, 5-fluorocytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) in vitro. Consistent with the in vitro results, for early stage brain tumors induced by intracranial inoculation of C6 cells, transplantation of CD-expressing MSCs reduced tumor mass in proportion to 5-FC dosages. However, for later stage, established tumors, a single treatment was insufficient, but only multiple transplantations were able to successfully repress tumor growth. Our findings indicate that the level of total CD enzyme activity is a critical parameter that is likely to affect the clinical efficacy for CD gene therapy. Our results also highlight the potential advantages of autograftable MSCs compared with other types of allogeneic stem cells for the treatment of recurrent glioblastomas through repetitive treatments.
    International Journal of Cancer 10/2010; 127(8):1975-83. · 6.20 Impact Factor
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    ABSTRACT: Reelin, an extracellular glycoprotein has an important role in the proper migration and positioning of neurons during brain development. Lack of reelin causes not only disorganized lamination of the cerebral and cerebellar cortex but also malpositioning of mesencephalic dopaminergic (mDA) neurons. However, the accurate role of reelin in the migration and positioning of mDA neurons is not fully elucidated. In this study, reelin-deficient reeler mice exhibited a significant loss of mDA neurons in the substantia nigra pars compacta (SNc) and a severe alteration of cell distribution in the retrorubal field (RRF). This abnormality was also found in Dab1-deficinet, yotari mice. Stereological analysis revealed that total number of mDA neurons was not changed compared to wild type, suggesting that the loss of mDA neurons in reeler may not be due to the neurogenesis of mDA neurons. We also found that formation of PSA-NCAM-positive tangential nerve fibers rather than radial glial fibers was greatly reduced in the early developmental stage (E14.5) of reeler. These findings provide direct evidence that the alteration in distribution pattern of mDA neurons in the reeler mesencephalon mainly results from the defect of the lateral migration using tangential fibers as a scaffold.
    Anatomy & cell biology 09/2010; 43(3):241-51.
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    ABSTRACT: Members of helix-loop-helix (HLH) protein family of Id (inhibitor of differentiation) dimerize with bHLH transcription factors and function as negative regulators of differentiation during development. Most of inhibitory roles of Id proteins have been demonstrated in non-neural tissues, and their roles in the developing nervous system are not clearly demonstrated. In this study, we show that Id1, Id2, and Id3 increase self-renewing and proliferation potential of cortical neural stem cells (NSCs) while inhibiting neuronal differentiation. In electrophoretic mobility gel shift and luciferase assays, Id proteins interfered with binding of NeuroD/E47 complexes to the E-box sequences and inhibited E-box-mediated gene expression. Overexpression of Id proteins in NSCs increased both the number and the size of neurospheres in colony-forming assays. Expression of Hes1 and Hes5 was not increased by overexpression of Id proteins under the condition in which Nestin expression was increased. In utero electroporation of Id yielded higher numbers of Ki67-positive and Sox2-positive cells in the mouse embryonic brain. The study suggests Id proteins play independent roles in the maintenance of neural stem properties.
    Stem cells and development 09/2009; 19(6):831-41. · 4.15 Impact Factor
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    ABSTRACT: We have analyzed the importance of substrate methylation by S-adenosylmethionine-dependent methyltransferases for neuronal differentiation of P19 embryonal carcinoma cells. We show that treatment of cells with methyltransferase inhibitor adenosine dialdehyde (AdOx) interferes with neuronal differentiation. Retinoic acid (RA) and AdOx co-treated cells had a decreased number of neurites and a flattened morphology compared with cells differentiated by RA. Also, the amount of neuronal class III tubulin (Tuj1) decreased from 76% to 9.6% with AdOx-treatment. Gene expression levels of wnt-1, brn-2, neuroD, and mash-1 were also down-regulated by AdOx-treatment. But AdOx-treatment did not up-regulate BMP-4 and GFAP genes. Treatment of RA decreased E-cadherin expression during neuronal differentiation. However, in AdOx/RA co-treated cells, E-cadherin expression was restored to the control level. Also, mRNA expression of N-cadherin decreased with AdOx-treatment. Taken together, these data show that methylation reactions might influence the cell-fate decision and neuronal differentiation of P19 cells.
    Biochemical and Biophysical Research Communications 01/2009; 377(3):935-40. · 2.28 Impact Factor
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    ABSTRACT: Disabled 1 (Dab1), a cytoplasmic adaptor protein expressed predominantly in the CNS, transduces a Reelin-initiated signaling that controls neuronal migration and positioning during brain development. To determine the role of Dab1 in neural stem cell (NSC) differentiation, we established a culture of neurospheres derived from the embryonic forebrain of the Dab1(-/-) mice, yotari. Differentiating Dab1(-/-) neurospheres exhibited a higher expression of GFAP, an astrocytic marker, at the expense of neuronal markers. Under Dab1-deficient condition, the expression of NeuroD, a transcription factor for neuronal differentiation, was decreased and the JAK-STAT pathway was evidently increased during differentiation of NSC, suggesting the possible involvement of Dab1 in astrocyte differentiation via JAK-STAT pathway. Notably, expression of neural and glial markers and the level of JAK-STAT signaling molecules were not changed in differentiating NSC by Reelin treatment, indicating that differentiation of NSC is Reelin-independent. Immunohistochemical analyses showed a decrease in the number of neurons and an increase in the number of GFAP-positive cells in developing yotari brains. Our results suggest that Dab1 participates in the differentiation of NSCs into a specific cell lineage, thereby maintaining a balance between neurogenesis and gliogenesis.
    Molecular and Cellular Neuroscience 10/2008; 40(1):50-61. · 3.84 Impact Factor
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    ABSTRACT: Mesenchymal stem cells (MSCs) secrete bioactive factors that exert diverse responses in vivo. In the present study, we explored mechanism how MSCs may lead to higher functional recovery in the animal stroke model. Bone marrow-derived MSCs were transplanted into the brain parenchyma 3 days after induction of stroke by occluding middle cerebral artery for 2 h. Stoke induced proliferation of resident neural stem cells in subventricular zone. However, most of new born cells underwent cell death and had a limited impact on functional recovery after stroke. Transplantation of MSCs enhanced proliferation of endogenous neural stem cells while suppressing the cell death of newly generated cells. Thereby, newborn cells migrated toward ischemic territory and differentiated in ischemic boundaries into doublecortin+ neuroblasts at higher rates in animals with MSCs compared to control group. The present study indicates that therapeutic effects of MSCs are at least partly ascribed to dual functions of MSCs by enhancing endogenous neurogenesis and protecting newborn cells from deleterious environment. The results reinforce the prospects of clinical application using MSCs in the treatment of neurological disorders.
    Experimental and Molecular Medicine 09/2008; 40(4):387-97. · 2.57 Impact Factor
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    ABSTRACT: Mesenchymal stem cells (MSCs) have been shown to ameliorate a variety of neurological dysfunctions. This effect is believed to be mediated by their paracrine functions, since these cells rarely differentiate into neuronal cells. It is of clinical interest whether neural induction of MSCs is beneficial for the replacement therapy of neurological diseases. Here we report that expression of Neurogenin1 (Ngn1), a proneural gene that directs neuronal differentiation of progenitor cells during development, is sufficient to convert the mesodermal cell fate of MSCs into a neuronal one. Ngn1-expressing MSCs expressed neuron-specific proteins, including NeuroD and voltage-gated Ca2+ and Na+ channels that were absent in parental MSCs. Most importantly, transplantation of Ngn1-expressing MSCs in the animal stroke model dramatically improved motor functions compared with the parental MSCs. MSCs with Ngn1 populated the ischemic brain, where they expressed mature neuronal markers, including microtubule associated protein 2, neurofilament 200, and vesicular glutamate transporter 2, and functionally connected to host neurons. MSCs with and without Ngn1 were indistinguishable in reducing the numbers of Iba1+, ED1+ inflammatory cells, and terminal deoxynucleotidyl transferase dUTP nick-end labeling(+) apoptotic cells and in increasing the numbers of proliferating Ki67+ cells. The data indicate that in addition to the intrinsic paracrine functions of MSCs, motor dysfunctions were remarkably improved by MSCs able to transdifferentiate into neuronal cells. Thus, neural induction of MSCs is advantageous for the treatment of neurological dysfunctions.
    Stem Cells 08/2008; 26(9):2217-28. · 7.70 Impact Factor
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    ABSTRACT: The profile of membrane currents was investigated in differentiated neuronal cells derived from human neural stem cells (hNSCs) that were obtained from aborted fetal cortex. Whole-cell voltage clamp recording revealed at least 4 different currents: a tetrodotoxin (TTX)-sensitive Na(+) current, a hyperpolarization-activated inward current, and A-type and delayed rectifier-type K(+) outward currents. Both types of K(+) outward currents were blocked by either 5 mM tetraethylammonium (TEA) or 5 mM 4-aminopyridine (4-AP). The hyperpolarization-activated current resembled the classical K(+) inward current in that it exhibited a voltage-dependent block in the presence of external Ba(2+) (30microM) or Cs(+) (3microM). However, the reversal potentials did not match well with the predicted K(+) equilibrium potentials, suggesting that it was not a classical K(+) inward rectifier current. The other Na(+) inward current resembled the classical Na(+) current observed in pharmacological studies. The expression of these channels may contribute to generation and repolarization of action potential and might be regarded as functional markers for hNSCs-derived neurons.
    Korean Journal of Physiology and Pharmacology 08/2008; 12(4):131-5. · 1.00 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a progressive disease which is caused by degeneration of motor neurons in the central nervous system. The incidence of ALS is higher in men than women, but the female advantage disappears with increased age. Here, we report evidence that the female advantage is due to the protective role of estrogen. In an ALS mouse model carrying the human Cu/Zn superoxide dismutase (hSOD1) G93A transgene, ovariectomy did not alter the onset age of the disease while reducing the female lifespan by 7 days and making it comparable to that of the male transgenic mice. Treatment of ovariectomized females with 17beta-estradiol (E2) did not delay the onset of disease, but prevented progression of ALS motor dysfunctions as shown by extension reflex test for a limited time window. Importantly, E2 treatment rescued the lifespans in overiectomized females. These findings will provide important new insights to interpretation of disease progression in post-menopausal female ALS patients.
    Journal of the Neurological Sciences 06/2008; 268(1-2):40-7. · 2.24 Impact Factor
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    ABSTRACT: G(o), a member of the G(o/i) family, is the most abundant heterotrimeric G protein in brain. Most functions of G(o) are mediated by the G(betagamma) dimer; effector(s) for its alpha-subunit have not been clearly defined. Here we report that G(oalpha) interacts directly with cAMP-dependent protein kinase (PKA) through its GTPase domain. This interaction did not inhibit the kinase function of PKA but interfered with nuclear translocation of PKA while sparing its cytosolic function. This regulatory mechanism by which G(o) bifurcates PKA signaling may provide insights into how G(o) regulates complex processes such as neuritogenesis, synaptic plasticity, and cell transformation.
    Proceedings of the National Academy of Sciences 01/2007; 103(50):19158-63. · 9.81 Impact Factor
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    ABSTRACT: Mesenchymal stem cells are able to trans-differentiate into nonmesodermal lineage cells. Here, we identified downstream signaling molecules required for acquisition of neuron-like traits by mesenchymal stem cells following the elevation of intracellular cAMP levels. We found that forskolin induced neuron-like morphology and expression of neuron-specific enolase and neurofilament-200 in mesenchymal stem cells. Forskolin sequentially activated protein kinase A and B-regulation of alpha-fetoprotein (Raf), which led to phosphorylation of extracellular signal-regulated kinase. Importantly, blockade of extracellular signal-regulated kinase phosphorylation with a mitogen-activated protein kinase (MAPK) kinase inhibitor abrogated the forskolin-induced morphological changes and induction of neuronal proteins. These results indicate that extracellular signal-regulated kinase/MAPK mediates both cAMP-induced early cytoskeletal rearrangement and the later induction of neuronal markers in mesenchymal stem cells.
    Neuroreport 09/2005; 16(12):1357-61. · 1.40 Impact Factor
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    ABSTRACT: 1. Neurogenin1 (Ngn1) is a basic helix-loop-helix (bHLH) transcription factor that is expressed in neuronal precursors during development of the nervous system. 2. In the present work, we investigated a instructive potential of Ngn1 in pluripotent embryonal carcinoma P19 cells. Treatment with retinoic acid (RA) induced expression of Ngn1 as well as NeuroD in P19 cells in early period of neuronal differentiation. P19 cells contained endogenous E47, a heterodimeric partner of neurogenic bHLH factors, and overexpression of Ngn1 alone was sufficient to induce the maximum activation of the E-box-mediated gene expression. 3. Sustained expression of Ngn1 in the absence of RA was sufficient to induce substantial expression of neuronal markers. The data indicate that Ngn1 is able to commit pluripotent P19 cells to adopt a neural cell phenotype in the absence of RA, which may finally lead to enhanced neuronal differentiation. The results also suggest that RA may induce neuronal differentiation of P19 cells by promoting a bHLH cascade including Ngn1.
    Cellular and Molecular Neurobiology 07/2004; 24(3):343-56. · 2.29 Impact Factor
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    ABSTRACT: Go, a heterotrimeric G-protein, is enriched in brain and neuronal growth cones. Although several reports suggest that Go may be involved in modulation of neuronal differentiation, the precise role of Go is not clear. To investigate the function of Go in neuronal differentiation, we determined the effect of Goalpha, the alpha subunit of Go, on the expression of Ca(v)2.2, the pore-forming unit of N-type calcium channels, at the transcription level. Treatment with cyclic AMP (cAMP), which triggers neurite outgrowth in neuroblastoma F11 cells, increased the mRNA level and the promoter activity of the Ca(v)2.2 gene. Overexpression of Goalpha inhibited neurite extension in F11 cells and simultaneously repressed the stimulatory effect of cAMP on the Ca(v)2.2 gene expression to the basal level. Targeted mutation of the Goalpha gene also increased the level of Ca(v)2.2 in the brain. These results suggest that Go may regulate neuronal differentiation through modulation of gene expression of target genes such as N-type calcium channels.
    Molecular Brain Research 05/2003; 112(1-2):95-102. · 2.00 Impact Factor