Human Serotonin Transporter: Regulation by the Neuroprotective Agent Aurintricarboxylic Acid and by Epidermal Growth Factor (original) (raw)
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Functional link between tyrosine phosphorylation and human serotonin transporter gene expression
European Journal of Pharmacology, 1997
Treatment of the JAR human placental choriocarcinoma cells with herbimycin A, an inhibitor of tyrosine kinases, led to an increase in the activity of the serotonin transporter. This effect was accompanied by an increase in the serotonin transporter density and in the steady-state levels of the serotonin transporter mRNA. A treatment time of) 4 h was necessary for herbimycin A to elicit its effect. Actinomycin D and cycloheximide blocked the effect. There was no increase in the steady-state levels of the serotonin transporter mRNA when cells were treated with herbimycin A in the presence of actinomycin D. The herbimycin A-induced increase in the transporter activity was abolished by genistein, another inhibitor of tyrosine kinases. But the increase in the transporter mRNA levels caused by herbimycin A was not affected by genistein. Treatment of cells with herbimycin A resulted in an increase in the tyrosine phosphorylation of specific cellular proteins, suggesting that herbimycin A directly or indirectly activates specific tyrosine kinases. It is concluded that tyrosine phosphorylation is an essential component in the signaling pathways participating in the regulation of the human serotonin transporter gene expression. q 1997 Elsevier Science B.V.
Acta Physiologica, 2008
Aim: The aim of this study was to determine the effect of long-term serotonin (5-hydroxytryptamine, 5-HT) treatment on the human serotonin transporter (hSERT) function and its expression.Methods: This study was carried out in the enterocyte-like cell line Caco-2. These cells constitutively express the hSERT and have been shown to be an excellent model for the study of this protein. We measured serotonin transport, levels of mRNA expression and of the SERT protein after treating the cells with serotonin.Results: Serotonin treatment diminished hSERT activity in a concentration and period-dependent way by increasing the Kt value and reducing Vmax. This inhibition was reversible and was not mediated by either the action of 5-HT2, 5-HT3 or 5-HT4 receptors, or by the intracellular second messengers, protein kinase C and cAMP. 5-HT did not seem to affect either the mRNA level of the SERT or the protein transporter measured in either the membrane or the cell lysate. The 5-HT treatment effect was additive to the inhibitory effect of treatment with a low concentration of citalopram and fluoxetine. Nevertheless, 5-HT did not increase the inhibition yielded by treatment with high concentration citalopram.Conclusion: The chronic increase in serotonin in the extracellular medium diminishes the function of the SERT. This effect seems to be due to an effect on the transporter molecule itself in the membrane, without altering protein synthesis, intracellular traffic, or its availability.
Serotonin transport is modulated differently by tetanus toxin and growth factors
2003
It has been previously shown that 5-HT uptake inhibition produced by tetanus toxin (TeTx) corresponds to a non-competitive inhibition, and it is preceded by phosphorylation of the tyrosine-kinase receptor trkA, phospholipase C activation and translocation of protein kinase C isoforms [FEBS Lett. 481 (2000) 177; FEBS Lett. 486 (2000) 136]. In the present work, it is shown that agonists of tyrosine-kinase receptors (NGF, EGF, basic FGF) enhance Na +-dependent, 5-hydroxytryptamine (serotonin, 5-HT) uptake in the synaptosomal-enriched P 2 fraction from rat-brain, suggesting a divergence in the intracellular signal pathways triggered by TeTx and by agonists of TyrK receptors. Co-applications of TeTx and agonists of TyrK receptors result in a mutual and partial reversion of their effects on 5-HT transport. In spite of their differences on transport, TeTx, TPA and NGF produce an increase in serotonin transporter phosphorylation in Ser separately, which is abolished by the PKC-inhibitor bisindolylmaleimide-1. Co-application of sodium vanadate, a tyrosine-phosphatase inhibitor, partially abolishes the effect produced by TeTx, whereas genistein, a tyrosine-kinase inhibitor, does not exert any variation of TeTx inhibition. Analyses by immunoblotting of the activation of specific PKC isoforms activation, determined as translocation to the membrane compartment, reveals differences in the pattern produced by NGF and TeTx. PKC␥, ␦, and ε isoforms are equally activated by both compounds, whereas the  isoform is activated in a sustained manner only by TeTx, and the ␣ isoform is only down-regulated by NGF. The aim of the present work was to explore whether NGF have the same effect on 5-HT transport than TeTx, since both compounds share the ability of activate part of the same transduction pathways. In spite of this, growth factors and TeTx show an opposite effect on 5-HT transport, even though SERT phosphorylation is enhanced in both cases. The differential effect on ␣and -PKC isoenzymes found between NGF and TeTx action could explain this apparent discrepancy.
Distribution and pharmacology of alanine-serine-cysteine transporter 1 (asc-1) in rodent brain
European Journal of Neuroscience, 2003
A polyclonal antibody against the Na-independent alanine±serine±cysteine transporter 1 (asc-1) was raised and the speci®city of the antibody veri®ed by Western blots performed on membranes prepared from HEK293 cells transiently transfected with the cloned murine asc-1. The antibody was then used to localize the transporter in the brain of two rodent species by using immunohistochemistry at the light and electron microscopical level. asc-1-immunoreactivity (asc-1-ir) was widely distributed throughout the mouse and rat brain. Areas with high levels of asc-1-ir included hypothalamus, the medial septal area, globus pallidus, entopeduncular nucleus, cingulate and retrosplenial cortices. Moderate asc-1-ir was observed in several areas including layers III and V of the neocortex, thalamus, nucleus accumbens, caudate putamen, bed nucleus of stria terminalis, all amygdaloid nuclei, hippocampus (CA1±CA3 and hilus of the dentate gyrus), as well as several brainstem nuclei. asc-1-ir was observed as punctuate staining consistent with varicosities matching neuronal cell bodies and dendritic ®elds. At the ultrastructural level, asc-1-ir was mainly con®ned to presynaptic terminals. Immunostaining in either glial cell bodies or perivascular sites was not observed and white matter was completely devoid of asc-1-ir. Furthermore, the pharmacology of the Na-independent uptake site for [ 3 H]D-serine in rat brain synaptosomal P2 fractions was compared with the substrate speci®city of the cloned human asc-1 transporter and a high degree of correlation was demonstrated. We conclude that asc-1-ir is widespread in the brain and limited to neuronal structures and that asc-1 may contribute to synaptic clearance of D-serine in brain.
Journal of physiology and pharmacology : an official journal of the Polish Physiological Society, 2006
The serotonin transporter (SERT) has shown itself to be an effective pharmacological target in the treatment of mood disorders and some kinds of gastrointestinal syndromes. Most of the molecular studies of SERT in humans have been carried out using heterologous models. In this work, we have investigated the human enterocyte-like Caco-2 cell line as a potential "in vitro" model to study the human SERT. The results show that these cells express a SERT mRNA identical to the human brain SERT, and a 70 kDa protein immunodetected using a specific antibody. The SERT activity levels in Caco-2 cells increased in correlation with the onset and maintenance of the morphological and functional differentiation of the cells. Caco-2 SERT was also shown to be a high affinity (Kt=0.216 microM) saturable, Na(+) -dependent transporter that was inhibited by fluoxetine (IC(50)=17.6 nM). In addition, SERT activity was inhibited by the intracellular modulators protein kinase C and cAMP, either af...
AJP: Gastrointestinal and Liver Physiology, 2011
Serotonin transporter (SERT) regulates extracellular availability of serotonin and is a potential pharmacological target for gastrointestinal disorders. A decrease in SERT has been implicated in intestinal inflammatory and diarrheal disorders. However, little is known regarding regulation of SERT in the intestine. Epidermal growth factor (EGF) is known to influence intestinal electrolyte and nutrient transport processes and has protective effects on intestinal mucosa. Whether EGF regulates SERT in the human intestine is not known. The present studies examined the regulation of SERT by EGF, utilizing Caco-2 cells grown on Transwell inserts as an in vitro model. Treatment with EGF from the basolateral side (10 ng/ml, 24 h) significantly stimulated SERT activity (∼2-fold, P < 0.01) and mRNA levels compared with control. EGF increased the activities of the two alternate promoter constructs for human SERT gene: SERT promoter 1 (hSERTp1, upstream of exon 1a) and SERT promoter 2 (hSERTp...
Research report Cellular localization and expression of the serotonin transporter in mouse brain
The high-affinity serotonin 5-HT transporter 5-HTT plays an important role in the removal of extracellular serotonin, thereby modulating and terminating the action of this neurotransmitter at various pre- and post-synaptic serotonergic receptors and heterorecep- tors. In order to characterize the anatomical distribution of the 5-HTT in mouse brain, in situ hybridization histochemistry using 35 w125 x S-labeled riboprobes was performed. These results were compared with 5-HTT binding site distribution as evaluated by I RTI-55 autoradiography. High levels of 5-HTT mRNA were detected in all brain stem raphe nuclei, with variations in labeling among the various subnuclei. Those brain areas known to possess serotonergic cell bodies stained intensely for both 5-HTT mRNA and 5-HTT binding sites. In contrast to previous findings in rat brain, the highest densities of 5-HTT sites were found in areas outside the raphe complex, particularly in the substantia nigra, globus pallidus, and superior...
Journal of Neuroimmunology, 2005
Serotonin transporter sites were characterized in blood lymphocytes of rats. Pharmacological characteristics of drug interactions were in concordance with recent studies in nervous and human immune cells. The potency order of inhibition of [ 3 H]paroxetine binding was imipramineNcitalopramNalaproclateNserotonin. Selective inhibitors of dopamine or noradrenaline transporters did not inhibit it. The specific binding of [ 3 H]paroxetine was higher at intermediate than at low concentrations, and the plot of free vs. specific binding had a sigmoid shape. The affinity constant or K d , 1.77 nM, was in close agreement with data obtained from kinetic studies (K d =1.33 nM), which evidences that the equilibrium was reached. In addition, serotonin transporter was evaluated by lipopolysaccharide or concanavalin A administration in vivo (0.1 mg/kg, i.p., 18 h). After the treatment with lipopolysaccharide, no changes were observed in the numbers of sites or B max or in the affinity, K d . The treatment with concanavalin A showed a significant reduction in B max and reduction in K d . Additionally, serotonin and 5hydroxyindoleacetic acid levels were determined in plasma and lymphocytes by high-performance liquid chromatography. Treatment with lipopolysaccharide produced a significant increased of serotonin levels in lymphocytes without changes in 5-hydroxyindoleacetic acid level; in plasma, it produced an increase in serotonin and 5-hydroxyindolacetic acid levels. In addition, serotonin synthesis was evaluated by adding 300 AM of tryptophan in the medium, which significantly increased serotonin levels in control lymphocytes. Moreover, the concentrations of 5-hydroxyindoleacetic acid was enhanced significantly, both in plasma and lymphocytes in the presence of tryptophan after treatment with lipopolysaccharide. The administration of concanavalin A significantly decreased plasma levels of serotonin, as well as the concentrations of serotonin and 5-hydroxyindoleacetic acid in lymphocytes. These results demonstrate the presence of serotonin transporter in lymphocytes of rat blood, the capacity for serotonin synthesis in lymphocytes, and the modulation of these parameters by systemic administration of mitogens. The findings of this work contribute to understanding the immunological role of serotonin and the communication of immune and nervous systems. D
Serotonin depletion decreases serotonin transporter mRNA levels in rat brain
Brain Research, 1995
In order to study the impact of serotonin depletion on gene expression of the serotonin transporter (5-HTt) we measured 5-HTt mRNA levels by Northern blot in rats treated with p-chlorophenylalanine methyl ester (PCPA) for 10 days. Six rats received PCPA i.p. only, and another 6 rats receiving 0.9% NaCl served as controls. An additional group of 6 rats received both PCPA i.p. and imipramine, 5 mg/kg/day by osmotic minipumps. 5-HTt mRNA levels decreased to 81.1% (P = 0.05) and 76.0% (P = 0.05) of the control level for PCPA treated animals without and with concomitant imipramine treatment, respectively. The average level of the PCPA treated groups was 78.6% (P = 0.03). The isolated effect of 21 days of imipramine treatment was a 5-HTt mRNA level of 89.4%, which was not significantly different from the control level. In conclusion, 5-HTt gene expression is suppressed in the serotonin depleted state. A decreased synaptic reuptake of 5-HT may be interpreted as a compensatory mechanism aiming at preserving adequate synaptic 5-HT levels in a generally deficient state.