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SLC6A6; solute carrier family 6 (neurotransmitter transporter), member 6 (3p25.1)

Gene Summary

Gene:SLC6A6; solute carrier family 6 (neurotransmitter transporter), member 6
Aliases: TAUT
Location:3p25.1
Summary:This gene encodes a multi-pass membrane protein that is a member of a family of sodium and chloride-ion dependent transporters. The encoded protein transports taurine and beta-alanine. There is a pseudogene for this gene on chromosome 21. Alternative splicing results in multiple transcript variants. [provided by RefSeq, May 2013]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:sodium- and chloride-dependent taurine transporter
HPRD
Source:NCBI
Updated:14 December, 2014

Gene
Ontology:

What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1989-2014)
Graph generated 14 December 2014 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 14 December, 2014 using data from PubMed, MeSH and CancerIndex

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Latest Publications: SLC6A6 (cancer-related)

Satofuka H, Okabe Y, Takano Y, et al.
Immunization method for multi-pass membrane proteins using highly metastatic cell lines.
Biochem Biophys Res Commun. 2014; 450(1):99-104 [PubMed] Related Publications
A novel method using metastatic breast cancer cell lines was established for producing monoclonal antibodies (mAbs) against multi-span membrane proteins. Grafting of metastatic cells (MCF7-14) into the mammary gland of BALB/cJ/nu/nu mice induced splenic hypertrophy (1.6-3.0×10(8)cells/spleen [n=6]). More than half of the mAbs against MCF7-14 cells reacted with the cell membrane. Inducing production of antibodies against the extracellular domain of multi-pass membrane proteins is difficult. Because the protein structure becomes more complex as the number of transmembrane domains increases, preparing antigens for immunization in which the original structure is maintained is challenging. Using highly metastatic MDA-MB231 cells as the host cell line, we produced mAbs against a 12 transmembrane protein, solute carrier family 6 member 6 (SLC6A6), as a model antigen. When SLC6A6-overexpressing MDA-MB231 cells were grafted into nude mice, the number of splenocytes increased to 2.7-11.4×10(8)cells/spleen (n=10). Seven mAb-producing clones that not only recognized the extracellular domain of SLC6A6 but also were of the IgG subclass were obtained. Immunocytochemistry and flow cytometry analyses revealed that these mAbs recognized the native form of the extracellular domain of SLC6A6 on the cell surface. Our novel immunization method involving highly metastatic cells could be used to develop therapeutic mAbs against other multi-pass membrane proteins.

Related: Monoclonal Antibodies


Yasunaga M, Matsumura Y
Role of SLC6A6 in promoting the survival and multidrug resistance of colorectal cancer.
Sci Rep. 2014; 4:4852 [PubMed] Free Access to Full Article Related Publications
The treatment of colorectal cancer (CRC) might be improved by the identification of a signalling pathway that could be targeted with novel therapeutics. The results of this study indicate that the taurine transporter SLC6A6 is highly expressed in CRC cells compared with normal colonocytes. SLC6A6 knockdown (KD) attenuated cell survival and was accompanied by enhanced drug sensitivity to 5-fluorouracil (5-FU), doxycycline (DOX) and SN-38. Both the population frequency of the side population (SP) cells and their cancer stem cell (CSC)-like properties (such as tumour initiation, differentiation and chemoresistance) were abrogated by SLC6A6-KD. Conversely, SLC6A6 overexpression increased cell survival and the proportion of SP cells, enhancing multidrug resistance (MDR). Additionally, SLC6A6-siRNA treatment enhanced the cytotoxic effects of all 3 drugs, whereas the efficacy of ABCG2-siRNA treatment was limited to its 2 substrate drugs, DOX and SN-38. This study indicates that SLC6A6 plays an important role in the maintenance of CSC characteristics, thus promoting cell survival signalling and chemoresistance. Therefore, SLC6A6 inhibition may be a promising therapeutic strategy for refractory CRC.

Related: Colorectal (Bowel) Cancer Fluorouracil Signal Transduction ABCG2


Kim SJ, Sohn I, Do IG, et al.
Gene expression profiles for the prediction of progression-free survival in diffuse large B cell lymphoma: results of a DASL assay.
Ann Hematol. 2014; 93(3):437-47 [PubMed] Related Publications
We performed the whole genome cDNA-mediated annealing, selection and ligation assay with 164 formalin-fixed paraffin-embedded (FFPE) tumor samples to develop robust prognostic gene expression profiles in patients with diffuse large B cell lymphoma. The prognostic gene expression profiles were developed and validated by a gradient lasso and leave-one-out cross-validation process. We identified a set of genes whose expression provided prognostic indicators from whole data set (PRKCDBP, CASP10, FAM3C, KCNK12, MAN1A2, PRND, RAB1A, TMEM39B, SLC6A6, MMP12, FEM1B, C3orh37, RBP1, HK1, LOC400464, KIAA0746, and SLC25A23). This gene expression profile-based risk model could classify patients into two cross-validated risk groups with a significant difference in 5-year progression-free survival rates (71.1 vs. 45.5 %) and with a hazard ratio for recurrence of 2.45 (95 % CI, 1.44-4.16, P = 0.001). This model provided prognostic information independent of the International Prognostic Index (IPI), and discriminated high-risk group from patients belong to high/high-intermediate risk of IPI and activated B cell-like type. Thus, gene expression profiling from FFPE could provide additional prognostic information for diffuse large B cell lymphoma and our data underscore the need for development of risk-adapted treatment strategies based on gene expression profiles.


Villumsen KR, Duelund L, Lambert IH
Acute cholesterol depletion leads to net loss of the organic osmolyte taurine in Ehrlich Lettré tumor cells.
Amino Acids. 2010; 39(5):1521-36 [PubMed] Related Publications
In mammalian cells, the organic osmolyte taurine is accumulated by the Na-dependent taurine transporter TauT and released though the volume- and DIDS-sensitive organic anion channel. Incubating Ehrlich Lettré tumor cells with methyl-β-cyclodextrin (5 mM, 1 h) reduces the total cholesterol pool to 60±5% of the control value. Electron spin resonance data indicate a concomitant disruption of cholesterol-rich micro-domains. Active taurine uptake, cellular taurine content, and cell volume are reduced by 50, 20 and 20% compared to control values, respectively, whereas the passive taurine release is increased 4.5-fold under isotonic conditions following cholesterol depletion. However, taurine release under isotonic conditions is insensitive to DIDS and inhibitors of the volume-regulated anion channel. Uptake and release of meAIB are similarly affected following cholesterol depletion. Kinetic analysis reveals that cholesterol depletion increases TauT's affinity toward taurine but reduces its maximal transport capacity. Cholesterol depletion has no impact on TauT regulation by protein kinases A and C. Phospholipase A2 activity, which is required for the activation of volume-sensitive organic anion channel (VSOAC), is increased under isotonic and hypotonic conditions following cholesterol depletion, whereas taurine release under hypotonic conditions is reduced following cholesterol depletion. Hence, acute cholesterol depletion of Ehrlich Lettré cells leads to reduced TauT and VSOAC activities and at the same time increases the release of organic osmolytes via a leak pathway different from the volume-sensitive pathways for amino acids and anions.


Sadzuka Y, Matsuura M, Sonobe T
The effect of taurine, a novel biochemical modulator, on the antitumor activity of doxorubicin.
Biol Pharm Bull. 2009; 32(9):1584-7 [PubMed] Related Publications
Taurine is contained in seafood and has been studied extensively on life-style related diseases. Theanine increased the effects of the doxorubicin (DOX) as an antitumor agent in some tumors and enhanced the DOX level in tumor cells. It is expected that the advanced effect of food uptake in cancer chemotherapy may be effective from the viewpoint of quality of life (QOL) improvement, although this approach has not been investigated in detail. In this study, the effect of taurine as a functional amino acid was examined. Taurine did not change the DOX influx into M5076 cells, whereas it significantly inhibited DOX efflux, which maintained the DOX level in tumor cells. Furthermore, experiments with taurine decreased tumor weight by 40%, compared to the DOX-alone group and significantly increased its antitumor effect. Moreover, as taurine did not increase DOX concentration in normal tissue, it is suggested that it increased the antitumor effect without enhancing DOX-induced adverse effects. DOX efflux is inhibited by beta-alanine as a taurine transporter inhibitor, therefore, enhancement of the DOX level by taurine was suggested to act via taurine transport. Namely, it was clarified that taurine was useful as a modulator to enhance the therapeutic index of cancer patients and improve QOL.

Related: Doxorubicin Cancer Prevention and Risk Reduction


Shennan DB, Thomson J
Estrogen regulation and ion dependence of taurine uptake by MCF-7 human breast cancer cells.
Cell Mol Biol Lett. 2007; 12(3):396-406 [PubMed] Related Publications
It has been reported that estrogen receptor-positive MCF-7 cells express TauT, a Na(+)-dependent taurine transporter. However, there is a paucity of information relating to the characteristics of taurine transport in this human breast cancer cell line. Therefore, we have examined the characteristics and regulation of taurine uptake by MCF-7 cells. Taurine uptake by MCF-7 cells showed an absolute dependence upon extracellular Na(+). Although taurine uptake was reduced in Cl(-) free medium a significant portion of taurine uptake persisted in the presence of NO(3) (-). Taurine uptake by MCF-7 cells was inhibited by extracellular beta-alanine but not by L-alanine or L-leucine. 17β-estadiol increased taurine uptake by MCF-7 cells: the V(max) of influx was increased without affecting the K(m). The effect of 17β-estradiol on taurine uptake by MCF-7 cells was dependent upon the presence of extracellular Na(+). In contrast, 17β-estradiol had no significant effect on the kinetic parameters of taurine uptake by estrogen receptor-negative MDA-MB-231 cells. It appears that estrogen regulates taurine uptake by MCF-7 cells via TauT. In addition, Na(+)-dependent taurine uptake may not be strictly dependent upon extracellular Cl(-).

Related: Breast Cancer


Kim C
Accumulation of taurine in tumor and inflammatory lesions.
Adv Exp Med Biol. 2006; 583:213-7 [PubMed] Related Publications


Warskulat U, Borsch E, Reinehr R, et al.
Chronic liver disease is triggered by taurine transporter knockout in the mouse.
FASEB J. 2006; 20(3):574-6 [PubMed] Related Publications
Taurine is an abundant organic osmolyte with antioxidant and immunomodulatory properties. Its role in the pathogenesis of chronic liver disease is unknown. The liver phenotype was studied in taurine transporter knockout (taut-/-) mice. Hepatic taurine levels were ~21, 15 and 6 mumol/g liver wet weight in adult wild-type, heterozygous (taut+/-) and homozygous (taut-/-) mice, respectively. Immunoelectronmicroscopy revealed an almost complete depletion of taurine in Kupffer and sinusoidal endothelial cells, but not in parenchymal cells of (taut-/-) mice. Compared with wild-type mice, (taut-/-) and (taut+/-) mice developed moderate unspecific hepatitis and liver fibrosis with increased frequency of neoplastic lesions beyond 1 year of age. Liver disease in (taut-/-) mice was characterized by hepatocyte apoptosis, activation of the CD95 system, elevated plasma TNF-alpha levels, hepatic stellate cell and oval cell proliferation, and severe mitochondrial abnormalities in liver parenchymal cells. Mitochondrial dysfunction was suggested by a significantly lower respiratory control ratio in isolated mitochondria from (taut-/-) mice. Taut knockout had no effect on taurine-conjugated bile acids in bile; however, the relative amount of cholate-conjugates acid was decreased at the expense of 7-keto-cholate-conjugates. In conclusion, taurine deficiency due to defective taurine transport triggers chronic liver disease, which may involve mitochondrial dysfunction.

Related: TNFRSF6 gene Apoptosis Cytokines TNF


Zielińska M, Zabłocka B, Dybel A, Albrecht J
The role of protein kinase C and cyclic AMP in the ammonia-induced shift of the taurine uptake/efflux balance towards efflux in C6 cells.
Neurochem Res. 2005; 30(3):349-54 [PubMed] Related Publications
A previous study showed that treatment of C6 glioma cells with 10 mM ammonium chloride monia") for 24 h decreases taurine uptake and evokes sodium-dependent taurine efflux, indicating reversal of the taurine transporter (TauT)-mediated transport as an underlying mechanism. Consistent with the involvement of TauT we now show that the ammonia-induced changes in Tau uptake and efflux are inhibited by the protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDBu). Ammonia treatment of C6 cells resulted in increased intracellular accumulation of cAMP. Incubation of the cells with dibutyryl cAMP (dbcAMP) mimicked the effects of ammonia on both taurine uptake and efflux. The effects of dbcAMP on taurine uptake and efflux were additive to the effects of ammonia. Collectively, the results suggest that the effects of ammonia on taurine uptake and efflux may be partly mediated by cAMP. Consistent with this mechanism, the adenyl cyclase inhibitor, miconazole reduced the stimulation of efflux by ammonia.


Mochizuki T, Satsu H, Nakano T, Shimizu M
Regulation of the human taurine transporter by TNF-alpha and an anti-inflammatory function of taurine in human intestinal Caco-2 cells.
Biofactors. 2004; 21(1-4):141-4 [PubMed] Related Publications
We investigated whether or not the inflammatory cytokines affect the activity of taurine transporter (TAUT) in human intestinal Caco-2 cells. Among the cytokines, tumor necrosis factor alpha(TNF-alpha) markedly augmented the TAUT activity. A kinetic analysis of the TAUT activity in TNF-alpha-treated Caco-2 cells suggests that this up-regulation was associated with both an increase in the amount of TAUT and an increase in its affinity. Considering these results, it seems that intracellular taurine plays a role in the intestinal epithelial cells under such an inflammatory condition as that caused by an excessive amount of TNF-alpha secreted by macrophages. To verify this hypothesis, we examined the effect of taurine on inflamed intestinal cells by using a co-culture system of Caco-2 cells with human macrophage-like THP-1 cells. The result shows that taurine significantly repressed the damage to Caco-2 cells caused by TNF-alpha secreted by THP-1 cells. Thus, taurine may be a useful substance against intestinal inflammation.

Related: Cytokines TNF


Hillenkamp J, Hussain AA, Jackson TL, et al.
Taurine uptake by human retinal pigment epithelium: implications for the transport of small solutes between the choroid and the outer retina.
Invest Ophthalmol Vis Sci. 2004; 45(12):4529-34 [PubMed] Related Publications
PURPOSE: To characterize the Michaelis-Menten kinetics of the taurine transporter (TT) in retinal pigment epithelium (RPE) freshly isolated from human donor eyes. To identify the rate limiting compartment in the pathway of taurine delivery from the choroidal blood supply to the outer retina composed by Bruch's-choroid (BC) and the RPE in the human older age group.
METHODS: In human donor samples (4 melanoma-affected eyes, and 14 control eyes; age range, 62-93 years), radiochemical techniques were used to determine the RPE taurine accumulation at various exogenous concentrations. The transport capability of human RPE was obtained from a kinetic analysis of the high-affinity carrier over a substrate concentration of 1 to 60 microM taurine.
RESULTS: Uptake of taurine into human RPE at a taurine concentration of 1 microM was independent of donor age (P > 0.05) and averaged at 2.83 +/- 0.27 (SEM) pmol/10 minutes per 6-mm trephine. Taurine transport by human RPE was mediated by a high-affinity carrier of K(m) 50 microM and V(max) of 267 pmol/10 minutes per 5-mm disc.
CONCLUSIONS: In human donor RPE, uptake of taurine remained viable in the age range 62 to 93 years. Taurine transport rates in the RPE were lower than across the isolated BC complex, and thus the data suggest that the former compartment houses the rate-limiting step in the delivery of taurine to the outer retina.

Related: Eye Cancer Melanoma


Williams JB, Mallorga PJ, Conn PJ, et al.
Effects of typical and atypical antipsychotics on human glycine transporters.
Schizophr Res. 2004; 71(1):103-12 [PubMed] Related Publications
Augmentation strategy in the treatment of schizophrenia with the NMDA receptor co-agonist glycine has demonstrated significant improvement in patient symptoms. Interestingly, the therapeutic efficacy of glycine was more consistent among patients that were not co-administered clozapine suggesting that clozapine modulates glycine levels in brain. Since cerebral glycine concentration in the vicinity of NMDA receptors is thought to be controlled by the glia expressed glycine transporter type 1 (GlyT1), the effects of several typical and atypical antipsychotics on glycine uptake were examined in human placenta choriocarcinoma (JAR) cells expressing human GlyT1a. The selectivity of these compounds was investigated by measuring their inhibitory potency at the closely related glycine transporter type 2 (GlyT2). Typical antipsychotics haloperidol, thioridazine and chlorpromazine non-selectively inhibited [(14)C]glycine uptake mediated by GlyT1a and GlyT2 with potency of 9-21 microM. The atypical antipsychotic, clozapine antagonized glycine transport by human GlyT1a with an IC(50) of 100 microM and was weaker at recombinant GlyT2. Its main metabolites, N-desmethylclozapine and clozapine N-oxide were very weak inhibitors at all glycine transporters. Similarly, olanzapine did not potently block GlyT1a- and GlyT2-mediated uptake. Detailed kinetic analysis of hGlyT1a in the presence and absence of haloperidol and clozapine revealed that both drugs were not competitive inhibitors of glycine uptake. Data also indicated that these compounds did not interact with the Na(+) and Cl(-) sites of hGlyT1a. Our results have revealed the existence of an inhibitory interaction between some antipsychotics and hGlyT1a and raise the possibility that these drugs could interact with GlyT1 function at therapeutic doses.


Satsu H, Manabe M, Shimizu M
Activation of Ca2+/calmodulin-dependent protein kinase II is involved in hyperosmotic induction of the human taurine transporter.
FEBS Lett. 2004; 569(1-3):123-8 [PubMed] Related Publications
We investigated the signaling pathways participating in hyperosmotic regulation of the human taurine transporter (TAUT) by using specific inhibitors of various intracellular signaling molecules. Among them, the specific inhibitor of calcium/calmodulin-dependent protein kinase II (Ca(2+)/CaM kinase II) completely repressed the hyperosmotic regulation of TAUT. The osmosensitive upregulation of TAUT was also significantly inhibited by calmodulin antagonists and calcium-chelators. The increased expression level of TAUT mRNA by hypertonicity was repressed by the specific Ca(2+)/CaM kinase II inhibitor. The activated form of Ca(2+)/CaM kinase II protein could only be detected in Caco-2 cells under hypertonic conditions.


Ito T, Fujio Y, Hirata M, et al.
Expression of taurine transporter is regulated through the TonE (tonicity-responsive element)/TonEBP (TonE-binding protein) pathway and contributes to cytoprotection in HepG2 cells.
Biochem J. 2004; 382(Pt 1):177-82 [PubMed] Free Access to Full Article Related Publications
In hypertonic environment, taurine accumulates in cells via activation of TauT (taurine transporter) as an adaptive regulation. Recent studies revealed that TonE (tonicity-responsive element)/TonEBP (TonE-binding protein) pathway regulated the expression of various molecules which protect cells against hypertonic stress. In the present study, we investigated the osmoregulatory mechanisms of TauT expression. TauT was up-regulated at both functional and transcriptional levels in HepG2 under hypertonic condition. The TonE site was identified in the promoter region of TauT gene. Reporter gene assay revealed that promoter activity was increased under hypertonic conditions, whereas deletion or mutation of TonE sequence abolished the induction of the promoter activity in response to hypertonicity. By using the reporter gene plasmids containing a TonE site of TauT promoter (p2xTonE-Luc), it was demonstrated that a TonE site was sufficient for the hypertonicity-mediated activation of TauT promoter. Importantly, co-transfection of TauT promoter gene plasmid with wild-type TonEBP expression vector enhanced promoter activity under isotonic conditions, whereas dominant-negative TonEBP abrogated the TauT promoter activity induced by hypertonicity. Finally, treatment with taurine prevented HepG2 cells from cell death induced by hypertonic medium. These findings suggested that induction of TauT by hypertonicity is mediated by the activation of the TonE/TonEBP pathway and confers resistance to hypertonic stress.

Related: Liver Cancer


Satsu H, Terasawa E, Hosokawa Y, Shimizu M
Functional characterization and regulation of the taurine transporter and cysteine dioxygenase in human hepatoblastoma HepG2 cells.
Biochem J. 2003; 375(Pt 2):441-7 [PubMed] Free Access to Full Article Related Publications
We investigated the characterization and the regulation of TAUT (taurine transporter) and CDO (cysteine dioxygenase), one of the key enzymes of taurine biosynthesis, in human hepatoblastoma HepG2 cells. The activity of TAUT in the HepG2 cells was evaluated by means of a sodium- and chloride-dependent high-affinity transport system, the characteristics of which were similar to those of the beta amino-acid-specific taurine transport system described previously for various tissues [Uchida, Kwon, Yamauchi, Preston, Marumo and Handler (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 8230-8234; Ramamoorthy, Leibach, Mahesh, Han, Yang-Feng, Blakely and Ganapathy (1994) Biochem. J. 300, 893-900; and Satsu, Watanabe, Arai and Shimizu (1997) J. Biochem. (Tokyo) 121, 1082-1087]. By culturing in a hypertonic medium, the intracellular taurine content of HepG2 cells was markedly increased. Under hypertonic conditions, the activity of TAUT was up-regulated, and the results of the kinetic analysis suggested that this up-regulation was associated with an increase in the amount of TAUT. The expression level of TAUT mRNA was markedly higher than that of the control cells. The expression level of CDO mRNA was also up-regulated under the hypertonic conditions. Culturing the cells in a taurine-rich medium resulted in both the activity of TAUT and the expression level of TAUT mRNA being down-regulated in HepG2 cells. On the other hand, the expression level of CDO mRNA was not affected under a taurine-rich condition. The present results show that both TAUT and CDO were co-operatively regulated in response to hypertonicity, but did not co-operatively respond to the change in extracellular taurine concentration. Generally, the TAUT and taurine biosynthetic enzymes have independent regulatory systems, but under certain conditions, they could be regulated in harmony with each other.


Poulsen KA, Litman T, Eriksen J, et al.
Downregulation of taurine uptake in multidrug resistant Ehrlich ascites tumor cells.
Amino Acids. 2002; 22(4):333-50 [PubMed] Related Publications
In daunorubicin resistant Ehrlich ascites tumor cells (DNR), the initial taurine uptake was reduced by 56% as compared to the parental, drug sensitive Ehrlich cells. Kinetic experiments indicated that taurine uptake in Ehrlich cells occurs via both high- and low-affinity transporters. The maximal rate constant for the initial taurine uptake was reduced by 45% (high-affinity system) and 49% (low affinity system) in the resistant subline whereas the affinity of the transporters to taurine was unchanged. By immunoblotting we identified 3 TauT protein bands in the 50-70 kDa region. A visible reduction in the intensity of the band with the lowest molecular weight was observed in resistant cells. Quantitative RT-PCR indicated a significant reduction in the amount of taurine transporter mRNA in the resistant cells. Drug resistance in DNR Ehrlich cells is associated with overexpression of the mdr1 gene product P-glycoprotein (P-gp). Using 5 progressively DNR resistant Ehrlich cell sublines with different P-gp expression pattern no correlation between taurine uptake and P-gp expression was found. Taurine uptake in MDR1 transfected NIH/3T3 mouse fibroblasts was in contrast to the findings in Ehrlich cells increased compared to the parental fibroblasts. It is concluded that the reduced taurine uptake in resistant Ehrlich cells reflects a down regulation of the taurine transporter at the mRNA and protein level and it is most probably not related to P-gp overexpression.

Related: Daunorubicin


Mollerup J, Lambert IH
Calyculin A modulates the kinetic constants for the Na+-coupled taurine transport in Ehrlich ascites tumour cells.
Biochim Biophys Acta. 1998; 1371(2):335-44 [PubMed] Related Publications
The effect of the phosphatase inhibitor calyculin A (cal A) on the kinetic parameters of the Na+-coupled taurine uptake via the taurine transporter in the Ehrlich ascites tumour cells has been investigated. Preincubation with cal A (100 nM) reduces the initial taurine influx by about 20%, but has no effect on the diffusional component of the taurine influx or on the taurine release from cells suspended in isotonic or in hypotonic medium. Thus, cal A-sensitive phosphatases only affect taurine transport mediated by the Na+-dependent taurine transporter. Cal A increases the Michaelis-Menten constant for binding of taurine to the transporter from 31+/-6 to 45+/-4 microM and reduces the taurine transport capacity from 210+/-20 to 170+/-10 nmol x g dry wt(-1) x min(-1) [corrected]. The Michaelis-Menten constant for binding of Na+ to the taurine transporter is concomitantly increased from 96+/-11 to 129+/-8 mM and the Na+:taurine coupling ratio for activation of the transport cycle is reduced from 3.3+/-0.6 to 2.4+/-0.2. This suggests that cal A-sensitive phosphatases maintain a high affinity of the taurine transporter towards Na+ and taurine as well as a high taurine transport capacity in unpertubated Ehrlich cells.


Warskulat U, Wettstein M, Häussinger D
Osmoregulated taurine transport in H4IIE hepatoma cells and perfused rat liver.
Biochem J. 1997; 321 ( Pt 3):683-90 [PubMed] Free Access to Full Article Related Publications
The effects of aniso-osmotic exposure on taurine transport were studied in H4IIE rat hepatoma cells. Hyperosmotic (405 mosmol/l) exposure of H4IIE cells stimulated Na+-dependent taurine uptake and led to an increase in taurine transporter (TAUT) mRNA levels, whereas hypo-osmotic (205 mosmol/l) exposure diminished both taurine uptake and TAUT mRNA levels when compared with normo-osmotic (305 mosmol/l) control incubations. Taurine uptake increased 30-40-fold upon raising the ambient osmolarity from 205 to 405 mosmol/l. When H4IIE cells and perfused livers were preloaded with taurine, hypo-osmotic cell swelling led to a rapid release of taurine from the cells. The taurine efflux, but not taurine uptake, was sensitive to 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS), suggestive of an involvement of DIDS-sensitive channels in mediating volume-regulatory taurine efflux. Whereas in both H4IIE rat hepatoma cells and primary hepatocytes TAUT mRNA levels were strongly dependent upon ambient osmolarity, mRNAs for other osmolyte transporters, i.e. the betaine transporter BGT-1 and the Na+/myo-inositol transporter SMIT, were not detectable. In line with this, myo-inositol uptake by H4IIE hepatoma cells was low and was not stimulated by hyperosmolarity. However, despite the absence of BGT-1 mRNA, a slight osmosensitive uptake of betaine was observed, but the rate was less than 10% of that of taurine transport. This study identifies a constitutively expressed and osmosensitive TAUT in H4IIE cells and the use of taurine as a main osmolyte, whereas betaine and myo-inositol play little or no role in the osmolyte strategy in these cells. This is in contrast with rat liver macrophages, in which betaine has been shown to be a major osmolyte.


Miyamoto Y, Liou GI, Sprinkle TJ
Isolation of a cDNA encoding a taurine transporter in the human retinal pigment epithelium.
Curr Eye Res. 1996; 15(3):345-9 [PubMed] Related Publications
Reverse transcription-polymerase chain reaction (RT-PCR) was performed to amplify a cDNA encoding a taurine transporter in the human retinal pigment epithelium (HRPE). The coding region of a PCR product was found to be 1863 bp long, predicting a 620-amino acid protein (69,826 Da). This cDNA sequence is almost identical to those taurine transporters recently determined in the human thyroid and placenta: 12 and 1 base pair(s) different from the reported thyroid and placenta transporter clones, respectively. The injection of mRNA in vitro transcribed from the PCR product markedly increased taurine uptake in Xenopus laevis oocytes. Taurine uptake is Na+ and Cl- dependent. Unlabeled taurine, beta-alanine and gamma-amino-n-butyric acid at 100 microM inhibited the uptake of radiolabeled taurine whereas 100 microM alpha-alanine and alpha-aminoisobutyric acid did not. A kinetic study showed that taurine uptake is mediated by a single carrier system with the apparent Michaelis-Menten constant of approximately 2 microM. These results suggest that the PCR product encodes a functional taurine transporter whose characteristics are similar to those of taurine uptake observed in the original HRPE cells. A DNA encoding the reported placental transporter was made from the PCR product by site-directed mutagenesis but it was not functional in the oocyte expression. A similar RT-PCR was performed with poly (A)+ mRNA isolated from JAR human placenta choriocarcinoma cells. This PCR product was identical to that from the HRPE. In addition, the clone of the human thyroid transporter was obtained and re-sequenced. Its translation coding region was also identical to that of the PCR product from the HRPE, showing that taurine transporters are identical in the human RPE, thyroid and placenta.


Tchoumkeu-Nzouessa GC, Rebel G
Characterization of taurine transport in human glioma GL15 cell line: regulation by protein kinase C.
Neuropharmacology. 1996; 35(1):37-44 [PubMed] Related Publications
Data describing characteristics of taurine transport system in human brain cells are not currently available. We have used GL15 cells, a cell line of human brain origin that keeps some properties of normal glial cells, to investigate these characteristics. The human glioma cell line GL15 was found to take up taurine. The uptake was strictly sodium-dependent. Replacement of NaCl with choline chloride almost totally abolished the uptake. There was also an anion requirement for the uptake system, and Cl- was the most potent among several monovalent anions tested. The uptake process was specific for beta-amino acids such as taurine, hypotaurine and beta-alanine. The kinetics of uptake were studied. Apparently, a single transport system with a K(m) of 8.95 +/- 0.26 microM was responsible for the uptake. A maximal velocity of 1.32 +/- 0.03 nmol/mg of protein/10 min was found. Stoichiometric analysis revealed that two Na+ and one Cl- ions were involved in the translocation of one taurine molecule. Phorbol 12-myristate 13-acetate (PMA), a potent stimulator of protein kinase C (PKC), inhibited taurine uptake. Maximal inhibition was obtained at 50 nM after 1 hr of treatment. This effect was prevented by pretreatment of the cells with chelerythrine, a potent and selective inhibitor of PKC. The transport of beta-alanine was inhibited to a comparative extent. The mechanism of this inhibition was not investigated, but it was found that this inhibitory effect was not prevented by cycloheximide, actinomycin D, colchicine or cytochalasin D, indicating that neither protein synthesis, nor microfilament function were involved. The effect of PMA was associated with an impairment of kinetic constants. It is concluded that human GL15 cells have a taurine transporter similar to that expressed in rodent glial cells, and that the activation of PKC can modulate the activity of this transporter.

Related: Cancer Prevention and Risk Reduction


Jayanthi LD, Ramamoorthy S, Mahesh VB, et al.
Substrate-specific regulation of the taurine transporter in human placental choriocarcinoma cells (JAR).
Biochim Biophys Acta. 1995; 1235(2):351-60 [PubMed] Related Publications
Exposure of the JAR human placental choriocarcinoma cells to taurine leads to a marked decrease in the activity of the taurine transporter in these cells. The ability to induce this adaptive response is not unique to taurine but is shared by other substrates of the transporter as well. Compounds such as betaine and alpha-aminoisobutyric acid which are not substrates for the transporter do not produce this effect. The change in the taurine transporter activity induced by taurine exposure is however unique to the taurine transporter because the activities of many other transport systems remain unaffected under these conditions. The adaptive regulation is not associated with any change in the dependence of the transporter activity on Na+ and Cl-, in the Na+/Cl-/taurine stoichiometry and in the affinities of the transporter for Na+ and Cl-. The decrease in the transporter activity caused by taurine exposure is due to a decrease in the maximal velocity of the transporter, and to a lesser extent, in the substrate affinity of the transporter. The decrease in the transporter activity observed in intact cells is demonstrable in plasma membrane vesicles after isolation from control and taurine-exposed cells. Cycloheximide and actinomycin D block the adaptive response in intact cells to a significant extent, but not completely. Northern blot analysis of mRNA from control and taurine-exposed cells shows that taurine exposure causes a significant decrease in the steady state levels of the taurine transporter mRNA. It is concluded that the activity of the taurine transporter in JAR cells is subject to substrate-specific adaptive regulation and that transcriptional as well as posttranscriptional events are involved in this regulatory process.

Related: Dactinomycin


Ramamoorthy S, Cool DR, Mahesh VB, et al.
Regulation of the human serotonin transporter. Cholera toxin-induced stimulation of serotonin uptake in human placental choriocarcinoma cells is accompanied by increased serotonin transporter mRNA levels and serotonin transporter-specific ligand binding.
J Biol Chem. 1993; 268(29):21626-31 [PubMed] Related Publications
Treatment of confluent cultures of JAR human placental choriocarcinoma cells with cholera toxin or forskolin for 16 h markedly stimulated (2.4-fold) serotonin transport activity in these cells. Cycloheximide, an inhibitor of protein synthesis or actinomycin D, an inhibitor of mRNA synthesis effectively blocked this stimulation. Northern blot analysis revealed that treatment with cholera toxin resulted in severalfold increase in the concentrations of the three mRNA species (6.8, 4.9 and 3.0 kilobases in size) which hybridized to the human placental serotonin transporter cDNA. Under similar conditions, the concentrations of the mRNA species which hybridized to the human placental taurine transporter cDNA or to the human beta-actin cDNA were not affected. Analysis of paroxetine-sensitive binding of the cocaine analog 2 beta-carbomethoxy-3 beta-(4- [125I]iodophenyl)tropane to the membranes prepared from control and cholera toxin-treated cells indicated that the maximal binding capacity was increased 2.5-fold by cholera toxin, with no significant change in the binding affinity. Thus, stimulation of serotonin transporter activity in the placental choriocarcinoma cells following cholera toxin treatment is likely a result of an increase in cell surface density of the serotonin transporter protein as a consequence of increased steady state serotonin transporter mRNA levels.

Related: Dactinomycin


Brandsch M, Miyamoto Y, Ganapathy V, Leibach FH
Regulation of taurine transport in human colon carcinoma cell lines (HT-29 and Caco-2) by protein kinase C.
Am J Physiol. 1993; 264(5 Pt 1):G939-46 [PubMed] Related Publications
The effect of phorbol 12-myristate 13-acetate (PMA), a phorbol ester known to stimulate protein kinase C, on taurine transport was studied in the human colon carcinoma cell line HT-29. PMA (1 microM) was found to inhibit taurine uptake in confluent monolayers of this cell line by approximately 70% after pretreatment of the cells with the compound for 1 h (IC50 = 42.7 +/- 2.6 nM). The inhibitory effect of PMA on the taurine transporter could be confirmed by using beta-alanine, another substrate for the transporter. Kinetic analysis of taurine uptake indicated that the PMA effect was associated with a decrease in the maximal velocity (954 +/- 26 vs. 676 +/- 28 pmol.10 min-1.mg of protein-1) and an increase in the Michaelis-Menten constant (9.8 +/- 0.5 vs. 13.3 +/- 1.0 microM). The inhibition of taurine uptake could be blocked by cotreatment of the cultures with staurosporine, an inhibitor of protein kinase C. The inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate had no effect. Treatment of the cells with PMA did not alter the uptake of leucine and lysine, stimulated the uptake of aspartic acid, and inhibited the uptake of proline. The PMA effect on taurine uptake was not prevented by cycloheximide, actinomycin D, colchicine, or cytochalasin D. Comparison of the taurine transport activity in HT-29 cells with that in Caco-2, another human colon carcinoma cell line, revealed that the latter cell line also expressed the taurine transporter but at a much reduced level (about one-fifth compared with HT-29).(ABSTRACT TRUNCATED AT 250 WORDS)

Related: Dactinomycin


Tiruppathi C, Brandsch M, Miyamoto Y, et al.
Constitutive expression of the taurine transporter in a human colon carcinoma cell line.
Am J Physiol. 1992; 263(5 Pt 1):G625-31 [PubMed] Related Publications
The human colon carcinoma cell line HT-29, when grown to confluence, was found to take up taurine and accumulate it against a concentration gradient from a NaCl-containing uptake medium. Replacement of NaCl with choline chloride almost totally abolished the uptake. Taurine uptake was dependent not only on Na+ but also on Cl-, because other anions failed to support the uptake in the presence of Na+. The uptake process was specific for beta-amino acids such as taurine, hypotaurine, and beta-alanine. Apparently, a single transport system with a Michaelis-Menten constant of 10.6 +/- 0.3 microM was responsible for the uptake. Stoichiometric analyses revealed that the Na+:taurine coupling ratio was 2:1, whereas the Cl-:taurine coupling ratio was 1:1. Culture of the cells in the presence of taurine caused downregulation of the uptake system. These cells were also capable of accumulating beta-alanine against a concentration gradient in the presence of NaCl. Beta-Alanine uptake occurred via a single transport system with an apparent Michaelis-Menten constant of 36 +/- 2 microM. Taurine and beta-alanine exhibited mutual interaction during uptake. Kinetic experiments strongly suggested that a common transporter was responsible for the uptake of these two beta-amino acids. It is concluded that the HT-29 cells constitutively express the taurine transporter and that this cell line may be a suitable model for investigations of intestinal taurine transporter.


Kulanthaivel P, Cool DR, Ramamoorthy S, et al.
Transport of taurine and its regulation by protein kinase C in the JAR human placental choriocarcinoma cell line.
Biochem J. 1991; 277 ( Pt 1):53-8 [PubMed] Free Access to Full Article Related Publications
The JAR human placental choriocarcinoma cell line transports taurine, concentrating it over 1000-fold inside the cell. The transport system is energized by a Na+ gradient and exhibits an absolute requirement for Cl-. Neutral beta-amino acids such as beta-alanine and hypotaurine effectively compete with the system, whereas neutral alpha-amino acids such as alanine, leucine and alpha-aminoisobutyric acid do not. The transport system interacts with gamma-aminobutyric acid to an appreciable extent. Kinetic analysis reveals that the taurine transport system in this cell line is of a high-affinity and low-capacity type (apparent dissociation constant 2.3 +/- 0.3 microM; maximal velocity 88.5 +/- 5.0 pmol/3 min per mg of protein). Pretreatment of the JAR choriocarcinoma cells with phorbol 12-myristate 13-acetate results in the inhibition of the taurine transport system in a dose-dependent manner. The inhibition is blocked by co-treatment of the cells with staurosporine, an inhibitor of protein kinase C. The inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate, has no effect on the transport system. These data show that the choriocarcinoma cells express a taurine transporter with characteristics similar to those of the taurine transporter described in the normal human placenta, and that the activity of the transporter in these cells is under the regulatory control of protein kinase C.


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