Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction

Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using α(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P< 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 × essential amino acids), SNAT2 mRNA levels showed further significant (P< 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P= 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adaptin vitroto nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

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Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00062.2006 ◽

2006 ◽

Vol 291 (5) ◽

pp. E1059-E1066 ◽

Cited By ~ 18

Author(s):

Adriana López ◽

Nimbe Torres ◽

Victor Ortiz ◽

Gabriela Alemán ◽

Rogelio Hernández-Pando ◽

...

Keyword(s):

Gene Expression ◽

Amino Acids ◽

Mammary Gland ◽

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Acid Transport ◽

Amino Acid Transport System ◽

System A ◽

Rat Mammary Gland

Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. β-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.

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Evidence for the transport of neutral as well as cationic amino acids by ATA3, a novel and liver-specific subtype of amino acid transport system A

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/s0005-2736(00)00390-4 ◽

2001 ◽

Vol 1510 (1-2) ◽

pp. 10-17 ◽

Cited By ~ 80

Author(s):

Takahiro Hatanaka ◽

Wei Huang ◽

Ruan Ling ◽

Puttur D Prasad ◽

Mitsuru Sugawara ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Acid Transport ◽

Amino Acid Transport System ◽

System A ◽

Cationic Amino Acids

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Osmotic Regulation of ATA2 mRNA Expression and Amino Acid Transport System A Activity

Biochemical and Biophysical Research Communications ◽

10.1006/bbrc.2001.4729 ◽

2001 ◽

Vol 283 (1) ◽

pp. 174-178 ◽

Cited By ~ 38

Author(s):

Roberta R. Alfieri ◽

Pier-Giorgio Petronini ◽

Mara A. Bonelli ◽

Alessandro E. Caccamo ◽

Andrea Cavazzoni ◽

...

Keyword(s):

Amino Acid ◽

Mrna Expression ◽

Transport System ◽

Amino Acid Transport ◽

Osmotic Regulation ◽

Acid Transport ◽

Amino Acid Transport System ◽

System A

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Expression and regulation of 4F2hc and hLAT1 in human trophoblasts

AJP Cell Physiology ◽

10.1152/ajpcell.2002.282.1.c196 ◽

2002 ◽

Vol 282 (1) ◽

pp. C196-C204 ◽

Cited By ~ 46

Author(s):

Yoko Okamoto ◽

Masahiro Sakata ◽

Kazuhiro Ogura ◽

Toshiya Yamamoto ◽

Masaaki Yamaguchi ◽

...

Keyword(s):

Amino Acid ◽

Cell Line ◽

Transport System ◽

Human Placenta ◽

Amino Acid Transport ◽

Calcium Ionophore ◽

Acid Transport ◽

Amino Acid Transport System ◽

System L ◽

Choriocarcinoma Cell Line

The neutral amino acid transport system L is a sodium-independent transport system in human placenta and choriocarcinoma cells. Recently, it was found that the heterodimer composed of hLAT1 (a light-chain protein) and 4F2 heavy chain (4F2hc), a type II transmembrane glycoprotein, is responsible for system L amino acid transport. We found that the mRNAs of 4F2hc and hLAT1 were expressed in the human placenta and a human choriocarcinoma cell line. The levels of the 4F2hc and hLAT1 proteins in the human placenta increased at full term compared with those at midtrimester. Immunohistochemical data showed that these proteins were localized mainly in the placental apical membrane. Data from leucine uptake experiments, Northern blot analysis, and immunoblot analysis showed that this transport system was partially regulated by protein kinase C and calcium ionophore in the human choriocarcinoma cell line. Our results suggest that the heterodimer of 4F2hc and hLAT1 may play an important role in placental amino acid transport system L.

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Cloning and functional characterization of a new subtype of the amino acid transport system N

AJP Cell Physiology ◽

10.1152/ajpcell.2001.281.6.c1757 ◽

2001 ◽

Vol 281 (6) ◽

pp. C1757-C1768 ◽

Cited By ~ 79

Author(s):

Takeo Nakanishi ◽

Ramesh Kekuda ◽

You-Jun Fei ◽

Takahiro Hatanaka ◽

Mitsuru Sugawara ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Mammalian Cells ◽

Functional Characterization ◽

Isobutyric Acid ◽

Xenopus Laevis Oocytes ◽

Acid Transport ◽

Amino Acid Transport System

We have cloned a new subtype of the amino acid transport system N2 (SN2 or second subtype of system N) from rat brain. Rat SN2 consists of 471 amino acids and belongs to the recently identified glutamine transporter gene family that consists of system N and system A. Rat SN2 exhibits 63% identity with rat SN1. It also shows considerable sequence identity (50–56%) with the members of the amino acid transporter A subfamily. In the rat, SN2 mRNA is most abundant in the liver but is detectable in the brain, lung, stomach, kidney, testis, and spleen. When expressed in Xenopus laevis oocytes and in mammalian cells, rat SN2 mediates Na+-dependent transport of several neutral amino acids, including glycine, asparagine, alanine, serine, glutamine, and histidine. The transport process is electrogenic, Li+tolerant, and pH sensitive. The transport mechanism involves the influx of Na+ and amino acids coupled to the efflux of H+, resulting in intracellular alkalization. Proline, α-(methylamino)isobutyric acid, and anionic and cationic amino acids are not recognized by rat SN2.

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Primary structure, functional characteristics and tissue expression pattern of human ATA2, a subtype of amino acid transport system A

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/s0005-2736(00)00252-2 ◽

2000 ◽

Vol 1467 (1) ◽

pp. 1-6 ◽

Cited By ~ 114

Author(s):

Takahiro Hatanaka ◽

Wei Huang ◽

Haiping Wang ◽

Mitsuru Sugawara ◽

Puttur D Prasad ◽

...

Keyword(s):

Amino Acid ◽

Expression Pattern ◽

Transport System ◽

Primary Structure ◽

Amino Acid Transport ◽

Tissue Expression ◽

Acid Transport ◽

Tissue Expression Pattern ◽

Amino Acid Transport System ◽

System A

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Acute Stimulation by IGF-I of Amino Acid Transport System A in Chromaffin Cells Depends on PI3 Kinase Activation and the Electrochemical Gradient of Na+

Annals of the New York Academy of Sciences ◽

10.1111/j.1749-6632.2002.tb04529.x ◽

2002 ◽

Vol 971 (1) ◽

pp. 573-575 ◽

Cited By ~ 6

Author(s):

TINE V. KARLSEN ◽

GULDBORG SERCK-HANSSEN

Keyword(s):

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Chromaffin Cells ◽

Acid Transport ◽

Electrochemical Gradient ◽

Amino Acid Transport System ◽

Kinase Activation ◽

System A ◽

Igf I

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Intestinal Transport of Two Dipeptides Containing the Same Two Neutral Amino Acids in Man

Clinical Science ◽

10.1042/cs0450291 ◽

1973 ◽

Vol 45 (3) ◽

pp. 291-299 ◽

Cited By ~ 6

Author(s):

D. B. A. Silk ◽

D. Perrett ◽

M. L. Clark

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Transport System ◽

Amino Acid Transport ◽

Amino Acid Mixture ◽

Acid Mixture ◽

Acid Transport ◽

Peptide Hydrolysis ◽

Amino Acid Transport System ◽

Neutral Amino Acids

1. A double lumen perfusion technique has been used in man to study the absorption of the two neutral amino acids glycine and l-alanine from the two dipeptides, l-alanylglycine and glycyl-l-alanine and from an equivalent amino acid mixture. 2. Glycine was absorbed faster from the dipeptides than from the equivalent amino acid mixture, and the difference in absorption rates of glycine and alanine seen when the equimolar mixture of the amino acids was perfused, was abolished when either dipeptide was perfused. This suggests that dipeptides are taken up by the mucosal cell by a mechanism independent of the amino acid-transport system. 3. The presence of free amino acids in the lumen during perfusion of both dipeptides suggests that hydrolysis occurs at some stage in the uptake process. Intraluminal hydrolysis was insufficient to account for the concentration of the amino acids seen, and their presence is thought to be due to hydrolysis of the dipeptides at the brush border. 4. It is suggested that these results confirm that at least two modes of peptide absorption occur simultaneously, namely, direct peptide uptake, and peptide hydrolysis with subsequent absorption of the released amino acids by the amino acid transport system.

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