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

H N Jones, C Ashworth, K R Page, H J McArdle (Corresponding Author)

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Abstract

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 alpha(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 x 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 adapt in vitro to nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

Original languageEnglish
Pages (from-to)951-960
Number of pages10
JournalReproduction
Volume131
Issue number5
DOIs
Publication statusPublished - 1 May 2006

Keywords

  • amino acid transport system A
  • amino acid transport system y+
  • amino acids
  • analysis of variance
  • antigens, CD98 light chains
  • biological transport
  • northern blotting
  • western blotting
  • tumor cell line
  • choriocarcinoma
  • culture media
  • electric impedance
  • epithelium
  • female
  • gene expression
  • humans
  • immunohistochemistry
  • placenta
  • messenger-RNA
  • trophoblasts

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