Regulation of amino acid transporters by glucose and growth factors in cultured primary human trophoblast cells is mediated by mTOR signaling

• Published in: American Journal of Physiology: Cell Physiology 2009-09, Vol.297 (3), p.C723-C731
• Main Authors: Roos, S, Lagerlof, O, Wennergren, M, Powell, T. L, Jansson, T
• Format: Article
• Language: English
• Subjects: Amino Acid Transport Systems - metabolism; Amino acids; Apoptosis - physiology; Biomarkers; Cell Survival; Cells; Cells, Cultured; Effects; Gene Expression Regulation - physiology; Glucose; Glucose - metabolism; Glucose - pharmacology; Humans; Insulin; Insulin - pharmacology; Insulin-Like Growth Factor I - pharmacology; Intercellular Signaling Peptides and Proteins - metabolism; Intercellular Signaling Peptides and Proteins - pharmacology; Kinases; Mammals; MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; Protein Kinases - metabolism; Signal Transduction; TOR Serine-Threonine Kinases; Trophoblasts - metabolism
• ISSN: 0363-6143; 1522-1563; 1522-1563
• DOI: 10.1152/ajpcell.00191.2009

1 Perinatal Center, Department of Physiology, Institute of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden; 2 Department of Obstetrics and Gynecology, Institute of Clinical Sciences, University of Gothenburg, Gothenburg, Sweden; and 3 Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Cincinnati, Ohio Submitted 30 April 2009 ; accepted in final form 3 July 2009 Inhibition of mammalian target of rapamycin (mTOR) signaling in cultured human primary trophoblast cells reduces the activity of key placental amino acid transporters. However, the upstream regulators of placental mTOR are unknown. We hypothesized that glucose, insulin, and IGF-I regulate placental amino acid transporters by inducing changes in mTOR signaling. Primary human trophoblast cells were cultured for 24 h with media containing various glucose concentrations, insulin, or IGF-I, with or without the mTOR inhibitor rapamycin, and, subsequently, the activity of system A, system L, and taurine (TAUT) transporters was measured. Glucose deprivation (0.5 mM glucose) did not significantly affect Thr172-AMP-activated protein kinase phosphorylation or REDD1 expression but decreased S6 kinase 1 phosphorylation at Thr389. The activity of system L decreased in a dose-dependent manner in response to decreasing glucose concentrations. This effect was abolished in the presence of rapamycin. Glucose deprivation had two opposing effects on system A activity: 1 ) an "adaptive" upregulation mediated by an mTOR-independent mechanism and 2 ) downregulation by an mTOR-dependent mechanism. TAUT activity was increased after incubating cells with glucose-deprived media, and this effect was largely independent of mTOR signaling. Insulin and IGF-I increased system A activity and insulin stimulated system L activity, effects that were abolished by rapamycin. We conclude that the mTOR pathway represents an important intracellular regulatory link between nutrient and growth factor concentrations and amino acid transport in the human placenta. placental transport; insulin; insulin-like growth factor I; mammalian target of rapamycin Address for reprint requests and other correspondence: S. Roos, Perinatal Center, Dept. of Physiology, Institute of Neuroscience and Physiology, Univ. of Gothenburg, P.O. Box 432, SE-405 30 Gothenburg, Sweden (e-mail: sara.roos{at}gu.se ).