title: IL-6 stimulates system A amino acid transporter activity in trophoblast cells through STAT3 and increased expression of SNAT2.
abstract: Changes in placental nutrient transport are closely associated with abnormal fetal growth. However, the molecular mechanisms underlying the regulation of placental amino acid transporters are unknown. We demonstrate that physiological concentrations of the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha stimulate the activity of amino acid transporter system A, but not system L, in cultured human primary trophoblast cells. Both cytokines increased the gene and protein expression of the Na(+)-coupled neutral amino acid transporter (SNAT)2 isoform and upregulated SNAT1 protein expression. IL-6 increased Tyr705 phosphorylation of signal transducer and activator of transcription 3 (STAT3). In cells transfected with small interfering RNA (siRNA) targeting STAT3, the RNA and protein expression of SNAT2, but not SNAT1, was reduced and the stimulating effect of IL-6 on system A activity was abolished. Despite eliciting similar responses in amino acid transport activity and transporter expression, TNF-alpha effects on system A activity were not mediated through the JAK/STAT pathway. In conclusion, we have identified a novel regulatory pathway involving increased gene expression of the SNAT2 isoform mediated by a STAT-dependent pathway, which links IL-6 to increased activity of system A, a ubiquitously expressed transporter of neutral amino acids. From these new findings, we propose that upregulation of amino acid transporters by cytokines may contribute to increased placental nutrient transport and fetal overgrowth, which are commonly found in pregnancies complicated by maternal diabetes and obesity.
authors.affiliation: Department of Obstetrics and Gynecology, College of Medicine, University of Cincinnati, Cincinnati, Ohio, USA. helen.jones@cchmc.org
authors.forename: H N
authors.initials: HN
authors.lastname: Jones
authors.forename: T
authors.initials: T
authors.lastname: Jansson
authors.forename: T L
authors.initials: TL
authors.lastname: Powell
mesh_terms: D026924:Amino Acid Transport System A / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015153:Blotting, Western; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015870:Gene Expression; D005786:Gene Expression Regulation; D006801:Humans; D015850:Interleukin-6; D011247:Pregnancy; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014327:Trophoblasts / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D026924:Amino Acid Transport System A; D015850:Interleukin-6; C498797:SLC38A2 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D014409:Tumor Necrosis Factor-alpha