Evidence for a regulatory protein involved in the increased activity of system A for neutral amino acid transport in osmotically stressed mammalian cells.

Ruiz-Montasell, Bonaventura; Gómez‐Angelats, Mireia; Casado, F. Javier; Felipe, Antônio; McGivan, J D; Pastor‐Anglada, Marçal

doi:10.1073/pnas.91.20.9569

Cited by 44 publications

(34 citation statements)

References 37 publications

(45 reference statements)

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“…Taken together, these data suggest that the insulin-stimulated system A transport in adipocytes is mediated by a mechanism different from that reported in hepatocytes (15)(16)(17). The lack of repressor-type control has been reported for regulation of system A transport by other factors such as osmotic stress (5,34).…”

Section: Discussionmentioning

confidence: 37%

Regulation of System A Amino Acid Transport in 3T3-L1 Adipocytes by Insulin

Su¹,

Wang²,

Syu³

et al. 1998

Journal of Biological Chemistry

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The insulin-stimulated uptake of 2-(methylamino) isobutyric acid (MeAIB), a nonmetabolizable substrate for system A, in 3T3-L1 adipocytes was investigated. As cells took on a more adipogenic phenotype, the insulinstimulated versus the saturable basal MeAIB uptake increased by 5-fold. The induced transport activity showed properties characteristic of system A, with a K m value of 190 M. The half-life of the induced system A activity was independent of de novo mRNA and protein synthesis and was not accelerated by ambient amino acids, therefore, it was mechanistically distinct from the previously described adaptive and hormonal regulation of system A. Inhibition of mitogen-activated protein kinase kinase by PD98059, Ras farnesylation by PD152440 and B581, p70 S6K by rapamycin, and phosphatidylinositol 3-kinase (PI 3-K) by wortmannin and LY294002 revealed that only wortmannin and LY294002 inhibited the insulin-induced MeAIB uptake with IC 50 values close to that previously reported for inhibition of PI 3-K. These results suggest that the Ras/mitogenactivated protein kinase and pp70 S6K insulin signaling pathways are neither required nor sufficient for insulin stimulation of MeAIB uptake, and activation of PI 3-K or a wortmannin/LY294002-sensitive pathway may play an important role in regulation of system A transport by insulin in 3T3-L1 cells.

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Section: Discussionmentioning

confidence: 37%

Regulation of System A Amino Acid Transport in 3T3-L1 Adipocytes by Insulin

Su¹,

Wang²,

Syu³

et al. 1998

Journal of Biological Chemistry

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“…Three isoforms of system A have been identified: sodium coupled neutral amino acid transporter (SNAT) 1 [3], SNAT2 [4,5], and SNAT4 [6]. Amino acid uptake by system A is highly regulated in many cell types by effectors such as pH, cell volume [7] and a variety of hormones such as insulin [8], glucagon [9] and cortisol [10]. In vitro studies have demonstrated that acute incubation of primary human placental trophoblast cells and the BeWo Choriocarcinoma cell line with exogenous insulin-like growth factor-1 (IGF-1) protein increased the uptake of small neutral amino acids via amino acid transport system A [11,12].…”

Section: Introductionmentioning

confidence: 99%

Regulation of amino acid transporters by adenoviral-mediated human insulin-like growth factor-1 in a mouse model of placental insufficiency in vivo and the human trophoblast line BeWo in vitro

2014

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Previous work in our laboratory demonstrated that over-expression of human insulin-like growth factor-11 (hIGF-1) in the placenta corrects fetal weight deficits in mouse, rat, and rabbit models of intrauterine growth restriction without changes in placental weight. The underlying mechanisms of this effect have not been elucidated. To investigate the effect of intra-placental IGF-1 over-expression on placental function we examined amino acid transporter expression and localization in both a mouse model of placental Insufficiency (PI) and a model of human trophoblast, the BeWo Choriocarcinoma cell line. For in vitro human studies, BeWo Choriocarcinoma cells were maintained in F12 complete medium + 10%FBS. Cells were incubated in serum-free control media ± Ad-IGF-1 or Ad-LacZ for 48 h. MOIs of 10:1 and 100:1 were utilized. In BeWo, transfection efficiency was 100% at an MOI of 100:1 and Ad-IGF-1 significantly increased IGF-1 secretion, proliferation and invasion but reduced apoptosis compared to controls. In vitro, amino acid uptake was increased following Ad-IGF-1 treatment and associated with significantly increased RNA expression of SNAT1, 2, LAT1 and 4F2hc. Only SNAT2 protein expression was increased but LAT1 showed relocalization from a perinuclear location to the cytoplasm and cell membrane. For in vivo studies, timed-pregnant animals were divided into four groups on day 18; sham-operated controls, uterine artery branch ligation (UABL), UABL + Ad-hIGF-1 (108 PFU), UABL + Ad-LacZ (108 PFU). At gestational day 20, pups and placentas were harvested by C-section. Only LAT1 mRNA expression changed, showing that a reduced expression of the transporter levels in the PI model could be partially rectified with Ad-hIGF1 treatment. At the protein level, System L was reduced in PI but remained at control levels following Ad-hIGF1. The System A isoforms were differentially regulated with SNAT2 expression diminished but SNAT1 increased in PI and Ad-hIGF1 groups. Enhanced amino acid isoform transporter expression and relocalization to the membrane may be an important mechanism contributing to Ad-hIGF-1 mediated correction of placental insufficiency.

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“…It is regulated by many effectors, including insulin (19), glucagon (37), cell volume (26), pH, and oxygen levels (21).…”

mentioning

confidence: 99%

Cortisol stimulates system A amino acid transport and SNAT2 expression in a human placental cell line (BeWo)

Jones¹,

Ashworth²,

Page³

et al. 2006

American Journal of Physiology-Endocrinology and Metabolism

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Both placental system A activity and fetal plasma cortisol concentrations are associated with intrauterine growth retardation, but it is not known if these factors are mechanistically related. Previous functional studies using hepatoma cells and fibroblasts produced conflicting results regarding the regulation of system A by cortisol. Using the b30 BeWo choriocarcinoma cell line, we investigated the regulation of system A by cortisol. System A function was analyzed using methyl amino isobutyric acid (MeAIB) transcellular transport studies. Transporter expression [system A transporter (SNAT)1/2] was studied at the mRNA and protein levels using Northern and Western blotting, respectively. Localization was carried out using immunocytochemistry. The [(14)C]MeAIB transfer rate across BeWo monolayers after preincubation with cortisol for 24 h was significantly increased compared with control. This was associated with a relocalization of the SNAT2 transporter at lower cortisol levels and significant upregulation of mRNA and protein expression levels at cortisol levels >1 microM. This is the first study to show functional and molecular regulation of system A by cortisol in BeWo cells. It is also the first study to identify which system A isoform is regulated. These results suggest that cortisol may be involved in upregulation of system A in the placenta to ensure sufficient amino acid supply to the developing fetus.

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Evidence for a regulatory protein involved in the increased activity of system A for neutral amino acid transport in osmotically stressed mammalian cells.

Cited by 44 publications

References 37 publications

Regulation of System A Amino Acid Transport in 3T3-L1 Adipocytes by Insulin

Regulation of System A Amino Acid Transport in 3T3-L1 Adipocytes by Insulin

Regulation of amino acid transporters by adenoviral-mediated human insulin-like growth factor-1 in a mouse model of placental insufficiency in vivo and the human trophoblast line BeWo in vitro

Cortisol stimulates system A amino acid transport and SNAT2 expression in a human placental cell line (BeWo)

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