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  • Title: Insulin-like growth factor-1 stimulates amino acid uptake by the cultured human placental trophoblast.
    Author: Karl PI.
    Journal: J Cell Physiol; 1995 Oct; 165(1):83-8. PubMed ID: 7559811.
    Abstract:
    Amino acid uptake by the human placenta is known to occur via several transport mechanisms. However, regulation by extracellular factors has received relatively little attention. A recent report by this laboratory characterized the uptake of alpha-aminoisobutyric acid (AIB) stimulated by insulin in the cultured human placental trophoblast. The current study evaluated the effect of insulin-like growth factor-1 (IGF-1) on AIB uptake in cultured human placental trophoblasts. Na(+)-dependent AIB uptake was significantly stimulated by IGF-I in a time-dependent manner, as early as 30 min after hormone exposure. The maximum effect was at 2-4 hr of continuous exposure to IGF-I and the stimulation was dependent upon IGF-1 concentration approaching maximal stimulation at 50 ng.ml-1. AIB uptake was inhibited by increasing concentrations of alpha-(methylamino)isobutyric acid (MeAIB). Approximately 75% of basal (unstimulated) Na(+)-dependent AIB uptake was inhibited by MeAIB. The IGF-1-stimulated increment above basal AIB uptake was completely inhibited by MeAIB. IGF-1 increased the maximum uptake velocity but not Km. Using equimolar concentrations, stimulation was greater with IGF-1 than with IGF-2. Stimulation by IGF-1, but not insulin, was inhibited by anti-IGF-1 receptor antibody, indicating mediation via the IGF-1 receptor. H7, a nonspecific inhibitor of serine-threonine kinase, inhibited IGF-1-dependent stimulation of AIB uptake. In addition, calphostin C (a specific inhibitor of protein kinase C), but not H89 (a specific inhibitor of protein kinase A), inhibited the IGF-1 action. This study further characterizes regulated amino acid uptake by the human placental trophoblasts and demonstrates that the Na(+)-dependent component of AIB uptake is stimulated by physiologic concentrations of IGF-1.
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