Cycloheximide Treatment Induces the Uptake of Neutral and Dibasic Amino Acids via the Activation of System b^<0,+> in Human Intestinal Caco-2 Cells

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Amino acids in enterocytes are thought to be absorbed in the intestinal epithelium via various types of amino acid transport, although the regulation of these amino acid transport systems has not been elucidated. We examined in the present study the effect of several inhibitors involved in mRNA and protein synthesis, and of protein translocation on the L-leucine (Leu) uptake in human intestinal epithelial-like Caco-2 cells. Culturing Caco-2 cells with cycloheximide (CHX) enabled the L-Leu uptake to be significantly increased in a dose- and time-dependent manner. The uptake of L-lysine (Lys) was also increased by the CHX treatment, whereas the uptake of L-glutamate, taurine, and Gly-Gln was not changed. Among the two transport systems, b^<0,+> and y^+, which are known to be involved in L-Lys uptake by Caco-2, the system b^<0,+> component was greatly increased by the CHX treatment, suggesting that system b^<0,+> was mainly responsible for the increase in L-Leu and L-Lys uptake. The mRNA levels of rBAT and b^<0,+> AT, whose molecules comprise system b^<0,+>, were both significantly increased by the CHX treatment in a time-dependent manner. These results strongly suggest that the CHX treatment increased the Leu and Lys uptake by activating system b^<0,+> and inducing rBAT and b^<0,+> AT mRNA expression in human intestinal epithelial Caco-2 cells.