Cycloheximide Treatment Induces the Uptake of Neutral and Dibasic Amino Acids via the Activation of System b0,+ in Human Intestinal Caco-2 Cells

摘要

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, b0,+ and y+, which are known to be involved in L -Lys uptake by Caco-2, the system b0,+ component was greatly increased by the CHX treatment, suggesting that system b0,+ was mainly responsible for the increase in L -Leu and L -Lys uptake. The mRNA levels of rBAT and b0,+AT, whose molecules comprise system b0,+, 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 b0,+ and inducing rBAT and b0,+AT mRNA expression in human intestinal epithelial Caco-2 cells.