Downregulation of LAT1 expression suppresses cholangiocarcinoma cell invasion and migration

Currently, there is no effective treatment for cholangiocarcinoma (CCA), which is the most prevalent in the northeastern part of Thailand. A new molecular target for the treatment of CCA is, therefore, urgently needed. Although L-type amino acid transporter 1 (LAT1) is highly expressed in CCA cells, its role in malignant phenotypes of CCA cells remains unclear. This study aimed to investigate the impact of LAT1 on proliferation, migration, and invasion of KKU-M213 cells, the CCA cells derived from Thai patients with intrahepatic cholangiocarcinoma. Results showed that KKU-M213 cells expressed all LAT isoforms (LAT1, LAT2, LAT3 and LAT4). The expressions of LAT1 and its associated protein 4F2hc were highest whereas those of LAT2 and LAT4 were extremely low. Treatment with 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) reduced l-leucine uptake concomitant with an inhibition of cell motility and, to a lesser extent, on cell proliferation. It also induced a time dependent up-regulation of LAT1 and 4F2hc expressions. Similarly, cell migration and invasion, but not proliferation, were reduced in LAT1 knockdown KKU-M213 cells. In addition, silencing of LAT1 inhibited the expressions of 4F2hc mRNA and protein whereas the expression of microRNA-7, the 4F2hc down-regulator, was increased. Furthermore, the phosphorylation levels of ERK1/2 and p70S6K were reduced after LAT1 knockdown. Collectively, these results suggest that suppression of cell invasion and migration in LAT1 knockdown KKU-M213 cells may be partly mediated through the inhibition of the 4F2hc-signaling pathway by the up-regulation of microRNA-7. Based on this finding, LAT1 may be a potential therapeutic target for treating CCA.