抄録
L-type amino acid transporter 1 (LAT1) is a major essential amino acid transporter in cancer cells and upregulated in various cancers including pancreatic cancer. Leucine, one of the LAT1 substrates, has been studied as a signaling molecule to regulate cell growth and proliferation by stimulating mTORC1 pathway. We previously showed that the inhibition of LAT1 suppressed mTORC1 pathway in vitro and, furthermore, vigorously arrested the growth of xenograft tumors in nude mouse as well as allograft tumors in mouse. Therefore, the inhibition of LAT1 seems to affect various cellular responses strikingly. However, the overall picture of cellular processes affected by LAT1 inhibition remains elusive. In this study, by using phosphoproteomics, we have aimed to obtain the overall cellular processes in pancreatic cancer cell lines affected by the inhibition of LAT1. Pancreatic cancer is one of the most aggressive tumors with a high degree of invasiveness and very difficult to be treated. We used MIA PaCa-2 and PANC-1 as models due to their LAT1 expression and leucine transport through LAT1. As reported in other cancer cell lines, BCH (2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid), one of the LAT1 inhibitors, suppressed the leucine transport and phosphorylation of p70S6K, a downstream target of mTORC1. Our phosphoproteome analysis revealed that the leucine transported by LAT1 altered numerous signaling pathways and regulated multiple cellular processes such as cellular assembly/organization and cell movement. Among signaling pathways involved in these processed, we identified that activation of RhoA pathway was suppressed by the LAT1 inhibitor. Wound healing assay supported that the inhibition of LAT1 impairs cell movement. The results indicate that leucine through LAT1 regulates multiple cellular processes involved in cellular assembly/organization and cell movement in pancreatic cancer cells as a signaling molecule. Our data suggest the inhibition of LAT1 arrests tumor cell growth by suppressing multiple cellular functions related to cellular assembly and organization and cellular movement. In addition, the LAT1 inhibition likely suppresses other cellular processes as well. Taken all together, LAT1 represents one of the promising novel targets for cancer therapeutics in the future.
