The RNA interference of amino acid transporter LAT1 inhibits the growth of KB human oral cancer cells

Background: Amino acid transporters are essential for growth and proliferation in all living cells. Among the amino acid transporters, the system L amino acid transporters are the major nutrient transport system responsible for the Na⁺-independent transport of neutral amino acids, including several essential amino acids. The L-type amino acid transporter 1 (LAT1) is overexpressed to support cell growth in malignant tumors. Double-stranded RNA-mediated RNA interference (RNAi) analysis can be used in a wide variety of eukaryotes to induce the sequence-specific inhibition of gene expression. The current study attempted to investigate the effects of silencing LAT1 expression with small interfering RNA (siRNA) on cell growth in the KB human oral squamous cell carcinoma. Materials and Methods: The effects of silencing LAT1 expression with siRNA KB on cell growth were examined using RT-PCR, Western blot analysis, amino acid transport measurement and the MTT assay. Results: In the RT-PCR and Western blot analyses, the siRNA of LAT1 inhibited the expressions of LAT1 mRNA and protein. The uptake of [¹⁴C]L-leucine was also inhibited by the siRNA of LAT1. In the MTT assay, the siRNA of LAT1 inhibited the growth of the KB cells in a time-dependent manner, indicating that this growth inhibition was induced by the LAT1-mediated blocking of neutral amino acid transport. Conclusion: The transport of neutral amino acids, including several essential amino acids, into the KB human oral squamous cell carcinoma is mainly mediated by LAT1. Furthermore, LAT1 could be a new target for the inhibition of cancer cell growth.