Overexpression of the neutral amino acid transporter ASCT2 in human colorectal adenocarcinoma.

Cancer cells have increased amino acid transport and retention. Our aim was to determine whether the neutral amino acid transporter ASCT2 is expressed in colorectal adenocarcinomas (CRC), and whether its expression is of biological significance. Western blot analysis was performed on 4 cases of CRC. Immunohistochemical staining was performed on sections of 63 CRC, and the percent of positive cells was determined. Survival analysis was performed using the Kaplan-Meier method. Western blot analysis showed a 50 kDa protein, corresponding to ASCT2, in 3 of the 4 CRC samples. Immunohistostaining showed lack of ASCT2 immunoreactivity in 41% of the cases. ASCT2 immunoreactivity was present in 1-25% of the cancer cells in 24% of the cases, 26-50% of the cells in 13%, and in > 50% of the cells in 22% of the cases. Patient survival decreased with increased percentage of ASCT2-positive cancer cells (p = 0.0002). These results indicate that ASCT2 is expressed in a significant number of CRC, and that ASCT2 expression is associated with aggressive biological behavior. Larger studies with multivariate analysis are needed to determine whether ASCT2 expression is an independent prognostic marker in CRC.