Overexpression of folate binding protein α is one of the mechanism explaining the adaptation of HT29 cells to high concentration of methotrexate

The human colon adenocarcinoma cell line HT29 can be adapted to 10(-7)-10(-4) M concentrations of methotrexate (MTX). Cells adapted to 10(-4) M MTX have an enterocyte-like phenotype with DHFR gene amplification. Presently, we hypothetized that an increased expression of folate binding protein (FBP) may participate to the MTX resistance of 10(-4) MTX HT29 cells. The cDNA FBP alpha/beta -actin ratio of amplified transcripts was 4.8- and 1.5- fold higher in 10(-4) and in 10(-7) M MTX HT29 respectively, than in standard type HT29 cells. An increase of transcript level was observed when decreasing folic acid concentration. PI-PLC cleaved 7.7 times more membrane FBP in 10(-4) M than in 10(-7) M MTX and wild type HT29 cells. In contrast to 10(-7) M MTX cells. growth of 10(-4) M MTX cells was dependent on folic acid concentration and abolished at a concentration lower than 0.9 muM. In conclusion, the adaptive mechanism of HT29 cells resistant to 10(-4) M MTX is the result of the synergistic overexpression of both DHFR and FBP alpha. Overexpression of FBP alpha may be related to the enterocyte-like phenotype of the cells. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.