Overexpression of folate binding protein alpha 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 ha ve 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 FB P alpha/beta -actin ratio of amplified transcripts was 4.8- and 1.5- fold h igher in 10(-4) and in 10(-7) M MTX HT29 respectively, than in standard typ e 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 conce ntration 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 res ult of the synergistic overexpression of both DHFR and FBP alpha. Overexpre ssion of FBP alpha may be related to the enterocyte-like phenotype of the c ells. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.