Resistance of the human colon carcinoma cell line HCT-8 to methotrexate results in selection of cells with features of enterocytic differentiation.

Results obtained previously with the human colon carcinoma cell line HT-29 have shown that the ability of the cells to develop resistance against methotrexate (MTX) or 5-fluorouracil is restricted to cells committed to differentiate. With the aim of investigating whether this observation is cell type-specific or more general, we have extended our studies to another colon cell line, HCT-8. We have compared HCT-8 parental cells and the MTX-resistant subline HCT8-MTX using transmission electron microscopy and immuno-fluorescence detection of markers of cell polarity and differentiation. Post-confluent parental HCT-8 cells appeared highly heterogeneous and occurred in clusters of piled-up cells in which the majority were unpolarized and undifferentiated, with a minority exhibiting features of enterocyte-like cells. In contrast, HCT8-MTX cells formed domes and appeared as a monolayer of polarized cells with tight junctions and a discrete apical brush border which expressed villin, dipeptidylpeptidase-IV, CEA and the epithelial mucin MUC1. Together, our results suggest that, as in HT-29 cells, induction of resistance to MTX of HCT-8 cells results in the selection of differentiated cell types.