Methotrexate-induced senescence in human adenocarcinoma cells is accompanied by induction of p21(waf1/cip1) expression and lack of polyploidy

Human colorectal adenocarcinoma C85 cells, treated with high dose methotrexate (1 microM; IC(50)=51 nM), undergo accelerated senescence, as the cells (i) are growth arrested at the G(1) and S phases of the cell cycle, (ii) are SA-beta-galactosidase-positive, (iii) show induced expression of p21(waf1/cip1) and decreased expression of p16(INK4a), and (iv) show DNA synthesis continued at the reduced level. The fraction of C85 cells with DNA content higher than 4N is maintained at the same level (14%) in cells untreated, as well as regrown after the treatment. Multinucleation is found as the main karyotypic abnormality.