Multidrug-resistant phenotype influences the differentiation of a human colon carcinoma cell line

The human colon carcinoma cell line HT29-D4, which constitutively expresses a very low level of the MDR1 gene product, was made multidrug resistant by transfection with a human MDR1 cDNA from the pHaMDR1/A expression vector a nd selection by colchicine. Resistant clones were 3- to 15-fold resistant t o colchicine and were cross-resistant to doxorubicin (3- to 4-fold). MDR1 g ene expression was associated with the expression of functional P-glycoprot ein (gp-170); the function was reversed by verapamil and cyclosporin A. HT2 9-D4 cells are able to differentiate in vitro by replacement of glucose by galactose in the culture medium and also to release the carcinoembryonic an tigen (CEA). Under these culture conditions, MDR1 mRNA and gp-170 were alwa ys expressed and the protein remained functional. Upon galactose treatment, resistant clones were less differentiated since they showed a heterogeneou s monolayer organization accompanied by heterogeneous staining of cell-surf ace CEA and a high decrease (60-90%) of CEA release. (C) 1999 Academic Pres s.