STABLE TRANSFECTION OF THE P-GLYCOPROTEIN PROMOTER REPRODUCES THE ENDOGENOUS OVEREXPRESSION PHENOTYPE - THE ROLE OF MED-1

Cellular resistance to multiple chemotherapeutic agents is most often due to the overexpression of P-glycoprotein (Pgp). The mechanism(s) un derlying Pgp overexpression had not been determined, due, in part, to a failure to reproduce the overexpression in transient transfection as says, We now report that stable transfection of a Pgp (pgp1) promoter/ luciferase construct in the drug-sensitive Chinese hamster cell line D C-3F and its drug-resistant sublines reproduced the overexpression phe notype, with up to 18-fold higher activity observed in the resistant c ell lines compared with DC-3F. Moreover, mutation of a pgp1 promoter e lement, multiple start site element downstream (MED-1), decreased tran scription in drug-resistant cells without affecting activity in drug-s ensitive cells, This is the first report of a Pgp promoter element dif ferentially regulated in drug-resistant cells, Moreover, these data su ggest that the regulation of Pgp transcription is modulated by chromat in structure, and that stable transfections may be more suitable for i dentifying promoter elements important for overexpression in drug-resi stant cells.