WILD-TYPE P53 STIMULATES EXPRESSION FROM THE HUMAN MULTIDRUG-RESISTANCE PROMOTER IN A P53-NEGATIVE CELL-LINE

The effect of human wild type and mutant p53 proteins on the human mul tidrug resistance (MDR1) promoter was studied in a p53-negative human cell line. Transient expression of MDR1 promoter-chloramphenicol acety ltransferase reporter gene constructs (MDRCAT) cotransfected with p53 expression vectors was analyzed in H358 lung carcinoma cells. Cotransf ection with a wild type p53 expression vector stimulated MDRCAT activi ty, while cotransfection with mutant p53 expression vectors altered at amino acid positions 181, 252, 258, or 273 failed to stimulate expres sion, Wild type p53 stimulation of MDRCAT activity was time dependent with maximal expression occurring 24-30 h following transfection and c orrelating with high p53 protein levels, MDR1 promoter deletion analys is suggested that the sequences involved in wild type p53 stimulation of MDRCAT activity were contained within the region from -39 to +53 re lative to the start of transcription at +1. This region contains no TA TA or p53 consensus binding sequence but does contain an initiator seq uence. Wild type p53 stimulation of MDRCAT expression also occurred in parental and doxorubicin-resistant SW620 colon and parental 2780 ovar ian cancer cell lines, indicating that wild type p53-mediated simulati on of the MDR1 promoter is not restricted to a single cell line.